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1 DOI: /NCHEM.1642 Isolation and characterization of a uranium(vi)-nitride triple bond David M. King, 1 Floriana Tuna, 2 Eric J. L. McInnes, 2 Jonathan McMaster, 1 William Lewis, 1 Alexander J. Blake, 1 Stephen T. Liddle 1* 1 School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK. 2 School of Chemistry and Photon Science Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK. * stephen.liddle@nottingham.ac.uk Index Materials and Methods...S2 Magnetometric Measurements...S10 EPR Measurements...S18 Electronic Absorption Spectra...S20 X-ray Crystallography...S24 DFT, NBO, and QTAIM Calculations...S81 References...S107 NATURE CHEMISTRY 1

2 Materials and Methods General All manipulations were carried out using Schlenk techniques, or an MBraun UniLab glovebox, under an atmosphere of dry nitrogen. Solvents were dried by passage through activated alumina towers and degassed before use or were distilled from calcium hydride. All solvents were stored over potassium mirrors except for ethers and pyridine which were stored over activated 4 Å sieves. Deuterated solvent was distilled from potassium, degassed by three freeze-pump-thaw cycles and stored under nitrogen. Sodium azide and 98% sodium azide 1-15 N were dried under vacuum for four hours prior to use. 15-crown-5 ether was dissolved in ether, dried over activated 4 Å molecular sieves for 24 hours, decanted and the ether removed prior to use. N(CH 2 CH 2 NH 2 ) 3 was distilled prior to use. Iodine was freshly sublimed before use. Me 3 SiCl was distilled from magnesium prior to use. [N 3 ][NBu n 4] was dried under vacuum for 4 hours prior to use. N 3 SiMe 3, N 3 Ad (Ad = adamantly), and AgPF 6 were used as supplied. [UCl(Tren TIPS )] (1, Tren TIPS = {N(CH 2 CH 2 NSiPr i 3) 3 } 3 ; Pr i = CH(CH 3 ) 2 ), [U(Tren TIPS )] (2), [{U(μ-N)(μ-Na)(Tren TIPS )} 2 ] (3) and [UN(Tren TIPS )][Na(12C4) 2 ] (4) were prepared as described previously. 1 1 H, 13 C, and 29 Si, NMR spectra were recorded on a Bruker 400 spectrometer operating at 400.2, 100.6, and 79.5 MHz respectively; chemical shifts are quoted in ppm and are relative to TMS ( 1 H, 13 C, 29 Si). FTIR spectra were recorded on a Bruker Tensor 27 spectrometer. UV/Vis/NIR spectra were recorded on a Perkin Elmer Lambda 750 spectrometer. Data were collected in 1mm path length cuvettes loaded in an MBraun UniLab glovebox and were run versus the appropriate reference solvent. Variable-temperature magnetic moment data were recorded in an applied dc field of 0.1 T on a Quantum Design MPMS XL5 superconducting quantum interference device (SQUID) magnetometer using doubly recrystallised powdered samples. Samples were carefully checked for NATURE CHEMISTRY 2

3 purity and data reproducibility between several independently prepared batches for each compound examined. Care was taken to ensure complete thermalisation of the sample before each data point was measured and samples were immobilised in an eicosane matrix to prevent sample reorientation during measurements. Diamagnetic corrections of , , , , , , , cm 3 mol 1 were applied for 5-13 using tabulated Pascal constants and measurements were corrected for the effect of the blank sample holders (flame sealed Wilmad NMR tube and straw) and eicosane matrix. Solution magnetic moments were recorded at room temperature using the Evans method. Variable temperature (300-5 K) EPR spectra were measured at S-band (ca. 3.8 GHz) and Q-band (ca GHz) on a Bruker Elexsys E500 spectrometer with an ER4118SMS5 or ER5106QT resonator, respectively. Polycrystalline samples were sealed under vacuum in 1mm i.d. silica tubing, and double-contained for EPR by insertion into an X-band silica tube or PTFE sleeve. Measurements were made on several independently prepared batches, which were also analysed by SQUID and CHN microanalyses, to ensure reproducibility. Spectra were background corrected against blank sample holders measured under identical conditions. Photochemical reactions were carried out in a quartz reactor well using a Photochemical Reactors Ltd model W medium pressure mercury-lamp, which emits predominantly nm radiation with smaller amounts at 254, 265, 270, 289, 297, 302, 313, 334, , 436, 546, and nm. CHN microanalyses were carried out by Tong Liu at the University of Nottingham. 2 Preparation of [U(I)(Tren TIPS )] (5) Method A: A solution of I 2 (0.07 g, 0.28 mmol) in toluene (2 ml) was added dropwise to a stirring solution of 3 (0.5 g, 0.28 mmol) in toluene (10 ml) at 78 C. The brown solution was allowed to warm to room temperature with stirring over 16 h. Volatiles were removed in vacuo and the product NATURE CHEMISTRY 3

4 was extracted into hexanes (10 ml). The mixture was filtered, concentrated and stored at 4 C to yield 5 as yellow crystals. Yield: 0.30 g, 54%. Method B: THF was added slowly to a stirring mixture of [UI 3 (THF) 4 ] (3.15 g, 3.88 mmol) and [Li 3 (Tren TIPS )] (2.46 g, 3.88 mmol) at 78 C. The mixture was allowed to warm to room temperature with stirring over 16 h. Volatiles were removed in vacuo and the product was extracted into hexanes (20 ml). The mixture was filtered away from the uranium metal and LiI precipitate. The mixture was concentrated and stored at 4 C to yield 5 as yellow crystals. Yield: 0.95 g, 25%. Method C: A solution of I 2 (0.07 g, 0.27 mmol) in toluene (2 ml) was added dropwise to a stirring solution of 2 (0.43 g, 0.51 mmol) in toluene (10 ml) at 78 C. The brown solution was allowed to warm to room temperature with stirring over 16 h. Volatiles were removed in vacuo and the product was extracted into hexanes (10 ml). The mixture was filtered, concentrated and stored at 4 C to yield 5 as yellow crystals. Yield: 0.23 g, 47%. Method D: Me 3 SiI (0.24 g, 1.20 mmol) was added dropwise to a stirring solution of 1 (0.89 g, 0.50 mmol) in THF (20 ml) at 78 C. The brown solution was allowed to warm to room temperature with stirring over 16 h. Volatiles were removed in vacuo and the product was extracted into toluene (10 ml). The mixture was filtered and all volatiles removed. 1 H NMR show 50 % conversion to 9 with 50% of 1 remaining; however, addition of excess Me 3 SiI does not result in complete conversion and eventually decomposition to unidentified products is observed. Crystals of 5 were found to be twinned. Although a qualitative solution confirming the formulation of 5 could be obtained, the twinning could not be resolved and the data could not be refined to publication standard. Anal. Calcd for C 33 H 75 IN 4 Si 3 U: C, 40.56; H, 7.74; N, Found: C, 40.57; H, 7.80; N, H NMR (C 6 D 6, 298 K): δ (s, 54H, CH(CH 3 ) 2 ), (s, 9H, CH(CH 3 ) 2 ), 2.52 (s, 6H, CH 2 ), (s, 6H, CH 2 ). 29 Si NMR (C 6 D 6, 298 K): δ FTIR ν/cm -1 (Nujol): 2956 (vs), 2925 (vs), 2855 (vs), 1460 (s), 1378 (m), 1260 (m), 1135 (w), 1094 (m), 1034 (m), 1014 (m), 926 (m), 883 (m), 800 (m), 724 (s), 676 (w), 634 (w). μ eff (Evans method, C 6 D 6 solution, 298 K): 2.99 μ B. NATURE CHEMISTRY 4

5 Preparation of [U(F)(Tren TIPS )] (6) Toluene (15 ml) was added slowly to a stirring mixture of 3 (0.75 g, 0.42 mmol) and AgPF 6 (0.21 g, 0.85 mmol) at 78 C. The mixture was allowed to warm to room temperature with stirring over 16 h. Volatiles were removed in vacuo and the product was extracted into hexanes (20 ml). The mixture was filtered away from the silver precipitate and volatiles were removed in vacuo. The product was washed with pentane to yield 6 as a brown solid. Brown crystals were grown from a saturated solution of toluene at 30 C. Yield: 0.17 g, 24%. Anal. Calcd for C 33 H 75 FN 4 Si 3 U: C, 45.60; H, 8.70; N, Found: C, 44.21; H, 8.58; N, H NMR (C 6 D 6, 298 K): δ (s, 6H, CH 2 ), (s, 6H, CH 2 ), 3.94 (s, 9H, CH(CH 3 ) 2 ), 5.05 (s, 54H, (CH(CH 3 ) 2 ). 29 Si NMR (C 6 D 6, 298 K): δ FTIR ν/cm -1 (Nujol): 2954 (vs), 2852 (vs), 1462 (vs) 1378 (s), 1342 (w), 1260 (m), 1133 (w), 1097 (m), 1060 (s), 1012 (s), 926 (s), 881 (m), 801 (m), 738 (s), 675 (m), 659 (w), 637 (m), 568 (w), 549 (w). μ eff (Evans method, C 6 D 6 solution, 298 K): 2.99 μ B. Preparation of [U(N)(Tren TIPS )] (7) A solution of I 2 (0.18 g, 0.70 mmol) in toluene (2 ml) was added dropwise to a stirring solution of 4 (1.73 g, 1.40 mmol) in toluene (10 ml) at 78 C. The brown solution was allowed to warm to room temperature with stirring over 16 h. Volatiles were removed in vacuo and the product was extracted into hexanes (10 ml). The mixture was filtered, concentrated and stored at 4 C to yield 7 as red crystals. Yield: 0.55 g, 46%. Anal. Calcd for C 33 H 75 N 5 Si 3 U: C, 45.86; H, 8.75; N, Found: C, 45.44; H, 8.68; N, H NMR (C 6 D 6, 298 K): δ 1.78 (d, 54H, CH(CH 3 ) 2 ), 2.42 (septet, 9H, CH(CH 3 ) 2 ), 2.58 (m, 6H, CH 2 ), 5.27 (m, 6H, CH 2 ). 13 C{ 1 H} NMR (C 6 D 6, 298 K): δ (CH(CH 3 ) 2 ), (CH(CH 3 ) 2 ), (CH 2 ), (CH 2 ). 29 Si NMR (C 6 D 6, 298 K): δ NATURE CHEMISTRY 5

6 FTIR ν/cm -1 (Nujol): 2956 (vs), 2925 (vs), 2855 (vs), 1461 (s), 1378 (m), 1261 (m), 1095 (m), 1073 (m), 1016 (m), 914 (w), 884 (m), 799 (m), 767 (m), 674 (w), 634 (w), 596 (w), 590 (w). Preparation of [U{(NHCMe 2 SiPr i 2NCH 2 CH 2 )N(CH 2 CH 2 NSiPr i 3) 2 }] (8) Method A: A solution of 7 (0.02 g, 0.02 mmol) in C 6 D 6 (1 ml) was irradiated with a 125 W medium pressure mercury lamp in a submersion well for 1 hour. 1 H NMR spectroscopy indicated complete conversion to 8. Method B: A solution of 9 (1.78 g, 2.00 mmol) in toluene (20 ml) was irradiated with a 125 W medium pressure lamp in a submersion well for 5 hours. Volatiles were removed in vacuo and the product was extracted into hexanes (20 ml). The product was extracted in hexanes, concentrated and stored at 4 C to yield colourless crystals of 8. Yield: 0.54 g, 31%. The 31% yield of 8 for method B reflects the solubility of 8; inspection of the crude mixture from method B by 1 H NMR spectroscopy showed complete consumption of 9 and conversion to 8. Method C: A solution of 4 (0.02 g, 0.02 mmol) in C 6 D 6 (1 ml) was irradiated with a 125 W medium pressure mercury lamp in a submersion well for 5 hours. 1 H NMR spectroscopy shows 5% conversion to 8. Anal. Calcd for C 33 H 75 N 5 Si 3 U: C, 45.86; H, 8.75; N, Found: C, 45.87; H, 8.78; N, H NMR (C 6 D 6, 298 K): δ (s, 1H, NH), (s, 1H, Si(CH(CH 3 ) 2 ), (s, 1H, Si(CH(CH 3 ) 2 ), (s, 2H, CH 2 ), (s, 12H, Si(CH(CH 3 ) 2 ) 2 ), 7.79 (s, 2H, CH 2 ), 2.71 (s, 2H, CH 2 ), 1.33 (s, 18H, Si(CH(CH 3 ) 2 ) 3 ), 1.27 (s, 2H, CH 2 ), 7.45 (s, 6H, Si(CH(CH 3 ) 2 ) 3 ), (s, 18H, Si(CH(CH 3 ) 2 ) 3 ), (s, 6H, N-C(CH 3 ) 2 ), (s, 2H, CH 2 ), (s, 2H, CH 2 ). 29 Si NMR (C 6 D 6, 298 K): δ 4.54, FTIR ν/cm -1 (Nujol): 3451 (vbr), 2956 (vs), 2924 (vs), 2855 (vs), 1462 (s), 1377 (m), 1261 (m), 1092 (m), 1023 (m), 909 (w), 882 (w), 849 (w), 799 (m), 774 (w), 745 (m), 670 (w), 633 (w). μ eff (Evans method, C 6 D 6 solution, 298 K): 2.87 μ B. NATURE CHEMISTRY 6

7 Preparation of [U(N 3 )(Tren TIPS )] (9) THF (20 ml) was added slowly to a stirring mixture of 1 (0.89 g, 1.00 mmol) and NaN 3 (0.08 g, 1.23 mmol) at 78 C. The brown solution was allowed to warm to room temperature with stirring over 16 h. Volatiles were removed in vacuo and the product was extracted into toluene (20 ml). The mixture was filtered and volatiles were removed in vacuo. The product was washed with hexanes (2 5 ml) to yield 9 as a brown solid. Yellow crystals of 9 were grown from a saturated solution of n- hexanes at 4 C. Yield: 0.31 g, 35%. Anal. Calcd for C 33 H 75 N 7 Si 3 U: C, 44.42; H, 8.47, N, Found: C, 42.81; H, 8.47; N, H NMR (C 6 D 6, 298 K): δ 7.67 (s, 6H, CH 2 ), 7.08 (d, 54H, CH(CH 3 ) 2 ), 6.12 (s, 9H, CH(CH 3 ) 2 ), (s, 6H, CH 2 ). 29 Si NMR (C 6 D 6, 298 K): δ FTIR ν/cm -1 (Nujol): 2925 (vs), 2856 (vs), 2086 (vs), 1463 (s), 1378 (m), 1363 (m), 1261 (m), 1096 (m), 1060 (m), 1013 (m), 924 (m), 883 (m), 801 (m), 737 (s) 676 (m) 634 (w), 600 (w), 551 (w). μ eff (Evans method, C 6 D 6 solution, 298 K): 2.83 μ B. Preparation of [U(NSiMe 3 )(Tren TIPS )] (10) Method A: Me 3 SiCl (0.01 g, 0.10 mmol) was added to a solution of 4 (0.12 g, 0.10 mmol) in toluene (1.5 ml) resulting in immediate precipitation of a white solid. The solution was filtered, and volatiles were removed in vacuo to afford a red-brown oil. Method B: Me 3 SiN 3 (0.12 g, 1.04 mmol) was added to a purple solution of 2 (0.85 g, 1.00 mmol) in toluene (2 ml) resulting in evolution of nitrogen and a colour change to red-brown; removal of volatiles in vacuo afforded a red-brown oil. Method C: Me 3 SiCl (0.02 g, 0.20 mmol) was added to a solution of 3 (0.18 g, 0.20 mmol) in toluene (5 ml) resulting in immediate precipitation of a white solid. The solution was filtered, and volatiles were removed in vacuo to afford a red-brown oil. Trituration of the red oils afforded by methods A-C with hexane afforded 10 as a red powder in all cases. The red powders gave NATURE CHEMISTRY 7

8 essentially identical characterisation data from all methods. Average yield: 43%. All three methods were shown by 1 H NMR spectroscopy to be essentially quantitative and gave essentially the same crystalline yield which reflects the solubility of 10. Anal. Calcd for C 36 H 84 N 5 Si 4 U: C, 46.12; H, 9.03; N, Found: C, 46.01; H, 9.19; N, H NMR (C 6 D 6, 298 K): δ (s, 6H, CH 2 ), (s, 9H, Si(CH 3 ) 3 ), 6.70 (s, 6H, CH 2 ), 2.77 (s, 54H, CH(CH 3 ) 2 ), 3.15 (s, 9H, CH(CH 3 ) 2 ). 29 Si NMR (C 6 D 6, 298 K): δ FTIR ν/cm -1 (Nujol): 2961 (vs), 2925 (vs), 2856 (vs), 1461 (m), 1414 (w), 1378 (w), 1261 (s), 1096 (s), 1017 (s), 927 (m), 880 (m), 797 (s), 750 (w), 724 (m). μ eff (Evans method, C 6 D 6 solution, 298 K): 2.24 μ B. Preparation of [U(NAd)(Tren TIPS )] (11) Toluene (10 ml) was added slowly to a stirring mixture of 2 (0.89 g, 1.00 mmol) and AdN 3 (0.18 g, 1.00 mmol) at 78 C. The dark brown solution was allowed to warm to room temperature with stirring over 16 h. Volatiles were removed in vacuo and the product was extracted into pentane (10 ml). The mixture was filtered, concentrated and stored at 30 C to yield 11 as dark brown crystals. Yield: 0.67 g, 67%. Anal. Calcd for C 43 H 90 N 5 Si 3 U: C, 51.67; H, 9.08; N, Found: C, 51.47; H, 9.02; N, H NMR (C 6 D 6, 298 K): δ (s, 6H, CH 2 ), (s, 6H, CH 2 ), (s, 3H, Ad- CH), (d, 3H, Ad-CH 2 ), 8.64 (d, 3H, Ad-CH 2 ), 4.81 (s, 6H, Ad-CH 2 ), 5.06 (s, 9H, CH(CH 3 ) 2 ), 5.47 (s, 54H, CH(CH 3 ) 2 ). 29 Si NMR (C 6 D 6, 298 K): δ FTIR ν/cm -1 (Nujol): 2921 (br vs), 2954 (vs), 2723 (w), 1587 (w), 1462 (s), 1378 (m), 1301 (w), 1261 (m), 1129 (m), 1094 (m), 1045 (m), 1018 (m), 960 (w), 929 (m), 882 (m), 803 (m), 726 (s), 674 (m), 631 (w), 567 (w), 545 (w). μ eff (Evans method, C 6 D 6 solution, 298 K): 1.75 μ B. NATURE CHEMISTRY 8

