Synthesis and initial reactivity studies of nickel complexes on a pincer scaffold
Date
2011
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Publisher
University of Delaware
Abstract
Catalytic oxidation reactions are prevalent in the chemical industry. The catalysts are often made with expensive metals and the mechanism(s) by which they operate are not well known. Studies of small molecules can lead to better understanding of mechanisms and thus lead to better catalysis design. Work has also been performed in designing catalysts using less costly metals. Nickel is one such metal, as it is a congener of platinum and palladium, two costly metals used widely in catalysis. Ligands can be altered to influence electronic and steric properties of the metal complexes, thus affecting catalytic activity. This thesis addresses the modification of an SCS pincer ligand and the synthesis of new nickel-SCS pincer complexes. Pincers are tridentate ligands that bind at adjacent coplanar sites. The designation "SCS" refers to the atoms at the coordination sites. The nickel-pincer complexes in this work are built from 2,6-
bis(alkylthiomethyl)bromobenzene skeletons, with the alkyl groups being altered. The work presented herein describes the synthesis and characterization of Ni(SCSiPr)Br, Ni(SCStBu)Br, Ni(SCSMe)OPh, and Ni(SCSMe)Me. The reactivity of Ni(SCSMe)Me was studied and found to form Ni(SCSMe)OPh when reacted with phenol. This showed that Ni(SCSMe)Me was able to deprotonate an acidic species to form a new complex. Ni(SCSMe)Me was also found to catalyze the oxidation of triphenylphosphine to triphenylphosphine oxide when dry O2 was introduced. Eight to ten turnovers were observed.