- Supplementary Information Appendix - Homologation and Functionalization of Carbon Monoxide by a Recyclable Uranium Complex

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1 - Supplementary Information Appendix - Homologation and Functionalization of Carbon Monoxide by a Recyclable Uranium Complex Benedict M. Gardner, John C. Stewart, Adrienne L. Davis, Jonathan McMaster, William Lewis, Alexander J. Blake, and Stephen T. Liddle* School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK. * stephen.liddle@nottingham.ac.uk Experimental General All manipulations were carried out using standard Schlenk techniques, or an MBraun UniLab glovebox, under an atmosphere of dry nitrogen or carbon monoxide. Solvents were dried by passage through activated alumina towers and degassed before use except for hexamethyldisiloxane which was dried over calcium hydride. All solvents were stored over potassium mirrors except for hexamethyldisiloxane which was stored over activated 4 Å molecular sieves. Deuterated solvent was distilled from potassium, degassed by three freeze-pump-thaw cycles and stored under nitrogen. [U(Tren DMSB )] [1, Tren DMSB = N(CH 2 CH 2 NSiMe 2 Bu t ) 3 ] and PhMe 2 SiI were synthesized according to published procedures. 1,2 Natural abundance and 99 atom% 13 C-enriched carbon monoxide were purchased from Aldrich. The organosilyl halides Me 3 SiI and Ph 3 SiI were purchased from Aldrich, filtered from activated magnesium to remove acid traces, degassed by three freezepump-thaw cycles and were stored under nitrogen. S1

2 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. The conversion of 2 to 3 was initially assessed by periodic monitoring of an NMR tube scale reaction at 80 C in an oil bath using 20 mg of 2 in 0.55 ml of C 6 D 6. The thermolysis reaction of 2 only occurs at elevated temperatures so cooling to room temperature then recording spectra can be assumed to be under steady state conditions. A VT NMR thermolysis experiment of 20 mg of 2 in 0.55 ml of C 7 D 8 at a constant temperature of 80 C on a Bruker 400 spectrometer did not reveal any intermediates. 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 which were loaded in an MBraun UniLab glovebox and were run versus the appropriate solvent reference. Variable-temperature magnetic moment data were recorded in an applied dc field of 0.1 T on a Quantum Design MPMS XL5 SQUID magnetometer using doublyrecrystallized powdered samples. Samples were checked for purity before and after use and data reproducibility was carefully checked. Care was taken to ensure complete thermalization of the sample before each data point was measured. Diamagnetic corrections of cm 3 mol 1 and cm 3 mol 1 were applied for 2 and 3, respectively, using tabulated Pascal constants and measurements were corrected for the effect of the blank sample holders (flame sealed Wilmad NMR tube and straw). The slight discrepancies between solution and solid state magnetic moment measurements is attributed to weighing errors and the change in medium from solution to solid state. Mass Spectrometry was carried out using Bruker Apex IV FT-ICR (EI-MS) and Bruker MicroTOF (ESI-MS) instruments. All possible combinations of EI and ESI (acetonitrile and methanol) were attempted for all compounds reported herein, but only combinations which gave assignable responses are detailed. Elemental microanalyses were carried out at the University of Nottingham and by Stephen Boyer at the London Metropolitan University (UK). S2

3 Preparation of [{U(Tren DMSB )} 2 (μ-η 1 :η 1 -OCCO)] (2) A Schlenk flask (100 cm 3 volume) containing a cold ( 78 C) dark purple solution of 1 (3.10 g, 4.28 mmol) in pentane (20 ml) at a static pressure of 10 2 mbar was exposed to CO gas until the pressure inside the flask reached 1 atm. A color change to brown was immediately observed and at this point the flask was sealed and connected to a supply of N 2. The resulting suspension was stirred for 1 hour at 78 C before being filtered, concentrated to 2 ml and stored at 30 C for 18 hours to yield pale green crystals of 2, which were isolated by filtration at 30 C. Yield: 1.98 g, 61%. Anal. calc d for C 50 H 114 N 8 O 2 Si 6 U 2 : C 39.92; H 7.64; N 7.45%. Found: C 39.72; H 7.60; N 7.49%. 1 H NMR (C 6 D 6, 298 K): δ (s, 36H, SiMe 2, fwhm = 10 Hz); 0.37 (s, 54H, Bu t, fwhm = 5 Hz); (s, 12H, CH 2, fwhm = 16 Hz); (s, 12H, CH 2, fwhm = 15 Hz). 13 C{ 1 H} NMR (C 6 D 6, 298 K): δ (CH 2 ), 1.17 (SiMe 2 ), (Bu t -Me), (Bu t -C), (CH 2 ). The C C resonance was not observed in natural abundance CO samples. 29 Si{ 1 H} NMR (C 6 D 6, 298 K): δ μ eff (Evans method, 298 K): 4.32 μ B. FTIR ν/cm 1 (Nujol): 1546 (w), 1404 (m), 1341 (s), 1248 (m), 927 (s), 905 (m), 827 (s), 776 (s), 755 (m), 742 (m), 661 (m), 582 (w), 558 (w), 521 (w), 442 (m). Preparation of [{U(Tren DMSB )} 2 (μ-η 1 :η 1 -O 13 C 13 CO)] ( 13 C-2) A Schlenk flask (100 cm 3 volume) containing a cold ( 78 C) dark purple solution of 1 (3.10 g, 4.28 mmol) in pentane (20 ml) at a static pressure of 10 2 mbar was exposed to 13 CO gas until the pressure inside the flask reached 1 atm. A color change to brown was immediately observed and at this point the flask was sealed and connected to a supply of N 2. The resulting suspension was stirred for 1 hour at 78 C and filtered, affording a pale yellow solid after volatiles were removed in vacuo. Dissolution in pentane (2 ml) and storage at 30 afforded pale green crystals of 13 C-2. S3

4 Yield: 2.00 g, 62%. Anal. calc d for C 50 H 114 N 8 O 2 Si 6 U 2 : C 40.01; H 7.63; N 7.44%. Found: C 39.83; H 7.59; N 7.42%. 1 H NMR (C 6 D 6, 298 K): δ (s, 36H, SiMe 2, fwhm = 10 Hz); 0.37 (s, 54H, Bu t, fwhm = 5 Hz); (s, 12H, CH 2, fwhm = 16 Hz); (s, 12H, CH 2, fwhm = 15 Hz). 13 C{ 1 H} NMR (C 6 D 6, 298 K): δ (CH 2 ), 1.17 (SiMe 2 ), (Bu t -Me), (Bu t -C), (CH 2 ). 29 Si { 1 H} NMR (C 6 D 6, 298 K): δ μ eff (Evans method, 298 K): 4.33 μ B. FTIR ν/cm 1 (Nujol): 1548 (w), 1407 (m), 1316 (s), 1248 (m), 926 (s), 905 (m), 827 (s), 776 (s), 755 (m), 742 (m), 661 (m), 583 (w), 559 (w), 521 (w), 442 (m). Preparation of [U(Tren DMSB )(O)U{N(CH 2 CH 2 NSiMe 2 Bu t ) 2 (CH 2 CH 2 NC[OSiMe 2 Bu t ]CHO)}] (3) A yellow solution of 2 (0.43 g, 0.57 mmol) in benzene (20 ml) was heated at reflux for 48 hours under dinitrogen to afford, after cooling to ambient temperature, a brown solution. Volatiles were removed in vacuo and the brown residue was dissolved in hot (70 C) hexane (1.5 ml). The resulting brown solution was stored at 5 C for 24 hours to afford green crystals of 3 which were isolated by filtration and washed with cold hexane (2 2 ml). Yield: 0.26 g, 60%. Anal. calc d for C 50 H 114 N 8 O 3 Si 6 U 2 : C 39.51; H 7.56; N 7.37%. Found: C 39.02; H 7.41; N 7.36%. 1 H NMR (C 6 D 6, 298 K): δ (s, 2H, CH 2, fwhm = 80 Hz); (s, 9H, Bu t SiO, fwhm = 100 Hz); (s, 2H, CH 2, fwhm = 100 Hz); (s, 6H, Me 2 SiO, fwhm = 100 Hz); (s, 18H, SiMe 2, fwhm = 98 Hz); (s, 2H, CH 2, fwhm = 80 Hz); (s, 2H, CH 2, fwhm = 32 Hz); 9.61 (s, 27H, Bu t, fwhm = 95 Hz); 6.19 (s, 18H, Bu t, fwhm = 100 Hz); 1.09 (s, 9H, Bu t, fwhm = 5 Hz); 5.46 (s, 6H, CH 2, fwhm = 93 Hz); (s, 12H, SiMe 2, fwhm = 100 Hz); (s, 2H, CH 2, fwhm = 44 Hz); (s, 2H, CH 2, fwhm = 100 Hz). The OC(H)C(OSiMe 2 Bu t )N hydrogen was not observed. Complex 3 exhibits poor solubility in arene solvents after recrystallization and appears to react in polar solvents to give unidentified products which precluded the acquisition of 13 C and 29 Si NMR spectra. μ eff (Evans method, 298 K): 4.14 μ B. FTIR ν/cm 1 (Nujol): 1645 (s), 1564 (w), 1554 (w), S4

5 1512 (w), 1306 (w), 1260 (s), 1126 (m), 1092 (s), 1073 (m), 1049 (m), 1023 (m), 944 (w), 930 (w), 915 (w), 896 (w), 880 (w), 826 (s), 806 (s), 722 (w), 696 (w), 676 (w), 659 (w), 580 (w), 540 (w), 520 (w), 510 (w) 419 (m). Characterization Data Fig. S1. Electronic Absorption Spectra of 2 in THF (bottom trace) and 1( top trace) in Pentane Fig. S2. Zoom-in of NIR region of 2 in THF (bottom trace) and 1 (top trace) in Pentane The electronic absorption spectrum of 2 is dominated by strong charge transfer bands which tail in from the high energy region. Weak (ε ~ 20 cm 1 ) absorptions are observed in the 9,000-15,000 cm 1 region, which are characteristic of Laporte forbidden f f transitions for uranium(iv). 3 The spectrum of 3 was not obtained due to its poor solubility in aromatic solvents and incompatibility with polar media. The spectrum of 2 contrasts to 1 4 which contains f d transitions as well as weak f f transitions which are characteristic of its uranium(iii) formulation. S5

6 Variable Temperature SQUID Magnetometry Fig. S3. μ eff vs T for μeff / μb T / K Fig. S4. χ vs T for χ / cm 3 mol T / K S6

