Significant progress has been made in the design of ligands with borane functionalities in the secondary coordination sphere to facilitate metal-borane cooperative processes. We will add to this growing field of research by synthesizing anionic, N-donating diborylamide ligands featuring boron Lewis acids proximate to the metal binding site. In this contribution, we report the synthesis of a 1,2-phenylenediboryl-based cyclic diborylamine compound. Deprotonation of the diborylamine with <i>n</i>-butyllithium results in the formation of the corresponding lithium diborylamide, which forms an unsolvated dimer structure in the solid state. Previously reported acyclic diborylamines give rise to linear, allene-like structures upon deprotonation, with a decrease in the B-N bond distance of nearly 0.1 Å due to nitrogen-boron pi-bonding. In contrast, our cyclic lithium diborylamide complex cannot achieve linearity due to ring constraints; in fact, there is no observed change in the B-N bond distance relative to the corresponding amine, indicating no enhancement in N-B pi-bonding. Furthermore, this bonding configuration preserves empty acceptor orbitals at boron, potentially enabling interactions with exogenous Lewis bases. Preliminary reactivity of this lithium diborylamide with iron and cobalt to form low-coordinate transition metal complexes will also be discussed. These findings will serve as the fundamental basis for the development of more robust chelating diborylamide ligands better suited for borane-assisted catalytic reactions.

Cyclic diborylamide complexes of lithium and first-row transition metals

ACS Spring Meeting 2021

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