BITE ANGLE DEPENDENCE OF THE RATE OF REDUCTIVE ELIMINATION FROM DIPHOSPHINE PALLADIUM COMPLEXES

The thermal stability of a set of complexes of the type P2PdMeR, generated in situ, has been investigated in the temperature range -30-degrees-C to ambient, with the intention of determining the relationship between the ligand bite angle and reactivity in reductive elimination. In this series P2 Was either 1,3-(diphenylphosphino)propane (dppp), 1,1'-(diphenylphosphino)ferrocene (dppf) or 1,1'-(diphenylphosphino)ruthenocene (dppr), and R was phenyl or E-2-(4-methoxyphenyl)ethenyl. Clear trends were observed; the dppp complexes were much more stable than the others, and the phenylpalladium complexes were more stable than their vinylpalladium counterparts. The observed trends fit with the idea that the reductive elimination step in palladium cross-coupling is facilitated by a ligand with a large interchelate angle. The dppr complexes were significantly more labile than their dppf analogues.