Rhenium(i) tricarbonyl complex of 5,20-bis(p-tolyl)-10,15-bis(p- methoxyphenyl)-21-selenaporphyrin: First X-ray structural characterization of metal complex of 21-selenaporphyrin

Article abstract of DOI:10.1039/c3dt51024g

Synthesis and first structural characterization of hexa coordinated rhenium(i) tricarbonyl complex of 5,20-bis(p-tolyl)-10,15-bis(p-methoxyphenyl)- 21-selenaporphyrin 3 are described. The Re(i) complex of 21-selenaporphyrin 3 was synthesized by treating free base 21-selenaporphyrin in 1,2-dichlorobenzene with Re(CO)₅Cl at reflux for 7 h and analyzed using mass, NMR, FT-IR, UV-vis and electrochemical techniques. The first structure of metal complex of 21-selenaporphyrin was determined by X-ray single crystal analysis. The crystal structure revealed that the Re(CO)₃ coordinates to two of the three inner nitrogens and one selenium to produce compound 3. The selenophene ring bent towards the Re(i) ion and the selenium is displaced by 0.41 A from the mean plane of 24-atoms to coordinate with Re(i) ion in η¹- fashion. The 21-selenaporphyrin is distorted in compound 3 compared to free base 21-selenaporphyrin. ¹H and ¹³C NMR studies indicated that compound 3 exhibits fluxional behaviour in coordination mode of binding in solution. The compound 3 is highly stable and does not undergo decomplexation under acidic conditions. The absorption spectra showed three broad Q-bands and splitted Soret band and electrochemical studies indicated that compound 3 is stable under redox conditions. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3dt51024g

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Rhenium(I) tricarbonyl complex of 5,20-bis(p-tolyl)-
10,15-bis(p-methoxyphenyl)-21-selenaporphyrin: first
X-ray structural characterization of metal complex of
21-selenaporphyrin†
Cite this: Dalton Trans., 2013, 42, 10798
Avijit Ghosh,a Rajesh Gonnadeb and Mangalampalli Ravikanth*a
Synthesis and first structural characterization of hexa coordinated rhenium(I) tricarbonyl complex of 5,20-
bis(p-tolyl)-10,15-bis(p-methoxyphenyl)-21-selenaporphyrin
3 are described. The Re(I) complex of
21-selenaporphyrin 3 was synthesized by treating free base 21-selenaporphyrin in 1,2-dichlorobenzene
with Re(CO)5Cl at reflux for 7 h and analyzed using mass, NMR, FT-IR, UV-vis and electrochemical tech-
niques. The first structure of metal complex of 21-selenaporphyrin was determined by X-ray single crystal
analysis. The crystal structure revealed that the Re(CO)3 coordinates to two of the three inner nitrogens
and one selenium to produce compound 3. The selenophene ring bent towards the Re(I) ion and the sel-
enium is displaced by 0.41 Å from the mean plane of 24-atoms to coordinate with Re(I) ion in η1-fashion.
The 21-selenaporphyrin is distorted in compound 3 compared to free base 21-selenaporphyrin. 1H and
13C NMR studies indicated that compound 3 exhibits fluxional behaviour in coordination mode of
binding in solution. The compound 3 is highly stable and does not undergo decomplexation under acidic
conditions. The absorption spectra showed three broad Q-bands and splitted Soret band and electro-
chemical studies indicated that compound 3 is stable under redox conditions.
Received 18th April 2013,
Accepted 16th May 2013
DOI: 10.1039/c3dt51024g
www.rsc.org/dalton
heteroporphyrins such as 21-thia5–9 and 21-oxaporphyrins10–14
can stabilize metals in unusual oxidation states5d,10,13 unlike
Introduction
21-Heteroporphyrins such as 21-oxaporphyrin,1 21-thiapor- their tetrapyrrolic analogues. However, among 21-heteropor-
phyrin,1 21-selenaporphyrin,1 21-telluraporphyrin,1 21-silaph- phyrins, the metal coordination chemistry of 21-thia and 21-
lorin,2 21-carbaporphyrin3 and 21-phosphaporphyrin4 resulted oxaporphyrins is relatively well developed. Grażyński et al. and
from the replacement of one pyrrole nitrogen with hetero others have shown that 21-thiaporphyrin forms coordinate
atoms like O, S, Se, Te, Si, C and P respectively, possess very complexes with Fe(II),5a Ni(II),5a Cu(II),5b,c Pd(II),5e Rh(III),5f
interesting properties which are quite different from normal Li(I),6 Hg(II)7 and Ru(II)9 whereas 21-oxaporphyrin forms com-
porphyrins with N4 core. The electronic properties of the plexes with Ni(II),10 Co(II),11 Mn(II),11 Zn(II),11,12 Cu(II)13 and
porphyrin macrocycle were significantly altered in 21-hetero- Fe(II).14 The metal coordination chemistry of other heteropor-
porphyrins compared to N4 porphyrins. Furthermore, 21-het- phyrins such as 21-selenaporphyrins and 21-telluraporphyrins
eroporphyrins possess unique coordination properties because has not been explored. A perusal of literature reveals that there
of their unique size, shape and charge. The binding ability of is only one report on metal complex of 21-selenaporphyrin
the macrocyclic platforms are dependent on the type of hetero describing the coordination of 21-selenaporphyrin with Ni(II)
atom present along with the three pyrrole nitrogens.1 Interest- ion which was not characterized structurally.15 This could be
ingly, the metal coordination chemistry of 21-heteroporphyrins because of large selenium atom that shrinks the porphyrin
is underdeveloped although it is established that 21- cavity size and also because of poor coordinating ability of sel-
enium. Recently, we successfully synthesized Re(CO)3 com-
plexes of 21-thiaporphyrin 1 and 21-oxaporphyrin 2 (Chart 1)
aDepartment of Chemistry, Indian Institute of Technology, Bombay, Powai, Mumbai
400 076, India. E-mail: ravikanth@chem.iitb.ac.in
and X-ray analysis revealed different coordination behaviour of
Re(CO)3 unit with 21-thiaporphyrin and 21-oxaporphyrin.16
The Re(CO)3 coordinates to two out of three inner nitrogens
and one sulphur instead of three inner nitrogens to form
Re(CO)3 complex of 21-thiaporphyrin 1 whereas the Re(CO)3
coordinates to three inner nitrogens but not with furan oxygen
bCentral Material Characterization Division, National Chemical Laboratory,
Dr. Homi Bhabha Road, Pune, 411 008, India
†Electronic supplementary information (ESI) available: All spectral and experi-
mental details. CCDC 923294. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c3dt51024g
10798 | Dalton Trans., 2013, 42, 10798–10806
This journal is © The Royal Society of Chemistry 2013

View Article Online
Dalton Transactions
Paper
dichlorobenzene under reflux for 7 h (Scheme 1) and the pro-
gress of the reaction was monitored by TLC and absorption
spectroscopy. The reaction colour changed to dark brown as
the reaction progressed. The TLC analysis indicated the dis-
appearance of spot corresponding to free base 21-selena-
porphyrin and appearance of new spot corresponding to the
required Re(I) complex of 21-selenaporphyrin 3 (Scheme 1).
