Synthesis and photophysical and electrochemical study of tyrosine covalently linked to high-valent copper (III) and manganese(IV) complexes

Article abstract of DOI:10.1002/hlca.200790056

As bio-inspired chemical model of the oxygen-evolving complex (OEC) in photosystem II, a new tyrosine-modified corrole ligand 3 and its high-valent copper and manganese complexes 3a and 3b were synthesized and characterized. The copper complexes 1a and 2a

Full text of DOI:10.1002/hlca.200790056

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553
Synthesis and Photophysical and Electrochemical Study of Tyrosine
Covalently Linked to High-Valent Copper(III)and Manganese(IV)
Complexes
by Ming Xiaa), Jianhui Liu*a), Yan Gaoa), Bjçrn Škermarkb), and Licheng Sun*a)c)
a) State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on
Molecular Devices, Dalian University of Technology (DUT), Zhongshan Road 158-40, Dalian 116012,
P. R. China (phone: þ 8641188993886; fax: þ 8641183702185; e-mail: liujh@dlut.edu.cn)
b) Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, S-10691 Stockholm
c) Department of Chemistry, Organic Chemistry, Royal Institute of Technology (KTH),
S-10044 Stockholm (e-mail: lichengs@kth.se)
As bio-inspired chemical model of the oxygen-evolving complex (OEC) in photosystem II, a new
tyrosine-modified corrole ligand 3 and its high-valent copper and manganese complexes 3a and 3b were
synthesized and characterized. The copper complexes 1a and 2a of corrole 1 and 2 were also prepared for
comparison. The emission property indicates that the emission of ligands 2 and 3 is located at 670 nm, but
no emission is observed for their metal complexes due to its suppression by the metal center. The
electrochemical study shows that 3a might dimerize at the first two reversible oxidations, a behavior
which was not observed in the case of 1a and 2a. The corrolato manganese(IV) complex 3b shows one
reversible reduction and one quasireversible oxidation at À 0.17 and 0.77 V vs. Ag/Agþ, respectively.
Introduction. – The four-electron oxidation of water in photosynthetic organisms is
achieved by an oxygen-evolving complex (OEC) in photosynthesis, which is one of the
most important and fundamental chemical processes in nature [1 – 3]. A series of X-ray
structure analysis of photosystem II (PS II) [4 – 6] indicated that the active site in a
photosynthetic OEC protein contains a Mn4Ca cluster [5][6], and a neighboring l-
tyrosine (Tyrz) is linked between P680 and OEC. By light absorption of the primary
electron donor P680 consisting of chlorophyll a molecules, electron transfer occurs from
the excited P680* to a primary electron acceptor, pheophytin, and subsequently to two
quinines, forming a P680 radical cation. The electrons produced by oxidation of water at
the Mn4Ca cluster are transferred through redox-active Tyrz to Pþ68ꢀ0, which is reduced to
P680 for another photosynthetic cycle. Tyrz is crucial for the stabilization of the primary
charge separation. Besides electron transfer, Tyrz is thought to transfer its phenolic
proton to a nearby base, leading to a neutral tyrosine radical [7 – 11]. Therefore, some
tyrosine-containing metal complexes have been studied as artificial OEC models
catalyzing water oxidation and simulating the process of proton-coupled electron
transfer (PCET) [12 – 15]. As to the electron donor, oxidation of water at the Mn4Ca
cluster occurs in four steps and involves at least five oxidation states (S0 – S4) [3][16].
Although the mechanism of O2 evolution has not been determined completely, the
stage of O2 evolution would involve a high-valent manganese species [3][16 – 19].
ꢀ 2007 Verlag Helvetica Chimica Acta AG, Zürich

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Corroles are aromatic tetrapyrrole macrocycles, i.e., ring-contracted analogues of
porphyrins, which have proved to stabilize higher oxidation states of coordinated
metals, comparable or superior to the more famous porphyrins, and many high-valent
metal complexes have been synthesized and studied as catalysts and photosensitizers
[20 – 26]. Therefore, we designed a ligand which contains a corrole and an l-tyrosine
moiety connected through an amide bond, as well as its Mn-complex with the objective
of studying water oxidation. In this paper, we report the synthesis and photophysical
and electrochemical properties of the corrole ligand 3 and of its copper complex 3a and
manganese complex 3b.
