Charge and Spin Confinement to the Amine Site in 3-Connected Triarylamine Vinyl Ruthenium Conjugates

Abstract

The triarylamine vinyl ruthenium conjugate (4-OMeC6H4)2N{C6H4-3-CH═CH-RuCl(CO)(PiPr3)2} (m-1) has been prepared and investigated in its neutral and one-electron-oxidized states. Comparison with tris(4-anisylamine), An3N, and the related 4-methoxystyryl complex 4-OMeC6H4-CH═CH-RuCl(CO)(PiPr3)2, 2, shows that the intrinsic formal potentials of the two nonidentical redox-active subunits of complex m-1 (triarylamine and vinyl ruthenium) are very similar. Complex m-1 is oxidized in two consecutive one-electron waves with a half-wave potential splitting of 320 mV. Detailed investigations of the one-electron-oxidized radical cation m-1•+ by IR and EPR spectroscopy and by quantum chemical calculations as well as comparison to An3N•+ and 2•+ indicate that the charge and the unpaired spin of m-1•+ are dominantly located on the triarylamine site. This is in stark contrast to the previously published para isomer p-1•+, which, despite the nonidentical redox sites, is a fully delocalized mixed-valent system of Class III. As a consequence of partial charge localization, the low-energy absorption bands in the near-infrared assume the character of ruthenium or styryl ruthenium to triarylamine intervalence charge-transfer (IVCT) transitions with significantly diminished absorptivities compared to the highly intense charge resonance bands of p-1•+. Hush analysis of the IVCT bands indicates that m-1•+ is a significantly coupled mixed-valent system of Class II. The crystallographically determined structures of complexes m-1 and 2 and of the amine precursor (4-OMeC6H4)2N(C6H4Br-3) (An2N-Br) are also reported.