An Anionic Ruthenium Dihydride [Cp*(iPr2MeP)RuH2]− and Its

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An Anionic Ruthenium Dihydride [Cp*(iPr2MeP)RuH2]− and Its Conversion to Heterobimetallic Ru(μ-H)2M (M = Ir or Cu) Complexes Patrick W. Smith, Scott R. Ellis, Rex C. Handford, and T. Don Tilley* Department of Chemistry, University of California, Berkeley, Berkeley, California 94720-1460, United States

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S Supporting Information *

ABSTRACT: A novel dihydridoruthenate, [(solv)Na][Cp*(iPr2MeP)RuH2] (2; solv = THF or OEt2), was synthesized from Cp*(iPr2MeP)RuCl (1) and sodium triethylborohydride. Compound 2 was used to generate “Cp*(iPr2MeP)RuH” equivalents by salt metathesis with 1, which resonance Raman spectroscopy indicates is a mixture of the terminal dinitrogen complex, Cp*(iPr2MeP)RuH(N2) (4), and diastereomers of the bridging dinitrogen complex [Cp*(iPr2MeP)RuH]2(μ-N2) (meso, 5, and a pair of enantiomers, 6). Compound 2 also reacted with the late transition metal chloride complexes [(COD)IrCl]2 and (IPr)CuCl [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene] to form hydride-bridged heterobimetallic complexes Cp*(iPr2MeP)Ru(μ-H)2Ir(COD) (7) and Cp*(iPr2MeP)Ru(μ-H)2Cu(IPr) (8), respectively, that feature weakened Ru−H interactions relative to those of 2.

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anions.28−45 More recently, this approach has been extended to include early metal polyhydride anions by using [Cp2TaH2]− in reactions with late metal halides.46 This report describes an anionic half-sandwich hydride complex of ruthenium, synthesized from Cp*(iPr2MeP)RuCl (1) by treatment with sodium triethylborohydride to afford {[Na(solv)][Cp*(iPr2MeP)RuH2]}2 (2) (solv = THF or Et2O). Reactivity studies with transition metal chloride complexes, including 1, [(COD)IrCl]2, and (IPr)CuCl [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene], indicate that compound 2 can react as either a hydride source, transferring one of the hydride ligands to form a well-defined mixture of Ru monohydride complexes, or a precursor to heterobimetallic Ru-M (M = Ir or Cu) complexes with bridging hydrides. Notably, while Ru-based hydride anions have previously been used in this manner, to the best of our knowledge previous examples were based exclusively on [(R3P)3RuH3]−.29−33

INTRODUCTION Compounds featuring hydride ligands that bridge two transition metal centers have been investigated as potential catalysts1,2,11−15,3−10 and for their relevance to biological systems such as hydrogenases.16−19 A particularly intriguing subset of this class of compounds involves hydride ligands bridging two different metal centers in heterobimetallic complexes. In such molecules, the interplay of the properties of the two different metal centers often gives rise to novel chemistry not observed for homobimetallic analogues.20−25 Many of the earliest heterometallic complexes with bridging hydrides were prepared from neutral metal hydride complexes as nucleophiles in reactions with other complexes bearing easily displaced ligands or open coordination sites.26 For example, Cp2MH2 (M = Mo or W) complexes were found to react with [(Ph3P)2Rh(H)2(OCMe2)2]+ to afford [Cp2M(μH)2Rh(PPh3)2]+ (eq 1, presumably following loss of H2 from Rh).27 However, while the terminal hydride complexes are ubiquitous, not all are sufficiently nucleophilic at H to engage in such reactions.

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RESULTS AND DISCUSSION New Ruthenium Hydrides. Treatment of an ethereal solution of the deep purple ruthenium chloride compound Cp*(iPr2MeP)RuCl (1) with 2 equiv of sodium triethylborohydride (1 M in THF) resulted in a color change to yellow and the precipitation of NaCl, indicating formation of the hydridoruthenate sodium dimer {[(solv)Na][Cp*(iPr2MeP)RuH2]}2 (2, eq 2), which incorporates a variable amount of diethyl ether and THF (2 equiv in total, vide infra). A similar synthetic procedure has been utilized for the preparation of ruthenium trihydrides of the type Cp*(R3P)RuH3,11 but these

