With osmium dihydrogen complexes

Cofacial ruthenium and osmium bisporphyrins proved to be moderate catalysts (6-9 turnover h 1) for the reduction of proton at mercury pool in THF.17,18 Two mechanisms of H2 evolution have been proposed involving a dihydride or a dihydrogen complex. A wide range of reduction potentials (from —0.63 V to —1.24 V vs. SCE) has been obtained by varying the central metal and the carbon-based axial ligand. However, those catalysts with less negative reduction potentials needed the use of strong acids to carry out the catalysis. These catalysts appeared handicapped by slow reaction kinetics. 

Preparation and reactivity with azo-species of hydride and dihydrogen complexes of osmium stabilised by tris(pyrazolyl)borate and phosphite ligands... 

In contrast to the reaction with phenylacetylene, the treatment of 190 with 2 equiv of methyl propiolate leads to the alkenyl-alkynyl compound 200 (Scheme 55). The use of a 1 1 molar ratio of alkyne to osmium complex gives the same product along with unreacted dihydride-dihydrogen complex [79]. The addition of a toluene solution of HCl to a toluene solution of 200 produces the carbon-carbon coupling of the alkynyl and alkenyl fragments to give selectively the... 

Few examples are known for this type of intramolecular dihydrogen bond. One of them is the trimetallic osmium cluster shown in Structure 5.15 [28]. This compound, described well by various methods, has revealed a number of problems connected with characterizations of dihydrogen-bonded complexes that deserve separate discussion. The hydrogen atoms localized in the x-ray molecular structure of complex 1 of Figure 5.17 provide a formulation of interaction N-H -... 

An experimental report of the effect of the ligand trans to dihydrogen confirmed these theoretical results. The acidity of a series of ruthenium and osmium complexes, iran -[M(H2)XL2] + (L = Ph2P(CH2)3PPh2 X = CO, Cl, H) has been determined [19]. The complex [Ru(H2)(CO)(dppp)2] is highly acidic with an estimated pAa of -6. 

Fig. 7.12 INS spectra (BT4, NIST) of (a) ethyne on platinum black annealed at 300 K with 500 mbar of dihydrogen (b) ethyne on platinum black adsorbed at 120 K, no dihydrogen. Reproduced from [64] with permission from the American Institute of Physics. [Os3(n2-CO)(CO)9( i3-Ti -C2H2)] (c) experimental, (d) modelled with the Wilson GF method. Reproduced from [67] with permission from the PCCP Owner Societies, (e) [Co2(CO)6(li2-ri -C2H2)], experimental (INBeF, ILL). Reproduced from [66] with permission from the American Chemical Society. Note that the peak pattern of adsorbed ethyne (b) is similar to that of ethyne in the osmium complex (c). Note also the additional peaks near 500 and 1400 cm when adsorbed ethyne was treated with hydrogen (a).

Photochemical reactions of Ru3(CO)i2 and Os3(CO)i2 with nitrogen hetero-cycles have been studied, with substitution products being formed in most cases. For example, with pyridine the ruthenium compound forms the ortho-metallated complex Ru3H(CO)i i(CsH4N), while the osmium compound gives the simple substitution product Os3(CO)n(py). The novel dihydrido triruthenium cluster H2Ru3(CO)io can be synthesized by photolysis of Ru3(CO)i2 under an atmosphere of dihydrogen. 

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