Eco-friendly molecular transformations catalyzed by a vitamin B 12 derivative with a visible-light-driven system

Article abstract of DOI:10.1039/c0gc00478b

A new bio-inspired system composed of a vitamin B₁₂ derivative and Rose Bengal, catalyzed the dehalogenations of various toxic alkyl halides such as 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) via a noble-metal-free and visible-light-driven process. This system also catalyzed radical-involved organic reactions such as the 1,2-migration of acyl group via a tin-free process. The Royal Society of Chemistry.

Full text of DOI:10.1039/c0gc00478b

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COMMUNICATION
Eco-friendly molecular transformations catalyzed by a vitamin B12
derivative with a visible-light-driven system†
a
a,b
Keishiro Tahara and Yoshio Hisaeda*
Received 24th August 2010, Accepted 16th December 2010
DOI: 10.1039/c0gc00478b
2
2
0
II
I)
20
A new bio-inspired system composed of a vitamin B12
derivative and Rose Bengal, catalyzed the dehalogena-
tions of various toxic alkyl halides such as 1,1-bis(4-
chlorophenyl)-2,2,2-trichloroethane (DDT) via a noble-
metal-free and visible-light-driven process. This system also
catalyzed radical-involved organic reactions such as the 1,2-
migration of acyl group via a tin-free process.
Co(I) species (E (Co /Co = -0.64 V vs. SCE), we expected
that the readily available xanthene dye could photochemically
reduce 1, and attempted to replace the previously reported B12
titanium dioxide system using ultraviolet light irradiation
with an environmentally benign method.
-
2
3,24
Dehalorespiration is an anaerobic metabolism by microbes in
which the dehalogenation of organic halides is coupled to
1
energy conservation. Certain microbes utilize electron transport
chains, which contain a vitamin B12 derivative as a co-factor of
2,3
the involved enzymes. This metabolism attracts great interest
due to its relevance to remediation technologies for reductively
degrading halogenated pollutants, in which a sustainable process
4–8
is also required.
We first attempted to activate 1 to the supernucleophilic
Co(I) species by a photocatalytic process. The UV-vis absorption
spectrum of an EtOH solution of 1 containing 2 (0.1 equiv. vs.
The use of solar energy for organic synthetic transformations
has received increasing attention because visible light is regarded
9–11
as a green and abundant reagent.
In this context, the
25,26
1) and triethanolamine (TEOA)
is shown in Fig. 1 (broken
photocatalysis of alkyl halides is appealing from the viewpoint
of organic syntheses and remediation technologies. Indeed, the
line). This is simply the sum of 1 and 2, indicating no interaction
between both compounds in the ground state. Upon visible light
irradiation (l > 440 nm), the characteristic strong absorption at
2
+
Ru(bpy) has been shown to act as an excellent photosensitizer
1
2–16
or photoredox catalyst.
However, the substrate scope of the
391 nm indicative of the Co(I) species of 1 was observed in Fig. 1
2
+
Ru(bpy) systems have been applied to benzyl halides or the
alkyl halides having the activated carbon-halogen bonds by
electron withdrawing groups. On the other hand, the application
of organic dyes to visible-light-driven reductive organic trans-
(
solid line). Such a spectral change is not observed in the absence
of TEOA, 2 or in the dark. This spectral change strongly suggests
that 2 sensitizes photochemically the reduction of 1 with TEOA
as an electron donor.
17,18
formations represents an almost unexplored research area,
due in part to their poor abilities to use the excited energies in
the redox or catalytic process. To overcome these limitations of
the inorganic and organic photosensitizers, we herein design a
new bioinspired system composed of a vitamin B12 derivative
19,20
21
1
and Rose Bengal 2 with a noble-metals-free process.
Based on the easy accessibility of 1 to the supernucleophilic
a
Department of Chemistry and Biochemistry, Graduate School of
Engineering, Kyushu University, Fukuoka, 819-0395, Japan.
