Selective C-H Oxidation Using a Heterogeneous Cobalt Catalyst and Green Oxidizers


Activating C-H bonds is highly attractive to the field of green chemistry because it can provide atom-economic syntheses and permit late-stage functionalization, even of complex organic molecules, without the introduction and removal of directing groups. It also has the potential to convert feedstock chemicals from oil, natural gas, and biomass into higher value chemicals. Since many of the catalysts that are currently employed in C-H activation require precious metals, our current challenge is to replace these catalysts using earth-abundant and cheaper first row transition metals. Using first row metals is more amenable to large scale application. Interestingly, first row metals are employed by enzymes for selective C-H activation reactions in nature.  


This project aims to develop an efficient system for selective oxidation of a wide range of organic substrates including compounds containing unactivated C-H bonds.  We recently reported the synthesis and characterization of a highly active heterogeneous cobalt water oxidation catalyst formed from simple and abundant starting materials. We are investigating its use in conjunction with an environmentally benign oxidant to selectively oxidize organic substrates under mild reaction conditions. 


Broad application of C-H oxidation in industry is limited by the cost of late transition metals as a result of their scarcity and the need to recover the metals post reaction due to recycling and toxicity concerns.  First row metals tend to be much more abundant and thus cheaper. The ability to incorporate oxidations late-stage in the synthetic scheme rather than having to use bulky protection groups early on can greatly improve atom-economy, reduce the use of solvents and waste generated, and reduce the overall number of steps required. Further refinement of the catalyst and conditions could also yield selective oxidations of complex organic molecules containing multiple functionalities. This would be of great interest in the synthesis of pharmaceuticals and natural products.