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 1 H NMR spectroscopy to monitor their competitive reactions. The dynamic behaviors of 15–18 at variable temperatures were monitored using 19 F NMR spectroscopy.

The Field of Main Group Lewis Acids and Lewis Superacids: Important Basics and Recent Developments

“…[184] Analogous reaction between RSi(OTf) 3 with terpyrdine leads to triple charged Si-based LA 69-71 (Scheme 49), also isolated with OTf À counterions. [184] These LA react with POEt 3 , forming structurally characterized octahedral 67(OPEt 3 ) 2 + and 68(OPEt 3 ) 2 + and 71(OPEt 3 ) [184] Series of bidentate silicon-boron LA (Scheme 50) were reported by Shimada et al [185] Competition experiments in THF indicate the following order of Lewis acidity: 72 < 73 < 74 < 75. Calculated FIA values (in kJ mol À 1 ) in the gas phase indicate slightly different order 72 (336) < 73 (339) = 75 (339) < 74 (352).…”

“…Series of bidentate silicon‐boron LA (Scheme 50) were reported by Shimada et al [185] . Competition experiments in THF indicate the following order of Lewis acidity: 72 < 73 < 74 < 75 .…”