|Coordination Chemistry of the PEP Pincer Complexes of Co, Ni, Cu|
: 175 : 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.