Aliphatic hydroxylation by a bis(μ-oxo)dinickel(III) complex [3]

Full text of DOI:10.1021/ja991326e

J. Am. Chem. Soc. 1999, 121, 8945-8946
8945
Aliphatic Hydroxylation by a Bis(µ-oxo)dinickel(III)
Complex
,
†
†
‡
Shinobu Itoh,* Hideki Bandoh, Shigenori Nagatomo,
,‡
,†
Teizo Kitagawa,* and Shunichi Fukuzumi*
Department of Material and Life Science
Graduate School of Engineering, Osaka UniVersity
2
-1 Yamada-oka, Suita, Osaka 565-0871, Japan
Institute for Molecular Science
Myodaiji, Okazaki 444-8585, Japan
ReceiVed April 26, 1999
The structure and reactivity of transition-metal complexes of
active oxygen species have long been among the most important
and attractive subjects not only in bioinorganic chemistry but also
in synthetic organic reactions.1 Among several types of mono-,
di-, and polynuclear transition-metal active oxygen complexes,
2 2
Figure 1. Spectral change observed upon addition of 1 equiv of H O
-7
H
II
-4
into an acetone solution of [(L Ni )
-90 °C in a 1-cm path length UV cell; 2-s interval. Inset: First-order
2
(µ-OH)
2
](ClO
4
)
2
(2.5 × 10 M) at
plot based on the absorption change at 408 nm.
2
high-valent bimetallic bis(µ-oxo) complexes [M(µ-O) M] have
recently attracted particular attention as possible reaction inter-
mediates in oxygen metabolism, such as dioxygen activation for
substrate hydroxylation and for tyrosyl radical formation by non-
heme metalloenzymes and dioxygen evolution in photosystem
Chart 1
8-12
II.
plexes have been well characterized by X-ray crystallographic
analyses on M(µ-O) M complexes where M ) Fe, Cu, Mn, and
The reactivities of M(µ-O) M complexes where M )
Fe, Cu, and Mn have also been explored in relation with aliphatic
The structures of high-valent bimetallic bis(µ-oxo) com-
2
11,13-17
Ni.
2
1
4c,18-20
C-H bond activation.
O) M complexes is currently receiving increased attention as the
key step in reactions of methane monooxygenases (MMO) and
Such C-H bond activation by M(µ-
reactivity of which can be finely tuned by varying the metals
and the ligands. In addition, the formation mechanism of M(µ-
2
O) M complexes has yet to be elucidated. We report herein the
2
9b,12
related enzymes.
To elucidate the C-H bond activation
III
III
2
first aliphatic ligand hydroxylation by a Ni (µ-O) Ni complex,
mechanism, it is highly desired to explore C-H bond activation
by different types of active oxygen-metal complexes, the
the formation and decay of which were directly followed by
spectroscopy.21 We have previously reported the same type of
aliphatic hydroxylation of the ligand sidearm in the reaction of
†
Osaka University.
‡
Institute for Molecular Science.
2
2
the Cu(I) complex with O , where a (µ-η :η -peroxo)dicopper-
2
(
1) Valentine, J. S., Foote, C. S., Greenberg, A., Liebman, J. F., Eds. ActiVe
Oxygen in Biochemistry; Chapman and Hall: London, 1995.
2) Foote, C. S., Valentine, J. S., Greenberg, A., Liebman, J. F., Eds. ActiVe
Oxygen in Chemistry; Chapman and Hall: London, 1995.
(II) complex rather than a bis(µ-oxo)dicopper(III) complex was
observed as a reaction intermediate.22 Thus, this study provides
an excellent opportunity to disclose the actual role and reactivity
(
(
(
(
3) Kitajima, N.; Moro-oka, Y. Chem. ReV. 1994, 94, 737-757.
4) Feig, A. L.; Lippard, S. J. Chem. ReV. 1994, 94, 759-805.
5) Pecoraro, V. L.; Baldwin, M. J.; Gelasco, A. Chem. ReV. 1994, 94,
2
2
of bis(µ-oxo) vs (µ-η :η -peroxo) bimetallic complexes in the
C-H bond activation process.
