[Mo2(MeCN)8][BF4]4 supported on silica: an efficient heterogeneous catalyst for the ring-opening metathesis polymerization of norbornene

Abstract

The dimolybdenum(II,II) complex salts [Mo₂(MeCN)₈][BF₄]₄, and [Mo₂(µ-O₂CMe)₂(MeCN)₆][BF₄]₂ have been supported on silica to give materials represented as [Mo₂(MeCN)₈][BF₄]₄–SiO₂ and [Mo₂(µ-O₂CMe)₂(MeCN)₆][BF₄]₂–SiO₂, respectively. Unsupported [Mo₂(MeCN)₈][BF₄]₄, [Mo₂(MeCN)₈][BF₄]₄–SiO₂, unsupported [Mo₂(µ-O₂CMe)₂(MeCN)₆][BF₄]₂ and [Mo₂(µ-O₂CMe)₂(MeCN)₆][BF₄]₂–SiO₂ were each tested as heterogeneous catalysts for the ring-opening metathesis polymerization of norbornene (bicyclo[2.2.1]hept-2-ene). In the absence of AlEtCl₂ cocatalyst [Mo₂(MeCN)₈][BF₄]₄–SiO₂was the only species to polymerize norbornene, and at 90°C and a reaction time of 48 h the polymerization was essentially quantitative. Species [Mo₂(MeCN)₈][BF₄]₄. [Mo₂(µ-O₂CMe)₂(MeCN)₆][BF₄]₂ and [Mo₂(µ-O₂CMe)₂(MeCN)₆][BF₄]₂–SiO₂ were found to be completely inactive without AlEtCl₂, even at elevated temperatures. In the presence of AlEtCl₂ cocatalyst [Mo₂(MeCN)₈][BF₄]₄–SiO₂ was the only material which failed to polymerize norbornene at room temperature.