Treatment of p-tert-butylcalix [4]arene with dichlorodimethylsilane yields a single product, p-tert-butylcalix [4]areneSiMe 2 (OH) 2 (4), in which one dimethylsilyl group bridges adjacent oxygens. Subsequent treatment of 4 with butyllithium and methyl trifluoromethanesulfonate yields two products, p-tert-butylcalix [4]arene(SiMe 2 ) 2 (5) and a lithium triflate complex of p-tert-butylcalix [4]arene(OMe) 4 , 6‚LiO 3 SCF 3 . No evidence is found for the expected product p-tert-butylcalix[4]areneSiMe 2 (OMe) 2 ( 7). This can be viewed as a formal disproportionation reaction of 7, although the mechanism of the formation of 5 and 6 likely does not involve initial formation of 7. A large difference in the 1 H NMR resonances for the nonequivalent methylsilyl groups in both 4 and 5 is found. This is attributed to the proximity of one methyl group to the π system of the aromatic rings of the calix[4]arene backbone. The structures of 4 and 5 were determined by X-ray diffraction.
Treatment of p-tert-butylcalix[5]arene with RMeSi(NMe2)2 (R = Me, Ph) yields both di-
and monosubstituted products: calix[5](RMeSi)2(OH) (1a, R = Me; 1b, R = Ph) and calix[5](RMeSi)(OH)3 (2a, R = Me; 2b, R = Ph). In all derivatives, the silicon atom bridges adjacent
oxygens on the calix[5]arene. Isolation of the monosubstituted compounds requires careful
control of stoichiometry using an excess of p-tert-butylcalix[5]arene. Variable-temperature
NMR spectra of 2a suggest that at least two different exchange processes are occurring; the
high-temperature process appears to involve complete inversion of the calixarene with an
activation energy of 64.4 (1.6) kJ/mol. These compounds are isolated and structurally
characterized. The four solid-state structures closely approximate the four different ideal
conformations of calix[5]arenes.
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