High-valent manganese(v)-oxo porphyrin complexes in hydride transfer reactions

Article abstract of DOI:10.1039/b814928c

Hydride transfer from dihydronicotinamide adenine dinucleotide (NADH) analogues to trans-dioxomanganese(v) porphyrin complexes proceeds via proton-coupled electron transfer, followed by rapid electron transfer. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b814928c

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COMMUNICATION
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High-valent manganese(V)–oxo porphyrin complexes in hydride
transfer reactionsw
Jung Yoon Lee,a Yong-Min Lee,a Hiroaki Kotani,b Wonwoo Nam*a and Shunichi Fukuzumi*b
Received (in Cambridge, UK) 27th August 2008, Accepted 18th November 2008
First published as an Advance Article on the web 19th December 2008
DOI: 10.1039/b814928c
Hydride transfer from dihydronicotinamide adenine dinucleotide
(NADH) analogues to trans-dioxomanganese(V) porphyrin com-
plexes proceeds via proton-coupled electron transfer, followed by
rapid electron transfer.
porphyrins and investigated their reactivities in hydride-transfer
reactions.12 In this communication, we report the first example of
hydride transfer from dihydronicotinamide adenine dinucleotide
(NADH) analogues to Mn(V)–oxo porphyrins.
trans-Dioxomanganese(V) porphyrins, [Mn(V)(O)2(TPFPP)]ꢀ
(1) (TPFPP = meso-tetrakis(pentafluorophenyl)porphinato
dianion), [Mn(V)(O)2(TDFPP)]ꢀ (2) (TDFPP = meso-tetra-
High-valent metal–oxo complexes are involved in a variety of
oxygenation reactions by metalloenzymes, such as cytochromes
P450 (CYP 450).1 Although high-valent iron–oxo species have
never been identified in CYP 450,2 a number of high-valent
iron(IV)–oxo porphyrin complexes have been synthesized,
characterized with various spectroscopic techniques, and exten-
sively investigated in the oxygenation of various organic sub-
strates, such as alkane hydroxylation and olefin epoxidation.3
Thus, reactivities of iron(IV)–oxo complexes are well understood
in biomimetic reactions.
kis(2,6-difluorophenyl)porphinato
dianion),
and
[Mn(V)(O)2(TDCPP)]ꢀ (3) (TDCPP = meso-tetrakis(2,6-di-
chlorophenyl)porphinato dianion) (see structures in Chart 1,
Mn(V)(O)2(Porp) Complexes), were prepared by the
published method;6,7 manganese(III) porphyrin chlorides were
reacted with m-chloroperbenzoic acid (m-CPBA, 5 equiv.) in the
presence of base (tetrabutylammonium hydroxide (TBAH),
20 equiv.) in a solvent mixture of CH3CN and CH2Cl2 (1 : 1)
at 25 1C. The UV-Vis spectrum of 1 exhibits a strong Soret band
at 431 nm and a Q-band at 551 nm, characteristic of Mn(V)–oxo
porphyrins (Fig. 1a).5–8 1 was quite stable at 25 1C (t1/2 E 3.5 h).
The reactivity of 1 was then investigated with NADH analogues,
10-methyl-9,10-dihydroacridine (AcrH2), 1-benzyl-1,4-dihydro-
nicotinamide (BNAH), and their derivatives (see Chart 1,
Hydride Donors). Upon addition of substrates to a solution of
1, the intermediate reverted to the starting manganese(III)
porphyrin complex, showing isosbestic points at 403, 439, and
558 nm (Fig. 1a). First-order rate constants, determined by the
pseudo-first-order fitting of the kinetic data for the decay of 1,
increased linearly with the increase in the substrate concentra-
tion, leading us to determine the second-order rate constants of
1.5(2) ꢁ 10 Mꢀ1 sꢀ1 for AcrH2 and 1.3(2) ꢁ 103 Mꢀ1 sꢀ1 for
BNAH (Fig. 1b). By using dideuterated compounds, AcrD2 and
BNAH-4,40-d2 (see Chart 1, Hydride Donors), large kinetic
isotope effect (KIE) values, such as KIE of 15(2) for the
reaction of AcrH2 and KIE of 10(2) for the reaction of
BNAH, were determined (Fig. 1b). The large KIE values
indicate that the C–H bond activation of NADH analogues is
High-valent manganese(V)–oxo porphyrin complexes have
also been implicated as reactive intermediates in the catalytic
oxidation of organic substrates by manganese(III) porphyrins and
terminal oxidants.4 In contrast to the iron–oxo porphyrin inter-
