Hydrogen bond controlled formation of trans-dihydroxo porphyrinato platinum(IV) complexes: Synthesis, characterization and catalytic activity in olefin epoxidation

Article abstract of DOI:10.1016/j.ica.2015.05.023

A number of trans-dihydroxo porphyrinato platinum(IV) complexes, [(porp)Pt^IV(OH)₂] have been synthesized and characterized from their platinum(II)-porphyrin precursors by spectroscopic methods. The crystal structure of the platinum complex of trans-dihydroxo-meso-tetramesitylporphyrinato platinum(IV) meta-chlorobenzoic acid ([(TMP)Pt^IV(OH)₂](m-CBA)₂) has also been determined. The porphyrin periphery is planar and the platinum atom has a slightly distorted octahedral environment. It must be noted that there is a very strong O-H?O hydrogen bond between the hydrogen atoms of m-chlorobenzoic acids and the two hydroxo ligands coordinated to the platinum center. This crystal structure has been previously described by us as trans-dihydroxo-meso-tetramesitylporphyrinato platinum(VI) meta-chlorobenzoate ([(TMP)Pt^VI(OH)₂](m-CB)₂), but the spectroscopic data has been reinterpreted due to the contradictory +6 oxidation state for platinum. The UV-Vis and NMR spectroscopic data suggest that the porphyrin skeleton is similar to that of normal porphyrins and are also indicative of the +4 oxidation state for platinum. Cyclic voltammetry studies also indicate that Pt^IITMP can oxidize up to Pt^IV(TMP⁺) species via three successive one-electron oxidation steps. The results of DFT studies and NBO analysis confirm that platinum has +4 oxidation state in both [(TMP)Pt(OH)₂](m-CBA)₂ and [(TMP)Pt(OH)₂](m-CB)₂ complexes. The catalytic activity of these porphyrin complexes has been investigated for the oxidation of various alkenes in the presence of iodosylbenzene.

Full text of DOI:10.1016/j.ica.2015.05.023

Inorganica Chimica Acta 434 (2015) 198–208
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Hydrogen bond controlled formation of trans-dihydroxo porphyrinato
platinum(IV) complexes: Synthesis, characterization and catalytic
activity in olefin epoxidation
b
a
a
Tahereh Alemohammad a, Nasser Safari a, , Saeed Rayati , Mahin Gheidi , Anahita Mortazavimanesh ,
⇑
Hamidreza Khavasi a
a Department of Chemistry, Shahid Beheshti University, P.O. Box 1983963113, G. C. Evin, Tehran, Iran
b Department of Chemistry, K.N. Toosi University of Technology, P.O. Box 16315-1618, Tehran 15418, Iran
a r t i c l e i n f o
a b s t r a c t
A number of trans-dihydroxo porphyrinato platinum(IV) complexes, [(porp)PtIV(OH)2] have been synthe-
sized and characterized from their platinum(II)-porphyrin precursors by spectroscopic methods. The
crystal structure of the platinum complex of trans-dihydroxo-meso-tetramesitylporphyrinato
platinum(IV) meta-chlorobenzoic acid ([(TMP)PtIV(OH)2](m-CBA)2) has also been determined. The por-
phyrin periphery is planar and the platinum atom has a slightly distorted octahedral environment. It
must be noted that there is a very strong O–HÁ Á ÁO hydrogen bond between the hydrogen atoms of m-
chlorobenzoic acids and the two hydroxo ligands coordinated to the platinum center. This crystal struc-
ture has been previously described by us as trans-dihydroxo-meso-tetramesitylporphyrinato
platinum(VI) meta-chlorobenzoate ([(TMP)PtVI(OH)2](m-CB)2), but the spectroscopic data has been rein-
terpreted due to the contradictory +6 oxidation state for platinum. The UV–Vis and NMR spectroscopic
data suggest that the porphyrin skeleton is similar to that of normal porphyrins and are also indicative
of the +4 oxidation state for platinum. Cyclic voltammetry studies also indicate that PtIITMP can oxidize
up to PtIV(TMP+Å) species via three successive one-electron oxidation steps. The results of DFT studies and
NBO analysis confirm that platinum has +4 oxidation state in both [(TMP)Pt(OH)2](m-CBA)2 and
[(TMP)Pt(OH)2](m-CB)2 complexes. The catalytic activity of these porphyrin complexes has been investi-
gated for the oxidation of various alkenes in the presence of iodosylbenzene.
Article history:
Received 1 February 2015
Received in revised form 13 May 2015
Accepted 23 May 2015
Available online 3 June 2015
Keywords:
Platinum(IV) porphyrins
Hydrogen bonding
Catalytic epoxidation
Porphyrin cyclic voltammetry
Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction
hydrocarbons catalyzed by Fe-, Mn-, and Ru- porphyrins
[1,15,25–29]. Although platinum porphyrins have been studied
Metalloporphyrins are known to mimic the activity of mono-
oxygenase enzymes [1–5]. In this regard, an extensive amount of
research has been focused on them, owing to the critical role they
play in electron transfer [6] and photosynthesis [7] processes and
also in catalytic oxygen atom transfer processes including hydrox-
ylation [8–11] and epoxidation [12–15] of hydrocarbons. It is
found that the reactivity of metalloporphyrin complexes depends
on the central metal [13,16], the substituents on the porphyrin
periphery [10,17,18], and the axially coordinated ligand [19–21].
Investigations in this area have been concentrated on the mecha-
nism of the function of heme-containing enzymes such as cyto-
chrome P-450 by designing metalloporphyrins as models [22–
24]. Considerable attention has been paid to the oxidation of
as oxygen sensing probes [30–32], photosensitizers [33–35],
potential antitumor agents [36], and molecular conductors
[37,38], there aren’t any studies on platinum porphyrins as oxida-
tion catalysts.
In addition, high oxidation states of Platinum are very rare [39].
PtF6 complex is the only compound that represents +6 oxidation
state of platinum [40,41] which is an extraordinarily powerful oxi-
dizing agent.
Initial reports on PtIV-oxo complex isolation were revisited to
confirm that the repulsion between filled d2z electrons and an elec-
tron rich ligand such as the oxo ligand prevents Pt-oxo formation
[42,43]. However, PtIV(porp)X2 (X = Cl, Br) has also been reported
[44–47]. Kadish et al. also reported on the formation of Pt(IV) por-
phyrin and Pt(IV) porphyrin
p-cation radical by spectroelecto-
chemical methods [48,49] although, to the best of our
knowledge, there is no report on Pt(IV) porphyrin complexes that
contains hydroxo groups as the axial ligand.