9 Preparation of [U(NH 2 )(Tren TIPS )] (12) A slurry of [N 3 ][NBu n 4] (0.24 g, 0.84 mmol) in toluene was added to a stirring solution of 2 (0.72 g, 0.84 mmol) in toluene at 78 C. The mixture was allowed to warm to room temperature with stirring over 16 h. Volatiles were removed in vacuo and the product was extracted into hexanes (20 ml). The mixture was filtered and volatiles were removed in vacuo. The product was washed with pentane (2 5 ml) to yield 12 as a brown solid. Yellow crystals were grown from a saturated solution of hexanes at 30 C. Yield: 0.21 g, 29%. Anal. Calcd for C 33 H 77 N 5 Si 3 U: C, 45.75; H, 8.96; N, Found: C, 45.50; H, 8.94; N, H NMR (C 6 D 6, 298 K): δ (s, 6H, CH 2 ), 7.92 (s, 6H, CH 2 ), 7.07 (s, 1H, NH 2 ), 5.03 (s, 1H, NH 2 ), 5.35 (s, 9H, CH(CH 3 ) 2 ), 5.87 (s, 54H, CH(CH 3 ) 2 ). 29 Si NMR (C 6 D 6, 298 K): δ FTIR ν/cm -1 (Nujol): 3387 (w), 3308 (w), 2959 (vs), 2854 (vs), 1462, (vs), 1377 (s), 1300 (w), 1260 (m), 1135 (m), 1050 (m), 1013 (m), 928 (m), 882 (m), 800 (m), 738 (s), 674 (m), 634 (w). μ eff (Evans method, C 6 D 6 solution, 298 K): 2.89 μ B. Preparation of [U(μ-N)(μ-Na15C5)(Tren TIPS )] (13) A solution of 15-crown-5 (0.12 g, 0.56 mmol) in pyridine (2 ml) was added dropwise to a stirring solution of 3 (0.50 g, 0.28 mmol) in pyridine (10 ml) at 78 C. The brown solution was allowed to warm to room temperature with stirring over 16 h. Volatiles were removed in vacuo and the product was extracted into hexanes (10 ml). The mixture was filtered, concentrated and stored at 4 C to yield 13 as red crystals. Yield: 0.19 g, 61%. Anal. Calcd for C 43 H 95 N 5 NaSi 3 U 0.5C 6 H 14 : C, 47.98; H, 9.01; N, Found: C, 48.16; H, 8.96; N, H NMR (C 6 D 6, 298 K): δ (s, 6H, CH 2 ), (s, 10H, OCH 2 ), (s, 10H, OCH 2 ), 7.52 (s, 6H, CH 2 ), 6.35 (s, 9H, CH(CH 3 ) 2 ), 7.73 (s, 54H, (CH(CH 3 ) 2 ). 29 Si NMR (C 6 D 6, 298 K): δ FTIR ν/cm -1 (Nujol): 2959 (vs), 2924 (vs), 2855 (vs), 1596 (vw), 1461 (m), 1413 (w), 1378 (m), 1354 (w), 1261 (s), 1094 (s), 1020 (s), 934 NATURE CHEMISTRY 9

10 (m), 880 (m), 863 (w), 799 (s), 744 (m), 704 (m), 671 (w), 630 (w). μ eff (Evans method, C 6 D 6 solution, 298 K): 2.34 μ B. Magnetometric Measurements Fig. S1. Left to right, top to bottom: χ vs T, 1/χ vs T, χt vs T, μ eff vs T for [U(I)(Tren TIPS )] (5). NATURE CHEMISTRY 10

11 Fig. S2. Left to right, top to bottom: χ vs T, 1/χ vs T, χt vs T, μ eff vs T for [U(F)(Tren TIPS )] (6). NATURE CHEMISTRY 11

12 Fig. S3. Left to right, top to bottom: χ vs T, 1/χ vs T, χt vs T, μ eff vs T for [U{(NHCMe 2 SiPr i 2NCH 2 CH 2 )N(CH 2 CH 2 NSiPr i 3) 2 }] (8). NATURE CHEMISTRY 12

13 Fig. S4. Left to right, top to bottom: χ vs T, 1/χ vs T, χt vs T, μ eff vs T for [U(N 3 )(Tren TIPS )] (9). NATURE CHEMISTRY 13

14 Fig. S5. Left to right, top to bottom: χ vs T, 1/χ vs T, χt vs T, μ eff vs T for [U(NSiMe 3 )(Tren TIPS )] (10). NATURE CHEMISTRY 14

15 Fig. S6. Left to right, top to bottom: χ vs T, 1/χ vs T, χt vs T, μ eff vs T for [U(NAd)(Tren TIPS )] (11). NATURE CHEMISTRY 15

16 Fig. S7. Left to right, top to bottom: χ vs T, 1/χ vs T, χt vs T, μ eff vs T for [U(NH 2 )(Tren TIPS )] (12). NATURE CHEMISTRY 16

17 Fig. S8. Left to right, top to bottom: χ vs T, 1/χ vs T, χt vs T, μ eff vs T for [U(μ-N)(μ- Na15C5)(Tren TIPS )] (13). NATURE CHEMISTRY 17

18 EPR Measurements (a) (b) Fig. S9. (a) S-band (ca GHz) EPR spectra of polycrystalline samples of [U(NSiMe 3 )(Tren TIPS )] (10; top), [U(NAd)(Tren TIPS )] (11; middle) and [U(μ-N)(μ- Na15C5)(Tren TIPS )] (13; bottom) at 5 K. Inset: expansion of low-field region. (b) Q-band (ca GHz) EPR spectra of polycrystalline samples of [U(NSiMe 3 )(Tren TIPS )] (10; top), [U(NAd)(Tren TIPS )] (11; middle) and [U(μ-N)(μ-Na15C5)(Tren TIPS )] (13; bottom) at 5 K. Insets: expansion of low-field regions. The features marked * are at g = 2.0 and persist to high temperatures, and are likely a small amount of radical impurity. Spectra of 10, 11 and 13 become observable below K in each case. 10 gives the richest spectra: at S-band (ca GHz) a highly rhombic set of effective g-values is observed, arising from the lowest Kramers doublet of the 2 F 5/2 ground state, with g eff = 3.30, 0.63, The extreme variation in linewidth is due to g-strain effects, as is commonly observed for, for example, six- NATURE CHEMISTRY 18

19 coordinate cobalt(ii) complexes where similarly very anisotropic effective g-values result from a J = ½ ground Kramers doublet. The spectra are consistent with higher frequency measurement at Q- band (ca GHz) where only the highest g eff -value is observable in the available field range (g = 0.63 and 0.48 would come into resonance at ca. 3.9 and 5.1 T at this frequency). Polycrystalline effects are seen at both frequencies, i.e. features due to incomplete averaging of the molecular orientations which change when the sample tube is rotated in the spectrometer cavity. This does not affect the main resonance fields observed in the S-band spectrum. Samples 11 and 13 show a similar low-field feature at g eff = 3.55 and 3.80, respectively, observed at both S- and Q-band. No further features are observed over the field range available (1.8 T): this could be due to extreme strain effects, or simply significantly lower g-values. In compound 10 a further signal is observed at g = 2.0 which is much sharper and persistent to much higher temperatures: we assume that this is due to a small quantity of free radical impurity. Cyclic Voltametry Like 3 and 4, the nitrides reported herein react with polar solvents such as ethers, chlorinated solvents, and acetonitrile which precluded CV studies. NATURE CHEMISTRY 19

20 Electronic Absorption Spectra Fig. S10. UV/Vis/NIR spectra of [U(NH 2 )(Tren TIPS )] (12, black), [U(I)(Tren TIPS )] (5, blue), [U(F)(Tren TIPS )] (6, red), [U{(NHCMe 2 SiPr i 2NCH 2 CH 2 )N(CH 2 CH 2 NSiPr i 3) 2 }] (8, green), and [U(N 3 )(Tren TIPS )] (9, purple). Fig. S11. Zoom-in of NIR region of [U(NH 2 )(Tren TIPS )] (12, black), [U(I)(Tren TIPS )] (5, blue), [U(F)(Tren TIPS )] (6, red), [U{(NHCMe 2 SiPr i 2NCH 2 CH 2 )N(CH 2 CH 2 NSiPr i 3) 2 }] (8, green), and [U(N 3 )(Tren TIPS )] (9, purple). NATURE CHEMISTRY 20

21 Fig. S12. UV/Vis/NIR spectra of toluene solutions of [U(NSiMe 3 )(Tren TIPS )] (10, black), [U(NAd)(Tren TIPS )] (11, blue), [U(μ-N)(μ-Na15C5)(Tren TIPS )] (13, red), and [U(N)(Tren TIPS )] (7, green). Fig. S13. Zoom-in of NIR region of [U(NSiMe 3 )(Tren TIPS )] (10, black), [U(NAd)(Tren TIPS )] (11, blue), [U(μ-N)(μ-Na15C5)(Tren TIPS )] (13, red), and [U(N)(Tren TIPS )] (7, green). NATURE CHEMISTRY 21

22 Discussion of UV/Vis/NIR and EPR Spectra It is informative to compare the UV/Vis/NIR electronic absorption and low temperature (5 K) electron paramagnetic resonance (EPR) spectra of 3, 4, 10, 11 and 13 since they all contain uranium(v) centres and are either clear-cut nitrides or can be viewed as masked nitrides. For 5f 1 uranium(v), the 2 F orbital manifold is split by spin orbit coupling into two J multiplets (where J is the total angular momentum), of J = 5/2 (ground) and 7/2 (excited) terms, respectively. Each J level is split further by the ligand crystal field into (2J + 1)/2 doubly degenerate levels such that in C 3v symmetry the 5/2 multiplet splits into two μ = 1/2 ( 2 Γ 4 ) and one μ = 3/2 ( 1 Γ Γ 6 ) Kramers doublets and the 7/2 multiplet splits into three μ = 1/2 ( 2 Γ 4 ) and one μ = 3/2 ( 1 Γ Γ 6 ) doublets, where μ is the crystal quantum number. Four optical transitions would therefore be expected in the NIR region. In addition to weak vibronic bands, broad Laporte forbidden f f transitions (ε = 8-20 cm 1 ) are observed for 3 and 4 which are void of axially bound groups. 1 In contrast, axially-coordinated 10, 11, and 13 exhibit well defined UV/Vis/NIR spectra in the 5,000-12,000 cm 1 NIR region. In each case four well resolved absorptions are observed corresponding to transitions to the three μ = 1/2 ( 2 Γ 4 ) and one μ = 3/2 ( 1 Γ Γ 6 ) Kramers doublets of the 7/2 multiplet (ε = M 1 cm 1 ) and these transitions compare well to data reported for terminal uranium(v)-oxo complexes. 3 For comparison, the NIR region of the UV/Vis/NIR spectrum of 7 is featureless in this region which is commensurate with the 1 S 0 electronic state of uranium(vi). Turning to the EPR data, whereas extensive solid-state and frozen-solution EPR measurements of 3 and 4 show no significant EPR spectral features down to 5 K, solid state S-band (3.87 GHz) and Q- band (34.2 GHz) EPR spectra of 10, 11, and 13 become observable below 20 K. At S-band, complex 10 exhibits a rhombic set of highly anisotropic g-values, arising from the lowest Kramers doublet of the 2 F 5/2 ground state, with g eff = 3.30, 0.63, The spectra are consistent with higher NATURE CHEMISTRY 22

23 frequency measurements at Q-band where only the highest g eff -value is observable in the available field range. Complexes 11 and 13 show a similar low-field feature at g eff = 3.55 and 3.80, respectively, observed at both S- and Q-band. No further features are observed over the field range available (1.8 T), which could be due to strain effects, or simply significantly lower g-values. This EPR-silent and -active behaviour of 3 and 4 and 10, 11, and 13, respectively, implies that the lowest Kramers doublet in the 2 F 5/2 ground term for 3 and 4 is the EPR-inactive μ = 3/2, as is the case for certain uranium(v) imido complexes, 3 whereas for 10, 11, and 13 the lowest Kramers doublet is μ = 1/2. We previously noted an antibonding interaction at short U-N distances between (for a U N bond orientated along the z-axis) the σ-orientated nitrogen 2p z orbital and the annular lobes of the uranium 6d and 5f orbitals. 1,4 From the EPR data we conclude that in a Tren-ligand environment when no axial group is coordinated to the U N triple bond that this antibonding interaction may result in the ground state being the EPR-inactive μ = 3/2, but when an axial group is coordinated this will destructively interfere with the antibonding component of the U N bond and thus the EPRactive μ = 1/2 state is instead adopted. NATURE CHEMISTRY 23

24 X-ray Crystallography (CCDC numbers , , , , , , , ) Table S1. Experimental X-ray crystallographic details for [U(F)(Tren TIPS )] (6), [U(N)(Tren TIPS )] (7), [U{(NHCMe 2 SiPr i 2NCH 2 CH 2 )N(CH 2 CH 2 NSiPr i 3) 2 }] (8), and [U(N 3 )(Tren TIPS )] (9) Chemical formula C 33 H 75 FN 4 Si 3 U C 33 H 75 N 5 Si 3 U C 33 H 75 N 5 Si 3 U C 33 H 75 N 7 Si 3 U M r Crystal system, space group Monoclinic, P2 1 /n Monoclinic, P2 1 Triclinic, P 1 Monoclinic, P2 1 /n Temperature (K) a, b, c (Å) (4), (5), (5) (6), (18), (9) (4), (4), (5),, ( ) 90, (2), 90 90, (8), (2), (2), (1) (2), (4), (3) 90, (17), 90 V (Å 3 ) (3) (3) (11) (15) Z Radiation type Cu K Cu K Mo K Cu K (mm -1 ) Crystal size (mm) Absorption correction Multi-scan Gaussian Multi-scan Gaussian T min, T max 0.430, , , , No. of measured, independent and observed [I > 2 (I)] reflections 45453, 16321, , 5700, , 9243, , 8522, 7729 R int (sin / ) max (Å -1 ) R[F 2 > 2 (F 2 )], wr(f 2 ), S 0.047, 0.116, , 0.070, , 0.070, , 0.069, 1.07 No. of reflections No. of parameters No. of restraints Weighting scheme w = 1/[ 2 (F o 2 ) + (0.043P) P] where P = (F o 2 + 2F c 2 )/3 w = 1/[ 2 (F o 2 ) + (0.0261P) P] where P = (F o 2 + 2F c 2 )/3 w = 1/[ 2 (F o 2 ) + (0.0335P) P] where P = (F o 2 + 2F c 2 )/3 w = 1/[ 2 (F o 2 ) + (0.0386P) P] where P = (F o 2 + 2F c 2 )/3 max, min (e Å -3 ) 6.78, , , , Flack parameter 0.0 (5) NATURE CHEMISTRY 24

25 Table S2. Experimental X-ray crystallographic details for [U(NSiMe 3 )(Tren TIPS )] (10), [U(NAd)(Tren TIPS )] (11), [U(NH 2 )(Tren TIPS )] (12), and [U(μ-N)(μ-Na15C5)(Tren TIPS )] (13) Chemical formula C 36 H 84 N 5 Si 4 U C 43 H 90 N 5 Si 3 U C 33 H 77 N 5 Si 3 U C 43 H 95 N 5 NaO 5 Si 3 U 1.5(C 6 H 14 ) M r Crystal system, space group Monoclinic, P2 1 /n Monoclinic, P2 1 /c Monoclinic, P2 1 /n Cubic, Pa 3 Temperature (K) a, b, c (Å) (11), (2), (18) (3), (9), (3) (2), (3), (4) (2), (2), (2),, ( ) 90, (10), 90 90, (3), 90 90, (19), 90 90, 90, 90 V (Å 3 ) (8) (2) (14) (19) Z (mm -1 ) Crystal size (mm) Absorption correction Gaussian Gaussian Gaussian Gaussian T min, T max 0.103, , , , No. of measured, independent and observed [I > 2 (I)] reflections , 9606, , 9708, , 7222, , 4240, 3683 R int (sin / ) max (Å -1 ) R[F 2 > 2 (F 2 )], wr(f 2 ), S 0.028, 0.076, , 0.150, , 0.096, , 0.081, 1.06 No. of reflections No. of parameters No. of restraints Weighting scheme w = 1/[ 2 (F o 2 ) + (0.0401P) P] where P = (F o 2 + 2F c 2 )/3 w = 1/[ 2 (F o 2 ) + (0.0328P) P] where P = (F o 2 + 2F c 2 )/3 w = 1/[ 2 (F o 2 ) + (0.0603P) 2 ] where P = (F o 2 + 2F c 2 )/3 w = 1/[ 2 (F o 2 ) + (0.0381P) P] where P = (F o 2 + 2F c 2 )/3 max, min (e Å -3 ) 1.41, , , , Table S3. Bond lengths (Å) for [U(NSiMe 3 )(Tren TIPS )] (10), [U(NAd)(Tren TIPS )] (11), [U(NH 2 )(Tren TIPS )] (12), [U(μ-N)(μ-Na15C5)(Tren TIPS )] (13), [U(F)(Tren TIPS )] (6), [U(N)(Tren TIPS )] (7), [U{(NHCMe 2 SiPr i 2NCH 2 CH 2 )N(CH 2 CH 2 NSiPr i 3) 2 }] (8), and [U(N 3 )(Tren TIPS )] (9). NATURE CHEMISTRY 25

