Covalently hooked EOSIN-Y in a Zr(IV) framework as visible-light mediated, heterogeneous photocatalyst for efficient C–H functionalization of tertiary amines

Article abstract of DOI:10.1016/j.jcat.2019.02.011

Herein, we report the synthesis of a novel heterogeneous photo-catalyst by utilizing post-synthetic modification of an amine functionalized Zr(IV) metal-organic framework (UiO-66-NH₂) through covalent hooking of EOSIN-Y via dehydrating coupling. The characterization of the catalyst was accomplished by FT-IR, XRD, BET surface analysis, TGA, as well as TEM, SEM, XPS, DRS-UV–visible, and NMR spectroscopy, confirming successful covalent linking of EOSIN-Y with the pendent –NH₂ functionality in the framework. That post-modified EY@UiO-66-NH₂ acts as simple and green visible light mediated photo-catalyst for the C–H activation of tertiary amines with excellent yields. Importantly, the activity of dye incorporated heterogeneous photo-catalyst is found superior to that for the homogeneous photo-catalyst EOSIN-Y. Thus, separation difficulty of homogeneous catalysis, as well as the environmental adverse effects of toxic EOSIN-Y can be excluded by developing such photo-catalyst. Moreover, EY@UiO-66-NH₂ catalyst could be consistently recycled up to 10 cycles, without any significant loss in activity. Based on literature report and experimental findings, we also propose a plausible mechanism for the reaction.

Full text of DOI:10.1016/j.jcat.2019.02.011

Journal of Catalysis 371 (2019) 298–304
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Covalently hooked EOSIN-Y in a Zr(IV) framework as visible-light
mediated, heterogeneous photocatalyst for efficient CAH
functionalization of tertiary amines
a,b
Gaurav Kumar a,b, Pratik Solanki a, Mohd Nazish a,b, Subhadip Neogi a,b, , Rukhsana I. Kureshy
,
⇑
Noor-ul H. Khan a,b,
⇑
a Inorganic Materials and Catalysis Division, CSIR-Central Salt and Marine Chemicals Research Institute (CSIR-CSMCRI), Council of Scientific & Industrial Research (CSIR), G. B.
Marg, Bhavnagar, 364002 Gujarat, India
b Academy of Scientific and Innovative Research (AcSIR), CSIR-CSMCRI, Bhavnagar, 364002 Gujarat, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Herein, we report the synthesis of a novel heterogeneous photo-catalyst by utilizing post-synthetic mod-
ification of an amine functionalized Zr(IV) metal-organic framework (UiO-66-NH2) through covalent
hooking of EOSIN-Y via dehydrating coupling. The characterization of the catalyst was accomplished
by FT-IR, XRD, BET surface analysis, TGA, as well as TEM, SEM, XPS, DRS-UV–visible, and NMR spec-
troscopy, confirming successful covalent linking of EOSIN-Y with the pendent ANH2 functionality in
the framework. That post-modified EY@UiO-66-NH2 acts as simple and green visible light mediated
photo-catalyst for the CAH activation of tertiary amines with excellent yields. Importantly, the activity
of dye incorporated heterogeneous photo-catalyst is found superior to that for the homogeneous
photo-catalyst EOSIN-Y. Thus, separation difficulty of homogeneous catalysis, as well as the environmen-
tal adverse effects of toxic EOSIN-Y can be excluded by developing such photo-catalyst. Moreover,
EY@UiO-66-NH2 catalyst could be consistently recycled up to 10 cycles, without any significant loss in
activity. Based on literature report and experimental findings, we also propose a plausible mechanism
for the reaction.
Received 16 November 2018
Revised 12 January 2019
Accepted 3 February 2019
Keywords:
Metal-organic framework
EOSIN-Y
Post-synthetic modification
Photo redox catalyst
Visible light
Ó 2019 Elsevier Inc. All rights reserved.
1. Introduction
oxide [15], and protuberant lychee-like goethite [16] for CAH func-
tionalization of tertiary amines. These processes utilize the thermal
In recent decade, the photo redox catalysed reaction by using
simple and green visible light has come up as an emerging strategy
towards a variety of CAH functionalization for the synthetic
organic chemists [1–6]. Given our prime interest involves CAH
activation of tertiary amines towards the synthesis of important
bioactive natural products, unnatural alpha amino acids or impor-
tant heterocyclic compounds, [7–9] one can synthesize them by
using conventional Strecker reaction between carbonyl group, ami-
nes and a cyanide source [10] However, instead of using a tedious
path, which produces undesirable waste, many groups have well
explored transition metal based catalysts such as RuCl3 [11],
MnO2 [12], Fe3O4 [13], V2O5 [14], Iron nanoparticles on Graphene
pathway to produce the alpha amino nitrile products.
In the meantime, molecular homogeneous photo-catalyst based
on metal (Ir and Ru) or organic dyes have been experimentally
used for these reactions [17–20]. However, high cost of transition
metals and limited scope to separate them from the reaction mix-
ture are the major shortcomings associated to the practical appli-
cations of this specific route. On the other hand, organic dyes
impose severe threat on environment due to their toxic nature
[21]. In contrast, heterogeneous catalysts promise the recyclability
that motivated many groups to explore heterogeneous photo catal-
ysed CAH activation of tertiary amines, to name a few such as Cu2O
mesoporous spheres [22], TiO2 based heterogeneous photocatalyst
[23], gold (III) complex [24], mesoporous graphitic carbon nitride
(mpg-C3N4) [25]. However, in most of the cases their usages are
limited to the active tertiary amines derivatives, besides the draw-
backs that they do not show satisfactorily high catalytic activity,
require high temperatures, and suffer from reusability.
