Bridging Hydride Ligands Research Articles

New Reactions of Terminal Hydrides on a Diiron Dithiolate

Mechanisms for biological and bioinspired dihydrogen activation and production often invoke the intermediacy of diiron dithiolato dihydrides. The first example of such a Fe2(SR)2H2 species is provided by the complex [(term-H)(μ-H)Fe2(pdt)(CO)(dppv)2] ([H1H](0)). Spectroscopic and computational studies indicate that [H1H](0) contains both a bridging hydride and a terminal hydride, which, notably, occupies a basal site. The synthesis begins with [(μ-H)Fe2(pdt)(CO)2(dppv)2](+) ([H1(CO)](+)), which undergoes substitution to afford [(μ-H)Fe2(pdt)(CO)(NCMe)(dppv)2](+) ([H1(NCMe)](+)). Upon treatment of [H1(NCMe)](+) with borohydride salts, the MeCN ligand is displaced to afford [H1H](0). DNMR (EXSY, SST) experiments on this complex show that the terminal and bridging hydride ligands interchange intramolecularly at a rate of 1 s(-1) at -40 °C. The compound reacts with D2 to afford [D1D](0), but not mixed isotopomers such as [H1D](0). The dihydride undergoes oxidation with Fc(+) under CO to give [1(CO)](+) and H2. Protonation in MeCN solution gives [H1(NCMe)](+) and H2. Carbonylation converts [H1H](0) into [1(CO)](0).

PNP-Ligated Heterometallic Rare-Earth/Ruthenium Hydride Complexes Bearing Phosphinophenyl and Phosphinomethyl Bridging Ligands

The reaction of rare-earth bis(alkyl) complexes containing a bis(phosphinophenyl)amido pincer (PNP), LnPNPiPr(CH2SiMe3)2 (1-Ln, Ln = Y, Ho, Dy), with ruthenium trihydride phosphine complexes, Ru(C5Me5)H3PPh3 and Ru(C5Me5)H3PPh2Me, gave the corresponding bimetallic Ln/Ru complexes bearing two hydride ligands and a bridging phosphinophenyl (μ-C6H4PPh2-κP:κC1, 2a-Ln) or a bridging phosphinomethyl ligand (μ-CH2PPh2-κP:κC, 2b-Ln), respectively. Reaction of 2a-Y with CO gas at 1 atm and at 20 °C in toluene-d8 afforded the complex 3a-Y, which bears a bridging pseudooxymethylene ligand (μ-OCH(o-C6H4)PPh2-κP:κO) and a bridging hydride ligand on the Y/Ru centers. Computational studies by the DFT method suggested that 3a-Y was formed in two steps: first the coordination of CO (ΔG(B3PW91) = 22.9; ΔG(M06) = 14.9 kcal/mol) and migratory insertion of the Y–C6H4 group (ΔG⧧(B3PW91) = 13.3; ΔG⧧(M06) = 16.7 kcal/mol), followed by a rapid intramolecular hydride migration to the resulting acyl group. Complex 2b-Y reacted with organic nitriles (tBuCN, CH3CN, PhCN), an aldimine (PhNCHPh), an isonitrile (tBuNC), and group IX transition-metal carbonyls (M(C5Me5)(CO)2, M = Rh, Ir) via insertion of the reactive Y–CH2 group into the unsaturated bond. These reactions afforded complexes with new ligand scaffolds, including a bridging alkylideneamidophosphine (4b-Y), an amidophosphine (7b-Y), an η2-iminoacylphosphine (8b-Y), and oxycarbenephosphine (9b-Y and 10b-Y) ligands at the binuclear Y/Ru core. All of these reaction products were structurally characterized by X-ray crystallography, NMR spectroscopy, and elemental analyses.

Observation of TiH5 and TiH7 in Bulk-Phase TiH3 Gels for Kubas-Type Hydrogen Storage

The lack of an efficient hydrogen storage material has so far hindered the implementation of hydrogen as an energy vector, that is, a substance that allows the transfer through space and time of a certain quantity of energy from its original source. This work presents porous Ti(III) hydride gels as a promising new hydrogen storage material, exploiting the first example of a solid-state homoleptic metal hydride that binds further H2 ligands using the Kubas interaction. These materials use bridging hydride ligands as an ultralightweight structural feature to support a microporous network of Ti binding sites for molecular H2 chemisorption. High-pressure Raman spectroscopy confirmed the first evidence of TiH5 and TiH7 species, in some ways analogous to hypervalent MH5 and MH7 (M = Si, Ge, Sn) species. The material with the highest capacity has an excess reversible storage of 3.49 wt % at 140 bar and 298 K without saturation, corresponding to a volumetric density of 44.3 kg/m3, comparable to the DOE 2017 volum...

