Studies on nucleophilic additions at bridging vinyl ligands in triosmium clusters

The bridging vinyl clusters HOs₃(CHCHR)(CO)₁₀] (R = H, Ph, or n-Bu) react with PMe₂Ph to give the zwitterionic adducts HOs₃(CHCHRPMe₂Ph)(CO)₁₀] which contain μ₂-alkylidene ligands. The adducts are not formed so readily when R = Ph or n-Bu but most readily when polar solvents are used. All three CHCHR complexes add cyanide ion irreversibly to give the anionic clusters which were isolated as N(PPh₃)₂]HOs₃(CHCHRCN)(CO)₁₀]. There is infrared evidence for the addition of various other anions. Acid reverses the addition of methoxide but HCl reacts with the cyanide adduct HOs₃(CHCH₂CN)(CO)₁₀]^? to give HOs₃Cl(CO)₁₀] and EtCN. No evidence for nucleophilic addition at HOs₃(PhCCHPh)(CO)₁₀] was obtained.