Results and Discussion. – Synthesis and Characterization. The synthesis of the l-
tyrosine-containing corrole ligand 3 was accomplished in two steps from corrole 1,
which was obtained by the acid-catalyzed condensation reaction of 5-(4-methylphe-
nyl)dipyrromethane and 3-nitrobenzaldehyde according to [27] (Scheme). After the
reduction of the nitro group of 1 in the presence of SnCl2 under acid conditions, 2 was
obtained in 78% yield. The carboxy group of the N-Boc-protected l-tyrosine was then
used to link to the amino group of 2. Dicyclohexylcarbodiimide (DCC) was used as a
dehydrating reagent and should be added after the mixture had been stirred at 08 for at
least 0.5 h. All the reactions to synthesize 1 – 3 were performed under Ar and in the
dark.
The preparation of [CuIII(corrole)] and [MnIV(corrole)] complexes from Cu-
(OAc)2 · H2O and Mn(OAc)2 · 4 H2O, respectively, have been reported [25][28 – 33].
Similarly, the Cu complexes 1a, 2a, and 3a, were obtained in high yield by reaction of
corroles 1 – 3 with Cu(OAc)2 · H2O in pyridine at room temperature under air,
decomposition being kept to a minimum. The Mn complex 3b was obtained in 54%
yield by reaction with Mn(OAc)2 · 4 H2O in DMF under reflux under air.
The MS data of all compounds are given in the Exper. Part. The peak of the
pseudomolecular ion [3 þ H]þ was observed at 833.4 in the API-ES-MS and at 833.3800
in the HR-ESI-MS, in agreement with the expected molecular formula. Well resolved
1H-NMRspectra of 2 and 3 could not be obtained due to significant line broadening,
which prevented a full assignment of the protons. In contrast, since a CuIII complex was
1
formed from 3, the evident diamagnetism of 3a made its H-NMRspectrum well-
resolved (Fig. 1). In addition, proton assignments for 3a were also made based on peak
intensity and multiplicity and verified by g-COSY. The two peaks located at d 10.19 and
9.16 correspond to the phenol proton and the amide proton HÀN(7)1) of 3a,
respectively. The signal of the amide proton HÀN(5)1) adjacent to the carbonyl group
at d 4.26, coupled with the signal at d 2.89 of a CH2 group. The four broad peaks at d
7.25, 7.35, 7.62, and 8.10 were attributed to the pyrrole protons. The signal around d 7.62
integrated to six protons, i.e., two pyrrole protons and four aromatic protons of the 4-
methylphenyl moieties, the latter protons coupling with the other four protons of the 4-
methylphenyl moieties at d 7.39. The two protons of the CH2 group are nonequivalent
due to the chiral center C(4), thus giving rise to two m centered at d 2.73 and 2.89. Only
the proton of the latter signal coupled with the adjacent methine proton. The tBu and
the tolyl Me group appeared at d 1.32 and 2.43, respectively. The MS, elemental
1
)
Arbitrary atom numbering (Fig. 1); for systematic names, see Exper. Part.

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Scheme. Synthetic Route for Compounds 3, 3a, 3b, 1a, and 2a
a) 3-Nitrobenzaldehyde, CH2Cl2, CF3COOH, r.t. 5 h; chloranil (¼2,3,5,6-tetrachlorocyclohexa-2,5-
diene-1,4-dione), 2 h. b) SnCl2 · 2 H2O, CHCl3/HCl/AcOH, 658, 12 h. c) Boc-Tyr-OH, CH2Cl2, 08, 0.5 h,
DCC (¼dicyclohexylcarbodiimide), r.t, 12 h. d) For 3a, Cu(OAc)2 · H2O, pyridine, r.t., 10 min; for 3b,
Mn(OAc)2 · 4 H2O, DMF, reflux, 10 min. e) Cu(OAc)2 · H2O, pyridine, r.t., 10 min.

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Fig. 1. 1H-NMR Spectra of 3a in (D6)DMSO at 258. Arbitrary atom numbering.
analysis, and UV/VIS spectrum of 3a not only confirmed the structure of the complex
but also that of ligand 3. Complex 3b could not be characterized by 1H-NMRas a result
of its paramagnetic Mn-center, but the peaks at m/z 884.4 ([M À OAc]þ) in the API-
ES-MS and at 884.2894 in the HR-ESI-MS and the UV/VIS data confirmed its
structure.
