Seven-Coordinate Dihydrido Complex OsH2(κ2-O2CCH3){κ1-OC(O)CH3}(PiPr3)2 as Precursor of New Organometallic Compounds Containing Unsaturated η1-Carbon Ligands

The dichloro−dihydrido complex OsH 2 Cl 2 (P i Pr 3 ) 2 ( 1 ) reacts with K[CH 3 CO 2 ] to give the seven-coordinate dihydrido OsH 2 Cl(κ 2 -O 2 CCH 3 )(P i Pr 3 ) 2 ( 2 ), while the reaction of 1 with Ag[CH 3 CO 2 ] affords OsH 2 (κ 2 -O 2 CCH 3 ){κ 1 -OC(O)CH 3 }(P i Pr 3 ) 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 hydrido ligands. The oxygen atoms of the acetato ligands are located in the second plane, which is rotated by 24.7° from the first one. Complex 3 reacts with 2-methyl-1-buten-3-yne to give the α,β-unsaturated vinylidene derivative OsH{ C CHC(CH 3 ) CH 2 }(κ 2 -O 2 CCH 3 )(P i Pr 3 ) 2 ( 4 ), which by reaction with HBF 4 ·OEt 2 affords the cationic carbyne complex [OsH{⋮CCH C(CH 3 ) CH 2 }(κ 2 -O 2 CCH 3 )(P i Pr 3 ) 2 ]BF 4 ( 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 hydrido, and the carbyne group. Under carbon monoxide atmosphere, complex 5 evolves into the ( Z )-dienyl complex Os{( Z )-CH CHC(CH 3 ) CH 2 }{κ 1 -OC(O)CH 3 }(CO) 2 (P i Pr 3 ) 2 ( 6 ), which does not isomerize into the ( E )-dienyl isomer Os{( E )-CH CHC(CH 3 ) CH 2 }{κ 1 -OC(O)CH 3 }(CO) 2 (P i Pr 3 ) 2 ( 7 ). Treatment of 6 with HBF 4 ·OEt 2 produces isoprene and the cis -dicarbonyl [Os(κ 2 -O 2 CCH 3 )(CO) 2 (P i Pr 3 ) 2 ]BF 4 ( 8 ). The ( E )-dienyl complex 7 has been prepared according to the following reaction sequence: the reaction of Os{( E )-CH CHC(CH 3 ) CH 2 }Cl(CO)(P i Pr 3 ) 2 ( 9 ) with Ag[CH 3 CO 2 ] leads to Os{( E )-CH CHC(CH 3 ) CH 2 }(κ 2 -O 2 CCH 3 )(CO)(P i Pr 3 ) 2 ( 10 ), which under carbon monoxide atmosphere gives 7 . The related chloro complex Os{( E )-CH CHC(CH 3 ) CH 2 }Cl(CO) 2 (P i Pr 3 ) 2 ( 11 ) is similarly prepared by starting from 9 . The protonation of 10 with HBF 4 ·OEt 2 leads to the α,β-unsaturated carbene [Os{ CHCH C(CH 3 ) 2 }(κ 2 -O 2 CCH 3 )(CO)(P i Pr 3 ) 2 ]BF 4 ( 12 ).