⇑
Corresponding author. Tel.: +98 21 29902886; fax: +98 21 22431661.
E-mail address: n-safari@sbu.ac.ir (N. Safari).
http://dx.doi.org/10.1016/j.ica.2015.05.023
0020-1693/Ó 2015 Elsevier B.V. All rights reserved.

T. Alemohammad et al. / Inorganica Chimica Acta 434 (2015) 198–208
199
Porphyrin macrocycles and their metal complexes have rich
redox chemistry. The macrocycle can have a versatile character;
the most stable and abundant oxidation state of the macrocycle
A home-made three-electrode cell consisting of a glassy carbon
working electrode, a platinum counter electrode and a silver chlo-
ride reference electrode (Ag/AgCl) was used for cyclic voltammetry
experiments. Cyclic voltammetry was carried out by using a
is the normal aromatic 18
has a À2 oxidation state. Under reducing conditions, monoanion
radical 19 -electron and anti-aromatic 20 -electron dianion sys-
tems have been recognized [50–53]. In the oxidative environment
of the enzyme, porphyrin -cation radical with 17 -electron sys-
tem has been proposed [22,54,55]. Vaid et al. and Yamamoto et al.
p-electron ring in which the macrocycle
lAutolab Type III potentiostat/galvanostat from Metrohm in com-
p
p
bination with the powerful GPES software at room temperature.
p
p
2.2. Preparation of platinum porphyrins
have reported anti-aromatic 16 p
-electron porphyrins and their Li+
Free base porphyrins were metalated with platinum(II) chlo-
ride, PtCl2, as described in the literature to give corresponding
meso-tetraphenylporphyrinato platinum (PtTPP), meso-tetrame-
sitylporphyrinato platinum (PtTMP) and meso-tetrakis(penta-fluo-
rophenyl)porphyrin (PtTPFPP) complexes [63]. A typical procedure
was as follows: typical free base porphyrins (0.2 mmol) were dis-
solved in 50 ml of anhydrous benzonitrile, then PtCl2 (0.4 mmol)
was added to the porphyrin solution. The mixture was then purged
with N2 as it was slowly heated to 190 °C. The mixture was
refluxed under N2 until there were no free base porphyrins
revealed by UV–Vis spectroscopy. The mixture was then cooled
to room temperature and the solvent was removed by vacuum dis-
tillation. The crude product was washed with 5 ml of methanol and
then purified by column chromatography. NMR and UV–Vis data
for these platinum porphyrins are given in Table 1.
and Zn2+ complexes [56–59]. All 20 or 16 anti-aromatic porphyrins
have similar features, such as (i) alternating C–C bond distances
along the 20 carbon periphery of their porphine ring system, (ii)
highly saddle or ruffle distortion of the porphine from planarity,
(iii) red shift in Soret band for 20
p-elecron system and blue shift
for 16 -electron system to that of normal porphyrin and (iv)
p
strong paratropic shift in NMR for anti-aromatic porphyrins com-
pared to that of diatropic shift normally seen in aromatic
porphyrins.
In our previous report [60], we proposed the formation of
[(TMP)PtVI(OH)2]2+ species on the basis of chemical and X-ray
studies. Complementary spectroscopic and electrochemical studies
motivated us to revisit our X-ray structure. In addition, the
results of our DFT studies and NBO analysis confirm that platinum
has +4 oxidation state in both [(TMP)PtIV(OH)2](m-CBA)2 and
[(TMP)Pt(OH)2](m-CB)2 complexes. Furthermore, DFT studies helped
us to revisit the crystal structure to find the exact position of protons
and come up with the correct interpretation of our X-ray data.
2.3. Synthesis of [(TMP)Pt(OH)2](m-CBA)2 complex
meso-Tetramesitylporphyrinato platinum(II) (PtTMP) (43 mg,
0.044 mmol) was dissolved in 10 ml CH2Cl2. To this solution,
meta-chloroperbenzoic acid (m-CPBA) (21.6 mg, 0.088 mmol) was
added. The color of the solution rapidly changed from orange to
red. The reaction mixture was stirred for 5 min and then CH2Cl2
was evaporated to dryness and then purified by passing through
a column of activated basic alumina by elution with dichloro-
methane. The obtained product was crystallized from a dichloro-
methane solution by slow evaporation. Spectroscopic data for
[(TMP)Pt(OH)2](m-CBA)2 are given in Table 1.
2. Experimental
2.1. Material and instruments
All chemicals and solvents were purchased from Merck, Fluka or
Aldrich chemical companies. The free bases, meso-tetraphenylpor-
phyrin (H2TPP), meso-tetramesitylporphyrin (H2TMP) and meso-te-
trakis(pentafluorophenyl)porphyrin (H2F20TPP or H2TPFPP), were
prepared according to the literature [61]. Iodosylbenzene was
obtained by the hydrolysis of iodosylbenzene diacetates [62].
The electronic absorption spectra were recorded on a SPECORD
S600 spectrophotometer from Analytikjena. The reaction products
were analyzed by gas chromatography using a Trace GC ultra from
Thermo equipped with an FID Detector and RtxÒ À1 capillary col-
umn. The chemical yields for the oxidation reactions were based on
iodosylbenzene, the limiting reactant.
2.4. General oxidation procedure
Stock solutions of the platinum porphyrins (3 Â 10À3 M) and
alkenes (0.5 M) were prepared in CH2Cl2. In a 10 ml round-bottom
flask, the reagents were added in the following order: alkene
(0.5 mmol, 1 ml), catalyst (4 Â 10À4 mmol, 0.14 ml) and odosyl-
benzene. PhIO (5 Â 10À3 g) was then added to the reaction mixture
Table 1
Electronic absorptions and multi-nuclear NMR data for some platinum porphyrins.
a
UV–Vis
Soret
1H NMRb
Hb
13C NMRc
Cm
195Pt NMRd
Refs.
e
f
Q-bands
Ho
Hm
Hp
C
Cb
a
PtIITMP
402
402
392
423
421
417
427
402
421
510, 540
510, 539
508, 539
536
534
532
536
510,540
538,575
8.56
8.77
8.83
8.84
8.79
9.09
8.79
8.74
9.06
1.85
8.14
–
1.88
1.91
8.16
1.89
8.14
8.27
7.25
7.72
–
7.28
7.29
7.74
7.3
2.6
7.72
–
2.62
2.62
7.74
2.65
7.7
–
–
–
–
–
–
138
–
–
–
–
2553.8
–
–
4395
–
–
4019
1235
4215
twg
tw
tw
tw
tw
tw
tw
[69]
[69]
PtIITPP
PtIITPFPP
[PtIV(TMP)(OH)2](m-CBA)2
[Pt(IV) (TMP)(OH)2](MeOH)2
[Pt(IV)(TPP)(OH)2](CF3COOH)2
PtIV(TMP)(Br)2
PtIITPP
119.1
–
–
119.1
122.3
121.4
129.7
–
–
131
130.7
132.1
–
138.5
140.9
138.3
7.7
7.8
PtIV(TPP)(Cl)2
7.8
a
b
c
d
e
f
k (in nm) and in CH2Cl2 solution.
