SUBSTITUENT EFFECTS ON THE ELECTROCHEMICAL OXIDATION OF N,N'N''-TRIPHENYL-1,3,5-TRIAMINOBENZENES

Correlation analysis of the oxidation potentials of a series of N,N',N ''-triphenyl-1,3,5-triaminobenzene (TPABs) substituted at the para po sitions of the outer phenyl rings shows a linear free energy relations hip with resonance-enhanced substituent parameters (sigma(+)). Reactio n parameters (rho(+)) for oxidation of TPABs were found to be -1.53, - 1.45 and -1.34 (per substituent) in methylene chloride, acetonitrile a nd propylene carbonate respectively. The resonance enhancement and sma ll magnitude of the rho(+) values are related to a significant but wea k delocalization of charge onto the outer phenyl rings in the molecula r orbitals of radical cations resulting from the oxidation of TPABs. D ata on the oxidation of p-substituted triphenylamines were treated sim ilarly and gave a rho(+) value of -3.27 (per substituent) in acetonitr ile, greater than that for TPABs owing to a more significant delocaliz ation of charge onto the phenyl rings in the molecular orbitals of the corresponding radical cations. To demonstrate their predictive value, these linear free energy correlations were used to estimate the oxida tion potentials of similarly substituted N,N,N',N '',N ''-hexaphenyl-1 ,3,5-triaminobenzenes which are of interest as building blocks for mol ecular magnetic materials. (C) 1998 John Wiley & Sons, Ltd.