Hydroperoxo-copper(II) complex stabilized by N3S-type ligand having a phenyl thioether [2]

Full text of DOI:10.1021/ja010689n

J. Am. Chem. Soc. 2001, 123, 7715-7716
7715
Scheme 1
Hydroperoxo-Copper(II) Complex Stabilized by
N3S-Type Ligand Having a Phenyl Thioether
Masahito Kodera,*,† Toshio Kita,† Izumi Miura,†
Noritoshi Nakayama,† Tomohisa Kawata,† Koji Kano,† and
Shun Hirota‡
Department of Molecular Science and Technology
Doshisha UniVersity, Kyotanabe
structures of 1 and 2 are revealed by X-ray analysis5 (Figure 1
and Supporting Information) where the Cu(II) ion in 1 takes
distorted square-pyramidal geometry on the basis of τ value6 0.39.
The PhS-sulfur in 1 weakly coordinates to Cu(II) ion with the
Cu-S bond length 2.6035(3) Å, similar to 2.68 Å in the oxidized
PHM.3 The S-CuII LMCT band of 1 in MeCN appears at 410
nm, clearly showing that the PhS-sulfur coordinates to Cu(II) ion
in solution.7 The highly polarizable sulfur donor in 1 stabilizes
the low-valence state of the Cu ion, as shown by the CuI/CuII
redox potentials, 0.124, 0.106, and 0.101 V versus SCE, for 1,
[Cu(L4)Cl](ClO4), and [Cu(L5)Cl](ClO4), respectively.8
Addition of 2.5 equiv of H2O2 to a solution of 2 in MeCN at
-40 °C generated a dark green species 3 that exhibits an intense
absorption band at 357 nm (4300 M-1 cm-1) and a d-d band at
600 nm (140 M-1 cm-1) (Scheme 2 and Figure 2). The former
band is close to the HO2--CuII LMCT bands at 380 nm (890
M-1 cm-1) of a five-coordinate CuO2H complex of bis(6-
pivalamide-2-pyridylmethyl)(2-pyridylmethyl)amine (bppa)9 and
at 395 nm (7000 M-1 cm-1) of a five-coordinate Cu2O2H complex
of 2,6-bis[bis[2-(2-pyridyl)ethyl]amino]phenolate (XYL-O-),10 but
far from that at 604 nm (1180 M-1 cm-1) of a four-coordinate
CuO2H complex of sterically hindered hydrotrispyrazolyl borate
ligand [HB(3-tBu-5-iPrpz)3].11 The bands at 357 and 600 nm of
3 are tentatively assigned to the HO2--CuII LMCT and d-d
transitions, respectively. The ESR spectrum of a frozen solution
of 3 (g| ) 2.24, g ) 2.06, A| ) 168 G) in MeCN at 77 K,12
similar to that of 1 (g| ) 2.25, g ) 2.09, A| ) 101 G), is
characteristic of a square-pyramidal mononuclear Cu(II) com-
plex.13 3 shows clear hyperfine splitting with relatively large A|
value, different from the broad ESR spectrum of the four-
coordinate CuO2H complex of HB(3-tBu-5-iPrpz)3.11 The reso-
Kyoto 610-0321, Japan
Department of Chemistry
Graduate School of Science, Nagoya UniVersity
Chikusa-ku, Nagoya 464-01, Japan
ReceiVed March 15, 2001
The hydroperoxo-copper(II) (CuO2H) complex is a key
intermediate in O2-activation by dopamine â-monooxygenase
(DBM), which has two copper ions (CuH and CuM) at a distance
larger than 4 Å, and the O2 molecule is activated at the CuM site
to hydroxylate the benzylic position of dopamine.1 The reduced
I
I
form of DBM has a CuH (His)3‚‚‚CuM (His)2X(Met)-type of
structure.2 In the oxidized form of peptidylglycine R-hydroxylating
monooxygenase (PHM), structurally and functionally similar to
II
DBM, the sulfur atom of the Met coordinates to the CuM ion
(Cu-S, 2.68 Å).3 Since the Met is essential for enzymatic activity
of PHM,3c it might participate, through coordination to the CuM,
in the formation and activation of the CuO2H intermediate.