8
07-826.
Bis(µ-hydroxo)dinickel(II) complexes of tridentate ligands LX
X ) OMe, Me, H, Cl; Chart 1) have been prepared as starting
(
6) Solomon, E. I.; Tuczek, F.; Root, D. E.; Brown, C. A. Chem. ReV.
(
1
994, 94, 827-856.
(
(
7) Shilvo, A. E.; Shul’pin, G. B. Chem. ReV. 1997, 97, 2879-2932.
8) Valentine, A. M.; Lippard, S. J. J. Chem. Soc., Dalton Trans. 1997,
materials by treating the ligand and Ni(ClO
presence of triethylamine in a mixed solvent system of acetone/
methanol/acetonitrile.23 Addition of 1 equiv of H
into an
at a low temperature
)
2
2
‚6H O in the
4
3
925-3931.
2 2
O
(
9) (a) Que, L., Jr. J. Chem. Soc., Dalton Trans. 1997, 3933-3940, (b)
H
II
2+
Shu, L.; Nesheim, J. C.; Kauffmann, K.; Munck, E.; Lipscomb, J. D.; Que,
acetone solution of [(L Ni )
2
(µ-OH) ]
2
L., Jr. Science 1997, 275, 515-518.
(
(
(
(
-90 °C) resulted in a spectral change, as shown in Figure 1,
10) Tommos, C.; Babcock, G. T. Acc. Chem. Res. 1998, 31, 18-25.
11) Ruttinger, W.; Dismukes, G. C. Chem. ReV. 1997, 97, 1-24.
12) Elliot, S. J.; Zhu, M.; Tso, L.; Nguyen, H.-H. T.; Yip, J. H.-K.; Chan,
-
1
where a characteristic absorption band at 408 nm (ꢀ ) 6000 M
-
1
cm ) due to an intermediate readily developed. The same
absorption intensity at 408 nm was obtained even when an excess
S. I. J. Am. Chem. Soc. 1997, 119, 9949-9955.
13) Hsu, H.-F.; Dong, Y.; Shu, L.; Young, V. G., Jr.; Que, L., Jr. J. Am.
Chem. Soc. 1999, 121, 5230-5237.
14) (a) Halfen, J. A.; Mahapatra, S.; Wilkinson, E. C.; Kaderli, S.; Young,
(
2 2
amount of H O
was added (S1).24 Thus, the stoichiometry of
H
II
(
H
O
2 2
to [(L Ni )
2
(µ-OH)
2
] has been determined to be 1:1. The
V. G., Jr.; Que, L., Jr.; Tolman, W. B. Science 1996, 271, 1397-1400. (b)
Mahapatra, S.; Halfen, J. A.; Wilkinson, E. C.; Pan, G.; Wang, X.; Young,
V. G., Jr.; Cramer, C. J.; Que, L., Jr.; Tolman, W. B. J. Am. Chem. Soc.
-1
18
intermediate exhibited a resonance Raman band at 612 cm ,
-
1
16
which shifted to 580 cm when H
2
O
2
was replaced by H
2
O
2
(S2).24 In addition, this intermediate was ESR silent.
1
996, 118, 11555-11574. (c) Mahadevan, V.; Hou, Z.; Cole, A. P.; Root, D.
E.; Lal, T. K.; Solomon, E. I.; Stack, T. D. P. J. Am. Chem. Soc. 1997, 119,
1996-11997.
15) (a) Que, L., Jr.; True, A. E. Prog. Inorg. Chem. 1990, 38, 97-200.
b) Lal, T. K.; Mukherjee, R. Inorg. Chem. 1998, 37, 2373-2382 and
references therein.
16) Limburg, J.; Vrettos, J. S.; Liable-Sands, L. M.; Rheingold, A. L.;
Crabtree, R. H.; Brudvig, G. W. Science 1999, 283, 1524-1527.
17) Hikichi, S.; Yoshizawa, M.; Sasakura, Y.; Akita, M.; Moro-ka, Y. J.
