Synthesis, Characterization, and Reactivity of Transition Metal Complexes Supported by Heteropolydentate Ligation

Abstract

Pincer complexes of the platinum group metals have been the subject of intense research in recent years, owing to the remarkable stoichiometric and catalytic reactivity exhibited by such complexes. In this context, research previously reported by the Turculet group has focused on developing the reactivity of new bis(phosphino)silyl pincer complexes that feature tridentate ligands of the type [R-PSiP] (R = alkyl or aryl). In an effort to further expand the scope of silyl pincer ligation, the study of complexes supported by new PSiN mixed donor ligands of the type [R-PSiN-R’] (R, R’ = alkyl or aryl) has been undertaken. This document details the synthesis of such PSiN ligand precursors, as well as the synthesis, characterization, and reactivity of platinum group metal complexes featuring such PSiN ligands.

In an effort to further expand the scope of silyl pincer ligation to non platinum-group metals, the study of Co complexes supported by PSiP ligation was undertaken. It was anticipated that such Co complexes featuring highly donating PSiP ligands could be able to mimic two-electron redox chemistry of the platinum group metals. The synthesis and characterization of [Cy-PSiP]Co complexes in both the CoI and CoII oxidation states is described, as well as an investigation of the ability of [Cy-PSiP]CoI to undergo two-electron oxidative addition reactions with substrates such as iodobenzene, and H2.

In order to further develop the applications of heteropolydentate ligands in transition metal chemistry, N-phosphinoamidine/amidinate ligands were identified as targets of inquiry. The exploration of the ability of sterically demanding N-phosphinoamidine/amidinate ligands to support reactive, low-coordinate complexes for use in catalytic applications is detailed. Of particular interest was the design of low-coordinate complexes that will be active in the iron and cobalt catalyzed reduction of unsaturated substrates. This thesis details the synthesis of novel sterically demanding N-phosphinoamidine/amidinate ligands and their corresponding low-coordinate iron and cobalt complexes. The remarkable activity of such iron and cobalt complexes in the catalytic hydrosilylation of carbonyl substrates as well as the catalytic hydroboration of alkenes is also discussed.