⇑
Corresponding authors at: Inorganic Materials and Catalysis Division, CSIR-
Central Salt and Marine Chemicals Research Institute (CSIR-CSMCRI), Council of
Scientific & Industrial Research (CSIR), G. B. Marg, Bhavnagar, 364002 Gujarat, India.
E-mail addresses: sneogi@csmcri.res.in (S. Neogi), khan251293@yahoo.in
(Noor-ul H. Khan).
https://doi.org/10.1016/j.jcat.2019.02.011
0021-9517/Ó 2019 Elsevier Inc. All rights reserved.

G. Kumar et al. / Journal of Catalysis 371 (2019) 298–304
299
In this scenario, the sustainability of organo-photo redox dyes
has been validated by several groups, [26,27] where EOSIN-Y turns
to be very promising, with the inherent difficulty related to its
tough separation from homogeneous conditions. Nevertheless,
the disadvantage of separation can be eradicated by hooking EOSIN
Y on solid support. In fact, Xiaobin Fan covalently hooked EOSIN-Y
on reduced graphene oxide for photo catalytic applications, [28]
while Cooper et al. successfully integrated Rose Bengal into conju-
gated micro porous polymers, [29] Nasalevich et al. implemented
methyl red in a MOF (NH2-MIL-125(Ti) [30] although such reports
are only handful.
modified framework exhibits well matched diffraction peaks, indi-
cating that the integrity and crystallinity of the UiO-66-NH2 frame-
work is well maintained during the coupling reaction. Given the
covalent structure has no obvious effect on the mother framework,
the PXRD result additionally attribute to the relatively low content
of EY with its well dispersed small particle size in EY@UiO-66-NH2.
Fig. S1 (supplementary data) compares the TGA curves of the pris-
tine MOF and EY@ UiO-66-NH2. The first weight losses upto 120 °C
is ascribed to the release of moisture, and solvent both in pristine
and modified MOF. The second weight loss in UiO-66-NH2 is attrib-
uted to the slow decomposition of material from 400 to 700 °C.
EY@UiO-66-NH2 shows weight loss from 150 to 400 °C, which is
ascribed to the degradation of EY, and second weight loss from
400 to 700 °C correlates to the degradation of pristine MOF. There-
fore, modified EY@UiO-66-NH2 shows comparatively higher
weight loss than pristine MOF at 700 °C. Fourier transform infrared
(FT-IR) spectroscopy provides strong evidence for the covalent
immobilization of EY (Fig. S2). For UiO-66-NH2, the absorption
peaks between 600 and 800 cmꢀ1 in the FT-IR correspond to ZrAO
as longitudinal and transverse modes, while intense doublets at
1433 and 1389 cmꢀ1 can be assigned to the stretching modes of
the carboxylic groups in the BDC-NH2 ligand. Two obvious absorp-
tion peaks at 3394 and 3242 cmꢀ1 were attributed to the asym-
metric and symmetric vibrations of NAH bonding in the amino
group. In the spectrum of EY, OAH stretching at 3136 cmꢀ1, C@O
stretching at 1591 cmꢀ1, and OAH bending at 1339 cmꢀ1 prove
the existence of free ACO2H groups. As for the modified EY@UiO-
66-NH2, most of the IR vibration bands are fully consistent with
those of the pristine framework, suggesting the composite have
the similar structure as of UiO-66-NH2. Importantly, the absorption
peaks for free amino groups in the BDC-NH2 ligand disappear after
the covalent functionalization with EY. Besides, the typical signal
of COANH at 1635 cmꢀ1 and the characteristic absorption of the
NAH stretching band at 3344 cmꢀ1 appears in the spectra of the
EY@UiO-66-NH2. Moreover, emergence of two new bands at
1615 cmꢀ1 and 1046–1090 cmꢀ1, corresponding to the vibration
of C@O and CAO from EY, respectively, confirms that ACO2H of
EY successfully reacted with ANH2 moiety in the framework.
It should be noted that due to the introduction of EY by dehy-
drate coupling reaction, the NAH stretching vibration and CAN
stretching vibration become less prominent. Additionally, after
the dehydration, the ACO2H bands from EY disappear (Fig. S2),
indicating the successful conversion of carboxyl groups into
O@CAN. The nitrogen adsorption isotherm of the as-prepared sam-
ple indicates a steep uptake at low relative pressure, and belong to
the typical type I isotherm, revealing microporous structure of the
framework (Fig. 1b). The BET surface area of pristine UiO-66-NH2 is
smaller than UiO-66 due to incorporation of pendent ANH2 groups
in pore structure [48]. After introduction of EY, the BET surface area
of EY@UiO-66-NH2 further decreases to 395.12 m2/g due to encap-
sulation of EY inside the pore. It should be noted that the BET sur-
face area is still adequate to supply more surface active sites for
enhanced photo catalytic performance.
