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

The synthesis, reactivity and full characterization of a series of meso-tet raalkyl porphyrins and metalloporphyrins with R = n-butyl (6), 2-methyl-pro pyl (7), isopropyl (8), 1-ethyl-propyl (10) and tert-butyl (11) groups are reported. Derivatives of the last of these show considerably bathochromical ly shifted absorption bands and the crystal structure of Zn(II)(pyr) exhibi ts a severely ruffled macrocycle conformation. Systematic crystallographic studies of the porphyrins showed that the free base porphyrins with R = n-b utyl (H(2)6), 2-methyl-propyl (H(2)7) and 1-ethyl-propyl (H(2)10) are plana r. A larger conformational variety was found for the metal complexes. While most Ni(II) derivatives and Pd(II)8 showed a ruffled macrocycle conformati on with a degree of ruffling exceeding that of meso-unsubstituted porphyrin s, both planar and non-planar forms were found for the related Cu(II) deriv atives, The Zn(II) complexes of porphyrins with isopropyl or I-ethyl-propyl exhibited conformations with variable degree of distortion. Together with comparative structures from the Literature, this study provides experimenta l evidence that considerable conformational flexibility exists for meso-alk ylporphyrins with substituents less bulky than tert-butyl groups. Copyright (C) 1999 John Wiley & Sons, Ltd.