| Abstract
| - 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 palladiumcomplexes containing trans-coordinating ligands that resist cis coordination (SPANphos, dtbpf) showed nomethanolysis. 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 complexesunderwent 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 ofactivation. It is concluded that ester elimination from acylpalladium complexes with alcohols requires cisgeometry of the acyl group and coordinating alcohol. The reductive elimination of methyl acetate is describedas a migratory elimination or a 1,2-shift of the alkoxy group from palladium to the acyl carbon atom. Ciscomplexes with bulky ligands such as dtbpx undergo an extremely fast methanolysis. An increasing stericbulk of the ligand favors the formation of methyl propanoate relative to the insertion of ethene leading toformation of oligomers or polymers in the catalytic reaction of ethene, carbon monoxide, and methanol.
|