A particularly successful method involves the reaction of an anionic metal hydride with a halide complex. Since the first report of such a reaction in 1984, between K[OsH3(PMe2Ph)3] and Cp2ZrXCl (X = Cl or H),28 this approach has been used to synthesize numerous heterobimetallic complexes particularly from late metal hydride © XXXX American Chemical Society

Received: October 10, 2018

A

DOI: 10.1021/acs.organomet.8b00738 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Scheme 1. Proposed Equilibria among 4−6

complexes were obtained after workup with alumina. The omission of the latter step and crystallization from diethyl ether allowed isolation of 2 rather than the previously described trihydride Cp*(iPr2MeP)RuH3 (3).47 The formation of 3 under these conditions is presumably due to adventitious protons provided by the alumina. Compound 2 crystallized from diethyl ether as yellow blocks, and X-ray crystallography shows that this complex exists as a Na-bridged dimer in the solid state, with one diethyl ether molecule coordinated to each Na atom (Figure 1). The

gave a yellow powder that rapidly decomposed in aromatic solvents such as benzene and toluene; therefore, NMR spectra were acquired with cyclohexane-d12 as the solvent. Three overlapping doublets were observed in the Ru−H region of the 1 H NMR spectrum (δ = −11.07, JHP = 40.8 Hz; δ = −11.09, JHP = 40.9 Hz; and δ = −11.22, JHP = 39.7 Hz; δRu−H = −15.62 for 2 in cyclohexane-d12). Neither 1H NMR spectroscopy nor elemental analysis was conclusive with respect to the composition of the isolated solid.49 The magnitude of the resonance at −11.22 ppm was reduced after several freeze−pump−thaw cycles, with a corresponding increase in the magnitudes of the two doublets at −11.07 and −11.09 ppm (relative to an internal standard of hexamethylbenzene). On the basis of these data, the resonance at −11.22 ppm is assigned to Cp*(iPr2MeP)RuH(N2) (4) and the resonances at −11.07 and −11.09 ppm are assigned as diastereomers of the nitrogen-bridged dinuclear complex Cp*(iPr2MeP)RuH(μ-N2)HRu(iPr2MeP)Cp* [meso compound 5 and a pair of enantiomers, 6 (Scheme 1)]. Subsequent exposure to 1 atm of H2 in pentane resulted in conversion of all three compounds to the trihydride 3 over the course of 20 h. Vibrational spectroscopy supports these structural assignments. A dinitrogen stretch is observed in the solution IR spectrum of the 4/5/6 mixture in cyclohexane at νN2 = 2090 cm−1 (Figure 2, top), and the complementary resonance Raman spectrum (514 nm excitation) exhibits the three expected N2 stretches, at 2039, 2049, and 2092 cm−1 (Figure 2, bottom). The dinitrogen stretches for compounds 5 and 6 are very similar in energy and lower in energy than the stretch observed for 4, as expected for these very similar bridging dinitrogen compounds. The energies of these bands are comparable to those of previously reported [Ru2(μ-N2)] complexes.48 In both spectra, broad absorptions corresponding to Ru−H stretching modes are observed from 1850 to 1950 cm−1 (Figure 2). While these bands are putatively the result of overlapping contributions from 4−6, deconvolution into their components is not straightforward. While monomeric complex 4 is an analogue of a recently reported iron dinitrogen complex Cp*(iPr2MeP)FeH(N2),50 there are some important differences in the behavior of these two compounds. The Fe analogue does not detectably dimerize to form analogues of 5 or 6; even after removal of nitrogen, no additional resonances that can be attributed to

Figure 1. Solid-state structure of the dimer of 2 (top). Carbon-bound hydrogen atoms have been omitted for the sake of clarity. View of the [RuH2Na]2 core of the molecule (bottom). Color code: C, gray; P, orange; H, white; O, red; Na, purple; Ru, teal.

dimer lies on a crystallographic inversion center at the center of an eight-membered [H−Ru−H−Na]2 ring. In the solid state, the hydride ligands are not related by symmetry, with each Na atom in close contact with three hydride ligands. This structure is not reflected by nuclear magnetic resonance (NMR) spectroscopy at room temperature in a benzene-d6 solution, which indicates that the hydride ligands are equivalent (δRu−H = −15.41 ppm, and JHP = 31.5 Hz). Hydride Transfer from 2 to 1. Treatment of a pentane slurry of 2 with 2 equiv of 1 in pentane resulted in precipitation of NaCl and a color change from purple to orange-red (Scheme 1). Workup and crystallization from diethyl ether B

