A molybdenum complex bearing PNP-type pincer ligands leads to the catalytic reduction of dinitrogen into ammonia

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1 SUPPLEMENTARY INFORMATION A molybdenum complex bearing PNP-type pincer ligands leads to the catalytic reduction of dinitrogen into ammonia Kazuya Arashiba, Yoshihiro Miyake, Yoshiaki Nishibayashi * Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo , Japan General Methods. 1 H NMR (270 MHz), 31 P{ 1 H} NMR (109 MHz), and 15 N{ 1 H} NMR (27 MHz) spectra were recorded on a JEOL Excalibur 270 spectrometer in suitable solvent, and spectra were referenced to residual solvent ( 1 H) or external standard ( 31 P{ 1 H}: 85% H 3 PO 4, 15 N{ 1 H}: CH 3 NO 2 ). IR spectra were recorded on a JASCO FT/IR 4100 Fourier Transform infrared spectrometer. Raman spectra were recorded on a JASCO NRS Absorption spectra were recorded on a Shimadzu MultiSpec Mass spectra were recorded on a JEOL Accu TOF JMS-T100LP. Evolved dihydrogen was quantified by a gas chromatography using a Shimadzu GC-8A with a TCD detector and a SHINCARBON ST (6 m x 3 mm). Elemental analyses were performed at Microanalytical Center of The University of Tokyo. All manipulations were carried out under an atmosphere of nitrogen by using standard Schlenk techniques or glovebox techniques unless otherwise stated. Solvents were dried by the usual methods, then distilled and degassed before use. CrCp 2 and CoCp 2 (Aldrich) were used without further purification. 2,6-Bis(di-tert-butylphosphinomethyl)pyridine (PNP) S1, [MoCl 3 (thf) 3 ] S2, CrCp* S3 2, [LutH]BAr 4 (Lut = lutidine; Ar = 3,5-(CF 3 ) 2 C 6 H 3 ) S4, and [LutH]Cl S5 nature chemistry 1

2 supplementary information were prepared according to the literature methods. [LutH]OTf S6 was prepared in a method similar to [LutH]Cl. Preparation of [MoCl 3 (PNP)] (1a). A mixture of 2,6-bis(di-tert-butylphosphinomethyl)pyridine (2.00 g, 5.06 mmol) and [MoCl 3 (thf) 3 ] (2.01 g, 4.80 mmol) in THF (60 ml) was stirred at 50 C for 18 h. The resultant orange suspension was concentrated under reduced pressure, and the residue was recrystallized from CH 2 Cl 2 (50 ml) hexane (100 ml) to give orange-brown crystals of 1a 0.75CH 2 Cl 2, which were collected by filtration and washed with Et 2 O (15 ml 3) and dried in vacuo to afford 1a as an orange-brown solid (2.71 g, 4.53 mmol, 94% yield). Anal Calcd for C 23 H 43 Cl 3 MoNP 2 : C, 46.21; H, 7.25; N, Found: C, 46.01; H, 7.25; N, Preparation of [Mo(N 2 ) 2 (PNP)] 2 ( -N 2 ) (2a). To Na-Hg (0.5 wt%, 47.0 g, 9.34 mmol) were added THF (30 ml) and then 1a (889.5 mg mmol), and the mixture was stirred at room temperature for 12 h under N 2. The resultant dark purple solution was filtered and extracted with THF (10 ml), and then the combined filtrate was concentrated in vacuo. The residue was extracted with benzene (15 ml), and slow addition of hexane (45 ml) to the obtained extract afforded a dark green crystalline solid, which was collected by filtration and washed with hexane (5 ml) and dried in vacuo to afford 2a as a dark green solid (524.2 mg, 0.47 mmol, 63% yield). 1 H NMR (THF-d 8 ) 7.07 (t, J = 7.3 Hz, ArH, 1H), 6.93 (d, J = 7.3 Hz, ArH, 2H), 3.37 (m, CH 2 P t Bu 2, 4H), 1.28 (pseudo t, CH 2 P t Bu 2, 36H). 31 P{ 1 H} NMR (THF-d 8 ) 94.6 (s). IR (KBr, cm 1 ) 1936 (s, NN ). IR (THF, cm 1 ) 1944 (s, NN ). Raman (THF, cm 1 ; excite = nm) 1890 ( NN ). The elemental analysis acceptable for the above formulation of 2a (Anal Calcd for C 46 H 86 Mo 2 N 12 P 4 : C, 49.20; H, 7.72; N, 14.97) is not obtained when the sample of 2a is dried in vacuo. We assume that dinitrogen ligands in 2a are quite labile even in a solid state. Analytic sample was prepared by drying a dark green crystalline solid under gentle N 2 stream. This sample included one molar benzene, which is determined by 1 H NMR in THF-d 8, while one of dinitrogen ligands was lost. Anal Calcd for C 52 H 92 Mo 2 N 10 P 4 : C, 53.24; H, 7.90; N, Found: C, 53.60; H, 7.70; N, Additionally, 2 nature chemistry

