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(kappa(2)-O2CCH3)(H2O)((PPr3)-Pr-i)(2)]BF4 (1) reacts wi th 2-phenyl-3-butyn-2-ol and 2-methyl-3-butyn-2-ol to give isomeric mixture s of the corresponding hydride-hydroxyosmacyclopropene, [OsH(kappa(2)-O2CCH 3){C[C(OH)MeR]CH2}((PPr3)-Pr-i)(2)]BF4 (R = Ph (3), Me (5)), and hydride-hy droxycarbyne, [OsH(kappa(2)-O2CCH3){=CCH2C(OH)MeR}((PPr3)-Pr-i)(2)]BF4 (R = Ph (4), Me (6)), derivatives. In solution, complexes 3 and 5 and the relat ed compound [OsH-(kappa(2)-O2CCH3){C[C(OH)Ph-2]CH2}((PPr3)-Pr-i)(2)]BF4 (2) is isomerize into the cyclic hydroxycarbenes [Os-(kappa(2)-O2CCH3){C(Me)C( OH)RR'}((PPr3)-Pr-i)(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-ra y diffraction analysis. The geometry around the osmium center can be ration alized as a very distorted octahedron, with the phosphine ligands occupying cis positions (P-Os-P = 103.71(6)degrees). Reaction of 2 with sodium metho xide leads to the eta(2)-vinyl alkoxide derivative Os{eta(2)-CH2=CHC(Ph)(2) O}-(kappa(2)-O2CCH3)((PPr3)-Pr-i)(2) (10), which by protonation with HBF4 a ffords the eta(2)-1,1-diphenyl-2-propenol complex [Os(kappa(2)-O2CCH3){eta( 2)-CH2=CHC(OH)Ph-2}((PPr3)-Pr-i)(2)]BF4_(11). The structure of 10 has also been determined by X-ray diffraction analysis. As for 8, the geometry aroun d the osmium atom can be rationalized as a very distorted octahedron with t he phosphine ligands occupying cis positions (P-Os-P = 106.72(4)degrees). T he reaction of 8 with sodium methoxide leads to the osmaoxacyclobutene deri vative Os{C(Me)C(O)MePh}(kappa(2)-O2CCH3)((PPr3)-Pr-i)(2) (12), which on pr otonation with HBF4. OEt2 regenerates 8. Treatment of 4 with sodium methoxi de gives the hydride-vinylidene OsH(kappa(2)-O2CCH3){=C=CHC(Ph)=CH2}((PPr3) -Pr-i)(2) (13). The formation of the hydride-alkenylcarbynes [OsH(kappa(2)- O2CCH3)(=CCH=CRMe)((PPr3)-Pr-i)(2)]BF4 (R = Ph (14), Me (15)) by dehydratio n of 4 and 6 is also reported.