Enthalpy of ligand substitution in cisorganopalladium complexes with monodentate ligands

Abstract

The enthalpy for the substitution reaction cis-[PdRf₂(THF)₂] + 2 L →cis-[PdRf₂L₂] + 2THF (THF = tetrahydrofuran) has been measured in THF by calorimetric methods for Rf = 3,5-dichloro-2,4,6-trifluorophenyl, L = PPh₃, AsPh₃, SbPh₃, PMePh₂, PCyPh₂, PMe₃, AsMePh₂, or L₂ = dppe (1,2-bis(diphenylphosphino)ethane), dppf (1,1′-bis(diphenylphosphino)ferrocene). The values determined show that the substitution enthalpy has a strong dependence on the electronic and steric properties of the ligand. The study of the consecutive substitution reactions cis-[PdRf₂(THF)₂] + L →cis-[PdRf₂L(THF)] + THF, and cis-[PdRf₂L(THF)] + L →cis-[PdRf₂L₂] + THF has been carried our for L = PPh₃ and L = PCyPh₂. The first substitution is clearly more favorable for the bulkier leaving ligand, but the second gives practically the same ΔH value for both cases, indicating that the differences in steric hindrance happen to compensate the electronic differences for both ligands. The X-ray structures of cis-[PdRf₂(PMePh₂)₂], cis-[PdRf₂(dppe)] and cis-[PdRf₂(dppf)] are reported.