3 supplementary information ESI TOF MS of 2a in THF shows that 2a retained the dinuclear structure in solution, whereas the elimination of terminal dinitrogen ligands in 2a was observed. ESI TOF MS (in THF) 1070 (M 2N 2 ), 1042 (M 3N 2 ). Reaction of 2a with 15 N N-enriched sample of 2a was prepared by bubbling of 15 N 2 gas to a THF solution of 2a. 15 N NMR (THF-d 8 ) 29.0 (dt, 1 J NN = 6.1 Hz, 2 J NP = 2.4 Hz, Mo N N), 16.5 (d, 1 J NN = 6.1 Hz, Mo N N), 8.5 (s, Mo N N Mo). IR (THF, cm 1 ) 1879 (s, 15 N 15 N). Preparation of [Mo(CO) 2 (PNP)] 2 ( -N 2 ) (3a). A solution of 2a (55.7 mg mmol) in THF (5 ml) was stirred at room temperature for 12 h under CO atmosphere. The resultant dark blue solution was concentrated in vacuo. The residue was extracted with THF (5 ml) and concentrated in vacuo to about 3 ml. Slow addition of hexane (20 ml) to the obtained solution afforded 3a C 6 H 14 as purple crystals, which were collected by filtration and dried in vacuo to afford 3a (35.6 mg, mmol, 64% yield). 1 H NMR (THF-d 8 ) 7.37 (br s, ArH, 2H), 6.64 (br s, ArH, 1H), 3.68 (br s, CH 2 P t Bu 2, 4H), 1.35 (br s, CH 2 P t Bu 2, 36H). 31 P{ 1 H} NMR (THF-d 8 ) (s). IR (KBr, cm 1 ) 1833 (s, CO ), 1801 (s, CO ), 1780 (br, CO ). Raman (THF, cm 1 ; excite = nm) 1893 ( NN ). Anal Calcd for C 50 H 86 Mo 2 N 4 O 4 P 4 : C, 53.48; H, 7.72; N, Found: C, 53.50; H, 8.00; N, Preparation of [Mo(N 2 ) 2 (PNP)(PMe 2 Ph)] (4a). To Na-Hg (0.5 wt%, g, mmol) were added THF (10 ml). After the sequential addition of PMe 2 Ph (0.25 ml, mmol) and 1a (103.1 mg mmol), the mixture was stirred at room temperature for 12 h under N 2 atmosphere. The resultant dark purple solution was filtered, and then the filtrate was concentrated. The residue was extracted with hexane. After the extract was concentrated to about 3 ml, the obtained solution was stood at 40 C to afford 4a as a purple solid (56.4 mg, mmol, 48% yield). 1 H NMR (C 6 D 6 ) (m, ArH, 2H), (m, ArH, 2H), (m, ArH, 1H), (m, ArH, 3H), 3.23 (br s, CH 2 P t Bu 2, 4H), 1.97 (d, 2 J PH = 5.1 Hz, PMe 2 Ph, 9H), 1.14 (pseudo t, CH 2 P t Bu 2, nature chemistry 3

