Ruthenium(II) complexes of meso-tetrakis(4-cyanophenyl)porphyrin

Article abstract of DOI:10.1016/j.inoche.2013.01.010

A novel synthesis is presented for the meso-tetrakis(4-cyanophenyl) porphyrin complex Ru(T-pCN-PP)(CO)(H₂O), the first Ru complex with this long-known porphyrin; compared to standard methods reported for other porphyrin analogues via Ru₃(CO)₁₂, extra steps involving addition of pyridine (Py) and its subsequent removal as [HPy⁺]Cl ^- are required. The Py breaks down coordination polymers (as yet uncharacterized) formed via the peripheral p-cyanophenyl moiety; these materials may offer potential as porphyrin-based supramolecular solids. Removal of the CO by photolysis in MeCN solution generates Ru(T-pCN-PP)(MeCN)₂, but attempts to make the bis(thiol) analogues from this precursor were unsuccessful, again due to formation of polymeric species.

Full text of DOI:10.1016/j.inoche.2013.01.010

Inorganic Chemistry Communications 30 (2013) 49–52
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Ruthenium(II) complexes of meso-tetrakis(4-cyanophenyl)porphyrin
b,
Júlio S. Rebouças a, , Brian R. James
⁎
⁎
a
Departamento de Química, CCEN, Universidade Federal da Paraíba, João Pessoa, PB, 58.051-900, Brazil
Department of Chemistry, University of British Columbia, Vancouver, BC, Canada V6T 1Z1
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel synthesis is presented for the meso-tetrakis(4-cyanophenyl)porphyrin complex Ru(T-pCN-PP)(CO)(H2O),
the first Ru complex with this long-known porphyrin; compared to standard methods reported for other porphyrin
analogues via Ru3(CO)12, extra steps involving addition of pyridine (Py) and its subsequent removal as [HPy+]Cl−
are required. The Py breaks down coordination polymers (as yet uncharacterized) formed via the peripheral
p-cyanophenyl moiety; these materials may offer potential as porphyrin-based supramolecular solids. Removal of
the CO by photolysis in MeCN solution generates Ru(T-pCN-PP)(MeCN)2, but attempts to make the bis(thiol) ana-
logues from this precursor were unsuccessful, again due to formation of polymeric species.
Received 17 October 2012
Accepted 14 January 2013
Available online 1 February 2013
Keywords:
Ruthenium
Porphyrin complexes
Cyano-porphyrins
Acetonitrile complexes
© 2013 Elsevier B.V. All rights reserved.
Introduction. We reported recently on just over one hundred
Ru(porp)(RSH)2 species formed in situ from the bis(acetonitrile)
species, where porp is the anion of the parent porphyrin H2(porp),
and R is an alkyl or aryl group [1,2], the key purpose being to measure
the 1H NMR resonances of the SH proton. The upfield shifts on coor-
dination of the thiol reflect changes in porphyrin ring current, and
the measured shifts were analyzed in terms of an empirical model
that depicted quantitatively the non-bonding, electronic and steric
interactions between the thiol ligands and the porphyrin plane. Ste-
ric factors were found to dominate the upfield shifts within variation
of the thiol, whereas electronic factors were most important within
the porphyrins used. More generally, such interactions are typically
involved in small-molecule recognition within metalloporphyrin
systems, and the findings offer an insight into this complex feature
of many metalloporphyrin-containing protein systems [1]. One se-
ries of porphyrins studied was meso-tetraphenylporphyrin (H2TPP)
and its p-substituted-tetraphenyl analogues (H2T-pX-PP, where X is
OMe, Me, F, Cl, CO2Me, and CF3), the electronic nature of the X sub-
stituent, as listed, going from electron-donor to increasingly
electron-withdrawing properties; more quantitatively, the Hammett
σ factor increases within this series from −0.28 to+0.53 [3]. In an
attempt to extend the electronic properties within this series, the
X=CN species with a greater electron-withdrawing ability (σ=
There are no previous reports on Ru/H2T-pCN-PP chemistry, ex-
cept for an oblique, non-detailed mention of Ru(T-pCN-PP)(MeCN)2
in our recent paper [1]. This current paper describes the lengthy,
non-routine synthesis of the required precursor meso-tetrakis(4-
cyanophenyl)porphyrin complex Ru(T-pCN-PP)(CO)(H2O), the syn-
thesis of Ru(T-pCN-PP)(MeCN)2, and our unsuccessful efforts to
make the corresponding bis(thiol) complexes likely due to forma-
tion of supramolecular species.
