Reactivity of co-ordinated ligands. Part VII. Reactions of diene complexes of palladium(II) and platinum(II) with carboxylic acids

Abstract

The preparation of a series of (diene)metal carboxylate complexes with general formula [(carboxycyclo-enyl)M-(OCOR)]₂ from the reaction of (diene)MCl₂(diene = cyclo-octa-1,5-diene, norbornadiene, cyclo-octatetraene, dicyclopentadiene, and tetraphenylcyclobutadiene; M = Pd, Pt; R = Bu^t, Me, Ph, CH₂Cl, CHCl₂, CCl₃, CF₃) with the appropriate carboxylic acid is described. The complexes are considered to be dimeric with carboxylate bridges and with the carboxycyclo-ene ligand linked to the metal by both a σ and an olefinic bond. Exchange equilibria involving the carboxylates have been examined using ¹H and ¹⁹F n.m.r. The platinum trifluoroacetates appear to exist in monomer–dimer equilibrium. Thermodynamic parameters for the exchange of trifluoroacetic acid for other carboxylate moieties in chloroform solution have been obtained, and indicate that formation of M–C bond is facilitated by electropositive substituents attached to the double bond. Complex formation generally appears to be dominated by the tendency toward M–C σ bond formation in this system.