Synthetic and mechanistic aspects of a new method for ruthenium-metalation of porphyrins and Schiff-bases

Article abstract of DOI:10.1021/ic800616q

A new method is presented for metalation of a wide range of free-base, neutral, cationic, and anionic porphyrins in refluxing dimethylformamide (DMF) using an easily prepared [Ru(DMF)₆](OTf)₃ complex, and comparisons are made with the more familiar metalation procedure using Ru ₃(CO)₁₂. Both procedures generate Ru^II(porp) (CO)L complexes (L = solvent); use of the Ru^III-triflate precursor gives yields comparable to, or greater than, those obtained with the carbonyl, and generates no Ru-chlorin impurities. Mechanistic studies on the meso-tetraphenylporphyrin system reveal that the DMF furnishes the CO, which in the presence of essential water reduces the metal, and metalation likely occurs via a Ru^II-CO species. Corresponding metalation of tetradentate Schiff-bases gives trans-[Ru^III(Schiff- base)(DMF)₂]OTf complexes in yields of ～50%, a limitation being the accompanying hydrolysis of the Schiff-base through the presence of trace water.

Full text of DOI:10.1021/ic800616q

Inorg. Chem. 2008, 47, 7894-7907
Synthetic and Mechanistic Aspects of a New Method for
Ruthenium-Metalation of Porphyrins and Schiff-Bases
Ju´lio S. Rebouc¸as,† Elizabeth L. S. Cheu,† Caroline J. Ware,† Brian R. James,*,† and Kirsten A. Skov‡
Department of Chemistry, UniVersity of British Columbia, VancouVer, BC V6T 1Z1, Canada, and
Department of AdVanced Therapeutics, British Columbia Cancer Research Centre, VancouVer,
BC V5Z 1L3, Canada
Received April 5, 2008
A new method is presented for metalation of a wide range of free-base, neutral, cationic, and anionic porphyrins
in refluxing dimethylformamide (DMF) using an easily prepared [Ru(DMF)6](OTf)3 complex, and comparisons are
made with the more familiar metalation procedure using Ru3(CO)12. Both procedures generate RuII(porp)(CO)L
complexes (L ) solvent); use of the RuIII-triflate precursor gives yields comparable to, or greater than, those
obtained with the carbonyl, and generates no Ru-chlorin impurities. Mechanistic studies on the meso-
tetraphenylporphyrin system reveal that the DMF furnishes the CO, which in the presence of essential water reduces
the metal, and metalation likely occurs via a RuII-CO species. Corresponding metalation of tetradentate Schiff-
bases gives trans-[RuIII(Schiff- base)(DMF)2]OTf complexes in yields of ∼50%, a limitation being the accompanying
hydrolysis of the Schiff-base through the presence of trace water.
Introduction
neous and supported catalysts (especially for oxidations),2,3
synthons within coordination and organometallic chemis-
Ruthenium porphyrins continue to reveal rich and diverse
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C.; Severin, K. Chem.sEur. J. 2005, 11, 5055. (g) Sun, L.; Du, C-P.;
Qin, J.; You, J-S.; Yang, M.; Yu, X-Q. J. Mol. Catal. 2005, 234, 29.
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* To whom correspondence should be addressed. E-mail: brj@
chem.ubc.ca. Phone: +1-604-822-6645. Fax: +1-604-822-4827.
†
University of British Columbia.
British Columbia Cancer Research Centre.
‡
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7894 Inorganic Chemistry, Vol. 47, No. 17, 2008
10.1021/ic800616q CCC: $40.75  2008 American Chemical Society
Published on Web 07/30/2008

Ruthenium-Metalation of Porphyrins and Schiff-Bases
try,4–7 building blocks for supra- or supermolecular as-
semblies,7,8 materials,9 and sensors,4 and in medicinal
chemistry.10 Compared to Fe-porphyrins, the range of Ru-
porphyrin systems studied is limited, the field being domi-
nated by “Ru(OEP)”, “Ru(TPP)”, “Ru(TMP)” and “Ru(T-
o,o′Cl2-PP)” derivatives (Scheme 1). In part, this likely
results from the limited synthetic methods for insertion of
Ru into the macrocycle, especially on comparison with the
many metalation methods developed for first-row transition
metals.5,11
The first Ru-porphyrin was reported in 1969, metalation being
accomplished by refluxing an ethanol solution of RuCl312 under
a CO atmosphere, although the RuIII(porp)(CO)Cl formulation
of the product was incorrect;13 the product was, in fact, a
solvated RuII(porp)(CO) species, as shown shortly afterward
when Ru3(CO)12 and [Ru(CO)3Cl2]2 were used as precursors.14
Subsequent Ru-metalations have generally been minor varia-
tions of these procedures, including the use of formaldehyde
as a source of CO.15
The popular choice of Ru3(CO)12 for metalation of porphyrins
results from the air-stable carbonyl being available commercially
but, because of its price, the dodecacarbonyl is commonly
prepared in-house via reduction of precursors such as RuCl3,
RuO2, or [Ru3(O)(OAc)6(H2O)3]OAc using CO at 1 atm or high
pressure.16 In these methods, the toxicity of CO17c and possible
formation of highly toxic phosgene16d,17a raise safety concerns;
indeed, two fatal accidents have occurred via open-air, CO
poisoning.17b Within the Ru3(CO)12 systems, general yield
comparisons are difficult. For example, metalation yields for
Ru(TMP)(CO)18 and Ru(T-o,o′Cl2-PP)(CO)6c are higher when
the carbonyl is added portion-wise (81-84%) versus a single
addition (25-44%). Of note, the Ru/porphyrin stoichiometry
is always >1, usually 9:1. The choice of solvent is also crucial:
a lower boiling point alcohol such as EtOH requires longer
refluxing time (∼24 h)13 than 2-(2′-methoxyethoxy)ethanol
(3-5 h),6a although an overnight reaction time has been reported
using this solvent.19 Similarly, refluxing in benzene14b,20
requires days, while use of decalin6c,11b,21,22 or dimethylfor-
mamide (DMF)10c,23 can reduce this to hours; a 1-3 week
reaction time was reported for metalation of Na4[H2(T-pSO3-
PP)] in DMF,23a but details (e.g., concentrations of Ru3(CO)12
and porphyrin) were not given, and others showed later that
this metalation is complete in 4 h when using a 3:1 Ru/porphyrin
molar ratio.24 Additives such as bis(triphenylphosphine)iminium
chloride10c,25 or 2,4,6-trimethylpyridine10c are reported to be
beneficial in certain cases. Ruthenium metalations of neutral,
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Inorganic Chemistry, Vol. 47, No. 17, 2008 7895

Rebouc¸as et al.
Scheme 1. Porphyrins and Schiff-Bases Relevant to This Work
In this paper we report a novel Ru-porphyrin metalation
method, which uses the air-stable [Ru(DMF)6](OTf)3 as metal
carrier, and refluxing DMF as solvent and CO source to
generate some RuII(porp)(CO) compounds in good, repro-
ducible yields; further, no Ru-chlorins are detected. Mecha-
nistic studies on the metalation are also presented. Addi-
tionally, we show here that the methodology may be adapted
to metalation of Schiff-bases.
The literature on Ru-Schiff-base chemistry is less extensive
than that of Ru-porphyrins but has flourished since the late
1990s; studies on coordination chemistry and small-molecule
chemistry27 have expanded to interest, for example, in
homogeneous/heterogeneous/asymmetric catalysis,2d,28 pho-
tochemistry and NO-chemistry,28m,29,30 materials chem-
istry,8f,30 and medicinal chemistry.30,31 Metalosalen com-
plexes, with their dianionic [N2O2] donor set, are easier to
prepare and purify than are the dianionic [N4] donor-
metaloporphyrins to which they are often compared.32 Metal
precursors have again included Ru3(CO)12,27a,d RuCl3-
(NO) · 3H2O,28b and RuCl2(PPh3)3,27b when the π-acceptor
ligands (CO, NO, and PPh3) are retained in the Ru(Schiff-
base) product; these species have been used as catalyst
precursors but require initial photolabilization of the π-ac-
Figure 1. Experimental setup for studying Ru-metalation of H2TPP.
synthetic porphyrins such as meso-tetraaryl- and meso-tetraalky-
lporphyrins, and H2OEP, typically require subsequent removal
of a “Ru-chlorin”,6a,21 usually via oxidation with 2,3-dichloro-
5,6-dicyano-1,4-benzoquinone DDQ).6a,19,26 Chromatographic
separation of Ru-porphyrinoid compounds is laborious,21 and
reported yields of Ru(porp)(CO) range from 20 to 60%.6a,19,26
Yield reproducibility is an issue when using the Ru3(CO)12
method, although this has provided an entry to all classes of
Ru-porphyrins: natural, synthetic, neutral, and charged, within
so-called first, second, or third generation compounds.11b
7896 Inorganic Chemistry, Vol. 47, No. 17, 2008

