Bis(carboxylato) complexes of platinum(II). Structural and bonding analysis of [Pt(O2CR)2(L–L)][L–L = 2PPh3, Ph2PCH2PPh2or Fe(C5H4PPh2)2; R = Me, CF3, Prior 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.

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