δ-Hydrogen abstraction from alkyl and phosphine ligands co-ordinated to platinum(II); formation of benzoplatinacyclopentene complexes

Abstract

Reactions of [Pt(cod)Cl₂](cod = cyclo-octa-1,5-diene) with Mg(CH₂C₆H₄Me-o)Br and tertiary phosphines (PR₃) afford cis-[Pt(CH₂C₆H₄Me)₂(PR₃)₂](R = Et or Ph), which on refluxing in xylene give the benzoplatinacyclopentene complexes [[graphic omitted]H₂)(PR₃)₂]viaδ-hydrogen abstraction reactions. Using PPh₂(C₆H₄Me-o), metallation of the phosphine is preferred and the first obtained product after refluxing in xylene is [[graphic omitted]Ph₂)(CH₂C₆H₄Me){PPh₂(C₆H₄Me-o)}]. On further refluxing in xylene, this compound again eliminates o-xylene to give the known [[graphic omitted]Ph₂)₂]. Using P(C₆H₄Me-o)₃, the bulkiness of the phosphine makes alkylation unfavourable and the fluxional [[graphic omitted](C₆H₄Me-o)₂}{P(C₆H₄Me-o)₃}Br] is obtained. The variable-temperature n.m.r. spectra of this compound are interpreted in terms of hindered rotation around the Pt–P and P–C bonds giving rise to two different conformers at low temperature, each with all methyl groups non-equivalent. The compounds have been identified by their spectroscopic properties and some of their reaction chemistry is discussed.