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

The new tertiary phosphines PBut2R 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)(PBut2)}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.