meso-porphyrinylphosphine oxides: Mono- and bidentate ligands for supramolecular chemistry and the crystal structures of monomeric {[10,20-diphenylporphyrinatonickel(II)-5,15-diyl]-bis-[P(O)Ph2] and polymeric self-coordinated {[10,20-diphenylpo

Article abstract of DOI:10.1021/ic060372u

A series of porphyrins substituted in one or two meso positions by diphenylphosphine oxide groups has been prepared by the palladium-catalyzed reaction of diphenylphosphine or its oxide with the corresponding bromoporphyrins. Compounds {MDPP-[P(O)Ph₂

Full text of DOI:10.1021/ic060372u

Inorg. Chem. 2006, 45, 6479−6489
meso-Porphyrinylphosphine Oxides: Mono- and Bidentate Ligands for
Supramolecular Chemistry and the Crystal Structures of Monomeric
[10,20-Diphenylporphyrinatonickel(II)-5,15-diyl]-bis-[P(O)Ph2] and
Polymeric Self-Coordinated
[10,20-Diphenylporphyrinatozinc(II)-5,15-diyl]-bis-[P(O)Ph2]
{
{
}
Farzad Atefi,† John C. McMurtrie,† Peter Turner,‡ Martin Duriska,§ and Dennis P. Arnold*,†
Synthesis and Molecular Recognition Program, School of Physical and Chemical Sciences,
Queensland UniVersity of Technology, GPO Box 2434, Brisbane 4001, Australia, Crystal Structure
Analysis Facility, School of Chemistry, UniVersity of Sydney, NSW 2006, Australia and School of
Chemistry, Monash UniVersity, Victoria 3800, Australia
Received March 6, 2006
A series of porphyrins substituted in one or two meso positions by diphenylphosphine oxide groups has been
prepared by the palladium-catalyzed reaction of diphenylphosphine or its oxide with the corresponding
bromoporphyrins. Compounds
were isolated in yields of 60
phosphination, and reductive elimination steps, as the stoichiometric reaction of
DPP)(dppe)] (H2DPP 5,15-diphenylporphyrin; dppe 1,2-bis(diphenylphosphino)ethane) with diphenylphosphine
oxide also results in the desired mono-porphyrinylphosphine oxide [H2DPP P(O)Ph2]. Attempts to isolate the tertiary
phosphines failed due to their extreme air-sensitivity. Variable-temperature 1H NMR studies of [H2DPP
P(O)Ph2]
{
MDPP
95%. The reaction is believed to proceed via the conventional oxidative addition,
1-palladio(II) porphyrin [PdBr(H2-
−[P(O)Ph2]n} (M ) H2, Ni, Zn; H2DPP ) 5,15-diphenylporphyrin; n ) 1, 2)
−
η
)
)
−
−
revealed an intrinsic lack of symmetry, while fluorescence spectroscopy showed that the phosphine oxide group
does not behave as a “heavy atom” quencher. The electron-withdrawing effect of the phosphine oxide group was
confirmed by voltammetry. The ligands were characterized by multinuclear NMR and UV
well as mass spectrometry. Single-crystal X-ray crystallography showed that the bis(phosphine oxide) nickel(II)
complex [NiDPP [P(O)Ph2]2 is monomeric in the solid state, with a ruffled porphyrin core and the two P
−visible spectroscopy, as
{
−
}
dO
fragments on the same side of the average plane of the molecule. On the other hand, the corresponding zinc(II)
complex formed infinite chains through coordination of one Ph2PO substituent to the neighboring zinc porphyrin
through an almost linear PdO‚‚‚Zn unit, leaving the other Ph2PO group facing into a parallel channel filled with
disordered water molecules. These new phosphine oxides are attractive ligands for supramolecular porphyrin
chemistry.
Introduction
carbon framework of porphyrinoid macrocycles has almost
exclusively been limited to nitrogen, oxygen, sulfur, and the
halides.2 Boron porphyrins have also been isolated in the
past decade3 and are now used as synthons in transition-
Due to their central role in the photosynthetic process of
plants and bacteria, porphyrins have attracted the attention
of scientists from various backgrounds.1 Although many
synthetic challenges have been overcome in the past decade,
the introduction of heteroatoms directly attached to the
(1) (a) The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard,
R., Eds.; Academic Press: New York, 2000; Vol. 1-10. (b) The
Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.;
Academic Press: New York, 2004; Vol. 11-20.
(2) Vicente, M. G. H. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: San Diego, 2000; Vol. 1,
pp 149-199.
(3) Hyslop, A. G.; Kellett, M. A.; Iovine, P. M.; Therien, M. J. J. Am.
Chem. Soc. 1998, 120, 12676-12677.
* To whom correspondence should be addressed. Email: d.arnold@
qut.edu.au.
† Queensland University of Technology.
‡ University of Sydney.
§ Monash University.
10.1021/ic060372u CCC: $33.50
Published on Web 07/14/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 16, 2006 6479

Atefi et al.
metal-catalyzed reactions. Just recently, a method for highly
regioselective â-borylation of disubstituted porphyrins has
been introduced.4 The formation of porphyrin mercurials was
reported more than 20 years ago,5 and these compounds were
recently rediscovered by our group as transmetallating
agents.6 One isolated example of a porphyrinyl arsonium salt
can also be found in the literature,7 as well as a meso
substituted tellurioporphyrin which was observed as an
intermediate in the formation of a doubly directly linked
porphyrin dimer.8 The only examples of compounds with
transition metal fragments directly attached to porphyrins
have been isolated by our group.9
Phosphine oxides are well-established ligands for a variety
of purposes10 and are, for example, an integral part in the
removal of radioactive waste from solutions.11 Although there
has been one report where a phosphine oxide has been
directly attached to a phthalocyanine,12 no such examples
exist for porphyrins. The formation of a phosphine oxide
attached to the meso position of an octaethylporphyrin via a
methylene spacer was observed by us during an attempt to
obtain an ylide from a porphyrinylmethylphosphonium
iodide,13 while a Japanese group14 reported a phosphine oxide
attached to a porphyrin via a biphenyl spacer group. Few
examples of phosphines attached to the meso position of
porphyrinyl macrocycles but separated by phenyl spacers
have been reported in the literature, with a meso-tetrakis[4-
(diphenylphosphino)phenyl]porphyrin being the first.15 The
authors described the extremely fast autoxidation of this
compound and therefore reported the crystal structure of its
tetraoxide. However, under strict exclusion of oxygen, a
cubelike octakis(phosphonium salt) was obtained directly
from the porphyrinylphosphine. In a second example of this
class, the phosphine is separated from the porphyrin mac-
rocycle by an alkynyl-phenyl spacer.16a Again, the authors
report the phosphine to be very air-sensitive. Consequently,
the product was protected in situ as the borane complex. The
formation of porphyrin dimers, trimers, and tetramers with
Ru(II)16b-d and Rh(III) porphyrins,16e,f as well as the forma-
tion of primary porphyrinylphosphines,16g have been reported
by the same group. The most recent example of a porphy-
rinylphosphine described in the literature is a bis-phosphine
in which biphenyl spacers separate the phosphine groups
from the carbon backbone of the macrocycle.17 In this case,
the authors do not mention any complications due to
oxidation processes. However, the product was isolated via
a phosphine sulfide intermediate and the crystal structure of
this sulfide was reported, rather than that of the phosphine
itself. Thus, the air sensitivity of this compound seems to
be self-evident. The formation of a tris(zinc(II) porphyrin)-
phosphite ligand has also been reported recently.18 Interest-
ingly, the authors report that the phosphorus donor atom of
this ligand does not coordinate to zinc(II) porphyrins and is
therefore accessible for selective coordination, in this case
to a Rh(I) catalyst.