26 10 C1 C (6) C9 H9A C1 C (6) C10 H10B C1 Si (4) C10 H10A C4 C (6) C11 H11B C4 C (6) C11 H11A C4 Si (4) C12 H C7 C (5) C13 H13C C7 C (5) C13 H13B C7 Si (4) C13 H13A C10 N (4) C14 H14C C10 C (5) C14 H14B C11 N (4) C14 H14A C12 C (5) C15 H C12 C (5) C16 H16C C12 Si (3) C16 H16B C15 C (5) C16 H16A C15 C (5) C17 H17C C15 Si (3) C17 H17B C18 C (5) C17 H17A C18 C (5) C18 H C18 Si (3) C19 H19C C21 N (4) C19 H19B C21 C (5) C19 H19A C22 N (5) C20 H20C C23 C24A (14) C20 H20B C23 C (5) C20 H20A C23 C (6) C21 H21B C23 Si (4) C21 H21A C26 C (7) C22 H22B C26 C (6) C22 H22A C26 Si (4) C23 H23A C29 C (7) C23 H C29 C (6) C24A H24F C29 Si (4) C24A H24E C32 N (4) C24A H24D C32 C (5) C24 H24C C33 N (4) C24 H24B C34 Si (4) C24 H24A C35 Si (4) C25 H25C NATURE CHEMISTRY 26

27 C36 Si (4) C25 H25B N1 Si (3) C25 H25A N1 U (3) C26 H N2 Si (3) C27 H27C N2 U (3) C27 H27B N3 Si (3) C27 H27A N3 U (3) C28 H28C N4 U (3) C28 H28B N5 Si (3) C28 H28A N5 U (3) C29 H C1 H C30 H30C C2 H2C C30 H30B C2 H2B C30 H30A C2 H2A C31 H31C C3 H3C C31 H31B C3 H3B C31 H31A C3 H3A C32 H32B C4 H C32 H32A C5 H5C C33 H33B C5 H5B C33 H33A C5 H5A C34 H34C C6 H6C C34 H34B C6 H6B C34 H34A C6 H6A C35 H35C C7 H C35 H35B C8 H8C C35 H35A C8 H8B C36 H36C C8 H8A C36 H36B C9 H9C C36 H36A C9 H9B U1 N (13) C8 H8B U1 N5A 2.00 (3) C8 H8A U1 N (8) C9 H9C U1 N (7) C9 H9B U1 N (6) C9 H9A U1 N (7) C10 H10B Si1 N (7) C10 H10A Si1 C1A 1.88 (3) C11 H11B NATURE CHEMISTRY 27

28 Si1 C (13) C11 H11A Si1 C (10) C12 H Si1 C (18) C13 H13C Si2 N (7) C13 H13B Si2 C (11) C13 H13A Si2 C (12) C14 H14C Si2 C (8) C14 H14B Si3 N (8) C14 H14A Si3 C (18) C15 H Si3 C26A 1.81 (5) C16 H16C Si3 C (2) C16 H16B Si3 C (16) C16 H16A Si3 C23A 2.19 (3) C17 H17C N1 C (10) C17 H17B N2 C (11) C17 H17A N3 C (11) C18 H N4 C (9) C19 H19C N4 C (10) C19 H19B N4 C (9) C19 H19A N5 C (19) C20 H20C N5A C34A 1.45 (4) C20 H20B C1 C (19) C20 H20A C1 C (3) C21 H21B C1A C3A 1.58 (4) C21 H21A C1A C2A 1.61 (6) C22 H22B C4 C (14) C22 H22A C4 C (19) C23A H23A C7 C (14) C23 H C7 C (14) C24A H24F C10 C (11) C24A H24E C12 C (19) C24A H24D C12 C (13) C24 H24C C15 C (12) C24 H24B C15 C (11) C24 H24A C18 C (19) C25A H25F C18 C (16) C25A H25E C21 C (11) C25A H25D C23 C (2) C25 H25C C23 C (2) C25 H25B C23A C24A 1.47 (5) C25 H25A NATURE CHEMISTRY 28

29 C23A C25A 1.57 (5) C26A H26A C26 C (3) C26 H C26 C (4) C27A H27F C26A C27A 1.43 (7) C27A H27E C26A C28A 1.66 (6) C27A H27D C29 C (17) C27 H27C C29 C (16) C27 H27B C32 C (12) C27 H27A C34 C (2) C28A H28F C34 C (2) C28A H28E C34 C (14) C28A H28D C34A C36A 1.47 (4) C28 H28C C34A C35A 1.54 (4) C28 H28B C34A C (3) C28 H28A C35 C (2) C29 H C35A C40A 1.56 (4) C30 H30C C36 C (2) C30 H30B C36A C42A 1.56 (4) C30 H30A C37 C (17) C31 H31C C37 C38A 1.71 (3) C31 H31B C38 C (2) C31 H31A C38 C (2) C32 H32B C38A C43A 1.44 (4) C32 H32A C38A C39A 1.52 (4) C33 H33B C39 C (17) C33 H33A C39A C40A 1.56 (3) C35A H35D C40 C (2) C35A H35C C40A C41A 1.52 (4) C35 H35B C41 C (2) C35 H35A C41A C42A 1.50 (4) C36A H36D C42 C (17) C36A H36C C42A C43A 1.55 (4) C36 H36B C1A H1AA C36 H36A C1 H1A C37 H37D C2A H C37 H37C C2A H2AB C37 H37B C2A H2AA C37 H37A C2 H2C C38A H38A C2 H2B C38 H C2 H2A C39A H39D NATURE CHEMISTRY 29

30 C3A H3AC C39A H39C C3A H3AB C39 H39B C3A H3AA C39 H39A C3 H3C C40A H40A C3 H3B C40 H C3 H3A C41A H41D C4 H C41A H41C C5 H5C C41 H41B C5 H5B C41 H41A C5 H5A C42A H42A C6 H6C C42 H C6 H6B C43A H43D C6 H6A C43A H43C C7 H C43 H43B C8 H8C C43 H43A C1 N (7) C2 H2A C1 C (7) C3 H3C C1A C (8) C3 H3B C1B C (10) C3 H3A C1C C (9) C4 H C1D C (10) C5 H C2 N (6) C6 H6B C2 C (7) C6 H6A C3 C (8) C7 H7B C4 C (7) C7 H7A C4 Si (6) C8 H C5 Si (6) C9 H9C C6 N (6) C9 H9B C6 C (7) C9 H9A C7 N (6) C10 H10B C8 C (8) C10 H10A C8 Si (6) C11 H11B C10 N (6) C11 H11A C11 N (6) C12 H C12 C (8) C13 H13C C12 Si (6) C13 H13B C15 C (8) C13 H13A C15 C (8) C14 H14C NATURE CHEMISTRY 30

31 C15 Si (5) C14 H14B C18 C (8) C14 H14A C18 C (7) C15 H C18 Si (5) C16 H16C C21 C (9) C16 H16B C21 C (9) C16 H16A C21 Si (6) C17 H17C C24 C (7) C17 H17B C24 C (8) C17 H17A C24 Si (6) C18 H C27 C (8) C19 H19C C27 C (8) C19 H19B C27 Si (6) C19 H19A N1 Si (4) C20 H20C N1 U (4) C20 H20B N2 Si (4) C20 H20A N2 U (4) C21 H N3 Si (5) C22 H22C N3 U (4) C22 H22B N4 U (4) C22 H22A N5 U (4) C23 H23C N5 H5B 0.92 (9) C23 H23B N5 H5A 0.90 (2) C23 H23A C1D H1DC C24 H C1D H1DB C25 H25C C1D H1DA C25 H25B C1C H1CC C25 H25A C1C H1CB C26 H26C C1C H1CA C26 H26B C1B H1BC C26 H26A C1B H1BB C27 H C1B H1BA C28 H28C C1A H1AC C28 H28B C1A H1AB C28 H28A C1A H1AA C29 H29C C1 H1B C29 H29B C1 H1A C29 H29A C2 H2B NATURE CHEMISTRY 31

32 U1 N (5) O4 C (13) U1 N1 i (3) C18 C (17) U1 N (3) C19 O (12) U1 N1 ii (3) O5 C (11) U1 N (5) C20 C (15) Si1 N (3) C1 H Si1 C (4) C2 H2C Si1 C (4) C2 H2B Si1 C (4) C2 H2A N1 C (4) C3 H3C N2 C (3) C3 H3B N2 C11 ii (3) C3 H3A N2 C11 i (3) C4 H N3 Na (5) C5 H5C C1 C (5) C5 H5B C1 C (5) C5 H5A C4 C (6) C6 H6C C4 C (5) C6 H6B C7 C (5) C6 H6A C7 C (5) C7 H C10 C (5) C8 H8C Na1 O (9) C8 H8B Na1 O2 i (9) C8 H8A Na1 O2 ii (9) C9 H9C Na1 O3 ii (8) C9 H9B Na1 O3 i (8) C9 H9A Na1 O (8) C10 H10B Na1 O1 ii (10) C10 H10A Na1 O1 i (10) C11 H11B Na1 O (10) C11 H11A Na1 O4 i (11) C12 H12B Na1 O4 ii (11) C12 H12A Na1 O (11) C13 H13B Na1 O5 i (10) C13 H13A Na1 O5 ii (10) C14 H14B Na1 O (10) C14 H14A O1 C (12) C15 H15B O1 C (11) C15 H15A C12 C (17) C16 H16B C13 O (13) C16 H16A NATURE CHEMISTRY 32

33 C13 Na1 i (15) C17 H17B C13 Na1 ii (15) C17 H17A O2 C (11) C18 H18B C14 C (17) C18 H18A C14 Na1 i (12) C19 H19B C14 Na1 ii (12) C19 H19A C15 O (12) C20 H20B O3 C (11) C20 H20A C16 C (16) C21 H21B C17 O (11) C21 H21A U2 F (4) C15 H U2 N (6) C16 H16C U2 N (5) C16 H16B U2 N (6) C16 H16A U2 N (6) C17 H17C Si4 N (6) C17 H17B Si4 C (9) C17 H17A Si4 C (8) C18 H Si4 C (9) C19 H19C Si5 N (6) C19 H19B Si5 C (10) C19 H19A Si5 C (10) C20 H20C Si5 C (12) C20 H20B Si6 N (6) C20 H20A Si6 C (7) C21 H21B Si6 C (7) C21 H21A Si6 C (8) C22 H22B N5 C (8) C22 H22A N6 C (9) C23 H N7 C (9) C24 H24C N8 C (9) C24 H24B N8 C (10) C24 H24A N8 C (9) C25 H25C C34 C (11) C25 H25B C34 C (11) C25 H25A C37 C (13) C26 H C37 C (12) C27 H27C C40 C (15) C27 H27B NATURE CHEMISTRY 33

34 C40 C (14) C27 H27A C43 C (11) C28 H28C C45 C (13) C28 H28B C45 C (15) C28 H28A C48 C (14) C29 H C48 C (17) C30A H30F C51 C (16) C30A H30E C51 C (15) C30A H30D C54 C (11) C30 H30C C56 C (10) C30 H30B C56 C (10) C30 H30A C59 C (12) C31 H31C C59 C (11) C31 H31B C62 C (11) C31 H31A C62 C (12) C32 H32B C65 C (10) C32 H32A U1 F (4) C33 H33B U1 N (6) C33 H33A U1 N (6) C34 H U1 N (6) C35 H35C U1 N (6) C35 H35B Si1 N (6) C35 H35A Si1 C (8) C36 H36C Si1 C (9) C36 H36B Si1 C (9) C36 H36A Si2 N (6) C37 H Si2 C (9) C38 H38C Si2 C (10) C38 H38B Si2 C (10) C38 H38A Si3 N (7) C39 H39C Si3 C (9) C39 H39B Si3 C (8) C39 H39A Si3 C (10) C40 H N1 C (9) C41 H41C N2 C (9) C41 H41B N3 C (9) C41 H41A N4 C (11) C42 H42C N4 C (11) C42 H42B N4 C (10) C42 H42A C1 C (12) C43 H43B NATURE CHEMISTRY 34

35 C1 C (11) C43 H43A C4 C (13) C44 H44B C4 C (13) C44 H44A C7 C (12) C45 H C7 C (16) C46 H46C C10 C (11) C46 H46B C12 C (13) C46 H46A C12 C (13) C47 H47C C15 C (14) C47 H47B C15 C (13) C47 H47A C18 C (17) C48 H C18 C (15) C49 H49C C21 C (11) C49 H49B C23 C (13) C49 H49A C23 C (12) C50 H50C C26 C (13) C50 H50B C26 C (12) C50 H50A C29 C30A 1.48 (3) C51 H C29 C (17) C52 H52C C29 C (3) C52 H52B C32 C (12) C52 H52A C1 H C53 H53C C2 H2C C53 H53B C2 H2B C53 H53A C2 H2A C54 H54B C3 H3C C54 H54A C3 H3B C55 H55B C3 H3A C55 H55A C4 H C56 H C5 H5C C57 H57C C5 H5B C57 H57B C5 H5A C57 H57A C6 H6C C58 H58C C6 H6B C58 H58B C6 H6A C58 H58A C7 H C59 H C8 H8C C60 H60C C8 H8B C60 H60B C8 H8A C60 H60A C9 H9C C61 H61C NATURE CHEMISTRY 35

36 C9 H9B C61 H61B C9 H9A C61 H61A C10 H10B C62 H C10 H10A C63 H63C C11 H11B C63 H63B C11 H11A C63 H63A C12 H C64 H64C C13 H13C C64 H64B C13 H13B C64 H64A C13 H13A C65 H65B C14 H14C C65 H65A C14 H14B C66 H66B C14 H14A C66 H66A U1 N (7) C8 H8B U1 N (8) C8 H8A U1 N1A (12) C9A H9AC U1 N (7) C9A H9AB U1 N2A (10) C9A H9AA U1 N3A (11) C9 H9C U1 N (8) C9 H9B U1 N (5) C9 H9A Si1 N1A (9) C10A H10D Si1 N (7) C10A H10C Si1 C (9) C10 H10B Si1 C (10) C10 H10A Si1 C4A (12) C11A H11D Si1 C (8) C11A H11C Si1 C7A (14) C11 H11B Si2 N (6) C11 H11A Si2 N2A (9) C12 H12A Si2 C (9) C12 H Si2 C15A (13) C13A H13F Si2 C (9) C13A H13E Si2 C (5) C13A H13D Si2 C18A (12) C13 H13C Si3 N3A (9) C13 H13B Si3 N (7) C13 H13A Si3 C29A (12) C14A H14F NATURE CHEMISTRY 36

37 Si3 C26A (14) C14A H14E Si3 C (9) C14A H14D Si3 C (9) C14 H14C Si3 C (10) C14 H14B N1 C (11) C14 H14A N1A C10A (14) C15A H15A N2 C (10) C15 H N2A C21A (14) C16A H16F N3 C (11) C16A H16E N3A C32A (14) C16A H16D N4 C (10) C16 H16C N4 C33A (14) C16 H16B N4 C22A (14) C16 H16A N4 C11A (15) C17A H17F N4 C (10) C17A H17E N4 C (10) C17A H17D C1 C (10) C17 H17C C1 C3A (13) C17 H17B C1 C2A (12) C17 H17A C1 C (10) C18A H18A C4 C (11) C18 H C4 C (11) C19A H19F C4A C5A (14) C19A H19E C4A C6A (14) C19A H19D C7 C (11) C19 H19C C7 C (11) C19 H19B C7A C9A (14) C19 H19A C7A C8A (14) C20A H20F C10 C (15) C20A H20E C10A C11A 1.48 (3) C20A H20D C12 C (11) C20 H20C C12 C13A (13) C20 H20B C12 C (12) C20 H20A C12 C14A (13) C21A H21D C15 C (11) C21A H21C C15 C (10) C21 H21B C15A C17A (14) C21 H21A C15A C16A (14) C22A H22D C18 C (11) C22A H22C C18 C (11) C22 H22B NATURE CHEMISTRY 37

38 C18A C19A (14) C22 H22A C18A C20A (15) C23 H23A C21 C (15) C23 H C21A C22A 1.52 (2) C24A H24F C23 C24A (13) C24A H24E C23 C (11) C24A H24D C23 C (11) C24 H24C C23 C25A (13) C24 H24B C26 C (12) C24 H24A C26 C (11) C25A H25F C26A C28A (14) C25A H25E C26A C27A (14) C25A H25D C29 C (12) C25 H25C C29 C (12) C25 H25B C29A C31A (14) C25 H25A C29A C30A (15) C26A H26A C32 C (18) C26 H C32A C33A 1.44 (2) C27A H27F C1 H1B C27A H27E C1 H1A C27A H27D C2A H2AC C27 H27C C2A H2AB C27 H27B C2A H2AA C27 H27A C2 H2C C28A H28F C2 H2B C28A H28E C2 H2A C28A H28D C3A H3AC C28 H28C C3A H3AB C28 H28B C3A H3AA C28 H28A C3 H3C C29A H29A C3 H3B C29 H C3 H3A C30A H30F C4A H4A C30A H30E C4 H C30A H30D C5A H5AC C30 H30C C5A H5AB C30 H30B C5A H5AA C30 H30A C5 H5C C31A H31F C5 H5B C31A H31E C5 H5A C31A H31D NATURE CHEMISTRY 38

