Tris(trimethylsilyl)methyl and tris(dimethylphenylsilyl)methyl derivatives of boron. Crystal structures of dihydroxy[tris(trimethylsilyl)methyl]borane and of the lithium–boron complex [(MeOH)2Li(µ-OMe)2B(OMe)2]

Abstract

Tris(trimethylsilyl)methyl-lithium, LiC(SiMe₃)₃, reacts with trimethoxyborane to give the compound (Me₃Si)₃CB(OMe)₂(7) and the lithium–boron complex LiB(OMe)₄(8). The latter is converted on crystallisation from methanol into the solvate [(MeOH)₂Li(µ-OMe)₂B(OMe)₂](11), which has been characterised by X-ray diffraction. The hydrolysis of (7) gives the dihydroxyborane (Me₃Si)₃CB(OH)₂(2), which may be converted into the dichloride (Me₃Si)₃CBCl₂(12), the difluoride (Me₃Si)₃CBF₂(14), the fluoride hydroxide (Me₃Si)₃CB(F)OH (15), the boranes (Me₃Si)₃CBR₂[R = Ph (16) or Me (17)], and the hydride [(thf)₃Li(µ-H)₃BC(SiMe₃)₃](3)(thf = tetrahydrofuran). An X-ray study shows that crystals of (2) consist of hydrogen-bonded dimers. Tris(dimethylphenylsilyl)methyl-lithium, LiC(SiMe₂Ph)₃, reacts with boron trifluoride–diethyl ether to give (PhMe₂Si)₃CBF₂(5), which may be hydrolysed to the dihydroxyborane (PhMe₂Si)₃CB(OH)₂(6).