4 supplementary information 36H). 31 P{ 1 H} NMR (C 6 D 6 ) 92.7 (d, 2 J PP = 5 Hz, PNP), 18.5 (t, 2 J PP = 5 Hz, PMe 2 Ph). IR (KBr, cm 1 ) 1915 (s, NN ). Anal Calcd for C 31 H 54 MoN 5 P 3 : C, 54.30; H, 7.94; N, Found: C, 54.11; H, 7.91; N, Preparation of [MoF(NNH 2 )(C 5 H 5 N)(PNP)]BF 4 0.5C 6 H 6 (7a 0.5C 6 H 6 ). To a solution of 2a (56.1 mg mmol) in THF (5 ml) was added HBF 4 OEt 2 (27 L, 0.20 mmol) and stirred at room temperature for 24 h. The resultant dark green solution was treated with pyridine (40 L, 0.50 mmol) and stirred at room temperature for additional 2 h. The volatile components were removed under vacuum. The residue was extracted with benzene THF (5 ml 3 ml), and slow addition of Et 2 O (15 ml) afforded green crystals, which were collected by filtration and dried in vacuo to obtain 7a 0.5C 6 H 6 as a green-brown crystalline solid (35.3 mg, mmol, 47% yield). 1 H NMR (THFd 8 ) 9.38 (d, J = 5.7 Hz, ArH, 2H), (br, ArH, 2H), 7.64 (d, J = 7.3 Hz, ArH, 2H), 7.54 (t, J = 7.3 Hz, ArH, 1H), (m, ArH and C 6 H 6, 4H), 6.82 (br, NNH 2, 2H) (m, CH 2 P t Bu 2, 4H), 1.21 (pseudo t, CH 2 P t Bu 2, 18H), 1.10 (pseudo t, CH 2 P t Bu 2, 18H). 31 P{ 1 H} NMR (THF-d 8 ) 77.6 (d, 2 J PF = 29.3 Hz, PNP). IR (KBr, cm 1 ) 3378, 3277 (s, NH ). Anal Calcd for C 31 H 53 BF 5 MoN 4 P 2 : C, 49.95; H, 7.17; N, Found: C, 49.56; H, 7.10; N, Protonolysis of 7a 0.5C 6 H 6. A mixture of 7a 0.5C 6 H 6 (30.0 mg, mmol) and [LutH]OTf (246.8 mg, 0.96 mmol) in toluene (5 ml) was stirred at room temperature for 20 h. The reaction mixture was evaporated under reduced pressure, and the distillate was trapped in dilute H 2 SO 4 solution (0.5 M, 10 ml). Potassium hydroxide aqueous solution (30 wt%; 5 ml) was added to the residue, and the mixture was distilled into dilute H 2 SO 4 solution (0.5 M, 10 ml) under reduced pressure. The amount of NH 3 was determined by the indophenol method. S mmol, 20% yield based on 7a 0.5C 6 H 6. Catalytic Reduction of Dinitrogen to Ammonia under N 2 Atmosphere (1 atm). A typical experimental procedure for the catalytic reduction of dinitrogen into ammonia using the dinitrogen 4 nature chemistry

5 supplementary information complex 2a is described below. In a 50 ml Schlenk flask were placed 2a (11.3 mg, mmol) and 2,6-lutidinium trifluoromethanesulfonate [LutH]OTf (246.8 mg, 0.96 mmol). Toluene (2.5 ml) was added under N 2 (1 atm), and then a solution of CoCp 2 (136.2 mg, 0.72 mmol) in toluene (2.5 ml) was slowly added to the stirred suspension in the Schlenk flask with a syringe pump at a rate of 0.5 ml per hour. After the addition of CoCp 2, the mixture was further stirred at room temperature for 15 h. The amount of dihydrogen of the catalytic reaction was determined by GC analysis. The reaction mixture was evaporated under reduced pressure, and the distillate was trapped in dilute H 2 SO 4 solution (0.5 M, 10 ml). Potassium hydroxide aqueous solution (30 wt%; 5 ml) was added to the residue, and the mixture was distilled into another dilute H 2 SO 4 solution (0.5 M, 10 ml). NH 3 present in each of the H 2 SO 4 solutions was determined by the indophenol method. S7 The amount of ammonia was mmol of NH 3 collected before base distillation of the reaction mixture and mmol of NH 3 collected after base distillation to fully liberate NH 3, respectively. The total amount of ammonia was mmol (11.8 mol equiv per 2a). No hydrazine was detected by the p-(dimethylamino)benzaldehyde method. S8 Detailed results are shown in Table S1. In addition, the yield of ammonium salt by using various solvents, reductants, and proton sources is shown in Tables S2 S4. nature chemistry 5