7 Fig. S5. χt vs T for 2 2 χt / cm 3 Kmol T / K Fig. S6. 1/χ vs T for χ -1 / mol cm T / K S7

8 Fig. S7. μ eff vs T for μeff / μb T / K Fig. S8. χ vs T for χ / cm 3 mol T / K S8

9 Fig. S9. χt vs T for χt / cm 3 Kmol T / K Fig. S10. 1/χ vs T for χ -1 / molcm T / K The μ eff values at 300 K for 2 and 3 are 4.00 and 4.28 μ B, respectively. These values decline slowly and smoothly to ~50 K where they begin to decrease more sharply. At 1.8 K the values for 2 and 3 are 0.69 and 0.87 μ B, respectively and the curves tend to zero. This is consistent with 2 and 3 containing f 2 uranium(iv) centers as 3 H 4 uranium normally has a singlet magnetic ground state. A plot of χ M vs T for 3 (Fig. S7.) shows a maximum at 3 K which is suggestive of antiferromagnetic exchange coupling which is very rare for U(IV). The analogous plot for 2 (Fig. S3.) is clearly approaching a maximum, but this is not reached in the experimentally accessible temperature range. S9

10 Treatment of 2 and 13 C-2 with Organosilyl Halides Treatment of 2 with Me 3 SiI Me 3 SiI (0.27 ml, 1.89 mmol) was added to a cold ( 10 C) solution of 2 (1.42 g, 0.94 mmol) in pentane (10 ml) under dinitrogen. The resulting pale brown suspension was allowed to warm to ambient temperature over 1 hour and stirred for a further 16 hours. Volatiles were removed in vacuo to yield a pale brown solid. To this was added HMDSO (5 ml), the resulting mixture was stored at 30 C for 16 hours and filtered to afford a pale brown solid and a brown solution. The pale brown solid was recrystallized from toluene to afford green crystals identified as [U(Tren DMSB )I] (4) by a unit cell check and NMR spectroscopy. Volatiles were removed from the mother liquor in vacuo to yield an oily brown solid (5a). Yield: 0.17 g, (90%). [U(Tren DMSB )I] (4) was recovered in essentially quantitative yield. Anal. calc d for C 8 H 18 O 2 Si 2 : C 47.51; H 8.98%. Found: C 39.39; H 4.67%. Several independently prepared batches all returned the same CHN data on freshly prepared samples indicating that the oily organic compound produced in this reaction is already undergoing further reaction at this stage as detailed below. FTIR ν/cm 1 (Nujol): 2958 (vs), 2925 (vs), 2854 (vs), 1462 (s), 1412 (m), 1377 (s), 1260 (vs), 1094 (vs), 1020 (vs), 927 (m), 803 (vs), 722 (m), 707 (m), 662 (m), 627 (m), 513 (w). MS-EI m/z: (8.4%) [(Me 3 SiOCCOSiMe 3 ) 2 ] +. Treatment of 13 C-2 with Me 3 SiI Me 3 SiI (0.19 ml, 1.32 mmol) was added to a cold ( 10 C) solution of 13 C-2 (1.00 g, 0.66 mmol) in pentane (10 ml) under dinitrogen. The resulting pale brown suspension was allowed to warm to ambient temperature over 1 hour and stirred for a further 16 hours. Volatiles were removed in vacuo to yield a pale brown solid. To this was added HMDSO (5 ml), the resulting mixture was stored at 30 C for 16 hours and filtered to afford a pale brown solid and a brown solution. The pale brown S10

11 solid was recrystallized from toluene to afford green crystals identified as [U(Tren DMSB )I] (4) by a unit cell check and NMR spectroscopy. Volatiles were removed from the mother liquor in vacuo to yield an oily brown solid ( 13 C-5a). Yield: 0.12 g, (90%). [U(Tren DMSB )I] (4) was recovered in essentially quantitative yield. Anal. calc d for 13 C 2 C 6 H 18 O 2 Si 2 : C 47.98; H 8.88%. Found: C 35.63; H 7.35%. Several independently prepared batches all returned the same CHN data on freshly prepared samples indicating that the oily organic compound produced in this reaction is already undergoing further reaction at this stage as detailed below. FTIR ν/cm 1 (Nujol): 2960 (vs), 2926 (vs), 2854 (vs), 1462 (s), 1411 (m), 1377 (s), 1261 (vs), 1098 (vs), 1021 (vs), 928 (m), 805 (vs), 705 (m), 662 (m), 627 (m), 512 (w). MS-EI m/z: (13.8%) [(Me 3 SiO 13 C 13 COSiMe 3 ) 2 ] +. Treatment of 2 with PhMe 2 SiI PhMe 2 SiI (0.27 g, 1.00 mmol) was added to a cold ( 10 C) solution of 2 (0.75 g, 0.50 mmol) in pentane (10 ml) under dinitrogen. The resulting pale brown suspension was allowed to warm to ambient temperature over 1 hour and stirred for a further 16 hours. Volatiles were removed in vacuo to yield a pale brown solid. To this was added pentane (5 ml), the resulting mixture was stored at 30 C for 16 hours and filtered to afford a pale brown solid and a brown solution. The pale brown solid was recrystallized from toluene to afford green crystals identified as [U(Tren DMSB )I] (4) by a unit cell check and NMR spectroscopy. Volatiles were removed from the mother liquor in vacuo to yield an oily brown solid (5b). Yield: 0.15 g, (90%). [U(Tren DMSB )I] (4) was recovered in essentially quantitative yield. Anal. calc d for C 18 H 22 O 2 Si 2 : C 66.21; H 6.79%. Found: C 66.12; H 6.70%. FTIR ν/cm 1 (Nujol): 3136 (w), 3069 (w), 3049 (w), 2956 (vs), 2925 (vs), 2854 (vs), 1464 (s), 1412 (m), 1377 (m), 1259 (vs), 1095 (vs), 1020 (vs), 924 (m), 897 (m), 874 (m), 826 (s), 802 (vs), 726 (w), 703 (m), 672 (w), 662 (m), 562 (w), 472 (w). MS-ESI (+ve mode) m/z: (37.9%) [5b-Ph] +. S11

12 Treatment of 13 C-2 with PhMe 2 SiI PhMe 2 SiI (0.32 g, 1.20 mmol) was added to a cold ( 10 C) solution of 13 C-2 (0.90 g, 0.60 mmol) in pentane (10 ml) under dinitrogen. The resulting pale brown suspension was allowed to warm to ambient temperature over 1 hour and stirred for a further 16 hours. Volatiles were removed in vacuo to yield a pale brown solid. To this was added pentane (5 ml), the resulting mixture was stored at 30 C for 16 hours and filtered to afford a pale brown solid and a brown solution. The pale brown solid was recrystallized from toluene to afford green crystals identified as [U(Tren DMSB )I] (4) by a unit cell check and NMR spectroscopy. Volatiles were removed from the mother liquor in vacuo to yield an oily brown solid ( 13 C-5b). Yield: 0.15 g, (90%). [U(Tren DMSB )I] (4) was recovered in essentially quantitative yield. Anal. calc d for 13 C 2 C 16 H 22 O 2 Si 2 : C 66.44; H 6.75%. Found: C 66.04; H 6.60%. FTIR ν/cm 1 (Nujol): 3136 (w), 3070 (w), 3050 (w), 2954 (vs), 2926 (vs), 2856 (vs), 1463 (s), 1408 (m), 1377 (m), 1260 (vs), 1095 (vs), 1020 (vs), 924 (m), 897 (m), 875 (m), 827 (s), 801 (vs), 728 (w), 701 (m), 675, (w), 662 (m), 564 (w), 471 (w). MS-ESI (+ve mode) m/z: (5.00%) [ 13 C-5b-Ph] +. Aqueous Work-Up of Product from Treatment of 2 with Me 3 SiI 5a (0.17 g, 0.84 mmol) was extracted into hexane (50 ml) and transferred to a separation funnel. Distilled water (30 ml) was added to the flask which was vigorously shaken and then allowed to settle. The aqueous layer was separated and this procedure repeated a further two times (2 30 ml distilled water). The organic layer was dried over magnesium sulphate, filtered, and volatiles were removed in vacuo to yield a pale yellow oil (6a) which was further dried (10-3 mm Hg) for 1 hour. Yield: 0.10 g, 91%. 1 H NMR (C 6 D 6, 298 K): δ 0.34 (s, 18H, SiMe 3 ), 3.90 (m, br 2H, CH 2 ). 13 C{ 1 H} NMR (C 6 D 6, 298 K): δ 1.16 (s, SiMe 3 ), (s, C 1 ), (s, C 3 ), (s, C 2 ), (s, C 4 ). S12

13 29 Si{ 1 H} NMR (C 6 D 6, 298 K): δ FTIR ν/cm 1 (Nujol): 2962 (vs), 2930 (vs), 2904 (s), 2857 (s), 1781 (s), 1471 (s), 1464 (m), 1446 (m), 1410 (m), 1376 (s), 1362 (m), 1333 (m), 1261 (vs), 1096 (vs), 1021 (vs), 938 (m), 863 (s), 804 (vs), 703 (m), 686 (m), 662 (m), 628 (m), 576 (w), 515 (w), 498 (m). MS-EI m/z: (40.7%) [6a-Me] +. MS-ESI ( ve mode) m/z: (100%) [6a- H]. Aqueous Work-Up of Product from Treatment of 13 C-2 with Me 3 SiI 13 C-5a (0.17 g, 0.84 mmol) was extracted into hexane (50 ml) and transferred to a separation funnel. Distilled water (30 ml) was added to the flask which was vigorously shaken and then allowed to settle. The aqueous layer was separated and this procedure repeated a further two times (2 30 ml distilled water). The organic layer was dried over magnesium sulphate, filtered, and volatiles were removed in vacuo to yield a pale yellow oil ( 13 C-6a) which was further dried (10-3 mm Hg) for 1 hour. Yield: 0.10 g, 90%. 1 H NMR (C 6 D 6, 298 K): δ 0.40 (s, 18H, SiMe 3 ), 3.90 (dm, 2H, J HC = 152 Hz, 2 J HH = 6 Hz, CH 2 ). 13 C{ 1 H} NMR (C 6 D 6, 298 K): δ 1.16 (s, SiMe 3 ), (dd, J C1C2 = 50 Hz, 2 J C1C3 = 11 Hz, CH [C 1 ]), (ddd, J C3C2 = 96 Hz, J C3C4 = 82 Hz, 2 J C3C1 = 11 Hz, (Me 3 SiO)C(C=O) [C 3 ]), (ddd, J C2C3 = 96 Hz, J C2C1 = 50 Hz, 2 J C2C4 = 23 Hz, (Me 3 SiO)C(CH) [C 2 ]), (dd, J C4C3 = 82 Hz, 2 J C4C2 = 23 Hz, C=O [C 4 ]). Additional CH coupling observed in 1 H-coupled 13 C NMR (C 6 D 6, 298 K): δ 1.16 (q, J CH = 150 Hz), [C1] (tdd, J CH = 152 Hz), [C3] (dddt, 3 J CH = 2.5 Hz), [C2] (dddt, 2 J CH = 6.3 Hz). 29 Si{ 1 H} NMR (C 6 D 6, 298 K): δ FTIR ν/cm 1 (Nujol): 2963 (vs), 2932 (s), 2896 (s), 2859 (s), 1754 (s), 1464 (m), 1445 (m), 1413 (s), 1364 (m), 1341 (m), 1313 (m), 1262 (vs), 1097 (vs), 863 (s), 797 (vs), 702 (m), 663 (m), 627 (m), 588 (w), 498 (w). MS-EI m/z: (47.4%) [ 13 C-6a SiMe 3 ] +. MS-ESI ( ve mode) m/z: (100%) [ 13 C-6b-SiMe 3 ]. MS-ESI (+ve mode) m/z: (21.2%) [ 13 C- 6a+HCOONa] +. S13

