Supporting Information Efficient Catalytic Conversion of Dinitrogen to N(SiMe 3 ) 3 Using a Homogeneous Mononuclear Cobalt Complex

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1 Supporting Information Efficient Catalytic Conversion of Dinitrogen to N(SiMe 3 ) 3 Using a Homogeneous Mononuclear Cobalt Complex Tatsuya Suzuki, 1,2 Keisuke Fujimoto, 1 Yoshiyuki Takemoto, 1 Yuko Wasada-Tsutsui, 1 Tomohiro Ozawa, 1 Tomohiko Inomata, 1 Michael D. Fryzuk, 2 * and Hideki Masuda 1 * 1 Department of Frontier Materials, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya , Japan 2 Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, BC. Canada, V6T 1Z1 Table of contents fryzuk@chem.ubc.ca, masuda.hideki@nitech.ac.jp Methods S2-S6 Experimental procedures Synthesis of CoCl(NpNP ipr ) and Co(NpNP ipr ) Catalytic, Kinetic and Mechanistic studies X-ray crystallography Spectroscopy S7-S13 Figure S1. ORTEP of 1 Figure S2. ORTEP of 2 Table S1. Crystallographic and structure refinement data for compounds 1 and 2 Figures S3 and S4. 1 H NMR spectra of 1 and 2 in benzene-d 6 Figure S5. 1 H NMR spectra of 2 in toluene-d 8 at various temperatures (under N 2 and Ar) Figure S6. Infrared spectra (KBr) of 2 Figure S7. UV-Vis spectra of 2 at different temperatures Figure S8. Calibration curve (λ max = 500 nm) for T-shaped complex 2 Figure S9. Measurement of the ratio of T-shaped 2 and dinitrogen complex 3 from K Catalytic, Kinetic and Mechanistic study...s14-s15 Figure S10. Indophenol calibration curve (λ max = 635 nm) for NH 3 quantification Figure S11. UV-Vis overlay of observed indophenol formation as a function of time Table S2. Catalytic conversion of N 2 to N(SiMe 3 ) 3 after hydrolysis to NH 4 Cl... Figure S12. 1 H NMR spectra of (a) Co(NpNP ipr ) 2, (b), CoCl(NpNP ipr ) 1, (c) the reaction of 2 with Me 3 SiCl forming some CoCl(NpNP ipr ) 1 in THF-d 8. DFT calculations...s16-s47 S1

2 Table S3. Selected parameters related to the N 2 binding and coordination structures of Co I (NpNP ipr )(N 2 ) and N-silylated derivatives Figure S13. Gibbs free energies of dinitrogen addition to Co I (NpNP ipr ) and silylation reaction for Co I (NpNP ipr )(N 2 ) at 80 C under 1 atm. Figure S14. Optimized structures of Co I (NpNP ipr )(N 2 ). N 2 addition energies are also shown. Figure S15. Optimized structures of monosilylated Co I (NpNP ipr )(N 2 ). Figure S16. Optimized structures of disilylated Co I (NpNP ipr )(N 2 ). Figure S17. Optimized structures of trisilylated Co I (NpNP ipr )(N 2 ). Figure S18. Summary of the DFT results Total energies and spins, and cartesian coordinates for optimized geometries References S48 S2

