Coordination Chemistry of the PEP Pincer Complexes of Co, Ni, Cu

조회수 : 76 등록일 : 2019.09.19 10:00

일시 : 2019.09.18 17:00
소속 : KAIST 화학과
발표자 : 이윤호
장소 : R404

Transition metal adduct formations with small molecules such as N2, H2, NOx and COx are drawing much

attention due to their importance in developing synthetic materials for various industrial applications. The

chemistry is based on pincer complexes with attention to the uniqueness of the coordination geometry found

in various metalloproteins. In our laboratory, a series of pincer complexes with low-valent 1st row transition

metals are currently under investigation. In this presentation, three topics will be presented regarding the

chemistry of four coordinate (PEP)M-L complexes (E = N, P or Si and M = Co, Ni, Cu), where the L site is

occupied by various ligands such as NHR2, N2, NOx and COx.

First, the chemistry inspired by an efficient enzymatic CO2 catalysis occurring at the active site of the

carbon monoxide dehydrogenase (CODH) will be discussed. Since the binding and reactivity toward CO2 is

controlled in part by the geometry of a L3Ni scaffold, we have explored the chemistry of low-valent nickel

supported by PEP pincer systems (E = P or N). By using PNP ligands, we have established the CODH like

closed synthetic cycle for CO2 reduction to CO occurring at the single nickel center. In addition, a (PNP)M

scaffold presenting unusual reactivity occurring at the structurally rigidified metal center will be introduced.

A T-shaped nickel(I) metalloradical reveals unique open-shell reactivity including the homolytic cleavage of

various s-bonds, such as H-H, N-N, and C-C, while its low spin cobalt congener shows s-complexation with

H2 and silane. Structurally rigidified species were utilized to explore CO2 hydrogenation and NOx conversion.

Secondly, metal-ligand cooperation (MLC) will be discussed. A (PEP)M scaffold having E = P or Si

reveals the interconversion between square planar and tetrahedral geometry, in which reversible group

transfer occurs between a phosphide/silyl moiety of a PPP ligand and a metal ion. This unusual group transfer

reaction is tightly coupled with metal’s local geometry and its 1 or 2 electron redox change. By employing

such cooperativity, nitrene group transfer was successfully accomplished to generate isocyanate.

Finally, the photophysical properties of copper complexes will be discussed. Since copper is a promising

candidate as a cheap and abundant light emitting material, we are currently working on developing new

organometallic copper-based light emitters. Inspired from the blue copper center, we prepared a series of 4-

coordinate copper complexes supported by tridentate RSiHP2 (RSiHP2 = RSi[2-PiPr2-C6H4]2, R = Me, Ph) with

a Si-H moiety as a weak axial ligand. Photophysical properties of such copper complexes will be presented.

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