39 C6A H6AC C31 H31C C6A H6AB C31 H31B C6A H6AA C31 H31A C6 H6C C32A H32D C6 H6B C32A H32C C6 H6A C32 H32B C7A H7A C32 H32A C7 H C33A H33D C8A H8AC C33A H33C C8A H8AB C33 H33B C8A H8AA C33 H33A C8 H8C U1 N5A (16) C7 H7B U1 N5B 2.21 (2) C7 H7A U1 N (3) C8 H U1 N (4) C9 H9C U1 N (3) C9 H9B U1 N (3) C9 H9A U1 N (3) C10 H10C Si1 N (4) C10 H10B Si1 C (4) C10 H10A Si1 C (4) C11 H11B Si1 C (4) C11 H11A Si2 N (3) C12 H12B Si2 C (4) C12 H12A Si2 C (4) C13 H13A Si2 C (4) C13 H Si3 N (3) C14 H14C Si3 C (4) C14 H14B Si3 C (4) C14 H14A Si3 C (4) C15 H15C N1 C (5) C15 H15B N2 C (4) C15 H15A N3 C (5) C16 H N4 C (5) C17 H17C N4 C (5) C17 H17B N4 C (5) C17 H17A N5 C (6) C18 H18C NATURE CHEMISTRY 39

40 C2 C (6) C18 H18B C2 C (5) C18 H18A C5 C (6) C19 H C5 C (7) C20 H20C C8 C (6) C20 H20B C8 C (6) C20 H20A C11 C (6) C21 H21C C13 C (5) C21 H21B C13 C (6) C21 H21A C13 N5B 1.65 (2) C22 H22B C16 C (5) C22 H22A C16 C (5) C23 H23B C19 C (6) C23 H23A C19 C (5) C24 H C22 C (6) C25 H25C C24 C (6) C25 H25B C24 C (6) C25 H25A C27 C (6) C26 H26C C27 N5A (17) C26 H26B C27 C (5) C26 H26A C30 C (5) C27 H27A C30 C (5) C27 H C33 C (6) C28 H28C N5B H5B C28 H28B N5A H5AA C28 H28A N5 H C29 H29C C2 H2B C29 H29B C2 H2A C29 H29A C3 H3C C30 H C3 H3B C31 H31C C3 H3A C31 H31B C4 H4C C31 H31A C4 H4B C32 H32C C4 H4A C32 H32B C5 H5A C32 H32A C6 H6C C33 H33B C6 H6B C33 H33A C6 H6A C34 H34B C7 H7C C34 H34A NATURE CHEMISTRY 40

41 9 U1 N (3) C8 H8C U1 N (3) C8 H8B U1 N (3) C8 H8A U1 N (3) C9 H9C U1 N (3) C9 H9B N1 C (4) C9 H9A N1 Si (3) C10 H10B N2 C (4) C10 H10A N2 Si (3) C11 H11B N3 C (4) C11 H11A N3 Si (3) C12 H N4 C (4) C13 H13C N4 C (4) C13 H13B N4 C (4) C13 H13A N5 N (5) C14 H14C N6 N (6) C14 H14B Si1 C (3) C14 H14A Si1 C (3) C15 H Si1 C (3) C16 H16C Si2 C (4) C16 H16B Si2 C (3) C16 H16A Si2 C (4) C17 H17C Si3 C (4) C17 H17B Si3 C (3) C17 H17A Si3 C (4) C18 H C1 C (5) C19 H19C C1 C (5) C19 H19B C4 C (5) C19 H19A C4 C (5) C20 H20C C7 C (5) C20 H20B C7 C (5) C20 H20A C10 C (5) C21 H21B C12 C (5) C21 H21A C12 C (5) C22 H22B C15 C (5) C22 H22A C15 C (5) C23 H C18 C (6) C24 H24C C18 C (5) C24 H24B C21 C (5) C24 H24A NATURE CHEMISTRY 41

42 C23 C (5) C25 H25C C23 C (5) C25 H25B C26 C (5) C25 H25A C26 C (5) C26 H C29 C (5) C27 H27C C29 C (5) C27 H27B C32 C (5) C27 H27A C1 H C28 H28C C2 H2C C28 H28B C2 H2B C28 H28A C2 H2A C29 H C3 H3C C30 H30C C3 H3B C30 H30B C3 H3A C30 H30A C4 H C31 H31C C5 H5C C31 H31B C5 H5B C31 H31A C5 H5A C32 H32B C6 H6C C32 H32A C6 H6B C33 H33B C6 H6A C33 H33A C7 H Table S4. Bond angles ( ) for [U(NSiMe 3 )(Tren TIPS )] (10), [U(NAd)(Tren TIPS )] (11), [U(NH 2 )(Tren TIPS )] (12), [U(μ-N)(μ-Na15C5)(Tren TIPS )] (13), [U(F)(Tren TIPS )] (6), [U(N)(Tren TIPS )] (7), [U{(NHCMe 2 SiPr i 2NCH 2 CH 2 )N(CH 2 CH 2 NSiPr i 3) 2 }] (8), and [U(N 3 )(Tren TIPS )] (9). 10 C2 C1 C (3) H11A C11 H11B C2 C1 Si (3) C10 C11 H11B C3 C1 Si (3) C10 C11 H11A C6 C4 C (3) Si2 C12 H C6 C4 Si (3) C13 C12 H C5 C4 Si (3) C14 C12 H C8 C7 C (3) H13B C13 H13C C8 C7 Si (3) H13A C13 H13C C9 C7 Si (3) H13A C13 H13B NATURE CHEMISTRY 42

43 N1 C10 C (3) C12 C13 H13C N4 C11 C (3) C12 C13 H13B C13 C12 C (3) C12 C13 H13A C13 C12 Si (2) H14B C14 H14C C14 C12 Si (2) H14A C14 H14C C16 C15 C (3) H14A C14 H14B C16 C15 Si (2) C12 C14 H14C C17 C15 Si (2) C12 C14 H14B C19 C18 C (3) C12 C14 H14A C19 C18 Si (2) Si2 C15 H C20 C18 Si (2) C16 C15 H N2 C21 C (3) C17 C15 H N4 C22 C (3) H16B C16 H16C C24A C23 C (7) H16A C16 H16C C24A C23 C (6) H16A C16 H16B C25 C23 C (4) C15 C16 H16C C24A C23 Si (6) C15 C16 H16B C25 C23 Si (3) C15 C16 H16A C24 C23 Si (3) H17B C17 H17C C28 C26 C (4) H17A C17 H17C C28 C26 Si (3) H17A C17 H17B C27 C26 Si (3) C15 C17 H17C C31 C29 C (4) C15 C17 H17B C31 C29 Si (3) C15 C17 H17A C30 C29 Si (4) Si2 C18 H N3 C32 C (3) C19 C18 H N4 C33 C (3) C20 C18 H C10 N1 Si (2) H19B C19 H19C C10 N1 U (2) H19A C19 H19C Si1 N1 U (14) H19A C19 H19B C21 N2 Si (2) C18 C19 H19C C21 N2 U (2) C18 C19 H19B Si2 N2 U (14) C18 C19 H19A C32 N3 Si (2) H20B C20 H20C C32 N3 U (2) H20A C20 H20C Si3 N3 U (15) H20A C20 H20B C22 N4 C (3) C18 C20 H20C C22 N4 C (3) C18 C20 H20B C33 N4 C (3) C18 C20 H20A C22 N4 U (2) N2 C21 H21B NATURE CHEMISTRY 43

44 C33 N4 U (2) N2 C21 H21A C11 N4 U (2) H21A C21 H21B Si4 N5 U (19) C22 C21 H21B N1 Si1 C (15) C22 C21 H21A N1 Si1 C (15) N4 C22 H22B C4 Si1 C (18) N4 C22 H22A N1 Si1 C (16) H22A C22 H22B C4 Si1 C (18) C21 C22 H22B C7 Si1 C (17) C21 C22 H22A N2 Si2 C (14) Si3 C23 H23A N2 Si2 C (14) Si3 C23 H C18 Si2 C (15) H23 C23 H23A N2 Si2 C (15) C24A C23 H23A C18 Si2 C (16) C24 C23 H C12 Si2 C (15) C25 C23 H23A N3 Si3 C (16) C25 C23 H N3 Si3 C (16) H24E C24A H24F C29 Si3 C (2) H24D C24A H24F N3 Si3 C (15) H24D C24A H24E C29 Si3 C (18) C23 C24A H24F C26 Si3 C (17) C23 C24A H24E N5 Si4 C (16) C23 C24A H24D N5 Si4 C (17) C23 C24 H24C C36 Si4 C (19) C23 C24 H24B N5 Si4 C (17) C23 C24 H24A C36 Si4 C (18) H25B C25 H25C C35 Si4 C (18) H25A C25 H25C N5 U1 N (12) H25A C25 H25B N5 U1 N (11) C23 C25 H25C N1 U1 N (10) C23 C25 H25B N5 U1 N (12) C23 C25 H25A N1 U1 N (10) Si3 C26 H N2 U1 N (10) C27 C26 H N5 U1 N (11) C28 C26 H N1 U1 N (9) H27B C27 H27C N2 U1 N (9) H27A C27 H27C N3 U1 N (9) H27A C27 H27B Si1 C1 H C26 C27 H27C C2 C1 H C26 C27 H27B C3 C1 H C26 C27 H27A NATURE CHEMISTRY 44

45 H2B C2 H2C H28B C28 H28C H2A C2 H2C H28A C28 H28C H2A C2 H2B H28A C28 H28B C1 C2 H2C C26 C28 H28C C1 C2 H2B C26 C28 H28B C1 C2 H2A C26 C28 H28A H3B C3 H3C Si3 C29 H H3A C3 H3C C30 C29 H H3A C3 H3B C31 C29 H C1 C3 H3C H30B C30 H30C C1 C3 H3B H30A C30 H30C C1 C3 H3A H30A C30 H30B Si1 C4 H C29 C30 H30C C5 C4 H C29 C30 H30B C6 C4 H C29 C30 H30A H5B C5 H5C H31B C31 H31C H5A C5 H5C H31A C31 H31C H5A C5 H5B H31A C31 H31B C4 C5 H5C C29 C31 H31C C4 C5 H5B C29 C31 H31B C4 C5 H5A C29 C31 H31A H6B C6 H6C N3 C32 H32B H6A C6 H6C N3 C32 H32A H6A C6 H6B H32A C32 H32B C4 C6 H6C C33 C32 H32B C4 C6 H6B C33 C32 H32A C4 C6 H6A N4 C33 H33B Si1 C7 H N4 C33 H33A C8 C7 H H33A C33 H33B C9 C7 H C32 C33 H33B H8B C8 H8C C32 C33 H33A H8A C8 H8C Si4 C34 H34C H8A C8 H8B Si4 C34 H34B C7 C8 H8C Si4 C34 H34A C7 C8 H8B H34B C34 H34C C7 C8 H8A H34A C34 H34C H9B C9 H9C H34A C34 H34B H9A C9 H9C Si4 C35 H35C H9A C9 H9B Si4 C35 H35B C7 C9 H9C Si4 C35 H35A NATURE CHEMISTRY 45

46 C7 C9 H9B H35B C35 H35C C7 C9 H9A H35A C35 H35C N1 C10 H10B H35A C35 H35B N1 C10 H10A Si4 C36 H36C H10A C10 H10B Si4 C36 H36B C11 C10 H10B Si4 C36 H36A C11 C10 H10A H36B C36 H36C N4 C11 H11B H36A C36 H36C N4 C11 H11A H36A C36 H36B N5 U1 N5A 17.9 (7) C10 C11 H11A N5 U1 N (5) Si2 C12 H N5A U1 N (8) C13 C12 H N5 U1 N (4) C14 C12 H N5A U1 N (7) H13B C13 H13C N3 U1 N (2) H13A C13 H13C N5 U1 N (4) H13A C13 H13B N5A U1 N (7) C12 C13 H13C N3 U1 N (3) C12 C13 H13B N2 U1 N (3) C12 C13 H13A N5 U1 N (4) H14B C14 H14C N5A U1 N (8) H14A C14 H14C N3 U1 N (2) H14A C14 H14B N2 U1 N (2) C12 C14 H14C N1 U1 N (2) C12 C14 H14B N1 Si1 C1A (11) C12 C14 H14A N1 Si1 C (4) Si2 C15 H C1A Si1 C (14) C16 C15 H N1 Si1 C (4) C17 C15 H C1A Si1 C (13) H16B C16 H16C C7 Si1 C (5) H16A C16 H16C N1 Si1 C (6) H16A C16 H16B C1A Si1 C (14) C15 C16 H16C C7 Si1 C (7) C15 C16 H16B C4 Si1 C (7) C15 C16 H16A N2 Si2 C (4) H17B C17 H17C N2 Si2 C (4) H17A C17 H17C C18 Si2 C (7) H17A C17 H17B N2 Si2 C (4) C15 C17 H17C NATURE CHEMISTRY 46

47 C18 Si2 C (5) C15 C17 H17B C12 Si2 C (5) C15 C17 H17A N3 Si3 C (6) Si2 C18 H N3 Si3 C26A (16) C19 C18 H C23 Si3 C26A 98.0 (18) C20 C18 H N3 Si3 C (8) H19B C19 H19C C23 Si3 C (10) H19A C19 H19C C26A Si3 C26 21 (2) H19A C19 H19B N3 Si3 C (5) C18 C19 H19C C23 Si3 C (7) C18 C19 H19B C26A Si3 C (2) C18 C19 H19A C26 Si3 C (10) H20B C20 H20C N3 Si3 C23A 95.9 (10) H20A C20 H20C C23 Si3 C23A 15.1 (10) H20A C20 H20B C26A Si3 C23A 99 (2) C18 C20 H20C C26 Si3 C23A (13) C18 C20 H20B C29 Si3 C23A (9) C18 C20 H20A C10 N1 Si (5) N2 C21 H21B C10 N1 U (5) N2 C21 H21A Si1 N1 U (4) H21A C21 H21B C21 N2 Si (5) C22 C21 H21B C21 N2 U (4) C22 C21 H21A Si2 N2 U (4) N4 C22 H22B C32 N3 Si (6) N4 C22 H22A C32 N3 U (5) H22A C22 H22B Si3 N3 U (4) C21 C22 H22B C22 N4 C (6) C21 C22 H22A C22 N4 C (6) Si3 C23A H23A C11 N4 C (6) C24A C23A H23A C22 N4 U (5) C25A C23A H23A C11 N4 U (4) Si3 C23 H C33 N4 U (5) C24 C23 H C34 N5 U (9) C25 C23 H C34A N5A U1 171 (2) H24E C24A H24F C3 C1 C (13) H24D C24A H24F C3 C1 Si (12) H24D C24A H24E C2 C1 Si (14) C23A C24A H24F C3A C1A C2A 126 (3) C23A C24A H24E C3A C1A Si1 117 (2) C23A C24A H24D C2A C1A Si1 110 (2) H25E C25A H25F NATURE CHEMISTRY 47

48 C6 C4 C (9) H25D C25A H25F C6 C4 Si (9) H25D C25A H25E C5 C4 Si (7) C23A C25A H25F C9 C7 C (10) C23A C25A H25E C9 C7 Si (7) C23A C25A H25D C8 C7 Si (7) Si3 C26A H26A N1 C10 C (6) C27A C26A H26A N4 C11 C (6) C28A C26A H26A C13 C12 C (11) Si3 C26 H C13 C12 Si (8) C27 C26 H C14 C12 Si (8) C28 C26 H C16 C15 C (7) H27E C27A H27F C16 C15 Si (6) H27D C27A H27F C17 C15 Si (6) H27D C27A H27E C20 C18 C (10) C26A C27A H27F C20 C18 Si (8) C26A C27A H27E C19 C18 Si (9) C26A C27A H27D N2 C21 C (7) H28E C28A H28F N4 C22 C (6) H28D C28A H28F C24 C23 C (13) H28D C28A H28E C24 C23 Si (13) C26A C28A H28F C25 C23 Si (12) C26A C28A H28E C24A C23A C25A 108 (3) C26A C28A H28D C24A C23A Si3 114 (2) Si3 C29 H C25A C23A Si3 105 (2) C30 C29 H C28 C26 C (2) C31 C29 H C28 C26 Si (17) H30B C30 H30C C27 C26 Si (16) H30A C30 H30C C27A C26A C28A 85 (4) H30A C30 H30B C27A C26A Si3 122 (3) C29 C30 H30C C28A C26A Si3 120 (3) C29 C30 H30B C31 C29 C (11) C29 C30 H30A C31 C29 Si (9) H31B C31 H31C C30 C29 Si (10) H31A C31 H31C N3 C32 C (6) H31A C31 H31B N4 C33 C (7) C29 C31 H31C N5 C34 C (12) C29 C31 H31B N5 C34 C (13) C29 C31 H31A C36 C34 C (12) N3 C32 H32B N5 C34 C (10) N3 C32 H32A NATURE CHEMISTRY 48