3 Experimental procedures All manipulations were carried out under an atmosphere of purified argon or dinitrogen gas in an mbraun MB 150B-G glovebox or by standard Schlenk techniques. Anhydrous toluene, THF, and diethyl ether were purchased from Wako Ltd., and passed through columns containing activated alumina and Ridox catalyst. C 6 D 6 and THF-d 8 were dried by distillation from sodium/benzophenone. 1 H NMR spectra were measured on a Varian Mercury 300 spectrometer, and 1 H chemical shifts were estimated relative to TMS as an internal standard, respectively. Fourier transform infrared (FT-IR) spectra of solid compounds were measured as KBr pellets using a JASCO FT/IR-410 spectrophotometer. UV-vis spectra were recorded on a JASCO V700 spectrophotometer. Elemental analyses were obtained with a Perkin-Elmer CHN-900 elemental analyzer. Magnetic moment measurements (Evans method) in the solution state were obtained using 1 H NMR spectroscopy. The solution state magnetic moments were determined by the Evans method using 1 H-NMR spectroscopy. KC 8 was prepared according to a literature procedure. 1 All other compounds were purchased from commercial suppliers and used as received. Li(NpNP ipr ) was synthesized according to the literature method. 2 All other reagents employed are commercially available. Synthesis of CoCl(NpNP ipr ) and Co(NpNP ipr ) Preparation of CoCl(NpNP ipr ) 1 Under a N 2 atmosphere, CoCl 2 (12 mg, mmol) was added to an Et 2 O solution (10 ml) of Li(NpNP ipr ) (50 mg, mmol), and the mixture stirred at room temperature for 1 day. The reaction mixture was filtered through Celite to give a brown solution, and then stored in a freezer at -35 C. The compound CoCl(NpNP ipr ) (1) was obtained as brown block crystals suitable for X-ray analysis. (48 mg, mmol, 83 %). 1 H-NMR (300 MHz, δ/ppm in benzene-d 6 ) δ 20.10, 15.62, 9.56, 6.51, 4.89, 3.30, 1.44, 0.01, 1.08, 1.47, 2.95, 3.66, 5.20, 10.02, 11.01, 11.91, 12.95, 16.04, 17.99, 18.24, 21.99, 22.15, 23.86, 28.42, 34.37, 41.05, 89.50, µ eff = 4.07 µ B (Evans in benzene-d 6 ). Anal. Calcd. for C 35 H 55 ClCoN 2 P 2 : C, 63.68; H, 8.40; N, Found: C, 63.44; H, 8.53; N, S3

4 Preparation of T-shaped Co(NpNP ipr ) 2 Under an Ar atmosphere, KC 8 (50 mg, mmol) was added to a slurry of CoCl(NpNP ipr ) (1) (200 mg, mmol) in Et 2 O (10 ml) and the reaction mixture stirred for 1 day at room temperature to yield a dark red solution. Graphite and KCl were removed by filtration, and the solvent was reduced to 1 ml in vacuo. After storing the solution at -35 C for a few days, red block crystals were obtained (102 mg, mmol, 54 %). 1 H-NMR (300 MHz, δ/ppm in benzene-d 6 ) δ 53.38, 30.46, 28.25, 24.19, 16.55, 11.90, 7.39, 2.92, 13.81, 15.83, 17.53, 21.01, 22.11, 22.50, 56.50, 63.50, µ eff = 2.40 ± 0.05 µ B (Evans in toluene-d 8 ) measured from K under Ar; under N 2 µ eff = 2.47 µ B at 293K and decreases to 2.25 µ B at 193K. Anal. Calcd. for C 35 H 55 CoN 2 P 2 : C, 67.29; H, 8.87; N, 4.48 Found: C, 67.01; H, 8.99; N, Typical procedure for the catalytic silylation reaction of N 2 into NH 4 Cl using 2 The catalyst precursor Co(NpNP ipr ) (2) (32 mg, mmol) was dissolved in THF (10 ml) to make a stock solution. A 1 ml aliquot of the solution plus 10 ml THF was added to a sealable Schlenk flask. To the flask was added KC 8 (1 g, 7.4 mmol = 1445 equiv). With stirring, a THF (20 ml) solution of Me 3 SiCl (1.3 ml, 10.2 mmol = 1992 equiv) was added dropwise at various temperatures (20, 40, 50, 60 ºC) and left stirring for 4 days with a color change the bronze hue of KC 8 to black. Graphite and KCl were removed by filtration, and the THF solution containing N(SiMe 3 ) 3 collected via vacuum transfer (to remove the catalyst precursor). The THF was removed under vacuum at -20 ºC, and then an Et 2 O solution of HCl (3 ml, 1.0 M) was added to the resulting colorless oil and the volatiles were removed under vacuum to obtain the NH 4 Cl salt, which was dissolved in H 2 O (10 ml) and analyzed by the indophenol method. 3 Kinetic studies of the catalytic silylation reaction of N 2 into NH 4 Cl using 2 The catalyst Co(NpNP ipr ) (2) (32 mg) was dissolved in THF (10 ml) to make a concentrated stock solution. A 1 ml aliquot of the solution plus 10 ml THF was added to a sealable schlenk. To the flask, KC 8 (1g) was added. And then, Me 3 SiCl (1.3 ml) dissolved THF (20 ml) solution were dropped using drop funnel at 50 ºC with stirring. Periodically, the 3 ml aliquots were removed from the stirring reaction (t = 0.5, 1, 2, 5, 12 and 24 h). Each aliquot was filtered through a glass plug in a pipette. To the resulting filtrate, an Et 2 O solution of HCl (3 ml, 1.0 M) was added and S4

