7-COORDINATE DIHYDRIDO COMPLEX OSH2(KAPPA(2)-O2CCH3) (K-1-OC(O)CH3)((PPR3)-PR-I)(2) AS PRECURSOR OF NEW ORGANOMETALLIC COMPOUNDS CONTAININGUNSATURATED ETA(1)-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)-O2CC H3)((PPr3)-Pr-i)(2) (2), while the re action of 1 with Ag[CH3CO2] affo rds appa(2)-O2CCH3){kappa(1)-OC(O)CH3}((PPr3)-Pr-i)(2) (3). The struct ure of 3 in the solid state has been determined by X-ray diffraction a nalysis. The geometry around the metal center could ideally be describ ed 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 l ocated 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 al pha,beta-unsaturated vinylidene derivative {=C=CHC(CH3)=CH2}(kappa(2)- O2CCH3)((PPr3)-Pr-i)(2) (4), which by reaction with HBF4. OEt2 affords the cationic carbyne complex H=C(CH3)=CH2}(kappa(2)-O2CCH3)((PPr3)-Pr -i)(2)]BF4 (5). The structure of 5 has been also determined by X-ray d iffraction analysis. The coordination geometry around the osmium atom could be rationalized as a distorted octahedron with the two phosphoru s atoms of the phosphine ligands occupying apical positions. The equat orial plane is formed by the bidentate ligand, the hydride, and the ca rbyne group. Under carbon monoxide atmosphere, complex 5 evolves into the (Z)-dienyl complex H3)=CH2}{kappa(1)-OC(O)CH3}(CO)(2)((PPr3)-Pr-i) (2) (6), which does not isomerize into the (E)-dienyl isomer H3)=CH2}{ kappa(1)-OC(O)CH3}(CO)(2)((PPr3)-Pr-i)(2) (7). Treatment of 6 with HBF 4. 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 prep ared 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 t o 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 (CH3)(2)}(kappa(2)-O2CCH3)(CO)((PPr3)- Pr-i)(2)]BF4 (12).