Chemical shifts in ppm from impurity of CHCl3 (7.26 ppm) in CDCl3 solvent.
Chemical shift in ppm referenced to TMS.
Pt referenced to PtCl26À = 4522 ppm.
Ortho-H or Me.
Para-H or Me.
This work.
g

200
T. Alemohammad et al. / Inorganica Chimica Acta 434 (2015) 198–208
at room temperature. The mixture was stirred for 24 h and then
was analyzed by gas chromatography. The yields were calculated
by the internal standard method.
vibrational frequencies were systematically computed to confirm
whether an optimized geometry correctly corresponds to a local
minimum that has only real frequencies. Atomic charge and spin
density studies were based on Mulliken calculations. The natural
bond orbital (NBO) analysis is used to explain electron distribution
in the d-orbitals of platinum and the macrocycle ring as well as to
assign the atomic charges. The molecular orbital analyses were
performed by Gauss View applied to the respective Gaussian out-
put file.
2.5. DFT calculations
The computational study performed on [(TMP)Pt(OH)2](m-
CBA)2 and [(TMP)Pt(OH)2](m-CB)2 complexes was accomplished
with DFT using the GAUSSIAN 98 A.9 program suite [64]. The energies
and geometries of different complexes were calculated and opti-
mized with the B3LYP hybrid functional method [65,66]. The 6-
31G (d,p) basis set was applied to the nonmetal atoms (hydrogen,
carbon, nitrogen and oxygen) while the LANL2DZ effective core
potential (ECP) and corresponding basis set functions [67] were
used for the platinum atom.
Full optimizations of the studied compounds in singlet spin
states, without any symmetry constraint, have been performed
with the FOPT keyword. The optimized structures for all species
are presented in the Supplementary materials. Harmonic
3. Results and discussion
3.1. UV–Vis spectra
The electronic spectra of the CH2Cl2 solution of PtIITMP complex
and the final Pt-complex product of its titration with 2.0 equiva-
lents of m-CPBA have been shown in Fig. 1.
According to Fig. 1, the Soret band of the Pt-complex has signif-
icant red shift (21 nm) relative to that of PtTMP, with no evidence
of an absorption band at 600–700 nm indicative of a porphyrin
cation ring [18]. This significant red shift that is in contrast to the
blue shift observed for the 16 -electron metalloporphyrins [57] is
p-
p
indicative of the oxidation of PtII to PtIV as seen in previous reports
[44,45,49]. This electronic spectrum resembles the PtIV(TMP)Br2
spectrum. As explicitly shown in Fig. 1, there is only a slight shift
(5 nm) in the Soret band of PtIVTMP(Br)2 compared to that of
Pt(TMP)(OH)2 which can be attributed to change occurring in the
axial ligand; this again provides another indication for the exis-
tence of PtIV in the latter Pt-complex [45].
The reaction of PtIITMP with two equivalents of iodosylbenzene
caused no dihydroxo formation after several days, but the addi-
tion of a few drops of methanol to the above solution exclu-
sively formed Pt(TMP)(OH)2 after 6 h at room temperature.
Furthermore, no new products were achieved with the reaction
of PtTPP and iodosylbenzene after 7 days while upon the addition
of 2.0 equivalents of trifluoroacetic acid, the corresponding species
formed and stabilized rapidly. Consequently, it seems that the
formation of hydrogen bonding between m-chlorobenzoic acids
and hydroxo groups is absolutely essential for the formation and
stabilization of such dihydroxo platinum complexes (Scheme 2).
Electronic and multi-nuclear NMR data for some PtII(porp) and
[(porp)Pt(OH)2)] complexes have been given in Table 1.
According to Table 1 and with respect to the 1H-NMR evidence
of very weak paratropic ring current effects [44,45] the involve-
Fig. 1. UV–Vis spectra for
(
)
PtTMP (5.3 Â 10À6 M),
( ) Pt(TMP)(OH)2
(2.4 Â 10À6 M) and ( ) Pt(TMP)Br2(3.4 Â 10À6 M) in CH2Cl2 solution.
ment of an 18
p-electron porphyrin ligand is supported.
Scheme 1. Three cartoons representing the different electronic aspects of the [(porp)Pt(OH)2]0 and [(porp)Pt(OH)2]2+
.

T. Alemohammad et al. / Inorganica Chimica Acta 434 (2015) 198–208
201
no new product
s
y
a
d
l
a
r
O
I
h
e
P
v
e
, s
l 2
C
H 2
C
Pt
P
C
h
X
H
2
I
Pt(porp)
O
X
C
2
l
+
p
H
H
r
o
H
H
t
i
c
a
O
O
g
e
n
t
rapid
PtIV
O
PtIV
O
H
H
H
H
X
X
Scheme 2. Hydrogen bond controlled formation of [Pt(porp)(OH)2]. 2X, (X = OMe, m-CB) and its proposed intermediate.
Moreover, 195Pt chemical shift confirms the oxidation of PtII(porp)
to corresponding PtIV(porp)X2 complexes [68,69]. In spite of some
positive indications resulting from the X-ray analysis of the crystal
structure and stoichiometric titration in which two mole ratios of
m-CPBA were consumed [60], our spectroscopic data do not con-
firm the formation of [Pt(TMP)(OH)2]2+ nor [(TMP0) PtIV(OH)2]2+
species, Scheme 1.
The consumption of 2.0 equivalents of oxidant may be an
indication that PtTMP would initially be oxidized to the
[Pt(TMP)(OH)2]2+ or [PtIV(TMP+Å)(OH)2] species, but these species
have an extremely short life time and hence rapidly reduce to a
[PtIV(TMP)(OH)2]0 complex as confirmed by its UV–Vis and NMR
data. Hydrogen bond formation between two axial hydroxo groups
and hydrogen atoms of meta-chlorobenzoic acids or any other
protic species such as methanol and trifluoroacetic acid enables
the formation and stabilization of such species (Scheme 2).
Table 2
Half-wave potentials (E1/2, V vs. Ag/AgCl) of platinum porphyrins in CH2Cl2 containing
0.05 M of TBAP.
Compound
Ox1
Ox2
Red1
Red2
Refs.
