Involvement of a Binuclear Species with the Re−C(O)O−Re Moiety in CO_2 Reduction Catalyzed by Tricarbonyl Rhenium(I) Complexes with Diimine Ligands: Strikingly Slow Formation of the Re−Re and Re−C(O)O−Re Species from Re(dmb)(CO)_3S (dmb = 4,4'-Dimethyl-2,2'-bipyridine, S = Solvent)
Abstract
Excited-state properties of fac-[Re(dmb)(CO)_3(CH_3CN)]PF_6, [Re(dmb)(CO)_3]_2 (where dmb = 4,4'-dimethyl-2,2'-bipyridine), and other tricarbonyl rhenium(I) complexes were investigated by transient FTIR and UV−vis spectroscopy in CH_3CN or THF. The one-electron reduced monomer, Re(dmb)(CO)_3S (S = CH_3CN or THF), can be prepared either by reductive quenching of the excited states of fac-[Re(dmb)(CO)_3(CH_3CN)]PF_6 or by homolysis of [Re(dmb)(CO)_3]_2. In the reduced monomer's ground state, the odd electron resides on the dmb ligand rather than on the metal center. Re(dmb)(CO)_3S dimerizes slowly in THF, k_d = 40 ± 5 M^(-1) s^(-1). This rate constant is much smaller than those of other organometallic radicals which are typically 10^9 M^(-1) s^(-1). The slower rate suggests that the equilibrium between the ligand-centered and metal-centered radicals is very unfavorable (K ≈ 10^(-4)). The reaction of Re(dmb)(CO)_3S with CO_2 is slow and competes with the dimerization. Photolysis of [Re(dmb)(CO)_3]_2 in the presence of CO_2 produces CO with a 25−50% yield based on [Re]. A CO_2 bridged dimer, (CO)_3(dmb)Re−CO(O)−Re(dmb)(CO)_3 is identified as an intermediate. Both [Re(dmb)(CO)_3]_2(OCO_2) and Re(dmb)(CO)_3(OC(O)OH) are detected as oxidation products; however, the previously reported formato-rhenium species is not detected.
Additional Information
© 2003 American Chemical Society. Received 5 May 2003. Published online 6 September 2003. Published in print 1 October 2003. We thank Dr. Norman Sutin, Dr. Carol Creutz, Prof. Osamu Ishitani, Dr. Kazuhide Koike, and Prof. Kazuteru Shinozaki for valuable discussions. This work was performed at Brookhaven National Laboratory, funded under Contract DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Division of Chemical Sciences, Office of Basic Energy Sciences. S.K. acknowledges financial support from the Mombu-Kagaku-sho, Japan, as a fellow for research-in-abroad.Attached Files
Supplemental Material - ja035960asi20030710_025231.pdf
Supplemental Material - ja035960asi20030710_025400.pdf
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Additional details
- Eprint ID
- 76680
- DOI
- 10.1021/ja035960a
- Resolver ID
- CaltechAUTHORS:20170419-105301537
- DE-AC02-98CH10886
- Department of Energy (DOE)
- Mombu-Kagaku-sho
- Created
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2017-04-19Created from EPrint's datestamp field
- Updated
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2021-11-15Created from EPrint's last_modified field