Experimental section. Reactions and manipulations were carried
out under anaerobic conditions. Ar (Praxair, 99.996%) was passed
through an active Ridox column (Fisher Scientific), and N2 (Praxair,
99.995%) was dried with Drierite (W.A. Hammond Co.). MeCN (Fisher
Scientific, HPLC grade) was stored over activated molecular sieves
(4 Å); C6H6 (Fisher Scientific) was treated with Na/benzoquinone,
distilled under N2, and used immediately. Other solvents were re-
agent grade and were deoxygenated by purging with Ar. Deuterated
NMR solvents were obtained from Cambridge Isotope Laboratories,
Inc. Ru3(CO)12 [5] and chlorin-free H2T-pCN-PP [4,6] were made by
reported methods.
1H-NMR spectra (s=singlet, m=multiplet) were measured at
room temperature (r.t., ~295 K) on a Bruker AV300 spectrometer, and
referenced to residual solvent protons of TMS-free C6D6 (δ 7.15). IR
spectra in KBr pellets were recorded on an ATI Mattson Genesis Series
FT-IR spectrometer. Electrospray ionization mass spectra in the positive
ion mode (ESI/MS+) were recorded on a Bruker Esquire-LC ion-trap in-
strument with 0.1% formic acid in MeOH being infused into the
ion-source by a syringe pump at a flow rate of 200 μL/min. UV–vis spec-
tra were carried out on a Hewlett Packard 8452 diode array spectropho-
tometer. Elemental analyses were performed using a Carlo Erba EA1108
elemental analyzer.
0.71 [3]) was an attractive candidate.
A further interest in
using H2T-pCN-PP was the possibility of synthesizing coordination
polymers and networked structures of porphyrin-based supramolecu-
lar solids, which have been formed via the N-atom of the linear –CN
function within CuII and ZnII systems with this porphyrin [4].
⁎
Corresponding authors.
Synthesis of Ru(T-pCN-PP)(CO)(H2O) (1). To a refluxing solution
of H2T-pCN-PP (103 mg, 0.14 mmol) in o-dichlorobenzene (15 mL),
E-mail addresses: jsreboucas@quimica.ufpb.br (J.S. Rebouças), brj@chem.ubc.ca
(B.R. James).
1387-7003/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.inoche.2013.01.010

50
J.S. Rebouças, B.R. James / Inorganic Chemistry Communications 30 (2013) 49–52
Ru3(CO)12 (138 mg, 0.22 mmol) was added portion-wise (~5–10 mg)
over 2.5 h. Pyridine (4 mL) was then added, and the refluxing contin-
ued for a further 20 min. The solvent was then removed, the residue
suspended in CH2Cl2, and the resulting suspension was transferred to
a neutral Al2O3 column containing CH2Cl2. The eluent was changed to
a 4:1 CH2Cl2/MeCN mixture and the running band was collected. This
fraction was taken to dryness and dissolved in CH2Cl2; the UV–vis spec-
trum of this solution showed a band at 608 nm, due to a chlorin con-
tamination [7]. The CH2Cl2 solution was washed with twelve 10 mL
aliquots of 6 M HCl, allowing 5–10 min of phase contact before the
aqueous phase was separated. These aqueous phases were analyzed
(C6D6): δ 8.58 (s, 8H, β-pyrrole), 8.08 (AA′BB′, 8H, o-C6H4CN),
7.26 (AA′BB′, 8H, m-C6H4CN), −2.09 (s, 6H, CH3CN). IR (see text).
