The coordination behaviors of chloro conphycenatoiron(III), a novel hemin i
somer with a trapezoidal metallo core, against imidazole, 1-methylimidazole
, and 2-methylimidazole were followed by spectrophotometry in chloroform at
room temperature. The examined compound is chloro 12,17-bis(ethoxycarbonyl
)-2,3,6,7, 11,18-hexamethylcorrphycenatoironcm,. Titration of 2-methylimida
zole and imidazole proceeded with and without accumulation of an intermedia
te mono imidazole species, respectively. On the other hand, a significant a
mount of an intermediate adduct was found to accumulate during 1-methylimid
azole binding despite the absence of any steric hindrance in the iron(III)-
N(1-methylimidazole) coordination bond. This is in remarkable contrast with
the conventional results for porphyrinatoiron(III). The proton NMR analysi
s of the mono 1-methylimidazole binding to conphycenatoiron(III) afforded a
formation constant closely similar to that obtained from the visible spect
ra. EPR definitely assigned the iron(III) high-spin state for the intermedi
ate. Accumulation of the mono 1-methylimidazole intermediate was explained
in terms of the contracted core in corrphycene. The narrow iron cavity weak
ens the axial iron-chloride bond facilitating coordination of the first 1-m
ethylimidazole. The four non-orthogonal iron(III)-N(pyrrole) bonds formed i
n the trapezoidal cavity further disturb the incoming motion of the iron(II
I) atom into conphycene plane upon second 1-methylimidazole ligation. Accum
ulation of mono 1-methylimidazole intermediate was more evident in ferric c
onphycenatoiron(III) with bromide and iodide, supporting the proposed chang
es in iron reactivity upon deformation of the equatorial coordination envir
onment.