14 Aqueous Work-Up of Product from Treatment of 2 with PhMe 2 SiI 5b (0.15 g, 0.46 mmol) was extracted into hexane (50 ml) and transferred to a separation funnel. Distilled water (30 ml) was added to the flask which was vigorously shaken and then allowed to settle. The aqueous layer was separated and this procedure repeated a further two times (2 30 ml distilled water). The organic layer was dried over magnesium sulphate, filtered, and volatiles were removed in vacuo to yield a pale yellow oil (6b) which was further dried (10-3 mm Hg) for 1 hour. Yield: 0.08 g, 88%. 1 H NMR (C 6 D 6, 298 K): δ 0.30 (s, 12H, SiMe 2 ), 3.83 (m, 2H, CH 2 ), 7.32 (m, 6H, Ph), 7.67 (m, 4H, Ph). 13 C{ 1 H} NMR (C 6 D 6, 298 K): δ 0.75 (s, SiMe 2 ), (s, C 1 ), (s, C 3 ), (s, Ph), (s, Ph), (s, C 2 ), (s, C 4 ). 29 Si{ 1 H} NMR (C 6 D 6, 298 K): δ FTIR ν/cm 1 (Nujol): 3136 (w), 3070 (w), 3051 (w), 2959 (vs), 2929 (vs), 2900 (m), 2856 (s), 1765 (m), 1471 (m), 1464 (m), 1428 (m), 1405 (m), 1361 (m), 1260 (vs), 1097 (vs), 1020 (vs), 938 (m), 867 (s), 804 (vs), 741 (m) 728 (m), 700 (m), 662 (m), 571 (w), 516 (w), 498 (m), 472 (w). MS-ESI (+ve mode) m/z: (60.6%) [6b Ph+NaNCMe] +. Aqueous Work-Up of Product from Treatment of 13 C-2 with PhMe 2 SiI 13 C-5b (0.15 g, 0.46 mmol) was extracted into hexane (50 ml) and transferred to a separation funnel. Distilled water (30 ml) was added to the flask which was vigorously shaken and then allowed to settle. The aqueous layer was separated and this procedure repeated a further two times (2 30 ml distilled water). The organic layer was dried over magnesium sulphate, filtered, and volatiles were removed in vacuo to yield a pale yellow oil ( 13 C-6b) which was further dried (10-3 mm Hg) for 1 hour. Yield: 0.08 g, 88%. 1 H NMR (C 6 D 6, 298 K): δ 0.39 (s, 12H, SiMe 2 ), 3.83 (dm, 2H, J HC = 151 Hz, 2 J HH = 6 Hz, CH 2 ), 7.32 (m, 6H, Ph), 7.67 (m, 4H, Ph). 13 C{ 1 H} NMR (C 6 D 6, 298 K): δ 1.06 (s, SiMe 2 ), (dd, J C1C2 = 48 Hz, 2 J C1C3 = 11 Hz, CH [C 1 ]), (ddd, J C3C2 = S14

15 94 Hz, J C3C4 = 83 Hz, 2 J C3C1 = 11 Hz, (Me 3 SiO)C(C=O) [C 3 ]), (s, Ph), (s, Ph), (ddd, J C2C3 = 94 Hz, J C2C1 = 48 Hz, 2 J C2C4 = 23 Hz, (Me 3 SiO)C(CH) [C 2 ]), (dd, J C4C3 = 83 Hz, 2 J C4C2 = 23 Hz, C=O [C 4 ]). Additional CH coupling observed in 1 H-coupled 13 C NMR (C6D6, 298 K): δ 1.06 (q, J CH = 118 Hz), [C1] (tdd, J CH = 103 Hz), [C3] (dddt, 3 J CH = 2.5 Hz), [C2] (dddt, 2 J CH = 6.1 Hz). 29 Si{ 1 H} NMR (C 6 D 6, 298 K): δ FTIR ν/cm 1 (Nujol): 3091 (w), 3071 (m), 3053 (m), 3024 (w), 2963 (vs), 2905 (s), 2858 (m), 1719 (m), 1487 (m), 1472 (m), 1463 (s), 1428 (s), 1363 (m), 1261 (vs), 1094 (vs), 865 (vs), 795 (s), 742 (m), 727 (m), 700 (s), 662 (m), 620 (w), 471 (m). MS-ESI ( ve mode) m/z: (100%) [ 13 C-6b H]. It should be noted that the accidental equivalence of the silyl resonances for 6 is commensurate with their remote placement on the ring. For example, the silyl methyls are 4 J with respect to the C2/3 positions. S15

16 Fig. S11. Initial 13 C{ 1 H} NMR of 13 C-5a/6a After Aqueous Wash Fig. S12. Final 13 C{ 1 H} NMR of 13 C-6a After Aqueous Wash S16

17 Fig. S C{ 1 H} NMR Comparison of Initial 13 C-5a/6a Mix (Top) and Final 13 C-6a (Bottom) Fig. S14. Comparison of 13 C{ 1 H} NMR of 6a (Top) versus 13 C NMR of 13 C-6a (Bottom) S17

18 Fig. S15. Initial 13 C{ 1 H} NMR of 13 C-5b/6b After Aqueous Wash Fig. S16. Final 13 C{ 1 H} NMR of 13 C-6b After Aqueous Wash S18

19 Fig. S C{ 1 H} NMR Comparison of Initial 13 C-5b/6b Mix (Top) and Final 13 C-6b (Bottom) Fig. S18. Comparison of 13 C{ 1 H} NMR of 6b (Top) versus 13 C NMR of 13 C-6b (Bottom) S19

20 Representative Conversion of 4 to 1 Under argon, complex 4 (1.50 g, 1.76 mmol), isolated from a liberation reaction as described above, in pentane (10 ml) was vigorously stirred over a potassium mirror (0.2 g, 5.1 mmol) until the green solution turned dark purple. The reaction was adjudged complete after 24 hours under these conditions by 1 H NMR spectroscopic analysis of an aliquot of the reaction mixture. The mixture was filtered and volatiles removed in vacuo to afford a dark purple solid. Yield: 1.08 g, 99%. Characterization data matches an authentic sample of 1 and exposure to dinitrogen affords the dinitrogen adduct as described by Scott. 1 Representative Recycling Procedure As described above, a solution of 1 in pentane was treated with CO. The CO atmosphere was replaced with dinitrogen and the relevant amount of silyl iodide was added. Following extraction and precipitation of 4 the isolated 4 was placed in pentane and stirred over a potassium mirror. Once 1 was obtained it was recycled back into another reaction. Typically, the first pass recovered 1 in essentially quantitative yield, but subsequent passes resulted in yields of 1 of ca 80-90%. Overall, at least 4 cycles could be accomplished, generating 5 in yields of ca 90% relative to the quantity of 1 used in a given cycle before separation became difficult due to reduced solvent volumes. X-ray Crystallography [{U(Tren DMSB )} 2 (μ-η 1 :η 1 -OCCO)] (2) and [U(Tren DMSB )(µ -O)U{N(CH 2 CH 2 NSiMe 2 Bu t ) 2 (CH 2 CH 2 -NC[OSiMe 2 Bu t ]CHO)}] (5) have been deposited with the CCDC, numbers and S20

21 Table S1. Crystal data and structure refinement for 2. Identification code 2 Chemical formula C 50 H 114 N 8 O 2 Si 6 U 2 Formula weight Temperature 90(2) K Radiation, wavelength MoKα, Å Crystal system, space group Monoclinic, P21 1 /n Unit cell parameters a = (5) Å α = 90 b = (12) Å β = (1) c = (5) Å γ = 90 Cell volume (3) Å 3 Z 2 Calculated density g/cm 3 Absorption coefficient μ mm 1 F(000) 1508 Crystal color and size pale green, mm 3 Reflections for cell refinement 8199 (θ range 2.29 to ) Data collection method Bruker SMART APEX CCD diffractometer ω rotation with narrow frames θ range for data collection 2.18 to Index ranges h 6 to 14, k 36 to 36, l 15 to 15 Completeness to θ = % Intensity decay 0% Reflections collected Independent reflections 7642 (R int = ) Reflections with F 2 >2σ 6401 Absorption correction semi-empirical from equivalents Min. and max. transmission and Structure solution direct methods Refinement method Full-matrix least-squares on F 2 Weighting parameters a, b , Data / restraints / parameters 7642 / 0 / 322 Final R indices [F 2 >2σ] R1 = , wr2 = R indices (all data) R1 = , wr2 = Goodness-of-fit on F Largest and mean shift/su and Largest diff. peak and hole and e Å 3 Table S2. Atomic coordinates and equivalent isotropic displacement parameters (Å 2 ) for 2. U(eq) is defined as one third of the trace of the orthogonalized U ij tensor. x y z U(eq) U(1) (15) (5) (13) (5) N(1) (4) (12) (3) (8) Si(1) (12) (4) (11) (2) C(1) (4) (15) (5) (10) S21

