Novel regioselection in insertion of a 1,4-disubstituted-1,3-enyne into ruthenium–hydrogen bonds

The reaction of a conjugated enyne, cis-(Me3Si)CHCHCCSiMe3, with [RuCl(CO)H(PPh3)3] gives a quantitative yield of a stable complex whose molecular structure is formally regarded as the result of either 1,2-addition of the H–Ru to the double bond or 1,4-addition of the H–Ru to the conjugated enyne; the former bonding scheme operates when the enyne is hydrogenated by [Ru(CO)H2(PPh3)3] or [RuH2(PPh3)4], the sole product being Me3SiCH2CH2CCSiMe3.