June 18, 2021
Synthesis and characterization of CCC-NHC manganese complex and catalytic activity in α- alkylation reaction of ketones using alcohols
Department of Chemistry
Mississippi State University
Friday, June 18, 2021
NHCs are essential ligands for the synthesis and stabilization of various transition metal and main group metal complexes due to the tendency to act as σ-donor of sp2 hybridized lone pair in carbene into σ- accepting orbital of metals. Utilizing advantages of both NHCs and the pincer structures, NHCs-based pincer complexes have been increasingly developed in recent years with their great potential in several processes such as CO2 reduction, borylation, nitrogen fixation, and C-X bond formation, etc... Meanwhile, the electronic and steric properties of pincer complexes can be fine-tuned by modifying three sites bonded to the metals without significant change in the coordination geometry, and thereby allowing variations in reactivity and selectivity of the pincer complexes toward different processes. After the first discovery of zirconium and rhodium complexes with CCC-NHC backbones reported in 2005, Hollis group has been interested in applying the CCC-NHC pincer precursor for other transition metals. Manganese, the third most abundant element in earth’s crust, is of significant advantages with its low-cost and less toxic features compared to most of the other transition metals. Herein, we extend the methodology to manganese and discuss the preparation of the first CCC-NHC manganese complex.
In previous years, transition-metal-catalyzed cross-coupling reactions have made great progress in the construction of C-C bond, which is one of the most fundamental synthetic methodologies. In 2016, Beller group first time applied manganese(I) pincer catalyst for the alkylation of ketones with primary alcohols. Inspired by the previous work on the synthesis and application of manganese complexes, the catalytic activity of air-stable CCC-NHC manganese pincer complex in α- alkylation reaction of ketones using alcohols was studied. The catalytic reaction proceeds via hydrogen autotransfer methodology and generates water as the only by-product. Low loading of catalyst (2 mol%) and base (20 mol%) were found sufficient for efficient cross-coupling. The CCC-NHCs manganese pincer complex is prepared, characterized and its catalytic activity in cross-dehydrogenative coupling reaction will be discussed.