PtIITMP
PtIITPP
1.19
1.23
–
1.67
1.60
1.7
À1.48
À1.3
–
–
tw
tw
tw
[49]
PtIITPFPP
PtIITPP
À0.85
À1.3
À1.3
1.20
1.52
–
Fig. 2. Voltammogram of a PtIITMP solution in CH2Cl2 containing 0.05 M TBAP as
supporting electrolyte at a scan rate of 0.1 V/s.
Table 3
Half-wave oxidation potentials (E1/2, V vs. Ag/AgCl) of platinum porphyrins in the
presence of three axial ligands in CH2Cl2 solution containing 0.05 M of TBAP.
Compound
Oxidation potential
Perchlorate
Methanol
Bromide
PtIITPP
1.23
1.19
–
1.59
1.67
1.7
1.23
1.19
–
1.53
1.55
1.7
1.44
1.37
v.ba
PtIITMP
PtIITPFPP
Fig. 3. Intermolecular O–HÁ Á ÁO hydrogen bonds between benzoic acid molecules
and OH–Pt–OH hydroxyl groups. Some of hydrogen atoms are omitted for better
clarity.
a
Very broad peak.

202
T. Alemohammad et al. / Inorganica Chimica Acta 434 (2015) 198–208
3.2. Cyclic voltammetry studies
PtIITPFPP due to the electron withdrawing effect of 20 fluorine
atoms (Table 2, Fig. S1).
Electrochemical behavior of three PtII(porp) complexes includ-
ing PtIITPP, PtIITMP and PtIITPFPP was investigated to find a clue
about what takes place during the stoichiometric titration. The
results have been summarized in Table 2. Cyclic voltammogram
of PtIITMP in CH2Cl2 in the presence of 0.05 M tetra-n-butylammo-
nium perchlorate (TBAP) as supporting electrolyte has been shown
in Fig. 2.
There are two reversible oxidation peaks in this voltammogram.
As expected [48], the first reversible oxidation of PtIITMP occurs at
slightly less positive potential than that of PtIITPP (Table 2), which
indicates that the first oxidation is macrocycle centered and leads
to the formation of PtII(TMP+Å) and PtII(TPP+Å) respectively. This is
The second oxidation peak takes place at around 1.6–1.7 V and
its position is independent of the macrocycle structure and shows
that it is a metal centered one. The current for the second peak
(19.2 lA) is approximately double that of the first peak (10 lA)
which indicates the involvement of a two-electron transfer process
in the second step. It seems that in total, three electrons are
abstracted from the initial PtIITMP to form the PtIV(TMP+Å) species.
Kadish et al. previously reported the formation of
the spectroelectrochemical method [44,48,49].
p
-cation PtIV by
Electrooxidation of PtIITMP in the presence of methanol, which
has a weak coordinating ability, caused no change in the first oxi-
dation potential, however it shifted the second one to a less posi-
tive potential (Table 3). This is an indication that the first
further confirmed by the absence of
p-cation formation for
Fig. 4. The observed out-of-plane displacement of the porphyrin core atoms from the mean plane of the porphyrin for the experimental and calculated structures of (A)
[(TMP)PtIV(OH)2](m-CBA)2 (blue and red, respectively) and (B) [(TMP)PtVI(OH)2TMP](m-CB)2 (orange and green, respectively) in units of Å. (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 5. The porphyrin core-superimposed of experimental and calculated structures of [(TMP)PtIV(OH)2](m-CBA)2 (blue and red, respectively) and [(TMP)PtVI(OH)2](m-CB)2
(orange and green, respectively). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

T. Alemohammad et al. / Inorganica Chimica Acta 434 (2015) 198–208
203
oxidation is ring-centered and the second oxidation peak is a
3.3. X-ray crystal structure of [(TMP)Pt(OH)2]Á2metachlorobenzoic
acid
metal-centered one. Electrochemistry studies were also performed
in the presence of 2.0 equivalent of bromide anion. In the presence
of bromide ion, a stronger coordinating ligand, only one reversible
oxidation peak at the less positive potential of 1.37 V was observed
which was assigned to the [PtIV(TMP)]Br2 species (Table 3 and
Figs. S2–S4).
In the present report, for Pt-complexes, two different structures,
either [PtVI(OH)2TMP](m-CB)2 or [PtIV(OH)2TMP](m-CBA)2 can be
refined. While the difference between these two structures is in
two hydrogen atoms, finding the correct structure from X-ray
diffraction data is too difficult (Figs. S9–S10 and Tables S5–S7).
Electron density can be measured by X-ray diffraction. Thus, the
heavier atoms have a stronger effect on the diffraction pattern.
This also means that, especially in the presence of heavy atoms,
the localization of the light atoms is more difficult. Here, in the
presence of a heavy atom such as platinum, light atoms such as
hydrogen, are somewhat more difficult to localize. On the other
hand, the treatment of hydrogen atoms in an X-ray structure
depends on many things, such as the geometry of the hydrogen
atom containing moiety and the element type of the atom bound
to hydrogen.
Electrochemistry shows that PtIITMP can be oxidized by a
maximum of three electrons and forms the PtIV(porp+Å) species,
but this species is very unstable and tends to reduce to a six
coordinate PtIV(porp) X2 complex in the presence of an axial
ligand even in electrochemical conditions. In our chemical condi-
tions, hydrogen bonding formation between hydrogen atoms of
meta-chlorobenzoic acids and hydroxo groups coordinated to
platinum provides very favorable conditions for reducing the
[PtIV(TMP+Å)(OH)2] intermediate to the [(TMP)Pt(OH)2)] complex.
Therefore, the reaction only progresses in the presence of a pro-
tic agent.
Table 4
The average bond lengths of 16
p
-, 18
p
-electron porphyrin rings in comparison with those of [(TMP)Pt(OH)2](m-CBA)2.
[(TMP)Pt(OH)2](m-CBA)2
beta
N
N
N
N
NH
22e - 18 pi
N
Npy
alpha
meso 16
p-electron
24e - 16 pi
N
HN
References:
1. Li+/BFÀ4
18
p-electron
2. Zn2+/Cl-/ZnCl-3
3. Octaethyl-Phenyl-Free
Cb–Cb (Å)
1.352
–
ꢀ1.350
1.352
–
–
Cb–C (Å)
1.466
–
ꢀ1.441
1.442
–
a
–
C –Cmeso (Å)
1.362
1.472
1.312
1.412
ꢀ1.393
1.395
–
1.366
1.380
a
–
C –Npy (Å)
a
ꢀ1.378
–
Fig. 6. Comparison between the structures of the Pt-complex as obtained with (A) X-ray, (B) (B3LYP/LANL2DZ) [(TMP)Pt(OH)2](m-CBA)2 and (C) (B3LYP/LANL2DZ)
[(TMP)Pt(OH)2](m-CB)2. Bond distances are in angstroms.

