New cyclopentadienylosmium compounds containing unsaturated carbon donor coligands:: Synthesis, structure, and reactivity of Os(η5-C5H5)Cl(=C=C=CPh2)(PiPr3)

The addition of 1,1-diphenyl-2-propyn-1-ol to pentane solutions of the cyclopentadienyl compound Os(eta(5)-C5H5)Cl((PPr3)-Pr-i)(2) (1.) produces the displacement of a phosphine ligand from 1 and the formation of the pi-alkyne complex Os(eta(5)-C5H5)Cl{eta(2)-HC=C-C(OH)Ph-2}((PPr3)-Pr-i) (2), which affords the allenylidene derivative Os(eta(5)-C5H5)Cl(=C=C=CPh2)((PPr3)-Pr-i) (3) in toluene at 85 degrees C. The structure of 3 has been determined by X-ray diffraction. The Os-C-alpha, C-alpha-C-beta, and C-beta-C-gamma bond lengths are 1.875(6), 1.222(9), and 1.344(9) Angstrom, respectively, while the Os-C-alpha-C-beta and C-alpha-C-beta-C-gamma angles are 171.6(6)degrees and 172.0(7)degrees, respectively. Protonation of 3 with HBF4 . OEt2 leads to the alpha,beta-unsaturated carbyne [Os(eta(5)-C5H5)Cl(=C-CH=CPh2)((PPr3)-Pr-i)]BF4 (4), as a result of the attack of the proton from the acid at the Cg 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(eta(5)-C5H5)Cl{=C=C(CO2Me)=C=CPh2}((PPr3)-Pr-i) (5). A second C-3 + C-2 coupling process is the formation of the pentatrienyl complex Os(eta(5)-C5H5){(3-5-eta)CH2CHC=C=CPh2}((PPr3)-Pr-i) (6) by reaction of 3 with CH2=CHMgBr. Complex 3 also reacts with KI to give Os(eta(5)-C5H5)I(=C=C=CPh2)((PPr3)-Pr-i) (7). The reduction of the C beta-C gamma double bond of the allenylidene ligand of 3, to form the vinylidene complex Os(eta(5)-C5H5)Cl(=C=CH-CHPh2)((PPr3)-Pr-i) (8), has been carried out in the presence of NaBH4 and methanol.