1H, 31P and 195Pt NMR characterization, and X-ray molecular structures of five and six-membered platinum(II) and palladium(II) metallacycles from the alcoholysis of di- and triazaphosphole complexes

Abstract

The 1,2,3-diazaphosphole P=C(H)C(Me)=NNMe (LA) (LA) and the 1,2,4,3-triazaphospholes P=NC(Ph)=NNMe (LB) (LB) and P=NN(Me)C(Me)=N (LC) (LC) form Pt(II) and Pd(II) complexes of stoichiometry MX2(PEt3)L (X = Cl, Br) whose controlled reactions with alcohols, generally methanol, have been studied by 1H, 31P and 195Pt NMR spectroscopy. Discrete intermediate species and the final novel monomeric phosphito metallacacycles (-P bonding of a {P(=O)(OR)RŒ}− function and N-coordination of either an imine or amine function) have been identified by their characteristic multinuclear NMR data. These data allow a stepwise mechanism for the azaphosphole ring-opening to be proposed. Two representative products of the series derived from LA and LC, namely [Pt{P(=O)(OMe)N(H)C(PH)=NN(H)Me}(Cl)(PEtA)] (19c) and [Pt{P(=O)(OMe)N(H)N(Me)C(Me)=NH}(Cl)(PEtA)] (20c) have been characterized by X-ray structure investigations. In the crystal the bonding of the P,N-chelating ligand in 19c is different to that identified in solution: the two ligand forms found can be described in terms of amidine tautomerism. (In this paper for simplicity we refer to a {P(=O)(OR)RŒ} ligand as a phosphite; this is strictly only correct if R is (bonded through) an electronegative element and in eases where R is C-bound the ligand is more properly a phosphinite.)