Visible light-driven photocatalytic duet reaction catalyzed by the B12-rhodium-titanium oxide hybrid catalyst

Article abstract of DOI:10.1016/j.jorganchem.2019.121058

The hybrid catalyst composed of the B₁₂ complex and rhodium ion (Rh³⁺) modified titanium oxide was synthesized for the visible light-driven B₁₂ inspired catalytic reaction. The hybrid catalyst contains 4.93 × 10^?6 molg^?1 of the B₁₂ complex and 5.43 × 10^?5 molg^?1 of the Rh(III) ion on the surface of titanium oxide. Visible light irradiation (λ ≧ 420 nm) of the hybrid catalyst in the presence of triethylamine (Et₃N) as a sacrificial reagent showed absorption at 390 nm, typical for the Co(I) state of the B₁₂ complex monitored by diffuse reflectance UV–vis analysis, which imply that electron transfer from the titanium oxide to Co(III) center of the B₁₂ complex occurred by the visible light irradiation. Benzotrichloride was converted to N,N-diethylbenzamide by the visible light irradiation catalyzed by the hybrid catalyst in air at room temperature. Both the conduction band electron and valence band hole of the catalyst were utilized for the reaction to form the amide product. The reaction mechanism of the duet reaction was proposed.

Full text of DOI:10.1016/j.jorganchem.2019.121058

Journal Pre-proof
Visible light-driven photocatalytic duet reaction catalyzed by the B - rhodium-
12
titanium oxide hybrid catalyst
Keita Shichijo, Mamoru Fujitsuka, Yoshio Hisaeda, Hisashi Shimakoshi
PII:
S0022-328X(19)30501-7
DOI:
https://doi.org/10.1016/j.jorganchem.2019.121058
JOM 121058
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 22 October 2019
Accepted Date: 29 November 2019
Please cite this article as: K. Shichijo, M. Fujitsuka, Y. Hisaeda, H. Shimakoshi, Visible light-driven
photocatalytic duet reaction catalyzed by the B - rhodium-titanium oxide hybrid catalyst, Journal of
12
Organometallic Chemistry (2020), doi: https://doi.org/10.1016/j.jorganchem.2019.121058.
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Visible light-driven photocatalytic duet reaction catalyzed by the B12-
rhodium-titanium oxide hybrid catalyst
Keita Shichijoa, Mamoru Fujitsukab, Yoshio Hisaedaa*, Hisashi
Shimakoshia*
aDepartment of Chemistry and Biochemistry, Graduate School of Engineering,
Kyushu University, Fukuoka 819-0395, Japan
bThe Institute of Scientific and Industrial Research (SANKEN), Osaka University,
Osaka 567-0047, Japan
*Corresponding authors. Tel.: +81-92-802-2828: fax: +-81-92-802-2828. E-mail
address:
yhisatcm@mail.cstm.kyushu-u.ac.jp
(Y.
Hisaeda)
and
shimakoshi@mail.cstm.kyushu-u.ac.jp (H. Shimakoshi)
Received
Accepted
ABSTRACT: The hybrid catalyst composed of the B12 complex and rhodium ion (Rh3+)
modified titanium oxide was synthesized for the visible light-driven B12 inspired catalytic
reaction. The hybrid catalyst contains 4.93
×
10-6 molg-1 of the B12 complex and 5.43
×
10-5
420
molg-1 of the Rh(III) ion on the surface of titanium oxide. Visible light irradiation (λ
≧
nm) of the hybrid catalyst in the presence of triethylamine (Et3N) as a sacrificial reagent
showed absorption at 390 nm, typical for the Co(I) state of the B12 complex monitored by
diffuse reflectance UV-vis analysis, which imply that electron transfer from the titanium
oxide to Co(III) center of the B12 complex occurred by the visible light irradiation.
Benzotrichloride was converted to N,N-diethylbenzamide by the visible light irradiation
catalyzed by the hybrid catalyst in air at room temperature. Both the conduction band
electron and valence band hole of the catalyst were utilized for the reaction to form the
amide product. The reaction mechanism of the duet reaction was proposed.
Keywords: Organometallic B12, Visible light, Titanium oxide, Rhodium modification, Duet
reaction, Amide
1. Introduction
Bioorganometallic compounds are unique metal complexes having a metal-
organic σ-bond present in biological systems such as various B12-dependent enzymes,
methyl-coenzyme M reductase, and hydrogenase [1]. Among the bioorganometallic
compounds, the cobalt alkylated complex, such as adenosylcobalamin, present in the
B12-dependent enzymes, is a useful intermediate to form reactive species [2-4].
Homolysis of the cobalt-carbon bond of the cobalt alkylated complex produces the
alkyl radical, and the alkyl radical initiates various reactions, such as H radical

