The synthesis and characterization of binuclear complexes of platinum (III)

Abstract

A reliable, high-yield synthetic method for the preparation of binuclear, metal-metal bonded platinum(III) complexes has been developed. A wide variety of complexes have been prepared by the following reaction sequence: Pt(,2)R(,4)((C(,2)H(,5))(,2)S)(,2) + 2Ag(xhp) (--->) Pt(,2)R(,4)(xhp)(,2)((C(,2)H(,5))(,2)S)(,n) + 2Ag('0) Pt(,2)R(,4)(xhp)(,2)((C(,2)H(,5))(,2)S)(,n) + xs pyridine (--->) Pt(,2)R(,4)(xhp)(,2)(py)(,n) + n(C(,2)H(,5))(,2)S where R = CH(,3) or Ph; xhp = 2-oxopyridinate anion where x = H, F, Cl, Br, or CH(,3); and n = 1 or 2. The coordination geometry of the product is dependent upon two factors. If the 6-substituent on the 2-oxopyridinate bridging ligand is large (i.e., Cl, Br, or CH(,3)) complexes are formed with a polar arrangement of bridging ligands and one axial ligand. These complexes are unique in that one platinum atom is penta-coordinated and the other platinum is hexa-coordinated. ('195)Pt NMR studies of these asymmetric complexes reveal very large Pt-Pt coupling constants, which range from 10-12000 Hz. Both polar and nonpolar complexes could be isolated if 2-oxopyridinate bridging ligands with relatively small 6-substituents (i.e. hp and fhp) were used. In these compounds the trans directing ability of the axial ligand plays an important role in determining the geometry of the products. If ligands such as R(,2)S or R(,3)P, which have strong trans directing capabilities, are coordinated to the axial positions, only polar complexes with one occupied axial site can be isolated. These compounds can be contrasted to those with weak or moderate trans directing ligands, such as pyridine or picoline, coordinated to the axial sites for which both polar and nonpolar complexes can be isolated. Moreover, these compounds can be reversibly interchanged by the addition or removal of an equivalent of the axial ligand. NMR studies of these compounds show that they form an equilibrium mixture of their polar and nonpolar forms over the course of several hours. X-ray crystal structures are reported for twelve new platinum(III) complexes. In addition, x-ray structures are reported for the very useful binuclear platinum(II) starting materials. Finally, UV/visible, ('195)Pt, ('13)C, and ('1)H NMR results are reported for most of the compounds.