Am. Chem. Soc. 1998, 120, 10567-10568.
1
(21) So far, only two examples of ligand hydroxylation of mononuclear
Ni(II) complexes by dioxygen have been reported. However, the structure of
the active oxygen intermediate has yet to be identified: (a) Kimura, E.;
Sakonaka, A.; Machida, R. J. Am. Chem. Soc. 1982, 104, 4225-4227. (b)
Chen, D.; Martell, A. E. J. Am. Chem. Soc. 1990, 112, 9411-9412.
(22) (a) Itoh, S.; Kondo, T.; Komatsu, M.; Ohshiro, Y.; Li, C.; Kanehisa,
N.; Kai, Y.; Fukuzumi, S. J. Am. Chem. Soc. 1995, 117, 4714-4715. (b)
Itoh, S.; Nakao, H.; Berreau, L. M.; Kondo, T.; Komatsu, M.; Fukuzumi, S.
J. Am. Chem. Soc. 1998, 120, 2890-2899.
(
(
(
(
(
18) Kim, C.; Dong, Y.; Que, L., Jr. J. Am. Chem. Soc. 1997, 119, 3635-
3
636.
(23) Experimental details about the synthesis and characterization of the
bis(µ-hydroxo)dinickel(II) complexes, the product analysis, and the kinetics
are deposited in Supporting Information.
(
19) Mahapatra, S.; Halfen, J. A.; Tolman, W. B. J. Am. Chem. Soc. 1996,
1
18, 11575-11586.
(
20) Wang, K.; Mayer, J. M. J. Am. Chem. Soc. 1997, 119, 1470-1471.
(24) See Supporting Information.
1
0.1021/ja991326e CCC: $18.00 © 1999 American Chemical Society
Published on Web 09/09/1999

8946 J. Am. Chem. Soc., Vol. 121, No. 38, 1999
Communications to the Editor
Scheme 1
The oxygen source for the OH group in LHOH has been confirmed
as hydrogen peroxide by the isotope labeling experiment using
1
8
26
H
2
O
2
.
The ligand hydroxylation process obeyed first-order
24
kinetics (S4), and from the temperature dependence of the decay
rate (k
24
d
) (Eyring plot, line H in S5) were obtained the activation
q -1 q
parameters ∆H
H
) 14.9 ( 0.2 kcal mol and ∆S
H
) -10.1 (
H
-
1
-1
0
.8 cal K mol . Perdeuteration of the ligand sidearm (L -d
4
;
1,1,2,2-tetradeuterated phenethylamine derivative) resulted in a
significant decrease in the decay rate, as shown in S5 (line D),
q
where the activation parameters were determined to be ∆H
D
)
-
1
q
-1
-1 28
1
7.2 ( 0.1 kcal mol and ∆S
D
) -7.0 ( 0.4 cal K mol .
A very large kinetic deuterium isotope effect was obtained for
the hydroxylation reaction (e.g., KIE ) 21.4 at -20 °C).
Furthermore, examination of the para-substituent effects (Ham-
The characteristic absorption band at 408 nm is fairly close to
that of Hikichi’s bis(µ-oxo)dinickel(III) complex (410 nm, ꢀ )
+
24
mett plot of k vs σ ) gave F ) -0.83 (R ) 0.98) (S6), which
d
-
1
-1 17
4
6
(
200 M cm ). The low-frequency resonance Raman band at
is nearly the same as the F value for the oxidative N-dealkylation
-1
2+
(p-R)Bn3
2+
(p-R)Bn3
12 cm is also very similar to those of [Cu
2 2
(µ-O) ]
complexes
in [(L
Cu) (µ-O) ] (F ) -0.8, L
) 1,4,7-tri(para-
2
2
-
1 14
∼600 cm ). In addition, the observed isotope shift of the
substituted-benzyl)triazacyclononane), where hydrogen atom ab-
-
1
19
resonance Raman band (∆ν ) 32 cm ) agrees well with the
straction by the bis(µ-oxo) complex is the rate-determining step.