Absorption spectroscopy also indicated the formation of Re(I)
complex of 21-selenaporphyrin 3. After standard work-up, the
crude reaction mixture was subjected to silica gel column
chromatography and afforded pure compound 3 as shiny dark
solid with greenish tinge in 94% yield. The compound 3 is
freely soluble in common organic solvents and very stable in
solution unlike the reported Ni(II) complex of 21-selenapor-
phyrin15 which showed a gradual decomplexation in solution.
The identity of compound 3 was confirmed by the molecular
ion peak at m/z 1038.1476 in the HR-MS mass spectrum (p. S3,
ESI†) and characterized by NMR, IR, absorption and electro-
chemical techniques.
Chart 1 The chemical structures of Re(CO)3 complexes of 21-thia (1) and 21-
oxaporphyrins (2).
NMR studies
The comparison of 1H NMR spectra of compound 1 with its
free base 21-selenaporphyrin 4 is presented in Fig. 1a and the
proton assignments were made based on the correlation
observed in the 1H–1H COSY spectrum shown in Fig. 1b. In
1H NMR, the free base 21-selenaporphyrin 4 showed one
singlet at δ 10.06 ppm for two selenophene protons and three
sets of doublets at 8.63, 8.69 and 8.90 ppm for six pyrrole
Scheme 1 Synthesis of compound 3.
to form Re(CO)3 complex of 21-oxaporphyrin 2 (Chart 1). In
this paper, we describe the successful synthesis of Re(CO)3
complex of 5,20-bis(p-tolyl)-10,15-bis(p-methoxyphenyl)-21-
selenaporphyrin 3 (Scheme 1) and first X-ray structural evi-
dence of metal coordination with 21-selenaporphyrin. Our
studies revealed that Re(CO)3 coordinates with two of the three
inner nitrogens and selenium and also showed the fluxional
behaviour in coordination mode of binding in solution in
compound 3 like Re(CO)3 complex of 21-thiaporphyrin 1.
protons. The compound
3 also showed one singlet at
10.16 ppm for two selenophene protons in 1H NMR which was
slightly downfield shifted compared to free base 21-selenapor-
phyrin 4. However, the six pyrrole protons appeared as cluster
of signals in 8.38–8.44 ppm region which were upfield shifted
in compound 3 compared to pyrrole signals of free base
21-selenaporphyrin 4. We also identified the meso-tolyl and
meso-anisyl protons of compound 3 by following cross-peak
connectivities observed in 1H–1H COSY NMR. For example, the
Results and discussion
The X-ray structure reported by Grażyński and co-workers for methyl signal of meso-tolyl group observed at 2.69 ppm
free base 5,20-diphenyl-10,15-bis(p-tolyl)-21-selenaporphyrin15 showed a cross peak correlation with c-type aryl protons
(SeDPDTPH) showed close resemblances with the structure of observed at 7.65 ppm which in turn showed cross peak cor-
5,20-bis(p-tolyl)-10,15-diphenyl-21-thiaporphyrin6 (SDTDPPH). relation with a broad signal at 8.14 ppm which was identified
The selenophene ring is out-of-plane of the macrocycle in as d-type protons. Similarly the methoxy protons of anisyl
21-selenaporphyrin like thiophene ring which is distorted out- group which appeared at 4.08 ppm showed a cross peak corre-
of-plane in 21-thiaporphyrin. Selenophene also has weak coor- lation with a-type protons at 7.28 ppm which in turn showed
dinating ability like thiophene. However, 21-thiaporphyrin has correlation with b-type protons at 8.14 ppm as broad signal
been shown to form four, five and six coordinate metal along with d-type protons. Thus, using 1H and 1H–1H COSY
complexes.5–9 In all metallothiaporphyrin complexes, the thio- NMR, all resonances observed in compound 3 were identified
phene ring is sharply bent out of the mean plane and binds to clearly. The only b and d-type meso-aryl signals appeared as a
the metal in a η1 (S)-fashion. Interestingly, the coordination broad peak due to their proximity with Re(CO)3 unit and these
chemistry of 21-selenoporphyrin has remained elusive observations were in line with our previously reported Re(CO)3
although one expects that 21-selenoporphyrin also prefer to complexes of 21-thiaporphyrin
1 and 21-oxaporphyrin 2
form metal complexes like 21-thiaporphyrin. Here, we show (Chart 1). Furthermore, the involvement of selenophene sel-
that the 21-selenaporphyrin also coordinates with Re(I) ion like enium in binding with Re(I) ion was confirmed by 77Se NMR
21-thiaporphyrin.
