THERMAL AND METHYLLITHIUM-ASSISTED CYCLOMETALLATION REACTIONS OF ETA-3-ALLYL(METHYL)(TERTIARY PHOSPHINE OR PHOSPHITE)PLATINUM(II) COMPLEXES

The complexes [Pt(eta-3-C3H5)Me(L)] [L = P(C6H4Me-o)3, PPh2(C6H4Me-o), PPh2(CH2Ph), PPr3 and P(OPh)3] have been prepared and characterized by H-1 and C-13 NMR spectroscopy. Four of these complexes decompose in boiling toluene to give the cyclometallated complexes [Pt(eta-3-C3H5)(P-C)] (P-C = cyclometallated phosphine or phosphite), which have also been characterized spectroscopically. The complex [Pt(eta-3-C3H5){o-CH2C6H4P(C6H4Me-o)2}] exists as a novel pair of conformers in solution. Addition of an equivalent of methyllithium to a solution of [Pt(eta-3-C3H5)Me{P(C6H4Me-o)3}] in toluene promotes cyclometallation of the phosphine ligand, giving the cyclometallated product without heating, while using tetrahydrofuran does not give a cyclometallated product. A tentative mechanism of the methyllithium-assisted cyclometallation reaction is proposed based on the product analysis.