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]

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).