(pp. S6–S7, ESI†). The free base 21-selenaporphyrin 4 exhibited
The free base 5,20-bis(p-tolyl)-10,15-bis(p-methoxyphenyl)- a signal at 639.4 ppm in 77Se NMR which was significantly
21-selenaporphyrin 4 was reacted with Re(CO)5Cl in 1,2- upfield shifted by ∼200 ppm and appeared at 404.4 ppm in
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 10798–10806 | 10799

View Article Online
Paper
Dalton Transactions
Fig. 1 (a) Comparison of 1H NMR spectra of compound 3 with free base 21-selenaporphyrin 4 recorded in CDCl3 at room temperature (* residual solvent peak).
(b) Partial 1H–1H COSY spectrum of compound 3 showing the cross-peak connectivity of meso-aryl groups, recorded in CDCl3 at room temperature.
compound 3. The presence of three carbonyls on Re(I) ion of protons appeared as three sets of signals like its free base
compound 3 was verified by two signals at 189.0 and 5,10,15,20-tetraphenylporphyrin (STPPH) supporting that com-
189.2 ppm in 13C NMR (pp. S8–S9, ESI†) and two strong pound 1 exists in the same symmetric environment as STPPH
absorptions at 2014, 1902 cm−1 in IR spectra (p. S10, ESI†).
and exhibits rapid fluxional behaviour16 at room temperature
Our earlier studies on compound 1 indicated fluxional be- (p. S12, ESI†). But in case of compound 3, the six pyrrole
haviour in solution.16 Since the crystal structure analysis of protons appeared as cluster of signals unlike its free base 4
compound 3 (vide infra) also showed that Re(I) ion coordinates which showed three sets of signals at room temperature
with selenium and two out of three pyrrole nitrogens like com- (Fig. 1a). This is because of slow fluxional behaviour of com-
pound 1, we anticipated similar fluxional behaviour for com- pound 3 compared to compound 1 at room temperature.
pound 3 in solution. The compound 3 is also expected to exist Hence, we carried out variable temperature 1H NMR studies
in two conformers which can interconvert to each other like on compound 3 in +50 to −40 °C range and presented in
compound 1 and the obtained 1H NMR spectrum of com- Fig. 2. At higher temperature (+50 °C), the six pyrrole protons
pound 3 is only for the average structure of these two confor- of compound 3 appeared as three sets of well resolved reson-
mers in solution (p. S11, ESI†). However, if the solid state ances similar like its free base porphyrin 4 (p. S13, ESI†). This
structure is retained in solution, we expect a higher number of is possible only if compound 3 exhibit rapid fluxional behav-
1
β-pyrrole and β-selenophene resonances in H NMR compared iour at that slightly higher temperature.17 However, compound 3
to its free base porphyrin due to asymmetric nature of the showed unresolved resonances for six pyrrole protons at room
compound 3. In the case of compound 1, the six pyrrole temperature due to slow fluxional behaviour. Thus, we
10800 | Dalton Trans., 2013, 42, 10798–10806
This journal is © The Royal Society of Chemistry 2013

View Article Online
Dalton Transactions
Paper
Fig. 2 Variable temperature 1H NMR spectra of compound 3 recorded in the
temperature range from +50 to −40 °C in CDCl3.
Fig. 3 1H NMR titration spectra of compound 3 by addition of increasing
amounts of trifluoroacetic acid (TFA) in CDCl3 recorded at room temperature.
the NMR spectrum of compound 3 under protonated con-
ditions and low temperature was almost similar supporting
the arrest of fluxionality at low temperature as well. The broad
signal observed for ortho protons of meso-aryl group in com-
pound 3 appeared as sharp signal on protonation. Further-
more, the asymmetric nature of compound 3 on protonation
was also reflected in the splitting of –OCH3 and –CH3 reson-
ances in 1H NMR (p. S18, ESI†). All these observations support
the arrest of fluxional behaviour of compound 3 on proto-
nation in solution. 13C NMR spectra (p. S19, ESI†) of com-
pound 3 in CDCl3 under protonated conditions exhibited three
signals for three carbonyl groups due to the asymmetric nature
of protonated compound 3. Thus, NMR studies of compound
3 supported the arrest of fluxional behaviour under protonated
as well as low temperature conditions.
anticipated that lowering temperature would stop the fluxion-
ality of compound 3 leading to only one type of conformer (A
or B, p. S11, ESI†). The 1H NMR studies at −40 °C on com-
pound 3 showed more number of resonances for β-pyrrole and
β-selenophene protons supporting the existence of one type of
conformer at this temperature. Unfortunately, due to our NMR
instrument limitation, we could not study the fluxional behav-
iour of compound 3 at much lower temperatures. Since the
rate of fluxional behaviour of compound 3 appeared to be slow
at room temperature, we expected that protonation studies on
compound 3 also would arrest fluxional behaviour of com-
pound 3 although the thia analogue 1 showed fluxional behav-
iour even upon protonation conditions (p. S14, ESI†). If
protonation arrests fluxionality of compound 3 leading to only
one type of conformer, we anticipate more AB type resonances
1
for chemically different pyrroles and selenophene in H NMR.