DOI: 10.1021/acs.organomet.8b00738 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

Figure 2. Infrared (top) and resonance Raman (bottom) spectra of the mixture of 4−6 in cyclohexane. A Gaussian function is centered at 1905 cm−1 (red). Lorenztians centered at 2039 cm−1 (orange), 2049 cm−1 (green), and 2092 cm−1 (bue) were fit to the Raman spectrum. Gaussian functions centered at 1896 cm−1 (red) and 2090 cm−1 (blue) were fit to the IR data. Residuals are colored gray.

dimeric complexes were detected.50 Most likely, the larger size of Ru (vs Fe) reduces the steric demands at the metal center in these systems, allowing dimerization in the Ru case. Heterobimetallic Complexes. Reactions of 2 with other metal halide complexes lead to formation of hydride-bridged heterobimetallic complexes (rather than H transfer as in Scheme 1). For example, 2 reacted with 1 equiv of [(COD)IrCl]2 in Et2O to form Cp*(iPr2MeP)Ru(μ-H)2Ir(COD) (7, eq 3). In the solid-state structure (Figure 3A), the

Figure 3. (A) Solid-state structure of Cp*(iPr2MeP)Ru(μ-H)2Ir(COD) (7). (B) Solid-state structure of Cp*(iPr2MeP)Ru(μH)2Cu(IPr) (8). C-Bound H atoms have been omitted for the sake of clarity. Color code: C, gray; P, orange; H, white; N, light blue; Ru, teal; Ir, dark blue; Cu, orange-red.

Complex 2 also reacted with 2 equiv of (IPr)CuCl to form the yellow hydride-bridged heterobimetallic complex Cp*(iPr2MeP)Ru(μ-H)2Cu(IPr) [8 (Figure 3B and eq 4)]. This

Ru−Ir separation is 2.5659(2) Å, a relatively short distance enforced by the Ru(μ-H)2Ir core, which is slightly puckered [Σ∠ = 355.13(1)°]. The Ir atom is in a square planar coordination environment defined by the hydride ligands and two COD olefin centroids (Σ∠ = 359.9°). The 1H NMR spectrum of 7 is consistent with a Cs symmetric complex. The bridging Ru−H−Ir resonance at −9.52 ppm appears somewhat downfield of the hydride shift in 2; more significantly, the H−P coupling constant of 7 (JHP = 15.2 Hz) is much smaller than that of 2 (JHP = 31.5 Hz). This is most likely due to a high degree of covalency in the Ir−H bonds of the [Ru(μ-H2)Ir] core of 7, resulting in decreased covalency in the Ru−H linkages relative to those in the [Ru(μH2)Na] core of 2.

complex features a slightly puckered [Ru(μ-H)2Cu] core [Σ∠ = 352.795(5)°], trigonal planar coordination about Cu [Σ∠ = 359.781(3)°], and a moderately short Ru−Cu distance of 2.4833(4) Å. C

DOI: 10.1021/acs.organomet.8b00738 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

