121st General Meeting of the KCS

Type Poster Presentation
Area Inorganic Chemistry
Room No. Event Hall
Time 4월 19일 (목요일) 11:00~12:30
Code INOR.P-99
Subject Kinetic Study on Group Transfer Reaction Occurring at a (PPP)Ni Center using Para-substituted Phenoxides
Authors Nara Kim, Yunho Lee*
Department of Chemistry, Korea Advanced Institute of Science and Technology, Korea
Abstract Metal-ligand cooperation (MLC) based on non-innocent ligands has recently been considered an important concept in transition metal catalysis. MLC is different from the classical catalytic reactions in a way that both the metal center and ligand are actively involved in the reaction. While there are several exemplified non-innocent ligands employing various π-conjugated systems such as aryl-substituted bis(imino)pyridine, there are only few examples of non-innocent phosphine containing ligands. Our group recently reported a unique example of MLC by utilizing a phosphide-based ligand, PPP ligand (PPP– = P[2-PiPr2-C6H4]2–). Reversible phosphide/phosphinite interconversion of the PPP ligand is coupled with a redox change at the central metal ion, which involves a structural change between square planar and tetrahedral. In order to understand this unusual MLC, (PPP)Ni(ER) with various ER groups (E = O or S, R = aryl or alkyl) were investigated with a π-acidic ligand such as CO and isocyanide. A nickel(II)-isopropoxide complex, (PPP)Ni(OiPr), undergoes two different pathways. While migratory insertion (MI) occurs with CO, the reaction of (PPP)Ni(OiPr) with CNtBu generates a MLC product having a P-O bond via reductive elimination (RE). In the case of thiolate group, a reversible intramolecular P-S bond formation via thiolate group transfer occurs with CO. In this presentation, we will discuss the mechanism of the metal-ligand cooperative reaction occurring at the nickel center supported by a PPP ligand. In order to understand the bond cleavage between nickel and the oxygen atom of phenol during the MLC involving reaction, para substituted phenoxides having electron-donating and –withdrawing substituents were utilized. A series of nickel(II) complexes, (PPP)Ni(OC6H4X) (X = H, OMe, Me, CF3) were synthesized by treating (PPP)NiCl with corresponding para substituted phenoxide and their reactivity toward a π-acidic ligand, CO were investigated. Conversion to a zero-valent nickel monocarbonyl complexes was achieved from the carbonylation reactions of these nickel(II)-phenoxide complexes. To obtain the reaction rates, each reaction was monitored using variable temperature UV-Vis spectroscopy. Based on resulting kinetic data revealing clean pseudo first-order fits, the observed rate constants were determined.
E-mail narakim@kaist.ac.kr