Achieving Control over the Reduction/Coupling Dichotomy of N2 by Boron Metallomimetics.

We report a detailed computational and experimental study of the fixation and reductive coupling of dinitrogen with low-valent boron compounds. Consistent with our mechanistic findings, the selectivity toward nitrogen fixation or coupling can be controlled through either steric bulk or the reaction conditions, allowing for the on-demand synthesis of nitrogen chains. The electronic structure and intriguing magnetic properties of intermediates and products of the reaction of dinitrogen with borylenes are also elucidated using high-level computational approaches.

Reduction and Rearrangement of a Boron(I) Carbonyl Complex.

The one-electron reduction of a cyclic (alkyl)(amino)carbene (CAAC)-stabilized arylborylene carbonyl complex yields a dimeric borylketyl radical anion, resulting from an intramolecular aryl migration to the CO carbon atom. Computational analyses support the existence of a [(CAAC)B(CO)Ar].- radical anion intermediate. Further reduction leads to a highly nucleophilic dianionic (boraneylidene)methanolate.

Main-Group Metallomimetics: Transition Metal-like Photolytic CO Substitution at Boron.

The carbon monoxide adduct of an unhindered and highly reactive CAAC-bound arylborylene, [(CAAC)B(CO)Ar] (CAAC = cyclic (alkyl) (amino)carbene), has been prepared using a transfer reaction from the linear iron borylene complex [(PMe3) (CO)3Fe=BAr]. [(CAAC)B(CO)Ar] is a source of the dicoordinate [(CAAC)ArB:] borylene that can be liberated by selective photolytic CO extrusion and that, although highly reactive, is sufficiently long-lived to react intermolecularly. Through trapping of the borylene generated in this manner, we present, among others, the first metal-free borylene(I) species containing a nitrogen-based donor, as well as a new boron-containing radical.

Reactivity study of Lewis superacidic carborane-based analogue of 9-bromo-9-borafluorene towards Lewis bases.

In this contribution, we present the reactions of the o-carborane-based analogue of 9-bromo-9-borafluorene, a Lewis superacid, with diverse Lewis bases. A range of acid-base adducts, along with an intramolecular C-H activation product, were generated. All new compounds have been fully characterized.

Avenue to novel o-carboranyl boron compounds - reactivity study of o-carborane-fused aminoborirane towards organic azides.

Herein we report the reactivity study of o-carborane-fused bis(trimethylsilyl)aminoborirane towards three different types of organic azides, i.e., aryl, alkyl, and silyl azides. The reaction with ArN3 (Ar = 2,6-iPr2C6H4, 2,6-C6H3Cl2, 2,4,6-C6H2Br3, C6F5) resulted in the cycloaddition of ArN3 to the borirane BN unit accompanied by silyl migration. Conversely, in the reaction with BnN3, only the BnN3 : borirane 1 : 2 ring expansion product was obtained. Finally, the reaction with Me3SiN3 resulted in a formal nitrene insertion product under thermal conditions. All of the newly obtained o-carborane-fused BN-containing heterocycles were fully characterized, and the mechanism of these substituent-dependent reactions was studied using DFT calculations.

A step-for-step main-group replica of the Fischer carbene synthesis at a borylene carbonyl.

The Fischer carbene synthesis, involving the conversion of a transition metal (TM)-bound CO ligand to a carbene ligand of the form [=C(OR')R] (R, R' = organyl groups), is one of the seminal reactions in the history of organometallic chemistry. Carbonyl complexes of p-block elements, of the form [E(CO)n] (E = main-group fragment), are much less abundant than their TM cousins; this scarcity and the general instability of low-valent p-block species means that replicating the historical reactions of TM carbonyls is often very difficult. Here we present a step-for-step replica of the Fischer carbene synthesis at a borylene carbonyl involving nucleophilic attack at the carbonyl carbon followed by electrophilic quenching at the resultant acylate oxygen atom. These reactions provide borylene acylates and alkoxy-/silyloxy-substituted alkylideneboranes, main-group analogues of the archetypal transition metal acylate and Fischer carbene families, respectively. When either the incoming electrophile or the boron center has a modest steric profile, the electrophile instead attacks at the boron atom, leading to carbene-stabilized acylboranes - boron analogues of the well-known transition metal acyl complexes. These results constitute faithful main-group replicas of a number of historical organometallic processes and pave the way to further advances in the field of main-group metallomimetics.