Until now, the only examples of phosphorus atoms directly
attached to the carbon framework of porphyrinoids remain
phosphonium salts. A phthalocyanine-phosphonium salt has
been obtained with a modest yield of 15% via a palladium-
catalyzed reaction. Under the same reaction conditions, a
bisphthalocyanine-phosphonium salt was obtainable in 50%
yield and the authors could even successfully isolate a
trisphthalocyanine-phosphonium salt with a modest yield
of 9%.19 Smith and co-workers reported the only example
of a porphyrin-phosphonium salt in which the phosphorus
atom is directly bonded to the meso position of the
macrocycle,7 while Shine’s group reported under similar
conditions the formation of a â-bonded phosphonium salt.20
In both cases, the porphyrin cation radical intermediate was
obtained chemically. A French group generated their por-
phyrin cation radicals electrochemically to obtain a phos-
phonium salt, in which the phosphorus is also â-bonded to
the macrocycle.21a The same group reported under similar
(4) Hata, H.; Shinokubo, H.; Osuka, A. J. Am. Chem. Soc. 2005, 127,
8264-8265.
(5) Smith, K. M.; Langry, K. C. J. Chem. Soc., Chem. Commun. 1980,
217-218.
(6) Kato, A.; Arnold, D. P.; Miyasaka, H.; Yamashita, M.; Sugiura, K.-i.
unpublished results.
(7) Smith, K. M.; Barnett, G. H.; Evans, B.; Martynenko, Z. J. Am. Chem.
Soc. 1979, 101, 5953-5961.
(8) Sugiura, K.-i.; Matsumoto, T.; Ohkouchi, S.; Naitoh, Y.; Kawai, T.;
Takai, Y.; Ushiroda, K.; Sakata, Y. J. Chem. Soc., Chem. Commun.
1999, 1957-1958.
(9) (a) Arnold, D. P.; Sakata, Y.; Sugiura, K.-i.; Worthington, E. I. J.
Chem. Soc., Chem. Commun. 1998, 2331-2332. (b) Arnold, D. P.;
Healy, P. C.; Hodgson, M. J.; Williams, M. L. J. Organomet. Chem.
2000, 607; 41-50. (c) Hodgson, M. J.; Healy, P. C.; Williams, M.
L.; Arnold, D. P. J. Chem. Soc., Dalton Trans. 2002, 4497-4504. (d)
Hartnell, R. D.; Arnold, D. P. Organometallics 2004, 23, 391-399.
(e) Hartnell, R. D.; Arnold, D. P. Eur. J. Inorg. Chem. 2004, 1262-
1269. (f) Hartnell, R. D.; Edwards, A. J.; Arnold, D. P. J. Porphyrins
Phthalocyanines 2002, 6, 695-707.
(10) See for example: (a) Karayannis, N. M.; Mikulski, C. M.; Pytlewski,
L. L. Inorg. Chim. Acta, ReV. 1971, 5, 69-105. (b) Sterenberg, B. T.;
Scoles, L.; Carty, A. J. Coord. Chem. ReV. 2002, 231, 183-197.
(11) Arnaud-Neu, F.; Browne, J. K.; Byrne, D.; Marrs, D. J.; McKervey,
M. A.; O’Hagan, P.; Schwing-Weill, M. J.; Walker, A. Chem.-Eur.
J. 1999, 5, 175-186.
(12) Ma¨rkl, G.; Gschwendner, K.; Roetzer, I.; Kreitmeier, P. HelV. Chim.
Acta 2004, 87, 825-844.
(13) Yashunsky, D. V.; Ponomarev, G. V.; Arnold, D. P. Tetrahedron Lett.
1996, 37, 7147-7150.
(16) (a) Darling, S. L.; Stulz, E.; Feeder, N.; Bampos, N.; Sanders, J. K.
M. New J. Chem. 2000, 24, 261-264. (b) Stulz, E.; Ng, Y.-F.; Scott,
S. M.; Sanders, J. K. M. J. Chem. Soc., Chem. Commun. 2002, 524-
525. (c) Stulz, E.; Maue, M.; Feeder, N.; Teat Simon, J.; Ng, Y.-F.;
Bond Andrew, D.; Darling Scott, L.; Sanders, J. K. M. Inorg. Chem.
2002, 41, 5255-5268. (d) Stulz, E.; Sanders, J. K. M.; Montalti, M.;
Prodi, L.; Zaccheroni, N.; Fabrizi de Biani, F.; Grigiotti, E.; Zanello,
P. Inorg. Chem. 2002, 41, 5269-5275. (e) Stulz, E.; Scott, S. M.;
Ng, Y.-F.; Bond, A. D.; Teat, S. J.; Darling, S. L.; Feeder, N.; Sanders,
J. K. M. Inorg. Chem. 2003, 42, 6564-6574. (f) Stulz, E.; Scott, S.
M.; Bond, A. D.; Otto, S.; Sanders, J. K. M. Inorg. Chem. 2003, 42,
3086-3096. (g) Stulz, E.; Maue, M.; Scott, S. M.; Mann, B. E.;
Sanders, J. K. M. New J. Chem. 2004, 28, 1066-1072.
(17) Saito, M.; Nishibayashi, Y.; Uemura, S. Organometallics 2004, 23,
4012-4017.
(18) Slagt, V. F.; van Leeuwen, P. W. N. M.; Reek, J. N. H. Angew. Chem.,
Int. Ed. 2003, 42, 5619-5623.
(19) De la Torre, G.; Gouloumis, A.; Vazquez, P.; Torres, T. Angew. Chem.,
Int. Ed. 2001, 40, 2895-2898.
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4075.
(14) Sawamura, M.; Nakamura, E. In 74th Annual Meeting of the Chemical
Society of Japan; Chemical Society of Japan: Kyoto, 1998; p 4A315.
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Ed. Engl. 1995, 34, 2230-2234.
(21) (a) Ruhlmann, L.; Giraudeau, A. J. Chem. Soc., Chem. Commun. 1996,
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Eur. J. 2003, 9, 5085-5096.
6480 Inorganic Chemistry, Vol. 45, No. 16, 2006

meso-Porphyrinylphosphine Oxides
Merck silica gel (230-400 mesh). NMR spectra were recorded on
reaction conditions the formation of porphyrin dimers and
trimers linked with diphosphonium and triphosphonium
bridges, respectively.21b,c
a Bruker Avance 400 MHz instrument with CHCl3 as internal
1
standard at 7.26 ppm for H spectra and 85% aqueous H3PO4 as
external standard for proton-decoupled 31P spectra. Quantitative UV/
vis spectra were recorded on a Cary 3 spectrometer. Fluorescence
spectra were recorded in dichloromethane solutions on a Varian
Cary Eclipse fluorescence spectrophotometer equipped with a
standard multicell Peltier thermostated sample holder. IR spectra
were recorded on a Nicolet 870 Nexus Fourier transform infrared
spectrometer equipped with a DTGS TEC detector and an ATR
objective. High-accuracy electrospray ionization (ESI) mass spectra
were recorded on a Bruker BioApex 47e FTMS fitted with an
Analytica electrospray source. Dichloromethane was used as a
solvent, and the samples were diluted either with dichloromethane/
methanol or just methanol. The samples were introduced into the
source by direct infusion (syringe pump) at 60 µL/h with a capillary
voltage of 80 V. Sodium iodide clusters were used as internal
standard for the calibration of the instrument. Laser desorption/
ionization (LDI) MS analysis was performed with an Applied
Biosystems Voyager-DE STR BioSpectrometry workstation. The
instrument was operated in positive polarity in reflecton mode for
analysis. Sample was spotted on a stainless steel sample plate and
allowed to air-dry. Data from 500 laser shots (337 nm nitrogen
laser) were collected, signal-averaged, and processed with the
instrument manufacturer’s Data Explorer software. Isotopic model-
ing was calculated by MassLynx V3.5 software by Micromass
Limited. Elemental analyses were carried out by the Microanalytical
Service, The University of Queensland.
From past reports, it seems evident that a directly linked
porphyrinylphosphine would be prone to autoxidation and
the isolation of such a compound would be at the best very
problematic. Porphyrinylphosphine oxides on the other hand
would not only be possible entry points for phosphines,22
but they also could themselves be very interesting new
building blocks for multi-porphyrin arrays, supramolecular
systems that could give new insights into the photosynthetic
reaction center.23 Moreover, porphyrinylphosphine oxides are
also interesting targets as ligands in other fields of coordina-
tion and organometallic chemistry. Bidentate phosphine
oxides especially have undergone a renaissance in recent
years due to the possibility of generating polymeric materials
with interesting geometrical and physical properties.24 We
report here both stoichiometric and catalytic formation in
excellent yields of a suite of porphyrin-based mono- and bis-
phosphine oxides, as well as their physical and structural
features, which clearly indicate the potential of these
substances as building blocks for multi-porphyrin arrays.