22 C(2) (5) (17) (4) (11) C(3) (5) (17) (4) (10) C(4) (5) (2) (4) (12) C(5) (6) (19) (5) (15) C(6) (6) (2) (5) (14) C(7) (5) (15) (5) (11) C(8) (5) (15) (5) (11) N(2) (4) (12) (3) (7) Si(2) (11) (4) (10) (2) C(9) (4) (16) (4) (9) C(10) (5) (16) (4) (10) C(11) (4) (15) (4) (9) C(12) (5) (18) (5) (12) C(13) (6) (2) (5) (15) C(14) (6) (19) (5) (14) C(15) (5) (15) (4) (10) C(16) (5) (16) (5) (11) N(3) (4) (12) (3) (7) Si(3) (12) (4) (10) (2) C(17) (5) (16) (4) (10) C(18) (5) (18) (4) (11) C(19) (4) (15) (4) (9) C(20) (5) (18) (5) (11) C(21) (5) (17) (4) (12) C(22) (5) (16) (4) (10) C(23) (5) (15) (4) (10) C(24) (5) (15) (4) (11) N(4) (4) (11) (3) (7) O(1) (3) (10) (3) (7) C(25) (5) (14) (4) (9) Table S3. Bond lengths [Å] and angles [ ] for 2. U(1) O(1) 2.156(3) U(1) N(2) 2.246(4) U(1) N(3) 2.263(3) U(1) N(1) 2.265(4) U(1) N(4) 2.534(3) N(1) C(7) 1.483(5) N(1) Si(1) 1.734(4) Si(1) C(1) 1.855(4) Si(1) C(2) 1.876(5) Si(1) C(3) 1.911(5) C(1) H(1B) C(1) H(1C) C(1) H(1A) C(2) H(2A) C(2) H(2C) C(2) H(2B) C(3) C(6) 1.519(7) C(3) C(4) 1.525(7) C(3) C(5) 1.541(7) C(4) H(4A) C(4) H(4C) C(4) H(4B) C(5) H(5B) C(5) H(5C) C(5) H(5A) C(6) H(6B) C(6) H(6C) C(6) H(6A) C(7) C(8) 1.490(7) C(7) H(7A) S22

23 C(7) H(7B) C(8) N(4) 1.469(5) C(8) H(8B) C(8) H(8A) N(2) C(15) 1.483(5) N(2) Si(2) 1.742(4) Si(2) C(9) 1.870(4) Si(2) C(10) 1.876(4) Si(2) C(11) 1.900(5) C(9) H(9B) C(9) H(9C) C(9) H(9A) C(10) H(10B) C(10) H(10C) C(10) H(10A) C(11) C(13) 1.523(6) C(11) C(12) 1.524(7) C(11) C(14) 1.530(6) C(12) H(12B) C(12) H(12C) C(12) H(12A) C(13) H(13A) C(13) H(13C) C(13) H(13B) C(14) H(14B) C(14) H(14C) C(14) H(14A) C(15) C(16) 1.505(6) C(15) H(15B) C(15) H(15A) C(16) N(4) 1.458(6) C(16) H(16A) C(16) H(16B) N(3) C(23) 1.474(5) N(3) Si(3) 1.750(3) Si(3) C(17) 1.867(5) Si(3) C(18) 1.872(5) Si(3) C(19) 1.900(5) C(17) H(17A) C(17) H(17C) C(17) H(17B) C(18) H(18B) C(18) H(18C) C(18) H(18A) C(19) C(20) 1.526(7) C(19) C(22) 1.535(6) C(19) C(21) 1.551(6) C(20) H(20A) C(20) H(20C) C(20) H(20B) C(21) H(21A) C(21) H(21C) C(21) H(21B) C(22) H(22B) C(22) H(22C) C(22) H(22A) C(23) C(24) 1.495(6) C(23) H(23B) C(23) H(23A) C(24) N(4) 1.484(5) C(24) H(24B) C(24) H(24A) O(1) C(25) 1.302(5) C(25) C(25)# (8) O(1) U(1) N(2) (12) O(1) U(1) N(3) (11) N(2) U(1) N(3) (13) O(1) U(1) N(1) (13) N(2) U(1) N(1) (13) N(3) U(1) N(1) (13) O(1) U(1) N(4) (11) N(2) U(1) N(4) 70.98(12) N(3) U(1) N(4) 70.65(11) N(1) U(1) N(4) 70.75(12) C(7) N(1) Si(1) 116.5(3) C(7) N(1) U(1) 120.8(3) Si(1) N(1) U(1) (17) N(1) Si(1) C(1) (19) N(1) Si(1) C(2) 111.1(2) C(1) Si(1) C(2) 108.1(2) N(1) Si(1) C(3) 112.7(2) C(1) Si(1) C(3) 107.0(2) C(2) Si(1) C(3) 109.0(2) Si(1) C(1) H(1B) Si(1) C(1) H(1C) H(1B) C(1) H(1C) Si(1) C(1) H(1A) H(1B) C(1) H(1A) H(1C) C(1) H(1A) Si(1) C(2) H(2A) Si(1) C(2) H(2C) H(2A) C(2) H(2C) Si(1) C(2) H(2B) H(2A) C(2) H(2B) H(2C) C(2) H(2B) C(6) C(3) C(4) 108.9(4) C(6) C(3) C(5) 107.8(5) C(4) C(3) C(5) 110.1(4) S23

24 C(6) C(3) Si(1) 109.8(3) C(4) C(3) Si(1) 109.1(3) C(5) C(3) Si(1) 111.2(4) C(3) C(4) H(4A) C(3) C(4) H(4C) H(4A) C(4) H(4C) C(3) C(4) H(4B) H(4A) C(4) H(4B) H(4C) C(4) H(4B) C(3) C(5) H(5B) C(3) C(5) H(5C) H(5B) C(5) H(5C) C(3) C(5) H(5A) H(5B) C(5) H(5A) H(5C) C(5) H(5A) C(3) C(6) H(6B) C(3) C(6) H(6C) H(6B) C(6) H(6C) C(3) C(6) H(6A) H(6B) C(6) H(6A) H(6C) C(6) H(6A) N(1) C(7) C(8) 111.1(4) N(1) C(7) H(7A) C(8) C(7) H(7A) N(1) C(7) H(7B) C(8) C(7) H(7B) H(7A) C(7) H(7B) N(4) C(8) C(7) 112.4(4) N(4) C(8) H(8B) C(7) C(8) H(8B) N(4) C(8) H(8A) C(7) C(8) H(8A) H(8B) C(8) H(8A) C(15) N(2) Si(2) 117.2(3) C(15) N(2) U(1) 120.6(3) Si(2) N(2) U(1) (18) N(2) Si(2) C(9) (19) N(2) Si(2) C(10) (19) C(9) Si(2) C(10) 108.3(2) N(2) Si(2) C(11) (19) C(9) Si(2) C(11) 108.6(2) C(10) Si(2) C(11) 109.4(2) Si(2) C(9) H(9B) Si(2) C(9) H(9C) H(9B) C(9) H(9C) Si(2) C(9) H(9A) H(9B) C(9) H(9A) H(9C) C(9) H(9A) Si(2) C(10) H(10B) Si(2) C(10) H(10C) H(10B) C(10) H(10C) Si(2) C(10) H(10A) H(10B) C(10) H(10A) H(10C) C(10) H(10A) C(13) C(11) C(12) 108.5(4) C(13) C(11) C(14) 109.0(4) C(12) C(11) C(14) 108.6(4) C(13) C(11) Si(2) 110.6(3) C(12) C(11) Si(2) 109.5(3) C(14) C(11) Si(2) 110.6(3) C(11) C(12) H(12B) C(11) C(12) H(12C) H(12B) C(12) H(12C) C(11) C(12) H(12A) H(12B) C(12) H(12A) H(12C) C(12) H(12A) C(11) C(13) H(13A) C(11) C(13) H(13C) H(13A) C(13) H(13C) C(11) C(13) H(13B) H(13A) C(13) H(13B) H(13C) C(13) H(13B) C(11) C(14) H(14B) C(11) C(14) H(14C) H(14B) C(14) H(14C) C(11) C(14) H(14A) H(14B) C(14) H(14A) H(14C) C(14) H(14A) N(2) C(15) C(16) 111.9(4) N(2) C(15) H(15B) C(16) C(15) H(15B) N(2) C(15) H(15A) C(16) C(15) H(15A) H(15B) C(15) H(15A) N(4) C(16) C(15) 112.1(4) N(4) C(16) H(16A) C(15) C(16) H(16A) N(4) C(16) H(16B) C(15) C(16) H(16B) H(16A) C(16) H(16B) C(23) N(3) Si(3) 113.2(3) C(23) N(3) U(1) 121.2(3) Si(3) N(3) U(1) (18) N(3) Si(3) C(17) (19) N(3) Si(3) C(18) 110.3(2) C(17) Si(3) C(18) 107.3(2) N(3) Si(3) C(19) (19) C(17) Si(3) C(19) 108.9(2) C(18) Si(3) C(19) 108.0(2) Si(3) C(17) H(17A) S24

25 Si(3) C(17) H(17C) H(17A) C(17) H(17C) Si(3) C(17) H(17B) H(17A) C(17) H(17B) H(17C) C(17) H(17B) Si(3) C(18) H(18B) Si(3) C(18) H(18C) H(18B) C(18) H(18C) Si(3) C(18) H(18A) H(18B) C(18) H(18A) H(18C) C(18) H(18A) C(20) C(19) C(22) 108.3(4) C(20) C(19) C(21) 109.2(4) C(22) C(19) C(21) 108.6(4) C(20) C(19) Si(3) 111.1(3) C(22) C(19) Si(3) 110.0(3) C(21) C(19) Si(3) 109.6(3) C(19) C(20) H(20A) C(19) C(20) H(20C) H(20A) C(20) H(20C) C(19) C(20) H(20B) H(20A) C(20) H(20B) H(20C) C(20) H(20B) C(19) C(21) H(21A) C(19) C(21) H(21C) H(21A) C(21) H(21C) C(19) C(21) H(21B) H(21A) C(21) H(21B) H(21C) C(21) H(21B) C(19) C(22) H(22B) C(19) C(22) H(22C) H(22B) C(22) H(22C) C(19) C(22) H(22A) H(22B) C(22) H(22A) H(22C) C(22) H(22A) N(3) C(23) C(24) 111.9(4) N(3) C(23) H(23B) C(24) C(23) H(23B) N(3) C(23) H(23A) C(24) C(23) H(23A) H(23B) C(23) H(23A) N(4) C(24) C(23) 112.3(4) N(4) C(24) H(24B) C(23) C(24) H(24B) N(4) C(24) H(24A) C(23) C(24) H(24A) H(24B) C(24) H(24A) C(16) N(4) C(8) 114.3(4) C(16) N(4) C(24) 111.8(4) C(8) N(4) C(24) 110.1(4) C(16) N(4) U(1) 106.1(2) C(8) N(4) U(1) 107.9(3) C(24) N(4) U(1) 106.2(2) C(25) O(1) U(1) 158.8(3) C(25)#1 C(25) O(1) 173.8(6) Symmetry transformations used to generate equivalent atoms: #1 -x,-y+1,-z+2 Table S4. Anisotropic displacement parameters (Å 2 ) for 2. The anisotropic displacement factor exponent takes the form: 2π 2 [h 2 a* 2 U hka*b*U 12 ] U 11 U 22 U 33 U 23 U 13 U 12 U(1) (8) (7) (8) (6) (6) (6) N(1) 0.024(2) (16) (19) (14) (16) (15) Si(1) (6) (5) (6) (5) (5) (5) C(1) 0.020(2) 0.026(2) 0.039(3) 0.003(2) 0.013(2) (18) C(2) 0.036(3) 0.037(3) 0.025(2) 0.003(2) 0.017(2) 0.000(2) C(3) 0.029(3) 0.036(3) 0.025(2) (19) 0.010(2) 0.008(2) C(4) 0.039(3) 0.051(3) 0.022(2) 0.001(2) 0.007(2) 0.002(3) C(5) 0.044(4) 0.044(3) 0.047(3) 0.010(3) 0.006(3) 0.021(3) C(6) 0.031(3) 0.064(4) 0.035(3) 0.011(3) 0.005(2) 0.003(3) C(7) 0.040(3) 0.019(2) 0.044(3) 0.002(2) 0.023(3) 0.000(2) C(8) 0.041(3) 0.020(2) 0.038(3) (19) 0.021(2) 0.002(2) N(2) (18) (17) (17) (14) (15) (14) S25

