Bis(carboxylato) complexes of platinum(II). Structural and bonding analysis of [Pt(O2CR)2(L–L)][L–L = 2PPh3, Ph2PCH2PPh2 or Fe(C5H4PPh2)2; R = Me, CF3, Pri or Ph]

Abstract

Treatment of [PtCl₂(L–L)][L–L = 2 PPh₃, Ph₂PCH₂PPh₂(dppm) or Fe(C₅H₄PPh₂)₂(dppf)] with Ag(O₂CR)(R = Me, CF₃, Prⁱ or Ph) at room temperature generally gave [Pt(O₂CR)₂(L–L)] in moderate to good yields. The crystal and molecular structures of [Pt(O₂CMe)₂(dppf)]·H₂O, [Pt(O₂CPh)₂(dppf)]·CH₂Cl₂ and [Pt(O₂CCF₃)₂(dppm)] have been determined by single-crystal X-ray diffractometry. All these complexes show a mononuclear square-planar structure with a chelating diphosphine and two neighbouring (cis) carboxylates in a monodentate mode. These structures contrast those of the parent [Pt₄(µ-O₂CMe)₈] and its derivative [Pt₄(en)₄(µ-O₂CMe)₄]⁴⁺(en = ethylenediamine) which are tetrameric, based on octahedral Pt^II, and contain bridging acetates and direct Pt–Pt bonds. Fenske–Hall molecular orbital calculations of these structures confirmed the existence of Pt–Pt bonding interactions. The presence of hard and electronegative ligands like en and acetate incurs a deficiency in σ-electron density, compared to virtually filled non-bonding orbitals; the former is alleviated by Pt–Pt bonding. d⁸ Complexes with ligands like phosphines possessing both σ-donating and π-accepting qualities appear to favour the usual square-planar geometry.