Carbon monoxide as a building block in organic synthesis. Part V. Involvement of palladium-hydride species in carbonylation reactions of monoterpenes. X-ray crystal structure of [Ph3PCH2CH=CHPh]4[PdCl6][SnCl6]

A palladium precursor and SnCl₂ as cocatalyst were used under 4 MPa of carbon monoxide for the catalytic alkoxycarbonylation of several monoterpenes into C₁₁ esters. The active catalyst involves a palladium-hydride species whose formation was investigated. In the case of the model substrate 3-phenylpropene, the source of the hydrido ligand was determined to be the alkene itself. Allylic hydrogen abstraction seems to be a general way to produce the active hydridopalladium species since monoterpenes having labile allylic hydrogens were converted under exceptional mild conditions. An X-ray crystal structure analysis was carried out on [(Ph₃PCH₂CH =MPh)₄(PdCl₆)(SnCl₆)]. kw]Palladium; X-ray structure; Terpenes; Carbonylation; Hydroesterification