Comparative Analysis of the Conformations of Symmetrically and Asymmetrically Deca- and Undecasubstituted Porphyrins Bearing Meso-Alkyl or -Aryl Groups

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• 作者：Mathias O. Senge ; Craig J. Medforth ; Timothy P. Forsyth ; David A. Lee ; Marilyn M. Olmstead ; Walter Jentzen ; Ravindra K. Pandey ; John A. Shelnutt ; and Kevin M. Smith
• 刊名：Inorganic Chemistry
• 出版年：1997
• 出版时间：March 12, 1997
• 年：1997
• 卷：36
• 期：6
• 页码：1149 - 1163
• 全文大小：515K
• 年卷期：v.36,no.6(March 12, 1997)
• ISSN：1520-510X

文摘

Conformational analysis of highly substituted porphyrins haspotential implications for modeling the behavior ofmacrocycles in tetrapyrrole-containing protein complexes and duringcatalytic reactions. In order to study theinfluence of different substituent patterns on the conformation of theporphyrin macrocycle, a series of metal freeand nickel(II) decasubstituted porphyrins bearing aryl or ethylgroups at opposite meso positions and alkyl groupsat the pyrrole positions have been synthesized and characterized byX-ray crystallography. Crystal structures ofthe free-base porphyrins with 5,15-diaryl substituents showednegligible out-of-plane distortion but a large amountof in-plane distortion along the 5,15-axis accompanied by largebond angle changes similar to those previouslyseen for related porphyrins with 5,15-dialkyl substituents.Nickel(II) complexes of the5,15-diaryl-substitutedporphyrins show planar or modestly nonplanar conformations, suggestingthat these complexes are not intrinsicallynonplanar, whereas a complex with 5,15-diethyl substituents has avery ruffled conformation similar to thoseobserved for related complexes with other metals. Thenickel(II) complexes are also elongated along the5,15-axis in a qualitatively similar but less dramatic fashion than are thefree-base porphyrins. Spectrosopic studies(¹H NMR, optical, and resonance Raman spectroscopy) suggestthat conformations similar to those determinedby X-ray crystallography are present in solution for the5,15-dialkyl- and 5,15-diaryl-substituted porphyrins.Severalasymmetric nickel(II) and metal-free deca- and undecasubstitutedporphyrins containing both aryl and alkyl meso-substituents were also investigated. Metal-free5,15-disubstituted porphyrins with one aryl and one alkylgroupshowed considerably elongated porphyrin cores, whereas nickel(II)complexes of porphyrins with 5,10- or 5,10,15-substitution patterns showed very nonplanar structures consisting mainlyof ruffle and saddle type distortions.