CARBON-MONOXIDE AS A BUILDING-BLOCK IN ORGANIC-SYNTHESIS .5. 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 C-11 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=CHPh)4(PdCl6)(SnCl6)].