Bimetallic osmium-tin complexes: Stannylene and hydrostannylene clusters upon addition of Ph3SnH to unsaturated triosmium clusters [(μ-H)2Os3(CO)8(μ-diphosphine)] (diphosphine = dppm, dppf)

Products of the addition of Ph3SnH to the unsaturated triosmium clusters [(μ-H)2Os3(CO)8(μ-dppm)] (1) and [(μ-H)2Os3(CO)8(μ-dppf)] (2) are highly dependent on the nature of the diphosphine. With the rigid bis(diphenylphosphino)methane (dppm), the stannylene complex [H2Os3(CO)7(μ-SnPh2)2(μ-dppm)] (3) is the major cluster product (35% yield), resulting from both Sn–H and Sn–C bond activation, while two previously reported triphenyltin complexes, [(μ-H)2Os3(CO)8(SnPh3)2(μ-dppm)] (4) (10% yield) and [(μ-H)2Os3(CO)8(SnPh3){μ-Ph2PCH2P(Ph)C6H4}] (5) (11% yield) also result. Biphenyl is also a co-product of this reaction and it is postulated to be formed concomitantly with 3. A similar reaction with the highly flexible 1,1′-bis(diphenylphosphino)ferrocene (dppf) complex leads to the formation of four tin-containing complexes: two previously reported compounds [HOs(CO)4(SnPh3)] (6) (8% yield) and [Os2(CO)6(SnPh3)2(μ-SnPh2)2] (8) (5% yield), and the new triphenyltin and hydrostannylene clusters [H(μ-H)2Os3(CO)8(SnPh3)(μ-dppf)] (10) (22% yield) and [(μ-H)Os2(CO)4(SnPh3)2(μ-HSnPh2)(μ-dppf)] (9) (12% yield) respectively, together with the dihydroxy cluster [Os3(CO)8(μ-OH)2(μ-dppf)] (7). Two of these new clusters have been characterized by X-ray crystallography. Cluster 3 consists of a central Os3 triangle with two stannylene groups, each bridging one Os–Os edge, a dppm ligand that bridges the third Os-Os edge, and two terminal hydride ligands. Cluster 10 consists of an Os3 triangle with a terminal SnPh3 group, one terminal and two bridging hydride ligands, and a bridging dppf ligand. The new compounds 3, 7, 9, and 10 have been investigated by electronic structure calculations, and the computed ground-state structures are discussed relative to the X-ray crystallographic structures.

2-[(Diphenylphosphino)methyl]-6-methylpyridine (PN) coordination chemistry at triosmium clusters: Regiospecific ligand activation and DFT evaluation of the isomeric Os3(CO)10(PN) clusters

