Synthesis of Pyridine– and Pyrazine–BF₃ Complexes and Their Characterization in Solution and Solid State

Abstract

Following the discovery of the redox-active 1,4bis-BF 3 -quinoxaline complex, we undertook a structure− activity study with the objective to understand the active nature of the quinoxaline complex. Through systematic synthesis and characterization, we have compared complexes prepared from pyridine and pyrazine derivatives, as heterocyclic core analogues. This paper reports the structural requirements that give rise to the electrochemical features of the 1,4-bis-BF 3 -quinoxaline adduct. Using solution and solidstate NMR spectroscopy, the role of aromatic ring fusion and nitrogen incorporation in bonding and electronics was elucidated. We establish the boron atom location and its interaction with its environment from 1D and 2D solution NMR, X-ray diffraction analysis, and 11 B solid-state NMR experiments. Crystallographic analysis of single crystals helped to correlate the boron geometry with 11 B quadrupolar coupling constant (C Q ) and asymmetry parameter (η Q ), extracted from 11 B solid-state NMR spectra. Additionally, computations based on density functional theory were performed to predict electrochemical behavior of the BF 3 −heteroaromatic complexes. We then experimentally measured electrochemical potential using cyclic voltammetry and found that the redox potentials and C Q values are similarly affected by electronic changes in the complexes.

Photochemical intermolecular dearomative cycloaddition of bicyclic azaarenes with alkenes

“…These observations strongly support an H-bonding interaction between the nitrogen atom of quinoline and the alcoholic proton of HFIP. The Lewis acid/base interaction between BF 3 •OEt 2 and quinolines has been previously disclosed (39). The proposal of these interactions to decrease the singlet-triplet energy gap was confirmed by density functional theory (DFT) calculations.…”

Triel‐Bonded Complexes between TrR3 (Tr=B, Al, Ga; R=H, F, Cl, Br, CH3) and Pyrazine

“…A survey of the CSD (Cambridge Structural Database) provides a number of examples of crystal structures that are similar to the complexes examined here, systems stabilized by π‐hole triel bonds. Several such examples, are illustrated in Figure S6. These examples contain not only a single triel bond but also symmetrical trimers with two π‐hole triel bonds engaging both pyrazine N atoms simultaneously.…”

Effects of crosslinking density and Lewis acidic sites on conductivity and viscoelasticity of dynamic network electrolytes

“…Boronic esters are well-known dynamic bonds, and the boron can act as a Lewis acid (electron acceptor) due to an empty p-orbital. [26][27][28][29][30] In our prior work, the addition of salt to a boronic ester network with ethylene oxide linkers resulted in a large drop in viscosity and modulus as the anion-boron coordination disrupted the network architecture. 17 Boron sites have also been pursued in linear, star, and network polymer electrolytes as they lead to improved salt dissociation and Li mobility by trapping or coordinating with the anion.…”