E-mail: yhistatcm@mail.cstm.kyushu-u.ac.jp; Fax: +81-92-802-2827;
Tel: +81-92-802-2826
b
International Research Center for Molecular Systems (IRCMS),
-5
Fig. 1 UV-vis spectra of EtOH solution containing 1 (2.5 ¥ 10 M), 2
Kyushu University, Fukuoka, 819-0395, Japan
-6
-2
†
Electronic supplementary information (ESI) available: Date of the laser
(2.5 ¥ 10 M) and TEOA (2.5 ¥ 10 M) before and after visible light
irradiation (l > 440 nm).
flash photolysis and the photocatalysis. See DOI: 10.1039/c0gc00478b
5
58 | Green Chem., 2011, 13, 558–561
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Table 1 Catalytic dehalogenations mediated by B12-Rose Bengal system
b
c
d
Entry
Substrate/conversion
Major product/Yield
Solvent
EtOH
Time/h
Turnovers
e
1
>99%
64%
1
~1000
2
3
58%
>99%
44%
96%
EtOH
MeOH
12
12
580
~1000
f
4
99%
84%
MeOH
3
2
~1000
B
r
CH
2
OOH
CH
3
COOH
g
5
86%
D
2
O
860
h
6
>99%
>99%
53%
47%
MeCN
MeCN
12
12
~1000
~1000
i
7
8
94%
59%
MeCN
6
940
a
-4
-5
-2
-1
[
1] = 5.0 ¥ 10b M, [2] = 5.0 ¥ 10 M, [Substrate] = 5.0 ¥ 10 M, [TEOA] = 5.0 ¥ 10 M, N
2
atmosphere with irradiation by a 200 W tungsten lamp
c
d
(
2
l > 440 nm). Estimated by the recovery of substrate. Analyzed by NMR, GC and GC-MS. Total turnovers based on the initial concentration of
. 1,1,4,4-tetrakis(4-chlorophenyl)-2,3-dichloro-2-butene was also formed in 25% (E, 23%; Z, 2%) yield. Isolated yield. Use of cyanocobalamin
h i -2
e
f
g
instead of 1. Propylbenzene was also formed with 25% yield. In the presence of methyl acrylate (5.0 ¥ 10 M); Propylbenzene and allylbenzene
were formed in 8% and 37% yields, respectively.
We then examined the dechlorination of 1,1-bis(4-
chlorophenyl)-2,2,2-trichloroethane (DDT), a well-known pow-
erful insecticide. DDT was successfully dechlorinated upon
visible light irradiation for 1 h using 1 (1 mol%), 2 (0.1
mol%) and TEOA (10 equiv.) to form 1,1-bis(4-chlorophenyl)-
formation of the products was largely inhibited (entry 5, Table
S1†), suggesting the involvement of a radical intermediate. The
deuterium incorporation in DDD was not observed when the
reaction was carried out in C
2
D
5
OD and C
2
5
H OD (Table S2†).
These results indirectly suggest that the TEOA is likely the major
hydrogen atom source of the catalytic hydrodehalogenation.
Based on the initial success, we probed the application range
of the present system using various toxic alkyl halides as
summarized in Table 1. The present system successfully reduces
both the C–Cl and C–Br bond which are activated by electron
withdrawing groups under optimized conditions (entries 2 to 5).
A a-halocarbonyl herbicide (Alachlor, entry 4) was efficiently
2
,2-dichloroethane (DDD) as the major product (entry 1,
Table 1). This dechlorination did not efficiently proceed in the
absence of either TEOA, 2 or in the dark (entries 2-4, Table
S1 in ESI†). Combined with the former spectroscopic study,
these results suggest that the generated Co(I) species of 1 is
the active form for dechlorination. Upon the addition of a
spin-trapping reagent, a-phenyl-N-(t-butyl)nitrone (PBN), the
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converted to the corresponding dehalogenated products, while a
dihalomethane insecticide, DDD (entries 2 and 3) was converted
within 1 h under the photocatalysis conditions, followed by UV-
vis spectroscopy as shown in Fig. S3 in ESI.† The UV-vis spectral
change in Fig. S3(c) revealed that over 80% of 2 was unchanged
after the photocatalysis of DDT. This result confirms the good
stability of the photosensitizer in the present system. This result
also suggests the efficient electron transfer from the electron
donor (TEOA) to the final electron acceptor (DDT) to afford
~1000 turnovers relative to 2.
into a substituted stilbene, consistent with a report using NaBH
as a chemical reductant. The use of cyanocobalamin (vitamin
4
4
B
12) instead of 1 reduced a water-soluble disinfection by-product
under an aqueous condition (a- haloacid, entry 5).
Using the radical generation capability of the alkyl-cobalt
20,23,24
complex form of 1 under the photochemical conditions,
we
2
+
then attempted to apply the present system to radical-involved
Our previously reported B12–Ru(bpy) system showed 210
27,28
2+
organic syntheses.