5 the volatiles were removed under vacuum to obtain NH 4 Cl, which was dissolved in H 2 O (100 ml) and analyzed by the indophenol method. 3 The following catalytic experiments were performed at -40 C with 2000 equiv of Me 3 SiCl and 1500 equiv of KC 8 for 24 h only to examine the effect of solvent, catalyst precursor and work up method; the results are presented in Table S2 (entries 10-13): entry 10 no catalyst gives 0 equiv of NH 4 Cl; entry 11 complex 1 as catalyst precursor gives 111 equiv of NH 4 Cl; entry 12 DME as solvent gives 130 equiv of NH 4 Cl; entry 13 toluene as solvent gives 21 equiv of NH 4 Cl. For homogeneity, we ran the reaction for 1 h as above, warmed to room temperature, filtered, and then added and additional 2000 equiv of Me 3 SiCl and 1500 equiv of KC 8 to the filtrate and ran the reaction for a further 24 h and analyzed to generate 109 equiv of NH 4 Cl after hydrolysis with HCl. To test catalyst robustness, after 240 h at -40 C in THF in the presence of 2000 equiv of Me 3 SiCl and 1500 equiv of KC 8 to generate 215 equiv of NH 4 Cl; after filtration, a further charge of 2000 equiv of Me 3 SiCl and 1500 equiv of KC 8 was added to the THF solution, and workup after a further 72 h produced an additional 55 equiv of NH 4 Cl (total = 270 equiv). Mechanistic studies of the catalytic silylation reaction with Me 3 SiCl using 2 Under an Ar atmosphere, Me 3 SiCl (11 µl, mmol) was added to Co(NpNP ipr ) 2 (50 mg, mmol) in Et 2 O (10 ml) solution. The reaction mixture stirred for 3 h at room temperature to yield a dark brown solution. After removing the solvent and volatiles in vacuo, the 1 H NMR spectrum was measured (Figure S11). X-ray crystallography Suitable single crystals were selected in a Glovebox, coated in Fomblin oil and mounted on a glass fiber. All the single crystals obtained, 1 and 2, were analyzed by X-ray diffraction method. The diffraction data were collected using a Rigaku/MSC Mercury CCD with graphite monochromated Mo-Kα radiation (λ = Å) at 100 C. All the crystal data and experimental details are listed in Table S1 (Supporting Information). The crystal structures were solved by a combination of direct methods (SIR92 4 ) and Fourier techniques. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were refined by the riding model using the appropriate HFIX command in SHELXL97. 5 The Sheldrick weighting scheme was applied for all crystals. Plots of Σ( F 0 F c ) 2 versus F 0, reflection order in data collection, sin θ/λ, and various classes of indices S5

6 showed no unusual trends. Neutral atomic scattering factors were taken from International Tables for X-ray Crystallography edited by Cromer and Waber. 6 Anomalous dispersion effects were included in F calc, 7 where the values for Δf and Δf were taken from those of Creagh and McAuley. 8 The values for the mass attenuation coefficients are those of Creagh and Hubbell. 9 All calculations were performed using the crystallographic software package, CrystalStructure. An attempt was made to model forming dinitrogen complex 3 as a disorder on the residual electron density in crystal data of 2 failed. S6

7 Figure S1. ORTEP drawing of CoCl(NpNP ipr ) 1 with ellipsoids at 30% probability level. All hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Cl(1) Co(1) (6), Co(1) P(2) (6), Co(1) N(1) (16), Co(1) N(2) (19), P(1) N(2) (18), P(1) C(17) 1.758(2), C(13) C(17) 1.391(3), Cl(1) Co(1) P(2) (3), Cl(1) Co(1) N(1) (5), Cl(1) Co(1) N(2) (5), P(2) Co(1) N(1) (5), P(2) Co(1) N(2) 87.05(5), N(1) Co(1) N(2) (7). S7

