Synthesis, structures, and aromaticity of phosphole-containing porphyrins and their metal complexes

Matano, Yoshihiro; Nakabuchi, Takashi; Imahori, Hiroshi

doi:10.1351/PAC-CON-09-08-05

Pure Appl. Chem., 2010, Vol. 82, No. 3, pp. 583-593

http://dx.doi.org/10.1351/PAC-CON-09-08-05

Published online 2010-02-14

Synthesis, structures, and aromaticity of phosphole-containing porphyrins and their metal complexes

Yoshihiro Matano¹*, Takashi Nakabuchi¹ and Hiroshi Imahori^1,2,3

¹ Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan
² Fukui Institute for Fundamental Chemistry, Kyoto University, Sakyo-ku, Kyoto 606-8103, Japan
³ Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan

Abstract: Our recent studies on the synthesis, structures, and aromaticity of phosphole-containing porphyrins and their metal complexes are summarized. Core-modified P,X,N₂-porphyrins (X = S, N) are accessible from a σ⁴-phosphatripyrrane and the corresponding 2,5-difunctionalized heteroles in a few steps. X-ray structural analysis of the σ³-P,N₃ porphyrin revealed that it possesses a slightly distorted 18π plane. The phosphorus atom incorporated at the core plays an important role in producing unprecedented reactivity and coordinating ability for the porphyrin ring. The P,N₃ free base reacts with [RhCl(CO)₂]₂ in dichloromethane, ultimately yielding an 18π P,N₃–rhodium(III) complex, whereas the P,S,N₂ free base undergoes redox-coupled complexation with zero valent group 10 metals to afford the corresponding P,S,N₂-isophlorin–metal(II) complexes. The aromaticity of the free-base porphyrins and the metal complexes was uncovered based on both experimental and theoretical results. It is of particular interest that the P,S,N₂-isophlorin–metal complexes exhibit only a weak antiaromaticity in terms of the magnetic criterion.