HYDROGEN-BONDING TO COORDINATED IMIDAZOLE - ASSOCIATION OF 1,10-PHENANTHROLINE AND OTHER BASES WITH BIS(IMIDAZOLE)METALLOPORPHYRINS

Qualitative results are presented which indicate that halide ions, 1, 10-phenanthroline, and substituted pyridines associate with the N-H group in bis(imidazole)metalloporphyrins. Electronic spectra indicate that 1, 10-phenanthroline shifts the equilibrium 2B + FePCl⇆(B)2FeP+ + Cl- to favor the product when the base is imidazole (ImH) but not when it is 1-methylimidazole (1-Melm). These spectra show no evidence for the formation of aromatic π complexes between 1, 10-phenanthroline and the porphyrin. The preparation and proton NMR spectrum of [(ImH)2Co(TPP)] [BF4] are reported. Addition of halide ions, 1, 10-phenanthroline, or substituted pyridines to dichloromethane solutions of [(ImH)2Co(TPP)] [BF4] causes the imidazole N-H resonance to shift to lower field due to the formation of hydrogen bonds. With 1, 10-phenanthroline this interaction also causes an upfield shift of the 2, 9 and 3, 8 protons of 1, 10-phenanthroline when the metalloporphyrin/1, 10-phenanthroline ratio is high. This shift results from positioning the 1, 10-phenanthroline so that it can chelate the imidazole NH unit and is caused by the ring current of the porphyrin. © 1979, American Chemical Society. All rights reserved.