title: Electrochemical Reduction of CO2Catalyzed by Re(pyridine-oxazoline)(CO)3Cl Complexes.
abstract: A series of rhenium tricarbonyl complexes coordinated by asymmetric diimine ligands containing a pyridine moiety bound to an oxazoline ring were synthesized, structurally and electrochemically characterized, and screened for CO2reduction ability. The reported complexes are of the type Re(N-N)(CO)3Cl, with N-N = 2-(pyridin-2-yl)-4,5-dihydrooxazole (1), 5-methyl-2-(pyridin-2-yl)-4,5-dihydrooxazole (2), and 5-phenyl-2-(pyridin-2-yl)-4,5-dihydrooxazole (3). The electrocatalytic reduction of CO2by these complexes was observed in a variety of solvents and proceeds more quickly in acetonitrile than in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). The analysis of the catalytic cycle for electrochemical CO2reduction by 1 in acetonitrile using density functional theory (DFT) supports the C-O bond cleavage step being the rate-determining step (RDS) (ΔG⧧= 27.2 kcal mol-1). The dependency of the turnover frequencies (TOFs) on the donor number (DN) of the solvent also supports that C-O bond cleavage is the rate-determining step. Moreover, the calculations using explicit solvent molecules indicate that the solvent dependence likely arises from a protonation-first mechanism. Unlike other complexes derived from fac-Re(bpy)(CO)3Cl (I; bpy = 2,2'-bipyridine), in which one of the pyridyl moieties in the bpy ligand is replaced by another imine, no catalytic enhancement occurs during the first reduction potential. Remarkably, catalysts 1 and 2 display relative turnover frequencies, (icat/ip)2, up to 7 times larger than that of I.
authors.affiliation: Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269-3060, United States.
authors.forename: John K
authors.initials: JK
authors.lastname: Nganga
authors.affiliation: Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269-3060, United States.
authors.forename: Christian R
authors.initials: CR
authors.lastname: Samanamu
authors.affiliation: Department of Chemistry, Vassar College , Poughkeepsie, New York 12604, United States.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Tanski
authors.affiliation: Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269-3060, United States.
authors.forename: Carlos
authors.identifier: http://orcid.org/0000-0002-5607-5517
authors.initials: C
authors.lastname: Pacheco
authors.affiliation: Department of Chemistry, DePaul University , Chicago, Illinois 60614, United States.
authors.forename: Cesar
authors.initials: C
authors.lastname: Saucedo
authors.affiliation: Department of Chemistry, Yale University , P.O. Box 208107, New Haven, Connecticut 06520, United States.
authors.forename: Victor S
authors.identifier: http://orcid.org/0000-0002-3262-1237
authors.initials: VS
authors.lastname: Batista
authors.affiliation: Department of Chemistry, DePaul University , Chicago, Illinois 60614, United States.
authors.forename: Kyle A
authors.initials: KA
authors.lastname: Grice
authors.affiliation: Department of Chemistry, Yale University , P.O. Box 208107, New Haven, Connecticut 06520, United States.|Chemistry Division, Energy & Photon Sciences Directorate, Brookhaven National Laboratory , Building 555A, Upton, New York 11973, United States.
authors.forename: Mehmed Z
authors.initials: MZ
authors.lastname: Ertem
authors.affiliation: Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269-3060, United States.
authors.forename: Alfredo M
authors.identifier: http://orcid.org/0000-0002-5560-4405
authors.initials: AM
authors.lastname: Angeles-Boza