Synthesis, reactivity and structural chemistry of 5,10,15,20-tetraalkylporphyrins

✍ Scribed by MATHIAS O. SENGE; INES BISCHOFF; NORA Y. NELSON; KEVIN M. SMITH

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 223 KB
• Volume: 03
• Category: Article
• ISSN: 1088-4246
• DOI: 10.1002/(sici)1099-1409(199902)3:2<99::aid-jpp109>3.0.co;2-6

✦ Synopsis

The synthesis, reactivity and full characterization of a series of meso-tetraalkyl porphyrins and metalloporphyrins with R n-butyl (6), 2-methyl-propyl (7), isopropyl (8), l-ethyl-propyl (10) and tertbutyl (11) groups are reported. Derivatives of the last of these show considerably bathochromically shifted absorption bands and the crystal structure of Zn(II)11(pyr) exhibits a severely ruffled macrocycle conformation. Systematic crystallographic studies of the porphyrins showed that the free base porphyrins with R n-butyl (H 2 6), 2-methyl-propyl (H 2 7) and 1-ethyl-propyl (H 2 10) are planar. A larger conformational variety was found for the metal complexes. While most Ni(II) derivatives and Pd(II)8 showed a ruffled macrocycle conformation with a degree of ruffling exceeding that of meso-unsubstituted porphyrins, both planar and non-planar forms were found for the related Cu(II) derivatives. The Zn(II) complexes of porphyrins with isopropyl or 1-ethyl-propyl exhibited conformations with variable degree of distortion. Together with comparative structures from the literature, this study provides experimental evidence that considerable conformational flexibility exists for meso-alkylporphyrins with substituents less bulky than tert-butyl groups.