Pa. Stuzhin et al., Reactions of the sigma-phenyl complex of Fe(III)-octaphenyltetraazaporphine with nitrous bases, RUSS J C CH, 25(2), 1999, pp. 113-117
The low-spin pentacoordinated Fe(III)-octaphenyltetraazaporphine sigma-phen
yl complex (Ph)FeOPTAP, obtained from the chloro complex (CI)FeOPTAP and ph
enylmagnesium bromide, reacts with nitrous bases L [L = pyridines (Py, 4-Me
Py, 4-PhPy, 3-CIPy, 3-CNPy, 4-CNPy, or 3, 4-Me2Py), imidazoles (Im, 1-MeIm,
and 2-MeIm), and aliphatic amines (Pip, BzNH(2), and c-HxNH(2))] to form t
he low-spin hexacoordinated extra complexes (L)(Ph)FeOPTAP. The concentrati
onal equilibrium constants for formation of the extra complexes (K-ex) were
determined by spectrophotometric titration in toluene. The stability of (L
)(Ph)FeOPTAP increases with an increase in the basicity of L. A correlation
between logK(ex) and Hammett sigma constants (rho = -1.98) was established
for a series of substituted pyridines. It is shown that, along with the co
ordination sigma-effect, the ability of L for pi-bonding exerts substantial
influence on the stability of the extra complex (L)(Ph)FeOPTAP.