Spectra were recorded at room temperature (∼22 °C) and referenced to the residual protonated solvent for 1H. 31P{1H} NMR spectra were referenced relative to an 85% H3PO4 external standard (δ = 0). 13 C{1H} NMR spectra were calibrated internally with the resonance for the solvent relative to tetramethylsilane. For 13C{1H} NMR spectra, resonances obscured by the solvent signal have been omitted. The following abbreviations have been used to describe infrared features: “s” for strong, “m” for medium, “w” for weak, “v” for very, and “b” for broad. Elemental analyses were performed by the College of Chemistry Microanalytical Laboratory at the University of California, Berkeley. Resonance Raman Spectroscopy. A 0.1 mM 4/5/6 solution was prepared in cyclohexane and flame-sealed inside borosilicate pipet tips (1.5 mm inside diameter) under an atmosphere of nitrogen gas. Resonance Raman spectra were acquired with 3 mW of 514.5 nm light. Samples were translated perpendicular to the beam at a rate of 0.5 mm/s to mitigate the effects of photoalteration. Both polarizations of scattered light were collected through a 100 μm slit in a 90° scattering geometry. Spectra were resolved in a 2 m Spex 1401 double spectrograph and read out on a liquid nitrogen-cooled CCD (Roper Scientific LN/CCD 1100). Synthesis of [Na(solv)][Cp*(iPr2MeP)RuH2] (2). Two equivalents of NaBHEt3 (1.0 mL, 1.0 M in THF) were added to a solution of 1 (200 mg, 0.50 mmol) in 10 mL of Et2O at −35 °C. The deep purple solution rapidly changed color to orange-yellow. The solution was allowed to warm to room temperature while being stirred for 2 h and then filtered through Celite. After removal of volatile components in vacuo, the resulting yellow solid was recrystallized from Et2O (∼10 mL) at −35 °C. Yield: 0.15 g, 64% over two crops. Anal. Calcd for C17H34NaPRu: C, 51.89; H, 8.71. Found: C, 52.08; H, 9.05. For analysis, the crystals were dried in vacuo for 12 h to remove Nacoordinated solvent; this procedure was not followed for crystals intended for synthetic applications, as the solvent-free compound was found to be unstable to long-term storage. 1H NMR (400 MHz, benzene-d6): δ 3.72−3.48 (m, 2H, THF OCH2), 3.26 (q, J = 7.0 Hz, 2H, Et2O OCH2), 2.18 (s, 15H, Cp*), 1.72 (h, J = 7.0 Hz, 2H, PCHMe2), 1.47−1.37 (m, 2H, THF OCH2CH2), 1.19−1.02 (m, 18H; PMe, PCHMe2, Et2O OCH2Me), −15.42 (d, J = 31.5 Hz, 2H, RuH). Chemical shifts and integrations provided a solvate containing an ∼1:1 THF:Et2O ratio; the solvated complex was used to improve solubility in benzene. 13C{1H} NMR (101 MHz, benzene-d6): δ 84.12, 67.87, 65.93, 27.74 (d, J = 19.5 Hz), 25.81, 19.50 (d, J = 6.3 Hz), 18.29, 15.61, 14.43, 12.61. 31P{1H} NMR (162 MHz, benzened6): δ 64.22. FTIR (benzene-d6): 2969 (s), 2950 (s), 2927 (m), 2897 (s), 2867 (s), 1811 (m, br), 1709 (m, br) cm−1. Synthesis of [Cp*(iPr2MeP)RuH]nN2 (n = 1 for 4, and n = 2 for 5 and 6). A solution of 1 (0.088 g, 0.22 mmol) in 2 mL of pentane was added to a slurry of 2 (0.100 g, 0.11 mmol) in 2 mL of pentane. The resulting solution was stirred for 1 h, over which time it turned from bright purple to red-orange. The solution was filtered and concentrated in vacuo to give a yellow-orange residue. This was crystallized from Et2O (4 mL) at −35 °C to give a microcrystalline yellow powder. Yield: 0.067 g, 39% (for n = 1). Anal. Calcd for C17H33N2PRu: C, 51.37; H, 8.37; N, 7.05. Found: C, 51.67; H, 8.24; N, 3.59. The low nitrogen content could be due to incomplete combustion or loss of dinitrogen. 1H NMR (600 MHz, cyclohexaned12): δ 1.85 (s), 1.84 (s), 1.80−1.65 (m), 1.13 (dd, J = 15.2, 7.2 Hz), 1.09−0.97 (m), 0.95 (d, J = 7.0 Hz), 0.85 (dd, J = 15.6, 7.1 Hz), −11.07 (d, J = 40.8 Hz, 2H, 5/6 RuH), −11.08 (d, J = 40.9 Hz, 5/6 RuH), −11.22 (d, J = 39.7 Hz, 4 RuH). 31P{1H} NMR (243 MHz, cyclohexane-d12): δ 59.41, 59.08, 55.70. FTIR (cyclohexane): 2090 (νN2), 1896 (νRuH) cm−1. Raman (cyclohexane): 2092 (νN2), 2049 (νN2), 2039 (νN2), 1905 (νRuH) cm−1. Synthesis of Cp*(iPr2MeP)Ru(μ-H)2Ir(COD) (7). A solution of [(COD)IrCl]2 (0.036 g, 0.055 mmol) in 4 mL of Et2O was added to a stirred solution of 2 (0.050 g, 0.055 mmol) in 2 mL of Et2O. The solution rapidly became deep red. After the solution had been stirred for 30 min, the volatile components were removed in vacuo and the resulting deep red residue was extracted with 2 × 4 mL of pentane.