To show the utility of the present system
turnovers for photocatalysis of DDT relative to Ru(bpy) as
13
involving the highly nucleophilic Co(I) species of 1, we here chose
the substrates of alkyl bromides having unactivated carbon-
halogen bonds, which cannot be easily reduced by the previously
shown in Entry 6 in Table S1.† It should be noted that the
turnover numbers of the present B12-Rose Bengal system is a
2
+
factor of 4.8 greater turnovers than those of the B12–Ru(bpy)
2
+
12–16
reported Ru(bpy) system.
3-Bromopropylbenzene was ef-
system. This enhanced catalytic activity results from the fact
that the compound 2 has a strong absorption in visible region
and the triplet excited state of 2 is efficiently quenched by
the oxidative quenching of 1. In comparison to Rose Bengal,
ficiently debrominated due to the Co(I) species of 1 to afford the
debrominated products (entry 6). When we performed the same
reaction in the presence of methyl acrylate, a carbon-carbon
bond formation through the 1,4-radical addition to the olefin
was achieved in a moderate yield (entry 7). The system effectively
catalyzed the 1,2-migrations of the acyl group with excellent
selectivity to the ring-expansion using an activated alkyl bromide
2
+
Ru(bpy) has a weaker absorption in the visible region and is
excited less efficiently because of the overlay of the absorption
with 1. Although we have reported the B12-titanium dioxide
system for photocatalysis of several alkyl halides, the system
23,24
(
Table 1, entry 8).
is driven by ultraviolet light.
In the present study, we have
To gain mechanistic insight into the photochemical reduction
successfully replaced the previous ultraviolet-light-driven system
to the visible-light-driven system under mild conditions as an
environmentally benign and noble-metal-free method.
In conclusion, we show that the present B12-Rose Bengal
system serves as a simplified analogy for the electron transport
chain of dehalorespiration to efficiently degrade various toxic
halogenated compounds. Furthermore, the present system can
serve as an effective alternative for traditional organic syntheses
with tin hydrides to access radical chemistry.
This work was supported by the Global COE Program
“Science for Future Molecular System” from MEXT of Japan,
and a Grant-in-Aid for Scientific Research (21.02310) and a
Grant-in-Aid for Scientific Research (A) (21245016) from the
Japan Society for the Promotion of Science (JSPS).
of 1, quenching experiments of both the singlet and triplet
excited states of 2 in MeOH were performed. No fluorescent
quenching of 2 was observed upon the addition either TEOA
or 1. On the other hand, the triplet quenching of 2 was
observed upon the addition of TEOA or 1, having quenching rate
6
9
-1 -1
constants (k ) of 1.0 ¥ 10 and 7.2 ¥ 10 M s , respectively (Fig.
q
S4 in ESI†). Based on these results, two possible mechanisms are
proposed as shown in Scheme 1. Not the singlet, but the triplet
of 2 participates in the electron transfer while both reductive
21
and oxidative quenching are thermodynamically possible. At
-
1
-4
the same concentrations of TEOA (5.0 ¥ 10 M) and 1 (5.0 ¥ 10
M) as those of the photocatalysis conditions, the reductive and
oxidative quenching rates are calculated using the k values and
q
5
-1
6
-1
determined to be 5.0 ¥ 10 s and 3.6 ¥ 10 s , respectively. Thus,
the oxidative quenching favorably proceeds over the reductive
quenching during photocatalysis because the former rate is a
factor of 7.2 greater than the latter rate.
Notes and references
1
C. Holliger, G. Wohlfarth and G. Diekert, FEMS Microbiol. Rev.,
999, 22, 383–398.
1
2
B. Kr a¨ utler, W. Fieber, S. Ostermann, M. Fasching, K. Ongania, K.
Gruber, C. Kratky, C. Mikl, A. Siebert and G. Diekert, Helv. Chim.
Acta, 2003, 86, 3698.
3
4
5
K. L. Brown, Chem. Rev., 2005, 105, 2075.
D. Zanette and F. Nome, J. Org. Chem., 1979, 44, 2308.
J. F. Rusling, C. L. Miaw and E. C. Couture, Inorg. Chem., 1990, 29,
2
025.
6
7
8
9
D. R. Burris, C. A. Delcomyn, M. H. Smith and A. L. Roberts,
Environ. Sci. Technol., 1996, 30, 3047.