6 supplementary information Table S1. Catalytic Reduction of Dinitrogen with CoCp 2 and [LutH]OTf in the Presence of Molybdenum Dinitrogen Complexes. N 2 (1 atm) run catalyst (0.010 mmol) 6 CoCp 2 6 [LutH]OTf toluene rt, 20 h catalyst CoCp 2 (mmol) [LutH]OTf (mmol) 2 NH 3 NH 3 (mol equiv/catalyst) a H 2 (mol equiv/catalyst) a 1 2a b 2a c 2a c 2a a a cis-[mo(n 2 ) 2 (PMe 2 Ph) 4 ] (5) trans-[mo(n 2 ) 2 (dppe) 2 ] (6) a Mol equiv based on the catalyst. b Under 1 atm of Ar. c In these reactions, to a suspension of 2a and [LutH]OTf in toluene (1 ml) was added a solution of CoCp 2 in toluene (4 ml) over a period of 5 h. 6 nature chemistry

7 supplementary information Table S2. Catalytic Reduction of Dinitrogen with CoCp 2 and [LutH]OTf in the Presence of 2a in Various Solvents. 2a (0.010 mmol) N 2 6 CoCp 2 6 [LutH]OTf (1 atm) (0.72 mmol) (0.96 mmol) solvent, rt, 20 h 2 NH 3 solvent toluene THF hexane NH 3 (mol equiv/2a) a H 2 (mol equiv/2a) a a Mol equiv based on 2a. nature chemistry 7

8 supplementary information Table S3. Catalytic Reduction of Dinitrogen with Reductant and [LutH]OTf in the Presence of 2a N 2 6 reductant 6 [LutH]OTf (1 atm) (0.72 mmol) (0.96 mmol) 2a (0.010 mmol) toluene rt, 20 h 2 NH 3 run reductant E 1/2 (V) a NH 3 (mol equiv/2a) b H 2 (mol equiv/2a) b 1 2 CoCp 2 c CrCp* CrCp a Electrochemical data (E 1/2 ) in MeCN vs. Ag/Ag + in 0.1 M AgNO 3. See Reference S9. b Mol equiv based on 2a. c In the absence of reductant. 8 nature chemistry

9 supplementary information Table S4. Catalytic Reduction of Dinitrogen with CoCp 2 and Proton Source in the Presence of 2a. 2a (0.010 mmol) N 2 6 CoCp 2 6 proton source (1 atm) (0.72 mmol) (0.96 mmol) toluene rt, 20 h 2 NH 3 run proton source pk a a NH 3 (mol equiv/2a) b H 2 (mol equiv/2a) b 1 2 [LutH]OTf c [LutH]BAr' 4 [LutH]Cl [2-PicH]OTf [PyH]OTf HOTf [3,5-LutH][OTf] [2,4,6-ColH][OTf] a pk a values in MeCN. See References S10 and S11. b Mol equiv based on 2a. c In the absence of proton source. nature chemistry 9