Absorption and Emission Spectra. The UV/VIS spectra of the free corrole ligand 3
and of the corresponding metal complexes 3a and 3b are shown in Fig. 2. The Soret
band of 3 is located at 418 nm and that of the corrolatocopper 3a at 417 nm. The Q-
band of 3 displays three obvious absorptions at 577, 617, and 650 nm, respectively, while
3a shows only one inconspicuous band at 539 nm. The compounds 1, 1a, 2, and 2a
exhibit the same trend as 3 and 3a (data, in the Exper. Part). Different from the
corrolatocopper complexes, the Soret band of the Mn-complex 3b is located at 437 nm,
red-shifted by 22 nm in comparison to that of 3. Besides this band, the UV/VIS
spectrum of 3b shows two other transitions at 317 and 367 nm and two poorly shaped
bands at 518 and 607 nm in the Q-band, the spectrum exhibiting the typical pattern of
[MnIV(corrolato)] complexes [32][33].

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Fig. 2. UV/VIS Spectra of 3, 3a, and 3b in CH2Cl2
The excitation and emission spectra of 3 and 2 were measured in CH2Cl2 at room
temperature (Fig. 3). There are two bands in the excitation spectrum of 3 and 2, with
almost the same maximal wavelength at 414 and 567 nm (566 nm for 2), belonging to
the Soret and Q-band, respectively. When exciting the Soret band (414 nm) and Q-band
(567 nm), the emission for both 3 and 2 is located at 670 nm. But the emission intensity
upon irradiation at the Soret band is higher than that produced upon irradiation of the
Q-band for both 3 and 2, they correspond to the excitation intensity. The same emission
wavelength of 3 and 2 means that the tyrosine moiety has little effect on the energy of
S0 and S1 states of the corrol moiety. No emission was observed for 2a, 3a, and 3b due to
the suppression by the metal center.
Fig. 3. Room-temperature emission and excitation spectrum of a) 3 and b) 2 in CH2Cl2

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Electrochemistry Study. The cyclic voltammetry for the corrolatometal complexes
1a, 2a, 3a, and 3b (Fig. 4) was examined in CH2Cl2 containing 0.1m (Bu4N)PF6.
Complex 1a undergoes two reversible reductions at E1/2 ¼ À1.45 and À 0.46 V vs. Ag/
Agþ, which can be confidently assigned to the reduction of the nitro group and the
metal center CuIII/CuII, respectively, based on a comparison with nonmetal complexes
of 1. There are also two reversible oxidations at E1/2 ¼ 0.54 and 1.28 V vs. Ag/Agþ. The
oxidation at E1/2 ¼ 0.54 V can be assigned to the oxidation of the corrole ring.
Compound 2a undergoes a single reversible reduction of CuIII/CuII at E1/2 ¼ À0.36 V.
Except for the two oxidations at E1/2 ¼ 0.56 V (oxidation of the corrole) and E1/2
¼
1.26 V, 2a undergoes an irreversible oxidation at Epa ¼ 1.10 V, caused by the oxidation
of the amine function.
Fig. 4. Cyclic voltammograms of 1a, 2a, 3a, and 3b in CH2Cl2 (Bu4N)PF6 (0.1m) as supporting
electrolyte, Ag/AgNO3 as reference electrode, glass carbon disc electrode as working electrode; scan rate
0.1 V/s.
No evidence of dimerization is observed for 1a and 2a in both the first oxidation and
the first reduction, which is different from the case of the well-known [Cu(oec)] (oec ¼
2,3,7,8,12,13,17,18-octaethylcorrolato(3À)) [34]. In the case of [Cu(oec)] the dimeri-
zation occurred upon oxidation, and the first two oxidations involved two stepwise

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abstractions of one electron from each macrocycle in the electrogenerated corrole p – p
dimer. It should be noted that also many triphenylcorrolato ligands show no evidence
of dimerization [25][31]. This means that the bulky substituents at the corrole
macrocycle must have a significant effect on the electrooxidation mechanism, and the
phenyl substituents at the corrole macrocycle preclude the formation of dimers.