Thus, we carried out the protonation studies by treating com-
Absorption and electrochemical studies
pound 3 with increasing amounts of trifluoroacetic acid (TFA)
The absorption properties of compound 3 along with free base
21-selenaporphyrin 4 were studied in dichloromethane and
data are presented in Table 1. The comparison of Q-band and
Soret band absorption spectra of compound 3 and free base
21-selenaporphyrin 4 is shown in Fig. 4. The free base 21-selena-
1
1
and followed by H NMR. In H NMR (Fig. 3), upon increasing
addition of TFA to compound 3 in CDCl3, the two selenophene
protons and six pyrrole protons appeared as different sets of
signals due to arrest of fluxionality leading to one conformer
(p. S15, ESI†). 1H NMR (Fig. 3) and 1H–1H COSY NMR (pp.
S16–S17, ESI†) studies revealed that on protonation of com-
pound 3, the two selenophene protons shifted downfield and
appeared as two doublets and the six pyrrole protons of three
pyrrole rings appeared as four doublets and one singlet. The
most downfield signal observed at 8.75 ppm for two pyrrolic
protons was from the pyrrole ring which was trans to seleno-
phene ring and involved in coordination with Re(I) ion. The
other four sets of doublets are due to the pyrrole which was
involved in bonding with Re(I) as well as the pyrrole which was
protonated. This observation is in contrast with compound 1
under similar protonated conditions. Since compound 1
showed fluxional behaviour even under protonated conditions,
the NMR pattern remained same (p. S14, ESI†). Interestingly,
porphyrin
4
exhibited four well-defined Q-bands in
700–500 nm region and one strong sharp Soret band at
436 nm like tetrapyrrolic porphyrin. In compound 3, the
number of Q-bands was reduced to three and Soret band was
split to two bands which may be due to distortion in the
macrocycle. Both Q- and Soret bands in compound 3 were
broad with low extinction coefficients compared to free base
21-selenaporphyrin 4. All these absorption features are in
agreement with our earlier reported Re(CO)3 complexes of
21-thia 1 and 21-oxaporphyrins 2.16 The protonation studies
were carried out by treating compound 3 and free base 21-sele-
naporphyrin 4 in CH2Cl2 with dilute trifluoroacetic acid. The
protonation of compound 3 resulted in the increase in the
intensity of the absorption bands in both Q- and Soret bands
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 10798–10806 | 10801

View Article Online
Paper
Dalton Transactions
Table 1 Absorption and redox data
Absorptiona
Redoxb
Compounds
Soret band (λ in nm) (log ε)
Q-bands (λ in nm) (log ε)
Oxidationc (V)
Reduction (V)
4
436 (5.12)
486 (3.86) (sh), 520 (4.24),
556 (3.79), 619 (3.61),
680 (3.69)
1.02
1.29
1.47
−1.01
−1.33
—
4+TFA
3
478 (4.99)
772 (4.48) (br)
—
—
431 (4.88)
484 (4.65) (br)
575 (4.12), 655 (3.65),
717 (3.67)
1.07
1.31
−0.86
−1.32
3+TFA
464 (4.96)
584 (4.08), 666 (3.92),
725 (4.11)
—
—
a Recorded in CH2Cl2 at room temperature. Concentration used for Soret and Q-bands are 10−5 M and 10−4 M respectively. b Recorded in CH2Cl2
at room temperature by using TBAP as supporting electrolyte and saturated calomel electrode (SCE) as reference electrode at a scan rate of
50 mV s−1 c Irreversible.
.
tetrabutylammonium perchlorate (TBAP) as supporting electro-
lyte (0.1 M) and saturated calomel electrode (SCE) as reference
electrode in dichloromethane. The compound 3 exhibited two
irreversible oxidations whereas the free base 21-selena-
porphyrin 4 exhibited three irreversible oxidations. However,
both compounds 3 and 4 exhibited two reversible reductions
(Table 1). The comparison of the reduction waves of com-
pound 3 and free base 21-selenaporphyrin 4 is shown in Fig. 5.
As clear from the data in Table 1 and Fig. 5, the first reduction
potential of compound 3 was shifted towards less negative by
150 mV compared to free base 21-selenaporphyrin 4. However,
the second reduction and oxidation potentials of both com-
pounds were in the same range. This indicated that Re(CO)3
complexation of 21-selenaporphyrin makes the porphyrin
ligand more electron rich in compound 3 and the compound 3
is stable under redox conditions.
Fig. 4 Comparison of Q-band absorption spectra of compound 3 (black), free
base 21-selenaporphyrin 4 (blue) and 3+TFA (red) recorded in CH2Cl2 at room
temperature. Inset shows the comparison of corresponding Soret band spectra.
Concentrations used were ∼10−5
M M for Soret and Q-band
and 10−4
respectively.
with slight shifts in their peak maxima (Fig. 4). On proto-
nation, the split Soret band of compound 3 changed to single
intense band. These observations suggest that the electronic
properties of macrocycle in compound 3 alter on protonation.
Furthermore, the addition of triethylamine to the protonated
derivative resulted in the restoration of the absorption spectra
of compound 3 (p. S20, ESI†). All these observations indicated
that the compound 3 is stable, free pyrrolic nitrogen is avail-
able to get protonated and does not undergo decomplexation
under acidic conditions.
