Synthesis and Catalytic Application of PSiP- and P,N-Ligated Complexes of First-Row Metals

Abstract

The study of PSiP pincer complexes of second- and third-row transition metals has led to the discovery of challenging bond activation chemistry as well as catalytic chemistry. While there now exists a considerable amount of literature regarding the behavior of PSiP complexes of the second- and third-row metals, comparatively little is known of the behavior of these ligands with the first-row metals. There has been a recent push toward the study of first-row transition metal chemistry in general, due to their high natural abundance and often lower toxicity when compared to their second- and third-row congeners. This document details progress toward the synthesis of a variety of novel Fe, Co and Ni complexes featuring PSiP ligation and application toward catalytic reduction of unsaturated substrates. In terms of (PSiP)Fe chemistry, considerable progress has been made toward the synthesis of novel coordination complexes, in particular the synthesis of hydride complexes of Fe. Organometallic hydride complexes are often implicated as important catalytic intermediates, and in this case a bis(dinitrogen) adduct of an Fe hydride has been identified as a highly active catalyst for the hydrogenation of olefins. Co chemistry with the same ligand has unveiled intriguing examples of both H2 and O2 bond cleavage chemistry, and again has led to an example of an alkene hydrogenation catalyst. A novel PSiP framework has been developed and applied toward chemistry of the group 10 transition metals, particularly nickel. In this regard, chemistry of complexes supported by this new ligand was found to be markedly different than that of similar complexes supported by the previous iteration of the ligand. In particular, a Ni hydride complex was successfully prepared and applied toward the selective reduction of CO2 to the formaldehyde level via hydroboration. Lastly, outside the realm of PSiP chemistry, a new monoanionic P,N-based ligand has been developed and its chemistry has been explored with respect to Fe and Co. Interesting coordination chemistry has been observed with this new ligand, and examples of reactive Fe and Co complexes have been obtained and applied toward the challenging reduction of tertiary amides to amines via catalytic hydrosilylation.