The electrochemical reduction of 3a occurred at À 0.49 V, which can be assigned to
the reduction of CuIII/CuII, while its electrochemical oxidation involves two reversible
oxidations at E1/2 ¼ 0.38 and 0.56 V and two irreversible oxidations at Epc ¼ 1.14 V and
at Epa ¼ 1.31 V (broad peak). The [Mn(corrolato)] 3b shows one reversible reduction
and one quasireversible oxidation, with the E1/2 values located at À 0.17 and 0.77 V,
respectively. Thus dimerization occurred in the case of 3a in the oxidation, similarly to
the behavior of [Cu(oec)], while no dimerization was found for the [MnIV(corrolato)]
complex 3b.
In contrast to what is seen for 3a, no evidence of dimerization is observed for 1a, 2a,
and many other triphenylcorrolatometals as mentioned above. This indicates that the
l-tyrosine unit in 3a must play a very important role in this dimerization reaction. The
possible structure of the involved CuIII dimer is currently under investigation.
Conclusions. – A novel l-tyrosine-modified corrole ligand and its copper(III) and
mangane(IV) complexes were synthesized and characterized. The [CuIII(Tyr-corrola-
to)] complex 3a undergoes a series of multiple oxidations in CH2Cl2. The first two
unusual reversible oxidations show that dimerization may occur, and only one electron
from each macrocycle in the electrogenerated corrole p – p dimer may be abstracted at
each oxidation. One reversible reduction of the [CuIII(Tyr-corrolato)] complex 3a is
also observed, this reduction involving the metal center.
We gratefully acknowledge the financial support of this work from the following sources: Natural
Science Foundation of China (Grant No. 20633020 and 20672017), the Ministry of Science and
Technology (MOST) (Grant No. 2001CCA02500), the Swedish Energy Agency, the Wallenberg
Foundation, and The Swedish Research Council (VR). This research was also supported by the
Programme of Introducing Talents of Discipline to Universities
Experimental Part
General. All the reactions to synthesize 1 – 3 were conducted under Ar and in the dark. All solvents
were dried and distilled prior to use according to the standard methods. Commercially available
chemicals were used as received. The reagent Boc-l-Tyr-OH was purchased from Aldrich Chemical Co.
CC ¼ Column chromatography. 1H-NMRSpectra: Varian Inova-400 NMRspectrometer at 400 MHz and
298 K. MS: HP 1100-MSD instrument; Micromass Q-TOF micro spectrometer for high-resolution (HR);
in m/z.
5,15-Bis(4-methylphenyl)-10-(3-nitrophenyl)corrole (1). To a soln. of 5-(4-methylphenyl)dipyrro-
methane (18.88 g, 80 mmol) and 3-nitrobenzaldehyde (6.08 g, 40 mmol) in CH2Cl2 (600 ml), CF3COOH
(30 ml, 0.39 mmol) was added, and the mixture was stirred at r.t. for 5 h. Then chloranil (19.68 g,
80 mmol) was added, and the mixture was stirred for another 2 h. The mixture was filtered through a
short silica gel column (CH2Cl2), affording a mixture of 1 and several unidentified compounds.
Subsequent CC (silica gel, CH2Cl2/hexanes 5 :4) afforded pure 1 (2.10 g, 11%). Dark green solid. UV/
1
VIS (CH2Cl2): 417, 580, 614, 655. H-NMR(CDCl 3, 400 MHz): 2.68 (s, 2 MeC6H4); 7.63 (d, J ¼ 7.2, 4
arom. H of MeC6H4); 7.92 (t, J ¼ 7.2, 1 arom. H of NO2C6H4); 8.23 (d, J ¼ 6.4, 4 arom. H of MeC6H4);
8.41 (s, of Pyr 2 H); 8.48 (d, J ¼ 7.2, 1 arom. H of NO2C6H4); 8.58 (s, 1 arom. H of NO2C6H4, 2 H of Pyr);

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8.90 (s, 2 H of Pyr); 8.93 (s, 2 H of Pyr); 9.04 (s, 1 arom. H of NO2C6H4). HR-ESI-MS (neg.): 598.2229
([M À H]À, C39H28N5OÀ2 ; calc. 598.2243).