Experimental Section
General Procedures and Instrumentation. All synthetic reac-
tions involving zerovalent palladium metal reagents or phosphines
were carried out in an atmosphere of high-purity argon using
standard Schlenk techniques.25 Chemical reagents and ligands were
of laboratory reagent (LR) or analytical reagent (AR) grade, received
from Sigma-Aldrich, and used without further purification. Solvents
used were AR grade where available. Solvents used in palladium-
catalyzed reactions were degassed by freeze/thawing three times
prior to their use. Toluene and diethyl ether were stored over sodium
wire. CH2Cl2 and CHCl3 were stored over anhydrous sodium
carbonate. Tetrahydrofuran (THF) was distilled immediately before
use from a dark blue sodium/benzophenone solution under an
atmosphere of high-purity argon. H2DPP,26 haloporphyrins 427 and
7,28 meso-palladioporphyrin 5,9a and palladium catalyst 1829 were
synthesized according to the literature. Metals were inserted into
the porphyrins following established procedures.30 Recrystallization
from two solvents was accomplished by dissolving the product in
a minimum amount of the first solvent and carefully layering the
solution with a 10-fold excess of the second solvent. Analytical
TLC was performed using aluminum-backed Merck silica gel 60
F254 plates, and column chromatography was carried out using
Diphenyl(10,20-diphenylporphyrin-5-yl)phosphine Oxide (6)
from 5. Porphyrin 5 (50 mg, 0.048 mmol), cesium carbonate (16
mg, 0.049 mmol), and 17 (10 mg, 0.049 mmol) were dried in a
Schlenk flask under high vacuum. After the vessel was flushed three
times with argon, toluene (7.5 mL) was added with a syringe and
the reaction mixture was stirred at 84 °C under an atmosphere of
argon for 4 h. The reaction mixture was loaded onto a column
packed with silica gel in toluene. Palladium complexes and excess
17 were eluted with toluene before the solvent was changed to
toluene/methanol (98:2). A dark red band was collected, and the
solvents were removed in vacuo. Product 6 was obtained as dark
purple crystals (27 mg, 0.041 mmol, 85%) after recrystallization
from toluene/pentane. 1H NMR (400 MHz, CDCl3, 25 °C): δ 10.23
(s, 1H, meso-H), 9.55 (br d, 2H, â-H), 9.28, 8.86, 8.65 (d, 3J(H,H)
) 4.6 Hz, each 2H, â-H), 8.15-8.12 (m, 4H, o-H 10,20-phenyl),
7.90-7.85 (m, 4H, o-H PPh2), 7.77-7.70 (m, 6H, m,p-H 10,20-
phenyl), 7.53-7.49 (m, 2H, p-H PPh2), 7.42-7.38 (m, 4H, m-H
PPh2), -2.54 (br s, 2H, NH). 31P NMR (162 MHz, CDCl3, 25 °C):
δ 34.2. IR (ATR): ν˜ [cm-1] 1183 (PdO). UV/vis (CH2Cl2): λmax
[nm], (ꢀ [103 mol-1 dm3 cm-1]) 416 (367), 514 (17.4), 548 (6.3),
586 (6.5), 639 (3.5). High-resolution ESI MS: m/z calcd for
[C44H31N4OP + H]+: 663.2314; found: 663.2305. Anal. Calcd for
C44H31N4OP: C 79.74, H 4.71, N 8.45; found: C 79.89, H 4.81,
N 8.19.
(22) Engel, R. In Handbook of Organophosphorus Chemistry; Engel, R.,
Ed.; M. Dekker: New York, 1992; pp 193-239.
(23) Burrell, A. K.; Officer, D. L.; Plieger, P. G.; Reid, D. C. W. Chem.
ReV. 2001, 101, 2751-2796.
(24) (a) Kim, S.-W.; Kim, S.; Tracy, J. B.; Jasanoff, A.; Bawendi, M. G.
J. Am. Chem. Soc. 2005, 127, 4556-4557. (b) Spichal, Z.; Necas,
M.; Pinkas, J. Inorg. Chem. 2005, 44, 2074-2080.
(25) Shriver, D. F.; Drezdzon, M. A. The manipulation of air-sensitiVe
compounds; Wiley: New York, 1986.
General Procedure for Palladium-Catalyzed Reactions. A
Schlenk flask was charged with the porphyrin, cesium carbonate,
and the catalyst 18. Phosphine oxide 17 (105 mg, 0.51 mmol) was
dissolved in toluene (50 mL) in a second Schlenk vessel to make
up a stock solution. The appropriate amount of this solution was
added to the porphyrin vessel with a syringe, and the reaction
mixture was stirred at 84 °C. The mixture was loaded onto a column
packed with silica gel in toluene. Palladium complexes and excess
17 were eluted before the solvent was changed to toluene/methanol.
The major red band was collected, and the residue recrystallized
as specified below.
(26) Laha, J. K.; Dhanalekshmi, S.; Taniguchi, M.; Ambroise, A.; Lindsey,
J. S. Org. Process Res. DeV. 2003, 7, 799-812.
(27) Shanmugathasan, S.; Johnson, C. K.; Edwards, C.; Matthews, E. K.;
Dolphin, D.; Boyle, R. W. J. Porphyrins Phthalocyanines 2000, 4,
228-232.
(28) DiMagno, S. G.; Lin, V. S. Y.; Therien, M. J. J. Org. Chem. 1993,
58, 5983-5993.
(29) Coulson, D. R. Inorg. Synth. 1971, 13, 121-124.
(30) Buchler, J. W. In The Porphyrins; Dolphin, D., Ed.; Academic Press:
Vancouver, 1978; Vol. 1, pp 389-483.
Inorganic Chemistry, Vol. 45, No. 16, 2006 6481

Atefi et al.
Diphenyl(10,20-diphenylporphyrin-5-yl)phosphine Oxide (6).
Porphyrin 4 (54 mg, 0.10 mmol), cesium carbonate (34 mg, 0.10
mmol), catalyst 18 (5 mg, 0.005 mmol), and 17 (23 mg, 0.11 mmol)
in toluene (11 mL) gave, after 24 h of stirring, column chroma-
tography (toluene/methanol ) 98:2), and recrystallization from
toluene/pentane, 64 mg of dark purple crystals (0.097 mmol, 97%).
(10,20-Diphenylporphyrin-5,15-diyl)bis(diphenylphosphine ox-
ide) (12). Porphyrin 7 (31 mg, 0.050 mmol), cesium carbonate (34
mg, 0.10 mmol), catalyst 18 (5 mg, 0.005 mmol), and 17 (23 mg,
0.11 mmol) in toluene (11 mL) gave, after 40 h of stirring, column
chromatography (toluene/methanol ) 98:2), and recrystallization
from toluene/pentane, 41 mg of dark purple crystals (0.048 mmol,
95%). 1H NMR (400 MHz, CDCl3, 25 °C): δ 9.43, 8.54 (d, 3J(H,H)
) 5.0 Hz, each 4H, â-H), 8.03-8.00 (m, 4H, o-H 10,20-phenyl),
7.91-7.86 (m, 8H, o-H PPh2), 7.73-7.69 (m, 2H, p-H 10,20-
phenyl), 7.67-7.62 (m, 4H, m-H 10,20-phenyl), 7.56-7.52 (m, 4H,
p-H PPh2), 7.45-7.40 (m, 8H, m-H PPh2), -1.95 (br s, 2H, NH).
4H, o-H 10,20-phenyl), 7.82-7.76 (m, 4H, o-H PPh2), 7.70-7.64
(m, 6H, m,p-H 10,20-phenyl), 7.47-7.43 (m, 2H, p-H PPh2), 7.35-
7.30 (m, 4H, m-H PPh2). 31P NMR (162 MHz, CDCl3 + 1 drop
pyridine-d5, 25 °C): δ 35.7. IR (ATR): ν˜ [cm-1] 1153 (PdO);
after addition of pyridine to recrystallization: 1177 (PdO). UV/
vis (CH2Cl2/5% pyridine): λmax [nm], (ꢀ [103 mol-1 dm3 cm-1])
427 (267), 558 (9.4), 589 (4.8). LDI MS: m/z calcd for [C44H29N4-
OPZn - H]+: 723.13; found: 723.24.
