Complexes of platinum(II), platinum(IV), rhodium(III) and iridium(III) containing orthometallated triphenylphosphine

Abstract

Treatment of [PtCl₂(SEt₂)₂] or [RhCl₃(SEt₂)₃] with 2-LiC₆H₄PPh₂ gives four-membered ring chelate arylplatinum(II) or arylrhodium(III) complexes [Pt{C₆H₄(PPh₂)-2}₂] and [Rh{C₆H₄(PPh₂)-2}₃], respectively, whereas the corresponding reaction of [IrCl₃(SEt₂)₃] gives IrCl{C₆H₄(PPh₂)-2}₂(PPh₃)] arising from cleavage of an Ir–C₆H₄(PPh₂) bond. The chemistry of [Pt{C₆H₄(PPh₂)-2}₂] is dominated by the lability of the Pt–P bonds, which are displaced sequentially by ligands at room temperature to give complexes containing monodentate C₆H₄(PPh₂), i.e. [Pt{C₆H₄(PPh₂)-2}{η¹-C₆H₄(PPh₂)-2}(L)] [L = PPh₃, P(OPh)₃, P(OMe)₃ or Bu^tNC] and [Pt{η¹-C₆H₄(PPh₂)-2}₂(R₂PCH₂CH₂PR₂)] (R = Ph, Me or Cy). In the cases of Me₂PCH₂CH₂PMe₂ and Cy₂PCH₂CH₂PCy₂, binuclear intermediates can be detected in which these ligands bridge two platinum atoms. Oxidative addition of methyl iodide or iodine to [Pt{C₆H₄(PPh₂)-2}₂] gives initially platinum(IV) complexes [PtI(R){C₆H₄(PPh₂)-2}₂] (R = Me or I) in which the added groups are mutually trans; in the final, stable products the added groups and the phosphorus atoms are, separately, mutually cis. Oxidative addition of bromine to [Pt{C₆H₄(PPh₂)-2}₂] gives initially trans-[PtBr₂{C₆H₄(PPh₂)-2}₂] but subsequent oxidation and hydrolysis at the phosphorus atoms gives chelate tertiary phosphine oxide complexes of platinum(IV). The molecular structures of [Rh{C₆H₄(PPh₂)-2}₃] and cis-[PtI(Me){C₆H₄(PPh₂)-2}₂] have been determined by X-ray crystallography.