8 Figure S2. ORTEP drawing of the solid-state molecular structure of Co(NpNP ipr ) 2 (ellipsoids at 30% probability level). The crystal selected consisted of a 90:10 mixture of 2 and 3, and modelled as such. All hydrogen atoms have been omitted for clarity. Selected bond length (Å), angles (deg): for 2: Co1 P (8), Co1 N (19), Co1 N (2), P1 N (6), P1 C (2), N1 C (4), C13 C (4), N1 Co1 P (8), P2 Co1 N (7), N1 Co1 N (10); for 3: Co2 P (7), Co2 N (19), Co2 N (3), Co2 N3 1.99(4), N3 N4 1.12(6), P2 Co2 N (7), P2 Co2 N (6), P2 Co2 N3 91.6(9), N1 Co2 N (9), N1 Co2 N (8), N2 Co2 N (9). Table S1. Crystallographic and structure refinement data for compounds Co(NpNP ipr )Cl 1 and Co(NpNP ipr ) 2. Compound Co(NpNP ipr )Cl 1 Co(NNpN ipr ) 2 Chemical formula C 70 H 110 Cl 2 Co 2 N 4 P 4 C 35 H 55 CoN 2 P 2 0.1(N 2 ) Formula weight Temp (ºC) Crystal system Monoclinic Monoclinic Space group P2 1 /n P2 1 /c a / Å (5) (3) b / Å (10) (7) c / Å (7) (4) α / - - β / (3) (8) γ / - - V / Å (3) (2) Z 2 4 D calc /g cm µ(mo-kα) / cm F(000) Reflections collected Independent reflections R(int) R1 (I > 2σ(I)) R1 (all) wr2 (all) GOF S8

9 Figure S3. 1 H NMR spectrum of CoCl(NpNP ipr ) 1 in benzene-d 6. Because this complex is tetrahedral and asymmetric, one would expect 31 resonances; although we are unable to assign the peaks, the number of peaks approximates that predicted and so confirms the structure in solution (see below). S9

10 Figure S4. 1 H NMR spectrum of Co(NpNP ipr ) 2 in benzene-d 6 under Ar. Because this complex is planar, one would expect 18 resonances; although we are unable to assign the peaks, the number of peaks matches that predicted and so confirms the structure in solution ppm K 283 K 273 K 263 K 253 K 243 K 233 K 223 K 213 K 203 K 193 K Figure S5. Partial 1 H NMR spectra of 2 in toluene-d 8 at various temperatures (293 K K) under Ar (black) and under N 2 (red) for 2 and 3 (peaks between +30 and -30 ppm removed for clarity). NMR spectroscopy is apparently not sensitive to the equilibrium. S10

11 Figure S6. Infrared spectra (KBr) of mixture of 2 and 3 showing ν( 14 N 2 ) and ν( 15 N 2 ) at 2071 and 2001 cm 1, respectively. S11

12 Figure S7. UV-Vis spectra of 2 in toluene at variable temperatures ranging from 293 to 203 K in 10 degrees increments: top - under an N 2 atmosphere; bottom - under an Ar atmosphere. The absorptions at 280 and 500 nm at 293 K change as a function of temperature under N 2 (top). The absorption at 500 nm was monitored under N 2 atmosphere as a function of temperature and shows a quantifiable decrease with decreasing temperature (see Figure S7). We interpret this decrease in intensity at 500 nm as a direct correlation to a decrease of the T-shaped complex 2 with concomitant formation of the dinitrogen adduct 3. The lack of change in this absorption under Ar as a function of temperature (bottom) is consistent with the presence of 2, even at 203 K. S12

13 Figure S8. Calibration curve (λ max = 500 nm) for the T-shaped complex 2 in toluene (under Ar). Figure S9. UV-Vis spectra of the same solution of 2 in toluene (0.10 M) under an Ar atmosphere (red) and under the N 2 atmosphere (blue) at 293 K. Based on these spectra one can estimate that the ratio of 2 to 3 is approximately 4:1 using the calibration curve in Figure S7: the absorption value of 2 under Ar at 500 nm is 0.26 and under N 2, the absorption is For the equilibrium 2 + N 2 <=> 3, we calculate the following: K 293K = 0.19; K 273K = 0.73, K 233K = 1.57; K 193K = 7.93, which corresponds to 89% 3 and 11% 2 at 193K. S13

14 Figure S10. Indophenol calibration curve (λ max = 635 nm) for NH 3 quantification. Figure S11. UV-Vis overlay of observed indophenol formation from the kinetic runs at 50 ºC. S14