abstraction, occurred in the adenosylcobalamin (coenzyme B12) dependent enzyme,
isomerization radical coupling, addition to unsaturated bonds, etc. Due to the
versatility of the reactions, the organometallic B12 initiated radical reaction expanded
to various molecular transformations in organic synthesis [5]. We recently
synthesized a hybrid catalyst composed of the B12 complex and titanium oxide (B12-
TiO2) and performed a unique ester and amide formation from trichlorinated organic
compounds by UV light irradiation (Scheme 1a~c) [6].
The cobalt (III) state of the immobilized B12 complex on the TiO2 surface was
reduced to low valence Co(I) species by electron transfer from the UV light excited
TiO2 and the supernucleophilic Co(I) species reacts with RCCl3 to form an ester or
amide with dechlorination in the presence of an alcohol or amine under aerobic
conditions. Though the unique B12 inspired reaction proceeded at room temperature in

air, UV light irradiation corresponding to the band gap excitation of TiO2 is required
for the reaction. To improve this problem, we explored the new photocatalyst having
a visible light responsibility as shown in Fig. 1.
To make the task specific TiO2, surface modification of the TiO2 with various
organic compounds, such as catechol [7], glucose [8], and indole [9] or inorganic
compounds [10-12] such as the rhodium (III) ion (Rh3+) and platinum ion, is a useful
and convenient method for providing the visible light responsibility in the TiO2
photocatalyst. The absorption band observed in the visible light region is ascribed to
the surface charge transfer band of the modified TiO2. Among the surface modified
TiO2s, metal ion modification is a promising method for the development of a good
catalyst due to its high stability as well as visible light responsibility. In this paper, we
report the synthesis of a visible light responsible B12 hybrid catalyst using the
rhodium modified TiO2 (Rh3+-TiO2). The unique photo duet reaction for amide
synthesis under mild conditions, visible light irradiation at room temperature in air,
was developed as shown in Scheme 1d.
Fig. 1. Visible light-driven duet reaction catalyzed by B12-Rh-TiO2 in air.

2. Results and discussion
2.1 Preparation of the hybrid catalyst (B12-Rh-TiO2)
The Rh3+ modification on the surface of TiO2 (anatase, average surface area: 52
m2g-1) was conducted based on a reported procedure [11]. The yellow colored Rh-
TiO2 showed absorption in the visible light region that reached about a 450 nm
wavelength in the diffuse reflectance (DR) UV-VIS spectrum (Fig. S2). The X-ray
photoelectron spectroscopy (XPS) analysis of Rh-TiO2 showed the 3d5/2 and 3d3/2
signals of Rh3+ at 309 and 314 eV, respectively (Fig. S3) and 0.559 wt% (1.39x10-4
molg-1) of Rh3+ was contained in the Rh-TiO2 determined by an X-ray fluorescence
analyses (XRF). The B12 complex was covalently immobilized on the Rh-TiO2
surface using the B12 derivative having two trimethoxysilyl groups,
(CN)2Cob(III)6C1esterCON{(CH2)3Si(OMe)3}2 (1) (Fig. S1), similar to that
previously reported for the preparation of B12-TiO2 [6]. The content of the B12
complex on the surface of the TiO2 was 4.93x10-6 molg-1 determined by a UV-vis
measurement, and the surface coverage by the B12 complex was 9.48x10-12 molcm-2.
This B12 complex covalently bonded hybrid catalyst, B12-Rh-TiO2, was characterized
by DR UV-vis (Fig. S4) and IR analyses (Fig. S5). The typical Q-band absorptions of
the B12 derivative having H2O and CN- axial ligands were observed at 500 and 545
nm upon the absorption of B12-Rh-TiO2 [13]. It is noted that no mass peak ascribed to
the B12 complex was detected by the MALDI-TOF MS of B12-Rh-TiO2 due to its
strong binding on the surface of the TiO2, which cannot be desorbed by laser
irradiation during the MALDI-TOF MS analysis (Fig. S6).
2. 2 Visible light response of the hybrid catalyst