Ruthenium-Metalation of Porphyrins and Schiff-Bases
ceptor ligands.28h,i The precursor K2[RuCl5(H2O)] has been
used to prepare K[RuCl2(Schiff-base)] derivatives,27e–h
while attempted reactions with the common precursors,
RuCl3, cis-RuCl2(MeCN)4, and cis-RuCl2(DMSO)4 were
unsuccessful.27c The presence of chloride ligand in Ru(Schiff-
base) catalysts has been reported undesirable for the asym-
metric oxidation of diols28i and epoxidation of cyclohexene.33
The complex [RuCl2(p-cymene)]2 has been used with chiral
Schiff-bases, but the products were not isolated;28c however,
subsequent treatment with pyridine generated the substitu-
tion-inert RuII(Schiff-base)(py)2 derivatives that catalyze
cyclopropanation of olefins;28f these appear to be the first
such complexes containing no chlorides or the π-acceptor
ancillary ligands listed above. The direct preparation of
π-acceptor-free and chloride-free Ru Schiff-base complexes
appeared challenging and led us to test (with some success)
the use of [Ru(DMF)6](OTf)3 for the metalation.
The use of [Ru(DMF)6](OTf)3 was motivated by a report,
describing a simple, one-pot, two-step procedure for its
synthesis from RuCl3,34c following earlier literature syntheses
via [Ru(DMF)6]2+ species.34a,b The RuIII complex was first
used in macrocyclic chemistry to synthesize encapsulated
Ru complexes34b and, more recently, homoleptic compounds
containing, for example, imidazoles,35a phosphines, arsines,
and stilbines,35b and selenoethers and telluroethers.35c Our
studies described here represent a contribution to the revival
of [Ru(DMF)6](OTf)3 as a convenient Ru-source in macro-
cyclic chemistry. Scheme 1 shows the structure and their
abbreviations for all of the porphyrin and Schiff-base systems
discussed in this Paper.
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Experimental Section
General Information. The yellow [Ru(DMF)6](OTf)3 complex
(1), prepared by a literature procedure,34c is indefinitely stable if
kept in the dark at room temperature (rt, ∼20 °C) under static
vacuum in a desiccator; when not stored properly, however, slow
decomposition generates a brownish gum impurity, which can be
removed by recrystallizing the sample from 2:1 CH2Cl2/EtOAc.
AgOTf, prepared via modification of a literature method (Ag2O
being replaced with Ag2CO3),36 was stored under dynamic vacuum
in the dark. H2MesoPIX-DME was prepared by H2-hydrogenation
of H2PPIX-DME (Midcentury).37 N-Methylation of H2TMP was
carried out by a literature procedure38 to yield N-MeHTMP. H2OEP
was a gift from Dr. D. Dolphin. Alkylation of H2T4PyP (Aldrich)
with MeOTs39 afforded [H2T-NMe-4PyP](OTs)4 and the tetrachlo-
ride was prepared by percolation through a ion-exchange column
(Dowex 2 × 8, Cl- form; MeOH as eluent). H2Br8TPP40 and
Na4[H2(T-pSO3-PP)]41 were prepared by literature methods. Other
free-base porphyrins were prepared by acid-catalyzed condensation
(33) de Souza, V. R.; Nunes, G. S.; Rocha, R. C.; Toma, H. E. Inorg.
Chim. Acta 2003, 348, 50.
(34) (a) Bernhard, P.; Lehmann, H.; Ludi, A. Comments Inorg. Chem. 1983,
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T.; Bu¨rgi, H.-B.; Merbach, A. E.; Ludi, A. Inorg. Chem. 1995, 34,
5080.
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1998, 274, 184. (b) Works, C. F.; Jocher, C. J.; Bart, G. D.; Bu, X.;
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D. L.; da Mota Neto, J. D.; da Cunha, C. J. Inorg. Chem. 2002, 41,
5410.
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Bickley, J. F. Inorg. Chem. Commun. 1999, 2, 524. (c) Levason, W.;
Orchard, S. D.; Reid, G. Chem. Commun. 1999, 1071.
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J. Am. Chem. Soc. 1990, 112, 7552.
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Daftari, A.; Salavati-Niasari, M. Electroanalysis 2004, 16, 922. (b)
Cai, P.; Li, M.; Duan, C-Y.; Lu, F.; Guo, D.; Meng, Q-J. New J. Chem.
2005, 29, 1011.
(31) (a) Ramesh, R.; Maheswaran, S. J. Inorg. Biochem. 2003, 96, 457.
(b) Prabhakaran, R.; Huang, R.; Natarajan, K. Inorg. Chim. Acta 2006,
359, 3359.
(39) Hambright, P.; Adeyemo, A.; Shamim, A.; Lemelle, S. Inorg. Synth.
1985, 23, 55.
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P.; Vigato, P. A.; Fenton, D. E.; Hellier, P. C. Acta Chem. Scand.
1992, 46, 1025. (c) Guerriero, P.; Tamburini, S.; Vigato, P. A. Coord.
Chem. ReV. 1995, 139, 17. (d) Collinson, S. R.; Fenton, D. E. Coord.
Chem. ReV. 1996, 148, 19.
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Wijesekera, T.; Dupre´, D.; Cader, M. S. R.; Dolphin, D. Bull. Soc.
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1994, 72, 2447.
Inorganic Chemistry, Vol. 47, No. 17, 2008 7897

Rebouc¸as et al.
of pyrrole and the appropriate aldehyde using literature protocols;42
free-base chlorins (if present) were eliminated either oxidatively43a,b
or chromatographically.43c Schiff-bases were made via condensation
of a diamine and a salicyladehyde derivative as described elsewhere:
Abderhalden pistol (H2O) for ∼24 h. The solid was exposed to the
atmosphere for ∼5 h to give Ru(T-pCO2Me-PP)(CO)(H2O). Yield:
19.2 mg (81%). Anal. Calcd for C53H38N4O10Ru: C, 64.17; H, 3.86;
N, 5.65. Found: C, 64.44; H, 4.09; N, 6.05. UV-vis (DMF): 414
nm (5.35), 532 (4.23), 566 (3.54). IR: 3428 (νOH), 1945 (νC≡O),
1725 (νCdO). 1H NMR (d6-DMSO): δ 8.56 (s, 8H, ꢀ-pyrrole),
8.38-8.21 (m, 16H, o- and m-C6H4CO2Me), 4.02 (s, 12H,
p-C6H4CO2CH3). ESI-MS (9:1 MeOH/CHCl3, positive mode), M
is defined as Ru(T-pCO2Me-PP)(CO): clusters centered at m/z 997
[M + Na]+, 975 [M + H]+, 946 [M - CO]+. ESI-MS (9:1 MeOH/
CHCl3 1:1, negative mode): m/z 1009 [M + Cl]-, 981 [M - CO
+ Cl]-. 1H NMR assignments are based on data for H2T-pCO2Me-
PP.45
30a
44c
H2Salen,44a H2Naphthophen,44b H2 Bu4Salen, H2 Bu4Salophen.
t
t
H2Salophen (Aldrich) was used as received.
DMF (Fisher Scientific, 0.02% H2O) and H2 (Praxair, 99.999%,
extra-dry) were used as received; Ar (Praxair, 99.996%) was dried
either with Drierite (W.A. Hammond) or with Aquasorb (Mallinck-
rodt). Gas flow was measured with a Hewlett-Packard soap film
flowmeter (HP0101-0113). Distilled H2O was deoxygenated by
saturation with Ar. UV-vis spectra, presented as λmax (log ε), were
measured at 25 ( 1 °C in quartz cells in a Hewlett-Packard 8452A
diode array spectrophotometer. 1H NMR spectra were recorded on
Bruker AV300 or AV400 spectrometers (300.13 and 400.13 MHz,
respectively), and referenced to residual solvent protons of d6-
DMSO (δ 2.49) or CD3OD (δ 3.30), TMS-free solvents from
Cambridge Isotope Laboratories. IR spectra (KBr, cm-1) were
recorded on a Nicolet 4700 FT-IR spectrometer. MS data were
collected on a Bruker Esquire ESI ion-trap spectrometer, or on a
Kratos Concept IIH, LSIMS spectrometer using a Cs+ gun as
ionizing source. Elemental analysis was performed on a Carlo Erba
EA 1108 analyzer. Thermal gravimetric analyses were obtained
using a TGA 51 Thermogravimetric Analyzer fitted with a quartz
furnace tube with a temperature range from ambient to 1200 °C.
Stationary phases for column chromatography, neutral, basic, or
acidic Al2O3 (Fisher Scientific, Brockman activity I, 60-325 mesh)
and diatomaceous earth (Fisher Scientific, Celite 545), were used
as received. Molar ionic conductance (ΛM, in Ω-1 mol-1 cm2) was
determined on a Serfass conductance bridge model RCM15B1
(Arthur H. Thomas Co. Ltd.) connected to a 3404 cell (Yellow
Springs Instruments Co.), using a 10-3 mol L-1 solution of the
complex in DMF at 25 ( 1 °C. Unless otherwise indicated, all
solvents and reagents were reagent grade and used as supplied by
Aldrich or Fisher Scientific.
In all metalation procedures, a glass pipet and not a stainless
steel needle was used to bubble gases into the reaction mixtures.
Metalation of H2T-pCO2Me-PP. H2T-pCO2Me-PP (20.4 mg,
0.024 mmol), [Ru(DMF)6](OTf)3 (1), (69.1 mg, 0.070 mmol), and
20 mL of DMF were added to a 3-neck flask equipped with
condenser and stir bar. The system was purged with Ar for 15 min
at room temperature (rt) and the contents then heated to reflux with
stirring under a slow Ar flow (0.88 mL s-1) in the dark for 24 h;
the solution gradually changed color from purple to red, and a Ru
mirror deposited on the flask wall. The reaction was monitored by
UV-vis in acidic medium (HOAc or TFA/CH2Cl2 mixtures), when
the Soret bands of the free-base (in its protonated form) and Ru(T-
pCO2Me-PP)CO species were well resolved (see Results and
Discussion). If the reaction was incomplete and Ru metal was not
yet evident, the conversion could be improved by addition of 5-10
µL of deoxygenated H2O and a further 3-4 h reflux. The resulting
solution was concentrated to dryness by rotary evaporation. The
residue was suspended in 10 mL of MeOH, the mixture filtered
through a Celite pad, and washed with small amounts of MeOH
until the washings were clear. The free-base and the Ru-porphyrin
were recovered from the Celite by elution with 3:1 CH2Cl2/MeCN.
The red CH2Cl2/MeCN solution was evaporated to dryness, the
residue dissolved in 20:1 CH2Cl2/MeCN, and purified by column
chromatography on neutral Al2O3. After the unreacted H2T-
pCO2Me-PP was eluted (with 20:1 CH2Cl2/MeCN), the polarity
of the eluent was increased (5:1 CH2Cl2/MeCN) and the product
fraction was collected; the solvent was removed by evaporation
and the resulting purple solid was subsequently dried in an
Metalation of H2T-m,m′Me2-PP. The metalation procedure was
analogous to the standard one described above, except that H2T-
m,m′Me2-PP (23.7 mg, 0.033 mmol) and 1 (96.4 mg, 0.098 mmol)
were used. The Ru-porphyrin retained in the Celite was washed
with small portions of MeOH, and recovered with 9:1 CH2Cl2/
MeCN. The collected red solution was then evaporated to dryness.
The resulting solid was dissolved in CH2Cl2 and the solution was
filtered through acidic Al2O3, from which the Ru porphyrin red
band was eluted with CH2Cl2. The solvent of this was removed by
evaporation and the purple residue was then treated as above to
yield Ru(T-m,m′Me2-PP)(CO)(H2O). Yield: 21.9 mg (77%). Anal.
Calcd for C53H46N4O2Ru: C, 73.00; H, 5.32; N, 6.42. Found: C,
72.57; H, 5.48; N, 6.39. UV-vis (DMF): 414 nm (5.42), 532 (4.27),
1
566 (3.67). IR: 3443 (νOH), 1945 (νCO). H NMR (d6-DMSO): δ
8.57 (s, 8H, ꢀ-pyrrole), 7.78 (s, 4H, o-C6H3Me2), 7.68 (s, 4H,
o-C6H3Me2), 7.40 (s, 4H, p-C6H3Me2), 2.56 (s, 12H, CH3), 2.55
(s, 12H, CH3). ESI-MS (1:1 MeOH/CHCl3, positive mode), M )
Ru(T-m,m′Me2-PP)(CO): m/z 855 [M + H]+, 826 [M - CO]+;
ESI-MS (1:1 MeOH/CHCl3, negative mode): m/z 889 [M + Cl].
1H NMR assignments are based on data for H2T-m,m′Me2-PP.46
Attempted Metalation of H2T-o,o′Cl2-PP and H2TMP. Meta-
lations of H2T-o,o′Cl2-PP and H2TMP following the standard
procedure were unsuccessful; use of 1:1 DMF/1,2-dichlorobenzene
as solvent also gave no formation of Ru-porphyrin. UV-vis spectra
showed that the free-base remained unchanged.
Metalation of H2T-oMe-PP. The standard metalation procedure
was used, but with H2T-oMe-PP (22.4 mg, 0.033 mmol of a mixture
of atropisomers) and 1 (97.4 mg, 0.099 mmol). The product mixture
was then evaporated to dryness, the residue suspended in minimum
4:1 MeOH/H2O, and the suspension then filtered through Celite.
The solid was washed with 5 mL of the MeOH/H2O mixture and
recovered from the Celite with CH2Cl2. The collected CH2Cl2
fraction contained some water, and so the organic phase was
separated, and the CH2Cl2 removed by evaporation; residual water
was removed by dissolving the sample in 20 mL of C6H6 and
(42) (a) Adler, A. D.; Longo, F. R.; Finarelli, J. D.; Goldmacher, J.; Assour,
J.; Korsakoff, J. L. J. Org. Chem. 1967, 32, 476. (b) Rocha Gonsalves,
A. M. d’A.; Vareja˜o, J. M. T. B.; Pereira, M. M. J. Heterocyclic Chem.
1991, 28, 635. (c) Lindsey, J. S. In Metalloporphyrins Catalyzed
Oxidations; Montanari, F., Casella, L., Eds.; Kluwer Academic
Publishers: Dordrecht, 1994; pp 49-86. (d) Johnstone, R. A. W.;
Nunes, M. L. P. G.; Pereira, M. M.; Rocha Gonsalves, A. M. d’A.;
Serra, A. C. Heterocycles 1996, 43, 1423. (e) Lindsey, J. S. In The
Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.;
Academic Press: San Diego, 2000; Vol. 1, Chapter 2.
(43) (a) Barnett, G. H.; Hudson, M. F.; Smith, K. M. Tetrahedron Lett.
1973, 14, 2887. (b) Rousseau, K.; Dolphin, D. Tetrahedron Lett. 1974,
15, 4251. (c) Adler, A. D.; Longo, F. R.; Va´radi, V. Inorg. Synth.
1976, 16, 213.
(44) (a) Alexander, P. W.; Sleet, R. J. Aust. J. Chem. 1970, 23, 1183. (b)
Teoh, S.-G.; Yeap, G.-Y.; Loh, C.-C.; Foong, L.-W.; Teo, S.-B.; Fun,
H.-K. Polyhedron 1997, 16, 2213. (c) Wo¨ltinger, J.; Ba¨ckvall, J.-E.;
Zsigmond, A. Chem.sEur. J. 1999, 5, 1460.
7898 Inorganic Chemistry, Vol. 47, No. 17, 2008