Zinc(II) Phosphine Oxide 15 from 6. Porphyrin 6 (3.3 mg,
0.0049 mmol) was dissolved in CH2Cl2 (2 mL). Zinc acetate (3.3
mg, 0.021 mmol) dissolved in MeOH (1 mL) was added, and the
reaction mixture was refluxed for 2 h. The precipitate was filtered
and washed three times with MeOH to give 3.6 mg (ca. 100%) of
a dark purple powder.
[10,20-Diphenylporphyrinatozinc(II)-5,15-diyl]bis(diphenyl-
phosphine oxide) (16). Porphyrin 11 (17 mg, 0.025 mmol), cesium
carbonate (17 mg, 0.055 mmol), catalyst 18 (2.5 mg, 0.0025 mmol),
and 17 (12 mg, 0.055 mmol) in toluene (5.5 mL) gave, after 24 h
of stirring, column chromatography (toluene/methanol ) 98:5), and
recrystallization from toluene/MeOH/pentane, 20 mg of dark purple
crystals (0.022 mmol, 87%). 1H NMR (400 MHz, CDCl3 + 1 drop
31P NMR (162 MHz, CDCl3, 25 °C): δ 32.9. IR (ATR): ν˜ [cm-1
]
1184 (PdO). UV/vis (CH2Cl2): λmax [nm], (ꢀ [103 mol-1 dm3
cm-1]) 423 (289), 526 (10.5), 567 (14.0), 600 (6.3), 657 (10.5).
High-resolution ESI MS: m/z calcd for [C56H40N4O2P2 + H]+:
863.2705; found: 863.2697. Anal. Calcd for C56H40N4O2P2: C
77.95, H 4.67, N 6.49; found: C 77.89, H 4.84, N 6.28.
3
pyridine-d5, 25 °C): δ 9.45, 8.50 (d, J(H,H) ) 4.9 Hz, each 4H,
â-H), 7.99-7.96 (m, 4H, o-H 10,20-phenyl), 7.88-7.83 (m, 6H,
m,p-H 10,20-phenyl), 7.80-7.75 (m, 8H, o-H PPh2), 7.36-7.32
(m, 8H, m-H PPh2), p-hydrogens of the PPh2 group overlap with
pyridine peaks. 31P NMR (162 MHz, CDCl3 + 1 drop pyridine-d5,
25 °C): δ 34.8. IR (ATR, pyridine added to recrystallization): ν˜[
cm-1] 1178 (PdO). UV/vis (CH2Cl2/5% pyridine): λmax [nm], (ꢀ
[103 mol-1 dm3 cm-1]) 436 (315), 573 (8.4), 620 (17.0). LDI MS:
m/z calcd for [C56H38N4O2P2Zn - H]+: 923.17; found: 923.23.
X-ray Single-Crystal Structure Determination of 14 and 16.
Crystal data for 14 were collected at 150(2) K with ω and φ scans
to approximately 56° 2θ using an APEXII-FR591 diffractometer
employing graphite-monochromated Mo KR radiation generated
from a rotating anode (0.71073 Å). Data for 16 were collected at
103(2) K with ω and φ scans to approximately 45° 2θ using a
Bruker Kappa diffractometer with SMART 6000 detector employing
Double Diamond 111 monochromated radiation generated from a
synchrotron. Data integration and reduction were undertaken with
SAINT and XPREP,31 and subsequent computations were carried
out using the WinGX-3232 graphical user interface. The structures
were solved by direct methods using SIR9733 then refined and
extended with SHELXL-97.34 Non-hydrogen atoms were refined
anisotropically. Carbon-bound hydrogen atoms were included in
idealized positions and were refined using a riding model. Hydrogen
atoms attached to partial occupancy water molecules were not
located in the difference Fourier map and have not been included
in the refinement models. The refinement residuals are defined as
Diphenyl[10,20-diphenylporphyrinatonickel(II)-5-yl]phos-
phine Oxide (13). Porphyrin 8 (60 mg, 0.10 mmol), cesium
carbonate (34 mg, 0.10 mmol), catalyst 18 (5 mg, 0.005 mmol),
and 17 (23 mg, 0.11 mmol) in toluene (11 mL) gave, after 46 h of
stirring, column chromatography (toluene/methanol ) 98:2), and
recrystallization from toluene/pentane, 69 mg of dark red crystals
1
(0.096 mmol, 96%). H NMR (400 MHz, CDCl3, 25 °C): δ 9.73
(s, 1H, meso-H), 9.14, 9.07, 8.73, 8.51 (d, 3J(H,H) ) 4.9 Hz, each
2H, â-H), 7.91-7.89 (m, 4H, o-H 10,20-phenyl), 7.72-7.60 (m,
10H;, m,p-H 10,20-phenyl, o-H PPh2), 7.36-7.31 (m, 4H, m-H
PPh2), 7.82-7.43 (m, 2H, p-H PPh2). 31P NMR (162 MHz, CDCl3,
25 °C): δ 29.4. IR (ATR): ν˜ [cm-1] 1183 (PdO). UV/vis (CH2-
Cl2): λmax [nm], (ꢀ [103 mol-1 dm3 cm-1]) 414 (252), 538 (13.5),
578 (13.5). LDI MS: m/z calcd for [C44H29N4NiOP - H]+: 717.14;
found: 717.17. Anal. Calcd for C44H29N4NiOP: C 73.46, H 4.06,
N 7.79; found: C 73.45, H 4.18, N 7.58.
[10,20-Diphenylporphyrinatonickel(II)-5,15-diyl]bis(diphen-
ylphosphine oxide) (14). Porphyrin 9 (34 mg, 0.05 mmol), cesium
carbonate (34 mg, 0.10 mmol), catalyst 18 (5 mg, 0.005 mmol),
and 17 (23 mg, 0.11 mmol) in toluene (11 mL) gave, after 24 h of
stirring, column chromatography (toluene/methanol ) 98:2), and
recrystallization from toluene/pentane, 44 mg of dark red crystals
(0.048 mmol, 95%). 1H NMR (400 MHz, CDCl3, 25 °C): δ 9.07,
3
8.39 (d, J(H,H) ) 5.1 Hz, each 4H, â-H), 7.86-7.73 (m, 12H,
o-H 10,20-phenyl, o-H PPh2), 7.60-7.48 (m, 10 H, m,p-H 10,20-
phenyl, p-H PPh2), 7.41-7.37 (m, 8H, m-H PPh2). 31P NMR (162
MHz, CDCl3, 25 °C): δ 29.2. IR (ATR): ν˜ [cm-1] 1181 (PdO).
UV/vis (CH2Cl2): λmax [nm], (ꢀ [103 mol-1 dm3 cm-1]) 428 (167),
565 (7.2), 608 (16.2). LDI MS: m/z calcd for [C56H38N4NiO2P2 -
H]+: 917.18; found: 917.21. Anal. Calcd for C56H38N4NiO2P2: C,
73.14; H, 4.17; N, 6.09; found: C, 73.10; H, 4.22; N, 6.10.
Diphenyl[10,20-diphenylporphyrinatozinc(II)-5-yl]phos-
phine Oxide (15). Porphyrin 10 (60 mg, 0.10 mmol), cesium
carbonate (34 mg, 0.10 mmol), catalyst 18 (5 mg, 0.005 mmol),
and 17 (29 mg, 0.14 mmol) in toluene (14 mL) gave, after 24 h of
stirring, column chromatography (toluene/methanol ) 98:3), and
recrystallization from toluene/MeOH/pentane, 44 mg of a dark
purple powder (0.061 mmol, 61%). 1H NMR (400 MHz, CDCl3 +
1 drop pyridine-d5, 25 °C): δ 10.17 (s, 1H, meso-H), 9.52, 9.27,
2
R1 ) ∑||Fo| - |Fc||/∑|Fo| for Fo > 2σ(Fo) and wR2 ) {∑[w(Fo
2
- Fc2)2]/∑[w(Fc2)2]}1/2 where w ) 1/[σ2(Fo ) + (AP)2 + BP], P )
(Fo2 + 2Fc2)/3 and A and B are listed with the crystal data for each
structure (Table 1).
