Activation of CH bonds by transition metals : V. A study of the mechanism of metallation reactions of benzyl- and meta-fluorobenzylphosphines with RhI,IrI, PdII and PtII compounds

Reaction of R₂PCH₂C₆H₅ (R = cyclohexyl or t-butyl) with [(COT)₂RhCl]₂, [(COT)₂IrCl]₂, PdCl₂ or PtCl₂(benzonitrile)₂ yields cyclometallated compounds. The reactivity appears to decrease in the order Ir^I ρ Rh^I ρ ρ Pd^II ≈ Pt^II, suggesting a different reaction mechanism for univalent and bivalent d⁸ metal atoms. Reaction of meta-FC₆H₄CH₂PR₂ with the same metal chlorides shows that for Rh^I and Ir^I a nucleophilic mechanism operates and for Pd^II an electrophilic one. For Pt^II no decision could be made on the basis of these experiments. Steric effects have a large influence on the rates of the reactions.