The reaction of 2-[(diphenylphosphino)methyl]-6-methylpyridine (PN) with Os3(CO)12−n(MeCN)n [where n = 0 (1), 1 (2), 2 (3)] has been investigated. Os3(CO)12 reacts with PN in the presence of Me3NO to afford the clusters Os3(CO)11(κ1-PN) (4) and 1,2-Os3(CO)10(κ1-PN)2 (5). X-ray diffraction analyses confirm the equatorial coordination of the phosphine(s) in 4 and 5, with the two phosphines in the latter cluster exhibiting a 1,2-trans orientation about the Os–Os vector that contains the two ligands. Treatment of the MeCN-substituted cluster Os3(CO)11(MeCN) and PN (1:1 ratio) in CH2Cl2 gives clusters 4 and 5, in addition to HOs3(η1-Cl)(CO)10(κ1-PN) (6) as a result of competitive activation of the reaction solvent. Cluster 6 contains 48e and the diffraction structure reveals the presence of axial chloride and equatorial phosphine ligands which are located on adjacent osmium atoms. The bridging hydride ligand in 6 spans the Cl,P-substituted Os–Os vector. The reaction of Os3(CO)10(MeCN)2 with PN furnishes 5, 6, and 1,1-Os3(CO)10(κ2-PN) (7) in yields that are dependent on the reagent stoichiometry and reaction solvent. The solid-state structure of 7 confirms the chelation of the PN ligand to a single osmium atom via the pyridine and phosphine moieties at axial and equatorial sites, respectively. The bonding in 7 relative to other possible stereoisomers has been explored by DFT calculations, and the diffraction structure is computed as the thermodynamically most stable form of this cluster. Cluster 4 is photosensitive and CO loss gives 7, in addition to the formation of the dihydride H2Os3(CO)8[μ-CH(NC5H3)CH2PPh2] (8), whose origin derives from the double metalation of the C-6 methyl group of the PN ligand in 7. Photolysis of 7 yields 8 without detectable observation of the expected intermediate hydride HOs3(CO)9[μ-CH2(NC5H3)CH2PPh2]. The PN ligand in 7 undergoes P–C bond activation in toluene at 110 °C to afford the 50e cluster Os3(CO)9(μ-C6H4)(μ-PPh) (9), which contains face-capping benzyne and phosphinidene moieties. The bonding between the benzyne moiety and the opened Os3 frame in 9 has been examined computationally, and these data are discussed relative to σ and π bonding contributions from the metalated aryl ring to the cluster polyhedron.

Isolation of a Mixed Valence Diiron Hydride: Evidence for a Spectator Hydride in Hydrogen Evolution Catalysis

The mixed-valence diiron hydrido complex (μ-H)Fe2(pdt)(CO)2(dppv)2 ([H1](0), where pdt =1,3-propanedithiolate and dppv = cis-1,2-C2H2(PPh2)2), was generated by reduction of the differous hydride [H1](+) using decamethylcobaltocene. Crystallographic analysis shows that [H1](0) retains the stereochemistry of its precursor, where one dppv ligand spans two basal sites and the other spans apical and basal positions. The Fe---Fe bond elongates to 2.80 from 2.66 Å, but the Fe-P bonds only change subtly. Although the Fe-H distances are indistinguishable in the precursor, they differ by 0.2 Å in [H1](0). The X-band electron paramagnetic resonance (EPR) spectrum reveals the presence of two stereoisomers, the one characterized crystallographically and a contribution of about 10% from a second symmetrical (sym) isomer wherein both dppv ligands occupy apical-basal sites. The unsymmetrical (unsym) arrangement of the dppv ligands is reflected in the values of A((31)P), which range from 31 MHz for the basal phosphines to 284 MHz for the apical phosphine. Density functional theory calculations were employed to rationalize the electronic structure of [H1](0) and to facilitate spectral simulation and assignment of EPR parameters including (1)H and (31)P hyperfine couplings. The EPR spectra of [H1](0) and [D1](0) demonstrate that the singly occupied molecular orbital is primarily localized on the Fe center with the longer bond to H, that is, Fe(II)-H···Fe(I). The coupling to the hydride is A((1)H) = 55 and 74 MHz for unsym- amd sym-[H1](0), respectively. Treatment of [H1](0) with H(+) gives 0.5 equiv of H2 and [H1](+). Reduction of D(+) affords D2, leaving the hydride ligand intact. These experiments demonstrate that the bridging hydride ligand in this complex is a spectator in the hydrogen evolution reaction.

Tetraruthenium carbonyl complexes containing germyl and stannyl ligands from the reactions of Ru4(CO)13(μ-H)2 with HGePh3 and HSnPh3

The compounds Ru4(CO)12(GePh3)2(μ-H)4, 1 and Ru4(CO)12(SnPh3)2(μ-H)4, 2 were obtained from the reactions of Ru4(CO)13(μ-H)2 with HGePh3 and HSnPh3, respectively. Both compounds contain a nearly planar butterfly structure for the four metal atoms with two GePh3/SnPh3 ligands and four bridging hydride ligands around the periphery of the cluster. When heated, 1 and 2 were converted into the complexes Ru4(CO)12(μ4-EPh)2, 3, E = Ge, and 4, E = Sn, by cleavage of two phenyl groups from each of the GePh3 ligands. Compounds 3 and 4 contain square planar arrangements of the four ruthenium atoms with quadruply bridging germylyne and stannylyne ligands on opposite sides of the square plane. The bonding and electronic transitions of 3 were analyzed by DFT computational analyses.

