Synthesis of new Mn19 analogues and their structural, electrochemical and catalytic properties

Abstract

We report the synthesis and structural characterisation of new Mn₁₉ and Mn₁₈M analogues, [Mn^III₁₂Mn^II₇(μ₄-O)₈(μ₃-OCH₃)₂(μ₃-Br)₆(HL^Me)₁₂(MeOH)₆]Br₂ (2) and [Mn^III₁₂Mn^II₆Sr(μ₄-O₈(μ₃-Cl)₈(HL^Me)₁₂(MeCN)₆]Cl₂ cluster (3), where H₃L^Me is 2,6-bis(hydroxymethyl)-p-cresol. The electrochemistry of 2 and 3 has been investigated and their activity as catalysts in the oxidation of benzyl alcohol has been evaluated. Selective oxidation of benzyl alcohol to benzaldehyde by O₂ was achieved using 1 mol% of catalyst with conversions of 74% (2) and 60% (3) at 140 °C using TEMPO as a co-catalyst. No partial conversion of benzaldehyde to benzoic acid was observed. The results obtained revealed that different operative parameters – such as catalyst loading, temperature, time, solvent and the presence of molecular oxygen – played an important role in the selective oxidation of benzyl alcohol.