The reductive formation of the Co(I) species of the B12 complex on the surface of
TiO2 under visible light irradiation was examined by DR-UV-vis spectroscopy. The
B12-Rh-TiO2 suspended in CH3CN containing 0.1 M triethylamine (Et3N) showed the
typical UV-vis spectrum of the Co(I) state of the B12 derivative with an absorption
maximum at 390 nm after visible light irradiation (λ≧420 nm) as shown in Fig. 2
[14].
Fig. 2. DR-UV-vis spectral change of the B12-Rh-TiO2 during visible light irradiation
in the presence of Et3N in CH3CN under N2: (a) before irradiation, (b) 1 min.
irradiation, (c) 30 min. irradiation.
The Co(II) complex having an absorption maximum at 470 nm was transitionally
formed during the visible light irradiation. The Et3N works as an electron source of a
hole quencher of the B12-Rh-TiO2 and sacrificially decomposed to diethyl amine and
acetoaldehyde (Eqs. 1-4) [15]. The produced Co(I) species could react with
benzotrichloride to form benzoyl chloride in the presence of oxygen as we previously
reported using B12-TiO2 (Eqs. 5-9) [6].

The reaction between benzoyl chloride and diethylamine should produce the amide as
shown in Scheme 2.
In this reaction, precursors of the product amide are formed by oxidation and
reduction processes produced by the B12-Rh-TiO2 catalyst. Thus we called it a photo-
duet reaction [6].

The initial photo-induced electron transfer process from the Rh3+ modified TiO2
to the immobilized Co(III) state of the B12 complex was investigated by time-resolved
diffuse reflectance spectroscopy (TDR). The TDR measurements of B12-Rh-TiO2 and
Rh-TiO2 were performed upon 405 nm pulse excitation. The Rh-TiO2 shows an
absorption band around 1000 nm assigned to trapped electrons [16], and the majority
of electrons decayed within 500 ps due to charge recombination of the electrons and
holes generated in the Rh-TiO2 (Fig. S7). While a similar absorption appeared in the
B12-Rh-TiO2 upon 405 nm pulse excitation (Fig. S8), the electrons showed quick
decay within 60 ps due to electron transfer from the Rh-TiO2 to the immobilized B12
complex. The time profile of the transient absorption at 1000 nm for B12-Rh-TiO2 was
fitted using exponential function and long-lived component, and the lifetime of short-
lived component was 10.4 ps. Therefore, fast electron transfer from the excited Rh-
TiO2 to B12 complex was confirmed.
Rh-TiO2
B12-Rh-TiO2
Fitting line
0
10
20
30
40
50
60
Time(ps)
Fig. 3. Time profiles of normalized transient absorption at 1000 nm of (a) B12-Rh-
TiO2 (blue) and (b) Rh-TiO2 (black) after irradiation by a 405 nm laser flash.

