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(eta(2)-H-2)(CO)((PPr3)-Pr-i)(2)]BF4 (1) reacts with methyl propiolate in acetone to give [Os{C[C(O)OCH3]=CH2}{eta(1)-OC(CH3)(2)}(CO)((PPr3)-Pr-i)(2)]BF4 (2) The acetone ligand of 2 can be easily displaced by methyl propiolate and 1,1-diphenyl-2-propyn-1-ol to afford [Os{C[C(O)OCH3]=CH2}(C=CHCO2CH3)(CO)((PPr3)-Pr-i)(2)]BF4 (3) and [Os{C[C(O)OCH3]=CH2}(C=C=CPh2)(CO)((PPr3)-Pr-i)(2)]BF4 (4), 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)degrees, the carbonyl group disposed trans to the oxygen atom. Complex 4 reacts with methyllithium to give the alkynyl derivative [Os{C[C(O)OCH3]=CH2}(C=CCPh2CH3)(CO)((PPr3)-Pr-i)(2) (5), which is unstable in methanol and quantitatively evolves into [Os{C[C(O)OCH3]=CH2}(C=CCPh2OCH3)(CO)((PPr3)-Pr-i)(2) (6). Complex 6 can be alternatively obtained from the reaction of 4 with NaOCH3. Complex 4 also reacts with NaCl to afford trans-chlorocarbonyl Os(C[C(O)OCH3]=CH2}Cl(C=C=CPh2)(CO)((PPr3)-Pr-i)(2) (7) and cis-chlorocarbonyl Os{C[C(O)OCH3]= CH2}Cl(C=C=CPh2)(CO)((PPr3)-Pr-i)(2) (8). At 60 degrees C, toluene solutions of 7 and 8 yield the allenyl derivative Os{C[C(=CH2)C(O)OCH3]=C=CPh2]Cl(CO)((PPr3)-Pr-i)(2) (9) 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)degrees, the carbonyl group disposed trans to the oxygen atom.