mediates, the nature of manganese(V)–oxo porphyrins has been
ambiguous until Groves and co-workers reported the UV-Vis
1
and H NMR spectra of manganese(V)–oxo porphyrins in aqu-
eous solution.5 Subsequently, Mn(v)–oxo porphyrins have been
synthesized in organic solvents in the presence of base and
characterized with resonance Raman and X-ray absorption
spectroscopy/extended X-ray absorption fine structure spectro-
1
scopy (XAS/EXAFS).6 The spectroscopic data from H NMR,
resonance Raman, and EXAFS suggested that the Mn(V)–oxo
species are diamagnetic with a low-spin (S = 0) state and with
double-bond character between the Mn(V) ion and the oxygen
atom.5,6 More recently, re-evaluation of the 1H NMR and
resonance Raman data revealed that the Mn(V)–oxo porphyrins
are trans-dioxomanganese(V) species [OQMnVQO].7
Since it is only recently that the synthesis of Mn(V)–oxo
porphyrins has become well established, only a few reactivity
studies have been performed with in situ-generated Mn(V)–oxo
species in oxidation and halogenation reactions.5,8–11 As our
ongoing efforts to elucidate the chemical properties of high-valent
metal–oxo species, we have generated trans-dioxomanganese(V)
a Department of Chemistry and Nano Science, Centre for Biomimetic
Systems, Ewha Womans University, Seoul, 120-750, Korea.
E-mail: wwnam@ewha.ac.kr; Fax: +82 2 3277 2392;
Tel: +82 2 3277 4441
b Department of Material and Life Science, Graduate School of
Engineering, Osaka University, SORST, Japan Science and
Technology Agency (JST), Suita, Osaka, 565-0871, Japan.
E-mail: fukuzumi@chem.eng.osaka-u.ac.jp; Fax: +81 6 6879 7370;
Tel: +81 6 6879 7368
w Electronic supplementary information (ESI) available: Experimental
and reactivity details. See DOI: 10.1039/b814928c
Chart 1
ꢂc
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Fig. 2 Plots of log k2 for hydride transfer from NADH analogues to
[MnV(O)2(TPFPP)]ꢀ (black circles), [MnV(O)2(TDFPP)]ꢀ (red circles),
and [MnV(O)2(TDCPP)]ꢀ (blue circles) vs. log k2 for hydride transfer
from the same series of NADH analogues to Cl4Q in MeCN at 298 K.
such as p-chloranil (Cl4Q) and 2,3-dichloro-5,6-dicyano-
p-benzoquinone, occurs via proton-coupled electron transfer
(PCET), followed by rapid electron transfer.14,15 Also, the
reactivity comparison of high-valent metal–oxo complexes
and Cl4Q was used as indirect evidence for proposing the
PCET mechanism in hydride transfer reactions.14 We there-
fore compared k2 values of the hydride transfer from NADH
analogues to Mn(V)–oxo complexes and Cl4Q. As shown in
Fig. 2, there is a good linear correlation between the k2 values
of [Mn(V)(O)2(Porp)]ꢀ and the corresponding values of Cl4Q.
Such a linear correlation implies that hydride transfer from
NADH analogues to [Mn(V)(O)2(Porp)]ꢀ follows the hydride-
transfer mechanism of Cl4Q. That is the PCET, followed by
rapid electron transfer.15 In addition, the k2 values of hydride
transfer from NADH analogues to Cl4Q are similar to that of
hydride transfer from NADH analogues to 1, indicating that
the reactivities of 1 and Cl4Q are similar in the hydride-
transfer reactions (compare the data in the columns of k2
([MnV(O)2(TPFPP)]ꢀ) and k2 (Cl4Q) in ESI, Table S1w). We
have also observed that the k2 values of hydride transfer from
NADH analogues to [Mn(V)(O)2(Porp)]ꢀ are well correlated
with the rate constants of deprotonation of radical cations of
NADH analogues (kd) (ESI, Fig. S1w), indicating that the
Fig. 1 (a) UV-Vis spectral changes of 1 (1 ꢁ 10ꢀ2 mM, blue line)
upon addition of AcrH2 (3 ꢁ 10ꢀ1 mM). Inset shows time course of the
decay of 1 monitored at 551 nm (blue) and the formation of
[MnIII(TPFPP)]+ species monitored at 569 nm (red). (b) Plot of kobs
against the concentration of AcrH2 and AcrD2 (left panel) and BNAH
and BNAH-4,40-d2 (right panel) to determine second-order rate con-
stants. Black circles indicate the oxidation of AcrH2 and BNAH; red
circles indicate the oxidation of AcrD2 and BNAH-4,40-d2.