It is known that N3S- and N2S2-type ligands having methyl
thioethers stabilize Cu(I) complexes by coordination of the sulfur
donors which may prevent O2-binding, and Cu(II) complexes of
N3S-type ligands react with H2O2 to only oxygenate the ligands
to the sulfoxide and sulfone derivatives.4 Here, we report the
synthesis and characterization of the CuO2H complex of N3S-
type ligand having a phenyl thioether (PhS-ether), 2-bis(6-methyl-
2-pyridylmethyl)amino-1-(phenylthio)ethane (L1), and that the
PhS-ether specifically stabilizes the CuO2H complex. This is the
first example for a CuO2H complex of a N3S-type ligand having
a thioether and may give some spectral and mechanistic informa-
tion for the O2-activation by DBM and PHM.
The ligand L1 forms Cu(II) complexes [Cu(L1)Cl](ClO4) (1)
and [Cu(L1)(OH)]2(ClO4)2 (2), and the other N3S-, N3-, and N3O-
type ligands (Ln, n ) 2-5) shown in Scheme 1 form similar
complexes. The mononuclear and di-µ-hydroxo-bridged dinuclear
(5) 1 (C22H25N3ScuCl2O4, MW 561.97) crystallized in the triclinic space
group P1h with a ) 12.718(1) Å, b ) 12.897(2) Å, c ) 7.7543(9) Å, R )
100.80(1)°, â ) 98.05(1)°, γ )76.431(9)°, V ) 1208.3(3) Å3, Z ) 2, R(Rw)
) 0.057(0.063), GOF ) 1.69. 2‚2MeCN‚H2O (C48H60N8S2Cu2Cl2O11, MW
1187.17) crystallized in the monoclinic space group P21/c with a ) 11.192-
(4) Å, b ) 19.327(4) Å, c ) 12.971(5) Å, â ) 101.97(3)°, V ) 2745(1) Å3,
Z ) 2, R(Rw) ) 0.083(0.094), GOF ) 1.31.
* To whom correspondence should be addressed. Dr. Masahito Kodera.
Department of Molecular Science and Technology, Faculty of Engineering,
DoshishaUniversity, Kyotanabe, Kyoto 610-0321, Japan. Telephone number:
+81-774-65-6652. Fax number: +81-774-65-6848. E-mail address: mkodera@
mail.doshisha.ac.jp.
(6) Addison, A. W.; Rao, T. N.; Reedijk, J.; Rijin, J. V.; Verschoor, G. C.
J. Chem. Soc., Dalton Trans. 1984, 1349.
(7) The UV-vis spectrum of 1 in MeCN shows three bands at 337 nm (ꢀ
† Doshisha University.
1280 M-1 cm-1), 410 nm (ꢀ 430 M-1 cm-1), and 650 nm (ꢀ 180 M-1 cm-1
)
‡ Nagoya University.
with a low-energy shoulder (750 nm, ꢀ 140 M-1 cm-1), which are respectively
assigned to Cl--CuII and S-CuII LMCTs and d-d transitions, while those
of [Cu(L4)Cl](ClO4) and [Cu(L5)Cl](ClO4) show two absorption bands at
around 340 and 740 nm respectively assigned to Cl--CuII LMCTs and d-d
transitions.
(1) (a) Stewart, L. C.; Klinman, J. P. Annu. ReV. Biochem. 1988, 57, 551.
(b) Blackburn, N. J.; Pettingill, T. M.; Seagraves, K. S.; Shigeta, R. T. J.
Biol. Chem. 1990, 265, 15383. (c) Pettingill, T. M.; Strange, R. W.; Blackburn,
N. J. J. Biol. Chem. 1991, 266, 16996. (d) Blackburn, N. J. In Bioinorganic
Chemistry of Copper; Karlin, K. D., Tyeclar, Z., Eds.; Chapman & Hall: New
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Biochemistry 1994, 33, 226. (f) Klinman, J. P. Chem. ReV. 1996, 96, 2541.
(g) Blackburn, N. J.; Rhames, F. C.; Ralle, M. Jaron, S. J. Biol. Inorg. Chem.
2000, 5, 341.
(8) The CVs of 1, [Cu(L4)Cl](ClO4), and [Cu(L5)Cl](ClO4) were measured
with a glassy carbon, a platinum, and a Ag/Ag+ (TBAP/MeCN) electrodes as
a working, a counter, and a reference electrodes, respectively, with a scan
rate of 1 × 102 mV s-1, at a concentration of 1 × 10-3 M in MeCN with 0.1
M tetra-n-butylammonium perchlorate (TBAP) under N2.