2.3 Photo-duet reaction catalyzed by the B12 immobilized hybrid catalyst (B12-Rh-
TiO2)
The visible light-driven photo-duet reaction was carried out using the B12-Rh-
TiO2 and benzotrichloride (PhCCl3) as the catalyst and substrate, respectively. The
results are summarized in Table 1. The N,N-diethylbenzamide (2a) was produced with
an 88% yield after a 3h visible light irradiation (λ≧420 nm), and the turnover number
(TON) based on the B12 complex was 133 (Entry 1 in Table 1). The product yields
dramatically decreased when B12-TiO2 or Rh-TiO2 (Entries 2 and 3 in Table 1) were
used as the catalyst. The bare TiO2 showed no catalysis by the VIS light irradiations
for this reaction (Entry 4 in Table 1). The reaction did not proceed in the dark or
without the B12-Rh-TiO2 catalyst (Entries 5 and 6 in Table 1). The catalytic reaction
was also carried out using a solar simulator to show the application of sunlight for the
reaction and 2a was produced in 84% yield (entry 7 in Table 1). If the B12 complex
(4) (Fig. S1) and Rh-TiO2 were used without connection, product yield decreased to
78% (Entry 8 in Table 1). Connection of the B12 complex to the photocatalyst as
denoted by B12-Rh-TiO2 should provide a better catalysis. The scope of the reaction
for amide formation is summarized in Table 2. Substituents on the phenyl ring in the
benzotrichloride showed no significant effect on the products yields and the desired
products were formed (2b-2f). Other tertiary amines, such as tripropylamine,
trihexylamine, and diisopropylethylamine, also worked as hole quenchers and the
corresponding amides (2g-2i) were obtained in moderate to good yields from the
benzotrichloride. From α, α, α, α’, α’, α’-hexachloro-m-xylene or α, α, α, α’, α’, α’-
hexachloro-p-xylene, the corresponding diamide, 3a and 3b, were formed.
To elucidate the reaction mechanism, a spin-trapping experiment was conducted
using 5,5-dimethylpyrroline N-oxide (DMPO) as the radical trap reagent and the yield

of 2a decreased to 3 % (Entry 9 in Table 1). The radical may be produced from
PhCCl3 by catalysis of the B12 complex during the reaction. When dry CH3CN was
used as the solvent, the yield of 2a decreased to 52% (Entry 10 in Table 1).
Hydrolysis of the oxidized species of Et3N is necessary to form diethylamine as
shown in equation (4) and the diethylamine reacts with benzoyl chloride to form 2a as
shown in Scheme 2. Furthermore, 2.9 equivalent moles of chloride ions vs. the
starting benzotrichloride were detected by spectrophotometry using the mercury(II)
thiocyanate method after the photo-reaction. The result supports the reaction steps for
the Cl- formations in equations (5) and (10), and Scheme 2. When CH3OH was used
as the solvent instead of CH3CN, the formation of 2a was inhibited and methyl
benzoate was formed with an 31% yield (Entry 11 in Table 1). The intermediate,
benzoyl chloride, should dominantly react with the solvent CH3OH instead of the in-
situ formed diethylamine (Eqs. 1-4) as shown in Scheme 3.

Table 1
Photo-duet reaction for amide (2a) formation from benzotrichloride by the B12-Rh-
a
TiO2
Entry
Catalyst
Light
Product yieldb/%
TONc
1
B12-Rh-TiO2
B12-TiO2
Rh-TiO2
Vis
Vis
Vis
Vis
88
10
14
0
133
15
-
2d
3e
4f
TiO2
-
5
6
B12-Rh-TiO2
None
Dark
Vis
0
0
0
0
7
B12-Rh-TiO2
B12 (4), Rh-TiO2
B12-Rh-TiO2
B12-Rh-TiO2
B12-Rh-TiO2
Solar simulator
84
78
3
52
14
127
117
4
78
21
8g
Vis
Vis
Vis
Vis
9h
10i
11j
aConditions:
B12-Rh-TiO2=20
mg
(B12
complex=1.97×10-5
M);
[benzotrichloride]=3×10-3 M; [triethylamine]=1×10-1 M, solvent: CH3CN 5 mL at
room temperature in air.
bYield of products is based on the initial concentration of the substrate.
cTON based on the B12 catalyst.
dB12-TiO2 (20 mg) (B12=1.22x10-5 M) was used as the catalyst.
eRh-TiO2 (20 mg) was used as the catalyst.
fTiO2 (20 mg) was used as the catalyst.
g[B12 complex, aqua cyano heptamethyl cobyrinate (4)]=1.97×10-5 M, Rh-TiO2=20
mg.
hRadical trapping reagent, DMPO (0.6 M) was used.
iDry CH3CN (H2O: <0.05%max) was used as the solvent.
jMethanol was used as the solvent instead of CH3CN. Methyl benzoate was formed in
an 31% yield.