49 C36 C34 C (12) H32A C32 H32B C35 C34 C (11) C33 C32 H32B N5A C34A C36A 111 (2) C33 C32 H32A N5A C34A C35A 108 (3) N4 C33 H33B C36A C34A C35A 111 (2) N4 C33 H33A N5A C34A C (19) H33A C33 H33B C36A C34A C (2) C32 C33 H33B C35A C34A C (2) C32 C33 H33A C34 C35 C (13) H35C C35A H35D C34A C35A C40A 110 (2) C34A C35A H35D C34 C36 C (12) C34A C35A H35C C34A C36A C42A 107 (2) C40A C35A H35D C38 C37 C (9) C40A C35A H35C C38 C37 C34A (12) H35A C35 H35B C34 C37 C34A 30.7 (11) C34 C35 H35B C38 C37 C38A 27.0 (11) C34 C35 H35A C34 C37 C38A (11) C40 C35 H35B C34A C37 C38A 97.7 (15) C40 C35 H35A C43 C38 C (12) H36C C36A H36D C43 C38 C (12) C34A C36A H36D C37 C38 C (12) C34A C36A H36C C43A C38A C39A 120 (3) C42A C36A H36D C43A C38A C (2) C42A C36A H36C C39A C38A C (2) H36A C36 H36B C40 C39 C (12) C34 C36 H36B C38A C39A C40A 109 (2) C34 C36 H36A C39 C40 C (12) C42 C36 H36B C39 C40 C (13) C42 C36 H36A C35 C40 C (13) H37C C37 H37D C41A C40A C35A 108 (2) H37B C37 H37D 63.2 C41A C40A C39A 108 (2) H37B C37 H37C 46.7 C35A C40A C39A 109 (2) H37A C37 H37D 45.4 C42 C41 C (12) H37A C37 H37C C42A C41A C40A 110 (2) H37A C37 H37B C41 C42 C (13) C34A C37 H37D C41 C42 C (12) C34A C37 H37C C36 C42 C (11) C34A C37 H37B C41A C42A C43A 116 (2) C34A C37 H37A 80.0 C41A C42A C36A 111 (3) C34 C37 H37D C43A C42A C36A 107 (2) C34 C37 H37C 81.8 NATURE CHEMISTRY 49

50 C38 C43 C (12) C34 C37 H37B C38A C43A C42A 105 (3) C34 C37 H37A Si1 C1A H1AA 99.2 C38A C37 H37D C2A C1A H1AA 99.2 C38A C37 H37C C3A C1A H1AA 99.2 C38A C37 H37B Si1 C1 H1A C38A C37 H37A 86.7 C2 C1 H1A C38 C37 H37D C3 C1 H1A C38 C37 H37C 85.9 H1 C2A H2AB C38 C37 H37B H1 C2A H2AA C38 C37 H37A H2AA C2A H2AB C37 C38A H38A C1A C2A H C39A C38A H38A C1A C2A H2AB C43A C38A H38A C1A C2A H2AA C37 C38 H H3AB C3A H3AC C39 C38 H H3AA C3A H3AC C43 C38 H H3AA C3A H3AB H39C C39A H39D C1A C3A H3AC C38A C39A H39D C1A C3A H3AB C38A C39A H39C C1A C3A H3AA C40A C39A H39D Si1 C4 H C40A C39A H39C C5 C4 H H39A C39 H39B C6 C4 H C38 C39 H39B H5B C5 H5C C38 C39 H39A H5A C5 H5C C40 C39 H39B H5A C5 H5B C40 C39 H39A C4 C5 H5C C35A C40A H40A C4 C5 H5B C39A C40A H40A C4 C5 H5A C41A C40A H40A H6B C6 H6C C35 C40 H H6A C6 H6C C39 C40 H H6A C6 H6B C41 C40 H C4 C6 H6C H41C C41A H41D C4 C6 H6B C40A C41A H41D C4 C6 H6A C40A C41A H41C Si1 C7 H C42A C41A H41D C8 C7 H C42A C41A H41C C9 C7 H H41A C41 H41B H8B C8 H8C C40 C41 H41B H8A C8 H8C C40 C41 H41A NATURE CHEMISTRY 50

51 H8A C8 H8B C42 C41 H41B C7 C8 H8C C42 C41 H41A C7 C8 H8B C36A C42A H42A C7 C8 H8A C41A C42A H42A H9B C9 H9C C43A C42A H42A H9A C9 H9C C36 C42 H H9A C9 H9B C41 C42 H C7 C9 H9C C43 C42 H C7 C9 H9B H43C C43A H43D C7 C9 H9A C38A C43A H43D N1 C10 H10B C38A C43A H43C N1 C10 H10A C42A C43A H43D H10A C10 H10B C42A C43A H43C C11 C10 H10B H43A C43 H43B C11 C10 H10A C38 C43 H43B N4 C11 H11B C38 C43 H43A N4 C11 H11A C42 C43 H43B H11A C11 H11B C42 C43 H43A C10 C11 H11B N4 C1 C (4) Si1 C5 H N1 C2 C (4) C1C C5 H C1B C4 C (5) C3 C5 H C1B C4 Si (4) N2 C6 H6B C9 C4 Si (4) N2 C6 H6A C3 C5 C1C (5) H6A C6 H6B C3 C5 Si (4) C10 C6 H6B C1C C5 Si (4) C10 C6 H6A N2 C6 C (4) N3 C7 H7B N3 C7 C (4) N3 C7 H7A C1D C8 C (5) H7A C7 H7B C1D C8 Si (4) C1 C7 H7B C14 C8 Si (4) C1 C7 H7A N4 C10 C (4) Si1 C8 H N4 C11 C (4) C1D C8 H C1A C12 C (5) C14 C8 H C1A C12 Si (4) H9B C9 H9C C13 C12 Si (4) H9A C9 H9C C16 C15 C (5) H9A C9 H9B NATURE CHEMISTRY 51

52 C16 C15 Si (4) C4 C9 H9C C17 C15 Si (4) C4 C9 H9B C20 C18 C (5) C4 C9 H9A C20 C18 Si (3) N4 C10 H10B C19 C18 Si (4) N4 C10 H10A C23 C21 C (5) H10A C10 H10B C23 C21 Si (4) C6 C10 H10B C22 C21 Si (4) C6 C10 H10A C25 C24 C (5) N4 C11 H11B C25 C24 Si (4) N4 C11 H11A C26 C24 Si (4) H11A C11 H11B C28 C27 C (5) C2 C11 H11B C28 C27 Si (4) C2 C11 H11A C29 C27 Si (4) Si2 C12 H C2 N1 Si (3) C1A C12 H C2 N1 U (3) C13 C12 H Si1 N1 U (2) H13B C13 H13C C6 N2 Si (3) H13A C13 H13C C6 N2 U (3) H13A C13 H13B Si2 N2 U (2) C12 C13 H13C C7 N3 Si (3) C12 C13 H13B C7 N3 U (3) C12 C13 H13A Si3 N3 U (2) H14B C14 H14C C1 N4 C (4) H14A C14 H14C C1 N4 C (4) H14A C14 H14B C11 N4 C (4) C8 C14 H14C C1 N4 U (3) C8 C14 H14B C11 N4 U (3) C8 C14 H14A C10 N4 U (3) Si2 C15 H N1 Si1 C (2) C16 C15 H N1 Si1 C (2) C17 C15 H C8 Si1 C (3) H16B C16 H16C N1 Si1 C (2) H16A C16 H16C C8 Si1 C (2) H16A C16 H16B C5 Si1 C (3) C15 C16 H16C N2 Si2 C (2) C15 C16 H16B N2 Si2 C (2) C15 C16 H16A C12 Si2 C (2) H17B C17 H17C N2 Si2 C (2) H17A C17 H17C C12 Si2 C (2) H17A C17 H17B NATURE CHEMISTRY 52

53 C18 Si2 C (2) C15 C17 H17C N3 Si3 C (2) C15 C17 H17B N3 Si3 C (2) C15 C17 H17A C21 Si3 C (3) Si2 C18 H N3 Si3 C (2) C19 C18 H C21 Si3 C (3) C20 C18 H C27 Si3 C (2) H19B C19 H19C N5 U1 N (17) H19A C19 H19C N5 U1 N (15) H19A C19 H19B N3 U1 N (15) C18 C19 H19C N5 U1 N (15) C18 C19 H19B N3 U1 N (15) C18 C19 H19A N2 U1 N (14) H20B C20 H20C N5 U1 N (16) H20A C20 H20C N3 U1 N (14) H20A C20 H20B N2 U1 N (13) C18 C20 H20C N1 U1 N (13) C18 C20 H20B U1 N5 H5B 127 (5) C18 C20 H20A U1 N5 H5A 122 (8) Si3 C21 H H5A N5 H5B 108 (9) C22 C21 H H1DB C1D H1DC C23 C21 H H1DA C1D H1DC H22B C22 H22C H1DA C1D H1DB H22A C22 H22C C8 C1D H1DC H22A C22 H22B C8 C1D H1DB C21 C22 H22C C8 C1D H1DA C21 C22 H22B H1CB C1C H1CC C21 C22 H22A H1CA C1C H1CC H23B C23 H23C H1CA C1C H1CB H23A C23 H23C C5 C1C H1CC H23A C23 H23B C5 C1C H1CB C21 C23 H23C C5 C1C H1CA C21 C23 H23B H1BB C1B H1BC C21 C23 H23A H1BA C1B H1BC Si3 C24 H H1BA C1B H1BB C25 C24 H C4 C1B H1BC C26 C24 H C4 C1B H1BB H25B C25 H25C C4 C1B H1BA H25A C25 H25C H1AB C1A H1AC H25A C25 H25B H1AA C1A H1AC C24 C25 H25C NATURE CHEMISTRY 53

54 H1AA C1A H1AB C24 C25 H25B C12 C1A H1AC C24 C25 H25A C12 C1A H1AB H26B C26 H26C C12 C1A H1AA H26A C26 H26C N4 C1 H1B H26A C26 H26B N4 C1 H1A C24 C26 H26C H1A C1 H1B C24 C26 H26B C7 C1 H1B C24 C26 H26A C7 C1 H1A Si3 C27 H N1 C2 H2B C28 C27 H N1 C2 H2A C29 C27 H H2A C2 H2B H28B C28 H28C C11 C2 H2B H28A C28 H28C C11 C2 H2A H28A C28 H28B H3B C3 H3C C27 C28 H28C H3A C3 H3C C27 C28 H28B H3A C3 H3B C27 C28 H28A C5 C3 H3C H29B C29 H29C C5 C3 H3B H29A C29 H29C C5 C3 H3A H29A C29 H29B Si1 C4 H C27 C29 H29C C1B C4 H C27 C29 H29B C9 C4 H C27 C29 H29A N3 U1 N1 i (6) O2 i Na1 O (3) N3 U1 N (6) O2 ii Na1 O (3) N1 i U1 N (7) O3 ii Na1 O (2) N3 U1 N1 ii (6) O3 i Na1 O (2) N1 i U1 N1 ii (7) O3 Na1 O (3) N1 U1 N1 ii (7) O1 ii Na1 O (4) N3 U1 N (9) O1 i Na1 O (3) N1 i U1 N (6) O1 Na1 O (3) N1 U1 N (6) O4 i Na1 O (3) N1 ii U1 N (6) O4 ii Na1 O (3) N1 Si1 C (14) O4 Na1 O (3) N1 Si1 C (14) O5 i Na1 O (15) C1 Si1 C (16) O5 ii Na1 O (15) N1 Si1 C (15) C12 O1 C (9) C1 Si1 C (17) C12 O1 Na (7) NATURE CHEMISTRY 54

55 C7 Si1 C (16) C21 O1 Na (8) C10 N1 Si (2) O1 C12 C (9) C10 N1 U (2) O2 C13 C (11) Si1 N1 U (14) C14 O2 C (10) C11 N2 C11 ii (19) C14 O2 Na (7) C11 N2 C11 i (19) C13 O2 Na (9) C11 ii N2 C11 i (19) O2 C14 C (10) C11 N2 U (2) O3 C15 C (10) C11 ii N2 U (2) C15 O3 C (11) C11 i N2 U (2) C15 O3 Na (7) U1 N3 Na (4) C16 O3 Na (7) C3 C1 C (3) O3 C16 C (10) C3 C1 Si (3) O4 C17 C (10) C2 C1 Si (3) C17 O4 C (11) C5 C4 C (3) C17 O4 Na (9) C5 C4 Si (3) C18 O4 Na (9) C6 C4 Si (3) O4 C18 C (11) C9 C7 C (3) O5 C19 C (10) C9 C7 Si (3) C19 O5 C (10) C8 C7 Si (3) C19 O5 Na (7) N1 C10 C (3) C20 O5 Na (8) N2 C11 C (3) O5 C20 C (9) N3 Na1 O (2) O1 C21 C (9) N3 Na1 O2 i (2) Si1 C1 H O2 Na1 O2 i 95.1 (3) C2 C1 H N3 Na1 O2 ii (2) C3 C1 H O2 Na1 O2 ii 95.1 (3) H2B C2 H2C O2 i Na1 O2 ii 95.1 (3) H2A C2 H2C N3 Na1 O3 ii (2) H2A C2 H2B O2 Na1 O3 ii (3) C1 C2 H2C O2 i Na1 O3 ii 44.3 (3) C1 C2 H2B O2 ii Na1 O3 ii 69.8 (3) C1 C2 H2A N3 Na1 O3 i (2) H3B C3 H3C O2 Na1 O3 i 44.3 (3) H3A C3 H3C O2 i Na1 O3 i 69.8 (3) H3A C3 H3B O2 ii Na1 O3 i (3) C1 C3 H3C O3 ii Na1 O3 i (18) C1 C3 H3B N3 Na1 O (2) C1 C3 H3A O2 Na1 O (3) Si1 C4 H O2 i Na1 O (3) C5 C4 H NATURE CHEMISTRY 55

56 O2 ii Na1 O (3) C6 C4 H O3 ii Na1 O (18) H5B C5 H5C O3 i Na1 O (18) H5A C5 H5C N3 Na1 O1 ii (3) H5A C5 H5B O2 Na1 O1 ii 36.5 (3) C4 C5 H5C O2 i Na1 O1 ii (3) C4 C5 H5B O2 ii Na1 O1 ii 69.0 (3) C4 C5 H5A O3 ii Na1 O1 ii (3) H6B C6 H6C O3 i Na1 O1 ii 80.1 (3) H6A C6 H6C O3 Na1 O1 ii 33.7 (3) H6A C6 H6B N3 Na1 O1 i (3) C4 C6 H6C O2 Na1 O1 i (3) C4 C6 H6B O2 i Na1 O1 i 69.0 (3) C4 C6 H6A O2 ii Na1 O1 i 36.5 (3) Si1 C7 H O3 ii Na1 O1 i 33.7 (3) C8 C7 H O3 i Na1 O1 i (3) C9 C7 H O3 Na1 O1 i 80.1 (3) H8B C8 H8C O1 ii Na1 O1 i (3) H8A C8 H8C N3 Na1 O (3) H8A C8 H8B O2 Na1 O (3) C7 C8 H8C O2 i Na1 O (3) C7 C8 H8B O2 ii Na1 O (3) C7 C8 H8A O3 ii Na1 O (3) H9B C9 H9C O3 i Na1 O (3) H9A C9 H9C O3 Na1 O (3) H9A C9 H9B O1 ii Na1 O (3) C7 C9 H9C O1 i Na1 O (3) C7 C9 H9B N3 Na1 O4 i (2) C7 C9 H9A O2 Na1 O4 i 21.7 (2) N1 C10 H10B O2 i Na1 O4 i (3) N1 C10 H10A O2 ii Na1 O4 i 77.3 (3) H10A C10 H10B O3 ii Na1 O4 i (3) C11 C10 H10B O3 i Na1 O4 i 66.0 (3) C11 C10 H10A O3 Na1 O4 i 48.1 (3) N2 C11 H11B O1 ii Na1 O4 i 15.3 (3) N2 C11 H11A O1 i Na1 O4 i (3) H11A C11 H11B O1 Na1 O4 i 89.1 (3) C10 C11 H11B N3 Na1 O4 ii (2) C10 C11 H11A O2 Na1 O4 ii 77.3 (3) O1 C12 H12B O2 i Na1 O4 ii 21.7 (2) O1 C12 H12A NATURE CHEMISTRY 56