3-[5,15-Bis(4-methylphenyl)corrol-10-yl]benzenamine (2). SnCl2 · 2 H2O (183 mg, 0.81 mmol) in
37% aq. HCl soln. (10 ml) was added to a soln. of 1 (120 mg, 0.2 mmol) in CHCl3 (5 ml) and AcOH
(10 ml). The resulting mixture was vigorously stirred under reflux (65 – 708) overnight. After cooling to
r.t., the pH of the mixture was brought to 8 – 9 with 25% NH3 soln. CHCl3 (50 ml) was added, the mixture
stirred for 1 h, the aq. phase extracted with CHCl3 (2 ꢁ 50 ml), the combined org. phase washed with 5%
NH3 soln. (1ꢁ) and H2O (3ꢁ) and then concentrated, and the crude solid subjected to CC (silica gel,
CH2Cl2/acetone 100 :4): pure 2 (91 mg, 78%). Violet solid. UV/VIS (CH2Cl2): 417, 615. API-ES-MS:
1139.6 ([2M þ H]þ), 570.3 ([M þ H]þ). HR-ESI-MS: 570.2658 ([M þ H]þ, C39H32Nþ5 ; calc. 570.2673).
N1-{3-[5,15-Bis(4-methylphenyl)corrol-10-yl]phenyl}-N2-[(tert-butoxy)carbonyl]-l-tyrosinamide
(3). A soln. of 2 (57 mg, 0.1 mmol) and Boc-l-Tyr-OH (35 mg, 0.125 mmol) in CH2Cl2 (30 ml) was
stirred at 08. After 0.5 h, DCC (26 mg, 0.125 mmol) was added, and the mixture was left at r.t. for ca. 12 h.
Then the mixture was concentrated and the residue subjected to CC (silica gel, CH2Cl2/acetone 1:1): 3
(79 mg, 95%). Violet solid. UV/VIS: 418, 577, 617, 650. API-ES-MS: 855.3 ([M þ Na]þ), 833.4 ([M þ
H])þ. HR-ESI-MS: 833.3800 ([M þ 1]þ, C53H49N6O4þ ; calc. 833.3815).
[5,15-Bis(4-methylphenyl)-10-(3-nitrophenyl)corrolato(3-)-kN21,kN22,kN23,kN24]copper (1a). The
soln. of 1 (60 mg, 0.1 mmol) and Cu(OAc)2 · H2O (60 mg, 0.3 mmol) in pyridine (10 ml) was stirred at
r.t. for 5 min. The solvent was then evaporated and the crude solid purified by CC (silica gel, CH2Cl2/
hexanes 1:2): 1a (59 mg, 90%). Dark gray solid. UV/VIS (CH2Cl2): 417, 533. 1H-NMR(CDCl
,
3
400 MHz): 2.43 (s, 2 MeC6H4); 7.15 (d, J ¼ 4.8, 2 H of Pyr); 7.31 (d, J ¼ 7.6, 4 arom. H of MeC6H4); 7.38
(d, J ¼ 4.8, 2 H of Pyr); 7.63 (t, J ¼ 7.6, 1 arom. H of NO2C6H4); 7.67 (d, J ¼ 7.6, 4 arom. H of MeC6H4);
7.69 (d, J ¼ 4.4, 2 H of Pyr); 7.90 (d, J ¼ 4.0, 2 H of Pyr); 7.98 (d, J ¼ 7.6, 1 arom. H of NO2C6H4); 8.44 (d,
J ¼ 8.8, 1 arom. H of NO2C6H4); 8.53 (s, 1 arom. H of NO2C6H4). HR-ESI-MS (neg.): 659.1373 (MÀ,
C39H26CuN5OÀ2 ; calc. 659.1382).
{3-[5,15-Bis(4-methylphenyl)corrol-10-yl-kN21,kN22,kN23 ;kN24]benzenaminato(3 À )}copper (2a).
As described for 1a from 2 (57 mg, 0.1 mmol): 2a (58 mg, 92%), after CC (silica gel, CH2Cl2/hexanes
1:1). UV/VIS (CH2Cl2): 415, 540. API-ES-MS: 625.5 ([M þ Na]þ), 630.6 ([M þ H]þ). 1H-NMR(CDCl 3,
400 MHz): 2.44 (s, 2 MeC6H4); 3.77 (s, NH2); 6.88 (d, J ¼ 7.6, 1 arom. H of NH2C6H4); 7.00 (s, 1 arom. H of
NH2C6H4); 7.08 (d, J ¼ 8.0, 1 arom. H of NH2C6H4); 7.23 (t, J ¼ 7.6, 1 arom. H of NH2C6H4); 7.30 (d, J ¼
7.6, 4 arom. H of MeC6H4); 7.35 (s, 4 H of Pyr); 7.68 (d, J ¼ 7.6, 2 H of Pyr, 4 arom. H of MeC6H4); 7.88
(br. s, 2 H of Pyr). HR-ESI-MS: found 630.1728 ([M þ H]þ, C39H29CuN5þ ; calc. 630.1719).