Electrochemical and Theoretical Investigations of the Role of the Appended Base on the Reduction of Protons by [Fe2(CO)4(κ2‐PNPR)(μ‐S(CH2)3S] (PNPR={Ph2PCH2}2NR, R=Me, Ph)

The behavior of [Fe(2)(CO)(4)(κ(2)-PNP(R))(μ-pdt)] (PNP(R) =(Ph(2)PCH(2))(2)NR, R=Me (1), Ph (2); pdt=S(CH(2))(3)S) in the presence of acids is investigated experimentally and theoretically (using density functional theory) in order to determine the mechanisms of the proton reduction steps supported by these complexes, and to assess the role of the PNP(R) appended base in these processes for different redox states of the metal centers. The nature of the R substituent of the nitrogen base does not substantially affect the course of the protonation of the neutral complex by CF(3)SO(3)H or CH(3)SO(3)H; the cation with a bridging hydride ligand, 1 μH(+) (R=Me) or 2 μH(+) (R=Ph) is obtained rapidly. Only 1 μH(+) can be protonated at the nitrogen atom of the PNP chelate by HBF(4)·Et(2)O or CF(3)SO(3)H, which results in a positive shift of the proton reduction by approximately 0.15 V. The theoretical study demonstrates that in this process, dihydrogen can be released from a η(2)-H(2) species in the Fe(I)Fe(II) state. When R=Ph, the bridging hydride cation 2 μH(+) cannot be protonated at the amine function by HBF(4)·Et(2)O or CF(3)SO(3)H, and protonation at the N atom of the one-electron reduced analogue is also less favored than that of a S atom of the partially de-coordinated dithiolate bridge. In this situation, proton reduction occurs at the potential of the bridging hydride cation, 2 μH(+). The rate constants of the overall proton reduction processes are small for both complexes 1 and 2 (k(obs) ≈4-7 s(-1)) because of the slow intramolecular proton migration and H(2) release steps identified by the theoretical study.

Synthesis, Characterization, and Fluxional Behavior of a 34 Electron Homochiral Dimetallic Complex with an Unsupported Hydride Bridge between Two Ru Atoms

The binuclear η6-benzene cycloruthenated complex 2, which bears an unsupported bridging hydride ligand, was synthesized by treating the monomeric cationic cycloruthenated (R)-(+)-1-(1-naphthyl)ethylamine 1 with potassium hydroxide under biphasic conditions and then with an alcoholic solvent. Alternatively, compound 2 was prepared from an equimolar amount of compound 1 and the homologous monomeric hydrido complex 3. The crystal structure of 2 revealed π-stacking interactions between the naphthyl groups of each cyclometalated amine; the hydride ligand is bent, with a Ru–H–Ru angle of 145.3(10)°. Compound 2 is fluxional as shown by variable-temperature NMR analysis. DFT analysis of homochiral 2 and of its hypothetical heterochiral counterpart 2* revealed that dispersion-based π–π interactions between the cyclometalated ring are not the only interactions that must be taken into account to rationalize the conformational preference for 2. Indeed, the overall dispersion-based interactions between all the ligands of the connected metallacycles provide an additional 5 to 6 kcal/mol of stabilization energy for 2 regardless whether the π-stacking interactions between the naphthyl rings exist or not.

Binuclear rare-earth polyhydride complexes bearing both terminal and bridging hydride ligands

The first binuclear rare-earth tetrahydride complexes [(NCN)LnH2]2(THF)3 (1-Ln; LnY, Lu; NCNPhC(NC6H3iPr2-2,6)2) bearing both terminal and bridging hydride ligands were obtained by hydrogenolysis of the dialkyl precursors. These novel binuclear hydride complexes underwent unique Ln-H addition reactions with various unsaturated compounds such as 2,6-dimethylphenyl isocyanide, diphenylacetylene and 1,4-diphenyl-1,3-butadiyne.

