METAL-HYDRIDES AS INTERMEDIATES IN THE REACTIONS OF COORDINATED UNSATURATED HYDROCARBONS-FORMATION OF PROPYNE BY PROTONATION OF TRANS-[WH(ETA(3)-C3H5)(PH2PCH2CH2PPH2)(2)]

The reaction of anhydrous HCl with trans-[WH(eta(3)-C3H5) (dppe)(2)] ( dppe = Ph2PCH2CH2PPh2) in tetrahydrofuran gives [WH2Cl2-(dppe)(2)] tog ether with propene and propyne. Detailed product analyses and kinetic studies demonstrate that propene and propyne are formed by protonation of the allyl residue and the metal, respectively. The most favoured s ite of protonation is the allyl group to form [WH(eta(2)MeCHCH(2)) (dp pe)(2)](+), which releases propene and subsequently forms [WH2Cl2(dppe )(2)]. This is the exclusive hydrocarbon-forming pathway at low concen trations of HCl. The propyne-forming pathway dominates at high concent rations of acid, and involves diprotonation of the metal followed by l oss of dihydrogen probably to give the coordinatively-unsaturated spec ies, [WH(eta(3)-C3H5) (dppe)(2)](2+) which rearranges to [WH2(eta(2)-M eCCH) (dppe)(2)](2+), then releases propyne and subsequently forms [WH 2Cl2(dppe)2]. The possible mechanisms for the allyl-to-propyne rearran gment are discussed in the light of GLC time-course experiments monito ring the release of the gases. The X-ray crystal structures of IMH(eta (3)-C3H5) (dppe)(2)] (M = Mo or W) show that both complexes have an ap proximate octahedral geometry about the metal with the hydride group t rans to the allyl residue.