Free Base and Metal Complexes of 5,15-Diaza-10,20-dimesitylporphyrins: Synthesis, Structures, Optical and Electrochemical Properties, and Aromaticities

• DOI: 10.1021/ic301835c
• Publication Date: 2012-11-08T14:48:22Z
• Authors: Yoshihiro Matano; Tarou Shibano; Haruyuki Nakano; Yoshifumi Kimura; Hiroshi Imahori
• Keywords: Base (topology)

The synthesis, structures, optical and electrochemical properties, aromaticity of a series 5,15-diaza-10,20-dimesitylporphyrins (M-DAP; M = Pb, H(2), Ni, Pd, Pt, Zn; mesityl 2,4,6-trimethylphenyl) are reported. Treatment mesityl-substituted bis(5,5'-dibromodipyrrin) with sodium azide in the presence lead(II) acetylacetonate afforded Pb-DAP, which was quantitatively converted to H(2)-DAP by acidolysis. free base reacted palladium(II), platinum(II), zinc(II) salts give Pd-DAP, Pt-DAP, Zn-DAP, respectively. crystal aromaticities these β-unsubstituted M-DAPs were comprehensively investigated X-ray crystallography, UV-vis absorption/fluorescence spectroscopy, nanosecond flash photolysis, cyclic differential pulse voltammetry, NMR density functional theory calculations. obtained data show that replacement 5- 15-methine carbons nitrogen atoms alters intrinsic properties porphyrin 18π system as follows: (i) coordination spheres at N(4) core become contracted while keeping high planarity; (ii) Q bands red shifted largely intensified; (iii) electron-accepting ability is enhanced, whereas electron-donating reduced; (iv) radiative decay rates from S(1) state enhanced; (v) circuit slightly reduced terms both geometric magnetic criteria. These stem their characteristic frontier orbitals; two HOMOs LUMOs nondegenerate result incorporation electronegative meso positions. In addition, group 10 metals incorporated finely tune fundamental DAP π systems through inductive effects well dπ-pπ antibonding orbital interactions; HOMO-LUMO gaps metal complexes increase order Ni-DAP < Pd-DAP Pt-DAP.