-1
X
III
2+
expected shift of 28 cm for diatomic Ni-O stretch. From these
Thus, ligand hydroxylation in [(L Ni ) (µ-O) ] may proceed
2
2
spectroscopic characteristics, together with the stoichiometry of
via the rate-determining hydrogen abstraction (k ), followed by
d
H
II
29
H
O
2 2
to [(L Ni )
2
(µ-OH)
2
] (1:1), the intermediate is most likely
hydroxyl rebound.
a bis(µ-oxo)dinickel(III) complex. The same absorption spectra
It is interesting to note that the nickel(II) complex affords a
X
with λmax ) 408 nm were obtained in other ligand systems (L ).
bis(µ-oxo)dinickel(III) complex, whereas the copper(II) complex
2
2
The increase of the absorption band at 408 nm obeyed first-
order kinetics, as shown in the inset of Figure 1. The rate constant
of the same ligand gives (µ-η :η -peroxo)dicopper(II) in the
22
reaction with H O . The higher stability of the Ni(III) state as
2
2
(k
f
) for formation of the bis(µ-oxo)dinickel(III) complex was
compared to that of the Cu(III) state may enhance O-O bond
homolysis of the peroxo intermediate, although the origin of such
a difference remains to be clarified in detail. We have also shown
that the bis(µ-oxo)dinickel(III) species shows a reactivity in C-H
bond activation similar to that of Tolman’s bis(µ-oxo)dicopper-
-
1
25
determined as 0.14 s at -90 °C. The activation parameters
for the formation process have been determined from the
q
-1
temperature dependence of k as ∆H ) 5.6 ( 0.1 kcal mol
f
-1
q
-1
24
and ∆S ) -30.9 ( 0.6 cal K mol (S3). Since the isotope-
18
labeled bis(µ-oxo) core was generated upon treatment with H
2
O
2
(III) complex: both species exhibit an electrophilic radical
1
6
19,30
instead of H
2
O
2
(demonstrated by the resonance Raman
character in nature.
In the previous study, we proposed that a
26
spectrum), the precursor of the bis(µ-oxo) intermediate may be
bis(µ-oxo)dicopper(III) complex is the real active intermediate
2
2
X
a (µ-η :η -peroxo)dinickel(II) complex. The activation parameters
of the k process are similar to those of the O-O bond homolysis
for the benzylic ligand hydroxylation of L in the reaction of
I
X
+
f
[Cu (L )] with O , even though such an intermediate could not
2
2
2
22b
in the (µ-η :η -peroxo)dicopper(II) complex of the same ligand
be detected directly. The present results, however, may suggest
q
-1
q
-1
(
∆H
H
) 6.7 ( 0.2 kcal mol and ∆S
H
) -37.1 ( 1.2 cal K
the validity of our proposed mechanism for the benzylic ligand
hydroxylation, where the high-valent bimetallic bis(µ-oxo) species
is involved as the real active species, as in the case of the nickel
system.31
-
1
22b
mol ). Such a similarity of the activation parameters indicates
that O-O bond homolysis of the peroxo species is the rate-
determining step for formation of bis(µ-oxo)dinickel(III) complex,
as shown in Scheme 1.27 In such a case, the formation rate of the
bis(µ-oxo)dinickel(III) complex should obey first-order kinetics
Acknowledgment. The present study was financially supported in
part by a Grant-in-Aid for Scientific Research on Priority Area (Molecular
Biometallics, 10129218 and 11116219; Electrochemistry of Ordered
Interface, 10131242 and 11118244) and a Grant-in-Aid for General
Scientific Research (11440197) from the Ministry of Education, Science,
Sports, and Culture of Japan. We thank Dr. Kiyoshi Fujisawa of University
X
II
in the equimolar reaction between [(L Ni )
as observed experimentally (the inset of Figure 1).
2 2 2 2
(µ-OH) ] and H O ,
The bis(µ-oxo)dinickel(III) complex is relatively stable at low
temperature (below -80 °C) but gradually decomposes at higher
24
temperature (above -50 °C) (S4), leading to benzylic ligand
of Tsukuba for his advice on the preparation of H218O .
