Synthesis of B/Si Bidentate Lewis Acids, o-(Fluorosilyl)borylbenzenes and o-(Difluorosilyl)borylbenzenes, and Their Fluoride Ion Affinities.

Abstract

Herein, we report detailed studies on a series of o-(silyl)(boryl)benzenes (1–4), in which the two Lewis acid centers consisting of silicon and boron atoms are linked via an o-phenylene skeleton. o-(Fluorosilyl)(dimesitylboryl)benzenes 1 and 2 were prepared by the reaction of fluorodimesitylborane with [o-(fluorodimethylsilyl)phenyl]lithium (7) and [o-(fluorodiphenylsilyl)phenyl]lithium (8), respectively. o-(Difluorosilyl)(dimesitylboryl)benzenes 3 and 4 were also prepared by the reaction of fluorodimesitylborane with o-{[di(methoxy)methylsilyl]phenyl}lithium (11) and o-{[di(methoxy)phenylsilyl]phenyl}lithium (12), respectively, and their subsequent treatment with HF·pyridine. Compounds 1–4 readily capture a fluoride ion in the presence of 18-crown-6 or [2.2.2]cryptand to afford their corresponding μ-fluoro-bridged ate complexes (15–18). The structures of 15–18 were revealed by NMR spectroscopy and X-ray crystallography. DFT studies and natural bond orbital analysis of 15–18 were conducted to elucidate the nature of the Si–F and B–F bonding interactions in the μ-fluoro-bridges. The fluoride ion affinities of 1–4 were investigated by 1H NMR spectroscopy to monitor their competitive reactions. The dynamic behaviors of 15–18 at variable temperatures were monitored using 19F NMR spectroscopy.