10 supplementary information Catalytic Reduction of Dinitrogen to Ammonia under 15 N 2. In a 50 ml Schlenk were placed 2a (11.2 mg, mmol) and [LutH]OTf (247.0 mg, 0.96 mmol). After the mixture was cooled at 196 C, toluene (2.5 ml) was added to the mixture by trap-to-trap distillation. The Schlenk flask was warmed to room temperature keeping reduced pressure, and then was filled with 15 N 2. Then a solution of CoCp 2 (136.1 mg, 0.72 mmol) in toluene (2.5 ml) was slowly added to the stirred suspension in the Schlenk flask with a syringe pump at a rate of 0.5 ml per hour. After the addition of CoCp 2 for 5 h, the mixture was further stirred at room temperature for 15 h. The reaction mixture was evaporated under reduced pressure, and the distillate was trapped in dilute H 2 SO 4 solution (0.5 M, 10 ml). Potassium hydroxide aqueous solution (30 wt%; 5 ml) was added to the residue, and the mixture was distilled into another dilute H 2 SO 4 solution (0.5 M, 10 ml). NH 3 present in each of the H 2 SO 4 solutions was determined by the indophenol method. S7 The amount of ammonium salt was 10.4 mol equiv per 2a. In separate run, an NMR sample of the ammonium salt was prepared as follows. In a 50 ml Schlenk were placed 2a (11.3 mg, mmol) and [LutH]OTf (247.0 mg, 0.96 mmol). After the mixture was cooled at 196 C, toluene (2.5 ml) was added to the mixture by trap-to-trap distillation. The Schlenk flask was warmed to room temperature keeping reduced pressure, and then was filled with 15 N 2. Then a solution of CoCp 2 (136.2 mg, 0.72 mmol) in toluene (2.5 ml) was slowly added to the stirred suspension in the Schlenk flask with a syringe pump at a rate of 0.5 ml per hour. After the addition of CoCp 2 for 5 h, the mixture was further stirred at room temperature for 15 h. After catalytic reduction was done, the volatiles were collected by trap-to-trap distillation. To the residual solid was added a solution of KO t Bu (4 mmol) in THF MeOH and the mixture was stirred at room temperature for 20 min. The volatile components in the mixture were collected to the Schlenk flask to which was added HCl in Et 2 O (2 M, 5 ml). The obtained colorless solution was dried up in vacuo to afford a colorless solid which contains 15 NH 4 Cl and [LutH]Cl. 1 H NMR spectrum of this mixture is shown in Figure S1. 1 H NMR (DMSO-d 6 ): 7.51 (d, J NH = 71.3 Hz, 15 NH 4 Cl). 15 N{ 1 H} NMR (DMSO-d 6 ) : (s, 15 NH 4 Cl). 10 nature chemistry

11 supplementary information (a) H N 15 NH 4 + (b) (c) 14 NH 4 + Figure S1. 1 H NMR spectra of (a) 15 NH 4 Cl obtained from the reaction of 2a with [LutH]OTf and CoCp 2 under 15 N 2, (b) a mixture of authentic 15 NH 4 Cl and [LutH]Cl, (c) 14 NH 4 Cl obtained from the reaction of 2a with [LutH]OTf and CoCp 2 under 14 N 2. nature chemistry 11

12 supplementary information X-ray Crystallography. Single crystals of 2a suitable for X-ray crystallography were obtained as 2a C 6 H 14 by recrystallization from benzene hexane. Crystallographic data of 1a 0.75CH 2 Cl 2, 2a C 6 H 14, 3a C 6 H 14, and 7a 0.5C 6 H 6 are summarized in Tables S5 and S6. Selected bond lengths and angles are summarized in Tables S7 S10, and their ORTEP drawings are shown in Figures S2 S5. Diffraction data were collected at 100 C on a Rigaku RAXIS RAPID imaging plate area detector with graphite-monochromated Mo K radiation ( = Å). Reflections were collected for the 2 range of 5 to 55. Intensity data were collected for Lorenz-polarization effects and for empirical absorption (REQAB). The structure solution and refinements were carried out by using the CrystalStructure crystallographic software package. S12 The positions of the non-hydrogen atoms were determined by heavy atom Patterson methods (PATTY S13 for 1a 0.75CH 2 Cl 2 ; SHELX- 97 S14 for 2a C 6 H 14 or direct methods (SHELX-97 S14 for 3a C 6 H 14 and 7 0.5C 6 H 6 ) and subsequent Fourier syntheses (DIRDIF-99 S15 ) and were refined F 2 o using all unique reflections by full-matrix least-squares with anisotropic thermal parameters except for a few solvated molecules (Cl13, C47, C48, C49, and C50 for 1a; C24, C25, C26, and C27 for 2a C 6 H 14 ; C26, C27, and C28 for 3a C 6 H 14 ; C29, C30, C31, and C32 for 7 0.5C 6 H 6 ), which were refined isotropically. Hydrogen atoms (H49 and H50) of 7a 0.5C 6 H 6 were placed in a difference Fourier map and were refined isotropically, while all the other hydrogen atoms were placed at the calculated positions with fixed isotropic parameter. Positional disorders in the crystal structures of 1a and 2a were indicated with the check CIF structure validation PLATON, which showed in the alert level B section significant Hirshfeld rigid bond test differences, su for Mo2 Cl6 in 1a and su for Mo1 N2 in 2a. Short intermolecular H H contacts of alert level B were also indicated for the H4 and H60 in 1a. Short C C bonds of alert level B in 3a were indicated due to possible disorders of hexane. However, we consider that these potential disorders did not affect the validity of the molecular structures of 1a, 2a, 12 nature chemistry

