Correlating Electronic and Physical Structure With Reactivity in Transition Metal Complexes for C-H Amination

Abstract

The development of efficient and selective routes for C–H amination is of interest as N–functionalities are an integral part of nature. To unveil essential attributes for facile C–H amination, the chemistry of cobalt nitrenoid complexes supported by a dipyrromethene ligand was explored through manipulation of their electronic and physical structure. In Chapter 2, the catalytic C–H amination mediated by open-shell Co(III) alkyl imido complexes (ArL)Co(NR) and (ArL)Co(NR)(py) (ArL = 5-mesityl-1,9-(2,4,6-Ph3C6H2)dipyrrin) is demonstrated, highlighting that a higher spin state renders the imido complexes more reactive. Chapter 3 describes the synthesis of a bent Co(III) alkyl imido complex (TrL)Co(NR) utilizing a sterically encumbered ligand (TrL = 5-mesityl-1,9-(trityl)dipyrrin). This subtle geometry modification of the imide substantially improves catalytic C–H amination performance in comparison to the linear congener (ArL)Co(NR). In an attempt to target higher-valent cobalt nitrenoid complexes, Chapter 4 presents the structural and spectroscopic characterization of Co(II) organoazide adduct precursors (ArL)CoBr(N3R) and the corresponding Co(III) alkyl iminyl complexes (ArL)CoBr(•NR) along with their C–H amination reactivity. Lastly, Chapter 5 describes intermolecular C–H activation and N–group transfer reactivity from a Co(II) aryl iminyl complex (TrL)Co(•NC6F5) to emphasize that the electronic structure and reactivity of the nitrenoid complex can also be tuned by the identity of the nitrene substituent.