57 O2 ii Na1 O4 ii (3) H12A C12 H12B O3 ii Na1 O4 ii 66.0 (3) C13 C12 H12B O3 i Na1 O4 ii 48.1 (3) C13 C12 H12A O3 Na1 O4 ii (3) O2 C13 H13B O1 ii Na1 O4 ii (3) O2 C13 H13A O1 i Na1 O4 ii 89.1 (3) H13A C13 H13B O1 Na1 O4 ii 15.3 (3) C12 C13 H13B O4 i Na1 O4 ii 94.8 (3) C12 C13 H13A N3 Na1 O (2) O2 C14 H14B O2 Na1 O (3) O2 C14 H14A O2 i Na1 O (3) H14A C14 H14B O2 ii Na1 O (2) C15 C14 H14B O3 ii Na1 O (3) C15 C14 H14A O3 i Na1 O (3) O3 C15 H15B O3 Na1 O (3) O3 C15 H15A O1 ii Na1 O (3) H15A C15 H15B O1 i Na1 O (3) C14 C15 H15B O1 Na1 O (3) C14 C15 H15A O4 i Na1 O (3) O3 C16 H16B O4 ii Na1 O (3) O3 C16 H16A N3 Na1 O5 i (2) H16A C16 H16B O2 Na1 O5 i 85.8 (3) C17 C16 H16B O2 i Na1 O5 i (3) C17 C16 H16A O2 ii Na1 O5 i 32.3 (3) O4 C17 H17B O3 ii Na1 O5 i 99.1 (2) O4 C17 H17A O3 i Na1 O5 i (3) H17A C17 H17B O3 Na1 O5 i 17.0 (2) C16 C17 H17B O1 ii Na1 O5 i 50.3 (3) C16 C17 H17A O1 i Na1 O5 i 65.6 (3) O4 C18 H18B O1 Na1 O5 i (4) O4 C18 H18A O4 i Na1 O5 i 64.1 (3) H18A C18 H18B O4 ii Na1 O5 i (3) C19 C18 H18B O4 Na1 O5 i 52.7 (3) C19 C18 H18A N3 Na1 O5 ii (2) O5 C19 H19B O2 Na1 O5 ii 32.3 (3) O5 C19 H19A O2 i Na1 O5 ii 85.8 (3) H19A C19 H19B O2 ii Na1 O5 ii (3) C18 C19 H19B O3 ii Na1 O5 ii (3) C18 C19 H19A O3 i Na1 O5 ii 17.0 (2) O5 C20 H20B O3 Na1 O5 ii 99.1 (2) O5 C20 H20A NATURE CHEMISTRY 57

58 O1 ii Na1 O5 ii 65.6 (3) H20A C20 H20B O1 i Na1 O5 ii (4) C21 C20 H20B O1 Na1 O5 ii 50.3 (3) C21 C20 H20A O4 i Na1 O5 ii 52.7 (3) O1 C21 H21B O4 ii Na1 O5 ii 64.1 (3) O1 C21 H21A O4 Na1 O5 ii (3) H21A C21 H21B O5 i Na1 O5 ii (15) C20 C21 H21B N3 Na1 O (2) C20 C21 H21A O2 Na1 O (3) 6 F2 U2 N (19) H19A C19 H19B F2 U2 N (19) C18 C19 H19C N7 U2 N (2) C18 C19 H19B F2 U2 N (19) C18 C19 H19A N7 U2 N (2) H20B C20 H20C N5 U2 N (2) H20A C20 H20C F2 U2 N (18) H20A C20 H20B N7 U2 N (2) C18 C20 H20C N5 U2 N (19) C18 C20 H20B N6 U2 N (2) C18 C20 H20A N5 Si4 C (4) N2 C21 H21B N5 Si4 C (3) N2 C21 H21A C37 Si4 C (4) H21A C21 H21B N5 Si4 C (3) C22 C21 H21B C37 Si4 C (4) C22 C21 H21A C34 Si4 C (4) N4 C22 H22B N6 Si5 C (4) N4 C22 H22A N6 Si5 C (4) H22A C22 H22B C48 Si5 C (5) C21 C22 H22B N6 Si5 C (4) C21 C22 H22A C48 Si5 C (5) Si3 C23 H C45 Si5 C (5) C24 C23 H N7 Si6 C (3) C25 C23 H N7 Si6 C (3) H24B C24 H24C C59 Si6 C (3) H24A C24 H24C N7 Si6 C (3) H24A C24 H24B C59 Si6 C (4) C23 C24 H24C C56 Si6 C (3) C23 C24 H24B C43 N5 Si (4) C23 C24 H24A NATURE CHEMISTRY 58

59 C43 N5 U (4) H25B C25 H25C Si4 N5 U (3) H25A C25 H25C C54 N6 Si (5) H25A C25 H25B C54 N6 U (5) C23 C25 H25C Si5 N6 U (3) C23 C25 H25B C65 N7 Si (5) C23 C25 H25A C65 N7 U (4) Si3 C26 H Si6 N7 U (3) C27 C26 H C66 N8 C (6) C28 C26 H C66 N8 C (6) H27B C27 H27C C55 N8 C (6) H27A C27 H27C C66 N8 U (4) H27A C27 H27B C55 N8 U (4) C26 C27 H27C C44 N8 U (4) C26 C27 H27B C35 C34 C (7) C26 C27 H27A C35 C34 Si (6) H28B C28 H28C C36 C34 Si (6) H28A C28 H28C C38 C37 C (8) H28A C28 H28B C38 C37 Si (6) C26 C28 H28C C39 C37 Si (7) C26 C28 H28B C41 C40 C (8) C26 C28 H28A C41 C40 Si (6) Si3 C29 H C42 C40 Si (7) C30A C29 H N5 C43 C (6) C30 C29 H N8 C44 C (6) C31 C29 H C46 C45 C (9) H30E C30A H30F C46 C45 Si (7) H30D C30A H30F C47 C45 Si (7) H30D C30A H30E C50 C48 C (10) C29 C30A H30F C50 C48 Si (8) C29 C30A H30E C49 C48 Si (7) C29 C30A H30D C52 C51 C (11) C29 C30 H30C C52 C51 Si (8) C29 C30 H30B C53 C51 Si (8) C29 C30 H30A N6 C54 C (6) H31B C31 H31C N8 C55 C (6) H31A C31 H31C C58 C56 C (6) H31A C31 H31B C58 C56 Si (5) C29 C31 H31C C57 C56 Si (5) C29 C31 H31B C60 C59 C (8) C29 C31 H31A NATURE CHEMISTRY 59

60 C60 C59 Si (6) N3 C32 H32B C61 C59 Si (6) N3 C32 H32A C63 C62 C (7) H32A C32 H32B C63 C62 Si (6) C33 C32 H32B C64 C62 Si (6) C33 C32 H32A N7 C65 C (6) N4 C33 H33B N8 C66 C (6) N4 C33 H33A F1 U1 N (19) H33A C33 H33B F1 U1 N (2) C32 C33 H33B N2 U1 N (2) C32 C33 H33A F1 U1 N (19) Si4 C34 H N2 U1 N (2) C35 C34 H N3 U1 N (2) C36 C34 H F1 U1 N (2) H35B C35 H35C N2 U1 N (2) H35A C35 H35C N3 U1 N (2) H35A C35 H35B N1 U1 N (2) C34 C35 H35C N1 Si1 C (3) C34 C35 H35B N1 Si1 C (4) C34 C35 H35A C1 Si1 C (4) H36B C36 H36C N1 Si1 C (3) H36A C36 H36C C1 Si1 C (4) H36A C36 H36B C4 Si1 C (4) C34 C36 H36C N2 Si2 C (3) C34 C36 H36B N2 Si2 C (4) C34 C36 H36A C12 Si2 C (4) Si4 C37 H N2 Si2 C (4) C38 C37 H C12 Si2 C (4) C39 C37 H C15 Si2 C (5) H38B C38 H38C N3 Si3 C (4) H38A C38 H38C N3 Si3 C (3) H38A C38 H38B C23 Si3 C (4) C37 C38 H38C N3 Si3 C (4) C37 C38 H38B C23 Si3 C (5) C37 C38 H38A C26 Si3 C (5) H39B C39 H39C C10 N1 Si (5) H39A C39 H39C C10 N1 U (4) H39A C39 H39B Si1 N1 U (3) C37 C39 H39C C21 N2 Si (5) C37 C39 H39B C21 N2 U (4) C37 C39 H39A NATURE CHEMISTRY 60

61 Si2 N2 U (3) Si4 C40 H C32 N3 Si (5) C41 C40 H C32 N3 U (5) C42 C40 H Si3 N3 U (3) H41B C41 H41C C33 N4 C (6) H41A C41 H41C C33 N4 C (6) H41A C41 H41B C22 N4 C (7) C40 C41 H41C C33 N4 U (5) C40 C41 H41B C22 N4 U (5) C40 C41 H41A C11 N4 U (4) H42B C42 H42C C2 C1 C (7) H42A C42 H42C C2 C1 Si (6) H42A C42 H42B C3 C1 Si (5) C40 C42 H42C C5 C4 C (8) C40 C42 H42B C5 C4 Si (6) C40 C42 H42A C6 C4 Si (7) N5 C43 H43B C9 C7 C (8) N5 C43 H43A C9 C7 Si (7) H43A C43 H43B C8 C7 Si (7) C44 C43 H43B C11 C10 N (6) C44 C43 H43A C10 C11 N (6) N8 C44 H44B C13 C12 C (8) N8 C44 H44A C13 C12 Si (7) H44A C44 H44B C14 C12 Si (7) C43 C44 H44B C16 C15 C (9) C43 C44 H44A C16 C15 Si (7) Si5 C45 H C17 C15 Si (8) C46 C45 H C20 C18 C (10) C47 C45 H C20 C18 Si (7) H46B C46 H46C C19 C18 Si (9) H46A C46 H46C N2 C21 C (6) H46A C46 H46B N4 C22 C (6) C45 C46 H46C C25 C23 C (9) C45 C46 H46B C25 C23 Si (6) C45 C46 H46A C24 C23 Si (6) H47B C47 H47C C28 C26 C (8) H47A C47 H47C C28 C26 Si (6) H47A C47 H47B C27 C26 Si (6) C45 C47 H47C C30A C29 C (16) C45 C47 H47B C31 C29 C (15) C45 C47 H47A NATURE CHEMISTRY 61

62 C30A C29 Si (12) Si5 C48 H C31 C29 Si (8) C49 C48 H C30 C29 Si (11) C50 C48 H N3 C32 C (7) H49B C49 H49C N4 C33 C (7) H49A C49 H49C Si1 C1 H H49A C49 H49B C2 C1 H C48 C49 H49C C3 C1 H C48 C49 H49B H2B C2 H2C C48 C49 H49A H2A C2 H2C H50B C50 H50C H2A C2 H2B H50A C50 H50C C1 C2 H2C H50A C50 H50B C1 C2 H2B C48 C50 H50C C1 C2 H2A C48 C50 H50B H3B C3 H3C C48 C50 H50A H3A C3 H3C Si5 C51 H H3A C3 H3B C52 C51 H C1 C3 H3C C53 C51 H C1 C3 H3B H52B C52 H52C C1 C3 H3A H52A C52 H52C Si1 C4 H H52A C52 H52B C5 C4 H C51 C52 H52C C6 C4 H C51 C52 H52B H5B C5 H5C C51 C52 H52A H5A C5 H5C H53B C53 H53C H5A C5 H5B H53A C53 H53C C4 C5 H5C H53A C53 H53B C4 C5 H5B C51 C53 H53C C4 C5 H5A C51 C53 H53B H6B C6 H6C C51 C53 H53A H6A C6 H6C N6 C54 H54B H6A C6 H6B N6 C54 H54A C4 C6 H6C H54A C54 H54B C4 C6 H6B C55 C54 H54B C4 C6 H6A C55 C54 H54A Si1 C7 H N8 C55 H55B C8 C7 H N8 C55 H55A C9 C7 H H55A C55 H55B H8B C8 H8C C54 C55 H55B H8A C8 H8C C54 C55 H55A NATURE CHEMISTRY 62

63 H8A C8 H8B Si6 C56 H C7 C8 H8C C57 C56 H C7 C8 H8B C58 C56 H C7 C8 H8A H57B C57 H57C H9B C9 H9C H57A C57 H57C H9A C9 H9C H57A C57 H57B H9A C9 H9B C56 C57 H57C C7 C9 H9C C56 C57 H57B C7 C9 H9B C56 C57 H57A C7 C9 H9A H58B C58 H58C N1 C10 H10B H58A C58 H58C N1 C10 H10A H58A C58 H58B H10A C10 H10B C56 C58 H58C C11 C10 H10B C56 C58 H58B C11 C10 H10A C56 C58 H58A N4 C11 H11B Si6 C59 H N4 C11 H11A C60 C59 H H11A C11 H11B C61 C59 H C10 C11 H11B H60B C60 H60C C10 C11 H11A H60A C60 H60C Si2 C12 H H60A C60 H60B C13 C12 H C59 C60 H60C C14 C12 H C59 C60 H60B H13B C13 H13C C59 C60 H60A H13A C13 H13C H61B C61 H61C H13A C13 H13B H61A C61 H61C C12 C13 H13C H61A C61 H61B C12 C13 H13B C59 C61 H61C C12 C13 H13A C59 C61 H61B H14B C14 H14C C59 C61 H61A H14A C14 H14C Si6 C62 H H14A C14 H14B C63 C62 H C12 C14 H14C C64 C62 H C12 C14 H14B H63B C63 H63C C12 C14 H14A H63A C63 H63C Si2 C15 H H63A C63 H63B C16 C15 H C62 C63 H63C C17 C15 H C62 C63 H63B H16B C16 H16C C62 C63 H63A H16A C16 H16C H64B C64 H64C NATURE CHEMISTRY 63

64 H16A C16 H16B H64A C64 H64C C15 C16 H16C H64A C64 H64B C15 C16 H16B C62 C64 H64C C15 C16 H16A C62 C64 H64B H17B C17 H17C C62 C64 H64A H17A C17 H17C N7 C65 H65B H17A C17 H17B N7 C65 H65A C15 C17 H17C H65A C65 H65B C15 C17 H17B C66 C65 H65B C15 C17 H17A C66 C65 H65A Si2 C18 H N8 C66 H66B C19 C18 H N8 C66 H66A C20 C18 H H66A C66 H66B H19B C19 H19C C65 C66 H66B H19A C19 H19C C65 C66 H66A N5 U1 N (4) Si1 C4 H N5 U1 N1A (5) C5 C4 H N1 U1 N1A 20.9 (4) C6 C4 H N5 U1 N (3) H5B C5 H5C N1 U1 N (3) H5A C5 H5C N1A U1 N (4) H5A C5 H5B N5 U1 N2A (3) C4 C5 H5C N1 U1 N2A (5) C4 C5 H5B N1A U1 N2A (5) C4 C5 H5A N2 U1 N2A 20.2 (3) H6B C6 H6C N5 U1 N3A (4) H6A C6 H6C N1 U1 N3A 90.0 (3) H6A C6 H6B N1A U1 N3A (4) C4 C6 H6C N2 U1 N3A (5) C4 C6 H6B N2A U1 N3A (5) C4 C6 H6A N5 U1 N (5) Si1 C7A H7A N1 U1 N (3) C8A C7A H7A N1A U1 N (3) C9A C7A H7A N2 U1 N (3) Si1 C7 H N2A U1 N (4) C8 C7 H N3A U1 N (4) C9 C7 H N5 U1 N (3) H8B C8 H8C N1 U1 N (2) H8A C8 H8C NATURE CHEMISTRY 64

65 N1A U1 N (3) H8A C8 H8B N2 U1 N (2) C7 C8 H8C N2A U1 N (3) C7 C8 H8B N3A U1 N (3) C7 C8 H8A N3 U1 N (3) H9B C9 H9C N1A Si1 C (7) H9A C9 H9C N1 Si1 C (5) H9A C9 H9B N1A Si1 C (6) C7 C9 H9C N1 Si1 C (5) C7 C9 H9B C4 Si1 C (7) C7 C9 H9A N1A Si1 C4A (7) N1A C10A H10D N1 Si1 C4A 85.3 (7) N1A C10A H10C C7 Si1 C4A (8) H10C C10A H10D N1A Si1 C (5) C11A C10A H10D N1 Si1 C (5) C11A C10A H10C C4 Si1 C (6) N1 C10 H10B C7 Si1 C (6) N1 C10 H10A C4A Si1 C (8) H10A C10 H10B N1A Si1 C7A (7) C11 C10 H10B N1 Si1 C7A (8) C11 C10 H10A C4 Si1 C7A 76.1 (9) N4 C11A H11D C4A Si1 C7A (10) N4 C11A H11C C1 Si1 C7A (10) H11C C11A H11D N2 Si2 C (5) C10A C11A H11D N2A Si2 C (6) C10A C11A H11C N2 Si2 C15A 86.6 (7) N4 C11 H11B N2A Si2 C15A (7) N4 C11 H11A C18 Si2 C15A (6) H11A C11 H11B N2 Si2 C (5) C10 C11 H11B N2A Si2 C (6) C10 C11 H11A C18 Si2 C (5) Si2 C12 H12A N2 Si2 C (3) Si2 C12 H N2A Si2 C (4) H12 C12 H12A 66.7 C18 Si2 C (7) C13A C12 H12A C15A Si2 C (10) C13A C12 H C15 Si2 C (6) C13 C12 H12A N2 Si2 C18A (7) C14A C12 H12A 47.2 N2A Si2 C18A (7) C14A C12 H C15A Si2 C18A (9) C14 C12 H12A C15 Si2 C18A 80.5 (6) C14 C12 H NATURE CHEMISTRY 65