204
T. Alemohammad et al. / Inorganica Chimica Acta 434 (2015) 198–208
Therefore, complementary studies must be used to distinguish
H2BÁ Á ÁO1 = 164(5)°], Fig. 3. It seems that the formation of such a
hydrogen bonding plays an extremely important role in the forma-
tion and stabilization of the crystal packing of this complex.
Comparison of out-of-plane displacement of the porphyrin core
atoms from the mean plane of the porphyrin for experimental and
optimized structures shows that there is much better fit between
the experimental and optimized structure of [PtIV(OH)2TMP](m-
CBA)2, Fig. 4. Moreover, this is confirmed by porphyrin core-super-
imposed between experimental and calculated structures, Fig. 5.
The alternative for [(TMP2À)PtVI(OH)2](m-CB)2 might be consid-
ered as [(TMP0)PtIV (OH)2](m-CB)2 in which the porphyrin core is a
these structures. In our previous report, the two hydroxo groups
were considered axial ligands coordinated to the PtVI center, and
two m-chlorobenzoate anions bound to it by a very strong hydro-
gen bonding, according to stoichiometric titration and primary
electronic spectral changes [60]. It should be noted, in our previous
report, the structure was reported as [PtVI(OH)2TMP](m-CB)2. Here,
our complementary work such as more completed spectroscopic
studies and electrochemistry results as well as theoretical calcula-
tions show that the metal center must be considered as PtIV
.
Thus, with the help of theoretical studies, the original crystallo-
graphic data were re-refined as PtIV central metal. This was done
by adding the contribution of two hydroxo axial ligands that are
bound to two m-chlorobenzoic acids via a very strong hydrogen
bond. The resulting crystal unit cell is almost the same as the orig-
inal one (see Table S5) meaning that an X-ray crystal structure
determination alone is not sufficient to decide which oxidation
state should be assigned to the metal center.
dication 16
p
-electron system. The bond lengths for 16
p-electron
[50,56,58] and 18
p-electron [46,51–53] porphyrin rings in com-
parison with those of the Pt-complex obtained from X-ray analysis
are listed in Table 4. From this table, it is found that there is much
similarity in the values of bond distances of 18
the Pt-complex reported here. However, the most important fea-
ture evident in the structure of the Pt-complex is that such C –
p-electron rings and
a
It is notable that two benzoic acid molecules are directed
toward hydroxo groups of OH–Pt–OH and form some very strong
O–HÁ Á ÁO hydrogen bonds. Coordinated hydroxyl groups to plat-
inum center act as hydrogen bond acceptor from the hydroxyl
group of benzoic acid (Obenzoic acid–HÁ Á ÁOhydroxy), [O2–
H2B = 0.96(3), H2BÁ Á ÁO1 = 1.59(4), O2Á Á ÁO1 = 2.522(5) Å and O2-
Cmeso and C –Npy single and double bond alternation seen in 16
a
p-electron rings cannot be observed here. Furthermore, the
observed bond lengths of the Pt-complex can be completely fitted
with the normal valent porphyrin bond lengths obtained from the
average of hundreds of crystal structures. Thus, the pi-system of
the Pt-complex should be an aromatic 18 p-electron system.
3.4. Theoretical studies
Table 5
NBO analysis of electron distribution for Pt in [(TMP)Pt(OH)2](m-CBA)2 and
[(TMP)Pt(OH)2](m-CB)2.
The X-ray structure obtained for the Pt-complex was optimized
with B3LYP with the LANL2DZ basis set. Platinum was set to have
oxidation states of IV and VI and oxygen atoms coordinated to plat-
inum atom were supposed to be hydroxo or oxo forms. Fig. 6
shows the optimized structures. Structure A belongs to the X-ray
determined structure, and structure B and C are for the same struc-
ture optimized by DFT studies, [(TMP)PtIV(OH)2](m-CBA)2 and
[(TMP)PtVI(OH)2](m-CB)2 respectively. The bond distances and
[(TMP)Pt(OH)2](m-CBA)2
[(TMP)Pt(OH)2](m-CB)2
Occupancy
Orbital
Occupancy
Orbital
1.91
1.95
1.96
LP (dxy)Pt
LP (dxz)Pt
LP (dyz)Pt
1.85
1.93
1.95
LP (dxy)Pt
LP (dxz)Pt
LP (dyz)Pt
Fig. 7. MO, KS, relevant to interaction between macrocycle and dxy Pt orbital. (a) a2u molecular orbital of porphyrin ring; (b) dxy orbital of Pt and (c) resulting molecular orbital
from their overlap.

T. Alemohammad et al. / Inorganica Chimica Acta 434 (2015) 198–208
205
Fig. 8. Kohn-Sham orbitals and their occupations in [(TMP)Pt(OH)2](m-CB)2.
overall conformations resulted from X-ray structure studies are
similar to those of optimized structure of [(TMP)PtIV(OH)2](m-
CBA)2 with close approximation (Figs. S5–S8 and Tables S1–S4).
To further confirm the electronic structures, we have performed
NBO analysis for form B and C. The results of NBO analysis are pre-
sented in Table 5. These data show that the occupancy numbers of
dxy, dxz and dyz orbitals for platinum of form B are 1.91, 1.95 and
1.96 respectively and for form C are 1.85, 1.93 and 1.95. Form C
has two less electrons than form B, as obvious from the NBO anal-
ysis, three paired electrons are presented for d-orbitals in form C to
make the whole system Pt(IV) d6 (See Fig. 8).
The observed lower occupancy for dxy with respect to the dxz
and dyz orbitals may be interpreted due to the effective overlap
between dxy and a2u molecular orbital of the porphyrin macrocycle.
The major molecular orbitals responsible for overlaps between dxy
and porphyrin macrocycles are seen in Fig. 7a–c. These interactions
orbitals for the last three doubly occupied molecular orbitals of
platinum in ([(TMP)Pt(OH)2](m-CB)2). Based on this figure, paired
electrons are placed on dxy, dxz and dyz. Calculated charges show
that in [(TMP)Pt(OH)2](m-CB)2 the charges on the macrocycle
and platinum are 1.34 and 1.20 respectively, while in
[(TMP)Pt(OH)2](m-CBA)2, the charges on the macrocycle and plat-
inum are À0.45 and 1.18 respectively. Therefore the ring in
[(TMP)Pt(OH)2](m-CB)2 has
p-dication nature. This shows that
two electrons can transfer from the ring to the platinum center
and the charge on the ring decreases from À0.45 in
([(TMP)Pt(OH)2](m-CBA)2) to 1.34 in ([(TMP)Pt(OH)2](m-CB)2),
while the charge density on the platinum going from
([(TMP)Pt(OH)2](m-CBA)2) to ([(TMP)Pt(OH)2](m-CB)2) remains
fixed at around 1.20; consistent with the formation of the
platinum(IV) oxidation state.