Ruthenium-Metalation of Porphyrins and Schiff-Bases
evaporating the solution to dryness. The residue was redissolved
in C6H6 and purified by chromatography on basic Al2O3. After traces
of unreacted free-base were collected with C6H6, the Ru-porphyrin
was eluted with 9:1 CH2Cl2/MeCN; the solvent was removed and
the resulting purple solid was converted by the described method
to a mixture of Ru(T-oMe-PP)(CO)(H2O) atropisomers. Yield: 25.9
mg (93%). Anal. Calcd for C49H38N4O2Ru: C, 72.13; H, 4.69; N,
6.87. Found: C, 72.33; H, 4.79; N, 7.22. UV-vis (DMF): 412 nm
(5.41), 532 (4.29), 562 (3.42). IR: 3435 (νOH), 1946 (νCO). 1H NMR
(d6-DMSO): δ 8.36, 8.35, 8.34, 8.33 (4 s, 8H, ꢀ-pyrrole), 8.06-7.87
(m, 4H, o-C6H4Me), 7.71-7.55 (m, 12H, m- and p-C6H4Me), 2.02,
2.01, 2.00, 1.96, 1.91 (5 br s, 12H, o-C6H4CH3). ESI-MS (1:1
MeOH:CHCl3, positive mode), M ) Ru(T-oMe-PP)(CO): m/z 821
Metalation of H2Br8TPP. The standard procedure was used with
H2Br8TPP (20.0 mg, 0.016 mmol), 1 (51.6 mg, 0.052 mmol), and
15 mL of DMF. The refluxing under Ar was continued for 3 h,
when the UV-vis spectrum showed the absence of free-base; the
solvent was removed, the residue suspended in MeOH, the mixture
filtered through Celite, and the solid washed with MeOH until
washings were clear. The Ru-porphyrin was recovered using 4:1
CH2Cl2/MeCN, and then the solvent was removed. The residue was
dissolved in CH2Cl2 and purified on a short, SiO2 column, using
CH2Cl2 as eluent. The first fraction was collected, mixed with an
equal volume of MeCN, and the solution evaporated to dryness to
yield Ru(Br8TPP)(CO)(MeCN). Yield: 3.1 mg (14%). UV-vis
1
(DMF): 434 nm (5.17), 496 (sh), 572 (4.19). IR: 1961 (νCO). H
NMR (d6-DMSO): δ 8.16-8.11 (m, 4 H, o- or o′-C6H5), 8.05-8.00
(m, 4 H, o′- or o-C6H5), 7.84-7.75 (m, 12 H, m-C6H5 and p-C6H5),
2.06 (s, 3 H, CH3CN). LSIMS, M ) Ru(Br8TPP)(CO): m/z 1374
[M + H]+, 1345 [M - CO]+, 1295 [M - Br + H]+, 1267 [M -
CO - Br + H]+.
1
[M + Na]+, 770 [M - CO]+. H NMR and UV-vis data are in
agreement with those previously reported for complexes containing
the Ru(T-oMe-PP)(CO) moiety.47a
Metalation of N-MeHTMP. The standard procedure, when
applied to N-MeHTMP, gave low conversion of the free-base
(<20%). The DMF solution of N-MeHTMP changed to green upon
addition of 1 and remained as such, UV-vis spectra being
characteristic of protonated N-MeHTMP species (see Results and
Discussion). As indicated by thin-layer chromatography (TLC)
analysis on basic Al2O3, the product composition varied with each
attempted synthesis. Most of the TLC spots fluoresced under 356
nm radiation, and all had lower Rf values than that of the starting
material; H2TMP was never observed. A small amount (<5%)
containing “Ru(TMP)(CO)” was once isolated, as evidenced by
UV-vis data which were comparable to those reported.18 Increased
reaction time and/or Ru load were ineffective.
Metalation of [H2T-NMe-4PyP](OTs)4. A procedure analogous
to the standard one was used with [H2T-NMe-4PyP](OTs)4 (26.0
mg, 0.020 mmol) and 1 (95.4 mg, 0.097 mmol). The reaction, as
monitored by UV-vis after adding a reaction sample to 1 M HCl,
was complete after 17 h. The mixture was then evaporated to
dryness, the residue washed with Et2O, dissolved in MeOH and
the suspension filtered through Celite. The red solution was
concentrated to ∼10 mL and filtered through Sephadex G-10. The
collected red solution was diluted to 50 mL, run through an anion
exchange resin (Bio-Rad AG 1-X2, Cl- form) to remove some Ru
species, and then evaporated to yield a gummy material; this was
dissolved in 10 mL of DMF, methyl tosylate (40.9 mg, 0.220 mmol)
was added, and the resulting solution was refluxed for 3 h. The
solvent was removed, and the residue was washed with dry acetone
(8 × 4 mL) in a Schlenk tube for protection against moisture. The
resulting solid, mainly [Ru(T-NMe-4PyP)(CO)](OTs)4 ·xH2O, was
always contaminated with ∼15% of the corresponding free-base,
as judged by 1H NMR.10c Attempts to produce an analytically pure
sample by either recrystallization or chromatography were unsuc-
cessful, as was the use of larger excesses of 1. Yield: ∼15 mg
(∼40%). ESI-MS (MeOH, positive mode), M ) Ru(T-NMe-
4PyP)(CO): clusters centered at m/z 574.2 [M + 2OTs]2+/2, 325.8
[M + OTs]3+/3, 259.4 [M - CO]3+/3, 209.6 [M + MeOH]4+/4,
201.6 [M]4+/4, 194.6 [M - CO]4+/4; ESI-MS (MeOH, negative
mode): m/z 171 [OTs]-.
Metalation of H2mesoPIX-DME. The standard procedure was
used with H2mesoPIX-DME (17.0 mg, 0.029 mmol) and 1 (90.1
mg, 0.091 mmol). The product mixture was evaporated to dryness,
the residue suspended in n-pentane, and the suspension then filtered
through Celite. The retained Ru-porphyrin was washed with portions
of n-pentane and recovered with CH2Cl2. The collected purple
solution was evaporated to dryness and the residue purified by
column chromatography on SiO2 using 9:1 CH2Cl2/MeCN. The
solvent of the first fraction was removed, and the residue dried
and converted by the standard method to Ru(mesoPIX-
DME)(CO)(H2O). Yield: 17.1 mg (81%). Anal. Calcd for Ru(me-
soPIX-DME)(CO)(H2O), C37H42N4O6Ru: C, 60.07; H, 5.72; N,
7.52. Found: C, 60.10; H, 5.53; N, 7.39. UV-vis (DMF): 394 nm
(5.29), 518 (4.10), 548 (4.30). IR: 3471 (νOH), 1933 (νCtO), 1736
Attempted Metalation of [H2T-NMe-4PyP]Cl4. The procedure
given above for metalation of [H2T-NMe-4PyP](OTs)4, when
applied to the chloride analogue, failed to yield any Ru-porphyrin;
UV-vis analysis in aq HCl showed that the free-base remained in
solution.
1
(νCdO). H NMR (d6-DMSO): δ 9.90, 9.89, 9.87, 9.86 (4 s, 4H,
meso-H), 4.40-4.18 (m, 4H, CH2CH2CO2CH3), 3.98 (q, 4H, 3JHH
) 7.46 Hz, CH2CH3), 3.55, 3.53 (2 s, 12H, CH3), 3.52 (s, 6H,
CH2CH2CO2CH3), 3.26 (m, 4H, CH2CH2CO2CH3), 1.81 (t, 6H, 3JHH
) 7.46 Hz, CH2CH3). ESI-MS (9:1 MeOH/CH2Cl2, positive mode),
M ) Ru(mesoPIX-DME)(CO): m/z 745 [M + Na]+, 722 [M]+,
695 [M - CO + H]+; ESI-MS (9:1 MeOH/CH2Cl2, negative mode):
m/z 753 [M + MeO]-. 1H NMR assignments are based on data for
the Ru complex derived from mesoporphyrin IX di-tert-butylester;1e
UV-vis and IR (νCO) data agree with those reported for complexes
containing the Ru(mesoPIX-DME)(CO) moiety.20a
Metalation of Na4[H2T-pSO3-PP]. The standard metalation
procedure was used with Na4[H2(T-pSO3-PP)]·15H2O (210 mg,
0.205 mmol) and 1 (614 mg, 0.622 mmol). After 24 h of reflux,
the dark red solution was concentrated to minimal volume, and
the product was purified as a purple-red band by chromatography
using silica gel with MeOH as eluant. The solvent was removed
by evaporation, and the product was collected and dried in vacuo
for 1 week. Yield: 133 mg (53%). Anal. Calcd for Na4[Ru(T-pSO3-
PP)(CO)]·4H2O, C45H32N4O17S4Na4Ru: C, 44.23; H, 2.64; N, 4.58;
S, 10.49. Found: C, 44.36; H, 2.70; N, 4.55; S, 10.68. UV-vis
(H2O): 410 nm (5.43), 528 (4.21). IR: 3460 (νOH), 1923 (νCO). 1H
NMR (CD3OD): δ 8.65, 8.60 (2 s, 8H, ꢀ-pyrrole), 8.25 (m, 16H,
MetalationofH2PPIX-DME.TheprocedureusedforH2mesoPIX-
DME, when applied to H2PPIX-DME, yielded a complex product
mixture, from which Ru(mesoPIX-DME)(CO) was isolated in low
1
-
m-C6H4SO3 and o-C6H4SO3-). TGA: Calcd loss of 4H2O: 5.9%.
yield (<10%). H NMR data, particularly a quartet at δ 3.98 and
Found: 5.1% (from ∼35 to ∼60 °C). The 1H NMR, IR (νCO), and
UV-vis data are consistent with those previously reported for the
a triplet at δ 1.81 of the CH2CH3 group, and MS data for this
compound agree with those given in the previous section.
Inorganic Chemistry, Vol. 47, No. 17, 2008 7899