Isolation, observation, and computational modeling of proposed intermediates in catalyticprotonreductions with the hydrogenase mimic Fe2(CO)6S2C6H4

Proposed electrocatalytic proton reduction intermediates of hydrogenase mimics were synthesized, observed, and studied computationally. A new mechanism for H(2) generation appears to involve Fe(2)(CO)(6)(1,2-S(2)C(6)H(4)) (3), the dianions {[1,2-S(2)C(6)H(4)][Fe(CO)(3)(μ-CO)Fe(CO)(2)](2-) (3(2-)), the bridging hydride {[1,2-S(2)C(6)H(4)][Fe(CO)(3)(μ-CO)(μ-H)Fe(CO)(2)]}(-), 3H(-)(bridging), and the terminal hydride 3H(-)(term-stag), {[1,2-S(2)C(6)H(4)][HFe(CO)(3)Fe(CO)(3)]}(-), as intermediates. The dimeric sodium derivative of 3(2-), {[Na(2)(THF)(OEt(2))(3)][3(2-)]}(2) (4) was isolated from reaction of Fe(2)(CO)(6)(1,2-S(2)C(6)H(4)) (3) with excess sodium and was characterized by X-ray crystallography. It possesses a bridging CO and an unsymmetrically bridging dithiolate ligand. Complex 4 reacts with 4 equiv. of triflic or benzoic acid (2 equiv. per Fe center) to generate H(2) and 3 in 75% and 60% yields, respectively. Reaction of 4 with 2 equiv. of benzoic acid generated two hydrides in a 1.7 : 1 ratio (by (1)H NMR spectroscopy). Chemical shift calculations on geometry optimized structures of possible hydride isomers strongly suggest that the main product, 3H(-)(bridging), possesses a bridging hydride ligand, while the minor product is a terminal hydride, 3H(-)(term-stag). Computational studies support a catalytic proton reduction mechanism involving a two-electron reduction of 3 that severs an Fe-S bond to generate a dangling thiolate and an electron rich Fe center. The latter iron center is the initial site of protonation, and this event is followed by protonation at the dangling thiolate to give the thiol thiolate [Fe(2)H(CO)(6)(1,2-SHSC(6)H(4))]. This species then undergoes an intramolecular acid-base reaction to form a dihydrogen complex that loses H(2) and regenerates 3.

Bonding and Reactivity in the Electronically Unsaturated Hydrogen-Bridged Dimer [Ru3(CO)8(μ3-CMe)(μ-H)2(μ3-H)]2

The electronically unsaturated complex [Ru3(CO)8(μ3-CMe)(μ-H)2(μ3-H)]2 (1), viewed as a dimer of the 46-electron fragment Ru3(CO)8(μ3-CMe)(μ-H)3, is held together by delocalized bonding involving two triply bridging hydride ligands. Compound 1 exhibits a dynamic activity in solution that equilibrates two of the three types of hydride ligands. Compound 1 reacts with 1,1-bis(diphenylphosphino)methane to form the macrocyclic complex [Ru3(CO)7(μ3-CMe)(μ-H)3]2(μ-dppm)2 (3).

Chalcogenide-capped triruthenium clusters: X-ray structures of [Ru3(CO)6(μ3-CO){P(C4H3S)3}(μ-dppm)(μ3-O)] and [(μ-H)2Ru3(CO)6{P(C4H3S)3}(μ-dppm)(μ3-S)

Treatment of [Ru3(CO)9{P(C4H3S)3}(μ-dppm)] (1) [dppm=bis(diphenylphosphino)methane] with molecular oxygen in benzene at 60°C affords oxo-capped [Ru3(CO)6(μ3-CO){P(C4H3S)3}(μ-dppm)(μ3-O)] (2), while with elemental sulfur and selenium related chalcogenide-capped clusters [Ru3(CO)6(μ3-CO){P(C4H3S)3}(μ-dppm)(μ3-E)] (3, E=S; 5, E=Se) and bis(chalcogenide) clusters [Ru3(CO)6{P(C4H3S)3}(μ-dppm)(μ3-E)2] (4, E=S; 6, E=Se) result. Reaction of 1 with H2S in refluxing THF affords the previously reported [(μ-H)2Ru3(CO)7(μ-dppm)(μ3-S)] (7) together with the new sulfido-capped dihydride [(μ-H)2Ru3(CO)6{P(C4H3S)3}(μ-dppm)(μ3-S)] (8). All new compounds have been characterized by spectroscopic data, and 2 and 8 by single-crystal X-ray diffraction analyses. Oxo-capped 2 consists of a triangular ruthenium framework capped on opposite sides by oxo and carbonyl groups, while 8 consists of a ruthenium triangle by a capping sulfido ligand and two inequivalent bridging hydride ligands.

