Hydride−Hydroxyosmacyclopropene versus Hydride−Hydroxycarbyne and Cyclic Hydroxycarbene: Influence of the Substituents at the C(OH) Carbon Atom of the Carbon Donor Ligand

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Abstract

The dihydride [OsH2(κ2-O2CCH3)(H2O)(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, (R = Ph (3), Me (5)), and hydride−hydroxycarbyne, [OsH(κ2-O2CCH3){⋮CCH2C(OH)MeR}(PiPr3)2]BF4 (R = Ph (4), Me (6)), derivatives. In solution, complexes 3 and 5 and the related compound (2) isomerize into the cyclic hydroxycarbenes (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 (10), which by protonation with HBF4 affords the η2-1,1-diphenyl-2-propenol complex (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 (12), which on protonation with HBF4·OEt2 regenerates 8. Treatment of 4 with sodium methoxide gives the hydride−vinylidene OsH(κ2-O2CCH3){CCHC(Ph)CH2}(PiPr3)2 (13). The formation of the hydride−alkenylcarbynes [OsH(κ2-O2CCH3)(⋮CCHCRMe)(PiPr3)2]BF4 (R = Ph (14), Me (15)) by dehydration of 4 and 6 is also reported.

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