Rebouc¸as et al.
Ru(T-pSO3-PP)(CO)4- moiety.10c,23a,b EI and LSIMS data showed
no parent peak or other peaks related to the title compound.
Metalation of H2OEP. The standard procedure was used with
H2(OEP) (60 mg, 0.11 mmol), 1 (312 mg, 0.316 mmol), and DMF
(30 mL), and a reaction time of 6 h. The product was purified by
chromatography using neutral alumina with CH2Cl2 as eluent for
unreacted H2(OEP), and with 10% THF/MeOH as eluent for the
product. Red, X-ray quality crystals of Ru(OEP)(CO)(THF) were
obtained from slow evaporation of a saturated solution of the
complex in 10% THF/toluene. Yield: 45 mg (56%). Anal. Calcd
for C41H52N4O2Ru: C, 67.09; H, 7.14; N, 7.63. Found: C, 66.51;
H, 7.17; N, 8.40. UV-vis (DMF): 396 nm (5.63), 518 (4.49), 548
(4.76). IR: 1925 (νCO). A sample was converted by the standard
to be Ru(TPP)(CO)(py), identical to that reported in 1973.49 The
BaCO3 (12.2 mg, 0.062 mmol) was isolated; (Anal. Calcd. C, 6.06.
Found: C, 6.28).
Expt. B. The procedure was identical to that described in Expt.
A, except that at time zero deoxygenated H2O (200 µL, 11.1 mmol)
was added. After 2.5 h, Ru metal was evident, and no further
metalation was seen. Work-up yielded 16.8 mg (68%) of
Ru(TPP)(CO)(H2O); 1.1 mg (5%) of unreacted H2TPP was
recovered from the neutral Al2O3 chromatography column.
Expt. C. DMF alone (20 mL) was used and the solvent was
purged with Ar for 15 min at rt, prior to being refluxed. After 15
min, 1 (96.3 mg, 0.098 mmol) was added (time zero), and the
system was sealed and samples taken subsequently. After 2 h,
H2TPP (20.4 mg, 0.033 mmol) was added. The reaction was
monitored for 7 h, when workup yielded 15.2 mg (60%) of
Ru(TPP)(CO)(H2O) and 5.9 mg (29%) of H2TPP.
1
procedure to give Ru(OEP)(CO)(H2O). H NMR (d6-DMSO): δ
9.88 (s, 4H, meso-H), 4.06-3.93 (m, 16H, CH2CH3), 1.86 (t, 24H,
CH2CH3). LSIMS, M ) Ru(OEP)(CO): m/z 662 [M]+ and 634 [M
- CO]+. The 1H NMR, IR (νCtO), and UV-vis spectroscopic data
are consistent with those previously reported for the Ru(OEP)(CO)
moiety.1a,g,6a,20e,47b
t
t
Metalation of H2 Bu4Salen. A mixture of H2 Bu4Salen (10.0 mg,
0.020 mmol) and 1 (60.1 mg, 0.061 mmol) in 10 mL of DMF was
refluxed for 3 h under air, protected from moisture (using Drierite)
and light (Al foil); the reaction was monitored by TLC (SiO2, 10:1
CH2Cl2:EtOH). The mixture was then concentrated to an oily
residue, and purified on SiO2, using 10:1 CH2Cl2/EtOH as eluent;
the blue band was collected, and the solution evaporated to dryness.
The product was dried in an Abderhalden pistol (EtOH) overnight.
Yield of [Ru(tBu4Salen)(DMF)2]OTf: 7.8 mg (44%). Anal. Calcd.
for C39H60F3N4O7RuS: C, 52.81; H, 6.82; N, 6.31. Found: C, 52.91;
H, 6.87; N, 6.06. UV-vis (DMF): 368 nm (4.28), 516 (3.36), 706
(3.71). IR: 1638 (νCO), 1267 (νSO3), 1031 (νCF3). ΛM (DMF): 67
Ω-1 mol-1 cm2. ESI-MS (1:1 CH2Cl2/MeOH, positive mode), M
) Ru(tBu4Salen)(DMF)2: m/z 738 [M]+, 592 [M - 2DMF]+. ESI-
MS (1:1 CH2Cl2/MeOH, negative mode): m/z 662 [M - 2DMF +
2Cl]-, 149 [OTf]-.
Mechanistic Studies with Metalation of H2TPP. This meta-
lation was studied in more detail using the apparatus shown in
Figure 1, to gain insight into the mechanism. In experiments A-C,
the Ar flow was 0.88 mL s-1. Reactions were monitored by
withdrawing samples (∼50 µL) via a syringe and quenching them
by cooling to rt; 2 µL of the sample were transferred to a 1 cm
quartz cell, diluted with 1.0 mL of glacial HOAc, and the UV-vis
spectrum then recorded. A solution of BaCl2 (1.00 g in 10 mL of
0.85 M NH4OH) was used to follow qualitatively any CO2
evolution;48 any precipitated BaCO3 was filtered off, washed with
MeOH, dried in an Abderhalden pistol overnight (EtOH), and
characterized by elemental analysis. Control experiments showed
no formation of BaCO3 until [Ru(DMF)6](OTf)3 (1) was introduced
into the system. Use of cold water (∼5 °C) in the condenser, and
Ar presaturated with DMF at rt, limited evaporation of reaction
solvent to ∼25% loss over 24 h.
t
Metalation of H2 Bu4Salophen. The procedure used was as
t
t
given for H2 Bu4Salen, but using H2 Bu4Salophen (10.9 mg, 0.020
mmol). A resulting green band on the silica gel was collected, and
the solution was evaporated to dryness, the product again being
similarly dried overnight. Yield of [Ru(tBu4Salophen)(DMF)2]OTf·
1/2H2O: 10.6 mg (57%). Anal. Calcd. For C43H61F3N4O7.5RuS: C,
54.70; H, 6.51; N, 5.93. Found: C, 54.82; H, 6.60; N, 5.83. UV-vis
(DMF): 300 nm (4.38), 312 (sh), 344 (sh), 376 (sh), 430 (4.32),
Expt. A. Using H2TPP (20.0 mg, 0.033 mmol) and DMF (20
mL), the system was purged with Ar for 15 min at rt. The solution
was then heated to reflux (153 °C). After 15 min, the thermometer
septum was removed, and 1 (95.7 mg, 0.097 mmol) added at time
zero, and the system was resealed; samples were then analyzed by
UV-vis spectroscopy. After 10.5 h, no Ru metal was observed,
and 10 µL (0.556 mmol) of degassed H2O was then added; after
32 h, metal was observed on the flask walls, and the mixture was
worked-up as described for the H2T-pCO2Me-PP system. Yield 23.7
mg (96%) of Ru(TPP)(CO)(H2O). Anal. Calcd for C45H30N4O2Ru:
C, 71.13; H, 3.98; N, 7.37. Found: C, 70.65; H, 4.31; N, 7.10.
UV-vis (DMF): 412 nm (5.60), 532 (4.72). IR: 3412 (νOH), 1946
576 (sh), 612 (sh), 830 (3.50). IR: 1637 (νCO), 1268 (νSO ), 1031
3
(νCF ). ΛM (DMF): 65 Ω-1 mol-1 cm2. ESI-MS (MeOH, positive
3
mode), M ) [Ru(tBu4Salophen)(DMF)2]: m/z 787 [M]+, 641 [M
- 2DMF]+. ESI-MS (MeOH, negative mode): 149 [OTf]-.
Attempted Metalation of H2Salen, H2Salophen, and H2Naph-
t
thophen. The procedure described for H2 Bu4Salen, when tried for
H2Salen, H2Salophen, or H2Naphthophen, yielded intractable
product mixtures. Attempts to isolate pure compounds by recrys-
tallization or chromatography were unsuccessful, although MS data
of the product mixtures showed that metalation did occur.
1
(νCO). H NMR (d6-DMSO) δ 8.55 (s, 8H, ꢀ-pyrrole), 8.20-8.17
(m, 4H, o- or o′-C6H5), 8.08-8.04 (m, 4H, o′- or o-C6H5),
7.80-7.73 (m, 12 H, m-C6H5 and p-C6H5). LSIMS, M ) Ru(TP-
1
P)(CO): m/z 742 [M]+, 714 [M - CO]+. The H NMR, IR (νCO
)
and UV-vis data agree with reported data for complexes containing
Ru(TPP)(CO).6g,14a,20a,b,d,21 Structural analysis of X-ray quality red
crystals, obtained by slow evaporation of a saturated solution of
the aqua complex in 5% pyridine/benzene, showed the molecule
Results and Discussion
Ru-Metalation of Porphyrins. The new protocol for
metalation of porphyrins with [Ru(DMF)6](OTf)3 was ap-
proached in a way to provide insight into the underlying
chemistry. Table 1 summarizes characteristics of the por-
phyrins studied and, in the case of successful metalations,
presents the yield of isolated product, which, with few
exceptions, was formulated as Ru(porp)(CO)(H2O); these
(45) Lindsey, J. S.; Schereiman, I. C.; Hsu, H. C.; Kearney, P. C.;
Marguerettaz, A. M. J. Org. Chem. 1987, 52, 827.
(46) Tamiaki, H.; Matsumoto, N.; Unno, S.; Shinoda, S.; Tsukube, H. Inorg.
Chim. Acta 2000, 300302, 243.
(47) (a) Eaton, S. S.; Eaton, G. R. J. Am. Chem. Soc. 1975, 97, 3660. (b)
Eaton, G. R.; Eaton, S. S. J. Am. Chem. Soc. 1975, 97, 235.
(48) Vogel, A. I. Macro and Semimicro QualitatiVe Inorganic Analysis,
5th ed.; Longman Group: New York, 1979, pp 278, 298-299.
(49) Little, R. G.; Ibers, J. A. J. Am. Chem. Soc. 1973, 95, 8583.
7900 Inorganic Chemistry, Vol. 47, No. 17, 2008

