Synthesis and characterization of monochelated carboxylatopalladium(II) complexes with nitrogen-donor chelating ligands. Crystal structures of diacetato(1,10-phenanthroline)- and diacetato(2,9-dimethyl-1,10-phenanthroline)-palladium(II)

Abstract

Two series of monochelated carboxylatopalladium(II) complexes of general formula [Pd(L–L)(MeCO₂)₂] and [Pd(L–L)(CF₃CO₂)₂][L–L = 1,10-phenanthroline (phen), 2,2′-bipyridine and their substituted derivatives] have been prepared and characterized. The chemical behaviour of the complexes in solution has been studied in different solvents mainly by means of ¹H NMR experiments. These showed that, unlike the acetato complexes, the trifluoroacetato derivatives undergo partial dissociation of the anionic ligand in Me₂SO solution at room temperature. A similar behaviour was also observed for the acetato complexes in CD₃OD. The signals of the H^2,9 protons in the phenanthroline series, and those of H^6,6 in the bipyridine one, are excellent probes for the evaluation of the environment of the palladium atom. The crystal structures of [Pd(phen)(MeCO₂)₂], [Pd(2,9-dmphen)(MeCO₂)₂]·0.40CH₂Cl₂ and [Pd(2,9-dmphen)(MeCO₂)₂]·0.25CHCl₃](2,9-dmphen = 2,9-dimethyl-1,10-phenanthroline) have been determined. The co-ordination geometry around palladium is square planar in all the structures, but significant deviations from the idealized geometry occur in the last two in order to relieve the interligand contacts. These monochelated carboxylatopalladium(II) complexes are active catalysts in carbon monoxide–olefin copolymerization. Some preliminary results on their catalytic activity are also reported.