26 Si(2) (6) (5) (5) (4) (5) (5) C(9) 0.023(2) 0.029(2) 0.024(2) (18) (19) (18) C(10) 0.028(2) 0.033(2) 0.020(2) (18) (19) 0.005(2) C(11) 0.025(2) 0.024(2) 0.021(2) (17) (19) (18) C(12) 0.030(3) 0.038(3) 0.054(3) 0.002(2) 0.019(3) 0.004(2) C(13) 0.034(3) 0.055(3) 0.041(3) 0.024(3) 0.004(3) 0.011(3) C(14) 0.059(4) 0.038(3) 0.048(3) 0.020(3) 0.029(3) 0.021(3) C(15) 0.026(3) 0.024(2) 0.027(2) (18) 0.001(2) (19) C(16) 0.029(3) 0.025(2) 0.038(3) 0.000(2) 0.006(2) 0.008(2) N(3) (19) (16) (16) (13) (15) (14) Si(3) (6) (6) (5) (4) (5) (5) C(17) 0.030(3) 0.035(2) 0.020(2) (19) 0.005(2) 0.010(2) C(18) 0.037(3) 0.048(3) 0.024(2) 0.005(2) 0.016(2) 0.009(2) C(19) 0.023(2) 0.024(2) 0.022(2) (18) (18) (18) C(20) 0.025(3) 0.036(3) 0.039(3) 0.003(2) 0.005(2) 0.005(2) C(21) 0.036(3) 0.035(3) 0.024(2) 0.011(2) 0.000(2) 0.007(2) C(22) 0.032(3) 0.030(2) 0.024(2) (18) 0.005(2) 0.007(2) C(23) 0.040(3) 0.024(2) 0.021(2) (18) 0.007(2) 0.007(2) C(24) 0.048(3) 0.017(2) 0.028(2) (18) 0.014(2) 0.005(2) N(4) (19) (15) (17) (13) (15) (14) O(1) (19) (13) (16) (12) (14) (13) C(25) 0.029(2) (17) 0.021(2) (16) (19) (17) Table S5. Hydrogen coordinates and isotropic displacement parameters (Å 2 ) for 2. x y z U(eq) H(1B) H(1C) H(1A) H(2A) H(2C) H(2B) H(4A) H(4C) H(4B) H(5B) H(5C) H(5A) H(6B) H(6C) H(6A) H(7A) H(7B) H(8B) H(8A) S26

27 H(9B) H(9C) H(9A) H(10B) H(10C) H(10A) H(12B) H(12C) H(12A) H(13A) H(13C) H(13B) H(14B) H(14C) H(14A) H(15B) H(15A) H(16A) H(16B) H(17A) H(17C) H(17B) H(18B) H(18C) H(18A) H(20A) H(20C) H(20B) H(21A) H(21C) H(21B) H(22B) H(22C) H(22A) H(23B) H(23A) H(24B) H(24A) S27

28 Table S6. Crystal data and structure refinement for 3. Identification code 3 Chemical formula C 56 H 115 D 6 N 8 O 3 Si 6 U 2 Formula weight Temperature 90(2) K Radiation, wavelength MoKα, Å Crystal system, space group Monoclinic, P21 1 /c Unit cell parameters a = (6) Å α = 90 b = (10) Å β = (1) c = (9) Å γ = 90 Cell volume (5) Å 3 Z 4 Calculated density g/cm 3 Absorption coefficient μ mm 1 F(000) 3220 Crystal color and size green, mm 3 Reflections for cell refinement (θ range 2.28 to ) Data collection method Bruker SMART APEX CCD diffractometer ω rotation with narrow frames θ range for data collection 1.95 to Index ranges h 18 to 18, k 28 to 31, l 25 to 28 Completeness to θ = % Intensity decay 0% Reflections collected Independent reflections (R int = ) Reflections with F 2 >2σ Absorption correction semi-empirical from equivalents Min. and max. transmission and Structure solution direct methods Refinement method Full-matrix least-squares on F 2 Weighting parameters a, b , Data / restraints / parameters / 0 / 706 Final R indices [F 2 >2σ] R1 = , wr2 = R indices (all data) R1 = , wr2 = Goodness-of-fit on F Largest and mean shift/su and Largest diff. peak and hole and e Å 3 Table S7. Atomic coordinates and equivalent isotropic displacement parameters (Å 2 ) for 3. U(eq) is defined as one third of the trace of the orthogonalized U ij tensor. x y z U(eq) U(1) (11) (7) (7) (5) N(1) (2) (16) (17) (8) Si(1) (8) (5) (6) (3) C(1) (3) (2) (2) (10) S28

29 C(2) (3) (19) (2) (10) C(3) (3) (2) (2) (10) C(4) (3) (2) (3) (12) C(5) (4) (2) (2) (13) C(6) (3) (2) (2) (12) C(7) (3) (19) (2) (10) C(8) (3) (2) (2) (10) N(2) (2) (16) (18) (8) Si(2) (9) (5) (6) (3) C(9) (4) (2) (2) (11) C(10) (3) (19) (2) (10) C(11) (3) (2) (2) (10) C(12) (3) (2) (2) (11) C(13) (3) (2) (2) (12) C(14) (3) (2) (2) (11) C(15) (3) (2) (2) (11) C(16) (3) (19) (2) (10) N(3) (3) (17) (18) (8) Si(3) (9) (6) (6) (3) C(17) (3) (2) (3) (12) C(18) (4) (2) (3) (13) C(19) (3) (2) (2) (11) C(20) (4) (2) (3) (13) C(21) (4) (3) (3) (16) C(22) (4) (3) (2) (13) C(23) (4) (2) (2) (12) C(24) (4) (2) (2) (11) N(4) (3) (16) (18) (8) O(1) (2) (13) (15) (7) U(2) (11) (7) (8) (5) N(5) (3) (16) (17) (8) Si(4) (9) (6) (6) (3) C(25) (3) (2) (2) (11) C(26) (4) (3) (2) (13) C(27) (3) (2) (2) (11) C(28) (4) (3) (3) (15) C(29) (4) (2) (3) (12) C(30) (4) (2) (3) (14) C(31) (4) (2) (2) (11) C(32) (4) (2) (3) (14) N(6) (3) (17) (17) (8) Si(5) (10) (5) (6) (3) C(33) (3) (2) (2) (11) C(34) (4) (2) (2) (12) C(35) (5) (2) (2) (14) C(36) (5) (3) (3) (19) C(37) (5) (2) (3) (18) C(38) (6) (3) (3) (19) C(39) (4) (2) (2) (11) C(40) (4) (3) (3) (14) S29

30 N(7) (3) (17) (2) (10) C(41) (4) (2) (3) (14) C(42) (4) (3) (3) (15) N(8) (3) (16) (19) (9) O(2) (3) (17) (17) (9) C(43) (4) (2) (3) (13) C(44) (4) (2) (2) (11) O(3) (3) (17) (19) (10) Si(6) (11) (7) (7) (3) C(45) (5) (3) (4) 0.067(2) C(46) (4) (3) (3) (17) C(47) (4) (3) (3) (16) C(48) (5) (3) (3) (19) C(49) (6) (3) (4) 0.071(2) C(50) (5) (3) (4) 0.077(2) C(51) (5) (3) (4) 0.070(2) C(52) (5) (3) (4) 0.074(2) C(53) (5) (3) (3) (17) C(54) (5) (2) (3) (14) C(55) (6) (3) (3) 0.069(2) C(56) (5) (3) (4) 0.066(2) Table S8. Bond lengths [Å] and angles [ ] for 3. U(1) O(1) 2.116(3) U(1) N(3) 2.284(4) U(1) N(1) 2.300(4) U(1) N(2) 2.316(4) U(1) N(4) 2.580(4) N(1) C(7) 1.473(6) N(1) Si(1) 1.720(4) Si(1) C(2) 1.864(5) Si(1) C(1) 1.885(5) Si(1) C(3) 1.904(4) C(1) H(1B) C(1) H(1C) C(1) H(1A) C(2) H(2B) C(2) H(2C) C(2) H(2A) C(3) C(6) 1.527(7) C(3) C(4) 1.539(7) C(3) C(5) 1.544(7) C(4) H(4B) C(4) H(4C) C(4) H(4A) C(5) H(5A) C(5) H(5C) C(5) H(5B) C(6) H(6B) C(6) H(6C) C(6) H(6A) C(7) C(8) 1.491(6) C(7) H(7A) C(7) H(7B) C(8) N(4) 1.488(5) C(8) H(8B) C(8) H(8A) N(2) C(15) 1.464(6) N(2) Si(2) 1.724(4) Si(2) C(9) 1.882(5) Si(2) C(10) 1.898(5) Si(2) C(11) 1.916(5) C(9) H(9B) C(9) H(9C) C(9) H(9A) C(10) H(10B) C(10) H(10C) C(10) H(10A) C(11) C(14) 1.519(7) C(11) C(13) 1.534(6) C(11) C(12) 1.542(7) C(12) H(12B) C(12) H(12C) S30