Table 2
Scope of reaction for amidation of benzotrichloride in air by visible light irradiationa
aConditions: B12-Rh-TiO2=20 mg (B12 complex=1.97×10-5 M); [substrate]=3×10-3 M;
[triethylamine]=1×10-1 M, solvent: 5 mL of CH3CN at room temperature in air. The
yield of the products was based on the initial concentration of the substrate.
b[tripropylamine]=1×10-1 M.
c[trihexylamine]=1×10-1 M.
d[diisopropylethylamine]=1×10-1 M.

3. Conclusion
In summary, we have developed the visible light responsive heterogeneous
hybrid catalyst, B12-Rh-TiO2, composed of the B12 complex, rhodium (III) ion, and
anatase type of TiO2 semiconductor. The reactive Co(I) species of the B12 complex
was efficiently formed by visible light irradiation in the hybrid catalyst in the
presence of the sacrificial reagent (Et3N). The hybrid catalyst converted
benzotrichloride to N,N-dialkylbenzamide under mild conditions, visible light
irradiation at room temperature in air, and in the presence of a tertiary alkyl amine.
The tertiary alkyl amine worked as a source of electrons and the secondary amine for
amide formation. Both the electrons and holes during the band gap excitation of the
catalyst are utilized for the reaction. The B12-inspired photocatalyst shown here can be
used for the sustainable production of fine chemicals with the possible expense of
energy economy. Investigations are ongoing on the related photo-duet reactions using
the visible light responsible catalyst in our laboratory.
4. Experimental section
4.1 Reagents and materials
The solvents and chemicals used in the syntheses were of reagent grade and used
without further purification. Anhydrous CH3CN (H2O: 0.05%max) was purchased
from
Kanto
Chemical
Co.,
Inc.
The
B12
complex,
(CN)2Cob(III)6C1esterCON{(CH2)3Si(OMe)3}2 (1) (Fig. S1), was synthesized by a
previously reported method [6]. The aqua cyano heptamethyl cobyrinate (4) (Fig. S1)
was synthesized by a previously reported method [13]. Titanium oxide (anatase,
AMT-600, surface area=52 m2g-1, diameter size=ca. 30 nm) was obtained from Tayca
Co., Ltd. The products were isolated by chromatography (Silica Gel 60N, spherical,

neutral) using dichloromethane as the eluent, and identified by GC-MS, 1H NMR, and
13C NMR (Figs. S9~S18). Authentic sample of the product 2a was purchased from
Tokyo Kasei Kogyo (TCI).
4.2 Synthesis of Rh-TiO2
TiO2 powder (602 mg) was suspended in 40 mL of H2O containing RhCl3•3H2O
˚
(20.1 mg, 7.63x10-5 mol) at 85 C. After stirring for 5 h, the TiO2 was filtered and
washed with water and methanol, then dried under vacuum. The obtained yellow
powder was calcined at 200 ˚C for 2 h in a muffle furnace.
Yield 505 mg. The Rh modified TiO2 was characterized by DR-UV-VIS (Fig. S2).
The Rh content immobilized on the surface of the TiO2 was determined by a XRF
analysis to be 1.39×10-4 molg-1, which corresponded to 0.559 wt% of the Rh3+ ion.
4.3 Synthesis of covalently immobilized B12-Rh-TiO2
Rhodium (III) modified TiO2 powder (Rh-TiO2) (150 mg,) was suspended in 1.5
mL of methanol containing B12 (1) (5.50 mg, 3.9x10-6 mol) at room temperature.
After stirring for 24 h, the red-purple TiO2 was filtered and washed with methanol,
then dried under vacuum. Yield 142 mg. The B12-Rh-TiO2 hybrid catalyst was
characterized by DR-UV-VIS (Fig. S4), IR (Fig. S5), XRF, and MALDI-TOF-MS
(Fig. S6). IR,
ν
/cm-1: 1717 (ester C=O, str.). The UV-VIS diffusion reflectance
analysis showed reflectance maxima around 500 and 545 nm, which are characteristic
of the α-band of the aqua cyano cobester [13]. The B12 content immobilized on the
surface of the TiO2 was determined by a UV-VIS analysis to be 4.93×10-6 molg-1, and
the apparent surface coverage by the B12 was 9.48×10-12 molcm-2.

