Trimethylsilyl-p-phenylenediamines

Kricheldorf has reported the synthesis of lyotropic poly(amide-imide)s and poly(benzoxazole-amide)s. These were prepared by the polycondensation of N,N-bis(trimethylsilyl)-p-phenylenediamine or N,AT -bis(trimethylsilyl)-3,3 -dim-ethylbenzidine with the diacyl chloride of trimellitimide of p-aminobenzoic acid, or the imide formed from p-amino benzoic acid and terephthalic acid. Lyotropic behaviour was observed in cone, sulphuric acid solution [38]. A series of thermotropic poly(imide-amide)s was prepared based on trimellitimides formed from trimellitic anhydride and an a, -bis(4-aminophenoxy) alkane with carbon chain lengths 9-12. Melting points were in the range 250-300 °C. They formed smectic A phases and tended to degrade around the isotropisation temperatures (around 350 °C). Pendant methyl groups or occupied meta- groups tended to prevent mesophase formation [39]. Novel LC poly(imide-amides) have also been synthesised from new diamine spacers derived from linear diaminoalkanes and 4-nitrophthalic anhydride. A smectic and nematic phase were observed when 4,4 -biphenyl dicarboxylic acid was used as co-monomer [40]. 

Exceeding the limitation of molecular dynamics, the steric requirement of trimethylsilyl groups can cause drastic changes both in structure and of molecular properties of organosilicon compounds. For illustration, the so-called "Wurster s-Blue11 radical ions are selected On one-electron oxidation of tetramethyl-p-phenylenediamine, its dark-blue radical cation, detected as early as 1879 [11a], is gene-... 

The ESR spectra of radical anions of the trimethylsilyl derivatives of diimine (95), 1,4-benzoquinone diimide (65), and N-trimethylsilyl derivatives of aniline and p-phenylenediamine (62) have been obtained, and the data are summarized in Table IX. The results for all the systems illustrate the ability of the trimethylsilyl group to withdraw electron density from nitrogen. Its ability to delocalize 7r-spin population lies intermediate between alkyl groups and the phenyl ring (93, 63). The N-trimethylsilyl aniline and p-phenylenediamine radical anions represent the only known cases of aniline radical anions in which the odd electron occupies the antisymmetric 7r -orbital (62). Other systems in which this orbital might be anticipated to be lower in energy than the symmetric 77 -orbital have not been successfully reduced (83). 

FIGURE 15. He I photoelectron spectra (6-18 eV) of (a) A,A,A,, A, -tetrakis(trimethylsilyl)-and (b) AA -bisitrimethylsilylj-p-phenylenediamines with Koopmans assignment based on the eigenvalues —s4M1 of geometry-optimized AMI calculations with structural data for the space-filling representations of the crystal molecular structures... 

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