Our DFT study and bond NBO analysis show that PtIITMP can be
oxidized by two electrons to form the PtIVTMP species. Further
might be responsible for delocalizing macrocycle
p electrons to the
dxy or vice versa. In the valance bond approach two resonance
forms are possible: p16 d2xydx2zd2yz(PtIV(porp0)) = p18 dx0yd2xzd2yz
(PtVI(porpÀ2)) and so the latter form prevents the anti-aromatic
behavior of the porphyrin ring. Calculated Mulliken charges pre-
sented in Table 6 indicate that the axial hydroxo groups are also
contributing to these molecular orbitals and have less negative
charges than those of [(porp)Pt(OH)2]0.
Table 6
Calculated Mulliken charges for the Pt, macrocycle, pyrrolic nitrogen and two OH
groups.
Compounds
Pt
Ring
2OH
N
Form B
Form C
1.18
1.20
À0.45
À0.70
À0.52
À0.65
À0.63
The NBO findings have been corroborated by the results
obtained from molecular calculations. Fig. 8 shows Kohn-Sham
1.34

206
T. Alemohammad et al. / Inorganica Chimica Acta 434 (2015) 198–208
Table 7
oxidation led to ring oxidation, the [(TMP)Pt(OH)2](m-CB)2 com-
plex has a PtIV center along with the two-electron oxidation of
Oxidation of various alkenes with iodosylbenzene in the presence of various Pt(II)-
porphyrin complexes.
the 18
tron porphyrin, but the effective overlap between the d2xy and the
16 -electron system of the ring prevents the anti-aromatic nature
p-electron porphyrin to make an anti-aromatic 16 p-elec-
% Yielda
p
Entry Alkene
Product(s)
PtTPP
32
PtTMP
35
PtTPFPP
58
of the ring. In the present work, DFT studies solved the contradic-
tion between X-ray diffraction and other spectroscopic data which
indicates the intrinsic limitation of X-ray diffraction techniques for
characterization of the compounds alone.
1
2
Cyclooctene
Epoxy
cyclooctene
Cyclohexene
oxide
2-Cyclohexene-
1-ole
Cyclohexene
4
40
17
7
50
21
24
32
47
2-Cyclohexene-
1-one
cis-Stilbene
oxide
3.5. Alkene epoxidation
3
4
cis-Stilbeneb
Not
46
100
Not
The [(TMP)Pt(OH)2] complex was formed from the addition of
2.0 equivalents of iodosylbenzene to a dichloromethane solution
of PtTMP in the presence of a few drops of methanol and used as
catalyst for the oxidation of cyclooctene. Isolated [(TMP)Pt(OH)2]X
(X = m-CBA, OMe) can convert two molecules of triphenylphosphine
to triphenylphosphine oxide, but is not capable in oxidizing alkenes.
Similar results were obtained by Gross et al. [70] in the oxidation
of different alkenes using the [(TMP)OsVI(O)2] complex. Both
[(TMP)Pt(OH)2] and PtTMP are able to catalyze the oxidation of
olefins in the presence of iodosylbenzene as an oxygen source.
Table 7 shows the results for the oxidation of various alkenes with
iodosylbenzene in the presence of different Pt-porphyrin catalysts.
The cyclohexene oxidation led to both epoxidation and allylic
oxidation whereas cyclooctene is clearly selective for epoxidation
[13].
detected Not
trans-Stilbene
oxide
Not
detected
detected detected
Styrene
Epoxy styrene
Benzaldehyde
Not
Not
40
detected detected 20
30
24
5
6
7
8
a-
a-Methylstyrene 38
37.5
52
Methylstyrene oxide
4-
4-Chlorostyrene
oxide
4-Methoxy
styrene oxide
1-Octene oxide
9.8
40
5
20.2
55
57.6
81.3
18.7
Chlorostyrene
4-Methoxy
styrene
1-Octene
2.3
Conditions: Catalyst 4 Â 10À4 mmol, PhIO 2 Â 10À2 mmol, Alkene 0.5 mmol,
a
25 °C, stirring for 24 h.
b
Epoxidation was performed in the absence of light.
Cis-stilbene was catalytically isomerized to trans-stilbene in the
presence of light and Pt-porphyrins, therefore the exclusion of light
is necessary to obtain cis-stilbene oxide as a product. To note,
PtTPP has no catalytic activity for cis-stilbene while it can catalyze
the oxidation of other alkenes which are less electron-rich than cis-
stilbene.
Table 8
Epoxidation of cis-stilbene in the presence of trace amounts of methanol.
Since alkenes should be considered nucleophiles in the oxida-
tion reaction, the olefins with electron donating substituent on
the aryl positions show better activity. In the case of 4-chlorostyr-
Amount of methanol (
l
l)
0
100
50
55
100
56
200
58
400
30
% Yielda
Conditions: PtTPFPP 4 Â 10À4 mmol, PhIO 2 Â 10À2 mmol, Alkene 0.5 mmol,
a
ene, the
p
-electron donation effects of chlorine to the double bond
-electron acceptation effects. Greater
25 °C, stirring for 24 h.
may be balanced with its
r
reactivity of
a-methylstyrene with respect to styrene, 4-
PhIO + CH2Cl2 (MeOH)
H
O
IV
Pt
Pt
no product
several days
O
H
PhIO
2 Ph3P
PtII
2 Ph3P(O)
O
PhIO
H
O
IV
Pt
O
H
Scheme 3. Proposed catalytic cycle.

T. Alemohammad et al. / Inorganica Chimica Acta 434 (2015) 198–208
[2] D. Dolphin, T.G. Traylor, L.Y. Xie, Acc. Chem. Res. 30 (1997) 251.
207
chlorostyrene and 4-methoxystyrene may be due to the
r-electron
[3] T.G. Traylor, J.C. Marsters, T. Nakano, B.E. Dunlap, J. Am. Chem. Soc. 107 (1985)
5537.
[4] M. Sono, M.P. Roach, E.D. Coulter, J.H. Dawson, Chem. Rev. 96 (1996) 2841.
[5] D. Mansuy, Pure Appl. Chem. (1987) 759.
[6] H. Strasdeit, Angew. Chem., Int. Ed. 107 (1995) 1019.
