Carbon–chlorine bond activation in 2-chloromethylallyl complexes of platinum(II)

Abstract

Treatment of [Pt(C₂H₄)(PPh₃)₂] or [Pt(PPh₃)₄] with 3-chloro-2-chloromethylprop-1-ene (1) and KPF₆ at room temperature affords [Pt{η³-CH₂C(CH₂Cl)CH₂}(PPh₃)₂][PF₆](3a). The carbon–chlorine bond in (3a) is reactive and treatment of (3a) with the Lewis bases L (L = PPh₃, NEt₃, or pyridine) in the presence of KPF₆ affords the dicationic salts [Pt{η³-CH₂C(CH₂L)CH₂}(PPh₃)₂][PF₆]₂. Reaction of (3a) with lithium bromide gives [Pt{η³-CH₂C(CH₂Br)CH₂}(PPh₃)₂][PF₆]. A phosphonium salt [Pt{σ-CH₂C(CH₂PPh₃)CH₂}{P(OMe)₃}₃][PF₆]₂ is formed on addition of trimethyl phosphite and KPF₆ to (3a). Evidence for the activation of the carbon–chlorine bond in (3a) is provided by the much slower reaction of (1) with PPh₃ and KPF₆ to give [CH₂C(CH₂Cl)(CH₂PPh₃)][PF₆] and triethylamine and KPF₆ with [Pt{σ-CH₂C(CH₂)CH₂Cl}(S₂CNMe₂)(PPh₃)] to give [Pt{σ-CH₂C(CH₂)CH₂NEt₃}(S₂CNMe₂)(PPh₃)][PF₆]. A bridging trimethylenemethane complex [Pt{η³-CH₂C[CH₂PtCl(PPh₃)₂]CH₂}(PPh₃)2][PF₆] is formed in the reaction of (3a) with [Pt(C₂H₄)(PPh₃)₂] and KPF₆. N.m.r. data for the complexes are reported, the assignments of the syn and anti protons in [Pt{η³-CH₂C(CH₂PPh₃)CH₂}(PPh₃)₂][PF₆]₂ being confirmed by a proton–proton nuclear Overhauser enhancement difference experiment.