Based on the aforesaid finding, and keeping our target to cova-
lently modify EOSIN-Y for efficient photo-catalytic applications, we
turned our attention to porous metal-organic frameworks (MOFs)
[31]. MOFs have emerged as promising heterogeneous catalysts
because of their (i) well-defined and tunable pores, (ii) versatile
structures, and (iii) easy functionalization [32–34]. Furthermore,
MOFs often endure covalent linkage with organic moieties even
after de novo synthesis, commonly called as post synthetic modifi-
cation (PSM), benefitting a way to further functionalize these
materials [35]. In this context, free amine moiety containing MOFs
are widely used because of its easy accessibility to take part in var-
ious reactions [36]. However, chemical stability of MOFs is of pri-
mary concern, because of the weak coordination bond, that limits
their applications towards such covalent functionalization [37].
To this end, employing Zr(IV) based metal nodes can dramatically
increase the stability of the MOFs [38]. The UiO-66-NH2 framework
is highly chemically stable, even defiant to acids [39], bases [40]
moisture [41] and shows extraordinary mechanical stability [42].
Cohen [43] and Tilset [44] pioneered the amino functionalized
UiO-66-NH2 using 2-amino-1,4-benzenedicarboxylate, where the
–NH2 group remains free and acts as potential functional organic
site (FOS) [45]. Afterwards, several other research groups have uti-
lized the post-synthetic activity of this free amine moiety, by using
anhydrides, [46] phthalocyanines [47] or amide functionalised
pores [48]. Keeping in mind the aforesaid rationale, we aimed to
heterogenise the organo-photo redox EOSIN-Y via PSM between
its free acid group and –NH2 functionality of UiO-66-NH2 by using
DCC as a dehydrating coupling reagent. The post synthetically
modified EY@UiO-66-NH2 was characterized by a battery of exper-
imental evidences including PXRD, FT-IR, XPS, NMR, CHN analysis
and used further for oxidative cyanation of tertiary amines. The
versatility of the photo-catalyst towards various other nucle-
ophiles was also cross-checked that revealed high yield of the
desired product is maintained in all the cases. Recyclability test
shows no loss of activity even upto ten cycles. Thus, heterogenizing
the EOSIN-Y via PSM in UiO-66-NH2 provides two fold benefit, (i)
avoiding the separation difficulty of homogeneous catalysis, and
(ii) controlling the adverse environmental effects of toxic organic
dye.
2. Results and discussion
We also recorded solid state 15N NMR of pristine UiO-66-NH2,
and its post synthetically modified analogue (Fig. 1c). While the
peaks of free NH2 in the pristine framework were located at –
322.79 ppm, the ANH of amide group in EY@UiO-66-NH2 down
field shifted (region ꢀ266.01 ppm) with no residue signal left at
–322.79 ppm that confirms the successful post synthetic covalent
modification. To demonstrate such small shift of the 15N NMR, cor-
responding to modification of amine to amide in the framework,
we conducted quantum chemical calculations using GAUSSIAN
09 [50]. Structures were fully optimized at B3LYP/genecp 6-31+g
(d) lanl2dz level of theory. Gauge-Independent Atomic Orbital
(GIAO) method [51] was used for calculating 15N chemical shift
at same level of theory. Model structures were used for calculation
2.1. Synthesis and characterization of the photocatalyst
The parent framework UiO-66-NH2 was prepared by using the
reported synthetic procedure [49]. For the as-prepared UiO-66-
NH2, the experimental powder X-ray diffraction (PXRD) pattern
exactly matches with the calculated one [48] confirming phase
purity (Fig. 1a).
As already described above, EY was introduced into the frame-
work via single step dehydrate coupling of the carboxyl group of
EOSIN-Y free acid (EY-FA) with primary amine group of UiO-66-
NH2 by using N,N-dicyclohexylcarbodiimide (DCC) as a dehydrat-
ing reagent in DMF solution. The PXRD pattern of the post-

300
G. Kumar et al. / Journal of Catalysis 371 (2019) 298–304
Fig. 1. PXRD patterns of UiO-66-NH2 and EY@UiO-66-NH2 (a) along with N2 adsorption isotherms of UiO-66-NH2 (black), and EY@UiO-66-NH2 (red) at 77 K (b). 15N CP MAS
NMR spectra of UiO-66-NH2 (black line, top) and EY@UiO-66-NH2 (red line, bottom) (c). (For interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
of free amine in pristine framework (Fig. 2b) and also the amide
group in EY@UiO-66-NH2 (Fig. 2c). Isotropic shielding constant
for ammonia was calculated at similar level of theory as reference
value. Shielding constants calculated are then converted to chem-
ical shift frequencies by calculating difference in theoretical isotro-
By comparing the XPS between UiO-66-NH2 and EY@UiO-66-
NH2, new signals of Br from EOSIN-Y emerge in the later frame-
work (Fig. 3a). The loading of EOSIN-Y were also confirmed by C
1s, N 1s, Br 3d. The deconvoluted EY@UiO-66-NH2 for C 1s spec-
trum depict the conversion to amide bond of O@CAN at 287.9 eV
(Fig. 3b) which is also reported in literature [54]. Two clear peaks
of N 1s were found after deconvolution (Fig. S6b), which corre-
spond to CANH2 (398.04 eV), and CANH+3 (400.60 eV). After PSM,
the N 1s peaks are deconvoluted into three peaks; however, a
new peak appears at 399.9 eV that confirms the formation of
NAC@O amide linkage, while other two peaks stand for CANH2
(398.17) and CANH+3 (401.49) (Fig. 3c). The ratio of EY in
EY@UiO-66-NH2 approximates to 0.14 mmol/g that exactly corre-
lates with the TEM analysis results (vide supra).
pic chemical shift value of ammonia using relation d = 262.35-
r
[52,53]. A lower 15N chemical shift of 44 ppm is observed for 2c
compared to 2b (Fig. 2), which is in accordance with experimental
results.