Ruthenium-Metalation of Porphyrins and Schiff-Bases
Table 1. Porphyrins Studied for Metalation by [Ru(DMF)6](OTf)3, and Yields of Ru-Carbonyl
substituents
aryl-substituents
porphyrin charge
anionic
porphyrin
meso- ꢀ-
p-
m,m′-
o-
o,o′-
neutral
cationic
% yielda
H2TPP
+
+
+
+
+
+
+
-
-
-
-
-
-
-
-
+
-
+
-
+
-
-
+
-
-
-
-
-
-
+
-
-
-
-
+
+
-
+
+
+
+
+
+
+
+
+
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
96
81
77
0b
H2T-pCO2Me-PP
H2T-m,m′Me2-PP
H2TMP
H2T-o,o′Cl2-PP
H2T-oMe-PP
N-MeHTMP
H2OEP
-
+
-
-
0b
-
93
-
0b
not applicable
56c
H2mesoPIX-DME
H2PPIX-DME
-
-
+
+
not applicable
not applicable
+
+
-
-
-
-
81
<10d, e
H2Br8TPP
+
+
+
+
+
-
-
-
-
+
+
+
-
-
-
-
-
-
-
-
-
-
-
-
+
-
-
-
-
+
-
-
-
-
+
+
14d, f
53
Na4[H2(T-pSO3-PP)]
[H2T-NMe-4PyP](OTs)4
[H2T-NMe-4PyP]Cl4
∼50d
0b
a Isolated. b Porphyrin free-base unreacted. c Recrystallized. d See text. e Yield refers to Ru(mesoPIX-DME)(CO)(H2O). f H2Br8TPP decomposes in refluxing
DMF. + Studied.
1
were characterized by spectroscopic (UV-vis, IR, and H
NMR), spectrometric (ESI-MS), and elemental analyses.
General Considerations. (a) Purification. When the
reaction product mixture was concentrated to a minimum
volume and directly purified by column chromatography
(using first an apolar eluent and then a more polar mixture),
some loss in Ru porphyrin was observed because residual
DMF in the sample modified the polarity of the initial eluent
(CH2Cl2 or C6H6) and resulted in some Ru-porphyrin being
eluted in the solvent front, together with unreacted free-base.
The purification procedure was improved by introducing a
filtration step prior to the chromatography to eliminate the
DMF. As neutral free-base porphyrins and Ru-porphyrins
are almost insoluble in MeOH and H2O, the rotovap-
concentrated product mixture was suspended in MeOH or
MeOH/H2O and filtered through Celite; the solid (unreacted
free-base, Ru-porphyrin, and Ru-metal) was washed with the
polar medium, and this eliminated residual DMF and some
brownish, uncharacterized Ru species (nonporphyrinic as
indicated by UV-vis spectra). The free-base and the Ru-
porphyrin were then extracted from the Celite with CH2Cl2,
and purified using an Al2O3 column (on which the Ru-
porphyrins were strongly adsorbed) using as eluents initially
CH2Cl2 (to collect the unreacted free-base) and then CH2Cl2/
MeCN mixtures (to recover the Ru-porphyrin). For the
metalation of H2TPP, for example, this modified procedure
increased the isolated yield of Ru-porphyrin from 50 to 96%.
for following metalation. Because Ru(porp)(CO) compounds
are stable under acidic conditions,11a a better way to monitor
metalation or detect free-base contamination in isolated
Ru(porp)(CO) fractions is to record the spectra in acidic
media (e.g., HOAc, TFA, or TFA/CH2Cl2), when the free-
base is protonated to so-called “dication” species,51 this
referring only to the charges on the porphyrin N4-core and
not those of peripheral substituents. These dications have
D4h symmetry and electronic spectra that resemble those of
Ru(porp)(CO) compounds, but all absorption maxima of the
dications are significantly red-shifted, allowing for unam-
biguous identification of mixtures of unmetalated porphyrin
and Ru(porp)(CO) species.
(c) IR Spectroscopy. This was used mainly to characterize
Ru(porp)(CO)(H2O) species by verifying the absence of νNH
of free-base porphyrins (∼3315 cm-1) and confirming the
presence of coordinated CO and H2O (νCO ∼ 1940, νOH
∼
3440 cm-1). Other functional-group bands are also reported
when present.
1
(d) H NMR Spectroscopy. Metalation results in the
disappearance of the distinct, ring-current shielded signal
associated with the free-base, inner core hydrogens (δ about
-3).521H NMR spectra were also useful in determining the
purity of the isolated complexes, because “grease” (δ ∼0)
and residual workup solvent, the common impurities, could
be easily identified.53 The purity of the Ru(porphyrin)(CO)
complexes depended on the solvent used in their synthesis.
Within Ru(porp)(CO)(L) complexes, the L was difficult to
identify when “non-coordinating solvents” such as C6D6 or
CDCl3 were used. Because of the trans-effect of CO, the
usually weak Lewis base L, which is derived from the
workup procedure (commonly MeCN, H2O, MeOH, DMF,
or a mixture of these), is typically in fast exchange with
(b) UV-vis Spectroscopy. Electronic spectroscopy is
valuable for monitoring metalation reactions and checking
product purity. A typical porphyrin shows an intense Soret
band (ε ∼105 M-1 cm-1) in the 350-450 nm region and
four weaker bands (ε ∼103-104) in the 450-800 nm region;
metalation increases the local symmetry from D2h (free-base)
to D4h (metaloporphyrin) and is accompanied by a collapse
in the number of the low-energy bands from 4 to 2 (or even
1).50 The Soret band of Ru(porp)(CO) species does not shift
appreciably from that of the corresponding free-base under
neutral conditions, but the low-energy bands can be used
(51) (a) Meot-Ner, M.; Adler, A. D. J. Am. Chem. Soc. 1975, 97, 5107.
(b) Dalton, J. M.; Milgrom, L. R.; Pemberton, S. M. J. Chem. Soc.
Perkin Trans. II 1980, 370.
(52) Medford, C. J. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: New York, 2000, Vol. 5,
Chapter 35.
(50) Gouterman, M. In The Porphyrins; Dolphin, D., Ed.; Academic Press:
New York, 1977; Vol. III, Chapter 1.
(53) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997, 62,
7512.
Inorganic Chemistry, Vol. 47, No. 17, 2008 7901

Rebouc¸as et al.
certain conditions, particularly using temperatures just below
that of refluxing DMF, Fe-porphyrins, characterized by MS
and UV-vis, were the major product; the needles became
visibly corroded, consistent with a reported metalation using
elemental Fe.54 Thus, such needles were replaced with long
glass pipettes.
Effects of Peripheral Substituents. The porphyrins were
selected for study so that the effects of peripheral substituents
on the metalation using [Ru(DMF)6](OTf)3 (1) could be
examined. Noticed was the successful metalation to form
Ru(TPP)(CO)(H2O), in contrast to the nonmetalation of
H2TMP. Electronic or steric effects of the meso-phenyl
substituents must play a role and, particularly because of
the intense interest in Ru(TMP)(CO) derivatives in catalytic
oxidations,2 studies with a series of meso-tetraarylporphyrins,
including para-, di-meta-, ortho-, and di-ortho-aryl substit-
uents, were undertaken. The Ru(T-pCO2Me-PP)(CO)(H2O)
complex was successfully prepared (Table 1), and this
p-substituted porphyrin was chosen because (i) (carbomethox-
y)phenyl-porphyrins are easy to prepare (and are available
commercially), (ii) their metal-derivatives are readily purified,
hydrolyzed, and ionized to their water-soluble, carboxylato
derivatives, and (iii) carboxyporphyrins and their metal
complexes are of use in diverse areas of chemistry and
biology, including medicinal chemistry,55 supramolecular
chemistry and materials,56 analytical chemistry,57 biomimetic
catalysis,58 and photochemistry.59 A Ru(T-pCO2Me-PP)(CO)
derivative has been prepared using Ru3(CO)12,58b but puri-
fication and characterization details were not provided;
however, base-hydrolysis to the water-soluble H4[Ru(T-
pCO2-PP)(CO)] was accomplished in high yield as shown
Figure 2. 1H NMR spectra of crude Ru(TPP)(CO)(MeCN) in C6D6 (top),
C6D6 + excess pyridine (middle), and d6-DMSO (bottom). Assignments:
a, ꢀ-pyrrole; b, o-Ph; c, m- and p-Ph; d, residual H2O; e, MeCN; f, free
pyridine; g, γ-pyridine (coord.); h, ꢀ-pyridine (coord.); i, R-pyridine (coord.);
S, solvent; st, solvent satellite (H-13C coupling).
residual water in the deuterated solvent; this yields a broad
signal, whose chemical shift is uninformative as it depends
on the relative concentrations of water and L (in free and
coordinated states) (Figure 2, top). To identify L in C6D6 or
CDCl3 solutions, addition of excess pyridine was usually
helpful (Figure 2, middle). An easier method for identifying
L was to record the 1H NMR spectrum in d6-DMSO (DMSO
was not used in any stage of the synthesis), when the
spectrum of “Ru(porp)(CO)(L)” corresponds to that of
Ru(porp)(CO)(d6-DMSO) and free L (Figure 2, bottom). The
1H assignments were made by comparison with data for the
corresponding free-base and/or a literature congener; Ru(por-
p)(CO)(L) species lack a horizontal plane of symmetry, and
the two faces of the porphyrin ring are inequivalent.
1
by H NMR, but the nature of the ligand trans to CO was
not discussed, and is presumably H2O. This reported
synthesis via the ester complex is more convenient than the
(54) Herrmann, O.; Mehdi, S. H.; Corsini, A. Can. J. Chem. 1978, 56,
1084.
(55) (a) Neurath, A. R.; Strick, N.; Debnath, A. K. J. Mol. Recognit. 1995,
8, 345. (b) Rahimi, R.; Hambright, P. J. Porphyrins Phthalocyanines
1998, 2, 493.
(56) Schiavon, M. A.; Iwamoto, L. S.; Ferreira, A. G.; Iamamoto, Y.;
Zanoni, M. V. B.; Assis, M das D. J. Braz. Chem. Soc. 2000, 11,
458. (b) Sacco, H. C.; Ciuffi, K. J.; Bizzotto, J. C.; Mello, C.; de
Oliveira, D.; Vidoto, E. A.; Nascimento, O. R.; Serra, A. O.; Iamamoto,
Y. J. Non-Cryst. Solids 2001, 284, 174. (c) Kosal, M. E.; Chou, J.-
H.; Suslick, K. S. J. Porphyrins Phthalocyanines 2002, 6, 377. (d)
Halma, M.; Wypych, F.; Drechsel, S. M.; Nakagaki, S. J. Porphyrins
Phthalocyanines 2002, 6, 502. (e) Pessoa, C. A.; Gushikem, Y.;
Nakagaki, S. Electroanalysis 2002, 14, 1072. (f) Lipstman, S.;
Muniappan, S.; George, S.; Goldberg, I. Dalton Trans. 2007, 3273.
(57) (a) Mizutani, T.; Wada, K.; Kitagawa, S. J. Am. Chem. Soc. 1999,
121, 11425. (b) Amao, Y.; Okura, I. Analyst 2000, 125, 1601. (c)
Amao, Y.; Asai, K.; Okura, I. J. Porphyrins Phthalocyanines 2000,
4, 179.
(e) Elemental Analysis. Samples recrystallized from (wet)
MeCN/CH2Cl2 mixtures sometimes contained a mixture of
Ru(porp)(CO)(MeCN) and Ru(porp)(CO)(H2O) as revealed
by NMR (in d6-DMSO). Although the elemental analysis
and 1H NMR data for these [Ru(porp)(CO)(MeCN)]x-
[Ru(porp)(CO)(H2O)]y samples (where x + y ) 1) were in
perfect agreement, such “fractional” formulations could be
avoided by converting the samples to Ru(porp)(CO)(H2O)
using a modification of a reported procedure:14a the sample
was heated at 100 °C under vacuum for up to 1 day in an
Abderhalden pistol (H2O), during which time coordinated
MeCN was eliminated (as revealed by 1H NMR). The sample
was then exposed to the atmosphere for ∼1 h to “pick up
water”, this procedure yielding solids that reproducibly
analyzed for Ru(porp)(CO)(H2O).
(58) (a) Iwado, A.; Mifune, M.; Harada, R.; Akizawa, H.; Motohashi, N.;
Saito, Y. Inorg. Chim. Acta 1998, 283, 44. (b) Nimri, S.; Keinan, E.
J. Am. Chem. Soc. 1999, 121, 8978. (c) Giger, R.; Hoffmann, P. J.
Porphyrins Phthalocyanines 2002, 6, 362. (d) do Nascimento, E.; Silva,
G.; de, F.; Caetano, F. A.; Fernandes, M. A. M.; da Silva, D. C.; de
Carvalho, M. E. M. D.; Pernaut, J. M.; Rebouc¸as, J. S.; Idemori, Y. M.
J. Inorg. Biochem. 2005, 1193. (e) Rebouc¸as, J. S.; Spasojeviæ, I.;
Batiniæc-Haberle, I. J. Biol. Inorg. Chem. 2008, 13, 289.
(59) (a) Cherian, S.; Wamser, C. C. J. Phys. Chem. B 2000, 104, 3624. (b)
Mosinger, J.; Kliment, V., Jr.; Sejbal, J.; Kubat, P.; Lang, K. J.
Porphyrins Phthalocyanines 2002, 6, 514. (c) MacAlpine, J. K.; Boch,
R.; Dolphin, D. J. Porphyrins Phthalocyanines 2002, 6, 146. (d)
Asakura, N.; Miyaji, A.; Kamachi, T.; Okura, I. J. Porphyrins
Phthalocyanines 2002, 6, 26.
(f) Avoidance of Stainless-Steel Needles. Contamination
by Fe-porphyrins was observed on using stainless-steel
needles for bubbling Ar through a reaction mixture. Under
7902 Inorganic Chemistry, Vol. 47, No. 17, 2008

