Application of triazolium-based metal complexes for catalytic oxidation of octane.

Abstract

A series of related 1,2,3-triazole compounds were synthesised and characterised by spectroscopic methods including NMR, IR, MS and X-ray diffraction. N-alkylation of the triazole compounds yielded 1,4-disubstituted triazolium ionic liquids (3.1-3.6). The ionic liquids were found to act as “green” solvent systems for the dissolution of an iron-based compound for the catalytic oxidation of n-octane. Recycling and re-usage of the system was found to be reproducible for three cycles and leaching of the catalyst to the product phase was associated with decrease of catalytic activity in subsequent cycles. Synthesis and characterisation of 1,2,3-triazolium-based nickel carbene complexes (4.1-4.6) by modification of reported synthetic methods was described. The molecular structures of three metal complexes (4.1, 4.3 and 4.4) were analysed by single crystal X-ray diffraction and fully discussed. The complexes were then tested for catalytic oxidation of alkanes in the presence of various oxidants under mild reaction conditions. Catalyst (4.3) with less bulky substituents on the triazolium ring exhibited the highest catalytic activity (15%) with H2O2 as the most productive oxidant. The main goals of this study were achieved because the catalyst systems were successfully synthesised, characterised and tested for activity in alkane oxidation. Indeed there was significant activity observed with all prepared catalysts, however from the results obtained, the nickel carbene catalysts in the presence of H2O2 demonstrated the highest efficiency in this work.