Inorganic Chemistry Seminar: Dr. Yunho Lee, KAIST

Dr. Yunho Lee

Coordination Chemistry of 1st-row Transition Metal Pincer Complexes

 Transition metal adduct formations with small molecules such as N2, H2, CO and CO2 are drawing much attention due to their importance in developing synthetic catalysts for various industrial processes. In our laboratory, a series of such species with low-valent 1st row transition metals are currently under investigation. This effort is to show their respective roles in small-molecule transformations that include the COx and NOx (x = 1 – 3) conversions for modeling ACS/CODH active site chemistry and biological denitrification processes, respectively. In this presentation, a particular study with pincer complexes (PEP)M-L (E = N, P or Si and M = Co, Ni, Cu), where the L site is occupied by various ligands such as NHR2, N2, COx and COOR will be discussed. Regarding the geometry and reactivity relationship, a (PPP)M scaffold reveals the interconversion between square planar and tetrahedral geometry in which reversible group transfer occurs between a phosphide moiety and a nickel ion via unanticipated metal-ligand cooperation. This unusual group transfer reaction is tightly coupled with metal’s local geometry and its 0/I/II redox couples. In contrast, a (PNP)M scaffold shows a selective reaction pattern occurring at the structurally rigidified nickel center. With a structurally rigidified acriPNP ligand, a T-shaped nickel(I) metalloradical species was successfully stabilized. Having a sterically exposed half-filled dx2-y2 orbital, this nickel(I) species reveals unique open-shell reactivity. Such modification is successful in selective conversion of CO2. The reduction of {(acriPNP)Ni(CO)}{BF4} also succeeded in generating mono- and zero-valent nickel carbonyl complexes. In fact, the Ni(0)-CO species reveals the selective addition of CO2 to give a nickel(II)-carboxylate species with the expulsion of CO. The closed synthetic cycle for CO2 reduction to CO was finally established with a (acriPNP)Ni system.

·       “Selective Transformation of CO2 to CO at a Single Nickel Center” Acc. Chem. Res., 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” J. Am. Chem. Soc., 2018, 140, 2179-2185.

·       “A T-Shaped Ni(I) Metalloradical Species” Angew. Chem., Int. Ed. 2017, 56, 9502.

·       “Carbon Dioxide Binding at a Ni/Fe Center; Synthesis and Characterization of Ni(η1-CO2-κC) and Ni-μ-CO2-κC:κ2O,O’-Fe” Chem. Sci. 2017, 8, 600.

·       “Phosphinite-Ni0 Mediated Formation of a Phosphide-NiII-OCOOMe Species via Uncommon Metal-Ligand Cooperation.” J. Am. Chem. Soc. 2015, 137, 4280.