Hydride Mobility in Trinuclear Sulfido Clusters with the Core [Rh3(μ‐H)(μ3‐S)2]: Molecular Models for Hydrogen Migration on Metal Sulfide Hydrotreating Catalysts

The treatment of [{Rh(μ-SH){P(OPh)(3)}(2)}(2)] with [{M(μ-Cl)(diolef)}(2)] (diolef=diolefin) in the presence of NEt(3) affords the hydrido-sulfido clusters [Rh(3)(μ-H)(μ(3)-S)(2)(diolef){P(OPh)(3)}(4)] (diolef=1,5-cyclooctadiene (cod) for 1, 2,5-norbornadiene (nbd) for 2, and tetrafluorobenzo[5,6]bicyclo[2.2.2]octa-2,5,7-triene (tfb) for 3) and [Rh(2)Ir(μ-H)(μ(3)-S)(2)(cod){P(OPh)(3)}(4)] (4). Cluster 1 can be also obtained by treating [{Rh(μ-SH){P(OPh)(3)}(2)}(2)] with [{Rh(μ-OMe)(cod)}(2)], although the main product of the reaction with [{Ir(μ-OMe)(cod)}(2)] was [RhIr(2)(μ-H)(μ(3)-S)(2)(cod)(2){P(OPh)(3)}(2)] (5). The molecular structures of clusters 1 and 4 have been determined by X-ray diffraction methods. The deprotonation of a hydrosulfido ligand in [{Rh(μ-SH)(CO)(PPh(3))}(2)] by [M(acac)(diolef)] (acac=acetylacetonate) results in the formation of hydrido-sulfido clusters [Rh(3)(μ-H)(μ(3)-S)(2)(CO)(2) (diolef)(PPh(3))(2)] (diolef=cod for 6, nbd for 7) and [Rh(2)Ir(μ-H)(μ(3)-S)(2)(CO)(2)(cod)(PPh(3))(2)] (8). Clusters 1-3 and 5 exist in solution as two interconverting isomers with the bridging hydride ligand at different edges. Cluster 8 exists as three isomers that arise from the disposition of the PPh(3) ligands in the cluster (cis and trans) and the location of the hydride ligand. The dynamic behaviour of clusters with bulky triphenylphosphite ligands, which involves hydrogen migration from rhodium to sulfur with a switch from hydride to proton character, is significant to understand hydrogen diffusion on the surface of metal sulfide hydrotreating catalysts.

Theoretical topological analysis of the electron density in a series of triosmium carbonyl clusters: [Os 3(CO) 12], [Os 3(μ-H) 2(CO) 10], [Os 3(μ-H)(μ-OH)(CO) 10], and [Os 3(μ-H)(μ-Cl)(CO) 10

A number of local and integral topological parameters of the electron density for the triosmium triangular carbonyl clusters [Os 3(CO) 12] ( 1), [Os 3(μ-H) 2(CO) 10] ( 2), [Os 3(μ-H)(μ-OH)(CO) 10] ( 3), and [Os 3(μ-H)(μ-Cl)(CO) 10] ( 4) have been calculated and interpreted under the perspective of the relativistic and non-relativistic Quantum Theory of Atoms in Molecules (QTAIM). These results have allowed a comparison between topological properties of related but different atom–atom interactions, such as different Os–Os bond orders, H-bridged versus X-bridged (X = OH, Cl) and ligand-unbridged Os–Os interactions, and Os–H versus Os–OH and Os–Cl interactions. For compound 1, an interaction of 3c–2e type between the three metal atoms has been found. The local topological parameters of the unbridged Os–Os bonds in compound 2 differ considerably from those of the bridged Os–Os bond, for which a bond path was nevertheless observed. The calculated topological indexes indicate that bridging OH and Cl ligands are more efficient than bridging hydride ligands in delocalizing the electron density of bridged metal atoms; in fact, no direct bond path has been found for the interaction between bridged Os atoms in 3 or 4, although a non-negligible delocalization index δ(Os⋯Os) has been obtained for these non-bonding interactions. A multicenter 4c–4e interaction is proposed to exist in the bridged parts, Os 2(μ-H)(μ-X) (X = H ( 2), OH ( 3), Cl ( 4)), of compounds 2– 4. Compared with compound 2, the smaller electron density shared by the bridged Os atoms in compounds 3 and 4 is compensated by a greater electron density shared by the atoms in Os–X (X = O, Cl) bonds.