31 C(12) H(12A) C(13) H(13A) C(13) H(13C) C(13) H(13B) C(14) H(14A) C(14) H(14B) C(14) H(14C) C(15) C(16) 1.527(6) C(15) H(15A) C(15) H(15B) C(16) N(4) 1.481(6) C(16) H(16B) C(16) H(16A) N(3) C(23) 1.480(6) N(3) Si(3) 1.724(4) Si(3) C(17) 1.866(5) Si(3) C(18) 1.877(5) Si(3) C(19) 1.900(5) C(17) H(17A) C(17) H(17C) C(17) H(17B) C(18) H(18A) C(18) H(18C) C(18) H(18B) C(19) C(22) 1.526(7) C(19) C(20) 1.531(7) C(19) C(21) 1.538(7) C(20) H(20B) C(20) H(20C) C(20) H(20A) C(21) H(21B) C(21) H(21C) C(21) H(21A) C(22) H(22A) C(22) H(22C) C(22) H(22B) C(23) C(24) 1.509(7) C(23) H(23B) C(23) H(23A) C(24) N(4) 1.473(6) C(24) H(24B) C(24) H(24A) O(1) U(2) 2.138(3) U(2) O(2) 2.186(4) U(2) N(6) 2.289(4) U(2) N(5) 2.322(4) U(2) N(7) 2.541(4) U(2) N(8) 2.691(4) N(5) C(31) 1.471(6) N(5) Si(4) 1.725(4) Si(4) C(25) 1.861(5) Si(4) C(26) 1.880(5) Si(4) C(27) 1.916(5) C(25) H(25B) C(25) H(25C) C(25) H(25A) C(26) H(26A) C(26) H(26C) C(26) H(26B) C(27) C(29) 1.517(7) C(27) C(28) 1.526(7) C(27) C(30) 1.537(7) C(28) H(28A) C(28) H(28C) C(28) H(28B) C(29) H(29B) C(29) H(29C) C(29) H(29A) C(30) H(30B) C(30) H(30C) C(30) H(30A) C(31) C(32) 1.466(8) C(31) H(31B) C(31) H(31A) C(32) N(8) 1.516(7) C(32) H(32A) C(32) H(32B) N(6) C(39) 1.474(6) N(6) Si(5) 1.714(4) Si(5) C(34) 1.863(5) Si(5) C(33) 1.867(5) Si(5) C(35) 1.913(6) C(33) H(33B) C(33) H(33C) C(33) H(33A) C(34) H(34B) C(34) H(34C) C(34) H(34A) C(35) C(38) 1.521(8) C(35) C(37) 1.534(8) C(35) C(36) 1.556(9) C(36) H(36B) C(36) H(36C) C(36) H(36A) C(37) H(37B) C(37) H(37C) C(37) H(37A) C(38) H(38A) C(38) H(38C) C(38) H(38B) S31

32 C(39) C(40) 1.533(8) C(39) H(39B) C(39) H(39A) C(40) N(8) 1.439(7) C(40) H(40A) C(40) H(40B) N(7) C(44) 1.254(6) N(7) C(41) 1.464(6) C(41) C(42) 1.573(8) C(41) H(41A) C(41) H(41B) C(42) N(8) 1.473(7) C(42) H(42B) C(42) H(42A) O(2) C(43) 1.343(7) C(43) C(44) 1.478(7) C(43) H(43) C(44) O(3) 1.372(6) O(3) Si(6) 1.684(4) Si(6) C(45) 1.851(6) Si(6) C(46) 1.868(7) Si(6) C(47) 1.871(7) C(45) H(45A) C(45) H(45C) C(45) H(45B) C(46) H(46B) C(46) H(46C) C(46) H(46A) C(47) C(49) 1.505(10) C(47) C(48) 1.536(8) C(47) C(50) 1.544(9) C(48) H(48B) C(48) H(48C) C(48) H(48A) C(49) H(49B) C(49) H(49C) C(49) H(49A) C(50) H(50A) C(50) H(50C) C(50) H(50B) C(51) C(56) 1.344(10) C(51) C(52) 1.412(10) C(51) D(51) C(52) C(53) 1.359(9) C(52) D(52) C(53) C(54) 1.382(9) C(53) D(53) C(54) C(55) 1.362(9) C(54) D(54) C(55) C(56) 1.380(9) C(55) D(55) C(56) D(56) O(1) U(1) N(3) 98.58(13) O(1) U(1) N(1) (13) N(3) U(1) N(1) (13) O(1) U(1) N(2) (13) N(3) U(1) N(2) (14) N(1) U(1) N(2) 97.12(13) O(1) U(1) N(4) (12) N(3) U(1) N(4) 68.70(13) N(1) U(1) N(4) 67.32(12) N(2) U(1) N(4) 71.37(12) C(7) N(1) Si(1) 115.5(3) C(7) N(1) U(1) 121.9(3) Si(1) N(1) U(1) (19) N(1) Si(1) C(2) 105.9(2) N(1) Si(1) C(1) 111.5(2) C(2) Si(1) C(1) 108.8(2) N(1) Si(1) C(3) (19) C(2) Si(1) C(3) 110.0(2) C(1) Si(1) C(3) 107.3(2) Si(1) C(1) H(1B) Si(1) C(1) H(1C) H(1B) C(1) H(1C) Si(1) C(1) H(1A) H(1B) C(1) H(1A) H(1C) C(1) H(1A) Si(1) C(2) H(2B) Si(1) C(2) H(2C) H(2B) C(2) H(2C) Si(1) C(2) H(2A) H(2B) C(2) H(2A) H(2C) C(2) H(2A) C(6) C(3) C(4) 109.7(4) C(6) C(3) C(5) 108.2(4) C(4) C(3) C(5) 108.1(4) C(6) C(3) Si(1) 109.2(3) C(4) C(3) Si(1) 111.5(3) C(5) C(3) Si(1) 110.1(3) C(3) C(4) H(4B) C(3) C(4) H(4C) H(4B) C(4) H(4C) C(3) C(4) H(4A) H(4B) C(4) H(4A) H(4C) C(4) H(4A) C(3) C(5) H(5A) C(3) C(5) H(5C) H(5A) C(5) H(5C) S32

33 C(3) C(5) H(5B) H(5A) C(5) H(5B) H(5C) C(5) H(5B) C(3) C(6) H(6B) C(3) C(6) H(6C) H(6B) C(6) H(6C) C(3) C(6) H(6A) H(6B) C(6) H(6A) H(6C) C(6) H(6A) N(1) C(7) C(8) 112.3(4) N(1) C(7) H(7A) C(8) C(7) H(7A) N(1) C(7) H(7B) C(8) C(7) H(7B) H(7A) C(7) H(7B) N(4) C(8) C(7) 111.2(4) N(4) C(8) H(8B) C(7) C(8) H(8B) N(4) C(8) H(8A) C(7) C(8) H(8A) H(8B) C(8) H(8A) C(15) N(2) Si(2) 116.3(3) C(15) N(2) U(1) 118.6(3) Si(2) N(2) U(1) 124.9(2) N(2) Si(2) C(9) 112.4(2) N(2) Si(2) C(10) 106.6(2) C(9) Si(2) C(10) 108.3(2) N(2) Si(2) C(11) 114.3(2) C(9) Si(2) C(11) 106.9(2) C(10) Si(2) C(11) 108.1(2) Si(2) C(9) H(9B) Si(2) C(9) H(9C) H(9B) C(9) H(9C) Si(2) C(9) H(9A) H(9B) C(9) H(9A) H(9C) C(9) H(9A) Si(2) C(10) H(10B) Si(2) C(10) H(10C) H(10B) C(10) H(10C) Si(2) C(10) H(10A) H(10B) C(10) H(10A) H(10C) C(10) H(10A) C(14) C(11) C(13) 107.9(4) C(14) C(11) C(12) 109.3(4) C(13) C(11) C(12) 108.8(4) C(14) C(11) Si(2) 111.8(3) C(13) C(11) Si(2) 110.0(3) C(12) C(11) Si(2) 109.0(3) C(11) C(12) H(12B) C(11) C(12) H(12C) H(12B) C(12) H(12C) C(11) C(12) H(12A) H(12B) C(12) H(12A) H(12C) C(12) H(12A) C(11) C(13) H(13A) C(11) C(13) H(13C) H(13A) C(13) H(13C) C(11) C(13) H(13B) H(13A) C(13) H(13B) H(13C) C(13) H(13B) C(11) C(14) H(14A) C(11) C(14) H(14B) H(14A) C(14) H(14B) C(11) C(14) H(14C) H(14A) C(14) H(14C) H(14B) C(14) H(14C) N(2) C(15) C(16) 112.8(4) N(2) C(15) H(15A) C(16) C(15) H(15A) N(2) C(15) H(15B) C(16) C(15) H(15B) H(15A) C(15) H(15B) N(4) C(16) C(15) 111.1(4) N(4) C(16) H(16B) C(15) C(16) H(16B) N(4) C(16) H(16A) C(15) C(16) H(16A) H(16B) C(16) H(16A) C(23) N(3) Si(3) 115.5(3) C(23) N(3) U(1) 120.6(3) Si(3) N(3) U(1) 120.9(2) N(3) Si(3) C(17) 107.7(2) N(3) Si(3) C(18) 110.6(2) C(17) Si(3) C(18) 107.6(3) N(3) Si(3) C(19) 114.5(2) C(17) Si(3) C(19) 108.4(2) C(18) Si(3) C(19) 107.8(2) Si(3) C(17) H(17A) Si(3) C(17) H(17C) H(17A) C(17) H(17C) Si(3) C(17) H(17B) H(17A) C(17) H(17B) H(17C) C(17) H(17B) Si(3) C(18) H(18A) Si(3) C(18) H(18C) H(18A) C(18) H(18C) Si(3) C(18) H(18B) H(18A) C(18) H(18B) H(18C) C(18) H(18B) C(22) C(19) C(20) 108.1(4) S33

