Cationic olefin complexes of platinum(II): Aspects of availability and reactivity

Abstract

The series of complexes of formula [PtCl(η2-olefin)(N^N)]+, previously investigated for N^N=N,N,N′,N′-tetramethyl-ethylenediamine (Me4en), has been extended to the case of aromatic diimines 1,10-phenanthroline (phen) and 3,4,7,8-tetramethyl-1,10-phenanthroline (Me4phen) and to a variety of olefins (ethene, propene and styrene). The complexes have been prepared by reaction of the [PtCl3(η2-olefin)]− anions (K[PtCl3(η2-styrene)] reported here for the first time) with N^N in basic methanol. The initial [PtCl{η1-CH2CH(R′)OMe}(N^N)] (R′=Me, Ph) complexes are formed in quantitative yield and as pure Markovnikov isomer. The reaction of the alkoxylic species with non coordinating acids, results in the quantitative formation of the desired cationic π-olefin complexes [PtCl(η2-olefin)(N^N)]+. The phenanthroline ligand confers peculiar properties to the new compounds. In particular, by reaction with triethylamine, [PtCl{η2-CH2CH(Me)}(N^N)]+ species, undergo deprotonation of the olefin and formation of the dimeric species [{PtCl(N^N)}2(μ-η1:η2-CH2CHCH2)]+ which could be isolated and characterized. Interestingly such product in acetonitrile gives a disproportionation with precipitation of [PtCl2(phen)] and formation in solution of the new η3-allyl complex [Pt(η3-C3H5)(phen)]ClO4.