Fig. 5 Comparison of reduction waves of cyclic voltammograms along with
differential pulse voltammograms of (a) free base 21-selenaporphyrin 4 and
(b) compound 3 recorded in CH2Cl2 solvent using 0.1 M tetrabutylammonium
perchlorate (TBAP) as supporting electrolyte and saturated calomel electrode
The electrochemical properties of compound 3 along with
its free base 21-selenaporphyrin 4 were investigated by cyclic
voltammetry and differential pulse voltammetry using
(SCE) as reference electrode at a scan rate of 50 mV s−1
.
10802 | Dalton Trans., 2013, 42, 10798–10806
This journal is © The Royal Society of Chemistry 2013

View Article Online
Dalton Transactions
Paper
Crystallographic characterization
Table 2 Crystallographic data for compounds 1 and 3
The proof for the coordination geometry of hexa coordinated
rhenium(I) tricarbonyl complex 3 was provided further by
single-crystal X-ray crystallography. The compound 3 was crys-
tallized via slow diffusion of n-hexane into the dry dichloro-
methane–chloroform solvent mixture for over a period of one
week. The crystal structure of 3 is shown in Fig. 6 along with
the coordination sphere and the bond lengths involving the
Re(I) ion. The crystal data and data collection parameters are
summarized in Table 2 and relevant bond lengths and bond
angles data are presented in Table 3. To the best of our know-
ledge, compound 3 is the first metal complex of 21-selena-
porphyrin characterized by single crystal X-ray analysis. The
single crystal X-ray structure of 3 obtained here is compared
with our earlier reported16 analogous hexa coordinated
Re(CO)3 complex of 21-thiaporphyrin 1 (Chart 1). The com-
pound 3 was found to be crystallized in the monoclinic space
group C2/c unlike compound 1 which crystallized in triclinic
Parameters
Compound 3
Compound 1
Mol formula
C51H36N3O5Re1Se1· C47H28N3O3ReS
0.5(CHCl3)
1095.67
Monoclinic
C2/c
23.2507(7)
14.6302(4)
25.5440(7)
90.00
93.682(2)
90.00
8671.2(4)
8
3.788
1.678
4324
52.00
8510 [R(int) =
0.0299]
0.0449, 0.1029
0.0497, 0.1054
1.089
fw
900.98
Triclinic
ˉ
P1
Cryst sym
Space group
a (Å)
b (Å)
c (Å)
10.7305(3)
11.5248(4)
14.9008(4)
91.772(2)
90.039(2)
94.915(3)
1835.07(10)
2
3.416
1.631
892
3.31–26.37
7507 [R(int) =
0.0000]
0.0411, 0.0813
0.0518, 0.0839
1.026
α (°)
β (°)
γ (°)
V (Å3)
Z
µ (mm−1
)
Dcalcd (g cm−3
F (000)
)
2θ range (°)
Independent reflections
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
GOF
ˉ
space group P1. The compound 3 was crystallized as six co-
ordinated complex and Re(I) ion is coordinated to two out of
three pyrrole nitrogens and selenophene selenium leaving one
pyrrole nitrogen uncoordinated like compound 1. The other
three coordinating sites of Re(I) were capped by three carbonyl
groups in compound 3. In compound 3, being a 5d transition
metal ion and large in size, the Re(I) ion coordinates to the
21-selenaporphyrin by sitting on top of the porphyrin plane
and Re(I) ion was placed at 1.52 Å above from the plane
defined by three coordinating atoms of 21-selenaporphyrin
(N1N2Se1 plane). This displacement of Re(I) ion from the
Largest diff. peak/hole, (e Å−3
)
6.508, −2.083
3.995, −2.363
porphyrin plane in compound 3 was in the same range
(1.51 Å) observed for compound 1 from the plane of three co-
ordinating atoms (N1N2S1) of 21-thiaporphyrin.16 This type of
metal displacement from the mean porphyrin plane was com-
monly observed for five coordinated metal complexes of
21-thiaporphyrin5a,6,7 and the maximum displacement of
1.41 Å was observed for Hg(STPP)Cl.7
Unlike free base 21-selenaporphyrin15 4 in which the por-
phyrin ring was essentially planar, in compound 3, the por-
phyrin ring was distorted like 1. The two pyrrole nitrogens and
selenophene selenium bent upward to coordinate to Re(I) ion
in compound 3 as observed for compound 1 and other metal
derivatives of 21-thiaporphyrin.5a,6,16 Because of out-of-plane
bending of the selenophene moiety to coordinate with the
Re(I) ion in η1 fashion in compound 3, the Se–Cα distance
(∼1.93 Å) was longer and the Cα–Cβ distance (∼1.40 Å) was
slightly shorter in 3 compared to free base 4 (∼1.85 Å and
∼1.42 Å respectively). On coordination with Re(I) ion, the
Cα–Se–Cα bond angle was slightly decreased (∼2°) in 3 as com-
pared to free base 4. However, the S–Cα, Cα–Cβ and Cβ–Cβ bond
lengths remained practically unchanged on complexation of
Re(I) ion in compound 1 compared to free base 21-thiap-
orphyrin (SDTDPPH).6 In compound 3, the Re(I) ion was not
positioned directly over the centre of the macrocycle but was
set to one side such that the Re(I) ion was in the midst of three
coordinating atoms as noted for 1. However, the porphyrin
skeleton was relatively more distorted in compound 3 com-
pared to 1 as revealed from the data given in Table 3. In com-
pound 3, the two coordinated pyrrole nitrogens N1 and N2
were displaced by ∼0.36 Å and ∼0.20 Å respectively which are
in the same range as observed for compound 1 (∼0.40 Å and
∼0.24 Å for N1 and N2 respectively). But the deviation of
selenophene selenium Se1 (∼0.41 Å) and non-coordinated
Fig. 6 Single crystal X-ray structure of compound 3: (a) perspective view; the
solvent of crystallization (one CHCl3 molecule) is removed for clarity, (b) side
view of compound 3 showing the distorted macrocyclic ring (meso-aryl rings
and hydrogen atoms are omitted for clarity) and (c) simplified geometrical rep-
resentation of compound 3 showing the coordination features around the
central Re(I) ion.
