Complexes of platinum and palladium with tertiary dimethoxyphenylphosphines: attempts to effect O- or C-metallation

Abstract

The new tertiary phosphines PBu^t₂R and PPh₂R (R = 2,3- or 2,6-dimethoxyphenyl) are described and characterized. The compound PPh₂[C₆H₃(OMe)₂-2,6] reacts with BBr₃ followed by acetic anhydride to give PPh₂[C₆H₃-(OCOMe)₂-2,6]. Conformational and steric effects of these new ligands are discussed and, as expected, bulky phosphines are demethylated more readily than less bulky ones on complex formation with platinum; 2,6-di-methoxyphenylphosphines lose one methyl group particularly easily on complex formation, 2,3-dimethoxyphenylphosphines less readily. Stable complexes of the type cis-[Pt{OC₆H₃(OMe)(PPh₂)}₂] and trans-[Pt{OC₆H₃-(OMe)(PBu^t₂)}₂] have been prepared, where the ligand chelates through the phenoxo-oxygen and the phosphinophosphorus atoms. The dichelate cis-[Pt{OC₆H₃(OMe-6)(PPh₂-2)}₂] is reduced by Na[BH₄] to the hydride [PtH{OC₆H₃(OMe-3)(PPh₂-2)}{PPh₂[C₆H₃(OH-2)(OMe-6)]}]. Although several palladium complexes of the above ligands have been prepared, attempts to effect O-metallation have been unsuccessful, palladium metal being obtained. O-Metallation is favoured by a polar solvent, but in xylene PPh₂[C₆H₃(OMe)₂-2,6] reacts with [PtCl₂-(NCPh)₂] to give the C-metallated complex [Pt₂Cl₂{CH₂OC₆H₃(OMe-3)(PPh₂-2)}₂], several derivatives of which have been prepared. Attempts to effect di-C-metallation have been unsuccessful; on heating the complex cis-[PtMe₂{PPh₂[C₆H₃(OMe)₂-2,6]}2] methane is evolved but crystalline products have not been isolated. Hydrogen-1 n.m.r. and i.r. data are given.