Spin Isomers and Ligand Isomerization in a Three-Coordinate Cobalt(I) Carbonyl Complex

Malik H. Al-Afyouni, Elizaveta Suturina, Shubhrodeep Pathak, Mihail Atanasov, Eckhard Bill, Daniel E. Derosha, William W. Brennessel, Frank Neese, Patrick L. Holland

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16 Citations (Scopus)

Abstract

Hemilabile ligands, which have one donor that can reversibly bind to a metal, are widely used in transition-metal catalysts to create open coordination sites. This change in coordination at the metal can also cause spin-state changes. Here, we explore a cobalt(I) system that is poised on the brink of hemilability and of a spin-state change and can rapidly interconvert between different spin states with different structures ("spin isomers"). The new cobalt(I) monocarbonyl complex LtBuCo(CO) (2) is a singlet (12) in the solid state, with an unprecedented diketiminate binding mode where one of the C=C double bonds of an aromatic ring completes a pseudo-square-planar coordination. Dissolving the compound gives a substantial population of the triplet (32), which has exceptionally large uniaxial zero-field splitting due to strong spin-orbit coupling with a low-lying excited state. The interconversion of the two spin isomers is rapid, even at low temperature, and temperature-dependent NMR and electronic absorption spectroscopy studies show the energy differences quantitatively. Spectroscopically validated computations corroborate the presence of a low minimum-energy crossing point (MECP) between the two potential energy surfaces and elucidate the detailed pathway through which the β-diketiminate ligand "slips" between bidentate and arene-bound forms: rather than dissociation, the cobalt slides along the aromatic system in a pathway that balances strain energy and cobalt-ligand bonding. These results show that multiple spin states are easily accessible in this hemilabile system and map the thermodynamics and mechanism of the transition.

Original languageEnglish
Pages (from-to)10689-10699
Number of pages11
JournalJournal of the American Chemical Society
Volume137
Issue number33
Early online date12 Aug 2015
DOIs
Publication statusPublished - 26 Aug 2015

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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    Al-Afyouni, M. H., Suturina, E., Pathak, S., Atanasov, M., Bill, E., Derosha, D. E., Brennessel, W. W., Neese, F., & Holland, P. L. (2015). Spin Isomers and Ligand Isomerization in a Three-Coordinate Cobalt(I) Carbonyl Complex. Journal of the American Chemical Society, 137(33), 10689-10699. https://doi.org/10.1021/jacs.5b06078