4.4 Apparatus and characterization
The NMR spectra were recorded by a Bruker Avance 500 spectrometer at the
Center of Advanced Instrumental Analysis of Kyushu University. The UV-vis
absorption spectra were measured by a Hitachi U-3300 spectrophotometer at room
temperature. The MALDI-TOF mass spectra were obtained by a Bruker autoflex II
using 6-aza-2-thiothymine as the matrix. An ASAHI SPECTRA HAL-320W with a
compact xenon light source was utilized as the sunlight simulator. The GC-mass
spectra were obtained using a Shimadzu GC-QP5050A equipped with a J&W
Scientific DB-1 column (length 30 m; ID 0.25 mm, film 0.25 µm). The diffuse
reflectance (DR) UV-vis reflectance spectra were measured by a JASCO V-670
spectrophotometer equipped with a Φ 60 integrating sphere at room temperature. The
MALDI-TOF mass spectra were obtained by a Bruker autoflex II using 6-aza-2-
thiothymine as the matrix. The IR spectra were recorded by a JASCO FT-IR 460 plus
KH spectrophotometer using KBr discs. The X-ray photoelectron spectroscopy (XPS)
experiments were performed using a Shimazu AXIS-ULTRA. The X-ray fluorescence
analyses (XRF) were performed using a Shimadzu EDX-7000.
4.5 General photocatalytic reaction
A mixture of benzotrichloride (2.9 mg, 3.0x10-3 M), triethylamine (50.0 mg,
1.0x10-1 M), and B12-Rh-TiO2 (20 mg, B12=1.97x10-5 M) was stirred in 5mL of
CH3CN in air at room temperature. After the solution was stirred for 3 hours during
irradiation by a 200 W tungsten lump equipped with a 420 nm cut-off filter (Sigma
Koki, 42 L) and a heat cut-off filter (Sigma Koki, 30 H), the B12-Rh-TiO2 was
removed by filtration. The resulting solution was analyzed by GC-MS and yields of

the products were calculated by comparison to the ratio of the peak area using
diphenyl as an internal standard.
4.6 Quantification of chloride ion
The chloride ions removed from the benzotrichloride by the photocatalytic
reaction under aerobic conditions was quantified using the mercury (II) thiocyanate
method [17]. After the photoreaction, 300 µL of the solution was added to 8 mL of
carbon tetrachloride, then 4 mL of water was added to extract the chloride ion. The
procedure was repeated two times and the chloride ion in the aqueous solution was
quantified by UV-vis spectroscopy.
Acknowledgements
We express our gratitude to Professor Tsuyohiko Fujigaya and Dr. Naoki Tanaka
(Kyushu University, Japan) for helping to measure the XPS. This study was partially
supported by a Grant-in-Aid for Scientific Research (B) (JP19H02735) from the
Japan Society for the Promotion of Science (JSPS), and KAKENHI Grant Number
JP18H04265 in Precisely Designed Catalysts with Customized Scaffolding. This
research was also supported by the Adaptable and Seamless Technology Transfer
Program through Target-driven R&D (A-STEP) (VP30118067023) from the Japan
Science and Technology Agency (JST). A part of the study was performed under the
Cooperative Research Program of “Network Joint Research Center for Materials and
Devices: Dynamic Alliance for Open Innovation Bridging Human, Environment and
Materials” (20193019).

Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/#####/j.jorganchem.2019.####.
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Graphical abstract
Cl
Cl
Cl
Vis. light
Me
O
O
R
e-
CoI
O
Si
Si
N
H3CO2C
H3CO2C
O
O
O2
N
R
O
CH3
CH3
H
RhIII
O
O
3 Me
TiO2
CO2CH
NC
H3C
H3C
RhIII
N
N
H
CoIII
RhIII
H
H
H
N
CH3
N
N
CoIII
=
CH3
H2O
H3CO2C
H
H3C
CH3
CO2CH3
CO2CH3

Highlights
ò
ò
The hybrid catalyst composed of the B12 complex, rhodium (III) ion, and TiO2
was synthesized.
The cobalt (III) state of the B12 complex was reduced to a monovalent species via
electron transfer from the rhodium (III) modified TiO2 by visible light
irradiation.
ò
Various amides were formed from the benzotrichloride derivative by the B12
modified photocatalyst under mild conditions, visible light irradiation at room
temperature in air.

