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 PtII, 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.