66 C12 Si2 C18A (8) C12 C13A H13F N3A Si3 C29A (8) C12 C13A H13E N3 Si3 C29A (9) C12 C13A H13D N3A Si3 C26A (8) H13B C13 H13C N3 Si3 C26A 84.2 (8) H13A C13 H13C C29A Si3 C26A (12) H13A C13 H13B N3A Si3 C (6) C12 C13 H13C N3 Si3 C (5) C12 C13 H13B C26A Si3 C (10) C12 C13 H13A N3A Si3 C (5) C12 C14A H14F N3 Si3 C (5) C12 C14A H14E C29A Si3 C (10) C12 C14A H14D C26A Si3 C (11) H14B C14 H14C C29 Si3 C (6) H14A C14 H14C N3A Si3 C (7) H14A C14 H14B N3 Si3 C (5) C12 C14 H14C C29A Si3 C (10) C12 C14 H14B C29 Si3 C (6) C12 C14 H14A C23 Si3 C (7) Si2 C15A H15A C10 N1 Si (6) C16A C15A H15A C10 N1 U (5) C17A C15A H15A Si1 N1 U (4) Si2 C15 H C10A N1A Si (9) C16 C15 H C10A N1A U (8) C17 C15 H Si1 N1A U (6) H16B C16 H16C C21 N2 Si (5) H16A C16 H16C C21 N2 U (5) H16A C16 H16B Si2 N2 U (4) C15 C16 H16C C21A N2A Si (8) C15 C16 H16B C21A N2A U (7) C15 C16 H16A Si2 N2A U (6) H17B C17 H17C C32 N3 Si (6) H17A C17 H17C C32 N3 U (6) H17A C17 H17B Si3 N3 U (4) C15 C17 H17C C32A N3A Si (9) C15 C17 H17B C32A N3A U (8) C15 C17 H17A Si3 N3A U (6) Si2 C18A H18A C33 N4 C33A 79.8 (18) C19A C18A H18A C33A N4 C22A (18) C20A C18A H18A C33 N4 C11A (7) Si2 C18 H NATURE CHEMISTRY 66

67 C33A N4 C11A 116 (2) C19 C18 H C22A N4 C11A (16) C20 C18 H C33 N4 C (11) H19B C19 H19C C22A N4 C (10) H19A C19 H19C C11A N4 C (18) H19A C19 H19B C33 N4 C (9) C18 C19 H19C C33A N4 C (10) C18 C19 H19B C22A N4 C (10) C18 C19 H19A C11 N4 C (10) H20B C20 H20C C33 N4 U (6) H20A C20 H20C C33A N4 U (7) H20A C20 H20B C22A N4 U (7) C18 C20 H20C C11A N4 U (8) C18 C20 H20B C11 N4 U (5) C18 C20 H20A C22 N4 U (5) N2A C21A H21D C2 C1 C2A 65.2 (13) N2A C21A H21C C3A C1 C2A (11) H21C C21A H21D C2 C1 C (8) C22A C21A H21D C3A C1 C (14) C22A C21A H21C C2A C1 C (13) N2 C21 H21B C2 C1 Si (7) N2 C21 H21A C3A C1 Si (10) H21A C21 H21B C2A C1 Si (9) C22 C21 H21B C3 C1 Si (7) C22 C21 H21A C6 C4 C (9) N4 C22A H22D C6 C4 Si (8) N4 C22A H22C C5 C4 Si (7) H22C C22A H22D C5A C4A C6A (13) C21A C22A H22D C5A C4A Si (11) C21A C22A H22C C6A C4A Si (10) N4 C22 H22B C8 C7 C (9) N4 C22 H22A C8 C7 Si (8) H22A C22 H22B C9 C7 Si (8) C21 C22 H22B C9A C7A C8A (13) C21 C22 H22A C9A C7A Si (13) Si3 C23 H23A C8A C7A Si (12) Si3 C23 H N1 C10 C (8) H23A C23 H C11A C10A N1A (14) C24A C23 H23A N4 C11 C (8) C24A C23 H C10A C11A N (16) C24 C23 H23A NATURE CHEMISTRY 67

68 C14 C12 C13A 45.2 (11) C25A C23 H C14 C12 C (9) C25 C23 H23A C13A C12 C (12) C25 C23 H C14 C12 C14A 62.7 (15) C23 C24A H24F C13A C12 C14A (11) C23 C24A H24E C13 C12 C14A (11) C23 C24A H24D C14 C12 Si (7) H24B C24 H24C C13A C12 Si (9) H24A C24 H24C C13 C12 Si (8) H24A C24 H24B C14A C12 Si (9) C23 C24 H24C C16 C15 C (8) C23 C24 H24B C16 C15 Si (7) C23 C24 H24A C17 C15 Si (7) C23 C25A H25F C17A C15A C16A (13) C23 C25A H25E C17A C15A Si (12) C23 C25A H25D C16A C15A Si (12) H25B C25 H25C C19 C18 C (9) H25A C25 H25C C19 C18 Si (7) H25A C25 H25B C20 C18 Si (7) C23 C25 H25C C19A C18A C20A (12) C23 C25 H25B C19A C18A Si (10) C23 C25 H25A C20A C18A Si (10) Si3 C26A H26A N2 C21 C (8) C27A C26A H26A N2A C21A C22A (13) C28A C26A H26A N4 C22 C (8) Si3 C26 H N4 C22A C21A (13) C27 C26 H C24A C23 C (15) C28 C26 H C25 C23 C (8) H27B C27 H27C C24A C23 C25A (11) H27A C27 H27C C25 C23 C25A 69.4 (15) H27A C27 H27B C24 C23 C25A (14) C26 C27 H27C C24A C23 Si (10) C26 C27 H27B C25 C23 Si (8) C26 C27 H27A C24 C23 Si (7) H28B C28 H28C C25A C23 Si (9) H28A C28 H28C C27 C26 C (9) H28A C28 H28B C27 C26 Si (8) C26 C28 H28C C28 C26 Si (8) C26 C28 H28B C28A C26A C27A (13) C26 C28 H28A C28A C26A Si (13) Si3 C29A H29A NATURE CHEMISTRY 68

69 C27A C26A Si (13) C30A C29A H29A C30 C29 C (10) C31A C29A H29A C30 C29 Si (8) Si3 C29 H C31 C29 Si (7) C30 C29 H C31A C29A C30A (13) C31 C29 H C31A C29A Si (12) H30E C30A H30F C30A C29A Si (12) H30D C30A H30F N3 C32 C (9) H30D C30A H30E C33A C32A N3A (13) C29A C30A H30F N4 C33 C (10) C29A C30A H30E C32A C33A N (13) C29A C30A H30D Si1 C1 H1B H30B C30 H30C Si1 C1 H1A H30A C30 H30C H1A C1 H1B 68.2 H30A C30 H30B C2A C1 H1A C29 C30 H30C C2 C1 H1B C29 C30 H30B C2 C1 H1A C29 C30 H30A C3A C1 H1B H31B C31 H31C C3A C1 H1A H31A C31 H31C C3 C1 H1B H31A C31 H31B H2AB C2A H2AC C29 C31 H31C H2AA C2A H2AC C29 C31 H31B H2AA C2A H2AB C29 C31 H31A C1 C2A H2AC N3A C32A H32D C1 C2A H2AB N3A C32A H32C C1 C2A H2AA H32C C32A H32D H2B C2 H2C C33A C32A H32D H2A C2 H2C C33A C32A H32C H2A C2 H2B N3 C32 H32B C1 C2 H2C N3 C32 H32A C1 C2 H2B H32A C32 H32B C1 C2 H2A C33 C32 H32B C1 C3A H3AC C33 C32 H32A C1 C3A H3AB N4 C33A H33D C1 C3A H3AA N4 C33A H33C H3B C3 H3C H33C C33A H33D H3A C3 H3C C32A C33A H33D H3A C3 H3B C32A C33A H33C C1 C3 H3C N4 C33 H33B C1 C3 H3B N4 C33 H33A NATURE CHEMISTRY 69

70 C1 C3 H3A H33A C33 H33B Si1 C4A H4A C32 C33 H33B C5A C4A H4A C32 C33 H33A C6A C4A H4A N5A U1 N5B 62.6 (7) C10 C8 H N5A U1 N (5) H9B C9 H9C N5B U1 N (7) H9A C9 H9C N5A U1 N (5) H9A C9 H9B N5B U1 N (6) C8 C9 H9C N1 U1 N (13) C8 C9 H9B N5A U1 N (5) C8 C9 H9A N5B U1 N (5) H10B C10 H10C N1 U1 N (11) H10A C10 H10C N5 U1 N (13) H10A C10 H10B N5A U1 N (4) C8 C10 H10C N5B U1 N (6) C8 C10 H10B N1 U1 N (12) C8 C10 H10A N5 U1 N (13) N1 C11 H11B N2 U1 N (11) N1 C11 H11A N5A U1 N (4) H11A C11 H11B N5B U1 N (6) C12 C11 H11B N1 U1 N (11) C12 C11 H11A N5 U1 N (13) N4 C12 H12B N2 U1 N (10) N4 C12 H12A N3 U1 N (10) H12A C12 H12B N1 Si1 C (19) C11 C12 H12B N1 Si1 C (18) C11 C12 H12A C5 Si1 C (18) Si2 C13 H13A N1 Si1 C (16) Si2 C13 H C5 Si1 C (2) C14 C13 H13A C8 Si1 C (18) C14 C13 H N2 Si2 C (15) C15 C13 H13A N2 Si2 C (16) C15 C13 H C16 Si2 C (16) H14B C14 H14C N2 Si2 C (16) H14A C14 H14C C16 Si2 C (18) H14A C14 H14B C19 Si2 C (18) C13 C14 H14C N3 Si3 C (16) C13 C14 H14B NATURE CHEMISTRY 70

71 N3 Si3 C (17) C13 C14 H14A C27 Si3 C (19) H15B C15 H15C N3 Si3 C (16) H15A C15 H15C C27 Si3 C (18) H15A C15 H15B C24 Si3 C (17) C13 C15 H15C C11 N1 Si (3) C13 C15 H15B C11 N1 U (3) C13 C15 H15A Si1 N1 U (15) Si2 C16 H C22 N2 Si (2) C17 C16 H C22 N2 U (2) C18 C16 H Si2 N2 U (14) H17B C17 H17C C33 N3 Si (3) H17A C17 H17C C33 N3 U (2) H17A C17 H17B Si3 N3 U (15) C16 C17 H17C C12 N4 C (3) C16 C17 H17B C12 N4 C (3) C16 C17 H17A C34 N4 C (3) H18B C18 H18C C12 N4 U (2) H18A C18 H18C C34 N4 U (2) H18A C18 H18B C23 N4 U (2) C16 C18 H18C C2 N5 U (3) C16 C18 H18B N5 C2 C (3) C16 C18 H18A N5 C2 C (3) Si2 C19 H C4 C2 C (3) C20 C19 H N5 C2 Si (3) C21 C19 H C4 C2 Si (3) H20B C20 H20C C3 C2 Si (3) H20A C20 H20C C6 C5 C (4) H20A C20 H20B C6 C5 Si (3) C19 C20 H20C C7 C5 Si (3) C19 C20 H20B C10 C8 C (3) C19 C20 H20A C10 C8 Si (3) H21B C21 H21C C9 C8 Si (3) H21A C21 H21C C12 C11 N (3) H21A C21 H21B N4 C12 C (3) C19 C21 H21C C15 C13 C (4) C19 C21 H21B C15 C13 N5B (8) C19 C21 H21A C14 C13 N5B (9) N2 C22 H22B C15 C13 Si (3) N2 C22 H22A C14 C13 Si (3) H22A C22 H22B NATURE CHEMISTRY 71

72 N5B C13 Si (8) C23 C22 H22B C18 C16 C (3) C23 C22 H22A C18 C16 Si (3) N4 C23 H23B C17 C16 Si (2) N4 C23 H23A C20 C19 C (3) H23A C23 H23B C20 C19 Si (3) C22 C23 H23B C21 C19 Si (3) C22 C23 H23A C23 C22 N (3) Si3 C24 H C22 C23 N (3) C25 C24 H C26 C24 C (4) C26 C24 H C26 C24 Si (3) H25B C25 H25C C25 C24 Si (3) H25A C25 H25C C28 C27 N5A 81.7 (8) H25A C25 H25B C28 C27 C (4) C24 C25 H25C N5A C27 C (7) C24 C25 H25B C28 C27 Si (3) C24 C25 H25A N5A C27 Si (6) H26B C26 H26C C29 C27 Si (3) H26A C26 H26C C31 C30 C (3) H26A C26 H26B C31 C30 Si (3) C24 C26 H26C C32 C30 Si (2) C24 C26 H26B N3 C33 C (4) C24 C26 H26A C33 C34 N (3) Si3 C27 H27A C27 N5A U (10) Si3 C27 H C13 N5B U (11) C28 C27 H27A U1 N5B H5B C28 C27 H C13 N5B H5B C29 C27 H27A U1 N5A H5AA C29 C27 H C27 N5A H5AA H28B C28 H28C U1 N5 H H28A C28 H28C C2 N5 H H28A C28 H28B Si1 C2 H2B C27 C28 H28C Si1 C2 H2A C27 C28 H28B C3 C2 H2B C27 C28 H28A C3 C2 H2A H29B C29 H29C C4 C2 H2B H29A C29 H29C C4 C2 H2A H29A C29 H29B H3B C3 H3C C27 C29 H29C H3A C3 H3C C27 C29 H29B H3A C3 H3B C27 C29 H29A NATURE CHEMISTRY 72

73 C2 C3 H3C Si3 C30 H C2 C3 H3B C31 C30 H C2 C3 H3A C32 C30 H H4B C4 H4C H31B C31 H31C H4A C4 H4C H31A C31 H31C H4A C4 H4B H31A C31 H31B C2 C4 H4C C30 C31 H31C C2 C4 H4B C30 C31 H31B C2 C4 H4A C30 C31 H31A Si1 C5 H5A H32B C32 H32C C6 C5 H5A H32A C32 H32C C7 C5 H5A H32A C32 H32B H6B C6 H6C C30 C32 H32C H6A C6 H6C C30 C32 H32B H6A C6 H6B C30 C32 H32A C5 C6 H6C N3 C33 H33B C5 C6 H6B N3 C33 H33A C5 C6 H6A H33A C33 H33B H7B C7 H7C C34 C33 H33B H7A C7 H7C C34 C33 H33A H7A C7 H7B N4 C34 H34B C5 C7 H7C N4 C34 H34A C5 C7 H7B H34A C34 H34B C5 C7 H7A C33 C34 H34B Si1 C8 H C33 C34 H34A C9 C8 H N1 U1 N (10) C7 C9 H9A N1 U1 N (10) N1 C10 H10B N3 U1 N (10) N1 C10 H10A N1 U1 N (10) H10A C10 H10B N3 U1 N (10) C11 C10 H10B N2 U1 N (10) C11 C10 H10A N1 U1 N (9) N4 C11 H11B N3 U1 N (9) N4 C11 H11A N2 U1 N (10) H11A C11 H11B N5 U1 N (10) C10 C11 H11B C10 N1 Si (2) C10 C11 H11A C10 N1 U (2) Si2 C12 H NATURE CHEMISTRY 73

74 Si1 N1 U (14) C13 C12 H C21 N2 Si (2) C14 C12 H C21 N2 U (2) H13B C13 H13C Si2 N2 U (14) H13A C13 H13C C32 N3 Si (2) H13A C13 H13B C32 N3 U (2) C12 C13 H13C Si3 N3 U (15) C12 C13 H13B C22 N4 C (3) C12 C13 H13A C22 N4 C (3) H14B C14 H14C C33 N4 C (3) H14A C14 H14C C22 N4 U (2) H14A C14 H14B C33 N4 U (19) C12 C14 H14C C11 N4 U (19) C12 C14 H14B N6 N5 U (3) C12 C14 H14A N7 N6 N (6) Si2 C15 H N1 Si1 C (14) C16 C15 H N1 Si1 C (14) C17 C15 H C7 Si1 C (15) H16B C16 H16C N1 Si1 C (14) H16A C16 H16C C7 Si1 C (15) H16A C16 H16B C4 Si1 C (15) C15 C16 H16C N2 Si2 C (14) C15 C16 H16B N2 Si2 C (14) C15 C16 H16A C12 Si2 C (15) H17B C17 H17C N2 Si2 C (15) H17A C17 H17C C12 Si2 C (16) H17A C17 H17B C15 Si2 C (15) C15 C17 H17C N3 Si3 C (14) C15 C17 H17B N3 Si3 C (15) C15 C17 H17A C29 Si3 C (16) Si2 C18 H N3 Si3 C (15) C19 C18 H C29 Si3 C (16) C20 C18 H C26 Si3 C (16) H19B C19 H19C C2 C1 C (3) H19A C19 H19C C2 C1 Si (3) H19A C19 H19B C3 C1 Si (2) C18 C19 H19C C6 C4 C (3) C18 C19 H19B C6 C4 Si (2) C18 C19 H19A C5 C4 Si (2) H20B C20 H20C C9 C7 C (3) H20A C20 H20C NATURE CHEMISTRY 74

75 C9 C7 Si (3) H20A C20 H20B C8 C7 Si (2) C18 C20 H20C N1 C10 C (3) C18 C20 H20B N4 C11 C (3) C18 C20 H20A C13 C12 C (3) N2 C21 H21B C13 C12 Si (3) N2 C21 H21A C14 C12 Si (2) H21A C21 H21B C17 C15 C (3) C22 C21 H21B C17 C15 Si (2) C22 C21 H21A C16 C15 Si (2) N4 C22 H22B C20 C18 C (3) N4 C22 H22A C20 C18 Si (3) H22A C22 H22B C19 C18 Si (2) C21 C22 H22B N2 C21 C (3) C21 C22 H22A N4 C22 C (3) Si3 C23 H C24 C23 C (3) C24 C23 H C24 C23 Si (3) C25 C23 H C25 C23 Si (2) H24B C24 H24C C28 C26 C (3) H24A C24 H24C C28 C26 Si (2) H24A C24 H24B C27 C26 Si (2) C23 C24 H24C C31 C29 C (3) C23 C24 H24B C31 C29 Si (3) C23 C24 H24A C30 C29 Si (2) H25B C25 H25C N3 C32 C (3) H25A C25 H25C N4 C33 C (3) H25A C25 H25B Si1 C1 H C23 C25 H25C C2 C1 H C23 C25 H25B C3 C1 H C23 C25 H25A H2B C2 H2C Si3 C26 H H2A C2 H2C C27 C26 H H2A C2 H2B C28 C26 H C1 C2 H2C H27B C27 H27C C1 C2 H2B H27A C27 H27C C1 C2 H2A H27A C27 H27B H3B C3 H3C C26 C27 H27C H3A C3 H3C C26 C27 H27B H3A C3 H3B C26 C27 H27A C1 C3 H3C H28B C28 H28C C1 C3 H3B H28A C28 H28C NATURE CHEMISTRY 75

