Two Push–Pull Channels Enhance the Dinitrogen Activation by Borylene Compounds

Abstract

Recently, Braunschweig et al. found that borylene (CAAC)DurB, in which CAAC is a cyclic alkyl(amino) carbene and Dur refers to 2,3,5,6‐tetramethylphenyl, can bind and activate N2, and the resulting [(CAAC)DurB]2N2 is of a bent BNNB core. The N2 ligand in transition metal complexes is generally linear, so herein, the bonding nature of both terminal end‐on and end‐on bridging borylene‐N2 complexes is investigated with valence bond (VB) theory. In the terminal end‐on (CAAC)HBN2 the bonding follows the mechanism in transition metals with a σ donation and a π back‐donation, but in the end‐on bridging borylene‐N2 complex, the σ donation comes from the π orbitals of N2, and thus, there are two opposite and perpendicular push–pull channels. It is the push–pull interaction that governs the enhanced activation of N2 and the BNNB bent geometry. It is expected that the substituents bonded to B can modulate the bent angle and the strength of the push–pull interaction. Indeed, (CAAC)FB exhibits enhanced catalytic capacity for the activation of N2.

Cleavage of the N≡N Triple Bond and Unpredicted Formation of the Cyclic 1,3‐Diaza‐2,4‐Diborete (FB)2N2 from N2 and Fluoroborylene BF

“…Activation of N 2 molecules and weakening of its π bonds can mainly be attributed to interactions that donate electron density to its π* antibonding orbitals, and remove electron density from the π bonding orbitals of N 2 [21] . Unlike transition metal complexes, which provide a σ acceptor and a π donor orbital to form N 2 complexes (Figure 5 c), singlet FB can be viewed as an electrophilic σ donor and π acceptor (Figure 5 a).…”

“…Activation of N 2 molecules and weakening of its p bonds can mainly be attributed to interactions that donate electron density to its p*a ntibonding orbitals,a nd remove electron density from the p bonding orbitals of N 2 . [21] Unlike transition metal complexes,w hich provide a s acceptor and a p donor orbital to form N 2 complexes (Figure 5c), singlet FB can be viewed as an electrophilic s donor and p acceptor (Figure 5a). Its side-on attack on N 2 (Figures 5c and S12) enables electron donation from its sigma donor orbital into the p*M Oo fN 2 and removal of p-bonding electrons into the p*M Oo fB F. These bonding interactions are supported by an energy decomposition analysis (EDA).…”

Recent Advances in the Domain of Cyclic (Alkyl)(Amino) Carbenes

“… [148] Zhang et al. have computationally studied the role of cAAC ligands in the activation of dinitrogen by borylenes [149] …”

“…[148] Zhang et al have computationally studied the role of cAAC ligands in the activation of dinitrogen by borylenes. [149] Unlike transition metal carbonyls, Radacki et al reported the conversion of a cAAC based boryl radical (75) to cAAC-stabilized borylene carbonyl complex (76) in the presence of KC 8 and CO. The further one-electron reduction of 76 produces a novel dimeric borylketyl radical anion (77) by intramolecular Dipp group transfer to the carbonyl carbon.…”

Push–Pull Activation of N 2 : Coordination of Lewis Acids to Dinitrogen Complexes

“…Scheme 19. Dinitrogen activation by borylene species (Dur = duryl, Dipp = 2,6-diisopropylphenyl, CAAC = cyclic alkyl amino carbene).DFT calculations by the team of Mo with the use of block localized wavefunctions on a simplified model have shed light on this particular bonding 167. They have shown that it is the result of two opposite and perpendicular push-pull channels and interactions with the orbitals of N2 with p geometry only, as well as the uniqueness of borylenes for acting both as a Lewis acid and Lewis base.…”