15 Table S2. Catalytic conversion of N 2 to N(SiMe 3 ) 3 after hydrolysis to NH 4 Cl using the indicated catalyst precursor with 2000 equiv of Me 3 SiCl and 1500 equiv of KC 8 at the given temperature in the solvent shown; unless otherwise indicated the amount of N(SiMe 3 ) 3 produced by determined by hydrolysis to NH 4 Cl and analyzed by the indophenol method. Entry Temperature (K) Solvent Time (h) Catalyst Precursor (a) Amount of NH 4 Cl (mmol) Equiv. of NH 4 Cl based on Co atom THF THF THF THF THF THF THF THF THF THF 24 No catalyst THF DME Toluene (b) 233 THF (a) Co(NpNP ipr ) 2; Co(NpNP ipr )Cl 1 (b) After acidification, NH 4 Cl analyzed by the NMR method described in Prokopchuk, D. E.; Wiedner, E. S.; Walter, E. D.; Popescu, C. V.; Piro, N. A.; Kassel, W. S.; Bullock, R. M.; Mock, M. T. J. Am. Chem. Soc. 2017, 139, Figure S12. 1 H NMR spectra of (a) Co(NpNP ipr ) 2, (b), CoCl(NpNP ipr ) 1, (c) the reaction of 2 with Me 3 SiCl forming some CoCl(NpNP ipr ) 1 in THF-d 8. S15

16 DFT calculation details. Geometry optimization of all the species taking part in the dinitrogen addition and following silylation to the dinitrogen moiety was carried out using the BP86 functional. 10 The following basis sets were used for the respective atoms: 6-311G(d) for Co, 11a,b G(d) for Si, P, 11c,d N, and olefin C of the chelate ring 11d,e and 6-31G(d) 11f,g for other C and H atoms. Two diffuse p functions, which were developed by Wachters, were added to the basis set of the Fe atom and multiplied by a For the spin state of the Fe atom in [Co(NpNP ipr )], S = 1, which was obtained from magnetic moment with Evans method, was employed. For the other species, the low-spin and high-spin states of the Co atom were considered and the pairs of S = 0 and 1 and S = 1/2 and 3/2 were calculated for even and odd electron species, respectively. Frequency calculations for all the species in this work confirmed that all the optimized structures were located at local minima. The natural atomic charges and spin densities were calculated to investigate the oxidation states of the Co atom and the bonding of the dinitrogen moiety. 12 The dinitrogen addtion and following silylation reactions were considered in Eqs. 1 and 2. [Co(NpNP ipr )] + N 2 [Co(NpNP ipr )(N 2 )] (1) [Co(NpNP ipr ) ((Me 3 Si) n 1 N 2 )] + Me 3 Si [Co(NpNP ipr )((Me 3 Si) n N 2 )], (n = 1-3) (2) In the silylation reactions (2), we considered that the active silyl species was a trimethylsilyl radical generated by trimethylsilyl chloride under the reductive condition provided by KC 8 in THF, as in the case of Na in THF. 13 All of the electronic structure calculations were performed using Gaussian 09, revision E.01,14 and the isosurfaces of the molecular orbitals were drawn using the MOPLOT and MOVIEW programs 15 on the Fujitsu CX400 system at the Nagoya University Information Technology Center. The selected parameters for optimized structures of Co I (NpNP ipr )(N 2 ) and N-Silylated Derivatives are listed in Table S3. The energy level diagram of dinitrogen addition to Co I (NpNP ipr ) and silylation reaction for Co I (NpNP ipr )(N 2 ) at 80 C under 1 atm are shown in Figure S13. The optimized structures of Co I (NpNP ipr )(N 2 ) and the mono-, di-, and trisilylated derivatives are shown in Figure S S16

