Stable η- and σ-ethene cationic complexes of platinum(II)

Abstract

Stable cationic complexes of platinum(II) with η- and σ-ethene have been obtained in the decomposition of five-co-ordinate [Pt(C 2H 4)Cl 2(Me 4en)] (1), (Me 4en = N,N,N′,N′-tetramethylethylenediamine) in methanol. First a chloride ion dissociates forming the cationic intermediate [Pt(C 2H 4)Cl(Me 4en)] +, (3); the two mol of (3) couple with a mol of diamine, via. nucleophilic attack on η-ethene, to give the bis σ-ethene dimeric cation [Me 4en)ClPtC 2H 4N(CH 3) 2C 2H 4N(CH 3) 2C 2H 4PtCl(Me 4en) 2+, (2). Complex (2) can be readily isolated at O°C as the stable perchlorate salt, and by reaction with stoicheiometric amounts of aqueous mineral acids regenerates the parent cation (3), which has also been isolated and characterized. The general validity of this stepwise decomposition mechanism for five-co-ordinate complexes of type (1), together with the reactivity of η-ethene in cationic platinum(II) complexes is discussed.