13 supplementary information Table S5. X-ray Crystallographic Data for [MoCl 3 (PNP)] 0.75CH 2 Cl 2 (1a 0.75CH 2 Cl 2 ), [Mo(N 2 ) 2 (PNP)] 2 ( -N 2 ) C 6 H 14 (2a C 6 H 14 ). 1a 0.75CH 2 Cl 2 2a C 6 H 14 chemical formula C H 44.5 Cl 4.5 MoNP 2 C 52 H 100 Mo 2 N 12 P 4 formula weight dimensions of crystals crystal system monoclinic trigonal space group C2 R3 c a, Å (1) (7) b, Å (8) (7) c, Å (7) (4), deg 90 90, deg (1) 90, deg V, Å (5) (9) Z 8 18 calcd, g cm F(000) , cm trans. factors range no. reflections measured no. unique reflections (R int = 0.026) 7056 (R int = 0.036) no. parameters refined R1 (I > 2 (I)) a wr2 (all data) b GOF (all data) c Flack parameters 0.00(2) max diff peak / hole, e Å / / 0.57 a R1 = F o F c / F o. b wr2 = [ w(f 2 o F 2 c ) 2 / w(f 2 o ) 2 ] 1/2, w = 4F 2 o /q (F 2 o ) [q = 3.9 (1a 0.75CH 2 Cl 2 ); q = 2.8 (2a C 6 H 14 )]. c GOF = [ w(f 2 o F 2 c ) 2 /(N o N params )] 1/2. nature chemistry 13

14 supplementary information Table S6. X-ray Crystallographic Data for [Mo(CO) 2 (PNP)] 2 ( -N 2 ) C 6 H 14 (3a C 6 H 14 ), [MoF(NNH 2 )(C 5 H 5 N)(PNP)]BF 4 0.5C 6 H 6 (7a 0.5C 6 H 6 ). 3a C 6 H 14 7a 0.5C 6 H 6 chemical formula C 56 H 100 Mo 2 N 4 O 4 P 4 C 31 H 53 BF 5 MoN 4 P 2 formula weight dimensions of crystals crystal system trigonal monoclinic space group R3 c C2/c a, Å (7) (1) b, Å (7) (3) c, Å (5) (7), deg 90 90, deg (1), deg V, Å (9) (4) Z 18 8 calcd, g cm F(000) , cm trans. factors range no. reflections measured no. unique reflections 7049 (R int = 0.025) 8415 (R int = 0.035) no. parameters refined R1 (I > 2 (I)) a wr2 (all data) b GOF (all data) c Flack parameters max diff peak / hole, e Å / / 0.75 a R1 = F o F c / F o. b wr2 = [ w(f 2 o F 2 c ) 2 / w(f 2 o ) 2 ] 1/2, w = 4F 2 o /q (F 2 o ) [q = 6.9 (3a C 6 H 14 ); q = 4.1 (7a 0.5C 6 H 6 )]. c GOF = [ w(f 2 o F 2 c ) 2 /(N o N params )] 1/2. 14 nature chemistry