Ruthenium-Metalation of Porphyrins and Schiff-Bases
direct, but troublesome, Ru3(CO)12-metalation of H4[H2(T-
pCO2-PP)].10c Our metalation of H2T-m,m′Me2-PP gave the
new compound, Ru(T-m,m′Me2-PP)(CO)(H2O), which may
be considered a “converse” Ru(TMP)(CO) derivative. Of
note, this new complex was the only one that was purified
on acidic Al2O3; attempts to find a solvent mixture to separate
the complex from its unreacted free-base on SiO2, and neutral
or basic Al2O3, were unsuccessful. In acidic Al2O3, the free-
base is presumably protonated and strongly held by the
stationary phase when using an apolar mobile phase.
Purification of Ru(T-m,m′Me2-PP)(CO) was thus accom-
plished by elution with CH2Cl2, which left the protonated
free-base at the top of the column as a green band that was
eluted with 1:1 MeOH/CH2Cl2; the pure free-base was
subsequently isolated using basic Al2O3. The acidic Al2O3
approach is novel and could be extended to other neutral
Ru-porphyrins, especially in high-yield metalation reactions
where the recovery of unreacted free-base is not essential.
The successful metalation of H2TPP, H2T-pCO2Me-PP,
and H2T-m,m′Me2-PP (unsubstituted, p-, and m-substituted
meso-tetraphenylporphyrin, respectively) strongly implies
that the nonmetalation of H2TMP is associated with the
o-phenyl substituents. To probe whether a steric and/or
electronic effect was involved, metalation of the di-ortho-
substituted porphyrin H2T-o,o′Cl2-PP was chosen because
the electron-withdrawing Cl and electron-donating Me groups
have similar van der Waals radii.60 The attempted metalation
of H2T-o,o′Cl2-PP using 1 was unsuccessful (as for H2TMP),
implying that steric effects are probably more significantsa
common feature in the metalation of porphyrins. Kinetic
studies on formation of first-row transition metal-porphyrin
complexes have established that di-o-substituted meso-
tetraarylporphyrins are the least reactive among various aryl-
substitution patterns, and that electronic factors are of minor
significance. For example, the relative rates of ZnII incor-
poration into substituted-H2TPP follow the order: para- (500)
g di-meta- (183) > ortho- (28) > di-ortho- (1).11c,61 Further,
a study of the p-substituted meso-tetraphenylporphyrins, H2T-
pX-PP (X ) Me, H, F, Cl, Br, CF3, NO2), showed that
electronic effects on the ZnII-metalation rate are generally
negligible, with exceptions (a 5- to 20-fold rate increase)
seen for X ) NH2, OMe, or OH groups that can donate
electron density by resonance into the porphyrin ring.11c The
(steric) “ortho effect” has been extensively studied, and there
is agreement that the rate-limiting step for metalation
involves the formation of a transient “sitting atop” (SAT)
complex. Although the exact nature of this species remains
debatable, the metal is considered to reside on one face of
the porphyrin ring, coordinated to one or two pyrrole
nitrogens; this forces the remaining nitrogens towards the
opposite face, away from the metal, and thus the porphyrin
ring is highly deformed.11c,61,62 This molecular flexibility
of a porphyrin ring, studied by X-ray and theoretical analysis
of diprotonated, metal-free porphyrin species, decreases with
the steric bulk of o-substituents because of their interaction
with the ꢀ-pyrrole hydrogens.63 The findings are consistent
with kinetic data for metal incorporation into porphyrins.11c,61
Our metalation procedure was successful with the mono-
ortho substituted derivative, H2T-oMe-PP. This porphyrin
exists as a mixture of atropisomers (rotational isomers), but
no attempt was made to isolate the isomers, as atropisomer-
ization is likely to occur under the refluxing DMF conditions
of the metalation; Ru(T-oMe-PP)(CO)(H2O) was isolated as
a mixture of atropisomers, in high yield. This finding suggests
that the limitation of the [Ru(DMF)6](OTf)3 method, with
regards to the “ortho effect”, is restricted to di-ortho
substituted meso-tetraarylporphyrins, because of the low
deformability of these porphyrin rings. Nevertheless, the
method is a facile, safe, high-yield process for Ru-metalation
of para-, (di-)meta-, and (mono-)ortho-aryl substituted
porphyrins.
Difficulty in metallating the di-ortho substituted porphy-
rins, H2TMP and H2T-o,o′Cl2-PP, is also reported when using
Ru3(CO)12; harsh conditions using high boiling-point solvents
such as decalin or 1,2-dichlorobenzene are required.6c,18,64
The high temperature likely overcomes the energy barrier
associated with the porphyrin ring deformation. Solvent
mixtures (1:1) of DMF with decalin and with 1,2-dichlo-
robenzene were tried with 1, but no Ru-porphyrin was
observed by UV-vis or TLC; the free-bases were stable
under such conditions, but 1 decomposed to a dark precipi-
tate. Faster metalation is needed, as the actual “active” Ru
species from the triflate precursor (see below) and from the
use of Ru3(CO)12 decompose to metal under the reaction
conditions. Another approach to overcome the “poor de-
formability problem” of di-ortho substituted porphyrins is
modification of the porphyrin ring to give a stable, more
deformed configuration prior to metalation, for example, by
replacing an inner-core hydrogen by Me to yield an N-alkyl-
porphyrin, which after metalation could be dealkylated by
base.65 Indeed, the rate of metalation of N-alkyl-porphyrins,
which do model the distorted porphyrin intermediate is
103-105 times higher than that of the corresponding por-
phyrins.66 However, the attempted metalation of N-MeHTMP
using 1 generated a green mixture, whose UV-vis spectrum
indicated the presence of protonated free-base. N-Methyl-
porphyrins are strong bases67 and the proton source is likely
H2O, possibly activated by coordination to the Ru; the use
(63) Cheng, B.; Munro, O. Q.; Marques, H. M.; Scheidt, W. R. J. Am.
Chem. Soc. 1997, 119, 10732.
(64) Collman, J. P.; Brauman, J. L.; Fitzgerald, J. P.; Hampton, P. D.;
Naruta, Y.; Sparapany, J. W.; Ibers, J. A. J. Am. Chem. Soc. 1988,
110, 3477.
(65) (a) Shears, B.; Hambright, P. Inorg. Nucl. Chem. Lett. 1970, 6, 679.
(b) Lavallee, D. K.; Gebala, A. E. Inorg. Chem. 1974, 13, 2004. (c)
Lavallee, D. K. Inorg. Chem. 1976, 15, 691. (d) Stinson, C.;
Hambright, P. Inorg. Chem. 1976, 15, 3181.
(66) (a) Bain-Ackerman, M. J.; Lavallee, D. K. Inorg. Chem. 1979, 18,
3358. (b) Funahashi, S.; Yamaguchi, Y.; Tanaka, M. Bull. Chem. Soc.
Jpn. 1984, 57, 204. (c) Inamo, M.; Tomita, A.; Inagaki, Y.; Asano,
N.; Suenaga, K.; Tabata, M.; Funahashi, S. Inorg. Chim. Acta 1997,
256, 77.
(60) Huheey, J. E. Inorganic Chemistry, 3rd ed.; Harper & Row: New York,
1983, pp 258-259.
(61) Lavallee, D. K. Coord. Chem. ReV. 1985, 61, 55.
(62) (a) Shen, Y.; Ryde, U. J. Inorg. Biochem. 2004, 98, 878. (b) Inada,
Y.; Sugimoto, Y.; Nakano, Y.; Itoh, Y.; Funahashi, S. Inorg. Chem.
1998, 37, 5519.
(67) Lavallee, D. K. The Chemistry and Biochemistry of N-Substituted
Porphyrins; VCH: New York, 1987, pp 104-106.
Inorganic Chemistry, Vol. 47, No. 17, 2008 7903

