CLEAVAGE OF METAL-CARBON BONDS IN HYDRIDE-BRIDGED PLATINUM AND PALLADIUM A-FRAME COMPLEXES

The hydride-bridged A-frame complexes [RPt(mu-H)(mu-dppm)(2)PtR']PF6 a nd [RPt(mu-H)(mu-dppm)(2)PdR']PF6 react with HCl (generated by reactio n of acetyl chloride with water) in acetone-d(6) solution by cleavage of one of the metal-carbon bonds. In the diplatinum systems the relati ve rates of Pt-C bond cleavage decrease in the order Me > Et > Ph, res ulting in a single product in each case. For the heterometallic comple xes reaction is faster at palladium, but mixtures of [RPt(mu-H)(mu-dpp m)(2)PdCl]PF6 and [ClPt(mu-H)(mu-dppm)(2)PdR']PF6 result in several in stances. Further reaction of these with HCl and/or CCl4 generates the chloride-bridged species [RPt(mu-Cl)(mu-dppm)(2)PdCl]PF6, formed, in s ome cases, by migration of the organic group from palladium to platinu m. These complexes have been prepared also by reaction of [PtR(dppm-PP )(dppm-P)]PF6 with [PdCl2(cod)]. The [RPt(mu-Cl)(mu-dppm)(2)PdCl]PF6 c omplexes are fluxional at 298 K, although the motion may be arrested s lightly below ambient temperature. A mechanism involving reversible br idge opening is proposed to account for the fluxional behavior.