The 1H NMR spectrum of 8 is consistent with Cs symmetry, with the two bridging hydrides manifested as a single resonance at −14.65 ppm with an H−P coupling constant (JPH = 23.9 Hz) intermediate between the values for 2 (31.5 Hz) and 7 (15.2 Hz). The different values for the coupling constants among these three complexes presumably reflect a variability in the strength of the bonding interactions of [Cp*(iPr2MeP)Ru] to the bridging hydride ligands (Table 1). Table 1. Comparison of NMR and IR Spectroscopic Data for 2, 7, and 8 2 7 8

δRuH (ppm)

JPH (Hz)

νRuH (cm−1)

dMM (Å)

FSRb

−15.41 −9.52 −14.65

31.5 15.2 23.9

1811, 1709 1556,a 1468a 1649, 1571

2.981(1) 2.5659(2) 2.4833(4)

1.06 1.04 1.05

a Broad IR bands partially obscured by other features. bDefined as dMM (RM1 + RM2)−1. Radii taken from ref 51.

Compound 8 bears a striking resemblance to an Fe complex described by Mankad and co-workers, Cp(PPh3)Fe(μH)2CuIPr.52 These molecules are structurally very similar, exhibiting M−Cu (M = Ru or Fe) distances with very similar formal shortness ratios [FSRs; 1.05 for 8 vs 1.04 for Cp(PPh3)Fe(μ-H)2CuIPr]. Infrared spectra suggest that the Ru−H bond strength decreases in the order 2 > 8 > 7 (Table 1). While the IR spectrum of 2 has two bands that can clearly be attributed to Ru−H stretches at 1811 and 1709 cm−1, these bands red-shift in 8 to 1659 and 1571 cm−1, respectively; for 7, these bands are even lower in energy, at 1556 and 1440 cm−1, respectively. This red-shifting of the IR bands is consistent with an increase in H−M (M = Ir or Cu) bond strength and a corresponding decrease in Ru−H bond strength for such a bridging ligand. This is further supported by the similar FSRs for all three metal complexes [1.04−1.06 (Table 1)].

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CONCLUSION The results described above demonstrate the utility of 2 as a hydride-based nucleophile to form bimetallic complexes, expanding the scope29−33,35 of nucleophilic Ru hydride anions to the ubiquitous half-sandwich architecture. The stability of bimetallic complexes with bridging μ-N2 or μ-H ligands likely reflects a high degree of electrophilicity on Ru in the Cp*(iPr2MeP)RuH fragment, and the dinitrogen equilibrium products should serve as a convenient synthon for this fragment. Between 2 and this Cp*(iPr2MeP)RuH synthon, functionalization at Ru in the [Cp*(iPr2MeP)Ru] fragment can make use of either electrophilic or nucleophilic strategies. Such studies with group 14 elements are currently underway.

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EXPERIMENTAL SECTION

General Considerations. All manipulations were carried out using standard Schlenk or inert atmosphere glovebox techniques with an atmosphere of dry dinitrogen. Pentane was dried over activated alumina and stored over molecular sieves (4 Å) prior to use. Benzened6 was degassed with three freeze−pump−thaw cycles and stored over activated molecular sieves (4 Å) for 24 h prior to use. [(COD)IrCl]2 was purchased from Strem chemicals. IPrCuCl was prepared by the reaction of free IPr with CuCl in THF; purification followed literature procedures.53 Cp*(iPr2MeP)RuCl54,55 and Cp*(iPr2MeP)RuH356,57 were prepared by literature procedures. NMR spectra were recorded using a Bruker Avance 400, 500, or 600 MHz spectrometer equipped with a 5 mm broad band probe. D