{N1-{3-[5,15-Bis(4-methylphenyl)corrol-10-yl-kN21,kN22,kN23,kN24]phenyl}-N2-(tert-butoxy)carbon-
yl]-l-tyrosinamidato(3À)}copper (3a). As described for 1a, from 3 (83 mg, 0.1 mmol): 3a (67mg, 75%),
after CC (silica gel, CH2Cl2/acetone 20 :1). UV/VIS (CH2Cl2): 417, 539. 1H-NMR(400 MHz, (D 6)DMSO,
258)1): 1.32 (s, tBu); 2.43 (s, 2 MeC6H4); 2.70 – 2.76 (m, 1 H, CH2(3)); 2.86 – 2.92 (m, 1 H, CH2(3)); 4.26
(br. s, HÀC(4)); 6.64 (d, J ¼ 8.4, 2 arom. H of Tyr); 7.05 (d, J ¼ 8.0, 1 H, CONH); 7.09 (d, J ¼ 8.4, 2 arom.
H of Tyr); 7.25 (br. s, 2 H of Pyr); 7.30 (d, J ¼ 7.6, 1 arom. H of NHC6H4); 7.35 (br. s, 2 H of Pyr); 7.39 (d,
J ¼ 7.6, 4 arom. H of MeC6H4); 7.49 (t, J ¼ 7.6, 1 arom. H of NHC6H4); 7.62 (br. s, 2 H of Pyr, 4 arom. H of
MeC6H4); 7.86 (d, J ¼ 9.2, 2 arom. H of NHC6H4); 8.10 (br. s, 2 H of Pyr); 9.16 (s, NHC6H4); 10.19 (s,
OH). API-ES-MS: 927 ([M þ Cl]À), 915.5 ([M þ Na]þ), 892.3 (MÀ). Anal. calc. for C53H45CuN6O4 · 0.5
CH2Cl2: C 68.65, H 4.95, N 8.98; found: C 68.97, H 5.04, N 9.38.
(Acetato-kO){N1-{3-[5,15-bis(4-methylphenyl)corrol-10-yl-kN21;kN22,kN23,kN24]phenyl}-N2-(tert-
butoxy)carbonyl]-l-tyrosinamidato(3À)}manganese (3b). A soln. of 3 (83 mg, 0.1 mmol) and an excess
of manganese(II) acetate tetrahydrate (0.25 g, 1.0 mmol) in DMF (10 ml) was refluxed under air for
10 min. After the solvent was evaporated, the residue was subjected to CC (silica gel, CH2Cl2/acetone
10 :1): pure 3b (48 mg, 54%). Brown solid. UV/VIS (CH2Cl2):317, 367, 437, 721. API-ES-MS: 884.4
([M À OAc]þ). HR-ESI-MS 884.2894 ([M À OAc]þ), C53H45MnN6Oþ4 ; calc. 884.2883).

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REFERENCES
[1] V. L. Pecoraro, M. J. Baldwin, A. Gelasco, Chem. Rev. 1994, 94, 807.
[2] W. Ruttinger, G. C. Dismukes, Chem. Rev. 1997, 97, 1.
[3] M. Yagi, M. Kaneko, Chem. Rev. 2001, 101, 21.
[4] N. Kamiya, J. R. Shen, Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 98.
[5] K. N. Ferreira, T. M. Iverson, K. Maghlaoui, J. Barber, S. Iwatal, Science (Washington, D.C.) 2004,
303, 1831.
[6] B. Loll, J. Kern, W. Saenger, A. Zouni, J. Biesiadka, Nature (London) 2005, 438, 1040.
[7] C. Turro, C. K. Chang, G. E. Leroi, R. I. Cukier, D. G. Nocera, J. Am. Chem. Soc. 1992, 114, 4013.
[8] X. G. Zhao, R. I. Cukier, J. Phys. Chem. 1995, 99, 945.