(2) (a) Blackburn, N. J.; Hasnain, S. S.; Pettingill, T. M.; Strange, R. W.
J. Biol. Chem. 1991, 266, 23120. (b) Reedy, B. J.; Blackburn, N. J. J. Am.
Chem. Soc. 1994, 116, 1924.
(3) (a) Merkler, D. J.; Kulathila, R.; Consalvo, A. P.; Young, S. D.; Ash,
D. E. Biochemistry 1992, 31, 7282. (b) Prigge, S. T.; Kolhekar, A. S.; Eipper,
B. A.; Mains, R. E.; Amzel, L. M. Science 1997, 278, 1300. (c) Eipper, B.
A.; Quon, A. S. W.; Mains, R. E.; Boswell, J. S.; Blackburn, N. J. Biochemistry
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(4) (a) Casella, L.; Gullotti, M.; Bartosek, M.; Pallanza, G.; Laurenti, E. J.
Chem. Soc., Chem. Commun. 1991, 1235. (b) Champloy, F.; Benali-Che´if,
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(c) Ohta, T.; Tachiyama, T.; Yoshizawa, K.; Yamabe, T.; Uchida, T.; Kitagawa,
T. Inorg. Chem. 2000, 39, 4358.
(9) Wada, A.; Harata, M.; Hasegawa, K.; Jitsukawa, K.; Masuda, H.; Mukai,
M.; Kitagawa, T.; Einaga, H. Angew. Chem., Int. Ed. 1998, 37, 798.
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(11) Chen, P.; Fujisawa, K.; Solomon, E. I. J. Am. Chem. Soc. 2000, 122,
10177.
(12) The ESR spectrum of 2 in MeCN at 77K shows broad signal with g
) 2.11 because of magnetic interaction operating between the two Cu(II) ions.
The broad signal of 2 was quantitatively changed to the sharp rohmbic signals
of 3 upon addition of H2O2.
10.1021/ja010689n CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/11/2001

7716 J. Am. Chem. Soc., Vol. 123, No. 31, 2001
Communications to the Editor
Figure 1. ORTEP view (40% probability) of [Cu(L1)Cl]+ (1). Unlabeled
atoms (open circles) represent carbon atoms. Selected bond lengths (Å)
and angles (deg): Cu-Cl(1), 2.2159(3); Cu-N(1), 2.0277(2); Cu-N(2),
2.0149(2); Cu-N(3), 2.0832(3); Cu-S, 2.6035(3); Cl(1)-Cu-N(1),
96.65(1); Cl(1)-Cu-N(2), 95.87(1); Cl(1)-Cu-N(3), 141.276(7); Cl-
(1)-Cu-S, 132.221(8); N(1)-Cu-N(2), 164.675(3); N(1)-Cu-N(3),
82.49(1); N(1)-Cu-S, 84.047(9); N(2)-Cu-N(3), 82.22(1); N(2)-Cu-
S, 94.015(9); N(3)-Cu-S, 86.37(1).
Figure 2. Electronic spectra of 2 (- - -) and 3 (s) in MeCN at -40 °C.
The inset shows the time course monitored at 350 nm for generation and
decomposition of the CuO2H complexes, 3 (×), 4 (b), and 5 (+) in MeCN
at -40 °C.
of the PhS-ether in L1 were used to clarify the effect of the PhS-
ether on the stabilization of 3. The CuO2H complexes [Cu(Ln)-
(O2H)](ClO4) {n ) 4 (4) and 5 (5)} were generated upon reaction
of the di-µ-hydroxo-dicopper(II) complexes of L4 and L5 with
-
Scheme 2
H2O2 in MeCN at -40 °C, and showed characteristic HO2
-
CuII LMCT bands and ESR spectra similar to those of 3. The
generation and decomposition of 4 and 5 monitored at around
350 nm are shown in Figure 2. The half-life times of 4 and 5 are
18 and 69 s at -40 °C, respectively, and are much shorter than
that of 3, demonstrating that the PhS-ether specifically stabilizes
the CuO2H complex. The highly polarizable PhS-sulfur donor may
enhance the covalent character of the Cu-O bond to stabilize 3.