15 supplementary information Figure S2. Molecular structure of [MoCl 3 (PNP)] 0.75CH 2 Cl 2 (1a 0.75CH 2 Cl 2 ). One of the two crystallographically independent molecules. Thermal ellipsoids are shown at the 50% probability level. Hydrogen atoms and solvated molecules are omitted for clarity. Table S7. Selected Bond Lengths (Å) for 1a 0.75CH 2 Cl 2. molecule 1 molecule 2 Mo(1) Cl(1) 2.420(2) Mo(2) Cl(4) 2.431(1) Mo(1) Cl(2) 2.400(2) Mo(2) Cl(5) 2.425(2) Mo(1) Cl(3) 2.397(2) Mo(2) Cl(6) 2.385(2) Mo(1) N(1) 2.199(4) Mo(2) N(2) 2.199(4) Mo(1) P(1) 2.618(1) Mo(2) P(3) 2.618(1) Mo(1) P(2) 2.600(1) Mo(2) P(4) 2.589(2) nature chemistry 15

16 supplementary information Figure S3. Molecular structure of [Mo(N 2 ) 2 (PNP)] 2 ( -N 2 ) C 6 H 14 (2a C 6 H 14 ). Thermal ellipsoids are shown at the 50% probability level. Hydrogen atoms and solvated molecules are omitted for clarity. Asterisks denote atoms related by the symmetrical operation +y, +x, z+1/2. Table S8. Selected Bond Lengths (Å) and Angles (deg) for 2a C 6 H 14. Mo(1) N(1) 2.182(3) N(2) N(3) 1.082(3) Mo(1) N(2) 2.018(2) N(4) N(5) 1.130(3) Mo(1) N(4) 2.035(2) N(6) N(6*) 1.146(4) Mo(1) N(6) 2.024(3) Mo(1) N(2) N(3) 179.2(2) Mo(1) P(1) (8) Mo(1) N(4) N(5) 176.2(2) Mo(1) P(2) 2.477(1) Mo(1) N(6) N(6*) 178.9(2) 16 nature chemistry

17 supplementary information Figure S4. Molecular structure of [Mo(CO) 2 (PNP)] 2 ( -N 2 ) C 6 H 14 (3a C 6 H 14 ). Thermal ellipsoids are shown at the 50% probability level. Hydrogen atoms and solvated molecules are omitted for clarity. Asterisks denote atoms related by the symmetrical operation +y, +x, z+1/2. Table S9. Selected Bond lengths (Å) and Angles (deg) for 3a C 6 H 14. Mo(1) N(1) 2.047(2) Mo(1) P(1) (8) Mo(1) N(2) 2.206(2) Mo(1) P(2) (8) Mo(1) C(24) 2.025(4) N(1) N(1*) 1.139(3) Mo(1) C(25) 1.999(4) Mo(1) C(24) O(1) 173.5(3) C(24) O(1) 1.167(5) Mo(1) C(25) O(2) 177.0(2) C(25) O(2) 1.169(5) Mo(1) N(1) N(1*) 178.5(2) nature chemistry 17

18 supplementary information Figure S5. Molecular structure of [MoF(NNH 2 )(C 5 H 5 N)(PNP)]BF 4 0.5C 6 H 6 (7a 0.5C 6 H 6 ). Thermal ellipsoids are shown at the 50% probability level. Hydrogen atoms and solvated molecules are omitted for clarity. Table S10. Selected Bond Lengths (Å) and Angles (deg) for 7a 0.5C 6 H 6. Mo(1) N(1) 1.754(2) Mo(1) P(2) (8) N(1) N(2) 1.330(4) Mo(1) F(1) 2.009(2) Mo(1) N(3) 2.197(2) H(49) F(2) 2.26(4) Mo(1) N(4) 2.195(2) Mo(1) N(1) N(2) 173.8(2) Mo(1) P(1) (8) N(2) H(49) F(2) 163(4) 18 nature chemistry

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