61st Annual Report on Research 2016

The efficient chemical conversion of carbon dioxide (CO₂) to useful fuels remains an unsolved and intriguing scientific problem. One promising approach that has emerged in the past forty years is to use electrocatalysts to convert CO₂ into commodity chemicals. If the requisite electrons for this process are obtained from renewable sources (e. g., solar, wind, hydroelectric, etc.), a carbon­–neutral process may be envisioned. However, the feasibility of large–scale systems that facilitate this electrocatalytic conversion depends on the development of active, selective, and affordable catalysts. Many electrocatalysts have been developed that can mediate these processes, including heterogeneous and homogenous transition–metal compounds. In the latter group, several first-row transition metal catalysts have been reported with manganese, iron, cobalt, nickel and copper metal centers. Our work focused on Mn(I)­–centered catalysts as a template. We preferred manganese to other catalysts because of its greater abundance and hence lower material costs, and because of its positively–shifted redox potential. During the grant period five modifications within the primary coordination sphere were achieved: 1) replacement of a pyridine in the 2,2’-bipyridine (bpy) backbone of MnBr(bpy)(CO)₃ with an N-heterocyclic carbine (NHC) (cf. 1 and 2); 2) substitution of the axial bromine ligand with other pseduo-halogen ligands, such as CN and NCS (3 and 4); and 3) modulation of the ligand p-acidity of a simple 2,2’-bipyridine derivative (cf. 5). In each case, the new catalyst produced was thoroughly characterized (including X-ray analysis) and then its effectiveness to reduced CO₂ was determined. These results show that our rationally designed NHC ligands have the potential to enhance the catalytic activity as well as increase the stability of Mn(I)­­–­catalyst systems. Many follow-up experiments are envisioned and these preliminary results were reported in the six publications listed below. Several NHC–rhenium centered catalysts were also prepared and investigated.

Personnel Report:

On October 20, 2016 Charles Stanton III defended his dissertation and was awarded a Ph.D. degree. One week later he drove to New Castle, Delaware and assumed a research position with Adesis, Inc. synthesizing organic ligands and organometallic compounds which are subsequently screened for their potential in OLED devices. Prior to that date he was supported continuously by this PRF NEW Directions grant as a research graduate assistant.

Funds provided by this grant were used to support Tom Irvin for 3 to 4 months in early 2015 until he obtained a postdoctoral research assistantship working at the N. I. H. (he defended his Ph.D. degree in December of 2014 while waiting for career opportunities to materialize).

Jonathan Vandezande, a doctoral candidate studying theoretical, computational chemistry, was supported in 2016 for three months by this grant. He is a co-author on four the six papers that were produced during the funding period.

Because no new students joined my research group for the duration of the grant, funds were used to support Charles Stanton and his ongoing research into the preparation of CO₂ reducing catalysts, which also represented a new research direction for me. A potentially positive effect of this grant was that six manuscripts on new CO₂ reducing catalysts were published in refereed journals which may benefit funding opportunities.