Synthesis and structural characterization of mixed carbene-carboxylate complexes of palladium(II)

Mixed carbene-carboxylate complexes of Palladium(II) have been prepared by reacting {1,1′-dimethyl-3,3′-methylenediimidazoline-2,2′-diylidene} palladium(II) diiodide (1) [Angew. Chem. 107 (1995) 2602; Angew. Chem. Int. Ed. Engl. 34 (1995) 2371; J. Organomet. Chem. 557 (1998) 93] with AgO2CR, where R=CF3, CF2CF3 and CF2CF2CF3. In this manner, {1,1′-dimethyl-3,3′-methylenediimidazoline-2,2′-diylidene} palladium(II) bis(trifluo-roacetate) (2), {1,1′-dimethyl-3,3′-methylenediimidazoline-2,2′-diylidene} palladium(II) bis(pentafluoropropionate) (3) and {1,1′-dimethyl-3,3′-methylenediimidazoline-2,2′-diylidene} palladium(II) bis(heptafluorobutyrate) (4) were obtained. All three complexes were fully characterized by 1H-, 13C- and 19F NMR spectroscopy as well as ESI mass spectrometry. X-ray crystal structure analyses of complexes 3 and 4 reveal mononuclear species with a square planar metal center coordinated by a cis-chelating dicarbene and two monodentate carboxylate ligands. The results show that the introduction of a cis-chelating N,N-heterocyclic carbene ligand stabilizes the palladium-carboxylate moiety effectively.