Hydride-hydroxyosmacyclopropene versus hydride-hydroxycarbyne and cyclic hydroxycarbene: Influence of the substituents at the C(OH) carbon atom of the carbon donor ligand

The dihydride [OsH2(κ2-O2CCH3)(H 2O)(PiPr3)2]BF4 (1) reacts with 2-phenyl-3-butyn-2-ol and 2-methyl-3-butyn-2-ol to give isomeric mixtures of the corresponding hydride-hydroxyosmacyclopropene, [OsH(κ2-O2CCH3){C[C(OH)MeR]CH 2}(PiPr3)2]BF4 (R = Ph (3), Me (5)), and hydride-hydroxycarbyne, [OsH(κ2-O2CCH3){≡CCH 2C(OH)MeR}(PiPr3)2]BF4 (R = Ph (4), Me (6)), derivatives. In solution, complexes 3 and 5 and the related compound [OsH-(κ2-O2CCH3){C[C(OH)Ph 2]CH2}(PiPr3)2]BF 4 (2) isomerize into the cyclic hydroxycarbenes [Os-(κ2-O2CCH 3){C(Me)C(OH)RR′}(PiPr3) 2]BF4 (R = R′ = Ph (7); R = Ph, R′ = Me (8); R = R′ = Me (9)). The structure of 8 in the solid state has been determined by X-ray diffraction analysis. The geometry around the osmium center can be rationalized as a very distorted octahedron, with the phosphine ligands occupying cis positions (P-Os-P = 103.71(6)°). Reaction of 2 with sodium methoxide leads to the η2-vinyl alkoxide derivative Os{η2-CH2=CHC(Ph)2O}-(κ 2-O2CCH3)(PiPr3) 2 (10), which by protonation with HBF4 affords the η2-1,1-diphenyl-2-propenol complex [Os(κ2-O2CCH3){η2-CH 2=CHC(OH)Ph2}(PiPr3) 2]BF4 (11). The structure of 10 has also been determined by X-ray diffraction analysis. As for 8, the geometry around the osmium atom can be rationalized as a very distorted octahedron with the phosphine ligands occupying cis positions (P-Os-P = 106.72(4)°). The reaction of 8 with sodium methoxide leads to the osmaoxacyclobutene derivative Os{C(Me)C(O)MePh}(κ2-O2CCH3)(P i-Pr3)2 (12), which on protonation with HBF4·OEt2 regenerates 8. Treatment of 4 with sodium methoxide gives the hydride-vinylidene OsH(κ2-O2CCH3){=C=CHC(Ph)=CH 2}(PiPr3)2 (13). The formation of the hydride-alkenylcarbynes [OsH(κ2-O2CCH3)(≡CCH=CRMe)(P iPr3)2]BF4 (R = Ph (14), Me (15)) by dehydration of 4 and 6 is also reported.We acknowledge financial support from the DGES of Spain (Project PB98-1591). C.G.-Y. thanks the CSIC-Repsol YPF for a postdoctoral grant.Peer Reviewe