The morphologies were determined by SEM analysis, which
revealed that both the pristine as well as covalently modified
frameworks have regular faceted surfaces (Figs. S3 and S4). Corre-
sponding energy dispersive X-ray spectroscopy (EDS) mapping was
employed to quantify the density and distribution of EY (Fig. 2a),
which shows that the elements C, N, O and Br are homogeneously
dispersed on the whole surface of EY@UiO-66-NH2, indicating uni-
form distribution of the dye. The elemental atomic ratio of Br in the
post-modified material has been calculated that proves the dye
loading of 0.13 mmol/g (corresponding to weight percentage)
(Table S1, supplementary data).
As depicted in Fig. S5 the UV–vis spectrum of EY@UiO-66-NH2
exhibits intense absorption bands in the lower energy region
(450 nm < k < 600 nm), demonstrating that the present system
incorporating EY is a visible light absorbing system. Further, the
compositions of UiO-66-NH2 after its post-synthetic modification
were evaluated by using X-ray photoelectron spectroscopy (XPS).
2.2. CAH functionalization reaction
After complete characterisation of the post-modified frame-
work, it was screened for CAH functionalization reaction of tertiary
amine (1) with TMSCN as cyanide source at room temperature
using a 16 W visible light source for 3 h. The product (2) was
obtained with good to moderate yield (Table 1). For optimisation
of the reaction conditions, several solvents including, DMF, ace-
tone, DCM, acetonitrile and methanol (Table 1, entries 1–5) were
screened. Among others, methanol was found to be the best choice
of solvent to achieve good yield of
a-amino nitrile product (2)
Fig. 2. Quantitative EDS mapping of Br, Zr, C, N and O of EY@UiO-66-NH2 by SEM (a). Model for free amine in pristine framework of UiO-66-NH2 (b), model for amide group in
EY@UiO-66-NH2 (c) the color of atoms are cyan for zirconium, red for oxygen, gray for carbon, blue for nitrogen and white for hydrogen. (For interpretation of the references
to colour in this figure legend, the reader is referred to the web version of this article.)

G. Kumar et al. / Journal of Catalysis 371 (2019) 298–304
301
Fig. 3. Full XPS spectra of (a) survey comparison of UiO-66-NH2 and EY@UiO-66-NH2, (b) C 1s XPS spectra and (c) N 1s XPS spectra of EY@UiO-66-NH2.
Table 1
Screening of the catalyst and reaction conditions.a
Entry
Photocatalyst
Solvent
CN– Source
Yieldb (%)
1
2
3
4
5
6
7
EY@UiO-66-NH2
EY@UiO-66-NH2
EY@UiO-66-NH2
EY@UiO-66-NH2
EY@UiO-66-NH2
EY@UiO-66-NH2
EY@UiO-66-NH2
EY@UiO-66-NH2
EY@UiO-66-NH2
UiO-66-NH2
ZrCl4
DMF
Acetone
DCM
TMSCN
TMSCN
TMSCN
TMSCN
TMSCN
KCN
75%
70%
40%
96%
45%
65%
80%
n.r.
MeOH
MeCN
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
NaCN
8c
9d
10e
11f
12g
13h
14i
15j
TMSCN
TMSCN
TMSCN
TMSCN
TMSCN
TMSCN
TMSCN
TMSCN
n.r.
30%
10%
95%
15
n.r.
n.r.
EOSIN-Y
Ligand
ZrCl4
–
a
Reaction Conditions: The reaction was performed with 1 (0.3 mmol), using 10 mg of catalyst in 2 mL solvent, using 16 W visible household light in 4 h. The CN source was
used (0.5 mmol).
b
Yield were determined by GC.
In the dark.
Under inert gas (N2).
UiO-66-NH2 reaction time 24 h.
Reaction performed thermally at 40 °C without light.
EOSIN-Y (2 mg).
c
d
e
f
g
h
Ligand ꢀ2-aminoterephthalic acid.
i
Reaction under light illumination.
j
Blank reaction n. r. = no reaction.
(Table 1, entry 4). Further, on varying the cyanide source viz.,
TMSCN, NaCN and KCN (entries 4, 6, 7) non-toxic trimethylsilyl
cyanide was found to be the safest source of cyanide for this partic-
ular reaction (Table 1, entry 4). To confirm the photocatalytic activ-
ity of EY@UiO-66-NH2, reaction was performed under dark
(Table 1, entry 8) that did not result any reaction. Additionally,
no product was formed when the reaction was performed under
inert atmosphere (Table 1, entry 9). The aforesaid observations
clearly indicate that visible light and aerobic condition are neces-
sary attributes to carry out CAH bond functionalization of tertiary
amines (Table 1, entry 4). We also checked if the precursor metal
Zirconium chloride (ZrCl4) itself can catalyse the reaction or not.
