ISSN 1070-3632, Russian Journal of General Chemistry, 2017, Vol. 87, No. 6, pp. 1175–1183. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © O.V. Maltceva, N.Zh. Mamardashvili, 2017, published in Zhurnal Obshchei Khimii, 2017, Vol. 87, No. 6, pp. 955–963.
The Effect of Chemical Modification of the Macrocycle
on the Complex Formation between Porphyrins
and Metal Salts in Organic Solvents
O. V. Maltceva* and N. Zh. Mamardashvili
Krestov Institute of Solutions Chemistry, Russian Academy of Sciences,
ul. Akademicheskaya 1, Ivanovo, 153045 Russia
*e-mail: olga_toldina@mail.ru
Received February 15, 2017
Abstract—The complex formation of β-octaethylporphyrin, β-octaethyl-meso-monophenylporphyrin, β-octaethyl-
meso-tetraphenylporphyrin, meso-diphenylporphyrin, meso-triphenylporphyrin, and meso-tetraphenylporphyrin
with Zn(II), Cu(II), Co(II), and Mn(II) acetates and chlorides in dimethylformamide, dimethylsulfoxide,
pyridine, acetic acid, and a chloroform–methanol 1 : 1 mixture has been studied by means of spectrophoto-
metry. The observed regulations are in line with the concept of chemical reactivity of the N–H bonds in
porphyrins of different complexity.
Keywords: porphyrin, complex formation, reaction rate, reactivity, spectrophotometry
DOI: 10.1134/S1070363217060123
Understanding the relationship between nonplanarity
of the porphyrins (H2P) macrocycle and reactivity of
the N–H bonds in their coordination site is a topical
issue. The NH-activation, an example of stepwise
change in the properties owing to conformational
rearrangements, is an important model in the study of
the in vivo processes involving porphyrins.
reactants is accompanied by ongoing deformation of
two neighbor M–Solv bonds due to the force field of
the porphyrin: these solvent molecules are no longer
bound to the cation and are expelled from its inner
coordination sphere, replaced by two tertiary nitrogen
atoms of the porphyrin. The formed donor-acceptor
M–N σ-bond is weak but partially compensate the
energy loss due to removal of two solvent molecules.
At this stage, the interaction follows one of the two
possible pathways. If the M–Solv bond as well as the
formed Н+···Solv and Х–···Solv bonds are not
sufficiently strong (in a low-polar solvent: HOAc,
CHCl3, etc.), activation energy of removal of two
solvent molecules is low, and the rest of the
coordination sphere of the salt is not involved. Other
М–Solv and М–Х bonds are practically not changed,
and the reaction can stop at the stage of the formation
of a mixed complex (intermediate) [5].
Porphyrins can form complexes with practically
any metal [1]. This is due to the formation of four
equivalent N→M σ-bonds: due to filling of
unoccupied s-, р-, and d-orbitals of the corresponding
symmetry, the cation can form either direct (М→N) or
reverse (М←N) dative π-bonds with the ligand [2].
Mechanism of coordination of conventional porphyrins
with metal cations has been elucidated in the studies of
kinetics of the process [1, 2]. In detail, when the
porphyrin molecule and the metal cation start to
interact, two neighbor M–Solv bonds are weakened,
the Solv–M–Solv bond angle is increased, and the
bonds are extended. Affected by the metal cation field,
two protons of the porphyrin macrocycle leave the
molecule plane and are located to the same side of the
plane (Scheme 1). This increases the polarity of the
N–H bond and strengthens the binding of the proton
with the solvent molecule. Further approaching of the
If the solvent is strongly bound to the cation, and
the solvation of the N–H···Solv and М–Х···Solv
bonds is significant (in a polar coordinating solvent),
removal of the two solvent molecules is restricted. Its
activation energy is high, and the process can occur
only in the proximity of the peak in the potential
barrier, when the other М–Solv, M–X, and N–H are
1175
Maltceva