involved as a rate-determining step in the hydride-transfer
reactions by 1. The hydride-transfer reaction was also investi-
gated with other AcrH2 derivatives bearing a substituent R at
the C-9 position, such as AcrHMe, AcrHPh, and AcrHEt (see
the structure of AcrHR in Chart 1, Hydride Donors), and it was
found that the reaction rates are significantly affected by the
substituent R in the AcrHR (ESI, Table S1w). Interestingly, the
reactivity of AcrHR bearing an electron-donating R group is
lower than that of AcrH2, suggesting that the hydride-transfer
reaction does not occurs via an one-step hydride-transfer
mechanism (vide infra).12
The porphyrin ligand effect on the reactivity of trans-
dioxomanganese(V) complexes in hydride-transfer reactions
was also investigated, and second-order rate constants of
15(2), 3.9(3), and 1.3(2) Mꢀ1 sꢀ1 were determined in the
oxidation of AcrH2 by 1, 2 and 3, respectively. These results
indicate that a Mn(V)–oxo complex bearing an electron-
deficient porphyrin ligand is more reactive in the hydride-
transfer reaction. The reactivity order of 1 4 2 4 3 is the same
as that observed in the olefin epoxidation and C–H activation
by Mn(V)–oxo complexes.9a In iron porphyrin systems, a high-
valent iron–oxo complex with an electron-deficient porphyrin
ligand is more reactive in electrophilic oxidation reactions,
including C–H activation and hydride-transfer reactions.13,14
The reactivity order of 1 4 2 4 3 was also observed in the
oxidation of other NADH analogues (ESI, Table S1w).
Further, as observed in the reaction of 1, large KIE values
of 6–20 were obtained in the reactions of AcrH2, BNAH, and
their deuterated compounds by 2 and 3 (ESI, Table S1w).
It has been reported previously that hydride transfer from
AcrH2, BNAH, and their derivatives to hydride acceptors,
+
proton transfer from AcrHRꢃ to Mn(IV)(O)(OH)(Porp) is in-
volved as a rate-determining step (Scheme 1, pathway PT).12,16
The latter was further supported by the large KIE values
determined in the oxidation of AcrH2, BNAH, and their
deuterated compounds by Mn(V)–oxo complexes. Further, as
we have discussed above, the significant decrease in the reactivity
by the introduction of a substituent R at the C-9 position can
hardly be reconciled by a one-step hydride transfer mecha-
nism.12 Based on the results of the mechanistic studies discussed
above, we propose the following mechanism: the hydride trans-
fer from NADH analogues to Mn(V)–oxo porphyrins occurs via
an uphill electron transfer from NADH analogues to
Mn(V)(O)(OH)(Porp),17 followed by the rate-limiting proton
transfer from the radical cations of NADH analogues to
[Mn(IV)(O)(OH)(Porp)]ꢀ (Scheme 1). Then, rapid electron trans-
fer from the deprotonated radicals to the Mn(IV)(OH)2(Porp)
species affords the final products, such as the corresponding
NAD+ analogues and the starting Mn(III) porphyrins.
ꢂc
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Bio-Environmental Chemistry’’ from the Ministry of Educa-
tion, Culture, Sports, Science and Technology, Japan (to S.F.).
Notes and references
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Mechanism, and Biochemistry, Kluwer Academic/Plenum
Publishers, New York, 2005, 3rd edn; (b) I. G. Denisov,
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Acc. Chem. Res., 2007, 40, 522; (c) Y. Watanabe, H. Nakajima and
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Scheme 1 Proposed mechanism of the hydride transfer from AcrH2
to a manganese(V)–oxo porphyrin complex.
4 B. Meunier, A. Robert, G. Pratviel and J. Bernadou, in The
Porphyrin Handbook, ed. K. M. Kadish, K. M. Smith and
R. Guilard, Academic Press, San Diego, 2000, vol. 4, ch. 31,
pp. 119–187.
5 (a) J. T. Groves, J. Lee and S. S. Marla, J. Am. Chem. Soc., 1997,
119, 6269; (b) N. Jin and J. T. Groves, J. Am. Chem. Soc., 1999,
121, 2923.