Reaction of 2 with thiols. To the C6D6 solution of Ru(T-pCN-
PP)(MeCN)2, about a 10-fold excess of RSH was added at r.t., exact-
ly as described previously [2] for the gaseous or liquid RSH (R=Me,
i
t
Et, nPr, Pr, nBu, Bu, nHex, Bn, Ph, and p-MeOC6H4); immediately
precipitated was a reddish brown solid that was collected, washed
with C6H6 and dried in vacuo. Insolubility has thwarted their
characterization.
Results and discussion. The syntheses and reactivity of the
Ru(T-pCN-PP) complexes are summarized in Scheme 1 shown
below. Although H2T-pCN-PP has been known since the 1960s [8],
and many Ru complexes containing various T-pX-PPs porphyrins
for pyridine hydrochloride ([HPy+]Cl−
) by UV–vis spectroscopy
(λmax=258 nm); non-detection implied the absence of Py in the
CH2Cl2 solution, which was then washed with water until the pH of
the aqueous phase was neutral. The organic phase was separated,
dried with Na2SO4, filtered, and taken to dryness. To remove the chlorin,
the residue was dissolved in a mixture of toluene (15 mL), CH2Cl2
(20 mL), and MeCN (5 mL); 2,3-dichloro-5,6-dicyano-benzoquinone
(DDQ, 15.8 mg) was then added and the solution was refluxed for
30 min. At r.t., 50 mL of an aqueous solution containing sodium
dithionite (~100 mg) and NaOH (~500 mg) were then added, and
the organic phase was separated, washed with water, dried with
Na2SO4, filtered, and taken to dryness. The resulting red solid was
dried overnight in an Abderhalden pistol (H2O), and then exposed to
the atmosphere for ~5 h to give 1. Yield: 70.2 mg (57%). Anal. Calcd for
Ru(T-pCN-PP)(CO)(H2O), C49H26N8O2Ru: C, 68.45; H, 3.05; N, 13.03.
Found: C, 68.7; H, 3.2; N, 13.4. 1H NMR (d6-DMSO): δ 8.55 (s, 8H,
β-pyrrole), 8.41–8.38 (m, 4 H, o- or o′-C6H4CN), 8.26–8.21 (m, 12H,
o′- (or o-), m-, and m′-C6H4CN). UV–vis (in DMF): 414 nm (log
ε/L mol–1 cm–1 =5.39), 532 (4.25), 564 (3.55). IR (cm–1): 3431
(νOH), 2227 (νCN) 1953 (νCO). ESI-MS: cluster centered at m/z
814 (100 %, [Ru(T-pCN-PP)(CO)−CO]+).
Synthesis of Ru(T-pCN-PP)(MeCN)2 (2). In a Wheaton vial, capped
with a rubber septum, complex 1 (5.2 mg, 6.0×10−3 mmol) was
dissolved in MeCN (18 mL), and the headspace and septum were then
completely covered with Al foil. An Ar inlet (stainless steel needle,
with the tip placed ~0.5 cm from the bottom of the vial) and outlet (dis-
posable needle, placed in the headspace) were attached, and the Ar flow
was adjusted to give a minimal flow of small bubbles through the so-
lution for ~15 min. The solution was then photolysed for 4 h under
Ar using a 450-Watt Hanovia Hg lamp (Fisher Scientific) that was
water-cooled using a glass jacket. Most of the MeCN evaporates dur-
ing the photolysis, and the remainder was pumped off at r.t. to
yield 2 quantitatively; the septum-sealed photolysis vial was
stored under Ar in a glove-box, where 2 was transferred to a
J-Young NMR tube to which C6D6 (~3 mL) was added. 1H NMR
i
(e.g. X=OMe, Me, Pr, F, Cl, Br, and CF3) have been described since
the 1970s [9], no reports have appeared on the Ru-metallation of
H2T-pCN-PP. This likely results from the difficulties in using a
standard synthesis of Ru(porp)(CO) from Ru3(CO)12 in various
solvents [7a,9e,10]. In decalin, often used for such a synthesis
[7a,9e,10a,11], we found no production of a Ru–porphyrin; the
H2T-pCN-PP remained insoluble in this solvent even at refluxing
conditions and the isolated purple solid was just free-base por-
phyrin. To overcome this solubility problem, the reaction was then car-
ried out in refluxing o-dichlorobenzene (also used previously for
metallation [12]), which dissolves both the carbonyl and free-base.