However, insignificant yield was obtained only under thermal con-
dition (Table 1, entry 11) and no reaction takes place under light
(Table 1, entry 14), confirming trivial effect. Additionally, the
carbon-carbon coupling reaction was also carried out using only
Eosin-Y, maintaining the similar protocol that result 95% yield
(Table 1, entry 12). Further, we examined whether reaction occurs
with the pristine framework UiO-66-NH2 (Table 1, entry 10), or
ligand 2-aminoterephthalic acid (Table 1, entry 13) as well as
under blank condition (Table 1, entry 15), using light only. To our
delight, no product formed in any of the cases. We also checked
the effectiveness of silica (MCM-41) supported EOSIN-Y towards
CAH functionalization of amines (Scheme S4) under identical reac-
tion condition that revealed much inferior yield (Table 3, 2q0).
Given EY@UiO-66-NH2 stands as an excellent photo-catalyst

302
G. Kumar et al. / Journal of Catalysis 371 (2019) 298–304
towards CAH functionalization, we tried to assess the recyclability
of the catalyst under optimized conditions. Impressively, EY@UiO-
66-NH2 catalyst could be consistently recycled up to 10 cycles,
without any significant loss in activity (Fig. S7a). We also per-
formed the recycling experiments after 30 min of reaction, which
corroborated significantly high conversion of the final product with
low yield (Fig. S7b). Clearly, heterogenising the dye over UiO-66-
NH2 is beneficial in terms of recyclability and yield of the product.
Additionally, to confirm the leaching of EOSIN-Y during catalysis,
we recorded UV-spectroscopy of the reaction medium after separa-
tion of the product and catalysts, which indicated that no material/
dye was leached out during the reaction.
hand, the product yield would be much poorer if EOSIN-Y present
at the outside of the MOF particles would have played significant
catalytic role. These cumulative results essentially points to the
active participation of MOF in size selectivity of EY@UiO-66-NH2
catalyst. However, the indole based substrate, which is converted
to corresponding product within 3 h with good yield (Table 3),
encompasses highly reactive nucleophilic centre that leads to min-
imise the energy barrier of the reaction, and increase the yield.
Hence, EY@UiO-66-NH2 proved to be an ideal and versatile
photo-catalyst for CAH functionalization reaction with different
nucleophile and also capable of using nascent oxygen from air in
visible light condition.
To further explore the versatility of the catalyst, coupling reac-
tion was extended with various secondary, as well as tertiary
2.3. Reaction mechanism
amine substrates (Tables
dimethylanilines with electron donating groups efficiently fur-
nished -aminonitrile products with good to excellent yield.
Besides, the high yield of -aminonitrile product was also achieved
2 and 3). To our delight, N,N-
Based on the earlier results [17], coupled with the aforemen-
tioned experimental outcome, we propose a plausible mechanism
(Scheme 1) for CAH functionalization reaction, using EY@UiO-66-
NH2. Upon excitation of EY@UiO-66-NH2 photo-system (PS) with
visible light, a single-electron transfer (SET) takes place from the
tertiary amine (1a) substrate to produce PS*, which ultimately gen-
erates the cationic radical 1aÅ+ and the radical anion (PSÅꢀ). Conse-
quently, PSÅꢀ transfers an electron to the molecular oxygen, leading
to the formation of OÅ2ꢀ, thereby regenerating the ground state PS.
In the meantime, OÅ2ꢀ abstracts one hydrogen from the cationic rad-
ical of tertiary amine 1aÅ+, generating a hydro peroxide (OH–) and
a
a
by conducting the CAH functionalization of several cyclic amines,
such as piperidine, pyrrolidine and tetrahydroisoquinoline, in
moderate to high yield. Remarkably, this protocol also works well
with other nucleophiles like nitroalkane, dimethylmalonate,
diethylphosphite, naphthol and indole to offer moderate to good
yield of desired products (Table 3). However, the percentage of
yield with larger sized substrates is not up to the mark, as have
been reported for other catalyst systems [55,56]. On the other
Table 2
Substrate scope for cyanation reaction.

G. Kumar et al. / Journal of Catalysis 371 (2019) 298–304
303
Table 3
Substrate scope with other nucleophiles.
Scheme 1. Plausible reaction mechanism for the EY@UiO-66-NH2 photocatalysed CAH activation of tertiary amines with molecular oxygen.
iminium cation intermediate (1a+). The latter species consequently
traps the attack by pronucleophile, resulting in the formation of
desired product. To crosscheck the above mechanistic conduit,
we endeavoured to trap the radical cation by using BHT radical
inhibitor, which revealed that the reaction does not proceed any-
more, confirming the radical pathway.
diethylphosphite, naphthol and indole to offer excellent yields of
desired products, and promises to be an ideal and versatile
photo-catalyst for CDC reaction with different nucleophile. In a
nutshell, the present study emphasises heterogenising the photo-
catalyst EOSIN-Y that benefits in two ways: (a) the separation dif-
ficulty, as well as recyclability issues of homogeneous catalysis can
be excluded and (b) the adverse environmental effects of toxic
EOSIN-Y can be optimised.