2
X
hydroxylation to give L OH (Chart 1), as obtained in the reaction
I
X
+
H
II
22,23
Supporting Information Available: Experimental details about the
synthesis and characterization of the bis(µ-hydroxo)dinickel(II) complexes;
the product analysis and kinetics of the ligand hydroxylation reaction;
of [Cu (L )] with O
2
(96% based on [(L Ni )
2 2
(µ-OH) ]).
(
25) Nearly the same first-order rate constants (k
f
) 0.14 ( 0.02 s-1) for
H
II
formation of the bis(µ-oxo)dinickel(III) complex were obtained even when
titration of [(L Ni )
(µ-OH)
](ClO
)
with H
O
2
(S1); resonance Raman
2
2
4
2
2
2
H
II
the concentrations of the starting material, [(L Ni )
2
(µ-OH)
2
](ClO
4
) , and H
2
2
O
O
2
2
]
H
III
16
2+
H
III
18
2+
2
spectra of [(L Ni )
2
(µ- O)
2
]
and [(L Ni )
(µ-OH) ](ClO
(µ- O) (S2); Eyring
]
-
4
-4
were varied {[bis(µ-hydroxo)dinickel(II)] ) 1.7 × 10 -5.0 × 10 M, [H
2
H
II
-4
-3
plot for the reaction of [(L Ni )
2
2
)
4 2
with H O (S3); spectral
2 2
)
2.5 × 10 -1.0 × 10 M}. This result firmly demonstrates that the
change and the first-order plot of the benzylic ligand hydroxylation process
(S4); Eyring plots for the ligand hydroxylation process (S5); and Hammett
plot for the benzylic ligand hydroxylation process (S6) (PDF). This
material is available free of charge via the Internet at http://pubs.acs.org.
formation of the bis(µ-oxo)dinickel(III) complex is first-order with respect to
the dinickel complex but zeroth-order in the H concentration.
26) Judging from the peak areas of the resonance Raman peaks obtained
2 2
O
(
H
II
2+
18
for the reaction of [(L Ni )(µ-OH)
2
]
with H O at -80 °C (S2, Supporting
2 2
18
Information), it has been confirmed that ca. 83% of O is incorporated into
the bis(µ-oxo)dinickel(III) core at the low temperature. In the product analysis
JA991326E
18
18
using H
2
O
2
at a higher temperature (-20 °C), however, only 42% of O is
H
1
incorporated into the hydroxylated ligand L OH. We presumed that the oxygen
(28) The H NMR spectrum of the organic product showed that the ethylene
atom of the bis(µ-oxo)dinickel(III) core was exchangeable with that of H
2
O
group of the pyridine sidearms remained intact after the ligand hydroxylation
H
at the higher temperature. Que and his co-worker also reported that the oxygen
of L -d
4
.
III
IV
18
atom of Fe (µ-O)
2
Fe core is easily replaced by that of H
2
O.
(29) The hydrogen atom abstraction and the hydroxyl rebound can proceed
19
(
27) There could be another intermediate, such as a (µ-1,1-hydroperoxo)-
in a concerted manner, as discussed for the copper system.
(
µ-hydroxo)dinickel(II) complex between the bis(µ-hydroxo)dinickel(II) com-
(30) The radical character of the bis(µ-oxo)dinickel(III) complex has also
been indicated by the reaction with phenol derivatives such as 2,4-di-tert-
2
2
plex (the starting material) and the (µ-η :η -peroxo)dinickel(II) complex, since
2
3
neither the characteristic absorption band nor the resonance Raman band due
butylphenol and 2,6-di-tert-butylphenol and 1,4-cyclohexadiene.
2
2
to (µ-η :η -peroxo)dinickel(II) intermediate has been detected in the expected
(31) Rapid preequilibration of the bis(µ-oxo)dinickel(III) species with a
small amount of the more reactive species could not be ruled out completely.
-1
region (UV-vis, ∼350 nm; resonance Raman, ∼750 cm ).