[9] C. Tommos, X.-S. Tang, K. Warncke, C. W. Hoganson, S. Styring, J. McCracken, B. A. Diner, G. T.
Babcock, J. Am. Chem. Soc. 1995, 117, 10325.
[10] M. R. A. Blomberg, P. E. M. Siegbahn, S. Styring, G. T. Babcock, B. Škermark, P. Korall, J. Am.
Chem. Soc. 1997, 119, 8285.
[11] C. W. Hoganson, G. T. Babcock, Science (Washington, D.C.) 1997, 277, 1953.
[12] P. Huang, J. Hçgblom, M. F. Anderlund, L. Sun, A. Magnuson, S. Styring, J. Inorg. Biochem. 2004,
98, 733.
[13] M. Sjçdin, S. Styring, B. Škermark, L. Sun, L. Hammarstrçm, J. Am. Chem. Soc. 2000, 122, 3932.
[14] L. Sun, M. Burkitt, M. Tamm, M. K. Raymond, M. Abrahamsson, D. LeGourrierec, Y. Frapart, A.
Magnuson, P. H. Kenez, P. Brandt, A. Tran, L. Hammarstrçm, S. Styring, B. Škermark, J. Am. Chem.
Soc. 1999, 121, 6834.
[15] J. P. Collman, R. A. Decreau, C. Zhang, J. Org. Chem. 2004, 69, 3546.
[16] M. Haumann, P. Liebisch, C. Müller, M. Barra, M. Grabolle, H. Dau, Science (Washington, D.C.)
2005, 310, 1019.
[17] G. C. Dismukes, K. Ferris, P. Watnick, Photobiochem. Photobiophys. 1982, 3, 243.
[18] V. L. Pecoraro, M. J. Baldwin, M. T. Caudle, W. Hsieh, N. A. Law, Pure Appl. Chem. 1998, 70, 925.
[19] P. E. M. Siegbahn, R. H. Crabtree, J. Am. Chem. Soc. 1999, 121, 117.
[20] Z. Gross, G. Golubkov, L. Simkhovich, Angew. Chem., Int. Ed. 2000, 39, 4045.
[21] L. Simkhovich, A. Mahammed, I. Goldberg, Z. Gross, Chem.–Eur. J. 2001, 7, 1041.
[22] J. Bendix, I. J. Dmochowski, H. B. Gray, A. Mahammed, L. Simkhovich, Z. Gross, Angew. Chem.,
Int. Ed. 2000, 39, 4048.
[23] A. Mahammed, Z. Gross, J. Inorg. Biochem. 2002, 88, 305.
[24] D. Aviezer, S. Cotton, M. David, A. Segev, N. Khaselev, N. Galili, Z. Gross, A. Yayon, Cancer Res.
2000, 60, 2973.
[25] I. Luobeznova, L. Simkhovich, I. Goldberg, Z. Gross, Eur. J. Inorg. Chem. 2004, 1724.
[26] G. Golubkov, Z. Gross, J. Am. Chem. Soc. 2005, 127, 3258.
[27] D. T. Gryko, K. Jadach, J. Org. Chem. 2001, 66, 4267.
[28] S. Will, J. Lex, E. Vogel, H. Schmickler, J.-P. Gisselbrecht, C. Haubtmann, M. Bernard, M. Gross,
Angew. Chem., Int. Ed. 1997, 36, 357.
[29] C. Bruckner, R. P. Brinas, J. A. Krause Bauer, Inorg. Chem. 2003, 42, 4495.
´ ˆ
[30] R. Guilard, C. P. Gros, J.-M. Barbe, E. Espinosa, F. Jerome, A. Tabard, J.-M. Latour, J. Shao, Z. Ou,
K. M. Kadish, Inorg. Chem. 2004, 43, 7441.
[31] I. H. Wasbotten, T. Wondimagegn, A. Ghosh, J. Am. Chem. Soc. 2002, 124, 8104.
[32] E. Steene, T. Wondimagegn, A. Ghosh, J. Inorg. Biochem. 2002, 88, 113.
[33] E. Steene, T. Wondimagegn, A. Ghosh, J. Phys. Chem. B. 2001, 105, 11406.
[34] K. M. Kadish, V. A. Adamian, E. Van Caemelbecke, E. Gueletii, S. Will, C. Erben, E. Vogel, J. Am.
Chem. Soc. 1998, 120, 11986.
Received October 17, 2006