Osmium dihydride

Two isomers of this compound (designated a and (3) have been claimed (see Table 10) although most preparations usually give the a-isomer which has the structure shown in Fig. 9. The osmium dihydride, Os4(CO)13H2, which is probably iso-structural with a-Ru4(CO)13H2, has been obtained from the mixture resulting on pyrolysis... 

DR. NORTON It is also worth noting that the osmium dihydride is a rather weak acid if you compare it to these others. 

The osmium dihydride cluster complex Os3(CO)joH2 loses hydrogen in the... 

This tetrahydridoborate complex reacts with Lewis bases L such as CO, P(OMe)3, PMe3, and P Pr3 to form dihydride-osmium(II) complexes OsH2(CO) L(P Pr3 )2, whereas the reactions with electrophiles afford monohydride derivatives (Scheme 35). The reaction with HBF4-OEt2 leads to the binuclear complex [(P Pr3 )2 (CO)HOs(p,-r 4-H2BH2)OsH(CO)(PI Pr3 )2]BF4, consisting of two OsH... 

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. 

DR. WILLIAM TROGLER (Northwestern University) You looked at exchange between the monohydride anion of osmium and the neutral dihydride. Have you ever studied the bimolecular self-exchange for a neutral dihydride This could be followed by mixing one sample labelled with deuterium and one with hydrogen. 

Osmium pentacarbonyl is a convenient precursor to other osmium carbonyl complexes. Hydrogenation gives the dihydride OsH2(CO)4. This hydride is not acidic with a p/fa of 18.5 but it can be deprotonated by strong bases to give [OsH(CO)4] and reduced by sodium (Scheme 23). Substitution of CO on Os(CO)5 by trialkyl or triarylphosphines, arsines, or stibenes gives Os(CO)4L or Os(CO)3L2. Other carbonyl phosphine complexes result from the reduction of osmium halides by alcohols in the presence of the tertiary phosphine. 

The dihydride-osmium(IV) complex OsH2Cl2(P Pr3)2 as a precursor for carbon-carbon, carbon-nitrogen, carbon-phosphoms, carbon- germanium, and carbon-silicon coupling reactions... 

Treatment of 164 with NaOMe in tetrahydrofliran produces its deprotonation and the formation of the dihydride-phosphinito-osmium(IV) derivative OsH2(ti5-C5Hj) P(0)Ph2 (P Pr3) (166). Under the same conditions, the deprotonation of 165 yields OsH( n5-C5H5) P(OMe)Ph2 (P Pr3) (167), as aresult of the extraction of one of the two hydrides. 

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... 

Egbert JD, Bullock RM, Heinekey DM (2007) Cationic dihydrogen/dihydride complexes of osmium structure and dynamics. Organometallics 26 2291-2295... 

Factors affecting simple reductive elimination versus other forms of elimination (e.g. a), especially with respect to dihydrides, dialkyls, and mixed alkyl-hydrides (which eliminate fastest) of mono- and di-nuclear osmium complexes, have been discussed. In compounds such as [OsHMe(CO)4] or [OsMe2(CO)4] simple reductive elimination does not occur for example, a mixture of [OsH(CD3)(CO>4] and [OsD(CH3)(CO)4] gave CH4, CH3D, CD3H, and CD4, and a dinuclear mechanism is proposed. ... 

It is interesting to consider Os6(CO)ig and Ose-(CO)igH2. Emperically these compounds appear very similar yet structurally they differ significantly (Fig. 21). The two additional valence electrons of the dihydride can account for this structural difference. The osmium core of Os6(CO)ig defines a bicapped tetrahedron therefore, 42 CVMOs are available and filled by the 84 cluster valence electrons. The two additional electrons of the dihydride Os6(CO)igH2 would occupy an HLAO unless a structural change in the Ose skeleton occurs. Rearrangement to a capped square pyramid increases the CVMO count by one to a net 43 which is sufficient to accept all 86 cluster valence electrons. 

The protonation of the iron-hydride complex [Fe Cp(PMe3)2(H)] leads to the H2 complex [Fe Cp(PMe3)2(H2)]+, because the iron atom in the starting complex is relatively electron poor, and the oxidation state Fe is much more favorable than Fe. On the other hand, the protonation of the osmium complex leads to the protonation of that is an electron-rich metal center, i.e. the oxidative addition occurs to yield the dihydride [Os Cp(PMe3)2(H)2], the oxidation state Os being much more common than Fe. ... 

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