Heterogeneous cobalt-catalyzed degradation of azo compounds using alcohols as the stoichiometric hydrogen source

Abstract

Degradation of azo compounds is challenging but exciting to explore from both environmental and fundamental science aspects. Instead of using high H2-pressure, heterogeneous cobalt catalyzed efficient tandem transformation of azo compounds to the corresponding imines using stochiometric amount of alcohol is reported. Several cobalt-based heterogeneous catalysts were synthesized by varying the cobalt-ligand ratio, where the catalyst with cobalt:phenanthroline=1:6 was found to be the most active. Utilizing this protocol, selective degradation of a library of azo compounds was effectively carried out using various alcohols.The recyclability test revealed the catalyst could be recycled up to 6th times. In addition, the control experiments and the Hammett studies revealed this transformation was favorable, with the substrates having electron-donating substituents. The KIE study suggested the alcohol dehydrogenation was one of the slow steps. Moreover, the involvement of ordered transition states was demonstrated by the Eyring analysis.