3. Conclusions
In conclusion, we have hooked the homogeneous photo-catalyst
dye EOSIN-Y into the functionalized Zr (IV) based framework (UiO-
66-NH2) via dehydrating coupling reaction with the pendent amine
moiety. The post-synthetically modified framework EY@UiO-66-
NH2 has been well characterized by FTIR, XRD, BET surface analy-
sis, TGA, as well as TEM, SEM, XPS, DRS-UV–visible, and NMR spec-
troscopy that confirms successful covalent linking of the dye with
the framework via formation of amide linkage. The post modified
EY@UiO-66-NH2 acts as a simple and green visible light mediated
photo-catalyst for the CAH activation of tertiary amines with
excellent yields. Importantly, the activity of dye incorporated
heterogeneous photo-catalyst is found superior to that for the
homogeneous photo-catalyst EOSIN-Y. Moreover, EY@UiO-66-
NH2 catalyst could be consistently recycled up to 10 cycles, with-
out any significant loss in activity. The system works well with
other nucleophiles including nitroalkane, dimethylmalonate,
Acknowledgements
We
are
thankful to
the
CSIR,
India, DST-SERB
(ECR/2016/000156), India, for financial support. The authors thank
Dr. Santanu Karan and Dr. Bishwajit Ganguly for helping in XPS and
computational analysis, respectively. Analytical support from
ADCIF is highly acknowledged. GK is thankful to CSIR for SRF,
and AcSIR for PhD registration. PS acknowledges Manipal Univer-
sity, India, for M.Sc. internship. CSIR-CSMCRI Communication No.
053/2018.
Appendix A. Supplementary material
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.jcat.2019.02.011.

304
G. Kumar et al. / Journal of Catalysis 371 (2019) 298–304
[29] J.X. Jiang, Y. Li, X. Wu, J. Xiao, D.J. Adams, A.I. Cooper, Conjugated microporous
References
polymers with Rose Bengal dye for highly efficient heterogeneous organo-
photocatalysis, Macromolecules 46 (2013) 8779–8783.
[30] M.A. Nasalevich, M.G. Goesten, T.J. Savenjie, F. Kapteijn, J. Gascon, Enhancing
optical absorption of metal organic frameworks for improved visible light
photocatalysis, Chem. Commun. 49 (2013) 10575–10577.
[31] J.R. Long, O.M. Yaghi, The pervasive chemistry of metal organic frameworks,
Chem. Soc. Rev. 38 (2009) 1213–1214.
[32] J. Gascon, A. Corma, F. Kapteijn, F.X.L. Xamena, Metal organic framework
catalysis: Quo vadis?, ACS Catal 4 (2014) 361–378.
[1] K.T. Yeung, W.P. To, C. Sun, G. Cheng, C. Ma, G.S.M. Tong, C. Yang, C.M. Che,
Luminescent tungsten(VI) complexes: photophysics and applicability to
organic light-emitting diodes and photocatalysis, Angew. Chem. Int. Ed. 56
(2017) 133–137.
[2] A.M. Nauth, A. Lipp, B. Lipp, T. Opatz, Sunflow: sunlight drives fast and green
photochemical flow reactions in simple microcapillary reactors-application to
photoredox and H-atom-transfer chemistry, Eur. J. Org. Chem. 2017 (2017)
2099–2103.
[3] Z. Li, Y. Pi, D. Xu, Y. Li, W. Peng, G. Zhang, F. Zhang, X. Fan, Utilization of MoS2
and graphene to enhance the photocatalytic activity of Cu2O for oxidative C-C
bond formation, Appl. Catal. B-Environ. 213 (2017) 1–8.
[4] J.M. Narayanam, C.R. Stephenson, Visible light photoredox catalysis:
applications in organic synthesis, Chem. Soc. Rev. 40 (2011) 102–113.
[5] C.K. Prier, D.A. Rankic, D.W. MacMillan, Visible light photoredox catalysis with
transition metal complexes: applications in organic synthesis, Chem. Rev. 113
(2013) 5322–5363.
[6] D.A. Nagib, D.W. MacMillan, Trifluoromethylation of arenes and heteroarenes
by means of photoredox catalysis, Nature 480 (2011) 224–228.
[7] D. Enders, J.P. Shilvock, Some recent applications of alpha amino nitrile
chemistry, Chem. Soc. Rev. 29 (2000) 359–373.
[8] S.I. Murahashi, N. Komiya, H. Terai, Ruthenium-catalyzed oxidative cyanation
of tertiary amines with hydrogen peroxide and sodium cyanide, Angew. Chem.
Int. Ed. 44 (2005) 6931–6933.
[33] A. Corma, H. Garcia, F.X.L. Xamena, Engineering metal organic frameworks for
heterogeneous catalysis, Chem. Rev. 110 (2010) 4606–4655.
[34] L. Zhu, X.Q. Liu, H.L. Jiang, L.B. Sun, Metal organic frameworks for
heterogeneous basic catalysis, Chem. Rev. 117 (2017) 8129–8176.
[35] K.K. Tanabe, S.M. Cohen, Postsynthetic modification of metal organic
frameworks a progress report, Chem. Soc. Rev. 40 (2011) 498–519.
[36] Y. Lin, C. Kong, L. Chen, Amine functionalized metal-organic frameworks, RSC
Adv. 6 (2016) 32598–32614.
[37] N.C. Burtch, H. Jasuja, K.S. Walton, Water stability and adsorption in metal
organic frameworks, Chem. Rev. 114 (2014) 10575–10612.
[38] J.H. Cavka, S. Jakobsen, U. Olsbye, N. Guillou, C. Lamberti, S. Bordiga, K.P.
Lillerud, A new zirconium inorganic building brick forming metal organic
frameworks with exceptional stability, J. Am. Chem. Soc. 130 (2008) 13850–
13851.