34 C(22) C(19) C(21) 108.9(4) C(20) C(19) C(21) 108.3(5) C(22) C(19) Si(3) 110.5(4) C(20) C(19) Si(3) 110.3(3) C(21) C(19) Si(3) 110.7(4) C(19) C(20) H(20B) C(19) C(20) H(20C) H(20B) C(20) H(20C) C(19) C(20) H(20A) H(20B) C(20) H(20A) H(20C) C(20) H(20A) C(19) C(21) H(21B) C(19) C(21) H(21C) H(21B) C(21) H(21C) C(19) C(21) H(21A) H(21B) C(21) H(21A) H(21C) C(21) H(21A) C(19) C(22) H(22A) C(19) C(22) H(22C) H(22A) C(22) H(22C) C(19) C(22) H(22B) H(22A) C(22) H(22B) H(22C) C(22) H(22B) N(3) C(23) C(24) 108.7(4) N(3) C(23) H(23B) C(24) C(23) H(23B) N(3) C(23) H(23A) C(24) C(23) H(23A) H(23B) C(23) H(23A) N(4) C(24) C(23) 109.6(4) N(4) C(24) H(24B) C(23) C(24) H(24B) N(4) C(24) H(24A) C(23) C(24) H(24A) H(24B) C(24) H(24A) C(24) N(4) C(16) 112.4(4) C(24) N(4) C(8) 110.3(4) C(16) N(4) C(8) 111.5(4) C(24) N(4) U(1) 111.1(3) C(16) N(4) U(1) 105.8(3) C(8) N(4) U(1) 105.5(3) U(1) O(1) U(2) (16) O(1) U(2) O(2) 88.19(13) O(1) U(2) N(6) 97.25(13) O(2) U(2) N(6) (14) O(1) U(2) N(5) (13) O(2) U(2) N(5) (13) N(6) U(2) N(5) (13) O(1) U(2) N(7) (12) O(2) U(2) N(7) 65.06(14) N(6) U(2) N(7) 89.23(14) N(5) U(2) N(7) 93.85(14) O(1) U(2) N(8) (12) O(2) U(2) N(8) (13) N(6) U(2) N(8) 67.73(13) N(5) U(2) N(8) 67.50(13) N(7) U(2) N(8) 63.30(12) C(31) N(5) Si(4) 113.6(3) C(31) N(5) U(2) 121.8(3) Si(4) N(5) U(2) (19) N(5) Si(4) C(25) 109.1(2) N(5) Si(4) C(26) 111.6(2) C(25) Si(4) C(26) 106.5(3) N(5) Si(4) C(27) 112.8(2) C(25) Si(4) C(27) 109.0(2) C(26) Si(4) C(27) 107.5(2) Si(4) C(25) H(25B) Si(4) C(25) H(25C) H(25B) C(25) H(25C) Si(4) C(25) H(25A) H(25B) C(25) H(25A) H(25C) C(25) H(25A) Si(4) C(26) H(26A) Si(4) C(26) H(26C) H(26A) C(26) H(26C) Si(4) C(26) H(26B) H(26A) C(26) H(26B) H(26C) C(26) H(26B) C(29) C(27) C(28) 109.4(4) C(29) C(27) C(30) 107.9(4) C(28) C(27) C(30) 109.1(5) C(29) C(27) Si(4) 111.0(3) C(28) C(27) Si(4) 110.2(3) C(30) C(27) Si(4) 109.2(3) C(27) C(28) H(28A) C(27) C(28) H(28C) H(28A) C(28) H(28C) C(27) C(28) H(28B) H(28A) C(28) H(28B) H(28C) C(28) H(28B) C(27) C(29) H(29B) C(27) C(29) H(29C) H(29B) C(29) H(29C) C(27) C(29) H(29A) H(29B) C(29) H(29A) H(29C) C(29) H(29A) C(27) C(30) H(30B) C(27) C(30) H(30C) H(30B) C(30) H(30C) C(27) C(30) H(30A) S34

35 H(30B) C(30) H(30A) H(30C) C(30) H(30A) C(32) C(31) N(5) 113.1(4) C(32) C(31) H(31B) N(5) C(31) H(31B) C(32) C(31) H(31A) N(5) C(31) H(31A) H(31B) C(31) H(31A) C(31) C(32) N(8) 111.7(4) C(31) C(32) H(32A) N(8) C(32) H(32A) C(31) C(32) H(32B) N(8) C(32) H(32B) H(32A) C(32) H(32B) C(39) N(6) Si(5) 119.3(3) C(39) N(6) U(2) 115.2(3) Si(5) N(6) U(2) 125.4(2) N(6) Si(5) C(34) 111.1(2) N(6) Si(5) C(33) 106.5(2) C(34) Si(5) C(33) 109.4(2) N(6) Si(5) C(35) 114.6(2) C(34) Si(5) C(35) 108.5(3) C(33) Si(5) C(35) 106.4(2) Si(5) C(33) H(33B) Si(5) C(33) H(33C) H(33B) C(33) H(33C) Si(5) C(33) H(33A) H(33B) C(33) H(33A) H(33C) C(33) H(33A) Si(5) C(34) H(34B) Si(5) C(34) H(34C) H(34B) C(34) H(34C) Si(5) C(34) H(34A) H(34B) C(34) H(34A) H(34C) C(34) H(34A) C(38) C(35) C(37) 108.1(5) C(38) C(35) C(36) 108.5(5) C(37) C(35) C(36) 108.4(5) C(38) C(35) Si(5) 108.4(4) C(37) C(35) Si(5) 112.5(4) C(36) C(35) Si(5) 110.7(4) C(35) C(36) H(36B) C(35) C(36) H(36C) H(36B) C(36) H(36C) C(35) C(36) H(36A) H(36B) C(36) H(36A) H(36C) C(36) H(36A) C(35) C(37) H(37B) C(35) C(37) H(37C) H(37B) C(37) H(37C) C(35) C(37) H(37A) H(37B) C(37) H(37A) H(37C) C(37) H(37A) C(35) C(38) H(38A) C(35) C(38) H(38C) H(38A) C(38) H(38C) C(35) C(38) H(38B) H(38A) C(38) H(38B) H(38C) C(38) H(38B) N(6) C(39) C(40) 109.0(4) N(6) C(39) H(39B) C(40) C(39) H(39B) N(6) C(39) H(39A) C(40) C(39) H(39A) H(39B) C(39) H(39A) N(8) C(40) C(39) 110.0(5) N(8) C(40) H(40A) C(39) C(40) H(40A) N(8) C(40) H(40B) C(39) C(40) H(40B) H(40A) C(40) H(40B) C(44) N(7) C(41) 120.4(4) C(44) N(7) U(2) 114.7(3) C(41) N(7) U(2) 124.8(3) N(7) C(41) C(42) 106.3(4) N(7) C(41) H(41A) C(42) C(41) H(41A) N(7) C(41) H(41B) C(42) C(41) H(41B) H(41A) C(41) H(41B) N(8) C(42) C(41) 109.1(5) N(8) C(42) H(42B) C(41) C(42) H(42B) N(8) C(42) H(42A) C(41) C(42) H(42A) H(42B) C(42) H(42A) C(40) N(8) C(42) 114.1(5) C(40) N(8) C(32) 108.5(4) C(42) N(8) C(32) 109.3(4) C(40) N(8) U(2) 110.4(3) C(42) N(8) U(2) 112.5(3) C(32) N(8) U(2) 101.2(3) C(43) O(2) U(2) 129.8(3) O(2) C(43) C(44) 109.8(5) O(2) C(43) H(43) C(44) C(43) H(43) N(7) C(44) O(3) 121.0(5) N(7) C(44) C(43) 119.6(5) O(3) C(44) C(43) 119.3(5) C(44) O(3) Si(6) 134.5(3) S35

36 O(3) Si(6) C(45) 107.5(3) O(3) Si(6) C(46) 112.7(2) C(45) Si(6) C(46) 110.2(3) O(3) Si(6) C(47) 102.1(2) C(45) Si(6) C(47) 112.4(3) C(46) Si(6) C(47) 111.7(3) Si(6) C(45) H(45A) Si(6) C(45) H(45C) H(45A) C(45) H(45C) Si(6) C(45) H(45B) H(45A) C(45) H(45B) H(45C) C(45) H(45B) Si(6) C(46) H(46B) Si(6) C(46) H(46C) H(46B) C(46) H(46C) Si(6) C(46) H(46A) H(46B) C(46) H(46A) H(46C) C(46) H(46A) C(49) C(47) C(48) 110.4(6) C(49) C(47) C(50) 108.2(6) C(48) C(47) C(50) 108.3(6) C(49) C(47) Si(6) 110.3(5) C(48) C(47) Si(6) 110.7(5) C(50) C(47) Si(6) 108.8(4) C(47) C(48) H(48B) C(47) C(48) H(48C) H(48B) C(48) H(48C) C(47) C(48) H(48A) H(48B) C(48) H(48A) H(48C) C(48) H(48A) C(47) C(49) H(49B) C(47) C(49) H(49C) H(49B) C(49) H(49C) C(47) C(49) H(49A) H(49B) C(49) H(49A) H(49C) C(49) H(49A) C(47) C(50) H(50A) C(47) C(50) H(50C) H(50A) C(50) H(50C) C(47) C(50) H(50B) H(50A) C(50) H(50B) H(50C) C(50) H(50B) C(56) C(51) C(52) 119.1(7) C(56) C(51) D(51) C(52) C(51) D(51) C(53) C(52) C(51) 119.9(7) C(53) C(52) D(52) C(51) C(52) D(52) C(52) C(53) C(54) 120.1(6) C(52) C(53) D(53) C(54) C(53) D(53) C(55) C(54) C(53) 119.6(6) C(55) C(54) D(54) C(53) C(54) D(54) C(54) C(55) C(56) 120.4(7) C(54) C(55) D(55) C(56) C(55) D(55) C(51) C(56) C(55) 120.8(7) C(51) C(56) D(56) C(55) C(56) D(56) Symmetry transformations used to generate equivalent atoms: Table S9. Anisotropic displacement parameters (Å 2 ) for 3. The anisotropic displacement factor exponent takes the form: 2π 2 [h 2 a* 2 U hka*b*U 12 ] U 11 U 22 U 33 U 23 U 13 U 12 U(1) (8) (9) (9) (6) (6) (6) N(1) (18) 0.028(2) (19) (15) (15) (15) Si(1) (6) (7) (6) (5) (5) (5) C(1) 0.035(2) 0.033(3) 0.026(3) 0.006(2) 0.011(2) 0.002(2) C(2) 0.031(2) 0.032(3) 0.018(2) (18) (18) (19) C(3) 0.024(2) 0.036(3) 0.021(2) (19) (18) (19) C(4) 0.029(2) 0.048(3) 0.036(3) 0.008(2) 0.003(2) 0.014(2) C(5) 0.030(3) 0.064(4) 0.025(3) 0.007(2) 0.004(2) 0.002(2) C(6) 0.022(2) 0.063(4) 0.028(3) 0.000(2) 0.006(2) 0.002(2) C(7) 0.023(2) 0.030(3) 0.027(2) (19) (18) (18) S36