Upon addition of the Ru3(CO)12, the color gradually changed from pur-
ple to reddish brown concomitantly with the formation of a dark pre-
cipitate, and UV–vis analysis of the filtrate indicated almost complete
conversion of the free-base porphyrin. The precipitate was insolu-
ble in common solvents, such as CH2Cl2, benzene, and DMF, in di-
rect contrast to other neutral Ru(T-pX-PP)(CO) complexes [9],
and implies that the product might be polymeric. This product
was not investigated further, but likely involves coordination of
peripheral p-CN groups to some Ru-carbonyl and/or Ru(T-pCN-PP)
moiety − a conclusion based on the facts that (a) benzonitriles are
good ligands for Ru–porphyrins [13], (b) Cu- and Zn-H2T-pCN-PP
complexes are excellent synthons for formation of multiporphyrin
architectures [4], and (c) the cyano moiety of CoII–porphyrin
complexes containing 4-cyanophenyl groups readily replaces the
aqua ligand of [Ru(NH3)5(H2O)]2+ [14]. Reports [15] that self-
coordinating metalloporphyrin dimers and polymers (including
Ru species [15b]), formed within pyridine-substituted porphyrins,
can be disassembled into monomers by treatment with exogenous
bases prompted us to treat the metallated mixture with excess Py
(see Experimental section); indeed, the supposed polymeric solid
then dissolved completely within 5 min of reflux to yield a red so-
lution. Chromatographic purification of this solution yielded a solid
O
C
O
R
R
R
C
HCl/H2O
CH2Cl2
1. Ru3(CO)12
2. Py
NH
N
N
HN
N
N
N
N
N
N
R
R
R
R
R
R
Ru
N
Ru
N
N
- [HPy]+Cl-
o-C6H4Cl2, Δ
R
OH
R
R
2
hν
MeCN
(1)
Me
C
R =
CN
- CO
- H2O
R
N
R1SH
C6H6
N
N
N
N
'polymer'
R
R
Ru
R1 = Me, Et, nPr, iPr, nBu, tBu,
nHex, Bn, Ph, p-MeOC6H4
N
C
R
Me
(2)
Scheme 1. Syntheses and reactivity of the Ru(T-pCN-PP) complexes.

J.S. Rebouças, B.R. James / Inorganic Chemistry Communications 30 (2013) 49–52
51
material whose UV–vis spectrum in CH2Cl2 showed major bands
(at 412 and 530 nm) typical of a Ru(porp)(CO)-containing species
[9b], but also a 608 nm band that was attributed to a “Ru chlorin”
impurity, often formed in syntheses of such a complex [7] — the
metallation was carried out with a chlorin-free porphyrin, and so
the chlorin is formed in situ during the metallation. The Py is al-
most certainly coordinated as the sixth ligand in any Ru(porp)(CO)
or Ru(chlorin)(CO) species present, and was considered disadvan-
tageous for the subsequent synthesis of Ru(porp)(MeCN)2, the re-
quired precursor for reaction with thiols (see Introduction). Thus,
the Py was subsequently removed by a solvent extraction proce-
dure involving treatment of the CH2Cl2 solutions of the carbonyl
species with aliquots of aqueous HCl; the extraction is convenient-
ly monitored by UV–vis spectroscopy, which also indicates com-
pletion when [HPy+]Cl- is no longer detected in the aqueous
phase. The organic phase was assumed to contain the aqua com-
plex of Ru(T-pCN-PP)(CO) and a corresponding Ru(chlorin)(CO)
complex, but these species were not separated at this stage. The
Ru-chlorin was first converted to its parent Ru(porp)(CO) species
via the oxidative, DDQ-based procedure, but using a toluene-
CH2Cl2-MeCN mixture in order to dissolve completely the porphy-
rin material, instead of the usual neat toluene medium [7b,16].