Rebouc¸as et al.
of dry DMF was not considered because H2O is needed for
successful metalation, see below.
DMF,11b,74 H2Br8TPP was tested because of its more
accessible synthesis than those of ꢀ-alkyl or ꢀ-aryl meso-
tetraarylporphyrins. The metalation reaction with the oc-
tabromo porphyrin was stopped after 3 h, since UV-vis
analysis then revealed the absence of free-base which had
been converted to Ru(Br8TPP)(CO) or destroyed; the com-
plex was isolated in 14% yield and, although low compared
to that of H2TPP (96%), the result is still conceptually
attractive. A Ru3(CO)12-metalation of H2Br8T-F5-PP, involv-
ing a 50 h reaction in refluxing benzene, has been reported
but no yield was given; longer reaction times led to porphyrin
dehalogenation and decomposition.20f Our attempts to meta-
late H2Br8TPP with Ru3(CO)12 in refluxing decalin yielded
no Ru(Br8TPP)(CO).
Our metalation method was also successful with H2OEP and
H2mesoPIX-DME, both neutral, ꢀ-octaalkylsubstituted porphy-
rins. The isolated Ru(OEP)(CO)(THF) was characterized by
an X-ray structure (see Figure S1 in the Supporting Informa-
tion), which is analogous to that of other Ru(OEP)(CO)(L)
complexes (e.g., L ) H2O68 and various N-donors69) and the
[Ru(T-oNHC(O)C(CF3)(OMe)Ph-PP)(CO)(THF)]4+ structure;70
all the Ru-C bond lengths are in the range 1.78-1.82 Å, and
the Ru-O bond length of 2.241(3) Å in Ru(OEP)(CO)(THF)
is close to those in Ru(OEP)(CO)(H2O) (2.253(2) Å)68 and
[Ru(T-oNHC(O)C(CF3)(OMe)Ph-PP)(CO)(THF)]4+ (2.28(1)
Å).70
The isolated Ru(mesoPIX-DME)(CO)(H2O) complex pro-
vides entry into effective preparation of natural porphyrin
complexes of Ru, of interest in biomimetic systems:1d,j
derivatives of Ru(mesoPIX-DME)(CO) have been used in
the reconstitution of myoglogin1b,e and horseradish
peroxidases.1h Attempts to metalate H2PPIX-DME, the ester
of the heme porphyrin, were unsuccessful, most of the free-
base being decomposed, presumably via some reaction
involving the vinyl groups of H2PPIX-DME.71 Nevertheless,
a small amount of a Ru(mesoPIX-DME)(CO) derivative was
isolated from the product mixture, showing that hydrogena-
tion of the vinyl groups had taken place; the nature of the
reduction is unclear. Literature reports on the metalation of
H2PPIX-DME using Ru3(CO)12 are somewhat contradictory:
one report1h states “the protoporphyrin complex was not
obtained due to the rigorous synthetic conditions” (referring
to refluxing C6H6), while another1j claims to have prepared
Ru(PPIX-DME)(CO) in refluxing toluene. However, the only
characterization given was a νCO IR stretch, presumably that
of a Ru-carbonyl porphyrin, but the nature of the peripheral
substituents is uncertain, particularly in reference to the
integrity of the vinyl groups.
Interest in the chemistry of water-soluble metallopor-
phyrins11c led us to test 1 for metalation of water-soluble
porphyrins. The complex Na4[Ru(T-pSO3-PP)(CO)]· 4H2O,
was isolated in 53% yield, the water-content being supported
by elemental analysis and by thermogravimetric analysis
(TGA), which showed a weight loss corresponding to
3.5H2O. Incorporation of Ru into [H2T-NMe-4PyP]4+ was
demonstrated, but a cationic Ru-porphyrin could not be
isolated pure. The procedure described gave a sample of
[Ru(T-NMe-4PyP)(CO)](OTs)4 · xH2O contaminated with
∼15% of the free-base, as judged by integration of the CH3
1
signals in H NMR spectrum. In the procedure, filtration
through Celite eliminated Ru metal, and polar, unidentified
impurities were removed by percolation through a size-
1
exclusion Sephadex column and a Cl--exchange resin. H
NMR analysis at this stage showed that the tosylate anions
were exchanged, and ESI-MS data indicated that partial
demethylation had occurred; thus, the sample of tetra- and
tricationic derivatives were remethylated with MeOTs to
yield the final mixture of [Ru(T-NMe-4PyP)(CO)]4+ and
[H2T-NMe-4PyP]4+ as tosylate salts, the chlorides being
eliminated as CH3Cl during reaction with the MeOTs.75 Of
note, metalation of [H2T-NMe-4PyP](OTs)4 with MnCl2 in
DMF, also shows instability of the macrocycle.76 Use of
[H2T-NMe-4PyP]Cl4 with 1 gave no metalation, demonstrat-
ing the significant role of the counterion; presumably, the
more strongly coordinating Cl- scavenges the Ru and
precludes metalation. There is a report on synthesis of a
cationic Ru-porphyrin, derived from meso-tetrakis(N-ethyl-
N,N-dimethylanilinium-4-yl)porphyrin, by heating the free-
base porphyrin with RuCl3 in water (pH 5) at 80 °C for 30
min, followed by treatment of the crude product with pyridine
at 80 °C for another 30 min; the product was formulated as
RuII(porp)(py)2, but associated counter-ions for the tetraca-
tionic Ru(porp) moiety were not mentioned, neither was
proof of the assigned oxidation state.77
The new metalation method was tested with fully substi-
tuted (dodecasubstituted) porphyrins, of which ꢀ-octahalo-
geno meso-tetraarylporphyrins have received intense interest
in a quest for robust oxidation catalysts.1m,3o,72 Dodecasub-
stituted porphyrins are highly distorted and, not surprisingly,
incorporate metals 103-105 times faster than planar tetra-
or octasubstituted analogues.73 Although ꢀ-octahalogeno
meso-tetraarylporphyrins are reportedly unstable in refluxing
(68) Kadish, K. M.; Hu, Y.; Mu, X. H. J. Heterocycl. Chem. 1991, 28,
1821.
(69) (a) Funatsu, J.; Kimura, A.; Imamura, T.; Ichimura, A.; Saski, Y. Inorg.
Chem. 1997, 36, 1625. (b) Lee, J.; Twamley, B.; Richter-Addo, G. B.
Chem. Commun. 2002, 380.
(70) Le Maux, P.; Bahri, H.; Simonneaux, G. Inorg. Chem. 1995, 34, 4691.
(71) Fuhrhop, J.-H.; Smith, K. M. In Porphyrins and Metalloporphyrins;
Smith, K. M., Ed.; Elsevier: Amsterdam, 1975, Chapter 19.
(72) (a) Senge, M. O. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: New York, 2000; Vol. 1,
Chapter 6. (b) Meunier, B.; Robert, A.; Pratviel, G.; Bernadou, J. In
The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R.,
Eds.; Academic Press: New York, 2000, Vol. 4, Chapter 31. (c) Ou,
Z.; Shao, J.; D’Souza, F.; Tagliatesta, P.; Kadish, K. M. J. Porphyrins
Phthalocyanines 2004, 8, 201.
The metalation procedures using [Ru(DMF)6](OTf)3 (or
Ru3(CO)12) are likely governed by a balance between
(74) Rebouc¸as, J. S.; de Carvalho, M. E. M. D.; Idemori, Y. M. J.
Porphyrins Phtalocyanines 2002, 6, 50.
(75) Weaver, W. M.; Hutchison, J. D. J. Am. Chem. Soc. 1964, 86, 261.
(76) Batinic´-Haberle, I.; Benov, L.; Spasojevic´, I.; Fridovich, I. J. Biol.
Chem. 1998, 273, 24521.
(73) (a) Takeda, J.; Ohya, T.; Sato, M. Inorg. Chem. 1992, 31, 2877. (b)
Sutter, T. P. G.; Hambright, P. J. Coord. Chem. 1993, 30, 317. (c)
Bhyrappa, P.; Nethaji, M.; Krishnan, V. Chem. Lett. 1993, 869.
(77) Szulbinski, W.; Lapkowski, M. Inorg. Chim. Acta 1986, 123, 127.
7904 Inorganic Chemistry, Vol. 47, No. 17, 2008

Ruthenium-Metalation of Porphyrins and Schiff-Bases
Figure 3. UV-vis spectral changes (in HOAc) over 32 h during metalation
of H2TPP with [Ru(DMF)6](OTf)3 (1); the 480-730 nm region is expanded
5 times for clarity.
Figure 4. Metalation of H2TPP with [Ru(DMF)6](OTf)3 (1) under
conditions given in Expts. A, B, and C (see text); arrows indicate addition
of water (#) or H2TPP (×).
antagonistic processes: decomposition of free-base porphyrin
and Ru species (into metal) and insertion of the Ru into the
porphyrin.
of H2TPP was calculated and plotted as a function of time
(Figure 4.) The trace is not that of a simple kinetic profile.
During the first 2 h, Ru insertion is slow, possibly involving
an induction period after which the metalation accelerated,
but leveled off at 8 h; CO2 production was evident throughout
the 8 h. From 8 to 10 h, both metalation and Ru reduction
slowed down considerably, as indicated by UV-vis analysis
and the lack of BaCO3 formation, respectively, although
almost half of the initial free-base was still present and there
was no sign of “over-reduction” of Ru to the metal. On
addition of 10 µL (0.56 mmol) of deoxygenated H2O, both
metalation and CO2 production resumed, establishing that
unreacted Ru was present and, most importantly, that
metalation is dependent on RuIII reduction. After 32 h, Ru
metal had deposited, while UV-vis analysis indicated ∼97%
conversion of H2TPP, and after workup the isolated yield
of Ru(TPP)(CO)(H2O) was 96%. The total collected BaCO3
was equivalent to 0.124 mmol of e- (eq 1b), more than
required to reduce the RuIII to RuII (0.097 mmol). Fixation
of CO2 as BaCO3 is not quantitative because some absorbed
CO2 may be present as bicarbonate that is not precipitated
by Ba2+.48 Any “lost” CO2 and the excess 0.027 mmol of
e- presumably account for the observed Ru over-reduction,
but measurement of the amount of Ru metal on the vessel
walls was impractical.
Mechanistic Aspects. The overall metalation involves at
least three distinct steps: reduction of RuIII to RuII, CO
abstraction from the DMF, and Ru incorporation into the
macrocycle; the finding that metalation does not occur under
air suggests that reduction of Ru is a prerequisite step. Studies
on metalation of H2TPP (Mechanistic Studies, Expts. A-C)
provided a reproducible, semiquantitative analysis of the
progress of the process. Figure 3 shows typical UV-vis
changes during the metalation, the spectra being recorded
in glacial HOAc for convenient resolution of the bands of
the diprotonated free-base and the metalation product (see
General Considerations, (b)). Whether there are real isos-
bestic points is unclear because of the reduction of the
reactant volume with time (∼20% over 24 h); any third
species such as a SAT intermediate, which might be
decomposed in HOAc to diprotonated species, is considered
undetectable. Nevertheless, with the protocol used, some
fundamental questions about the [Ru(DMF)6](OTf)3 method
can be addressed.
Carbon monoxide, formed from DMF (eq 1a), can reduce
metal ions in solution (eq 1b),
DMF f CO + NHMe2
(1a)
In Expt. B (again using 0.097 mmol RuIII), 200 µL (11.1
mmol) of deoxygenated H2O was added prior to the addition
of 1. The reaction now proceeded without an induction period
and was complete in 2.5 h (Figure 4), accompanied by
production of CO2 and Ru metal; the H2TPP conversion of
∼90% realized a yield of only ∼70% of isolated
Ru(TPP)(CO)(H2O), the fate of the ∼20% H2TPP being
unknown. This experiment confirmed the role of adventitious
water; in freshly opened DMF bottles, [H2O] is ∼10-3 mol
L-1, of the same order as concentrations of H2TPP and 1.
The water in commercial DMF likely provides the driving
force (or even limits the yields) for the Ru-metalation and
provides a further example of the role of trace water in
organic and organometallic transformations.80
CO + H2O f CO2+2H++2e-
(1b)
including reduction of Ru(III) to Ru(0),78 and is considered
to be the reductant in the metalation process: CO2 was
evolved as demonstrated by its conversion to BaCO3 (reliable
18th century chemistry!79).Indeed, CO2 was detected in
successful and unsuccessful metalations, as well as in the
absence of porphyrin, implying that the Ru reduction is a
porphyrin-independent process. These data do not rule out
CO-reduction of a RuIII-porphyrin to a RuII analogue, but
other findings (see below) suggest that RuIII is reduced prior
to metalation. Figure 3 shows data for Expt. A under the
standard metalation conditions, from which the consumption
(78) (a) James, B. R.; Rempel, G. L.; Teo, W. K. Inorg. Syn. 1976, 16, 45.
(b) Sheldon, R. A. Chemicals from Synthesis Gas; Reidel Publishing
Co.: Dordrecht, 1983, p 32.
(80) (a) Ribe, S.; Wipf, P. Chem. Commun. 2001, 299. (b) Marcazzan, P.;
Abu-Gnim, C.; Seneviratne, K. N.; James, B. R. Inorg. Chem. 2004,
43, 4820.
(79) Ball, P. The Ingredients; Oxford University Press: New York, 2002;
p 33.
Inorganic Chemistry, Vol. 47, No. 17, 2008 7905