Scheme 1
J. A. Shey and W. A. Van Der Donk, J. Am. Chem. Soc., 2000, 122,
1
2403–12404.
A previously reported study has shown that 2 is reductively
K. M. McCauley, D. A. Pratt, S. R. Wilson, J. Shey, T. J. Burkey and
W. A. Van Der Donk, J. Am. Chem. Soc., 2005, 127, 1126.
A. Albini and M. Fagnoni, Green Chem., 2004, 6, 1.
26
photobleached in the presence of TEOA, and the present
photocatalysis is also accompanied with the bleaching of 2 as
indicated in Fig. 1. This bleaching is due to the hydrogen atom
1
0 G. Palmisano, V. Augugliaro, M. Pagliaro and L. Palmisano, Chem.
Commun., 2007, 3425.
∑
3-
3- 26
abstraction of RB to form the hydrated species (RBH ), and
11 M. Fagnoni, D. Dondi, D. Ravelli and Angelo Albini, Chem. Rev.,
2007, 107, 2725.
∑
3-
RB is more easily formed as the concentration of 1 (Co(II)
species) decreases in the absence of halogenated substrates.
Actually, this photobleaching was well suppressed upon the
addition of 1, and efficiently upon the addition of 1 and DDT
1
1
2 S. Fukuzumi, Bull. Chem. Soc. Jpn., 1997, 70, 1.
3 H. Shimakoshi, M. Tokunaga, T. Baba and Y. Hisaeda, Chem.
Commun., 2004, 1806.
14 D. A. Nicewicz and D. W. C. MacMillan, Science, 2008, 322, 77.
5
60 | Green Chem., 2011, 13, 558–561
This journal is © The Royal Society of Chemistry 2011

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1
1
1
1
1
2
2
5 M. A. Ischay, M. E. Anzovino, J. Du and T. P. Yoon, J. Am. Chem.
Soc., 2008, 130, 12886.
6 J. M. R. Narayanam, J. W. Tucker and R. J. Stephenson, J. Am. Chem.
Soc., 2009, 131, 8756.
7 T. Lazarides, T. McCormick, P. Du, G. Luo, B. Lindley and R.
Eisenberg, J. Am. Chem. Soc., 2009, 131, 9192.
(ref. 17), see: D. C. Neckers, J. Photochem. Photobiol., A, 1989, 47, 1;
V. Wintgens, J. C. Scaiano, S. M. Linden and D. C. Neckers, J. Org.
Chem., 1989, 54, 5242.
22 G. N. Schrauzer, E. Deutsch and R. J. Windgassen, J. Am. Chem.
Soc., 1968, 90, 2441.
23 H. Shimakoshi, M. Abiru, S. Izumi and Y. Hisaeda, Chem. Commun.,
8 D. B u¨ rget, J. P. Fouassier, F. Amat-Guerri, R. Mallavia and R. Sastre,
Acta Polym., 1999, 50, 337.
2009, 6427.
24 H. Shimakoshi, M. Abiru, K. Kuroiwa, N. Kimizuka, M. Watanabe
and Y. Hisaeda, Bull. Chem. Soc. Jpn., 2010, 83, 170.
25 A. Mills, C. Lawrence and P. Douglas, J. Chem. Soc., Faraday Trans.
2, 1986, 82, 2291.
26 A. Zakrzewski and D. C. Neckers, Tetrahedron, 1987, 43, 4507.
27 J. Yang and M. Brookhart, J. Am. Chem. Soc., 2007, 129, 12656.
28 H. Gong, R. S. Andrews, J. L. Zuccarello, S. J. Lee and M. R. Gagn e´ ,
Org. Lett., 2009, 11, 879.
9 Y. Murakami, Y. Hisaeda and A. Kajihara, Bull. Chem. Soc. Jpn.,
1
983, 56, 3642.
0 Y. Hisaeda, T. Nishioka, Y. Inoue, K. Asada and T. Hayashi, Coord.
Chem. Rev., 2000, 198, 21.
1 Our choice of 2 is based on its promising properties of the triplet
excited state and its advantage as a potential electron mediator
0
∑-
3
2-
0
2
∑3-
(
E (RB / RB *) = -1.02 V, E (RB */RB ) = -0.98 V vs. SCE
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Green Chem., 2011, 13, 558–561 | 561