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 10798–10806 | 10803

View Article Online
Paper
Dalton Transactions
and Re–Se distance is shorter than their sum of the van der
Waals radii (3.55 Å and 3.90 Å respectively) supporting Re
interaction with core N/Se in compound 3. The carbonyl
groups are aligned with the respective Re–N and Re–Se bonds
in compound 3. The Re–C bond lengths (av. 1.91 Å) in com-
pound 3 were in the same range observed for 1 (av. 1.90 Å).
The three C–O bond lengths were not equal in compound 3
but the average C–O bond length (av. 1.15 Å) was in the same
range as observed in compound 1 (av. 1.16 Å). Interestingly, in
compound 3, the Se–N2 bond length has remained almost
same compared to free base 4. It is noted that the N1–N3 dis-
tance was substantially longer in compound 3 compared to
free base 4 indicating the elongation of porphyrin moiety
along the N1–N3 axis on complexation with Re(I) ion. A similar
observation was also noted in case of compound 1. Thus, the
X-ray crystal structure analysis revealed that 21-selenoporphyrin
ring in compound 3 was more distorted compared to 21-thia-
porphyrin ring in compound 1 on complexation with Re(I) ion.
Table 3 Comparison of some selected crystal structure parameters for com-
pounds 1 and 3
Parameter
Compound 3
Compound 1
Re a
Δ
1.571
0.406
0.360
0.204
0.249
1.666
0.159
0.401
0.245
0.118
24
Se/S b
Δ
24
N1 c
Δ
24
N2 d
Δ
24
N3 e
Δ
24
ΔR3e f
1.421
0.357
1.448
0.226
ΔS3e/S g
ΔR4e h
ΔS4e/S i
ΔN4 1 j
ΔN4 2 k
ΔN4 3 l
1.486
0.121
0.102
0.086
0.104
1.491
0.071
0.063
0.055
0.063
Re–N1m
Re–N2m
Re–N3m
Re–S/Om
N1–N3m
Se/S–N2m
Re–COm
2.176(5)
2.217(5)
3.318(5)
2.591(2)
4.598(7)
3.351(5)
1.909(5)
1.916(6)
1.912(6)
1.164(7)
1.153(8)
1.134(8)
2.190(4)
2.255(4)
3.243(5)
2.553(2)
4.502(6)
3.457(5)
1.898(6)
1.907(6)
1.885(6)
1.166(8)
1.158(7)
1.158(7)
Conclusions
ReC–Om
Except for one report by Grażyński and co-workers on Ni(II)
complex of 21-selenaporphyrin, to the best of our knowledge,
the metal coordination chemistry of 21-selenaporphyrin
a Displacement (in Å) of rhenium from the 24-atom mean plane of the remains largely unexplored. We successfully synthesized
porphyrin core. b Displacement (in Å) of hetero-atom (X = Se/S) from
Re(CO)3 complex of 21-selenaporphyrin and characterized crys-
the 24-atom mean plane of the porphyrin core. c Displacement (in Å)
tallographically the first structure of metal complex of 21-selena-
of N1 from the 24-atom mean plane of the porphyrin core.
d Displacement (in Å) of N2 from the 24-atom mean plane of the porphyrin. The X-ray structure revealed that the compound is
porphyrin core. e Displacement (in Å) of N3 from the 24-atom mean
hexa coordinated and Re(I) ion is bound to two of three inner
plane of the porphyrin core. f Displacement (in Å) of rhenium from the
nitrogens and selenium of 21-selenaporphyrin and the other
mean plane of three coordinated atoms of porphyrin core.
g Displacement (in Å) of hetero-atom (X = Se/S) from the mean plane of three coordinating sites are occupied by three carbonyl groups.
three nitrogen atoms of porphyrin core. h Displacement (in Å) of
The compound is highly stable in solution and solid state and
rhenium from the mean plane of the four porphyrin core atoms.
i Displacement (in Å) of hetero-atom (X = Se/S) from the mean plane of
does not undergo demetallation under acidic conditions. The
the four porphyrin core atoms. j Displacement (in Å) of N1 from the compound shows fluxional behaviour in solution and exhibits
mean plane of the four porphyrin core atoms. k Displacement (in Å) of
interesting optical and electrochemical properties. Currently,
we are exploring the metal coordination chemistry of 21-sele-
naporphyrins with other 4d and 5d metal ions.