[7] J.P. McEvoy, G.W. Brudvig, Chem. Rev. 106 (2006) 4455.
[8] T.G. Traylor, K.W. Hill, W.P. Fann, S. Tsuchiya, B.E. Dunlap, J. Am. Chem. Soc.
114 (1992) 1308.
donation effects of the methyl group to the double bond. Terminal
double bond (Table 7, entry 8) is less reactive than the conjugated
double bonds and shows lower activity.
The results of cis-stilbene epoxidation in the presence of
PtTPFPP as catalyst and trace amounts of methanol are shown in
Table 8. These data provide an indication that the coordinating
ligand favors the formation of inactive six-coordinate
PtIV(porp)(OH)2 versus PtIV(porp+Å)(OH)2 and reduces the yield of
products.
[9] J.T. Groves, P. Viski, J. Org. Chem. 55 (1990) 3628.
[10] N. Safari, F. Bahadoran, M.R. Hoseinzadeh, R. Ghiasi, J. Porphyrins
Phthalocyanines 4 (2000) 285.
[11] M. Costas, Coord. Chem. Rev. 255 (2011) 2912.
[12] J.T. Groves, T.E. Nemo, J. Am. Chem. Soc. 105 (1983) 5786.
[13] T.G. Traylor, A.R. Miksztal, J. Am. Chem. Soc. 111 (1989) 7443.
[14] E. Rose, M. Quelquejeu, R.P. Pandian, A. Lecas-Nawrocka, A. Vilar, G. Ricart, J.P.
Collman, Z. Wang, A. Straumanis, Polyhedron 19 (2000) 581.
[15] J. Collman, X. Zhang, V. Lee, E. Uffelman, J. Brauman, Science 261 (1993) 1404.
[16] H.R. Khavasi, N. Safari, J. Porphyrins Phthalocyanines 9 (2005) 75.
[17] A. Aghabali, N. Safari, J. Porphyrins Phthalocyanines 14 (2010) 335.
[18] H. Fujii, J. Am. Chem. Soc. 115 (1993) 4641.
[19] D. Mohajer, G. Karimipour, M. Bagherzadeh, New J. Chem. 28 (2004) 740.
[20] W. Nam, M.H. Lim, S.-Y. Oh, J.H. Lee, H.J. Lee, S.K. Woo, C. Kim, W. Shin, Angew.
Chem., Int. Ed. 39 (2000) 3646.
[21] Z. Gross, S. Nimri, Inorg. Chem. 33 (1994) 1731.
[22] W. Nam, Acc. Chem. Res. 40 (2007) 522.
3.6. Proposed mechanism
In the catalytic cycle, PhIO can lead to the PtIV(porp+Å)(OH)2
complex which initiates a catalytic cycle as shown in Scheme 3.
Formation of such an intermediate in the catalytic cycle was con-
firmed by cyclic voltammetry studies. Groves et al. also reported
such a route in the hydroxylation of alkanes by ruthenium por-
phyrins [71]. In the absence of substrate and in the presence of
coordinating ligands, PtIV(porp+Å)(OH)2 rapidly reduced to a more
stable PtIV(porp)(OH)2 which is unreactive toward alkenes which
were capable of oxidizing PPh3 to PPh3(O).
[23] B. Sheldon, R.A. Meunier, Biomimetic Oxidations Catalysed by Transition Metal
Complexes, Imperial College Press, 2000.
[24] D. Mansuy, Coord. Chem. Rev. 125 (1993) 129.
[25] E. Mesbahi, N. Safari, M. Gheidi, J. Porphyrins Phthalocyanines 18 (2014) 354.
[26] T. Alemohammad, N. Safari, S. Osati, J. Porphyrins Phthalocyanines 15 (2011)
181.
4. Conclusion
[27] N. Jin, J.L. Bourassa, S.C. Tizio, J.T. Groves, Angew. Chem., Int. Ed. 39 (2000)
3849.
[28] N. Jin, M. Ibrahim, T.G. Spiro, J.T. Groves, J. Am. Chem. Soc. 129 (2007) 12416.
[29] B. Meunier, Chem. Rev. 92 (1992) 1411.
[30] S.-K. Lee, I. Okura, Anal. Chim. Acta 342 (1997) 181.
[31] A. Mills, A. Lepre, Anal. Chem. 69 (1997) 4653.
[32] D.B. Papkovsky, G.V. Ponomarev, O.S. Wolfbeis, Spectrochim. Acta, Part A 52
(1996) 1629.
Oxidation of PtIITMP consumes 2.0 equivalents of m-CPBA and
forms a new Pt-complex that we have previously reported as
[PtVI(TMP)(OH)2](m-CB)2 based on stoichiometric titration and X-
ray analysis. Complementary spectroscopic, electrochemical and
theoretical studies suggested +4 oxidation state for the platinum
center. DFT studies were employed to find the correct position of
hydrogen atoms and hence, the correct structure. Finally, we refor-
mulated the crystal structure as [(TMP)PtIV(OH)2](m-CBA)2 corre-
sponding to DFT results, which shows Pt-oxo and dioxo species
are not stable and tend to form platinum dihydroxo species.
It is notable that there is a strong hydrogen bonding between
two hydroxo groups coordinated to platinum and hydrogen atoms
of m-chlorobenzoic acids (or trifluoroacetic acid or methanol) that
is a crucial factor for the formation and stabilization of this species.
While the [(porp)Pt(OH)2] complexes are not active oxidants
toward the oxidation of olefins, they can oxidized two molecules
of triphenylphosphine. These complexes and their corresponding
PtII(porp) complexes showed catalytic activity toward olefin epox-
idation in the presence of iodosylbenzene. Catalytic oxidation reac-
tions also indicate the involvement of a PtIV(porp+Å) intermediate in
catalytic cycle confirmed by electrochemistry studies.
[33] R.R. de Haas, R.P.M. van Gijlswijk, E.B. van der Tol, J. Histochem. Cytochem. 45
(1997) 1279.
[34] H. Kunkely, A. Vogler, Inorg. Chim. Acta 254 (1997) 417.
[35] H. Brunner, K.-M. Schellerer, Monatsh. Chem. 133 (2002) 679.
[36] H. Brunner, K.M. Schellerer, B. Treittinger, Inorg. Chim. Acta 264 (1997) 67.
[37] A. Ferri, G. Polzonetti, S. Licoccia, R. Paolesse, D. Favretto, P. Traldi, M.V. Russo,
J. Chem. Soc., Dalton Trans. (1998) 4063.
[38] H. Yuan, L. Thomas, L.K. Woo, Inorg. Chem. 35 (1996) 2808.
