Five-coordinate complexes of palladium(II) and platinum(II) with α-diimine and 1,5-cyclooctadiene ligands.

The five-coordinate complexes [PtMe(cod)(N–N)]BF4 [cod = η2,η2-cyclooctadiene, N–N = (6-R2)C5H3N-2-CH NR1 (R1 = C6H4OMe-4, R2 = H (1), Me (2); R1 = CMe3, R2 = H (3), Me (4); R1 = (R)-bornyl, R2 = Me (5))] are readily obtained from the reaction of [PtClMe(cod)] with N–N in the presence of NaBF4. The preparation of [PtMe(cod)(6)]BF4 (6 = 4-MeOC6H4NCHCHNC6H4OMe-4), [PdMe(cod)(N–N)]BF4 and [PtCl(cod)(N–N)]BF4 (N–N = 2, 4) requires chloride abstraction by AgBF4 from [PtClMe(cod)], [PdClMe(cod)] and [PtCl2(cod)], respectively, followed by coordination of N–N. The NMR spectral data suggest a trigonal-bipyramidal structure with chelating cod and N–N ligands, where the α-diimine and one CC bond are on the equatorial plane and the second CC bond in an axial position. The complexes [PtMe(cod)(1)]BF4 and [PtCl(cod)(2)]BF4 undergo dynamic processes in solution which bring about N–N ligand site exchange for the former, and exchange of all the olefinic protons for the latter. The X-ray diffraction analysis of [PtMe(cod)(2)]BF4 indicates that in the solid state, the complex assumes a distorted trigonal-bipyramidal geometry, similar to that proposed to exist in solution. For the two independent molecules in the asymmetric unit cell, the differences in the structural parameters between the equatorial Pt–(CHCH) bond [Pt–C 2.08(1), 2.09(2) Å, CC 1.43(2) Å (molecule I); Pt–C 2.13(2), 2.10(2) Å, CC 1.42(2) Å(molecule II)] and the axial Pt–(CHCH) bond [Pt–C 2.35(1), 2.34(1) Å, CC 1.39(2) Å (molecule I); Pt–C 2.37(2), 2.34(1) Å, CC 1.38(2) Å (molecule II)] are related to the high trans influence of the methyl ligand and to greater d–π back-donation in the equatorial bond.