PROJECT 1
Carbon Dioxide Activation at a Single Metal Center; CODH Modeling
Carbon dioxide conversions mediated by transition metal complexes continue to attract much attention due to its future potential utilization as a nontoxic and inexpensive C1 source for the chemical industry. Given the presence of nickel in natural systems that allow for extremely efficient catalysis, studies that focus on selective CO2 conversion with synthetic nickel species are currently of considerable interest in our group. Nickel species discussed in this work that are low-valent typically having 0, 1+ or 2+ oxidation states have been of specific interest. In Nature, an efficient catalytic transformation of both CO2 and CO occurs in an enzyme possessing nickel containing active sites. In carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS), CO is generated from the reduction of CO2 by CODH, and then delivered to the active site of ACS where acetyl-CoA is catalytically generated. In both active sites of enzymes important C-O bond activation and C-C bond formation occur at a 4-coordinate nickel center. Geometry and electronic structure of each nickel center are crucial to control the reactivity of corresponding nickel-carbon species. In order to explore the transformation of CO2 at a 4-coordinate metal center, we have worked with a series of 4-coordinate metal-CO2 (and CO) complexes supported by a PEP pincer-type ligand; E = N, P, Si. By systematic modification using a different central donor atom, successful electronic and structural tuning of the metal complexes was achieved.
By controlling the local environment of the metal center, certain CO2 coordination modes can be allowed and ultimately its selective conversion to desired products can be accomplished. Several examples of CO2 coordination modes to a single metal center as shown below are reported by our group. These geometries provide crucial mechanistic snapshots for the activation of carbon dioxide.
Selected Publications
“Selective Transformation of CO2 to CO at a Single Nickel Center” Yoo, C., Kim, Y.-E. and Lee, Y.* Acc. Chem. Ses. 2018,51, 1144-1152.
“Direct CO2 addition to a Ni(0)-CO species allowing the selective generation of a nickel(II) carboxylate with expulsion of CO” Sahoo, D., Yoo, C., and Lee, Y.* J. Am. Chem. Soc. 2018. 140, 2179-2185.
“Carbon Dioxide Binding at a Ni/Fe Center; Synthesis and Characterization of Ni(η1-CO2-κC) and Ni-μ-CO2-κC:κ2O,O’-Fe” Yoo, C., Lee, Y.,* Chem. Sci. 2017, 8, 600-605.
“Formation of a Tetranickel Octacarbonyl Cluster from the CO2 Reaction of a Zero-valent Nickel Monocarbonyl Species” Yoo, C. and Lee, Y.* Inorg. Chem. Front. 2016, 3, 849-855. Invited as a part of themed collection: 2015 Emerging Investigators by ICF.
“Formation of a Nickel Carbon Dioxide Adduct and its Transformation Mediated by a Lewis Acid” Kim, Y.-E., Kim, J. and Lee, Y.* Chem. Commun. 2014, 50, 11458-11461. Selected as an inside back cover.
Chemistry of Mononuclear Nickel(I) and Cobalt(I)
Paramagnetic d9 nickel(I) species have been proposed as potential active species in the paramagnetic mechanisms of various organometallic and bioinorganic reactions. Their particular reactivity toward small molecules such as CO, CO2, CH4 and H2 has been explored in the Lee group. Three distinct oxidation states of a nickel carbonyl species, formally Ni(II), +1 and 0 have been realized using both PNP and acriPNP systems. Unusual C-C bond coupling occurs at the single nickel center of (PNP)NiI-CO.
More recently, a T-shaped nickel(I) species, (acriPNP)Ni(I) having a sterically exposed nickel center possessing a half-filled dx2-y2 orbital was generated from our group. Its bond formation with various substrates is efficiently coupled with an inner-sphere single electron transfer resulting in the reduction of unsaturated molecules such as C2H4 and CO2 and homolytic cleavage of various σ-bonds including H-H, H2N-NH2 and H3C-CN. Such reactions instantaneously occur at room temperature suggesting that the preorganized nickel(I) center may provide a lower activation barrier.
Selected Publications
“A Low Spin Three Coordinate Cobalt(I) Complex and its Reactivity toward H2” Choi, J. and Lee, Y.* Angew. Chem. Int. Ed. 2019, 58, 6938-6942.
“A T-Shaped Ni(I) Metalloradical Species” Yoo, C., and Lee, Y.* Angew. Chem., Int. Ed. 2017, 56, 9502-9506. Selected as a Hot Paper and a back cover.
“Mechanistic Study on C-C Bond Formation of a Nickel(I) Monocarbonyl Species with Alkyl Iodide: Experimental and Computational Investigations” Yoo, C., Ajitha, M. J., Jung, Y. and Lee, Y.* Organometallics 2015, 34, 4305-4311.
“Transmethylation of a Four-Coordinate Nickel(I) Monocarbonyl Species with Methyl Iodide” Yoo, C., Oh, S., Kim, J. and Lee, Y.* Chem. Sci. 2014, 5, 3853-3858.
Transition Metal Mediated Carbon Dioxide Conversion
Developing efficient catalytic processes for utilization of CO2 has a tremendous impact directly in industrial chemistry. Formic acid and organic carbonates from the CO2 conversion are two major products explored in our group. Catalytic formate generation with cobalt complexes supported by PNP ligands are currently under investigation. By controlling the local geometry of the metal center, dramatic improvement in TOF was observed.
Selected Publications
“Catalytic Hydrogenation of CO2 with a Rigidified Cobalt Center” Choi, J. and Lee, Y.* Inorg. Chem. Front. 2020, Advance Article.
“Computer-Aided Rational Design of Fe(III)-Catalysts for the Selective Formation of Cyclic Carbonates from CO2 and Internal and Epoxides” Sinha, I., Lee, Y., Bae, C., Tussupbayev, S., Lee, Y., Seo, M.-S., Kim, J., Baik, M.-H.,* Lee, Y.,* and Kim, H.* Cat. Sci. Tech. 2017, 7, 4375-4387. From the themed collection: 2017 Catalysis, Science and Technology Hot Articles