Reactions of co-ordinated ligands. Part 57. Synthesis, structure and interrelationship of 2-σ-butadienyl and cationic (1,2,3-η)-trans-butadienyl-platinum and -palladium complexes; crystal structures of cis-[PtCl{σ-C(CH2)C(Et)CH2}(dppf)] and [Pt{(1,2,3-η)-trans-CH2C(Et)CCH2}(PPh3)2][PF6][dppf = 1,1′-bis(diphenylphosphino)ferrocene]

Abstract

Reaction of the platinum(0) complexes [Pt(C₂H₄)(PPh₃)₂], [Pt(C₂H₄)(dppf)][dppf = 1,1-bis(diphenylphosphino)ferrocene], [Pt(cod)₂](cod = cyclocta-1,5-diene) and the palladium(0) complex [Pd(PPh₃)₄] with the 4-chlorobuta-1,2-dienes CH₂CC(R)CH₂Cl (R = Me or Et) affords trans or cis 2-σ-butadienyl complexes of the general formula [MCl{σ-C(CH₂)C(R)CH₂}L₂]; the structural identity of cis-[PtCl{σ-C(CH₂)C(Et)CH₂}(dppf)] was confirmed by single-crystal X-ray diffraction. Treatment of [Pt(C₂H₄)(PPh₃)₂] or [Pt(C₂H₄)(dppf)] with an excess of 2-chlorobuta-1,3-diene leads to the formation of the corresponding unsubstituted 2-σ-butadienyl platinum complexes. Addition of thallium hexafluorophosphate to these 2-σ-butadienyl complexes results in elimination of TICI and formation in high yield of a range of cationic (1,2,3-η)-trans-butadienyl complexes characterised by NMR spectroscopy, and in the case of [Pt{1,2,3-η)-trans-CH₂C(Et)CCH₂}(PPh₃)₂][PF₆] by single crystal X-ray diffraction.