76 C1 C3 H3A H28A C28 H28B Si1 C4 H C26 C28 H28C C5 C4 H C26 C28 H28B C6 C4 H C26 C28 H28A H5B C5 H5C Si3 C29 H H5A C5 H5C C30 C29 H H5A C5 H5B C31 C29 H C4 C5 H5C H30B C30 H30C C4 C5 H5B H30A C30 H30C C4 C5 H5A H30A C30 H30B H6B C6 H6C C29 C30 H30C H6A C6 H6C C29 C30 H30B H6A C6 H6B C29 C30 H30A C4 C6 H6C H31B C31 H31C C4 C6 H6B H31A C31 H31C C4 C6 H6A H31A C31 H31B Si1 C7 H C29 C31 H31C C8 C7 H C29 C31 H31B C9 C7 H C29 C31 H31A H8B C8 H8C N3 C32 H32B H8A C8 H8C N3 C32 H32A H8A C8 H8B H32A C32 H32B C7 C8 H8C C33 C32 H32B C7 C8 H8B C33 C32 H32A C7 C8 H8A N4 C33 H33B H9B C9 H9C N4 C33 H33A H9A C9 H9C H33A C33 H33B H9A C9 H9B C32 C33 H33B C7 C9 H9C C32 C33 H33A C7 C9 H9B NATURE CHEMISTRY 76

77 Fig. S14. Molecular structure of [U(F)(Tren TIPS )] (6). Hydrogen atoms omitted for clarity. Fig. S15. Molecular structure of [U(N)(Tren TIPS )] (7). Hydrogen atoms omitted for clarity. NATURE CHEMISTRY 77

78 Fig. S16. Molecular structure of [U{(NHCMe 2 SiPr i 2NCH 2 CH 2 )N(CH 2 CH 2 NSiPr i 3) 2 }] (8). Hydrogen atoms omitted for clarity. Fig. S17. Molecular structure of [U(N 3 )(Tren TIPS )] (9). Hydrogen atoms omitted for clarity. NATURE CHEMISTRY 78

79 Fig. S18. Molecular structure of [U(NSiMe 3 )(Tren TIPS )] (10). Hydrogen atoms omitted for clarity. Fig. S19. Molecular structure of [U(NAd)(Tren TIPS )] (11). Hydrogen atoms omitted for clarity. NATURE CHEMISTRY 79

80 Fig. S20. Molecular structure of [U(NH 2 )(Tren TIPS )] (12). Hydrogen atoms omitted for clarity. Fig. S21. Molecular structure of [U(μ-N)(μ-Na15C5)(Tren TIPS )] (13). Hydrogen atoms omitted for clarity. Crystallographic Alerts: Compound 6 generates an isotropic non-h atom alert because one isopropyl group is disordered and the minor component was modelled better isotropically due to the NATURE CHEMISTRY 80

81 low occupancy of carbon in a heavy atom structure. Compound 8 returns an apparent short H H contact alert which is due to the NH group being disordered over the three silyl groups and the disorder model not being recognised by the checking procedure. Compound 9 returns a large nonsolvent U eq ratio for two atoms in the azide which is reflective of the non-spherical electron density of the NN bond in the azide which cannot be adequately modelled with a spherical scattering factor. Compound 12 diffracted poorly at wide angle which generates a diffraction θ low value. Compound 13 crystallises with highly disordered lattice solvent which was treated with the Platon SQUEEZE procedure which generates a spurious mismatch between listed and actual cell contents. DFT, NBO, and QTAIM Calculations General Unrestricted and restricted geometry optimisations were performed as appropriate for full models of 7, 9, 10, 11, 13 [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ] (Ar = 3,5-Me 2 C 6 H 3 ), 5 [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ], 5 [U(NBu t ) 2 (I) 2 (THF) 2 ], 6 [Me 3 SiNU(N") 3 ] [N" = N(SiMe 3 ) 2 ], 7 [Me 3 SiNU(N") 3 F], 8 [U(NPh) 2 (Cp*) 2 ] [Cp* = C 5 Me 5 ], 9 [CrN(NPr i 2) 3 ], 10 [MoN(NArBu t ) 3 ], 11 and [WN(NArPr i ) 3 ], 12 using coordinates derived from their X-ray crystal structures. Calculated data for 3 and 4 have been reported previously. 1 Restricted calculations for [UN 2 ] and [NUF 3 ] were performed on models constructed in silico. No constraints were imposed on the structures during the geometry optimisations. The calculations were performed using the Amsterdam Density Functional (ADF) suite version ,14 The DFT geometry optimisations employed Slater type orbital (STO) triple-ζ-plus polarisation all-electron basis sets (from the ZORA/TZP database of the ADF suite). Scalar relativistic approaches were used within the ZORA Hamiltonian for the inclusion of relativistic effects and the local density approximation (LDA) with the correlation potential due to Vosko et al 15 was used in all of the calculations. Gradient corrections were performed using the functionals of NATURE CHEMISTRY 81

82 Becke 16 and Perdew. 17 MOLEKEL 18 was used to prepare the three-dimensional plot of the electron density. Natural Bond Order (NBO) analyses were carried out with NBO The Atoms in Molecules analysis was carried out with Xaim The calculated structures compare very well to the experimental structures with bond lengths and angles computed to within 0.05 Å and 2. Since 16 of the 18 calculations have experimentally verifiable structures, and that [UN 2 ] 23,24 and [NUF 3 ] 25 have previously been matched to matrix isolation FTIR data the calculations report a qualitatively reliable and internally consistent series. Table S5. Calculated and experimental bond lengths, and calculated bond orders, atomic charges, and spin densities for [{U(μ-N)(μ-Na)(Tren TIPS )} 2 ] (3), [UN(Tren TIPS )] (anion of 4), [U(μ-N)(μ- Na15C5)(Tren TIPS )] (13), [U(N)(Tren TIPS )] (7), [U(N 3 )(Tren TIPS )] (9), [U(NSiMe 3 )(Tren TIPS )] (10), [U(NAd)(Tren TIPS )] (11), [UN 2 ], [NUF 3 ], [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ], [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ], [U(NBu t ) 2 (I) 2 (THF) 2 ], [Me 3 SiNU(N") 3 ], [Me 3 SiNU(N") 3 F], [U(NPh) 2 (Cp*) 2 ], [CrN(NPr i 2) 3 ], [MoN(NArBu t ) 3 ], and [WN(NArPr i ) 3 ]. Compound Metal O.S. MN Bond Lengths (Å) and Indices Atomic MDC q Charges Atomic MDC m Spin Densities Expt Calc. Mayer q-m q-n m-m m-n 3 V 1.883(4) U-containing anion from 4 V 1.825(15) V 1.810(5) VI 1.799(7) IV 2.305(3) V 1.945(3) V 1.946(13) [UN 2 ] VI [NUF 3 ] VI [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ] V 1.916(4) [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ] VI 1.880(4) [U(NBu t ) 2 (I) 2 (THF) 2 ] VI 1.848(4) [Me 3 SiNU(N") 3 ] V 1.910(16) [Me 3 SiNU(N") 3 F] VI 1.854(23) [U(NPh) 2 (Cp*) 2 ] VI 1.952(7) [CrN(NPr i 2) 3 ] VI 1.544(3) [MoN(NArBu t ) 3 ] VI 1.651(4) [WN(NArPr i ) 3 ] VI 1.669(5) NATURE CHEMISTRY 82

83 Table S6. Calculated NBO compositions of the M N and M=N linkages for [{U(μ-N)(μ- Na)(Tren TIPS )} 2 ] (3), [UN(Tren TIPS )] (anion of 4), [U(μ-N)(μ-Na15C5)(Tren TIPS )] (13), [U(N)(Tren TIPS )] (7), [U(N 3 )(Tren TIPS )] (9), [U(NSiMe 3 )(Tren TIPS )] (10), [U(NAd)(Tren TIPS )] (11), [UN 2 ], [NUF 3 ], [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ], [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ], [U(NBu t ) 2 (I) 2 (THF) 2 ], [Me 3 SiNU(N") 3 ], [Me 3 SiNU(N") 3 F], [U(NPh) 2 (Cp*) 2 ], [CrN(NPr i 2) 3 ], [MoN(NArBu t ) 3 ], and [WN(NArPr i ) 3 ]. Compound σ-bond π-bond π-bond %M:N M s:p:d:f N s:p %M:N M f:d N s:p %M:N M f:d N s:p 3 25:75 4:4:43:49 10:90 20:80 66:34 0:100 23:77 73:27 0:100 U-containing anion from 4 32:68 5:4:44:47 7:93 27:73 72:28 0:100 27:73 71:29 0: :73 5:4:49:42 9:91 23:77 61:39 0:100 25:75 67:33 0: :59 1:1:9:89 8:92 30:70 81:19 0:100 30:70 81:19 0: :100 68: :86 1:5:56:38 40:60 20:80 71:29 0:100 19:81 70:30 0: :89 1:4:59:36 47:53 23:77 65:35 0:100 23:77 61:39 0:100 [UN 2 ] 43:57 34:0:17:49 8:92 25:75 50:50 0:100 25:75 50:50 0:100 [NUF 3 ] 44:56 2:1:12:85 6:94 30:70 66:34 0:100 30:70 66:34 0:100 [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ] 0:100 67:33 27:73 90:10 0:100 25:75 90:10 0:100 [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ] 0:100 75:25 25:75 66:34 0:100 25:75 70:30 0:100 [U(NBu t ) 2 (I) 2 (THF) 2 ] 14:86 18:2:34:46 48:52 18:82 51:49 0:100 18:82 51:49 0:100 [Me 3 SiNU(N") 3 ] 14:86 1:9:32:58 62:38 20:80 61:39 0:100 20:80 60:40 0:100 [Me 3 SiNU(N") 3 F] 21:79 1:2:11:86 57:43 20:80 67:33 0:100 20:80 67:33 0:100 [U(NPh) 2 (Cp*) 2 ] 29:71 0:0:5:95 0:100 21:79 73:27 0:100 %M:N M s:p:d N s:p %M:N M s:p:d N s:p %M:N M s:p:d N s:p [CrN(NPr i 2) 3 ] 40:60 24:2:74 17:83 43:57 0:23:77 0:100 43:57 0:24:76 0:100 [MoN(NArBu t ) 3 ] 38:62 18:0:82 14:86 42:58 10:0:90 0:100 46:54 1:1:98 0:100 [WN(NArPr i ) 3 ] 33:67 24:0:76 23:77 44:56 0:0:100 0:100 44:56 0:0:100 0:100 NATURE CHEMISTRY 83

84 Table S7. Calculated QTAIM bond critical point data of the M N and M=N linkages for [{U(μ- N)(μ-Na)(Tren TIPS )} 2 ] (3), [UN(Tren TIPS )] (anion of 4), [U(μ-N)(μ-Na15C5)(Tren TIPS )] (13), [U(N)(Tren TIPS )] (7), [U(N 3 )(Tren TIPS )] (9), [U(NSiMe 3 )(Tren TIPS )] (10), [U(NAd)(Tren TIPS )] (11), [UN 2 ], [NUF 3 ], [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ], [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ], [U(NBu t ) 2 (I) 2 (THF) 2 ], [Me 3 SiNU(N") 3 ], [Me 3 SiNU(N") 3 F], [U(NPh) 2 (Cp*) 2 ], [CrN(NPr i 2) 3 ], [MoN(NArBu t ) 3 ], and [WN(NArPr i ) 3 ]. Compound Metal O.S. ρ(r) ²ρ(r) G(r) V(r) H(r) 3 V U-containing anion from 4 V V VI IV V V [UN 2 ] VI [NUF 3 ] VI [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ] V [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ] VI [U(NBu t ) 2 (I) 2 (THF) 2 ] VI [Me 3 SiNU(N") 3 ] V [Me 3 SiNU(N") 3 F] VI [U(NPh) 2 (Cp*) 2 ] VI [CrN(NPr i 2) 3 ] VI [MoN(NArBu t ) 3 ] VI [WN(NArPr i ) 3 ] VI Fig. S22. Selected α-spin Kohn Sham frontier molecular orbitals for [U(N)(Tren TIPS )] (7) hydrogen atoms are omitted for clarity. Left to right: HOMO (218a, ev), HOMO 1 (217a, ev), HOMO 2 (216a, ev). NATURE CHEMISTRY 84

85 Fig. S23. Selected α-spin Kohn Sham frontier molecular orbitals for [U(N 3 )(Tren TIPS )] (9) hydrogen atoms are omitted for clarity. Left to right: LUMO+6 (236a, ev), LUMO+5 (235a, ev), HOMO (229a, ev), HOMO 1 (228a, ev). Fig. S24. Selected α-spin Kohn Sham frontier molecular orbitals for [U(NSiMe 3 )(Tren TIPS )] (10) hydrogen atoms are omitted for clarity. Left to right: HOMO (242a, ev), HOMO 4 (238a, ev), HOMO x (237a, ev), HOMO 18 (224a, ev). Fig. S25. Selected α-spin Kohn Sham frontier molecular orbitals for [U(NAd)(Tren TIPS )] (11) hydrogen atoms are omitted for clarity. Left to right: HOMO (259a, ev), HOMO 4 (255a, ev), HOMO 5 (254a, ev), HOMO 45 (214a, ev). NATURE CHEMISTRY 85

86 Fig. S26. Selected α-spin Kohn Sham frontier molecular orbitals for [U(μ-N)(μ- Na15C5)(Tren TIPS )] (13) hydrogen atoms are omitted for clarity. Left to right: HOMO (287a, ev), HOMO 1 (286a, ev), HOMO 4 (284a, ev), HOMO 5 (283a, ev). Fig. S27. Selected α-spin Kohn Sham frontier molecular orbitals for [UN 2 ] hydrogen atoms are omitted for clarity. Left to right: HOMO (53a, ev), HOMO 1 (52a, ev), HOMO 2 (51a, ev), HOMO 3 (50a, ev), HOMO 4 (49a, ev), HOMO 5 (48a, ev). Fig. S28. Selected α-spin Kohn Sham frontier molecular orbitals for [NUF 3 ] hydrogen atoms are omitted for clarity. Left to right: HOMO (63a, ev), HOMO 1 (62a, ev), HOMO 2 (61a, ev). NATURE CHEMISTRY 86

87 Fig. S29. Selected α-spin Kohn Sham frontier molecular orbitals for [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ] hydrogen atoms are omitted for clarity. Left to right: HOMO (320a, ev), HOMO 4 (316a, ev), HOMO 5 (315a, ev), HOMO 21 (299a, ev). Fig. S30. Selected α-spin Kohn Sham frontier molecular orbitals for [(C 6 F 5 ) 3 BNU(NArBu t ) 3 ] hydrogen atoms are omitted for clarity. Left to right: HOMO 15 (304a, ev), HOMO 16 (303a, ev), HOMO 19 (300a, ev). Fig. S31. Selected α-spin Kohn Sham frontier molecular orbitals for [U(NBu t ) 2 (I) 2 (THF) 2 ] hydrogen atoms are omitted for clarity. Left to right: HOMO 5 (174a, ev), HOMO 6 (173a, ev), HOMO 7 (172a, ev), HOMO 9 (170a, ev), HOMO 11 (168a, ev), HOMO 17 (162a, ev). NATURE CHEMISTRY 87

88 Fig. S32. Selected α-spin Kohn Sham frontier molecular orbitals for [Me 3 SiNU(N") 3 ] hydrogen atoms are omitted for clarity. Left to right: HOMO (204a, ev), HOMO 4 (200a, ev), HOMO 5 (199a, ev), HOMO 17 (187a, ev). Fig. S33. Selected α-spin Kohn Sham frontier molecular orbitals for [Me 3 SiNU(N") 3 F] hydrogen atoms are omitted for clarity. Left to right: HOMO 3 (205a, ev), HOMO 4 (204a, ev), HOMO 14 (194a, ev). Fig. S34. Selected α-spin Kohn Sham frontier molecular orbitals for [U(NPh) 2 (Cp*) 2 ] hydrogen atoms are omitted for clarity. Left to right: HOMO (169a, ev), HOMO 1 (168a, ev), HOMO 4 (165a, ev), HOMO 7 (162a, ev). The σ-bonds are extensively delocalised. NATURE CHEMISTRY 88

89 Fig. S35. Selected α-spin Kohn Sham frontier molecular orbitals for [CrN(NPr i 2) 3 ] hydrogen atoms are omitted for clarity. Left to right: HOMO 3 (98a, ev), HOMO 4 (97a, ev), HOMO 5 (96a, ev). Fig. S36. Selected α-spin Kohn Sham frontier molecular orbitals for [MoN(NArBu t ) 3 ] hydrogen atoms are omitted for clarity. Left to right: HOMO 9 (161a, ev), HOMO 10 (160a, ev), HOMO 11 (159a, ev). Fig. S37. Selected α-spin Kohn Sham frontier molecular orbitals for [WN(NArPr i ) 3 ] hydrogen atoms are omitted for clarity. Left to right: HOMO 9 (165a, ev), HOMO 10 (164a, ev), HOMO 11 (163a, ev). NATURE CHEMISTRY 89