Date of Award

3-26-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Applied Science

First Advisor

Anindya Ghosh

Abstract

Pincer type ligands have received much attention, especially for their ease of synthesis employing easily available and inexpensive starting materials. Excellent thermal stability and high melting points enable these complexes to be potentially used in a range of organometallic catalysis. In recent years, the use of nitrogenous donors at the central coordinating-group position, such as pyridines, has gained much interest for their application in various organic transformation reactions. Main examples include the activation of carbon-halogen bond, carbon-hydrogen bond, activation of small molecules (CO2, N2), polymerization of alkenes, dehydrogenation reactions, and the transfer hydrogenation reaction. In this study, we synthesized pyridine based NNN pincer ligand (1) and its nickel (2) and iron (3) complexes and studied them for C-Cl and C-H activation reactions followed by cross-coupling with various Grignard reagents. The metals used for the study were considered based on their potential for high catalytic activity while being less toxic and economical. The catalysts showed unprecedented activity towards cross-coupling reactions with Grignard reagents and polychlorinated molecules. Cross-coupling reactions employing 3 were completed within 5 minutes. A turnover number (TON) and turnover frequency (TOF) as high as 483 and 5800 h-1 , respectively, with a catalyst loading of only 0.2 mol% were obtained for the reaction using 3, which to the best of our knowledge is the highest reported for such a transformation. The complexes were also found to be effective in sp3 and sp2 C-H activation of oxygen containing heterocycles (tetrahydrofuran, methyl-tetrahydrofuran, dioxane and furan) and coupling with Grignard reagents. These reactions were carried out under ambient reaction conditions with reaction time of about 0.5-1 h. To the best of our knowledge, this is the first example of a nickel based organometallic complex system capable of catalyzing C-C cross-coupling reaction involving the activation of a sp3 C-H. The nickel catalyst (2) showed high efficiency with a high TOF of 4100 h-1 and a catalyst loading of only 0.01 mol%. Iron complex 3 also demonstrated exceptional activity with a TOF of 1700 h-1, and the reactions completed within 1 h. This catalytic route could prove to be an efficient mode of activation of sp3 and sp2 C-H bonds in various heterocycles for the preparation of synthetically and pharmaceutically relevant molecules.

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