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Organometallics The combined extracts were concentrated to 1 mL and stored at −35 °C to afford deep red blocks. Yield: 0.028 g, 38%. Anal. Calcd for C25H46IrPRu: C, 44.75; H, 6.91. Found: C, 44.87; H, 7.09. 1H NMR (600 MHz, benzene-d6): δ 4.20 (d, J = 4.0 Hz, 4H, COD CH), 2.31 (s, 2H, COD CH2), 2.11 (s, 2H, COD CH2), 1.87 (d, J = 1.6 Hz, 15H, Cp*), 1.80−1.69 (sept, J = 7.0 Hz, 2H, PCHMe2), 1.61 (s, 2H, COD CH2), 1.56 (s, 2H, COD CH2), 1.25 (d, J = 6.6 Hz, 3H, PCH3), 1.17 (dd, J = 15.2, 7.0 Hz, 6H, PCHMe2), 0.97 (dd, J = 13.4, 6.9 Hz, 6H, PCHMe2), − 9.52 (d, J = 15.2 Hz, 2H, RuHIr). 13C{1H} NMR (151 MHz, benzene-d6): δ 84.78 (d, J = 2.4 Hz), 32.69 (br), 30.67 (d, J = 23.7 Hz), 18.84 (d, J = 4.5 Hz), 18.14, 13.22, 9.21 (d, J = 16.0 Hz). 31P{1H} NMR (243 MHz, benzene-d6): δ 53.66. FTIR (benzene-d6): 2972 (s), 2959 (s), 2917 (s), 2871 (s), 2826 (m), 1575 (m), 1556 (m, br), 1539 (m), 1468 (m, br) 1431 (m), 1374 (m) cm−1. Synthesis of Cp*(iPr2MeP)Ru(μ-H)2Cu(IPr) (8). Complex 2 (0.060 g, 0.065 mmol) was dissolved in 6 mL of Et2O, and the resulting solution was added dropwise to a suspension of IPrCuCl (0.060 g, 0.13 mmol) in 2 mL of Et2O. The resulting solution was stirred for 30 min and then filtered before the volatile components were removed in vacuo. The resulting yellow residue was dissolved in 4 mL of pentane and stored at −35 °C to afford yellow blocks. Yield: 0.080 g, 76%. Anal. Calcd for C44H70CuN2PRu: C, 64.24; H, 8.58; N, 3.41. Found: C, 64.24; H, 8.64; N, 3.44. 1H NMR (600 MHz, benzene-d6): δ 7.24 (t, J = 7.8 Hz, 2H, Dipp p-CH), 7.13 (d, J = 7.8 Hz, 4H, Dipp o-CH), 6.29 (s, 2H, NHC CH), 2.86 (hept, J = 6.9 Hz, 4H, Dipp CHMe2), 2.02 (d, J = 1.1 Hz, 15H, Cp*), 1.54 (d, J = 6.9 Hz, 12H, Dipp CHMe2), 1.37 (sept, J = 6.9 Hz, 2H, PCHMe2), 1.08 (d, J = 6.9 Hz, 12H, Dipp CHMe2), 1.05−0.98 (m, 12H, PCHMe2), 0.69 (d, J = 6.1 Hz, 3H, PCH3), −14.65 (d, J = 23.9 Hz, 2H, RuHCu). 13 C{1H} NMR (151 MHz, benzene-d6): δ 145.81, 136.70, 130.05, 124.34, 121.58, 86.21 (d, J = 2.2 Hz), 28.97 (d, J = 19.9 Hz), 28.95, 24.51, 23.96, 19.28 (d, J = 6.0 Hz), 18.13, 13.96. 31P{1H} NMR (243 MHz, benzene-d6): δ 62.97. FTIR (benzene-d6): 2962 (s), 2915 (s), 2866 (s), 1649 (m, br), 1571 (m, br) cm−1.

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research used resources of the Advanced Light Source, which is a U.S. Department of Energy Office of Science User Facility under Contract DE-AC02-05CH11231