N2 from the mean plane of the four core atoms. l Displacement (in Å)
of N3 from the mean plane of the four porphyrin core atoms. m Value
in Å.
pyrrole nitrogen N3 (∼0.25 Å) from the 24 atom plane was
more pronounced in compound 3 compared to the deviation
of thiophene sulphur S1 (∼0.16 Å) and non-coordinating
pyrrole nitrogen N3 (∼0.12 Å) in compound 1 indicating the
more distorted structure of 3. In compound 3, the distance
between the two coordinating pyrrole nitrogens and Re(I) (Re–
N1 = ∼2.18 Å; Re–N2 = ∼2.22 Å) was much shorter than the dis-
tance between Re(I) ion with the non-coordinated pyrrole nitro-
gen (Re–N3 = 3.32 Å). This observation is in agreement with
Re–N distances observed for compound 1 (Re–N1 = ∼2.19 Å;
Re–N2 (∼2.25 Å) Re–N3 (∼3.24 Å). Furthermore, the Re–Se dis-
tance in compound 3 (Re–Se = 2.59 Å) was in the same range
of Re–S (2.55 Å) bond length in 1 but much shorter than the
reported Hg–S distance in Hg(STPP)Cl7 (Hg–S = ∼2.8 Å) and
longer than the M–S distances observed for various metal com-
plexes of 21-thiaporphyrin5,6,9 (M–S = 2.0 to 2.4 Å). The Re–N
Experimental section
Chemical
All general chemicals and solvents were procured from S.D.
Fine Chemicals, India. Column chromatography was per-
formed using silica gel and basic alumina obtained from Sisco
Research Laboratories, India. Tetrabutylammonium perchlo-
rate was purchased from Fluka and used without further puri-
fications. All NMR solvents were used as received. Solvents like
dichloromethane, tetrahydrofuran (THF) and n-hexane were
purified and distilled by standard procedures.
Instrumentation
The 1H, 13C and 77Se NMR (δ in ppm) spectra were recorded by
using a Bruker AVANCE III 400 MHz spectrometer. Tetra-
methylsilane (TMS) was used as an internal reference for
10804 | Dalton Trans., 2013, 42, 10798–10806
This journal is © The Royal Society of Chemistry 2013

View Article Online
Dalton Transactions
Paper
1
recording H NMR spectra (residual proton; δ = 7.26 ppm) in metalated porphyrin on TLC, the solvent was removed comple-
CDCl3. The HR-MS spectra were recorded with a Q-Tof micro- tely under reduced pressure and afforded crude compound.
mass spectrometer. IR spectra were recorded with Perkin The crude solid was subjected to a silica gel column chromato-
Elmer Spectrum One FT-IR spectrometer. Absorption spectra graphy and the fast moving yellowish-deep brown colour band
were obtained with Varian cary eclipse. Cyclic voltam- of desired compound was collected by using CH2Cl2–pet-
metry (CV) and differential pulse voltammetry (DPV) studies roleum ether (3 : 7) solvent mixture as eluent. The solvent was
were carried out with a BAS electrochemical system by utilizing removed on rotary evaporator and afforded a dark shiny solid.
the three-electrode configuration consisting of glassy carbon The compound was recrystallized from CH2Cl2–n-hexane
(working electrode), platinum wire (auxiliary electrode), and mixture and afforded pure compound 3 as purple solid in 94%
saturated calomel (reference electrode) electrodes. The experi- yield (127 mg, 0.122 mmol). 1H NMR (400 MHz, CDCl3): δ =
ments were done in dry dichloromethane with 0.1 M tetra- 10.16 (s, 2H, β-selenophene H), 8.38–8.44 (m, 6H, β-pyrrole H),
butylammonium perchlorate as the supporting electrolyte.
8.14 (brs, 8H, Ar), 7.65 (d, J (H,H) = 7.96 Hz, 4H, Ar), 7.28 (d,
J (H,H) = 8.64 Hz, 4H, Ar), 4.08 (s, 6H, –OCH3), 2.69 (s, 6H,
–CH3) ppm; 13C NMR (400 MHz, CDCl3): 21.70, 55.77, 112.38,
X-ray crystallography
X-ray intensity data measurements of compound 3 were 128.52, 129.20, 133.51, 133.97, 136.84, 137.06, 138.48, 153.17,
carried out on a Bruker SMART APEX II CCD diffractometer 160.02, 160.82, 189.02, 189.18 ppm. IR (KBr, cm−1): 2014,
with graphite-monochromatized (MoKα = 0.71073 Å) radiation 1902. UV-vis (λmax nm (log ε), CH2Cl2): 431 (4.88), 484 (br,
at 297(2) K. The X-ray generator was operated at 50 kV and 4.65), 575 (4.12), 655 (3.65), 717 (4.67). HR-MS: m/z: 1038.1476
30 mA. Data were collected with ω scan width of 0.5° at [M + 1]+. Anal. Calcd for C51H36N3O5ReSe: C, 59.07; H, 3.47;
different settings of φ and 2θ with a frame time of 5 s keeping N, 4.05. Found: C, 59.12; H, 3.44; N, 4.06.
the sample-to-detector distance fixed at 50 mm. The X-ray data
collection was monitored by APEX2 program (Bruker, 2006).18
The data was corrected for Lorentzian, polarization and
absorption effects using SAINT and SADABS programs (Bruker,
Acknowledgements
2006). SHELX-97 was used for structure solution and full MR thanks the Council of scientific and Industrial Research,
matrix least-squares refinement on F2.19 All the H-atoms were Govt. of India for financial support and AG thanks CSIR, India
placed in geometrically idealized position and constrained to for fellowship.
ride on their parent atoms.
We have refined the crystal data of compound 3. In the
structure both selenophene and pyrrole rings displayed statisti-
cal disorder over two positions with occupancies 0.95 and 0.05
References
respectively and vice versa. The included chloroform molecule
also exhibited orientational disorder across the two fold axis
passing from Cl1 atom and atoms Cl2, C52 and H52 are stat-
istically distributed along the two-fold axis. In case of com-
pound 1, we observed the similar type of disorder of
thiophene ring such that two adjacent rings had a contri-
bution from both N and S. CCDC 923294 (3) contains the sup-
plementary crystallographic data for this paper.†
1 (a) L. Latos-Grażyński, Core modified heteroanalogues of
porphyrins and metalloporphyrins, in The Porphyrin Hand-
book, ed. K. M. Kadish, K. M. Smith and R. Guilard,
Academic Press, New York, 2000, vol. 2, p. 361; (b) I. Gupta
and M. Ravikanth, Coord. Chem. Rev., 2006, 250, 468.