Results and Discussion
Synthesis and Characterization of meso-Porphyri-
nylphosphine Oxides. Traditionally, phosphine oxides are
(31) SAINT and XPREP; Bruker Nonius Analytical X-ray Instruments,
Inc.: Madison, WI, 2003.
(32) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837-838.
(33) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115-119.
(34) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1998.
3
8.86, 8.63 (d, J(H,H) ) 4.6 Hz, each 2H, â-H), 8.11-8.09 (m,
6482 Inorganic Chemistry, Vol. 45, No. 16, 2006

meso-Porphyrinylphosphine Oxides
Table 1. Experimental Crystallographic Data for 14 and 16
14
C56H40N4NiO3P2
16
formula
Mw
C56H41N4O35P2Zn
937.57
953.24
cryst color
cryst size (mm3)
cryst syst
recryst from
space group
a (Å)
dark red
dark purple
0.291 × 0.085 × 0.052
0.110 × 0.020 × 0.008
monoclinic
monoclinic
toluene/pentane
C2/c (No. 15)
20.2401(7)
toluene/MeOH/pentane
P21/c (No. 14)
19.984(3)
b (Å)
18.7057(7)
9.8207(14)
c (Å)
16.0264(6)
27.682(5)
â (deg)
123.651(2)
5050.9(3)
95.812(7)
4593.5(13)
V (Å3)
Z
D
4
4
calcd (g cm-3
)
1.233
1.378
λ (Å)
0.71073
0.495
56.58
0.48595
0.494
45.12
µ (mm-1
2θmax
)
hkl range
N
-26 to 26, -24 to 24, -21 to 21
39 751
-26 to 25, -15 to 14, -43 to 43
130 658
Nind
6262 (Rmerge ) 0.142)
17 545 (Rmerge ) 0.114)
Nobs (I > 2σ(I))
3410
9860
Nvar
309
608
R1(F, 2σ)
wR2(F2, all)
A
0.055
0.1547
0.084
0.0497
0.1279
0.083
B
0.0
0.0
GOF (all)
0.934
-0.276/0.536
0.907
-0.294/1.176
∆Fmin/max(e Å-3
)
Scheme 1. Formation of meso-Porphyrinylphosphine Oxide by the
Stille Method
prepared from lithium or Grignard reagents.35 Unfortunately,
no lithiated porphyrin macrocycle has been reported in the
literature. The only example of a meso-magnesiopor-
phyrin is mentioned in a patent.36 In 1980, Hirao and co-
workers reported the first palladium-catalyzed formation of
a P-C bond.37 In the past 25 years, this methodology has
emerged to be one of the most versatile, mild, and effective
approaches to generate various phosphonates, phosphites,
phosphine oxides, and phosphines.38 Although widely used
in porphyrin chemistry to generate new C-C bonds,39 there
are fewer examples of the formation of heteroatom-
substituted porphyrins promoted by Pd(0). Only boron,3
nitrogen,40 oxygen,41 and sulfur42 have been successfully
coupled to porphyrinyl macrocycles. Nonetheless, we decided
to pursue this avenue in order to synthesize the desired
ligands.
(35) Engel, R. Handbook of organophosphorus chemistry; M. Dekker: New
York, 1992.
(36) Therien, M. J. International Patent, WO 02/104072, 2002.
(37) Hirao, T.; Masunaga, T.; Ohshiro, Y.; Agawa, T. Tetrahedron Lett.
1980, 21, 3595-3598.
(38) For recent reviews see: (a) Hartwig, J. F. In Handbook of Organo-
palladium Chemistry for Organic Synthesis; Negishi, E.-i., Ed.; John
Wiley and Sons: 2002; Vol. 1, pp 1051-1096. (b) Schwan, A. L.
Chem. Soc. ReV. 2004, 33, 218-224.
(39) See for example: (a) Sharman, W. M.; Van Lier, J. E. J. Porphyrins
Phthalocyanines 2000, 4, 441-453. (b) Setsune, J.-i. J. Porphyrins
Phthalocyanines 2004, 8, 93-102.
(40) (a) Gao, G. Y.; Chen, Y.; Zhang, X. P. J. Org. Chem. 2003, 68, 6215-
6221. (b) Takanami, T.; Hayashi, M.; Hino, F.; Suda, K. Tetrahedron
Lett. 2003, 44, 7353-7357. (c) Chen, Y.; Zhang, X. P. J. Org.
Chem. 2003, 68, 4432-4438. (d) Gao, G.-Y.; Chen, Y.; Zhang, X. P.
Org. Lett. 2004, 6, 1837-1840. (e) Esdaile, L. J.; McMurtrie, J. C.;
Turner, P.; Arnold, D. P. Tetrahedron Lett. 2005, 46, 6931-
6935.
(41) Gao, G.-Y.; Colvin, A. J.; Chen, Y.; Zhang, X. P. Org. Lett. 2003, 5,
3261-3264.
(42) Gao, G.-Y.; Colvin, A. J.; Chen, Y.; Zhang, X. P. J. Org. Chem. 2004,
69, 8886-8892.
Our initial attempts to isolate meso-porphyrinyl phosphines
by the method of Stille and co-workers43 yielded the
corresponding phosphine oxide in very low yields of 2%, if
starting from bromoporphyrin 1. Not surprisingly, the cor-
responding iodoporphyrin (2)44 yielded the target compound
in more respectable yield of 20%, as iodide is known to be
more reactive in such processes.45 (Scheme 1)
Although the major product of these reactions was always
5,15-bis(3,5-di-tert-butylphenyl)-10-phenylporphyrin (H2-
(43) Tunney, S. E.; Stille, J. K. J. Org. Chem. 1987, 52, 748-753.
(44) Atefi, F.; Locos, O. B.; Senge, M. O.; Arnold, D. P. J. Porphyrins
Phthalocyanines 2006, 10, 176-185.
(45) Tsuji, J. Palladium reagents and catalysts: innoVations in organic
synthesis; Wiley and Sons: Chichester; New York, 1996.
Inorganic Chemistry, Vol. 45, No. 16, 2006 6483

Atefi et al.
Scheme 2. Synthesis of meso-η1-Palladioporphyrin
Table 2. Conditions and Yields (%) for Stoichiometric Reactions to
Form 6
Ph2P source
base
yielda
Ph2PH
-
<10
<20
35
<5
65
Ph2PSiMe3
Ph2P(BH3)H
Ph2P(BH3)H
Ph2P(BH3)H
Ph2P(O)H
Ph2P(O)H
-
-
DBUb
Cs2CO3
-
70
85
Cs2CO3
a Yield by 1H NMR, purified yield only for last entry. b DBU ) 1,5-
diazabicyclo[5.4.0]undec-7-ene.
Scheme 3. Stoichiometric Formation of meso-Porphyrinylphosphine
Oxide 6
We assume that the oxidation of the phosphine is facilitated
by the porphyrin itself, as already noted by Ma¨rkl and co-
workers.15 Both acidic and basic reagents can lead to the
cleavage of the Pd-C bond in meso-palladioporphyrins.47
DBU seems to promote this cleavage, and the major product
in all cases, besides the desired porphyrinylphosphine oxide,
was unsubstituted 5,15-diphenylporphyrin (H2DPP). The last
entry of Table 2 shows, however, that a heterogeneous base
improves the yield of the desired product. Encouraged by
this result, our next goal was to repeat these results under
catalytic conditions (Scheme 4, Table 3).
It is important to note that these results are only reproduc-
ible using freshly prepared Pd(0) catalyst (18). Purification
of the free base and nickel products was easily achieved, as
the reaction mixture can be loaded onto a short silica column
without removal of the solvent. Excess diphenylphosphine
oxide 17 can be eluted with toluene, while the products are
retained on the column. The addition of small amounts of
MeOH is sufficient to elute the porphyrins. The lower yield
for the zinc analogues (15, 16) can be explained by the
problematic purification process. Both of these ligands
self-coordinate, as indicated to us by the lower solubility
and slow elution of these products. Even higher amounts of
MeOH still result in streaking on the column. These Zn(II)
products are also very insoluble in organic solvents, and
a mixture of toluene/MeOH with the aid of sonication is
needed for recrystallization. Fortunately for the prospects
of these porphyrins as ligands, these findings indicate a very
strong O-metal coordination. Porphyrin 15 is also obtain-
able from its free base analogue 6 in almost quantitative
yield by the standard metal insertion method with zinc
acetate.
