Seven-coordinate dihydrido complex OsH2(κ2-O2CCH3) {K1-OC(O)CH3}(PiPr3)2 as precursor of new organometallic compounds containing unsaturated η1-carbon ligands

The dichloro-dihydrido complex OsH2Cl2((PPr3)-Pr-i)(2) (1) reacts with K[CH3CO2] to give the seven-coordinate dihydrido OsH2Cl(kappa(2)-O2CCH3)((PPr3)-Pr-i)(2) (2), while the re action of 1 with Ag[CH3CO2] affords OsH2(kappa(2)-O2CCH3){kappa(1)-OC(O)CH3}((PPr3)-Pr-i)(2) (3). The structure of 3 in the solid state has been determined by X-ray diffraction analysis. The geometry around the metal center could ideally be described as derived from a distorted square antiprism with a missing vertice. One of the two square planes is made up by the two phosphorus atoms and the hydride Ligands. The oxygen atoms of the acetato ligands are located in the second plane, which is rotated by 24.7 degrees from the first one. Complex 3 reacts with 2-methyl-1-buten-3-yne to give the alpha,beta-unsaturated vinylidene derivative OsH{=C=CHC(CH3)=CH2}(kappa(2)-O2CCH3)((PPr3)-Pr-i)(2) (4), which by reaction with HBF4. OEt2 affords the cationic carbyne complex [OsH{=CCH=C(CH3)=CH2}(kappa(2)-O2CCH3)((PPr3)-Pr-i)(2)]BF4 (5). The structure of 5 has been also determined by X-ray diffraction analysis. The coordination geometry around the osmium atom could be rationalized as a distorted octahedron with the two phosphorus atoms of the phosphine ligands occupying apical positions. The equatorial plane is formed by the bidentate ligand, the hydride, and the carbyne group. Under carbon monoxide atmosphere, complex 5 evolves into the (Z)-dienyl complex Os{(Z)-CH=CHC(CH3)=CH2}{kappa(1)-OC(O)CH3}(CO)(2)((PPr3)-Pr-i)(2) (6), which does not isomerize into the (E)-dienyl isomer Os{(E)-CH=CHC(CH3)=CH2}{kappa(1)-OC(O)CH3}(CO)(2)((PPr3)-Pr-i)(2) (7). Treatment of 6 with HBF4. OEt2 produces isoprene and the cis-dicarbonyl [Os(kappa(2)-O2CCH3)(CO)(2)((PPr3)-Pr-i)(2)]BF4 (8). The (E)-dienyl complex 7 has been prepared according to the following reaction sequence: the reaction of Os{(E)-CH=CHC(CH3)=CH2}Cl(CO)((PPr3)-Pr-i)(2) (9) with Ag[CH3CO2] leads to Os{(E)-CH=CHC(CH3)=CH2}(kappa(2)-O2CCH3)(CO)((PPr3)-Pr-i)(2) (10), which under carbon monoxide atmosphere gives 7. The related chloro complex Os{(E)-CH=CHC(CH3)=CH2}Cl(CO)(2)((PPr3)-Pr-i)(2) (11) is similarly prepared by starting from 9. The protonation of 10 with HBF4. OEt2 leads to the alpha,beta-unsaturated carbene [Os{=CHCH=C(CH3)(2)}(kappa(2)-O2CCH3)(CO)((PPr3)-Pr-i)(2)]BF4 (12).