New Cyclopentadienylosmium Compounds Containing Unsaturated Carbon Donor Coligands: Synthesis, Structure, and Reactivity of Os(η5-C5H5)Cl(CCCPh2)(PiPr3)

Abstract

The addition of 1,1-diphenyl-2-propyn-1-ol to pentane solutions of the cyclopentadienyl compound Os(η5-C5H5)Cl(PiPr3)2 (1) produces the displacement of a phosphine ligand from 1 and the formation of the π-alkyne complex Os(η5-C5H5)Cl{η2-HC⋮C−C(OH)Ph2}(PiPr3) (2), which affords the allenylidene derivative Os(η5-C5H5)Cl(CCCPh2)(PiPr3) (3) in toluene at 85 °C. The structure of 3 has been determined by X-ray diffraction. The Os−Cα, Cα−Cβ, and Cβ−Cγ bond lengths are 1.875(6), 1.222(9), and 1.344(9) A, respectively, while the Os−Cα−Cβ and Cα−Cβ−Cγ angles are 171.6(6)° and 172.0(7)°, respectively. Protonation of 3 with HBF4·OEt2 leads to the α,β-unsaturated carbyne [Os(η5-C5H5)Cl(⋮C−CHCPh2)(PiPr3)]BF4 (4), as a result of the attack of the proton from the acid at the Cβ carbon atom of the allenylidene. The nucleophilicity of this atom is also revealed by the reaction of 3 with dimethyl acetylenedicarboxylate, which leads to the allenylvinylidene Os(η5-C5H5)Cl{CC(CO2Me)C(CO2Me)CCPh2}(PiPr3) (5). A second C3 + C2 c...