Synthesis and solid-state molecular structures of nitrosoalkane complexes of iron porphyrins containing methanol, pyridine, and 1-methylimidazole ligands

Nitrosoalkanes belong to the family of C-nitroso compounds and are known to bind to the iron center in heme proteins. We have prepared and characterized a series of new nitrosoalkane heme model complexes of the form (por)Fe(RNO)(L) (por = porphyrinato dianion; R = isopropyl; L = MeOH, pyridine, 1-methylimidazole) by infrared and H-1 NMR spectroscopy and X-ray crystallography. Within the set of octaethylporphyrinato (OEP) compounds, the infrared stretching frequencies of the NO groups decrease in the order (OEP)Fe((PrNO)-Pr-i)(MeOH) (.) MeOH (1433 cm(-1)) > (OEP)Fe((PrNO)-Pr-i)(py) (1429 cm(-1)) > (OEP)Fe((PrNO)-Pr-i)(1-MeIm) (1423 cm(-1)), reflecting the increased backdonation of electron density in the 1-methylimidazole derivative. The molecular structures of the compounds as determined by crystallography reveal N-binding of the nitrosoalkane ligands to the formally ferrous metal centers. (C) 2004 Elsevier Inc. All rights reserved.