[39] N.N. Greenwood, A. Earnshaw, Chemistry of the Elements, Elsevier, 1997.
[40] B. Weinstock, H.H. Claassen, J.G. Malm, J. Am. Chem. Soc. 79 (1957) 5832.
[41] B. Weinstock, J.G. Malm, E.E. Weaver, J. Am. Chem. Soc. 83 (1961) 4310.
[42] T.M. Anderson, W.A. Neiwert, M.L. Kirk, P.M.B. Piccoli, A.J. Schultz, T.F. Koetzle,
D.G. Musaev, K. Morokuma, R. Cao, C.L. Hill, Science 306 (2004) 2074.
[43] K.P. O’Halloran, C. Zhao, N.S. Ando, A.J. Schultz, T.F. Koetzle, P.M.B. Piccoli, B.
Hedman, K.O. Hodgson, E. Bobyr, M.L. Kirk, S. Knottenbelt, E.C. Depperman, B.
Stein, T.M. Anderson, R. Cao, Y.V. Geletii, K.I. Hardcastle, D.G. Musaev, W.A.
Neiwert, X. Fang, K. Morokuma, S. Wu, P. Kögerler, C.L. Hill, Inorg. Chem. 51
(2012) 7025.
[44] L.M. Mink, M.L. Neitzel, L.M. Bellomy, R.E. Falvo, R.K. Boggess, B.T. Trainum, P.
Yeaman, Polyhedron 16 (1997) 2809.
[45] L.M. Mink, J.W. Voce, J.E. Ingersoll, V.T. Nguyen, R.K. Boggess, H. Washburn, D.I.
Grove, Polyhedron 19 (2000) 1057.
[46] J.R. Tate, K. Kantardjieff, G. Crundwell, L.M. Mink, Acta Crystallogr., Sect. C 58
(2002) m485.
Acknowledgments
[47] J. Buchler, K. Lay, H. Stoppa, Z. Naturforsch. 35b (1980) 433.
[48] P. Chen, O.S. Finikova, Z. Ou, S.A. Vinogradov, K.M. Kadish, Inorg. Chem. 51
(2012) 6200.
[49] Z. Ou, P. Chen, K.M. Kadish, Dalton Trans. 39 (2010) 11272.
[50] J.A. Cissell, T.P. Vaid, A.L. Rheingold, Inorg. Chem. 45 (2006) 2367.
[51] J.A. Cissell, T.P. Vaid, A.L. Rheingold, J. Am. Chem. Soc. 127 (2005) 12212.
[52] J.A. Cissell, T.P. Vaid, G.P.A. Yap, J. Am. Chem. Soc. 129 (2007) 7841.
[53] C. Liu, D.-M. Shen, Q.-Y. Chen, J. Am. Chem. Soc. 129 (2007) 5814.
[54] A.B. McQuarters, M.W. Wolf, A.P. Hunt, N. Lehnert, Angew. Chem., Int. Ed. 53
(2014) 4750.
[55] A. Gebauer, D.Y. Dawson, J. Arnold, J. Chem. Soc., Dalton Trans. (2000) 111.
[56] Y. Yamamoto, A. Yamamoto, S.-Y. Furuta, M. Horie, M. Kodama, W. Sato, K.-Y.
Akiba, S. Tsuzuki, T. Uchimaru, D. Hashizume, F. Iwasaki, J. Am. Chem. Soc. 127
(2005) 14540.
[57] J.A. Cissell, T.P. Vaid, G.P.A. Yap, Org. Lett. 8 (2006) 2401.
[58] Y. Yamamoto, Y. Hirata, M. Kodama, T. Yamaguchi, S. Matsukawa, K.-Y. Akiba,
D. Hashizume, F. Iwasaki, A. Muranaka, M. Uchiyama, P. Chen, K.M. Kadish, N.
Kobayashi, J. Am. Chem. Soc. 132 (2010) 12627.
We would like to thank the Graduate Study Councils of Shahid
Beheshti University and K.N. Toosi University of Technology for
financial support.
Appendix A. Supplementary material
CCDC 1043896 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif. Supplementary data associated with this arti-
cle can be found, in the online version, at http://dx.doi.org/10.
1016/j.ica.2015.05.023.
[59] T. Kakui, S. Sugawara, Y. Hirata, S. Kojima, Y. Yamamoto, Chem. Eur. J. 17
(2011) 7768.
References
[60] N. Safari, S. Rayati, A. Ghaemi, F. Bahadoran, H.R. Khavasi, Inorg. Chem.
Commun. 11 (2008) 1459.
[1] P.R. Ortiz de Montellano, Cytochrome P450: Structure, Mechanism, and
Biochemistry: Plenum Press, New York, 2004.

208
T. Alemohammad et al. / Inorganica Chimica Acta 434 (2015) 198–208
[61] J.S. Lindsey, I.C. Schreiman, H.C. Hsu, P.C. Kearney, A.M. Marguerettaz, J. Org.
Chem. 52 (1987) 827.
[62] H.S.A.J.G. Sharefkin, Org. Synth. 5 (1973) 660.
P.M. Gill, B.G. Johnson, W. Chen, M. Wong, J.L. Andres, M. Head-Gordon, E.S.
Replogle, J.A. Pople, GAUSSIAN 98 (revision A.9) Gaussian: Pittsburgh, PA, 98.
[65] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.
[63] K.-L.L.U.H.S. Johann, W. Buchler, Z. Naturforsch 35b (1980) 433.
[64] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, J.R. Cheeseman, M.A. Robb,
V.G. Zakrzewski, J.A. Montgomery, R.E. Stratmann, J.C. Burant, S. Dapprich, J.M.
Millam, A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V. Barone, M.
Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G.A.
Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, D.K. Malick, A.D. Rabuck, K.
Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, B.B. Stefanov, G. Liu, A.
Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L. Martin, D.J. Fox, T. Keith,
M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, C.V. Ghonzalez, M.W. challacombe,
[66] W.Y. Chengteh, Phys. Rev. B 37 (1988) 785.
[67] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 299.
[68] L.R. Milgrom, R.J. Zuurbier, J.M. Gascoyne, D. Thompsett, B.C. Moore,
Polyhedron 11 (1992) 1779.
[69] L.R. Milgrom, R.J. Zuurbier, J.M. Gascoyne, D. Thompsett, B.C. Moore,
Polyhedron 13 (1994) 209.
[70] Z. Gross, A. Mahammed, J. Mol. Catal. A 142 (1999) 367.
[71] J.T. Groves, M. Bonchio, T. Carofiglio, K. Shalyaev, J. Am. Chem. Soc. 118 (1996)
8961.