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Organosilicon aroxyls form disiloxybiaryls via C-C dimerization with simultaneous (or subsequent) isomerization of the dimeric intermediate, involving migration of the ortho-organosilyl substituents from carbon to oxygen.

A series of aroxytetraphenylstiboranes, Ph4SbOAr, were obtained by the reaction of pentaphenylstiborane with phenols at ∼20 °C. The thermolysis of these compounds givesO- or o-C-phenylation products. The thermolysis of stiboranes, which incorporate aryl groups containing electron-withdrawing substituents (Ar=2,4-Br2, 2,4-Cl2, 2-NO2, 4-OPh) produces predominantly simple diaryl ethers of asymmetric structure in 58 %, 90 %, 32 %, and 60 % yields, respectively.

The rate and pathway of reactions of 3,5-di-tert-butylbenzoyl trifluoroacetate with tert-butylphenols depend on the number and position of bulky substituents determining the extent of steric shielding of the phenolic hydroxyl.

The ESR method was used to study a series of sterically hindered silicon-containing phenoxyls — 2-trialkyl(dialkylalkoxy)silyl-4,6-di-tert-butylphenoxyls. The parameters of the ESR spectra were determined: the constants of splitting of the unpaired electron on meta-protons of the phenoxyl ring, protons of the organosilyl substituents, and magnetic silicon nuclei, as well as the spectroscopic splitting factors. The stability of the silicon-containing phenoxyls relative to one another was determined. The influence of a second Si-containing substituent in the ortho-position and an alkyl substituent in the para-position was followed on the example of 2,6-triphenylsilyl-4-tert-butylphenoxyl and the 2,6-trimethylsilyl-4-ethylphenoxyl radical. The stability of the aroxyls is determined primarily by the steric shielding of the radical site responsible for the dimerization-rearrangement reaction.

1. The stability of silicon-containing phenoxyl radicals depends on the degree of steric shielding of the reaction center, responsible for the dimerization, by the trialkylsilyl groups. 2. A linear relationship exists between the logarithms of the relative destruction rate constants of silicon-containing phenoxyl radicals and the sum of the steric constants of the alkyl substituents on the silicon atom. 3. The conversion of silicon-containing phenoxyl radicals to tetrasubstituted disiloxybiphenyls proceeds via the dimerization of the radicals to theα-ketomethyl form at the carbon atoms to which the trialkylsilyl groups, which migrate to the oxygen, are attached.

The 1,3-anionic rearrangement of aryloxysilanes is an intramolecular process that does not depend on the nature of the migrating organosilyl group but is controlled by the reactivities of the labile halogen of the aryloxysilane and of the organolithium compound in the halogen-lithium exchange reaction, which generates the silyloxyarenide ion.

1. The formation of three isomeric tetra-substituted disiloxydiphenyls in the dimerization-rearrangement of 2-trimethylsilyl-4-tert-butyl-6-triethylsilylphenoxyl is attributed to presence of two reaction sites which determine the ability of both the trimethylsilyl and triethylsilyl groups to undergo dimerization with migration. 2. The steric interaction of the ortho-organosilyl substituants in 2-trimethylsilyl-4-tert-butyl-6-triethylsilylphenoxyl alters the relative migratory capacity of these substituents relative to that in 2-trimethylsilyl- and 2-triethylsilyl-4,6-di-tert-butylphenoxyls.

1. The reaction of substituted o-bromophenoxysilanes with n-butyllithium leads to the lithium salts of substituted o-hydroxyphenylsilanes. 2. The formation of the lithium salts of substituted o-hydroxyphenylsilanes, instead of the expected aromatic organolithium compounds, is explained by anionic rearrangement, where 1,3-migration of the organosilyl groups occurs.

1. The oxidation of isotactic polypropylene, inhibited by additions of 2, 2′-dihydroxy-3, 3′, 5, 5′-tetra-tert-butyldiphenyl, 2, 2′-dihydroxy-3, 3′-bis-trimiethylsilyl-5, 5′-di-tert-butyldiphenyl, 4, 4′-bis-(2, 6-di-tert-butylphenol), and di-(3, 5-di-tert-butyl-4-hydroxybenzyl) sulfide, was studied; the first two are weak antioxidants, while the other two are strong antioxidants. 2. In the absence of reducing agents for the hydroperoxide groups, high antioxidative activity is possessed by conformations in which the OH groups are bonded together by a hydrogen bond. Of the biphenols with unbonded OH groups, substituted 4, 4′-dihydroxydiphenyl proved to be an effective antioxidant.

In the dimerization-rearrangement of silicon-containing aroxyls, the relative migration ability of o-organosilyl substituents decreases in the series PhMe2Si > Me3Si > MePh2Si > Ph3Si.

The character of the transformations of silicon-containing phenoxyl radicals depends on both the type of the alkyl substituent (disproportionation in the case of para-methyl group, dimerization-rearrangement in the case of para-isopropyl and para-cyclohexyl groups) and type of organosilyl substituent (dimerization-rearrangement in the case of ortho-trimethylsilyl group, disproportionation in the case of ortho-triethylsilyl and orthotriphenylsilyl groups).