[39] H.L. Jiang, D. Feng, K. Wang, Z.Y. Gu, Z. Wei, Y.P. Chen, H.C. Zhou, An
exceptionally stable, porphyrinic Zr metal organic framework exhibiting pH-
dependent fluorescence, J. Am. Chem. Soc. 135 (2013) 13934–13938.
[40] M. Kandiah, M.H. Nilsen, S. Usseglio, S. Jakobsen, U. Olsbye, M. Tilset, C. Larabi,
E.A. Quadrelli, F. Bonino, K.P. Lillerud, Synthesis and stability of tagged UiO-66
Zr-MOFs, Chem. Mater. 22 (2010) 6632–6640.
[9] M. North, Oxidative Synthesis of alphaꢀamino nitriles from tertiary amines,
Angew. Chem. Int. Ed. 43 (2004) 4126–4128.
[10] C. Wiles, P. Watts, SolidꢀSupported Gallium Triflate: an efficient catalyst for
the three-component ketonic strecker reaction, ChemsusChem 5 (2012) 332–
338.
[11] S.I. Murahashi, N. Komiya, H. Terai, T. Nakae, Aerobic ruthenium-catalyzed
oxidative cyanation of tertiary amines with sodium cyanide, J. Am. Chem. Soc.
125 (2003) 15312–15313.
[41] J.E. Mondloch, M.J. Katz, N. Planas, D. Semrouni, L. Gagliardi, J.T. Hupp, O.K.
Farha, Are Zr6-based MOFs water stable? Linker hydrolysis vs. capillary-force-
driven channel collapse, Chem. Commun. 50 (2014) 8944–8946.
[42] P.G. Yot, K. Yang, F. Ragon, V. Dmitriev, T. Devic, P. Horcajada, C. Serre, G.
Maurin, Exploration of the mechanical behavior of metal organic frameworks
UiO-66(Zr) and MIL-125(Ti) and their NH2 functionalized versions, Dalton
Trans. 45 (2016) 4283–4288.
[12] K. Yamaguchi, Y. Wang, N. Mizuno, A widely applicable regioselective aerobic
a
-cyanation of tertiary amines heterogeneously catalyzed by manganese
oxides, ChemCatChem 5 (2013) 2835–2838.
[13] K. Tadele, S. Verma, M.N. Nadagouda, M.A. Gonzalez, R.S. Varma, A rapid flow
strategy for the oxidative cyanation of secondary and tertiary amines via C-H
activation, Scientific Reports volume 7 Article number: 16311 (2017).
[14] S. Singhal, S.L. Jain, B. Sain, An efficient aerobic oxidative cyanation of tertiary
amines with sodium cyanide using vanadium based systems as catalysts,
Chem. Commun. (2009) 2371–2372.
[15] D. Verma, S. Verma, A.K. Sinha, S.L. Jain, Iron nanoparticles supported on
Graphene Oxide: a robust, magnetically separable heterogeneous catalyst for
the oxidative cyanation of tertiary amines, Chempluschem 78 (2013) 860–865.
[16] S. Verma, R.B. Baig, M.N. Nadagouda, R.S. Varma, Oxidative C-H activation of
amines using protuberant lychee-like goethite, Sci. Rep. 8 (2018), Article
number 2024.
[17] D.P. Hari, B. Konig, Eosin Y catalyzed visible light oxidative C-C and C-P bond
formation, Org. Lett. 13 (2011) 3852–3855.
[18] Y. Pan, C.W. Kee, L. Chen, C.H. Tan, Dehydrogenative coupling reactions
catalysed by Rose Bengal using visible light irradiation, Green Chem. 13 (2011)
2682–2685.
[43] S.J. Garibay, S.M. Cohen, Isoreticular synthesis and modification of frameworks
with the UiO-66 topology, Chem. Commun. 46 (2010) 7700–7702.
[44] M. Kandiah, S. Usseglio, S. Svelle, U. Olsbye, K.P. Lillerud, M. Tilset, Post-
synthetic modification of the metal–organic framework compound UiO-66, J.
Matter. Chem. 20 (2010) 9848–9851.
[45] J. Liu, L. Chen, Hao Cui, J. Zhang, L. Zhang, C.Y. Su, Applications of metal–
organic frameworks in heterogeneous supramolecular catalysis, Chem. Soc.
Rev. 43 (2014) 6011–6061.
[46] H. Hintz, S. Wuttke, Solvent-free and time efficient postsynthetic modification
of amino-tagged metal-organic frameworks with carboxylic acid derivatives,
Chem. Mater. 26 (2014) 6722–6728.
[47] Qian Liang, Miao Zhang, Z. Zhang, C. Liu, S. Xu, Z. Li, Zinc phthalocyanine
coupled with UIO-66 (NH2) via a facile condensation process for enhanced
visible-light-driven photocatalysis, J. Alloy Compd. 690 (2017) 123–130.
[48] Z. Wang, K.K. Tanabe, S.M. Cohen, Accessing postsynthetic modification in a
series of metal organic frameworks and the influence of framework topology
on reactivity, Inorg. Chem. 48 (2008) 296–306.
[19] X.Z. Wang, Q.Y. Meng, J.J. Zhong, X.W. Gao, T. Lei, L.M. Zhao, Z.J. Li, B. Chen, C.H.
Tung, L.Z. Wu, Singlet excited state of BODIPY promoted aerobic cross
dehydrogenative coupling reactions under visible light, Chem. Commun. 51
(2015) 11256–11259.
