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

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• 作者：Etienne Chénard ; Andre Sutrisno ; Lingyang Zhu ; Rajeev S. Assary ; Jeffrey A. Kowalski ; John L. Barton ; Jeffery A. Bertke ; Danielle L. Gray ; Fikile R. Brushett ; Larry A. Curtiss ; Jeffrey S. Moore
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：April 28, 2016
• 年：2016
• 卷：120
• 期：16
• 页码：8461-8471
• 全文大小：554K
• 年卷期：0
• ISSN：1932-7455

文摘

Following the discovery of the redox-active 1,4-bis-BF<sub>3sub>-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<sub>3sub>-quinoxaline adduct. Using solution and solid-state 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 <sup>11sup>B solid-state NMR experiments. Crystallographic analysis of single crystals helped to correlate the boron geometry with <sup>11sup>B quadrupolar coupling constant (C<sub>Qsub>) and asymmetry parameter (η<sub>Qsub>), extracted from <sup>11sup>B solid-state NMR spectra. Additionally, computations based on density functional theory were performed to predict electrochemical behavior of the BF<sub>3sub>–heteroaromatic complexes. We then experimentally measured electrochemical potential using cyclic voltammetry and found that the redox potentials and C<sub>Qsub> values are similarly affected by electronic changes in the complexes.