Spectroscopic and Structural Characterization of the CyNHC Adduct of B₂pin₂ in Solution and in the Solid State

Abstract

The Lewis base adduct of B(2)pin(2) and the NHC (1,3-bis(cyclohexyl)imidazol-2-ylidene), which was proposed to act as a source of nucleophilic boryl groups in the β-borylation of α,β-unsaturated ketones, has been isolated, and its solid state structure and solution behavior was studied. In solution, the binding is weak, and NMR spectroscopy reveals a rapid exchange of the NHC between the two boron centers. DFT calculations reveal that the exchange involves dissociation and reassociation of NHC rather than an intramolecular process.

Easy access to nucleophilic boron through diborane to magnesium boryl metathesis

“…3a). In common with the comparable distances within compounds such as 5 and 6 , the B–B bond of compound 9 [1.7503(18) Å] is only marginally elongated in comparison to that reported for B 2 pin 2 itself determined at both high [295 K; 1.716 Å] and low [120 K, 1.7041(15) Å] temperatures48.…”

Singular Metal Activation of Diboron Compounds

“…However, the progress in this field has opened a new window toward the activation of tetra(alkoxy) diboron compounds in a metal-free context by the formation of Lewis acid-base adducts [167][168][169][170][171][172][173][174][175] and their addition to unsaturated substrates can be performed with total chemo-, regio-, and stereoselectivity. Therefore, this historical prospection toward the activation of diboron has moved from direct reaction of Cl 2 B-BCl 2 with alkenes to the current methodology that circumvent the activation of tetra(alkoxy)diboron reagents with simple LBs.…”

Asymmetric Catalytic Borylation of α,β-Unsaturated Acceptors

“…NHC-bound diboron (III) adds to the substrate and a carbene intermediate is regenerated. Marder and co-workers carried out the spectroscopic and structural characterization of the Lewis adduct [42]. The crystal structure of the Lewis adduct was elucidated, and NMR revealed weak binding and rapid exchange of the NHC between the two boron centers in solution.…”