Synthesis and Reactivity of Bis(alkoxyalkylidene)platinum(II)\nComplexes^§

Abstract

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