Reactivity and mechanism in the oxidative addition of iodoalkanes and di-iodoalkanes to a dimethylplatinum(II) complex

Abstract

The complex [PtMe₂(phen)], (1)(phen = 1,10-phenanthroline), reacts with primary alkyl iodides by the S_N2 mechanism. Cyclopropylmethyl bromide adds to (1) without any ring opening of the cyclopropyl group. The reactivity ratio towards (1) for MeI:EtI:PrI:BuI = 1 000:1:0.5:0.6 and the much greater reactivity of Mel is due to the bulky nature of the nucleophile (1). Di-iodoalkanes I(CH₂)_nI also react by the S_N2 mechanism to give first [PtIMe₂{(CH₂)_nI}(phen)] and then, with excess of complex (1), [{PtlMe₂(phen)}₂(µ-CH₂)_n], when n= 3–5. The neighbouring platinum atom in the Pt(CH₂)₃I group is found to activate the C–I bond by a factor of 5.6, compared to PrI, in oxidative addition to (1). The di-iodoalkanes CH₂I₂ and C₂H₄I₂ react with complex (1), at least in part, by a free-radical mechanism and the reasons for the change in mechanism are discussed.