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

The five-coordinate complexes [PtMe(cod)(N-N')]BF4 [cod = eta(2), eta(2)-cyclooctadiene, N-N' = (6-R-2)C5H3N-2-CH=NR1 (R-1 = C6H4OMe-4, R-2 = H (1), Me (2); R-1 = CMe3, R-2 = H (3), Me (4); R-1 = (R)-bornyl, R-2 = 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-MeOC6H4N=CHCHN=C6H4OMe-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 alpha-diimine and one C=C bond are on the equatorial plane and the second C=C 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-(CH=CH) bond [Pt-C2.08(1), 2.09(2) Angstrom, C=C 1.43(2) Angstrom (molecule I); Pt-C 2.13( 2), 2.10(2) Angstrom, C=C 1.42(2) Angstrom (molecule II)] and the axial Pt-(CH=CH) bond [Pt-C 2.35(1), 2.34(1) Angstrom, C=C 1.39(2) Angstrom (molecule I); Pt-C 2.37(2), 2.34(1) Angstrom, C=C 1.38(2) Angstrom (molecule II)] are related to the high trans influence of the methyl ligand and to greater d-pi back-donation in the equatorial bond.