Ruthenium-assisted synthesis of gem-deuterated alkenes from monosubstituted propargyl alcohols and D2O

The cyclohexenylvinylidene complex fac,cis-[(PNP)RuCl2{H2)}] (2) is synthesized by reaction of mer,trans-[(PNP)RuCl2(PPh3)] (1) with 1-ethynylcyclohexanol [PNPCH3CH2CH2N(CH2CH2PPh2)2]. Complex 2 reacts with water yielding fac,cis-[(PNP)RuCl2(CO)] and methylenecyclohexane. The regioselective incorporation of deuterium from D2O into the methylene group of methylenecyclohexane is consistent with the intermediacy of an η1-allyl ruthenium complex along the metal-assisted hydrolysis of the vinylidene CC bond. The hydrolysis of the alkenylvinylidenes fac,cis-[(PNP)RuCl2{CCHCRCH2}] (R=Me, Ph) proceeds similarly but the regioselectivity of deuterium incorporation depends on the temperature due to η1⇔η3 allyl interconversion.