17 Table S3. Selected parameters related to the N 2 binding and coordination structures of Co I (NpNP ipr )(N 2 ) and N-silylated derivatives energy a) (kcal/mol) Co N (Å) N 2 binding structure N N v(nn) (Å) (cm 1 ) Co-N-N (degrees) Co P (Å) coordination structure N-Co-N (degrees) P-Co-N (degrees) N 2 S = b) S = b) monosilyl-n 2 S = 1/2, 2-silyl S = 3/2, 2-silyl S = 1/2, 1-silyl S = 3/2, 1-silyl disilyl-n 2 S = 0, 2,2-disilyl S = 1, 2,2-disilyl S = 0, cis-1,2-disilyl S = 1, cis-1,2-disilyl S = 1, trans-1,2-disilyl trisilyl-n 2 S = 1/2, 1,2,2-trisilyl S = 3/2, 1,2,2-trisilyl a) The successive silylation energy at K, 1atm, Co I (NpNP ipr )(N 2 (Me 3 Si) n 1 ) + Me 3 Si Co I (NpNP ipr )(N 2 (Me 3 Si) n 1 ) (n = 1, 2, and 3). The reactant Co I (NpNP ipr )(N 2 (Me 3 Si) n 1 ) is the lowest state of the (n 1)silylated species. b) The N 2 addition energy at K, 1atm, Co I (NpNP ipr ) + N 2 Co I (NpNP ipr )(N 2 ). S17

18 Figure S13. Gibbs free energies of dinitrogen addition to Co I (NpNP ipr ) and silylation reaction for Co I (NpNP ipr )(N 2 ) at 80 C under 1 atm. Energy levels in the diagram mean the relative energies with respect to the system {Co(I)-N 2 }(S=1) + 3Me 3 Si and indicate energies of the reverse reaction of the N 2 addition (1) and the total silylation, as follows, {Co-N 2 } + n(si) {Co-N 2 (Si) n } (n = 1, 2, and 3) (1) {Co}, {Co(I)-N 2 }, and (Si) represent Co I (NpNP ipr ), Co I (NpNP ipr )(N 2 ), and Me 3 Si, respectively. The values by the energy levels of silylated species denote the successive silylation energies for the lowest energy {Co-N 2 (Si) n 1 } of reactant in the reaction (2). S18

19 Co I (NpNP ipr )(N 2 ) (S = 0, 6.6 kcal/mol) Co I (NpNP ipr )(N 2 ) (S = 1, 8.7 kcal/mol) Figure S14. Optimized structures of Co I (NpNP ipr )(N 2 ). N 2 addition energies are also shown. 1-N-silyl (S = 1/2, kcal/mol) 1-N-silyl (S = 3/2, kcal/mol) 2-N-silyl (S = 1/2, 4.9 kcal/mol) Figure S15. Optimized structures of monosilylated Co I (NpNP ipr )(N 2 ). 2-N-silyl (S = 3/2, +2.9 kcal/mol) S19

20 1,2-N,N -disilyl (S = 0, +7.6 kcal/mol) 1,2-N,N -disilyl (S = 1, +1.9 kcal/mol) 1,2-N,N -disilyl (S = 1, +3.0 kcal/mol) 2,2-N,N-disilyl (S = 0, 11.3 kcal/mol) Figure S16. Optimized structures of disilylated Co I (NpNP ipr )(N 2 ). 2,2-N,N-disilyl (S = 1, 8.9 kcal/mol) S20

21 1,2,2-N,N,N -trisilyl (S = 1/2, +2.1 kcal/mol) 1,2,2-N,N,N -trisilyl (S = 3/2, 10.4 kcal/mol) Figure S17. Optimized structures of trisilylated Co I (NpNP ipr )(N 2 ). P N N Co P N N Co 2 N(SiMe 3 ) 3 P P 3 Me 3 Si SiMe 3 N SiMe 3 N SiMe N P N Co II P N G values in kcal/mol P N Co I + N 2 N N P N P N 2 N Co I -8.7 Me 3 Si P S = 1 N N SiMe 3 SiMe 3 SiMe 3 S = P N N Co II P N S = 1/2 SiMe 3 N SiMe S = 3/2 N P N SiMe N 3 N Co I Me 3 Si Me 3 Si P S = 0 Figure S18. Summary of the DFT results - proposed mechanism of the three initial Me 3 Si additions; spin states and optimized structures determined by DFT. The last step to eliminate S21

22 N 2 (SiMe 3 ) 3 is exergonic driven by a large entropy term; in the presence of excess Me 3 Si, N 2 (SiMe 3 ) 3 converts spontaneously to 2 equiv of N(SiMe 3 ) 3 ; see Tanaka, H.; Sasada, A.; Kouno, T.; Yuki, M.; Miyake, Y.; Nakanishi,H.; Nishibayashi, Y.; Yoshizawa K. J. Am. Chem. Soc. 2011, 133, Calculated free energy changes are given in kcal/mol for the indicated steps and refer to the process [Co(NpNP ipr )] + N Me 3 Si. Total energies and spins, and cartesian coordinates for optimized geometries Co I (NpNP ipr ) (S = 1) Total energy: a.u. Gibbs free energy ( K, 1 atm): a.u. <Sx>= <Sy>= <Sz>= <S**2>= S= Nuclear repulsion energy: a.u. Atomic Coordinates (Angstroms) Symbol X Y Z Co P P N N C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C H H S22