[49] M.J. Katz, Z.J. Brown, Y.J. Colón, P.W. Siu, K.A. Scheidt, R.Q. Snurr, J.T. Hupp, O.K.
Farha,
A facile synthesis of UiO-66, UiO-67 and their derivatives, Chem.
Commun. 49 (2013) 9449–9451.
[50] G.E.S.M.J. Frisch, G.W. Trucks, H.B. Schlegel, B.M.M.A. Robb, J.R. Cheeseman, G.
Scalmani, V. Barone, H.P.H.G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, M.H.
A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, T.N.M. Ehara, K. Toyota, R.
Fukuda, J. Hasegawa, M. Ishida, J.Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A.
Montgomery, E.B.J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, J.N.K.N. Kudin,
V.N. Staroverov, T. Keith, R. Kobayashi, J.T.K. Raghavachari, A. Rendell, J.C.
Burant, S.S. Iyengar, J.B.C.M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, R.E.
S.V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, J.W.O.O. Yazyev, A.J. Austin, R.
Cammi, C. Pomelli, G.A.V.R.L. Martin, K. Morokuma, V.G. Zakrzewski, A.D.D.P.
Salvador, J.J. Dannenberg, S. Dapprich, J.C.O. Farkas, J.B. Foresman, J.V. Ortiz, J.
Cioslowski, D.J. Fox, Gaussian 09, Gaussian Inc, Wallingford CT, 2013.
[51] J. Gauss, Calculation of NMR chemical shifts at second-order many-body
perturbation theory using gauge-including atomic orbitals, Chem. Phys. Lett.
191 (1992) 614–620.
[52] M. Sandy, A. Butler, Microbial iron acquisition: marine and terrestrial
siderophores, Chem. Rev. 109 (2009) 4580–4595.
[53] C.J. Jameson, A.K. Jameson, S.M. Cohen, H. Parker, D. Oppusunggu, P.M. Burrell,
S. Wille, Temperature dependence of the 15N and 1H nuclear magnetic
shielding in NH3, J. Chem. Phys. 74 (1981) 1608–1612.
[54] S. Karan, Z. Jiang, A.G. Livingston, Sub–10 nm polyamide nanofilms with
ultrafast solvent transport for molecular separation, Science 348 (2015) 1347–
1351.
[55] J.J. Zhong, Q.Y. Meng, G.X. Wang, Q. Liu, B. Chen, K. Feng, L.Z. Wu, A highly
efficient and selective aerobic cross dehydrogenative coupling reaction
photocatalyzed by a Platinum(II) Terpyridyl complex, Chem. Eur. J. 19 (2013)
6443–6450.
[20] G. Kumar, S. Verma, A. Ansari, N.H. Khan, R.I. Kureshy, Enantioselective cross
dehydrogenative coupling reaction catalyzed by Rose Bengal incorporated-Cu
(I)-dimeric chiral complexes, Catal. Commun. 99 (2017) 94–99.
[21] D.P. Hari, B. Konig, Synthetic applications of eosin y in photoredox catalysis,
Chem. Commun. 50 (2014) 6688–6699.
[22] J. Wang, J. Ma, X. Li, Y. Li, G. Zhang, F. Zhang, X. Fan, Cu2O mesoporous spheres
with a high internal diffusion capacity and improved catalytic ability for the
aza-Henry reaction driven by visible light, Chem. Commun. 50 (2014) 14237–
14240.
[23] C. Vila, M. Rueping, Visible light mediated heterogeneous C-H
functionalization: oxidative multi-component reactions using
a recyclable
titanium dioxide (TiO2) catalyst, Green Chem. 15 (2013) 2056–2059.
[24] W. Yang, L. Wei, T. Yan, M. Cai, Highly efficient heterogeneous aerobic
oxidative C-C coupling from
Csp3-H bonds by a magnetic nanoparticles-
immobilized bipy-gold (III) Catalyst, Cat. Sci. and Tech. 7 (2017) 1744–1755.
[25] S. Verma, R.B. Baig, C. Han, M.N. Nadagouda, R.S. Varma, Magnetic graphitic
carbon nitride: its application in the C-H activation of amines, Chem. Commun.
51 (2015) 15554–15557.
[26] H. Liu, W. Feng, C.W. Kee, Y. Zhao, D. Leow, Y. Pan, C.H. Tan, Organic dye
photocatalyzed a-oxyamination through irradiation with visible light, Green
Chem. 12 (2010) 953–956.
[27] J.H. Park, K.C. Ko, E. Kim, N. Park, J.H. Ko, D.H. Ryu, T.K. Ahn, J.Y. Lee, S.U. Son,
Photocatalysis by Phenothiazine dyes: Visible-light-driven oxidative coupling
of primary amines at ambient temperature, Org. Lett. 14 (2012) 5502–5505.
[28] Z. Li, W. Zhang, Q. Zhao, H. Gu, Y. Li, G. Zhang, F. Zhang, X. Fan, Eosin Y
Covalently anchored on reduced Graphene Oxide as an efficient and recyclable
[56] C.J. Wu, J.J. Zhong, Q.Y. Meng, T. Lei, X.W. Gao, C.H. Tung, L.Z. Wu, Cobalt-
catalyzed cross dehydrogenative coupling reaction in water by visible light,
Org. Lett. 17 (2015) 884–887.
photocatalyst for the aerobic oxidation of
Sustain. Chem. Eng. 3 (2015) 468–474.
aꢀaryl halogen derivatives, ACS