The Five-Coordinate Hydrido−Dihydrogen Complex [OsH(η2-H2)(CO)(PiPr3)2]BF4 Acting as a Template for the Carbon−Carbon Coupling between Methyl Propiolate and 1,1-Diphenyl-2-propyn-1-ol

The five-coordinate hydrido−dihydrogen complex [OsH(η 2 -H 2 )(CO)(P i Pr 3 ) 2 ]BF 4 ( 1 ) reacts with methyl propiolate in acetone to ( 2 ). The acetone ligand of 2 can be easily displaced by methyl propiolate and 1,1-diphenyl-2-propyn-1-ol to ( 3 ) respectively. The structure of 4 has been determined by X-ray diffraction. The geometry around the osmium atom can be rationalized as a distorted octahedron with the phosphine ligands occupying opposite positions. The remaining perpendicular plane is formed by the chelating alkenyl ligand, which acts with a bite angle of 62.8(2)°, the carbonyl group disposed trans to the oxygen atom. Complex 4 reacts with methyllithium to give the alkynyl derivative which is unstable in methanol and quantitatively evolves Complex 6 can be alternatively obtained from the reaction of 4 with NaOCH 3 . Complex 4 also reacts with NaCl to afford trans -chlorocarbonyl Os{C[C(O)OCH 3 ] CH 2 }Cl(C C CPh 2 )(CO)(P i Pr 3 ) 2 ( 7 ) and cis -chlorocarbonyl Os{C[C(O)OCH 3 ] CH 2 }Cl(C C CPh 2 )(CO)(P i Pr 3 ) 2 ( 8 ). At 60 °C, toluene solutions of 7 and 8 yield the as a result from the migratory insertion of the allenylidene ligand into the Os−C(alkenyl) bond of 7 and 8 . The structure of 9 has been also determined by X-ray diffraction. The geometry around the osmium atom can be described as a distorted octahedron with the phosphine ligands occupying two relative trans positions. The ideal equatorial plane is formed by the chelate allenyl ligand which acts with a bite angle of 78.66(12)°, the carbonyl group disposed trans to the oxygen atom.