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.