New access to vinylidenes from ruthenium polyhydrides

Reaction of the terminal acetylenes RC=CH (R = Ph and SiMe3) with RuH3XL2 (X = Cl, I; L = (PBu2Me)-Bu-t) occurs (in the time of mixing) in a 2:1 stoichiometry to release RHC=CH2 and form the vinylidene complexes RuHX(CCHR)L-2. Ab initio DFT (B3LYP) calculations show that the vinylidene complex has a Y structure with a CI at the foot of the Y. No intermediate is-seen for this reaction, even at low temperature, or for the analogous reaction of OsH3Cl((PPr3)-Pr-i)(2). Since PhC=CD forms only the isotopomer RuDI(CCHPh)L-2 and PhHC=CHD, a mechanism is proposed where an early event is addition of Ru-H across the C=C bond. Preliminary computational studies of the reaction path for the formation of the vinylidene complex support this step of insertion of the acetylene into the Ru-H bond.