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A. Zabardasti , M. Asadi and A. Kakanejadifard
Vol 43
deformation of porphyrin structure from planarity and so
decreasing of the aromatic ring current.
According to H NMR pattern, it seems that adduct has a
observations suggest a similar distortion in the free base
porphyrin structure after both organotin adduct and diacid
formation.
1
Our results suggest the presence of the SAT intermediate,
which have been kinetically deduced in the course of the
mechanistic studies of metallation of the free base porphyrins [7-
12,18]. A SAT complex is a complex of a free base porphyrin
with a metal ion, where the latter coordinates to both of the
unprotonated pyrrole nitrogen atoms. The protons on two of the
pyrrole nitrogen atoms prohibit the metal ion from residing in
the centre of the porphyrin plane therefore it lies above the ring
plane [8,9]. Here dealing with stable adducts, because of our
bulky and stable Lewis acids, organotin(IV) halides couldn’t
drop into the porphyrin cavity. We think, that our results can
give good information about details of the SAT structure and
make help in better understanding the kinetic of metallation of
the free base porphyrins.
symmetric structure, so that coordination of porphyrin to
organotin(IV) halide couldn’t differentiate between each class of
the free base protons (N-H, Hꢀ, Ho, and Hm,p ) with adduct
formation and these protons remained equivalent after
complexation. On the other hand, we only see a definite shift for
each class of protons in the adduct with respect to the
corresponding free base porphyrin protons.
The elemental analysis data show that these adducts have the
stoichiometry 2:1 of acceptor to donor, [(Me2SnCl2)2(H2T(4-
X)PP)], [(Ph2SnCl2)2(H2T(4-X)PP)], and [(Ph2SnBr2)2(H2T(4-
X)PP)]. It is in a good agreement with our previous results on
thermodynamic studies of these adducts [5,6]. For this mole
ratio we sketched the proposed structures in Figure 4. In Figure
4 (a), because of the attachment of tin atoms to two of the
pyrrolenine nitrogen atoms, splitting of 1H NMR signal of Hꢀs to
produce a doublet for beta hydrogens is expected. On the other
hand, in Figure 4(b) Hꢀs have identical environment, therefore
we predict a singlet for them. Experimentally, in the low-
REFERENCES
1
temperature H NMR spectra of the adducts a singlet appeared
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for Hꢀs. This confirms the structure shown in Figure 4(b) for
these adducts. On the basis of these results we suggest that free
base porphyrin as a bidentate bridging ligand forms a bridge
between two molecules of the Lewis acid. It is probable that two
neighboring nitrogen atoms of the porphyrin bind to one of the
organotin(IV) chloride molecules which are positioned above of
the porphyrin plane and the other two nitrogen atoms bind to the
second organotin(IV) chloride molecule from below this plane.
CH3
CH3
CH3
CH3
Sn
Sn
Cl
Ph
Cl
H
Cl
Cl
H
H
H
H
H
H
Cl
N
Ph
N
H
H
H
N
N
H
Cl
N
N
N
Cl
H
H
H
H
H
N
H
Ph
H
Cl
Cl
Ph
H
H
Cl
Sn
Cl
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Inorg. Chem., 39, 4793 (2000).
Cl
CH3
Sn
CH3
CH3
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Inorg. Chem., 40, 5636 (2001).
CH3
(a)
(b)
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Figure 4. Proposed structures of [(R2SnCl2)2H2TPP] adduct. (a) H2TPP as a
monodentate bridging ligand made adducts with five-coordinated trigonal
bipyramidal structure for tin atoms; (b) H2TPP as a bidentate bridging
ligand make adducts with six-coordinated octahedral structure around the
tin atoms. Our 1H NMR data are in consistent with structure (b).
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1
The close resemblance between H NMR and especially the
electronic spectra of H2T(4-X)PP in these adducts with those
reported for the corresponding porphyrin diacid, H4T(4-X)PP2+
is an interesting feature of these studies [16,17]. These
Zabardasti, Abedien
