Hydrocarbon Functionalization by Cobalt Quaterpyridine Complexes

Project: Research project

Project Details


Direct functionalization of unactivated C–H bonds is a promising strategy in organic synthesis. This transformation provides a simple and cost effective alternative to traditional multiple step reactions. Owing to the inertness of C–H bonds, the initial activation step often requires harsh reaction conditions. For example, cyclohexane is oxidised to cyclohexanol and cyclohexanone at >100 o C in the presence of cobalt salts as catalyst in industry. Hence, the development of an efficient catalytic system to oxidise hydrocarbons at ambient condition will be highly desirable.

We have recently synthesized a highly electrophilic cobalt(III) tert-butylperoxo complex, [CoIII (qpy)(OOt Bu)(NCCH3 )] 2+ , supported by the strong p-accepting qpy ligand (qpy = 2,2’:6’,2”:6”,2”’-quaterpyridine). This complex is able to efficiently functionalize a variety of hydrocarbons at ambient condition. However, the drawback of this cobalt quaterpyridine system is its reactivity limited to hydrocarbons with weak or mild C–H bonds. In this project, we aim to enhance the oxidising ability of our cobalt system towards functionalization of hydrocarbon in a wider substrate scope at ambient condition. On the basis of some promising preliminary results, we propose to tune the electronic effects on the qpy ligand with various substituents, and to replace the tert-butylperoxo group with other more oxidising analogs. Currently we have been able to generate in situ Co(qpy)hydroperoxo and Co(qpy)nitrene species which are significantly more reactive. These species can oxidise cyclohexane (with C– H bond dissociation energy of 99 kcal/mol) within minutes at ambient condition. Apart from C–H functionalization, [CoIII (qpy)(OOt Bu)(NCCH3 )] 2+ is also able to functionalize unsaturated hydrocarbons (e.g. styrene), via t BuOO transfer to the corresponding C=C bond at ambient condition. We propose to study the reaction mechanisms of the above reactions in detail using various kinetic and spectroscopic methods. These mechanistic insights would help us to develop an efficient catalytic system for hydrocarbon functionalization based on our cobalt quaterpyridine complexes. Our proposal should lead to the discovery of efficient catalytic systems for functionalization of hydrocarbons under mild conditions. Mechanistic studies, including trapping of intermediates, should provide insights in biological dioxygen activation processes.

Effective start/end date1/07/2130/06/24


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