ChemInform Abstract: Metal—Metal Bonding in Bridging Hydride and Alkyl Compounds

AbstractReview: 114 refs.

A nickel–manganese catalyst as a biomimic of the active site of NiFe hydrogenases: a combined electrocatalytical and DFT mechanistic study

The dinuclear nickel–manganese complex [Ni(xbsms)Mn(CO)3(H2O)]+ (H2xbsms = 1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl)benzene) is reported as a bio-inspired mimic of the active site of NiFe hydrogenases catalyzing hydrogen evolution from trifluoroacetic acid in DMF with an overpotential requirement of 860 mV. This is higher than that displayed by Ni–Ru systems [Canaguier et al., Chem.–Eur. J., 2009, 15, 9350–9364] but similar to that found for related noble metal free Ni–Fe mimics [Canaguier et al., Chem. Commun. 2010, 46, 5876–5878]. A combined electrochemical and theoretical (DFT) study suggests a heterolytic mechanism for hydrogen evolution from a hydride derivative. The structure of the active intermediate, with a bridging hydride ligand between Ni and Mn, resembles that of the Ni–C active state of NiFe hydrogenases.

Transformations of Triphenylgermyl Ligands in Iridium−Ruthenium Carbonyl Cluster Complexes

The new compound IrRu3(CO)11(GePh3)3(μ-H)4, 1, was obtained in 64% yield from the reaction of IrRu3(CO)13(μ-H) with HGePh3 at room temperature. Compound 1 has a butterfly structure for the four metal atoms with three GePh3 ligands and four bridging hydride ligands around the periphery of the cluster. When the reaction was performed at hexane reflux for 10 min, a second, minor compound, Ir2Ru2(CO)11(GePh3)(μ-H)3, 2, was formed. Compound 2 contains a closed cluster having two iridium and two ruthenium atoms, one GePh3 ligand, and three bridging hydride ligands. When compound 1 was heated to 68 °C for 6 h, two new compounds, IrRu3(CO)10(μ-η2-C6H5)(μ4-GePh)2, 3, and IrRu3(CO)9(μ-η2-C6H5)(μ4-GePh)2(μ-GePh2), 4, were formed by cleavage of phenyl rings from the GePh3 ligands. Compounds 3 and 4 contain square IrRu3 clusters of the metal atoms with quadruply bridging GePh germylyne ligands on opposite sides of the cluster. Both compounds also contain a rare η2-bridging phenyl ligand. Compound 4 was found to react ...

Influence of the [2Fe]H Subcluster Environment on the Properties of Key Intermediates in the Catalytic Cycle of [FeFe] Hydrogenases: Hints for the Rational Design of Synthetic Catalysts

Nature's recipe: A theoretical study analyzes how the environment of the [FeFe] hydrogenase's catalytic cofactor affects its chemical properties, particularly the relative stability of complexes with bridging and terminal hydride ligands (see picture; Fe teal, S yellow, C green, N blue, O red, H gray). The results help to elucidate key rules for the design of bioinspired synthetic catalysts for H(2) production.

Decarbonylation Reaction of [Os3(CO)10(μ-H)(μ-SN2C4H5)]: X-ray Structures of the Two Isomers of [Os3(CO)9(μ-H)(μ 3-η 2-SN2C4H5)

The thermal reaction of [Os3(CO)10(μ-H)(μ-SN2C4H5)] (1) at 110 °C afforded the new compound [Os3(CO)9(μ-H)(μ 3-η 2-SN2C4H5)] (2) in 84% yield. Compound 2 exists as two isomers, which differ in the disposition of the bridging hydride ligand. Both of the isomers of 2 have been characterized by a combination of elemental analysis, infrared and 1H NMR spectroscopic data together with single crystal X-ray crystallography. The isomers crystallize together in the triclinic space group P-1 with a = 10.4775(2), b = 13.3056(3), c = 15.0325(3) A, α = 110.8890(10), β = 99.3880(10), γ = 96.1620(10)°, Z = 2 and V = 1900.31(7) A3. The synthesis and the molecular structures of the two isomers of [Os3(CO)9(μ-H)(μ 3-η 2-SN2C4H5)] are described. The isomers differ in the disposition of the hydride ligand.