23 H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H Co I (NpNP ipr )(N 2 ) (S = 0, 6.6 kcal/mol) Total energy: a.u. Gibbs free energy ( K, 1 atm): a.u. Nuclear repulsion energy: a.u. Atomic Coordinates (Angstroms) Symbol X Y Z Co P P N N C C C S23

24 C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H S24

25 H H H H H H H H H H H H H H H N N Co I (NpNP ipr )(N 2 ) (S = 1, 8.7 kcal/mol) Total energy: a.u. Gibbs free energy ( K, 1 atm): a.u. <Sx>= <Sy>= <Sz>= <S**2>= S= Nuclear repulsion energy: a.u. Atomic Coordinates (Angstroms) Symbol X Y Z Co P P N N C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C H H S25

26 H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H N N (CH 3 ) 3 Si Total energy: a.u. Gibbs free energy ( K, 1 atm): a.u. <Sx>= <Sy>= <Sz>= <S**2>= S= Nuclear repulsion energy: a.u. Atomic Coordinates (Angstroms) Symbol X Y Z Si C C C S26

27 H H H H H H H H H N-silyl Co I (NpNP ipr )(N 2 ) (S = 1/2, 4.9 kcal/mol) Total energy: a.u. Gibbs free energy ( K, 1 atm): a.u. <Sx>= <Sy>= <Sz>= <S**2>= S= Nuclear repulsion energy: a.u. Atomic Coordinates (Angstroms) Symbol X Y Z Co P P N N C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C H H H H H H H H H H S27

28 H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H N N Si C C C H H H H H H H H H N-silyl Co I (NpNP ipr )(N 2 ) (S = 3/2, +2.9 kcal/mol) Total energy: a.u. Gibbs free energy ( K, 1 atm): a.u. <Sx>= <Sy>= <Sz>= <S**2>= S= Nuclear repulsion energy: a.u. Atomic Coordinates (Angstroms) Symbol X Y Z S28

29 Co P P N N C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H S29

30 H H H H H H H H H H H H H H H H H H H H H H H H N N Si C C C H H H H H H H H H N-silyl Co I (NpNP ipr )(N 2 ) (S = 1/2, kcal/mol) Total energy: a.u. Gibbs free energy ( K, 1 atm): a.u. <Sx>= <Sy>= <Sz>= <S**2>= S= Nuclear repulsion energy: a.u. Atomic Coordinates (Angstroms) Symbol X Y Z Co P P N N C C C C C C C C C C C C C C C S30

31 C C C C C C C C C C C C C C C C C C C C H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H S31

32 H H H N N Si C C C H H H H H H H H H N-silyl Co I (NpNP ipr )(N 2 ) (S = 3/2, kcal/mol) Total energy: a.u. Gibbs free energy ( K, 1 atm): a.u. <Sx>= <Sy>= <Sz>= <S**2>= S= Nuclear repulsion energy: a.u. Atomic Coordinates (Angstroms) Symbol X Y Z Co P P N N C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C H S32

33 H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H N N Si C C C H H H H H H H H H S33

34 2,2-N,N-disilyl Co I (NpNP ipr )(N 2 ) (S = 0, 11.3 kcal/mol) Total energy: a.u. Gibbs free energy ( K, 1 atm): a.u. Nuclear repulsion energy: a.u. Atomic Coordinates (Angstroms) Symbol X Y Z Co P P N N C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C H H H H H H H H H H H H H H H H H H H H H H H S34

35 H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H N N Si C C C H H H H H H H H H Si C C C H H H H H H H H H ,2-N,N-disilyl Co I (NpNP ipr )(N 2 ) (S = 1, 8.9 kcal/mol) Total energy: a.u. Gibbs free energy ( K, 1 atm): a.u. <Sx>= <Sy>= <Sz>= <S**2>= S= Nuclear repulsion energy: a.u. Atomic Coordinates (Angstroms) Symbol X Y Z S35