DAPP), these initial experiments supplied us with important
insights into these reactions. As already expected, phosphines
tend to oxidize very readily and rapidly in the presence of
porphyrins to the corresponding phosphine oxide.15,16a The
optimum reaction temperature for the formation of the new
carbon-phosphorus bond is apparently ∼85 °C. At lower
temperatures (<80 °C), no reactions were observed, while
higher temperatures (>90 °C) favor the dehalogenation of
the porphyrin, as do reaction times over 72 h. We also found
that the phosphine oxide 3 is soluble in most common
organic solvents except pentane.
To optimize our reaction conditions, it was decided to
continue the experiments with a meso-η1-palladioporphyrin
as starting material. These meso-metalloporphyrins are
readily available from a stoichiometric oxidative addition of
a haloporphyrin with [Pd2dba3] (dba ) dibenzylideneacetone)
and a ligand, in this case dppe [dppe ) 1,2-bis(diphenyl-
phosphino)ethane]9b (Scheme 2).
Palladioporphyrin 5 was chosen for several reasons. As
the halogen is in the cis position to the porphyrin macrocycle,
we anticipated it might increase the rate of our reactions and
thus reduce the reaction times. We replaced the substituted
aryl groups on the porphyrin by simple phenyls to lower the
solubility of the target compound and therefore simplify the
purification process. The remaining vacant meso position of
the macrocycle provides the opportunity to carry out further
reactions at a later stage. Palladioporphyrin 5 was reacted
with various phosphines and phosphine oxides under different
conditions, as shown in Scheme 3 and summarized in Table
2.
The first five entries underline our findings from the
previous experiments that porphyrinylphosphines are readily
and rapidly oxidized to the corresponding phosphine oxide.
The widely used borane protecting group46 seems in this case
to be ineffective, although the Sanders group successfully
protected their porphyrinylphosphine as such a complex.16a
High-resolution ESI mass spectrometry (MS) was used as
first evidence for the formation of the free base ligands (6,
12), and indeed, the results confirmed the proposed formula-
tions. As the metalated porphyrins (13-16) could not be
protonated by ESI, we choose to perform LDI on them. This
“harder” ionization technique leads in the case of phosphine
oxides to the detection of an (M - H)+ ion instead of the
(M + H)+ ion found for 6 and 12. Williams et al.48 studied
the mass spectral fragmentation of various di- and triph-
enylphosphine oxides and concluded from isotopic labeling
that the prominent (M - H)+ fragments are cyclic quasi-
(47) Kato, A.; Hartnell, R. D.; Yamashita, M.; Miyasaka, H.; Sugiura, K.-
i.; Arnold, D. P. J. Porphyrins Phthalocyanines 2005, 8, 1222-1227.
(48) Williams, D. H.; Ward, R. S.; Cooks, R. G. J. Am. Chem. Soc. 1968,
90,; 966-972.
(46) Imamoto, T.; Takeyama, T.; Kusumoto, T. Chem. Lett. 1985, 1491-
1492.
6484 Inorganic Chemistry, Vol. 45, No. 16, 2006

meso-Porphyrinylphosphine Oxides
Scheme 4. Catalytic Formation of meso-Porphyrinylphosphine Oxides
Table 3. Conditions and Yields (%) for Catalytic Reactions
observe such a self-coordination feature for their zinc
phthalocyanine.12 The chemical shifts in the 31P NMR
spectra, between 29.2 and 35.7 ppm, also agree well with
the values reported for the phthalocyanines.
ratio
halo-porphyrin/17
reaction
time (h)
product
yield
6
1:1.1
1:2.2
1:1.1
1:2.1
1:1.4
1:2.2
24
40
46
24
24
24
>95
>95
>95
>95
61a
12
13
14
15
16
Variable-Temperature 1H NMR Studies of 6. The
effects of the large delocalized aromatic system of porphyrins
1
can be observed in their H NMR spectra. Shielding of the
80b
inner nitrogen protons shifts the peaks representing them far
upfield, while a deshielding effect shifts the peaks of the
protons attached to the outer carbon skeleton downfield into
the region of 8-11 ppm. Due to this feature, porphyrinyl
compounds can be very easily detected by 1H NMR
spectroscopy, even in reaction mixtures. The spectrum of
porphyrin 6 has an added interesting feature. Instead of the
expected four doublets, each representing two â-protons,
three doublets and a broad peak at ∼9.3 ppm can be
b
a Yield by 1H NMR higher, purification problematic. 1H NMR of
reaction mixture shows only one porphyrin, purification problematic.
1
observed. Two-dimensional H NMR studies (dqf-COSY,
Figure 1. Quasi-onium ion.
NOESY) showed us that this broad peak represents the two
protons next to the C-P bond. Intrigued by this phenomenon,
we decided to conduct some variable-temperature 1H NMR
studies.
onium ions, the analogues of which for our compounds
would be the structure shown in Figure 1.
Traditionally, infrared spectroscopy (IR) has played a
significant role in the characterization of phosphine oxides
and their complexes due to the ease of observation of the
strong PdO vibration [ν˜(PO)]. IR is still a very useful tool
for the identification of these ligands. Table 4 shows the
collected ν˜(PO) data for porphyrins 6 and 12-16 together
with simpler models triphenylphosphine oxide (OPPh3) and
17.
Again, the two free base analogues 6 and 12 and the two
nickel porphyrins 13 and 14 behave in a similar manner.
The ν˜(PO) for these compounds agree well with the literature
values for Ma¨rkl’s12 phosphine oxide-substituted phthalo-
cyanine. The decrease in ν˜(PO) by ∼25 cm-1 for 15 can be
explained by its self-coordination. Due to the interaction with
a Lewis acidic metal ion, complexed phosphine oxides are
known to have a lower ν˜(PO) value.49 After treatment of 15
and 16 with excess pyridine, the ν˜(PO) value for the isolated
solids indicates the presence of uncomplexed phosphine
oxide ligand. Interestingly, Ma¨rkl and co-workers did not
The spectra on the left-hand side of Figure 2 were recorded
at 23-55 °C. The broad peak sharpens upon raising the
temperature. By lowering the temperature (right-hand side
of Figure 3, CD2Cl2 as solvent), all doublets broaden and at
-40 °C no doublets can be observed. By lowering the
temperature even further to -90 °C, instead of the four
doublets, eight emerge. The arrows show the two peaks
which diverge from the broad room-temperature peak. The
peak representing the inner NH protons (-2.5 ppm) also
splits into two signals at this low temperature. We attribute
these features to the tautomerism of the inner N-protons.
(Figure 3)
Similar features can be observed for meso-substituted
porphyrins with other crowded substituents, like the meso-
palladioporphyrins (e.g., 5); however, the peak broadening
in those compounds occurs at much lower temperatures (-30
°C).
Electronic Absorption Spectra, Emission Spectra, and
Redox Properties. The main electronic absorption bands for
the porphyrinylphosphine oxides (Figure 4, Table 5) show
Table 4. IR Frequencies (cm-1) of Porphyrinylphosphine Oxides
compound OPPh3 17
ν˜(PO) 1192 1192 1183 1184 1183 1182 1177 1153 1178
a Solid isolated after addition of pyridine to a solution in CH2Cl2.
6
12
13
14
15a
15
16a
(49) Cotton, F. A.; Barnes, R. D.; Bannister, E. J. Chem. Soc. 1960, 2199-
2203.
Inorganic Chemistry, Vol. 45, No. 16, 2006 6485

Atefi et al.
1
Figure 2. Variable-temperature H NMR spectra in CDCl3 (left) and CD2Cl2 (right) of 6.
Figure 3. Tautomerism of inner N-protons.
the expected characteristics for substituted DPP.50 Several
trends can be recognized even in this limited set of data. A
bathochromic shift in comparison to DPP51 can be observed
with increasing number of substituents. The shift is greatest
for zinc porphyrins 15 and 16 followed by the nickelated
compounds (13, 14) and least for the free base porphyrins
(6, 12). As usual, the presence of a metal coordinated to the
macrocycle raises its symmetry, which is reflected in only
two observable Q-bands, instead of the four detected for the
free base porphyrins.
