Five-coordinate complexes of palladium(ii) and platinum(ii) with α-diimine and 1,5-cyclooctadieneligands

Abstract

The five-coordinate complexes [PtMe(cod)(N–N′)]BF₄ [cod = η²,η²-cyclooctadiene, N–N′ = (6-R²)C₅H₃N-2-CHNR¹ (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.