A planar dodecasubstituted porphyrin

• Published in: Inorganic chemistry 1993-04, Vol.32 (9), p.1716-1723
• Main Authors: Senge, Mathias O, Medforth, Craig J, Sparks, Laurie D, Shelnutt, John A, Smith, Kevin M
• Format: Article
• Language: English
• Subjects: 140505 - Solar Energy Conversion- Photochemical, Photobiological, & Thermochemical Conversion- (1980-); 400201 - Chemical & Physicochemical Properties; ABSORPTION; ABSORPTION SPECTROSCOPY; CARBOXYLIC ACIDS; COHERENT SCATTERING; COMPLEXES; Condensed matter: structure, mechanical and thermal properties; COPPER COMPLEXES; CRYSTAL STRUCTURE; DIFFRACTION; Exact sciences and technology; FLEXIBILITY; HETEROCYCLIC ACIDS; HETEROCYCLIC COMPOUNDS; Inorganic compounds; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; LASER SPECTROSCOPY; MAGNETIC RESONANCE; MATHEMATICAL MODELS; MECHANICAL PROPERTIES; Metal complexes; MOLECULAR STRUCTURE; NICKEL COMPLEXES; NUCLEAR MAGNETIC RESONANCE; ORGANIC ACIDS; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; Physics; PORPHYRINS; RAMAN SPECTROSCOPY; RESONANCE; SCATTERING; SOLAR ENERGY; SORPTION; SPECTROSCOPY; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; TENSILE PROPERTIES; TRANSITION ELEMENT COMPLEXES; X-RAY DIFFRACTION
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic00061a030

Structural investigations of copper and nickel complexes of dodecasubstituted porphyrins bearing aryl groups at the meso positions and propano rings at the pyrrole [beta] positions reveal considerable differences in their macrocycle conformations. While the nickel complex NiTC5T(3,4,5-OMeP)P was found to exhibit a nonplanar conformation which is considerably more planar than that of other dodecasubstituted porphyrins, the corresponding copper complex CuTC5T(3,4,5-OMeP)P was planar. CuTC5T(3,4,5-OMeP)P thus represents the first example of a completely planar dodecasubstituted porphyrin. The crystal structures of both porphyrins reveal that the C[sub b]-C[sub b]-CH[sub 2] angle is 13[degrees] smaller than in OEP derivatives. This change, which moves the methylene and aryl substituents further apart, effectively removes the steric repulsion responsible for the very nonplanar conformations observed for other dodecasubstituted porphyrins. Molecular mechanics calculations using a porphyrin force field correctly predict a planar macrocycle conformation. The possible reasons for the discrepancy between the observed moderately nonplanar structure and the calculated planar structure for NiTC5T(3,4,5-OMeP)P are discussed. The usefulness of spectroscopic probes (NMR, resonance Raman, electronic absorption) in predicting the planarity of dodecasubstituted porphyrins is also examined. The identification of a planar dodecasubstituted porphyrin further indicates the flexibility of the tetrapyrrole macrocycle and has implications for the study of nonplanarity in synthetic porphyrins and metallotetrapyrrole containing biomolecules. 32 refs., 6 figs., 7 tabs.