We were also very much interested to explore whether
the phosphine oxide substituent would have any effects on
the fluorescence behavior of the macrocycle. Figure 5 shows
the fluorescence spectra of the two free base porphyrins (6,
12) together with the spectrum of H2DPP for comparison.
All three compounds were excited at their respective Soret
band maxima, while the intensities are normalized to 0.1
absorbance. From these data, we calculated the fluorescence
quantum efficiency (Φ) for the three porphyrins according
to the comparative method.52
Astd
A
F
Fstd
Figure 4. UV/vis absorption spectra for porphyrinyl phosphine oxides
(in CH2Cl2 solution; with 5% pyridine for 15 and 16).
Φ ) Φstd
×
×
underneath the curve and A represents the absorbance. As
standard, the well-known quantum efficiency of 5,10,15,-
20-tetraphenylporphyrin (Φstd ) 0.11) was used.53 Our results
indicate that increasing the number of substituents raises the
quantum yield only slightly. The quantum yield of H2DPP
where F is the fluorescence obtained by integrating the area
(50) Ryppa, C.; Senge, M. O.; Hatscher, S. S.; Kleinpeter, E.; Wacker, P.;
Schilde, U.; Wiehe, A. Chem.-Eur. J. 2005, 11, 3427-3442.
(51) Bru¨ckner, C.; Posakony, J. J.; Johnson, C. K.; Boyle, R. W.; James,
B. R.; Dolphin, D. J. Porphyrins Phthalocyanines 1998, 2, 455-465.
(52) Ogunsipe, A.; Nyokong, T. J. Porphyrins Phthalocyanines 2005, 9,
121-129.
(53) Seybold, P. G.; Gouterman, M. J. Mol. Spectrosc. 1969, 31, 1-13.
6486 Inorganic Chemistry, Vol. 45, No. 16, 2006

meso-Porphyrinylphosphine Oxides
Table 5. Wavelengths for the UV/vis Absorption Bands for
Porphyrinylphosphine Oxides (in CH2Cl2 Solution; with 5% Pyridine for
15 and 16)
λ [nm]
product
soret band
Q-bands
6
416
423
415
428
427
436
514, 548, 585, 639
526, 567, 600, 657
538, 578
565, 608
558, 589
12
13
14
15
16
573, 620
was calculated to be 0.07, while the addition of one
substituent (6) raises this value to 0.08 and the second
substituent (12) increases the quantum yield even further to
0.10. Notably, the diphenylphosphine oxide does not behave
as a “heavy atom” quencher.
The redox properties of the free base oxides 6 and 12 were
studied briefly by cyclic and square wave voltammetry at a
Pt working electrode in CH2Cl2 containing 0.1 M Bu4NPF6.
(vs Ag/Ag+; ferrocene/ferrocinium couple at +0.55 V).
While H2DPP showed reversible first reduction and oxidation
waves at -1.05 and +1.16 V, respectively,9c 6 was reduced
at -0.96 V (reversible) and oxidized at +1.24 V (partly
reversible). The corresponding data for bis-oxide 12, were
-0.73 and +1.33 V. These results indicate the electron-
withdrawing properties of the phosphine oxide substituent-
(s), which cause anodic shifts of both reduction and oxidation
potentials.
Crystal Structures. Nickel(II) Bis(phosphine oxide)
(14). In the crystal structure of 14 (Figure 6a), the complex
has 2-fold crystallographic symmetry [Ni(II) on 2-fold special
position with the 2-fold axis being normal to mean plane of
the complex]. Selected geometric parameters are provided
in Table 6. The nickel(II) center, which occupies the
porphyrin cavity, is four coordinate and very close to square
planar with a maximum deviation of N atoms from the mean
N4 plane of 0.034 Å. The porphyrin ring is significantly
distorted from planarity (Figure 6b), having a distinctive
saddle-like conformation. The maximum deviations from the
mean plane of the macrocycle occur for the meso carbon
atoms [distance; meso-C(5) to mean plane 0.814 Å, meso-
Figure 6. (a) ORTEP representation of {[10,20-diphenylporphyrinato-
nickel(II)-5,15-diyl]-bis-[P(O)Ph2}‚H2O. The complex has 2-fold symmetry
(1 - x, y, -z + 3/2). Ellipsoids are depicted with 30% probability, and
water and H atoms have been omitted. (b) Illustration of the {[10,20-
diphenylporphyrinatonickel(II)-5,15-diyl]-bis-[P(O)Ph2}‚H2O complex show-
ing the almost perfect square planar coordination contrasting with the
distorted macrocycle framework. Note also the cis-like arrangement of the
diphenylphosphine oxide groups.
Table 6. Selected Bond Lengths (Å) and Angles (deg) for
{[10,20-diphenylporphyrinatonickel(II)-5,15-diyl]-bis-[P(O)Ph2}‚H2O
Ni(1)-N(1)
Ni(1)-N(2)
P(1)-O(1)
1.8941(19) P(1)-C(5)
1.817(3)
1.777(4)
1.810(3)
1.891(2)
1.487(2)
P(1)-C(11)
P(1)-C(17)
N(2)a-Ni(1)-N(2) 179.19(13)
O(1)-P(1)-C(17)
110.93(14)
C(11)-P(1)-C(17) 105.24(14)
N(2)-Ni(1)-N(1)a
N(2)-Ni(1)-N(1)
90.70(9)
89.32(9)
O(1)-P(1)-C(5)
C(11)-P(1)-C(5)
C(17)-P(1)-C(5)
114.77(14)
105.42(14)
108.77(11)
N(1)a-Ni(1)-N(1) 176.81(12)
O(1)-P(1)-C(11)
111.15(15)
a -x, y, -z + 3/2.
C(10) to mean plane 0.747 Å], and as such, the porphyrin
complex has the conformation type generally referred to as
ruffled.54 The diphenylphosphine oxide groups project on
the same side of the macrocycle in a cis-like geometry.
Figure 5. Fluorescence spectra of H2DPP, 6, and 12 (in CH2Cl2 solution).
Inorganic Chemistry, Vol. 45, No. 16, 2006 6487

Atefi et al.
Table 7. Selected Bond Lengths (Å) and Angles (deg) for
{[10,20-diphenylporphyrinatozinc(II)-5,15-diyl]-bis-[P(O)Ph2]}n‚
{1.5H2O}n
Zn(1)-N(1)
Zn(1)-N(2)
Zn(1)-N(3)
Zn(1)-N(4)
Zn(1)-O(2)a
P(1)-O(1)
P(1)-C(5)
2.0805(15) P(1)-C(21)
2.0719(14) P(1)-C(27)
2.0679(15) P(2)-O(2)
2.0575(15) P(2)-C(15)
2.0224(14) P(2)-C(39)
1.4899(17) P(2)-C(45)
1.8353(18)
1.816(2)
1.7971(19)
1.4856(15)
1.8108(17)
1.8054(19)
1.8048(19)
N(1)-Zn(1)-N(2)
87.56(6)
O(1)-P(1)-C(21)
112.99(10)
110.35(9)
105.05(9)
111.58(9)
N(1)-Zn(1)-N(3) 164.11(7)
O(1)-P(1)-C(27)
C(5)-P(1)-C(21)
C(5)-P(1)-C(27)
N(1)-Zn(1)-N(4)
N(1)-Zn(1)-O(2)a 97.97(6)
90.46(6)
88.85(6)
N(2)-Zn(1)-N(3)
C(21)-P(1)-C(27) 102.41(9)
N(2)-Zn(1)-N(4) 160.09(6)
O(2)-P(2)-C(15)
O(2)-P(2)-C(39)
O(2)-P(2)-C(45)
112.96(8)
109.37(9)
111.44(8)
N(2)-Zn(1)-O(2)a 97.13(6)
N(3)-Zn(1)-N(4)
87.66(6)
N(3)-Zn(1)-O(2)a 97.91(6)
C(15)-P(2)-C(39) 114.41(8)
C(15)-P(2)-C(45) 105.83(9)
C(39)-P(2)-C(45) 102.30(9)
P(2)1-O(2)1-Zn(1) 177.56(9)
N(4)-Zn(1)-O(2)a 102.76(6)
O(1)-P(1)-C(5)
113.80(9)
a -x + 1, y - 1/2, -z + 1/2.
