Guino-o Research Group

 

Since the first reported N-heterocyclic carbene ligands (NHCs, Chart 1) by Wanzlick and Ofele and the later isolation by Arduengo in 1991, a rapid increase in number of this class of ligands is seen recently, as shown by a special issue of Coordination Chemistry Reviews in 2007 focusing on synthetic methodologies, structural coordination, electronic nature, and catalytic and bioinorganic applications.

Chart 1. a) Structural motif of common N-heterocyclic carbenes, b) 2 modes of coordination of imidazolylidenes.

The effectiveness of NHC-M (M = metal) complexes in catalysis is generally attributed to the donor ability of the carbene ligands and the strong NHC-metal bond formed, as a result, they are usually seen as “mimics” of phosphine ligands. However, compared to the phosphine ligands, these species are usually more stable towards heat, oxygen and moisture; consequently, more resistant to dissociation from the metal center.
Among the heterocycles, imidazolium derivatives have received most attention as ligands due to their strong nucleophilic nature, in addition to their ability to bind to metals in two different carbon atom positions, C2 and C4 (Chart 1). Triazolylidenes are less studied as ligands because of their relatively weaker donating ability. However, the transition metal complexes containing these ligands are in general, still kinetically stable species.

Students will use these carbene ligands to synthesize new catalyst systems that will be tested for dehydrogenation ability, a current interest in the field of hydrogen storage.

Students interested in joining the Guino-o research group will learn air-sensitive techniques such as use of a Schlenk-line and dry-box. If you are interested, please contact Dr. Guino-o at guin3862@stthomas.edu