After removal of the chlorin, as indicated by the disappearance of
the 608 nm band, the Ru porphyrin complex was purified by reduc-
ing the excess DDQ with dithionite and extracting the resulting hy-
droquinone (the co-product of the chlorin oxidation) with aqueous
alkaline solution, followed by washing of the organic phase with
water [7b].
of two axial MeCN ligands. An IR spectrum of a sample with limited
exposure to air showed no νCO band, proving that the carbonyl li-
gand of 1 has been fully photo-dissociated; in the absence of the
Al foil, some of the septum was degraded to a yellow product that
was extracted by the solvent during the photolysis and led to con-
tamination of 2.
Room temperature treatment of a C6D6 solution of Ru(T-
pCN-PP)(MeCN)2 with excess of an aliphatic or aromatic thiol
yielded solids that were completely insoluble in common solvents,
including MeCN. The reactions proceeded with loss of 1H signals of
the bis-nitrile reactant and appearance of the 6-proton signal for
free MeCN (δ 0.59). Elemental analyses of the products were exten-
sively variable and of no value for characterization. They are likely
to be self-assembled polymers involving coordination of the
p-cyanophenyl arms of the porphyrin; several types of lattice
structures have been reported within ZnII- and CuII-(T-pCN-PP)
systems, some incorporating benzene as a guest solvent [4]. A
thiol does not appear to be a sufficiently strong binding ligand to
prevent formation of the polymeric structures, which contrasts
with the behavior of Py in disassembling polymer formation during
synthesis of Ru(T-pCN-PP)(CO)(H2O) (see above). Synthesis of
Ru(T-pCN-PP)(MeCN)2 by the photolysis procedure implies that
MeCN can compete with the peripheral p-cyanophenyl as an axial li-
gand. Thus, the reactivity trend at a RuII-porp centre appears to be
Py>MeCN>porp-C6H4-CN>RSH, although a thiol is likely occluded/
bonded somewhere in the polymeric, lattice structure. Studies continue
on the characterization of the Ru(T-pCN-PP)-based coordination poly-
mers and their potential as porphyrin-based supramolecular solids,
which are of general interest because of their optical and/or redox
properties [4,21].
The isolated Ru(T-pCN-PP)(CO)(H2O) complex (1) was charac-
terized by elemental analysis, UV–vis, IR and 1H NMR spectroscopies
and mass spectrometry, the data resembling closely those of other
Ru(T-pX-PP)(CO)(H2O) species (X=H and CO2Me) [9e]. Briefly,
Acknowledgements
−1
metallation is marked by the loss of the 3314 cm
ν
stretch in
NH
the IR and the 1H NMR resonance of the NH proton (δ –2.89, CDCl3)
of the free-base H2T-pCN-PP; the reduced number of bands in the
visible region of the UV–vis spectrum compared to that of the
free-base is also consistent with metal insertion [17]; the presence
of the H2O, CN and CO moieties is evident in the IR spectra (bands
at 3431, 2227 and 1953 cm−1, respectively); the complex 1H NMR
pattern for the phenyl protons, with assignments aided by data for
H2T-pCN-PP [18], reveals the lack of axial symmetry; the isotopic dis-
tribution pattern for the peak cluster seen in the MS spectrum agrees
with that calculated for [Ru(T-pCN-PP)]+; and the elemental analy-
sis is consistent with the formulation. The use of the Abderhalden
pistol (H2O) and exposure to the atmosphere for a few hours guaran-
tees the presence of the aqua ligand [9].
We thank the Natural Sciences and Engineering Research Council of
Canada for funding, and Colonial Metals Inc. for the loan of RuCl3∙xH2O.
J.S.R. acknowledges Fundação CAPES (The Ministry of Education of
Brazil) and The University of British Columbia for graduate scholarships.
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