37 C(8) 0.029(2) 0.034(3) 0.025(2) (19) (19) (19) N(2) (17) 0.027(2) 0.027(2) (16) (15) (15) Si(2) (6) (7) (7) (5) (5) (5) C(9) 0.035(3) 0.045(3) 0.026(3) 0.002(2) 0.007(2) 0.000(2) C(10) 0.026(2) 0.029(3) 0.031(3) 0.002(2) 0.007(2) (19) C(11) 0.026(2) 0.036(3) 0.029(3) 0.003(2) 0.013(2) (19) C(12) 0.024(2) 0.043(3) 0.036(3) 0.001(2) 0.004(2) 0.001(2) C(13) 0.030(2) 0.039(3) 0.040(3) 0.006(2) 0.014(2) 0.001(2) C(14) 0.027(2) 0.039(3) 0.037(3) 0.002(2) 0.010(2) 0.008(2) C(15) 0.027(2) 0.031(3) 0.039(3) 0.003(2) 0.010(2) 0.003(2) C(16) 0.026(2) 0.025(2) 0.033(3) (19) (19) (18) N(3) (19) 0.031(2) 0.023(2) (16) (16) (16) Si(3) (6) (8) (7) (6) (5) (5) C(17) 0.029(2) 0.041(3) 0.035(3) 0.003(2) 0.007(2) 0.006(2) C(18) 0.032(3) 0.053(4) 0.042(3) 0.006(3) 0.004(2) 0.005(2) C(19) 0.031(2) 0.045(3) 0.022(2) 0.007(2) (19) 0.003(2) C(20) 0.037(3) 0.054(3) 0.029(3) 0.011(2) 0.003(2) 0.008(2) C(21) 0.037(3) 0.073(4) 0.040(3) 0.019(3) 0.005(3) 0.004(3) C(22) 0.048(3) 0.060(4) 0.022(3) 0.001(2) 0.005(2) 0.005(3) C(23) 0.040(3) 0.038(3) 0.027(3) 0.004(2) 0.005(2) 0.005(2) C(24) 0.035(3) 0.037(3) 0.032(3) 0.001(2) 0.003(2) 0.003(2) N(4) (18) 0.033(2) 0.021(2) (16) (15) (15) O(1) (16) (18) (18) (13) (14) (13) U(2) (8) (10) (9) (6) (6) (6) N(5) (18) 0.035(2) (19) (16) (15) (16) Si(4) (6) (7) (6) (5) (5) (5) C(25) 0.024(2) 0.034(3) 0.036(3) 0.002(2) 0.010(2) (19) C(26) 0.038(3) 0.055(4) 0.030(3) 0.008(2) 0.003(2) 0.006(2) C(27) 0.025(2) 0.039(3) 0.031(3) 0.004(2) (19) 0.000(2) C(28) 0.026(2) 0.078(4) 0.040(3) 0.003(3) 0.002(2) 0.001(3) C(29) 0.033(3) 0.035(3) 0.042(3) 0.003(2) 0.011(2) 0.004(2) C(30) 0.033(3) 0.040(3) 0.058(4) 0.010(3) 0.019(3) 0.000(2) C(31) 0.039(3) 0.040(3) 0.023(3) 0.010(2) 0.002(2) 0.003(2) C(32) 0.047(3) 0.054(4) 0.035(3) 0.012(3) 0.007(2) 0.004(3) N(6) (19) 0.033(2) 0.019(2) (16) (15) (16) Si(5) (7) (7) (7) (5) (5) (5) C(33) 0.033(2) 0.040(3) 0.025(3) 0.004(2) 0.005(2) 0.003(2) C(34) 0.038(3) 0.050(3) 0.026(3) 0.001(2) 0.005(2) 0.007(2) C(35) 0.079(4) 0.029(3) 0.025(3) 0.003(2) 0.009(3) 0.007(3) C(36) 0.078(5) 0.051(4) 0.054(4) 0.002(3) 0.001(4) 0.030(3) C(37) 0.104(5) 0.030(3) 0.041(4) 0.002(3) 0.028(4) 0.005(3) C(38) 0.116(6) 0.038(3) 0.028(3) 0.008(2) 0.009(3) 0.017(3) C(39) 0.032(2) 0.046(3) 0.023(3) 0.002(2) 0.001(2) 0.011(2) C(40) 0.060(4) 0.050(4) 0.033(3) 0.009(3) 0.008(3) 0.012(3) N(7) 0.037(2) 0.032(2) 0.032(2) (18) (18) (18) C(41) 0.041(3) 0.043(3) 0.045(3) 0.024(3) 0.002(3) 0.019(3) C(42) 0.051(3) 0.057(4) 0.044(4) 0.020(3) 0.010(3) 0.001(3) N(8) (19) 0.029(2) 0.029(2) (17) (17) (16) S37

38 O(2) 0.040(2) 0.055(2) 0.029(2) (18) (16) (18) C(43) 0.048(3) 0.041(3) 0.039(3) 0.012(2) 0.010(3) 0.007(2) C(44) 0.035(2) 0.038(3) 0.028(3) 0.002(2) 0.007(2) 0.003(2) O(3) 0.037(2) 0.057(3) 0.042(2) (19) (18) (18) Si(6) (7) (10) (8) (7) (6) (7) C(45) 0.066(4) 0.053(4) 0.089(6) 0.004(4) 0.035(4) 0.006(3) C(46) 0.047(3) 0.085(5) 0.036(3) 0.001(3) 0.002(3) 0.001(3) C(47) 0.033(3) 0.065(4) 0.055(4) 0.020(3) 0.001(3) 0.008(3) C(48) 0.055(4) 0.069(5) 0.060(5) 0.006(4) 0.016(3) 0.011(3) C(49) 0.084(5) 0.047(4) 0.077(5) 0.005(4) 0.019(4) 0.017(4) C(50) 0.064(4) 0.064(5) 0.103(7) 0.024(5) 0.017(4) 0.001(4) C(51) 0.052(4) 0.083(6) 0.073(5) 0.001(4) 0.009(4) 0.012(4) C(52) 0.066(5) 0.068(5) 0.086(6) 0.018(4) 0.004(4) 0.022(4) C(53) 0.054(4) 0.070(5) 0.042(4) 0.011(3) 0.002(3) 0.007(3) C(54) 0.054(4) 0.046(4) 0.039(3) 0.002(3) 0.001(3) 0.000(3) C(55) 0.095(6) 0.050(4) 0.057(4) 0.012(3) 0.022(4) 0.016(4) C(56) 0.065(4) 0.071(5) 0.057(5) 0.010(4) 0.022(4) 0.008(4) Table S10. Hydrogen coordinates and isotropic displacement parameters (Å 2 ) for 3. x y z U(eq) H(1B) H(1C) H(1A) H(2B) H(2C) H(2A) H(4B) H(4C) H(4A) H(5A) H(5C) H(5B) H(6B) H(6C) H(6A) H(7A) H(7B) H(8B) H(8A) H(9B) H(9C) H(9A) H(10B) H(10C) H(10A) S38

39 H(12B) H(12C) H(12A) H(13A) H(13C) H(13B) H(14A) H(14B) H(14C) H(15A) H(15B) H(16B) H(16A) H(17A) H(17C) H(17B) H(18A) H(18C) H(18B) H(20B) H(20C) H(20A) H(21B) H(21C) H(21A) H(22A) H(22C) H(22B) H(23B) H(23A) H(24B) H(24A) H(25B) H(25C) H(25A) H(26A) H(26C) H(26B) H(28A) H(28C) H(28B) H(29B) H(29C) H(29A) H(30B) H(30C) H(30A) H(31B) H(31A) H(32A) S39

40 H(32B) H(33B) H(33C) H(33A) H(34B) H(34C) H(34A) H(36B) H(36C) H(36A) H(37B) H(37C) H(37A) H(38A) H(38C) H(38B) H(39B) H(39A) H(40A) H(40B) H(41A) H(41B) H(42B) H(42A) H(43) H(45A) H(45C) H(45B) H(46B) H(46C) H(46A) H(48B) H(48C) H(48A) H(49B) H(49C) H(49A) H(50A) H(50C) H(50B) D(51) D(52) D(53) D(54) D(55) D(56) S40

41 Density Functional Calculations of 2 and Reaction Enthalpy Calculations General Unrestricted geometry optimizations were performed for the full models of 2, 4 5, [(UN 3 ) 2 (μ-η 1 :η 1 - OCCO)], 6 and [UN" 3 I] 7 using coordinates derived from the experimental X-ray crystal structures. Restricted calculations were performed on models of Me 3 SiI, PhMe 2 SiI, Ph 2 MeSiI, Ph 3 SiI, Me 3 SiOCCOSiMe 3 (5a), PhMe 2 SiOCCOSiMe 2 Ph (5b), Ph 2 MeSiOCCOSiMePh 2, and Ph 3 SiOCCOSiPh 3, generated in silico. No constraints were imposed on the structures during the geometry optimizations. The calculations were performed using ADF version ,9 The DFT geometry optimizations employed Slater-type orbital (STO) triple-ζ-plus polarization 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. 10 was used in all of the calculations. Gradient corrections were performed using the functionals of Becke 11 and Perdew. 12 MOLEKEL 13 was used to prepare the three-dimensional electron density plots. Ligand Relaxation Energy Calculation The coordinates for the [U(Tren DMSB )] + fragment were extracted from the crystal structure of 2 and a single point energy calculation was performed. A geometry optimization was run on the same coordinates and then a single point energy was calculated on the optimized structure. The difference in energies is 10.8 kcal mol 1, which equates to the ligand relaxation energy. The single point energy and geometry optimized structures are illustrated below viewed down the uranium-amine vector and they reveal very little difference in the geometries (Fig. S19). S41

42 Fig. S19. Single Point Energy Geometry Optimized The Six Highest Occupied Frontier Orbitals of A 13.13% 1 P:z C 13.13% 1 P:z C 9.07% 1 P:y C 9.07% 1 P:y C 7.98% 1 P:z O 7.98% 1 P:z O 5.49% 1 P:y O 5.49% 1 P:y O 1.64% 2 F:x U 1.64% 2 F:x U 1.47% 1 P:y N 1.47% 1 P:y N 1.04% 1 P:z N 1.04% 1 P:z N 1.02% 1 P:y N 1.02% 1 P:y N A 13.03% 1 P:y C 13.03% 1 P:y C 8.91% 1 P:z C 8.91% 1 P:z C 7.92% 1 P:y O 7.92% 1 P:y O 5.27% 1 P:z O 5.27% 1 P:z O 2.72% 1 P:y N 2.72% 1 P:y N 1.47% 2 F:y U S42