Rebouc¸as et al.
In Expt. C, H2TPP was added after [Ru(DMF)6](OTf)3 had
been in refluxing DMF for 2 h (Figure 4). During this time,
formation of BaCO3 showed reduction of Ru and, as
anticipated, metalation was fast upon addition of H2TPP. The
induction period seen in Expt. A is indeed associated with
the reduction of RuIII to, most likely, a RuII species (eq 2),
(vs RuII); nonmetalation was noted when anhydrous RhCl3
was used,88 and the water almost certainly reduces (cf. eqs
1b and 2) substitution-inert RhIII to a labile RhI intermedi-
ate.89 Similarly, CuII metalation of porphyrins in water is
accelerated by the presence of reducing agents that generate
in situ CuI ions.90 The reported synthesis of [Rh(TPP)-
(NHMe2)2]Cl via metalation with [Rh(CO)2Cl]2 in refluxing
DMF requires air, presumably for reoxidation of a putative
RhI-porphyrin intermediate.91 Details of the Rh systems
remain uncertain since substitution-inert metal ions become
less inert through pronounced cis-effects seen in metallopor-
phyrins.87,92 The use of metal salts (usually chlorides) for
metalation of porphyrins in refluxing DMF is well estab-
lished,93 and mechanistic aspects revealed in our studies with
[Ru(DMF)6](OTf)3 are likely quite general.
2“[RuIII](OTf)3” + CO + H2O f 2“[RuII](OTf)2” + CO2 +
2HOTf (2)
which is then incorporated into the porphyrin ring; no
porphyrin species participate in the reduction process. Con-
sidering the affinity of RuII compounds for CO,19,81 and the
continuous production of CO from thermal decomposition
of DMF,82 this intermediate is probably a RuII-CO deriva-
tive. Of note, RuCl3 in refluxing DMF yields several Ru
carbonyl species, whose nature depends on the reaction
conditions and workup procedure.83 DMF decomposition can
also be catalyzed by acids,84 and so complex 1, Ru-porphyrin,
or any other Lewis acid Ru-species, may accelerate the
reaction. Indeed, RuII-porphyrins under appropriate condi-
tions are active catalysts for decarbonylation of aldehydes85
and DMF itself,86 while reaction of 1 with 2-methylimidazole
in refluxing MeOH generates [Ru(CO)(DMF)(2-MeIm)4]-
(OTf)2 via decarbonylation of coordinated DMF.35a Less
clear is whether the CO of the Ru(porp)(CO) products is
derived from an intermediate RuII-carbonyl species, or from
a putative RuII(porp)(DMF)2 intermediate; abstraction of an
acetyl group from coordinated N,N-dimethylacetamide has
been observed in a Rh-porphyrin system.87 For each equiva-
lent of CO produced, one equivalent of NHMe2 is also
formed (eq. 1a),and this may be responsible for neutralization
of the acid resulting from the reduction of RuIII and from
metalation. The overall reaction can be summarized in the
speculative, stoichiometric eq 3.
Ru-Metalation of Schiff-Bases. Application of the
[Ru(DMF)6](OTf)3 method for metalation of Schiff-bases
revealed a key difference from the porphyrin systems in that
CO-free, RuIII complexes were isolated. Metalation of
t
t
H2 Bu4Salen and H2 Bu4Salophen, as monitored by TLC, was
complete in 3 h, the conversion of free-base being ac-
companied by the appearance of dark blue or dark green
species, respectively. The complexes were isolated by
chromatography (SiO2, 10:1 CH2Cl2/EtOH), and character-
ized as [Ru(Schiff-base)(DMF)2]OTf species by elemental
analysis, UV-vis, IR, conductivity, and MS, but attempts
at crystallization were unsuccessful.
The observed single νCO band at 1637/1638 cm-1 (vs 1673
cm-1 for free DMF) is consistent with the presence of trans-
DMF ligands and is in accordance with data for other RuIII-
DMF complexes.94 The tetradentate [N2O2] Schiff-base pre-
sumably occupies the equatorial plane, although there are
examples where the Schiff-base ligand is nonplanar.44b The
ionic character of the triflate was demonstrated by conductivity
data (in DMF), which are in the range for 1:1 electrolytes,95
and by the IR data (νSO and νCF at 1267/1268 and 1031 cm-1),
2H2(porp) + 2“[RuIII](OTf)3” + 6DMF +
H2O f 2Ru(porp)(CO) + CO2+3CO + 6[NH2Me2]OTf(3)
3
3
which agree with literature values for ionic OTf- rather than
oxygen-coordinated triflate.96 The UV-vis spectra of the two
complexes, presented in Supporting Information, Figure S2, are
similar to those of other RuIII-compounds such as
Ru(Salen)(PPh3)Cl;27b the visible region is dominated by a
broad, ligand-to-metal charge-transfer band at 700-900 nm,
which is shifted to ∼500 nm in RuII derivatives.8f (Of note,
UV-vis spectra of RuIII-porphyrins also show a characteristic,
broad band in the 700-900 region1g).
We are unaware of similar systematic studies on porphyrin
metalation using Ru3(CO)12.
Worth noting is that metalation of a free-base porphyrin
with hydrated RhCl3 in refluxing DMF generates
[RhIII(porp)(NHMe2)2]Cl,88 bonding of the amine fragment
being preferred over CO for the higher oxidation state metal
(81) Barley, M. H.; Dolphin, D.; James, B. R. J. Chem. Soc., Chem.
Commun. 1984, 1499.
(89) Thackray, D. C.; Ariel, S.; Leung, T. W.; Menon, K.; James, B. R.;
Trotter, J. Can. J. Chem. 1986, 64, 2440.
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267. (b) Serp, P.; Hernandez, M.; Richard, B.; Kalck, P. Eur. J. Inorg.
Chem. 2001, 2327.
(90) Tabata, M.; Mabasaki, M. Inorg. Chem. 1992, 31, 5268.
(91) Fleischer, E. B.; Dixon, F. L.; Florian, R. Inorg. Nucl. Chem. Lett.
1973, 9, 1303.
(84) Perrin; D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
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(85) Domazetis, G.; Tarpey, B.; Dolphin, D.; James, B. R. J. Chem. Soc.,
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7906 Inorganic Chemistry, Vol. 47, No. 17, 2008

Ruthenium-Metalation of Porphyrins and Schiff-Bases
Work-up of the Ru-complexes, at the stage when TLC
analysis of the crude product mixtures showed complete
consumption of free-base, gave only ∼50% isolated yields.
1H NMR analysis of the colorless fraction revealed, as well
as DMF, the presence of tert-butylsalicylaldehyde as shown
by comparison of its NMR spectrum with that of an
authentic, commercial sample; hydrolysis of a Schiff-base
to its constituent aldehyde and amine, which is susceptible
to catalysis by transition metals, is well-known.80b,97 Thus,
water plays a positive role in the metalation of porphyrins
(previous Sections), and a negative role in the Schiff-base
systems. Pure complexes were not obtained with the non-
tert-butyl- substituted Schiff-bases, H2(Salen), H2Salophen,
and H2Naphthophen; MS data of crude product mixtures
showed that metalation did occur but chromatography and
crystallization procedures were unsuccessful.
the solvent, gives RuII(porp)(CO) complexes in yields
comparable to, or higher than, those obtained via the
established method using thermal oxidative-decarbonylation
of Ru3(CO)12. No Ru-chlorin impurity is detected when using
the [Ru(DMF)6](OTf)3 method, thus eliminating a postmeta-
lation benzoquinone oxidative step typically necessary when
using the Ru3(CO)12 method. Limitations of this new method
are associated with di-ortho substituted meso-tetraarylpor-
phyrins, a porphyrin with an N-Me substituent, and porphy-
rins that are unstable toward refluxing DMF. Comparisons
between apparently dissimilar metalation of porphyrins with
Ru, Rh, and Cu species in DMF suggest that the underlying
mechanisms in these systems are closely related. The
methodology was also extended to metalation of tetradentate
Schiff-bases to yield chloride-free Ru complexes of general
formula [RuIII(N2O2-Schiff base)(DMF)2]OTf.
Acknowledgment. We thank the Natural Sciences and
Engineering Research Council and Medical Research Council
of Canada for financial support, and Colonial Metals Inc.
for the loan of RuCl3 · xH2O. J.S.R. acknowledges Fundac¸a˜o
CAPES (The Ministry of Education of Brazil) and The
University of British Columbia for graduate scholarships.
Concluding Remarks
A new, convenient and efficient methodology for insertion
of Ru into a range of free-base porphyrins is described using
[Ru(DMF)6](OTf)3, which is made via a simple literature
procedure. The in situ reduction of RuIII to RuII in refluxing
“wet” DMF under Ar, coupled with CO abstraction from
Supporting Information Available: ORTEP diagram (Figure
S1) and cif file for Ru(OEP)(CO)(THF); UV-vis spectra in DMF
of [Ru(tBu4Salen)(DMF)2]OTf and [Ru(tBu4Salophen)(DMF)2]OTf
(Figure S2). This material is available free of charge via the Internet
at http://pubs.acs.org.
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