Figure 7. ORTEP representation of the asymmetric unit of {[10,20-
diphenylporphyrinatozinc(II)-5,15-diyl]-bis-[P(O)Ph2]}n‚{1.5H2O}n 50%
probability ellipsoids, disordered water omitted). The coordination sphere
of the complex is shown in Figure 8.
The crystal structure of the nickel(II) complex 14 is
characterized by a number of different aryl-aryl intermo-
lecular interactions that involve diphenylphosphine oxide
phenyl rings, the meso substituent phenyl rings, and the
aromatic porphyrin framework. Notable interactions are
described here. The meso substituent phenyl ring C(23)-
C(28) is simultaneously involved in edge-to-face-type in-
teractions with the aromatic porphyrin face of an adjacent
complex (CHedge‚‚‚porphyrin face ) 2.6 Å), the diphe-
nylphosphine oxide phenyl group comprising C(11)-C(16)
(CHedge‚‚‚Phplane ) 2.7 Å) and the diphenylphosphine oxide
phenyl group comprising C(17)-C(22) (CHedge‚‚‚Phplane
)
3.3 Å). The complexes are organized in such a way as to
create continuous channels that run parallel to the crystal-
lographic c axis. These channels are filled with diffuse
solvent molecules (modeled as partial occupancy water
molecules, O(1w)-O(5w).
Zinc(II) Bis(phosphine oxide) (16). In the crystal struc-
ture of {[10,20-diphenylporphyrinatozinc(II)-5,15-diyl]-bis-
[P(O)Ph2]}n‚{1.5H2O}n, the asymmetric unit comprises a
single zinc(II) porphyrin complex and 1.5 molecules of water
that are positionally disordered over seven sites (O1w-O7w).
An ORTEP55 representation of the asymmetric unit is
provided in Figure 7, and selected geometric data are
provided in Table 7. The zinc(II) center [Zn(1)] is five-
coordinate with approximate square pyramidal stereochem-
istry, as shown in Figure 8. The four nitrogen atoms of the
macrocycle [N(1)-N(4)] are arranged in a square planar
configuration with the maximum deviation from the mean
N4 plane occurring for N(4) [0.0355(8) Å]. The zinc(II) atom
is located 0.321 Å from the mean N4 plane, and the apical
coordination site is occupied by an oxygen atom [O(2)] from
one of the diphenylphosphine oxide groups of an adjacent
Figure 8. Section of the one-dimensional coordination polymer in
{[10,20-diphenylporphyrinatozinc(II)-5,15-diyl]-bis-[P(O)Ph2]}n‚{1.5H2O}n.
complex. This coordination configuration propagates along
the crystallographic b axis to produce a chainlike, one-
dimensional, coordination polymer, as illustrated in Figure
8. The oxygen atom [O(1)] of the second diphenylphosphine
oxide group plays no part in proliferation of the polymer
but rather is directed into a cavity in the lattice that is also
occupied by disordered water molecules [PO‚‚‚Owater dis-
tances range between 2.61 and 3.47 Å for O(1w), O(2w),
O(3w), and O(4w)]. Contact distances to the other partial
(54) Senge, M. O. Chem. Commun. 2006, 243-256.
(55) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
6488 Inorganic Chemistry, Vol. 45, No. 16, 2006

meso-Porphyrinylphosphine Oxides
occupancy water sites are too long to be considered
significant H-bond interactions. The cavity containing the
disordered water molecules is surrounded on all other sides
by hydrophobic phenyl rings of the ligands.
Other aryl-aryl interactions connect adjacent coordinate
polymer chains in the third dimension (parallel to the a axis).
The diphenylphosphine phenyl ring comprising C(27)-C(32)
is involved in two interactions; one being an offset face-to-
face interaction with the diphenylphosphine phenyl ring
C(45)-C(50) (mean Phplane‚‚‚Phplane ) 3.4 Å) and the other,
a vertex-to-face interaction with C(39)-C(44). There are
other, longer-range interactions, but these do not warrant
particular mention.
The phenyl rings (and therefore the oxygen atoms) of the
two diphenylphosphine oxide groups protrude on opposite
sides of the mean plane of the macrocycle in a trans-like
arrangement. The carbon framework of the porphyrin ring
is distorted from planarity. The maximum deviation from
the mean plane of the ring occurs for the â-carbon C(17) at
0.42 Å. Of interest with respect to molecular geometry is
the almost linear bonding configuration around the coordi-
nated diphenylphosphine oxide oxygen atom O(2) [P(2)-
O(2)-Zn(1) ) 177.56(9)°]. Similar compounds in the
literature show bond angles between 140° and 180° for
analogous phosphine oxide coordinating groups, so this
situation is not considered abnormal.56
The phenyl rings of the diphenylphosphine oxide groups
bound to zinc are sandwiched by alternating pairs of
porphyrin rings in the chain. There are intrachain aryl-aryl
interactions of the edge-to-face type between the edges of
the diphenylphosphine oxide phenyl rings [C(39)-C(44) and
C(45)-C(50)] and the faces of the aromatic porphyrin rings
(CHedge‚‚‚Porphyrinplane contact distances between 2.65 and
2.80 Å). Each phenyl ring is involved in two edge-to-face
interactions, and as such, these contacts bridge alternating
porphyrin rings within the chain. The contact distances are
quite short and may be responsible for some of the distortion
observed for the carbon framework of the macrocycles.
There are notable interchain aryl-aryl interactions that
involve both diphenylphosphine oxide phenyl rings and the
meso substituent phenyl rings of the macrocycle. Adjacent
chains are connected to one another by vertex-to-face-type
interactions between the meso phenyl rings comprising
C(33)-C(38) (vertex) and the diphenylphosphine oxide
phenyl rings comprising C(21)-C(26) (face) (CHvertex‚‚‚
Phplane ) 3.10 Å) that propagate the lattice in the c direction.
Also, connecting adjacent chains in the c direction are offset
face-to-face π-stacking interactions between meso phenyl
rings [C(51)-C(56)]. Each ring is involved in two such
interactions, with interaction distances Phplane‚‚‚Phplane ) 3.53
and 3.61 Å, which form a continuous thread, normal to the
ac plane, that propagates with crystallographic inversion
symmetry.
Conclusions
Several representatives of a new class of porphyrins with
one and two diphenylphosphine oxide substituents in the
meso position(s) have been prepared in very good to excellent
yields by both stoichiometric and palladium-catalyzed reac-
tions. Their structures have been demonstrated unambigu-
ously by various spectroscopic techniques and single-crystal
structures. As part of their investigation into the potential
applications of porphyrins as molecular tectons, Deiters et
al.57 report a similar coordination polymer motif for zinc
complexes of porphyrins bearing coordinating pyridine
N-oxide groups (as opposed to the coordinating diphe-
nylphosphine oxide groups in the present study). This motif
may be a recurring one and therefore be applicable to crystal
engineering by functional group variation. In the future, we
will be investigating the complexation properties of our new
phosphine oxides in solution. There is also scope for the
construction of more elaborate coordination frameworks
based on these bis-diphenylphosphine oxide porphyrin
ligands by combination with metals that adopt six-coordinate
configurations [e.g., Cr(III), Ru(II), Os(II)] when complexed
with porphyrinoid ligands. In addition, we propose that these
phosphine oxides could be utilized as interesting new ligands
for non-porphyrinic organometallic and inorganic centers.
Acknowledgment. F.A. would like to thank the Depart-
ment of Education, Science and Training (DEST) and the
Faculty of Science, Queensland University of Technology
for Post-Graduate Scholarships.
Supporting Information Available: CIF files for compounds
14 and 16. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC060372U
(56) Inamo, M.; Matsubara, N.; Nakajima, K.; Iwayama, T. S.; Okimi, H.;
(57) Deiters, E.; Bulach, V.; Kyritsakas, N.; Hosseini, M. W. New J. Chem.
2005, 29, 1508-1513.
Hoshino, M. Inorg. Chem. 2005, 44, 6445-6455.
Inorganic Chemistry, Vol. 45, No. 16, 2006 6489