Research on Synthesis and Aromaticity of Diaza [n] annulenes

Secondly, aromaticity of octaethylporphyrin (OEP) was studied from various structural viewpoints. Complexes of vinylene-bridged bis(OEP)-M and tris(OEP)-M with d^8 transition-metal ions (M=Ni(II), Pd(II), and Pt(II)) were synthesized. ^1H NMR spectra varied more drastically for (Z)-bis(OEP)-M, with respect to those of OEP-M, while electronic absorption spectra for (E)-isomers. Electronic properties at the ground state were examined, proving that the interaction between the constituent QEP rings through the vinylene-linkages is more intensive for tris(OEP)-M than for bis(OEP)-M and yet for the Ni complex than for the Pd and Pt ones. Various mixed complexes of vinylene-bridged bis- and tris(octaethylporphyrin)s (bis(OEP)-(M I-M2) and tris(OEP)-(M1-M2-M3)) with d^8 transition-metal ions M ((M1, M2, M3) : (Ni(II), Pd(lI), Pt(II)) were also synthesized by selective metalations of the corresponding free-bases with M(TI)X salts. Electronic structures of tris(OEP)-(M1-M2-M3) proved to be affected by the heavier metals more intensively, resulting in the largest splitting of Soret band for the Ni-Pd-Pt complex. Oxidation potential E_t values of tris(OEP)-(M1-M2-M3) suggested that the Ni-Pd-Pt complex possesses the electron-releasing ability almost the same as the Pd-Pd-Pd one. In the case of bis(OEP)-(M1-M2), the (E)-isomers exhibited the reduction of electron-releasing ability regularly in order of the heavier metal complexes, while the (Z)-isomers exhibited little dependency of the electron-releasing ability upon the incorporated metals.