2 J. Skonieczny, L. Latos-Grażyński and L. Szterenberg,
Chem.–Eur. J., 2008, 14, 4861.
3 P. J. Chmielewski and L. Latos-Grażyński, Coord. Chem.
Rev., 2005, 249, 2510.
General synthesis
4 Y. Matano and H. Imahori, Acc. Chem. Res., 2009, 42, 1193.
5 (a) L. Latos-Grażyński, J. Lisowski, M. M. Olmstead and
A. L. Balch, Inorg. Chem., 1989, 28, 1183; (b) L. Latos-
Grażyński, J. Lisowski, M. M. Olmstead and A. L. Balch,
J. Am. Chem. Soc., 1987, 109, 4428; (c) J. Lisowski,
M. Grzeszczuk and L. Latos-Grażyński, Inorg. Chim. Acta,
1989, 161, 153; (d) J. P. Chmielewski, M. Grzeszczuk,
L. Latos-Grażyński and J. Lisowski, Inorg. Chem., 1989, 28,
3546; (e) L. Latos-Grażyński, J. Lisowski, J. P. Chmielewski,
M. Grzeszczuk, M. M. Olmstead and A. L. Balch, Inorg.
Chem., 1994, 33, 192; (f) L. Latos-Grażyński, J. Lisowski,
M. M. Olmstead and A. L. Balch, Inorg. Chem., 1989, 28,
3328; (g) L. Latos-Grażyński, M. M. Olmstead and
A. L. Balch, Inorg. Chem., 1989, 28, 4065.
Free base 5,20-bis(p-tolyl)-10,15-bis(p-methoxyphenyl)-21-sele-
naporphyrin
method.20
4 was synthesized by following literature
Synthesis of compound 3
sample of 5,20-bis(p-tolyl)-10,15-bis(p-methoxyphenyl)-
A
21-selenaporphyrin (100, mg, 0.130 mmol) was dissolved in
dry 1,2-dichlorobenzene (30 mL) and Re(CO)5Cl (70 mg,
0.193 mmol) was added and the reaction mixture was heated
to reflux for 7 h. The deep orange colour of the solution
turned into dark brown colour as the reaction progressed. The
reaction progress was followed by TLC analysis and absorption
spectroscopy. After completion of reaction as judged by the
disappearance of the spot corresponding to free base por-
phyrin and appearance of the new spot corresponding to
6 A. Gebauer, J. A. R. Schmidt and J. Arnold, Inorg. Chem.,
2000, 39, 3424.
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 10798–10806 | 10805

View Article Online
Paper
Dalton Transactions
7 J.-Y. Tung, B.-C. Liau, S. Elango, J.-H. Chen, H.-Y. Hsieh, 14 M. Pawlicki and L. Latos-Grażyński, Inorg. Chem., 2002, 41,
F.-L. Liao, S.-L. Wang and L.-P. Hwang, Inorg. Chem.
Commun., 2002, 5, 150.
8 R. P. Pandian and T. K. Chandrashekar, Inorg. Chem., 1994,
33, 3317.
5866.
15 L. Latos-Grażyński, E. Pacholska, P. J. Chmielewski,
M. M. Olmstead and A. L. Balch, Inorg. Chem., 1996, 35,
566.
9 C.-H. Chuang, C.-K. Ou, S.-T. Liu, A. Kumar, W.-M. Ching, 16 A. Ghosh and M. Ravikanth, Inorg. Chem., 2012, 51, 6700.
P.-C. Chiang, M. A. C. dela Rosa and C.-H. Hung, Inorg. 17 M. Tsutsui, C. P. Hrung, D. Ostfeld, T. S. Srivastava,
Chem., 2011, 50, 11947.
D. L. Cullen and E. F. Meyer Jr., J. Am. Chem. Soc., 1975, 97,
3952 and reference cited therein.
18 Bruker. APEX2, SAINT and SADABS. Bruker AXS Inc.,
Madison, Wisconsin, USA, 2006.
19 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystal-
logr., 2008, 64, 112.
20 (a) M. Abe, D. G. Hilmey, C. E. Stilts, D. K. Sukumaran and
M. R. Detty, Organometallics, 2002, 21, 2986; (b) R. Pandian
and T. K. Chandrashekar, J. Chem. Soc., Dalton Trans.,
1993, 119.
10 P. J. Chmielewski, L. Latos-Grażyński, M. M. Olmstead and
A. L. Balch, Chem.–Eur. J., 1997, 3, 268.
11 M. J. Broadhurst, R. Grigg and A. W. Johnson, J. Chem. Soc.
C, 1971, 3681.
12 R. Ambre, C.-Y. Yu, S. B. Mane, C.-F. Yao and C.-H. Hung,
Tetrahedron, 2011, 67, 4680.
13 B.
Sridevi,
S.
J.
Narayanan,
A.
Srinivasan,
T. K. Chandrashekar and J. Subramanian, J. Chem. Soc.,
Dalton Trans., 1998, 1979.
10806 | Dalton Trans., 2013, 42, 10798–10806
This journal is © The Royal Society of Chemistry 2013