6 W. J. Song, M. S. Seo, S. D. George, T. Ohta, R. Song,
M.-J. Kang, T. Tosha, T. Kitagawa, E. I. Solomon and
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11 Y. Shimazaki, T. Nagano, H. Takesue, B.-H. Ye, F. Tani and
Y. Naruta, Angew. Chem., Int. Ed., 2004, 43, 98.
Scheme 1 shows that the final products formed in the
hydride transfer from AcrH2 to [Mn(V)(O)2(Porp)]ꢀ are
[Mn(III)(OH)2(Porp)]ꢀ and 10-methylacridinium ion (AcrH+).
Although we have observed the conversion of 1 to the starting
manganese(III) complex in the reaction of 1 and AcrH2, we did
not observe the formation of AcrH+, which should exhibit an
absorption band at 357 nm in the UV-Vis spectrum
(Fig. 1).12,18 Since no detection of AcrH+ might be due to
the instability of the AcrH+ ion in the presence of OHꢀ, we
carried out a control reaction by adding OHꢀ to a solution
containing AcrH+. As we expected, the AcrH+ ion was
converted to AcrH(OH) immediately with a rate of 4 108 sꢀ1
(ESI, Fig. S2aw), followed by the slow conversion of AcrH(OH)
to Acr(O) (ESI, Fig. S2b) [eqn (1)].19 Thus, we carried out the
reaction of 1 and AcrH2 and confirmed that Acr(O) was formed
as the final product by analyzing product(s) with 1H NMR after
column chromatography (ESI, Fig. S3w).19
12 S. Fukuzumi, Y. Tokuda, T. Kitano, T. Okamoto and J. Otera,
J. Am. Chem. Soc., 1993, 115, 8960.
13 Y. M. Goh and W. Nam, Inorg. Chem., 1999, 38, 914.
14 Y. J. Jeong, Y. Kang, A.-R. Han, Y.-M. Lee, H. Kotani,
S. Fukuzumi and W. Nam, Angew. Chem., Int. Ed., 2008, 47, 7321.
15 (a) S. Fukuzumi, S. Koumitsu, K. Hironaka and T. Tanaka, J. Am.
Chem. Soc., 1987, 109, 305; (b) S. Fukuzumi, K. Ohkubo,
Y. Tokuda and T. Suenobu, J. Am. Chem. Soc., 2000, 122, 4286.
16 (a) S. Fukuzumi, O. Inada and T. Suenobu, J. Am. Chem. Soc.,
2002, 124, 14538; (b) S. Fukuzumi, O. Inada and T. Suenobu,
J. Am. Chem. Soc., 2003, 125, 4808.
17 Although it has been proposed from DFT studies that trans-
dioxomanganese(V) porphyrins are unreactive and their
protonated species, such as OQMn(V)–OH and OQMn(V)–OH2,
are active oxidants in oxidation reactions, the nature of the active
Mn(V)–oxo species is still ambiguous and remains elusive:
(a) D. Balcells, C. Raynaud, R. H. Crabtree and O. Eisenstein,
Chem. Commun., 2008, 744; (b) F. De Angelis, N. Jin, R. Car and
J. T. Groves, Inorg. Chem., 2006, 45, 4268; (c) S. P. de Visser,
F. Ogliaro, Z. Gross and S. Shaik, Chem.–Eur. J., 2001, 7, 4954.
18 (a) S. Fukuzumi, K. Okamoto, Y. Tokuda, C. P. Gros and
R. Guilard, J. Am. Chem. Soc., 2004, 126, 17059; (b) J. Yuasa,
S. Yamada and S. Fukuzumi, Angew. Chem., Int. Ed., 2008, 47,
1068.
ð1Þ
In conclusion, we have reported the first example of
the oxidation of NADH analogues by manganese(V)–oxo
porphyrin complexes. We have demonstrated that hydride
transfer from a series of NADH analogues to Mn(V)–oxo
species proceeds via PCET, followed by rapid electron trans-
fer, rather than one-step hydride transfer. Other mechanistic
aspects, such as porphyrin ligand effect and KIE, have also been
discussed in the oxidation of NADH analogues by Mn(V)–oxo
porphyrin complexes.
This research was supported by the Korea Science and
Engineering Foundation and the Ministry of Science and
Technology of Korea through CRI Program (to W.N.), a
Grant-in-Aid (No. 19205019 to S.F.), and a Global COE
program, ‘‘the Global Education and Research Centre for
19 (a) S. Fukuzumi, M. Fujita and J. Otera, J. Org. Chem., 1993, 58,
5405; (b) T. Matsuo and J. M. Mayer, Inorg. Chem., 2005, 44, 2150.
ꢂc
This journal is The Royal Society of Chemistry 2009
706 | Chem. Commun., 2009, 704–706