Table and Figure captions
Table 1 Photo-duet reaction in amide formation from benzotrichloride by the B12-
a
Rh-TiO2
Table 2 Scope of reaction for amidation of benzotrichloride under air by visible light
irradiationa
Fig. 1. Visible light-driven duet reaction catalyzed by B12-Rh-TiO2 in air.
Fig. 2. DR-UV-vis spectral change of the B12-Rh-TiO2 during visible light irradiation
in the presence of Et3N in CH3CN under N2: (a) before irradiation, (b) 1 min.
irradiation, (c) 30 min. irradiation.
Fig. 3. Time profiles of normalized transient absorption at 1000 nm of (a) B12-Rh-
TiO2 (blue) and (b) Rh-TiO2 (black) after irradiation by a 405 nm laser flash.

Fig. 1. Visible light-driven duet reaction catalyzed by B12-Rh-TiO2 under air.
Fig. 2. DR-UV-vis spectral change of the B12-Rh-TiO2 during visible light irradiation
in the presence of Et3N in CH3CN under N2: (a) before irradiation, (b) 1 min.
irradiation, (c) 30 min. irradiation.

Rh-TiO2
B12-Rh-TiO2
Fitting line
0
10
20
30
40
50
60
Time(ps)
Fig. 3. Time profiles of normalized transient absorption at 1000 nm of (a) B12-Rh-
TiO2 (blue) and (b) Rh-TiO2 (black) after irradiation with a 405 nm laser flash.

Table 1
Photo-duet reaction for amide (2a) formation from benzotrichloride by the B12-Rh-
a
TiO2
Entry
Catalyst
Light
Product yieldb/%
TONc
1
B12-Rh-TiO2
B12-TiO2
Rh-TiO2
Vis
Vis
Vis
Vis
88
10
14
0
133
15
-
2d
3e
4f
TiO2
-
5
6
B12-Rh-TiO2
None
Dark
Vis
0
0
0
0
7
B12-Rh-TiO2
B12 (4), Rh-TiO2
B12-Rh-TiO2
B12-Rh-TiO2
B12-Rh-TiO2
Solar simulator
84
78
3
52
14
127
117
4
78
21
8g
Vis
Vis
Vis
Vis
9h
10i
11j
aConditions:
B12-Rh-TiO2=20
mg
(B12
complex=1.97×10-5
M);
[benzotrichloride]=3×10-3 M; [triethylamine]=1×10-1 M, solvent: CH3CN 5 mL at
room temperature in air.
bYield of products is based on the initial concentration of the substrate.
cTON based on the B12 catalyst.
dB12-TiO2 (20 mg) (B12=1.22x10-5 M) was used as the catalyst.
eRh-TiO2 (20 mg) was used as the catalyst.
fTiO2 (20 mg) was used as the catalyst.
g[B12 complex, aqua cyano heptamethyl cobyrinate (4)]=1.97×10-5 M, Rh-TiO2=20
mg.
hRadical trapping reagent, DMPO (0.6 M) was used.
iDry CH3CN (H2O: <0.05%max) was used as the solvent.
jMethanol was used as the solvent instead of CH3CN. Methyl benzoate was formed in
an 31% yield.

Table 2
Scope of reaction for amidation of benzotrichloride in air by visible light irradiationa
aConditions: B12-Rh-TiO2=20 mg (B12 complex=1.97×10-5 M); [substrate]=3×10-3 M;
[triethylamine]=1×10-1 M, solvent: 5 mL of CH3CN at room temperature in air. The
yield of the products was based on the initial concentration of the substrate.
b[tripropylamine]=1×10-1 M.
c[trihexylamine]=1×10-1 M.
d[diisopropylethylamine]=1×10-1 M.

Scheme 1
Scheme 2

Scheme 3
Equations

Declaration of interests
☐The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
Hisashi Shimakoshi
Kyushu University
Japan