Synthesis and Reactivity of Bis(alkoxyalkylidene)platinum(II) Complexes

Abstract

The reaction of hexachloroplatinic acid with bis(trimethylsilyl)acetylene in various alcohols (EtOH, i-PrOH, n-BuOH, BnOH) led to the formation of the platina-β-diketone [Pt2(μ-Cl)2{(COMe)2H}2] (1a). Unexpectedly, in absolute MeOH the reaction of hexachloroplatinic acid with trimethylsilyl-substituted alkynes yielded the cis-dichlorobis(methoxyalkylidene)platinum(II) complexes [PtCl2{C(OMe)R‘}2] (R = Me (2a), Et (2b), Hex (2c)). These complexes reacted in wet solvents, yielding the corresponding platina-β-diketones. Hexabromoplatinic acid was found to react with bis(trimethylsilyl)acetylene in different alcohols, resulting in the formation of the cis-dibromobis(alkoxyethylidene)platinum(II) complexes [PtBr2{C(OR)Me}2] (R = Me (3a), Et (3b), i-Pr (3c), n-Bu (3d)). In contrast to this, analogous reactions with hexaiodoplatinic acid afforded the trans-diiodobis(alkoxyethylidene)platinum(II) complexes [PtI2{C(OR)Me}2] (R = Me (4a), Et (4b), i-Pr (4c), n-Bu (4d), (S)-2-Bu (4e)). It was observed that complex 4a isomerizes in CH2Cl2 to cis-diiodobis(methoxyethylidene)platinum(II), [PtI2{C(OMe)Me}2] (5). All complexes were characterized by microanalyses and IR and 1H and 13C NMR spectroscopy. Complexes 2a,b were also characterized by single-crystal X-ray diffraction analysis. Additionally, quantum-chemical calculations on the DFT level of theory dealing with the stability of cis-/trans-dihalobis(alkoxyalkyliden)platinum(II) complexes and rotational barriers were performed.