Alcoholysis of Acylpalladium(II) Complexes Relevant to the Alternating Copolymerization of Ethene and Carbon Monoxide and the Alkoxycarbonylation of Alkenes: the Importance of Cis-Coordinating Phosphines

The mechanism and kinetics of the solvolysis of complexes of the type [(L−L)Pd(C(O)CH3)(S)]+[CF3SO3]- (L−L = diphosphine ligand, S = solvent, CO, or donor atom in the ligand backbone) was studied by NMR and UV−vis spectroscopy with the use of the ligands a−j:  SPANphos (a), dtbpf (b), Xantphos (c), dippf (d), DPEphos (e), dtbpx (f), dppf (g), dppp (h), calix-6-diphosphite (j). Acetyl palladium complexes containing trans-coordinating ligands that resist cis coordination (SPANphos, dtbpf) showed no methanolysis. Trans complexes that can undergo isomerization to the cis analogue (Xantphos, dippf, DPEphos) showed methanolyis of the acyl group at a moderate rate. The reaction of [trans-(DPEphos)Pd(C(O)CH3)]+[CF3SO3]- (2e) with methanol shows a large negative entropy of activation. Cis complexes underwent competing decarbonylation and methanolysis with the exception of 2j, [cis-(calix-diphosphite)Pd(C(O)CH3)(CD3OD)]+[CF3SO3]-. The calix-6-diphosphite complex showed a large positive entropy of activation. It is ...