We also found that a methyl and an isopropyl thioethers of
the N3S-type ligands (L2 and L3) are not effective to stabilize
the CuO2H complex. Upon addition of H2O2 to the di-µ-hydroxo-
dicopper(II) complexes of L2 and L3 in MeCN at -40 °C, the
CuO2H complexes were not detected at all, and the alkyl thioethers
were converted to the sulfoxides and sulfones, indicating that the
alkyl thioethers are directly oxidized by H2O2 added. The most
significant characteristic of the PhS-ether, compared with the alkyl
thioethers, is high stability against oxidation by H2O2. That is
why the PhS-ether of L1, being not oxidized by H2O2, can stabilize
the CuO2H complex through coordination. Although the Met
residue at the CuM site is an alkyl thioether, it may be protected
from oxidation in the active site of DBM and PHM,15 and
furthermore it is not likely that the Met is directly oxidized by
free H2O2 because the CuO2H species is formed reductively via
O2-binding. Therefore, we propose that the Met in DBM and
PHM, being not oxidized in the catalytic cycle, may be responsible
for formation of the CuO2H intermediate through coordination
to the CuM ion.
nance Raman spectrum obtained with 363.8 nm excitation of 3
in MeCN at -30 °C shows a strong resonance-enhanced Raman
band at 881 cm-1, which shifted to 832 cm-1 (∆ν ) 49 cm-1
)
when 3 was labeled with H218O2.14 The ∆ν value observed is
almost equal to the calculated one at 50 cm-1. These values are
in the range of νO-O vibrations typical of peroxide species. The
ν
O-O vibration at 881 cm-1 of 3 is close to those at 856 cm-1 for
the CuO2H complex of bppa,9 at 843 cm-1 for the CuO2H complex
of HB(3-tBu-5-iPrpz)3,11 and at 892 cm-1 for the Cu2O2H complex
of (XYL-O-).10c These Raman data indicate that the hydroperoxo
moiety is bound to the Cu(II) ion and the intense absorption band
at 357 nm can be assigned to the HO2--CuII LMCT. A relatively
weak S-CuII LMCT band might be involved in the wide-based
low-energy region of the HO2--CuII LMCT band (Figure 2).
These data demonstrate that 3 is a mononuclear CuO2H complex
[Cu(L1)(O2H)](ClO4) where the PhS-sulfur coordinates to Cu-
(II) ion.
Acknowledgment. This work was supported by a grant to RCAST
at Doshisha University from the Ministry of Education, Science, Sports,
and Culture, Japan. We thank Professor Teizo Kitagawa, Institute for
Molecular Science, for permission to use the resonance Raman equipment.
As shown in Figure 2, relatively high stability of 3 was
observed with measurement of the decomposition rate in MeCN
at -40 °C. The spontaneous decomposition of 3 monitored at
357 nm obeys good first-order kinetics with k ) 5.9 × 10-5 s-1
at -40 °C (half-life time τ1/2 ) 3.3 h). The N3- and N3O-type
ligands having a phenyl (L4) and a phenoxy (L5) group instead
Supporting Information Available: Tables S1-S8: crystallographic
experimental details, final atomic coordinates, thermal parameters, and
full bond distances and angles for 1 and 2, and syntheses and spectroscopic
data of L1 and complexes 1 and 2, and Figures S1-S3: ORTEP view of
2, ESR, and resonance Raman spectra of 3. (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
(13) (a) Sugiura, Y. Inorg. Chem. 1978, 17, 2176. (b) Duggan, M.; Ray,
N.; Hathaway, B.; Tomlinson, G.; Brint, P.; Plein, K. J. Chem. Soc., Dalton
Trans. 1980, 1342. (c) Karlin, K. D.; Hayes, J. C.; Juen, S.; Hutchinson, J.
P.; Zubieta, J. Inorg. Chem. 1982, 21, 4108.
JA010689N
(14) The resonance Raman spectrum of 3 shows a very weak signal at 569
cm-1, which shifts to 552 cm-1 with 18O2 labeling. It is difficult to assign the
peak to νCu-O due to the poor quality. Similar difficulty to observe the νCu-O
was reported by Root and Solomon with the Cu2O2H complex of (XYL-O-)
in ref 10c.
(15) Although the Met residue of the DBM and PHM is not oxidized in
the catalytic cycle, it is reported that in nitrile hydratase, cysteine thiolate
groups bound to iron (or cobalt) ion are oxidized to sulfenate and sulfinate.
See for example: Tyler, L. A.; Noveron, J. C.; Olmstead, M. M.; Mascharak,
P. K. Inorg. Chem. 2000, 39, 357.