Skeletal rearrangement during rhodium-promoted ring opening of 1,2-diphenyl-3-vinyl-1-cyclopropene. Preparation and characterization of 1,2-and 2,3-diphenyl-3,4-pentadienediyl rhodium complexes and their ring closure to a 1,2-diphenylcyclopentadienyl complex

Under conditions of kinetic control, 1,2-diphenyl-3-vinyl-1-cyclopropene un dergoes ring opening with the [Rh(Cl)(PMe3)(2)] fragment to give two isomer ic eta(3):eta(1)-1,3-pentadienediyl compounds: the expected 1,2-diphenyl is omer, and the 2,3-diphenyl isomer resulting from an apparent skeletal rearr angement reaction. The latter complex has been characterized by X-ray cryst allography. Both complexes underwent ring closure to give the same 1,2-diph enylcyclopentadienyl complex on treatment with silver ion. Addition of a th ird equivalent of trimethylphosphine to the 2,3-diphenyl isomer produced tw o meridional rhodacyclohexadienes, which exhibit-facile solvent-dependent c hloride dissociation. In contrast, phosphine added reversibly to the 1,2-di phenyl isomer to give only the chloride-dissociated compound, and the tris( phosphine) product could only be isolated after anion exchange with hexaflu orophosphate. No deprotonation to give rhodabenzene complexes could be achi eved. The mechanism of rearrangement is proposed to involve a carbocation r earrangement during the ring-opening reaction and is compared to other meta l-promoted reactions of vinylcyclopropenes.