SELECTIVE SYNTHESIS OF AMINES, IMINES AND NITRILES BY A WELL-DEFINED COBALT CATALYST

Abstract

The chemistry of amine, imine and nitrile-containing compounds plays a central role in synthesizing high-value products, e.g., drugs, fertilizer, and fine chemicals. The unquestionable benefits from these products to our society have prompted pharmaceutical and agricultural industries to develop better protocols for their synthesis. The traditional synthetic methods for these chemicals depend on toxic and mutagenic reagents and release huge waste. Hence, it is desirable to find an alternative way that circumvents these issues. Catalytic dehydrogenative coupling of alcohols provides an appealing approach since only water, or hydrogen gas are the possible byproducts, and alcohols are environmentally benign. So far, this research field has been predominated by catalysts containing noble metals, e.g., Pd, Ir, Rh, and Ru. These metals are rare, expensive, and toxic. So, it is highly desirable to search for more sustainable metal alternatives. In recent years, there have been a few breakthroughs on non-precious metal (Fe, Co, Mn, and Ni) based catalysts. However, the pincer ligand-supported catalyst dominates this field, and chemoselectivity control strategies are missing in most studies. Recently, our group developed an air and moisture-stable cobalt molecular catalyst stabilized by a tripodal mixed P/N donor ligand. The cobalt metal is earth-abundant, cheap, and less toxic. This cobalt catalyst showed excellent activities for the dehydrogenation of secondary alcohol into ketone, dehydrogenative homocoupling of primary alcohol into ester, and coupling of a secondary alcohol and primary alcohol into corresponding alcohol and ketone products. In my projects, I further explore the catalytic activities into a dehydrogenative hetero couple of primary alcohol and amine to secondary imine and amine. Also, the hetero couple of primary alcohol and nitrile into α-olefinic and α-alkylated nitrile product with water and/or hydrogen as byproducts. It is discovered that the product's selectivity strongly depends on the amount of base used in the reaction. A catalytic amount of base leads to an imine and α-olefinic nitrile product, while an excess base loading results in an amine and α-alkylated nitrile product. We expect that this study could provide helpful insight into selective organic synthesis and catalyst design.