摘要：

A series of palladium(II) and platinum(II) complexes with the mono- and bis-chelate ligands bis[o-(methylthio)phenyl]phosphine and tris[o-(methylthio)phenyl]phosphine have been prepared and characterised. Despite the potential tridenticity of the first ligand it acts as a P/S monochelate to form square-planar complexes of type [M{PPh(C6H4SMe-o)2}X2](M = Pd, X = Cl, Br or I; M = Pt, X = Cl). Variable-temperature one- and two-dimensional NMR spectroscopy showed that pyramidal inversion of the co-ordinated sulfur atoms was accompanied by an exchange of pendant and bound methylthio groups. The ΔG values for both processes were in the range 43–69 kJ mol–1, being strongly metal and halogen dependent. The bis(chelate) complexes [M{P(C6H4SMe-o)3}2][ClO4]2 are also square planar with metal co-ordination involving one phosphorus and one sulfur of each ligand, the other two pairs of SMe groups being unco-ordinated. The X-ray crystal structure of [Pd{P(C6H4SMe-o)3}2][ClO4]2 shows the co-ordinated S-methyls to be mutually cis with respect to the metallocycle plane. In low-temperature solutions of this complex this cis form is assumed to be predominant. At higher solution temperatures a facile intramolecular exchange of all six methylthio groups occurs. The energy and probable mechanism of this fluxion are reported.

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