SYNTHESIS, CHARACTERIZATION AND DYNAMIC BEHAVIOR OF PALLADIUM COMPLEXES CONTAINING THE NOVEL TERDENTATE NITROGEN LIGAND 2,6-BIS(PYRIMIDIN-2-YL)PYRIDINE

The ionic methylpalladium complexes [Pd(Me)(bppy)]X {X = Cl la, SO3CF3 1b, [3,5-(CF3)(2)C6H3](4)B 1c}, containing the novel flexible terdent ate nitrogen ligand 2,6-bis(pyrimidin-2-yl)pyridine, have been synthes ised. Complexes la-le reacted quantitatively with carbon monoxide, res ulting in formation of the acylpalladium complexes [Pd{C(O)Me}(bppy)]X {X = Cl 2a, SO3CF3 2b, [3,5-(CF3)(2)C6H3](4)B 2c}. Complexes 1a-1c an d 2a-2c have been isolated and fully characterised. In chloroform as w ell as in methanol, all the complexes show dynamic behaviour due to ex change of the co-ordinated and unco-ordinated pyrimidinyl nitrogen ato ms. The influence of solvent, methyl and acyl ligand, counter ion and the presence of free Cl- and CO on the dynamic behaviour has been stud ied and the thermodynamic parameters have been determined. A mechanism for the observed exchange process has been proposed. This mechanism i nvolves (a) dissociation of one of the pyrimidinyl nitrogen atoms, whi ch may be initiated by chloride, solvent or CO co-ordination, (b) rota tion about the pyrimidinyl-pyridine bond and (c) reformation of the ni trogen-palladium bond.