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(1) Churchill, M. R.; Ni, S. W. Y. Crystal Structure and Location of the Bridging Hydride Ligand in μ-Chloro-μ-Hydrido-Bis[Chloro(Pentamethylcyclopentadi-enyl)Rhodium(III)], a Homonogeneous Hydrogenation Catalyst. J. Am. Chem. Soc. 1973, 95, 2150−2155. (2) Green, M.; Howard, J. A. K.; Proud, J.; Spencer, J. L.; Stone, F. G. A.; Tsipis, C. A. A New Class of Hydride-Bridged Platinum Complex with Application as Hydrosilylation Catalysts; Molecular and X-Ray Crystal Structure of trans–Di-μ-Hydrido-Bis(Tricyclohexylphosphine)Bis(Triethylsilyl) Diplatinum(Pt−Pt). J. Chem. Soc., Chem. Commun. 1976, 671−672. (3) Shvo, Y.; Czarkie, D.; Rahamim, Y.; Chodosh, D. F. A New Group of Ruthenium Complexes: Structure and Catalysis. J. Am. Chem. Soc. 1986, 108, 7400−7402. (4) Bianchini, C.; Meli, A.; Vacca, A.; Laschi, F.; Zanello, P.; Ramirez, J. A. Synthesis, Characterization, and Electrochemical Properties of a Family of Dinuclear Rhodium Complexes Containing Two Terminal Hydride Ligands and Two Hydride (or Chloride) Bridges. Stoichiometric and Catalytic Hydrogenation Reactions of Alkynes and Alken. Inorg. Chem. 1988, 27, 4429−4435. (5) Fuchikami, T.; Ubukata, Y.; Tanaka, Y. Group 6 Anionic μhydride Complexes HM2(CO)10]− (M = Cr, Mo, W): New Catalysts for Hydrogenation and Hydrosilylation. Tetrahedron Lett. 1991, 32, 1199−1202. (6) Brunner, H.; Mijolovic, D. Enantioselective Catalysis: Part 129. A New Rhodium(I) Complex with a μ2-H Bridged Cp2WH2 Ligand. J. Organomet. Chem. 1999, 577, 346−350. (7) Tsipis, C. A.; Kefalidis, C. E. How Efficient Are the HydridoBridged Diplatinum Catalysts in the Hydrosilylation, Hydrocyanation, and Hydroamination of Alkynes: A Theoretical Analysis of the Catalytic Cycles Employing Electronic Structure Calculation Methods. Organometallics 2006, 25, 1696−1706. (8) Esteruelas, M. A.; García-Yebra, C.; Oñate, E. [H(EtOH)2][{OsCl(η4-COD)}2(μ-H)(μ-Cl)2] as an Intermediate for the Preparation of [OsCl2 (COD)]x and Its Activity as an Ionic Hydrogenation and Etherification Catalyst. Organometallics 2008, 27, 3029−3036. (9) Albahily, K.; Al-Baldawi, D.; Gambarotta, S.; Koç, E.; Duchateau, R. Isolation of a Chromium Hydride Single-Component Ethylene Polymerization Catalyst. Organometallics 2008, 27, 5943−5947. (10) Yi, C. S.; Lee, D. W. Efficient Dehydrogenation of Amines and Carbonyl Compounds Catalyzed by a Tetranuclear Ruthenium-μ-oxoμ-hydroxo-Hydride Complex. Organometallics 2009, 28, 947−949. (11) Kure, B.; Taniguchi, A.; Nakajima, T.; Tanase, T. HydrideBridged NiRh Complexes with Tunable N3S2 Dithiolato Ligands and Their Utilization as Catalysts for Hydrogenation of Aldehydes and CO2 in Aqueous Media. Organometallics 2012, 31, 4791−4800. (12) Chatterjee, B.; Gunanathan, C. Ruthenium Catalyzed Selective Hydrosilylation of Aldehydes. Chem. Commun. 2014, 50, 888−890. (13) Chen, J.; Chen, X.; Zhu, C.; Zhu, J. Room Temperature Polymerization of Norbornene with a Hydride-Bridged Dinuclear Ruthenium Complex System. J. Mol. Catal. A: Chem. 2014, 394, 198− 204. (14) Tong, P.; Xie, W.; Yang, D.; Wang, B.; Ji, X.; Li, J.; Qu, J. Structural Characterization and Proton Reduction Electrocatalysis of Thiolate–Bridged Bimetallic (CoCo and CoFe) Complexes. Dalt. Trans. 2016, 45, 18559−18565. (15) Crimmin, M. R.; Hicken, A.; White, A. J. P. Selective Reduction of CO2 to a Formate Equivalent with Heterobimetallic Gold−Copper Hydride Complexes. Angew. Chem., Int. Ed. 2017, 56, 15127−15130. (16) Barton, B. E.; Rauchfuss, T. B. Terminal Hydride in [FeFe]Hydrogenase Model Has Lower Potential for H2 Production than the Isomeric Bridging Hydride. Inorg. Chem. 2008, 47, 2261−2263.

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CCDC 1872548−1872550 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Patrick W. Smith: 0000-0001-5575-4895 Rex C. Handford: 0000-0002-3693-1697 T. Don Tilley: 0000-0002-6671-9099 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was funded by the National Science Foundation via Grant CHE-1566538. UC Berkeley ChexRay is funded by the National Institutes of Health via Grant S10-RR027172. This E

DOI: 10.1021/acs.organomet.8b00738 Organometallics XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.organomet.8b00738 Organometallics XXXX, XXX, XXX−XXX