2
38
H.T. Dang et al. / Journal of Molecular Catalysis A: Chemical 420 (2016) 237–245
works [34,39–45]. Indeed, numerous carbon-carbon [37,46–55]
and carbon-heteroatom forming transformations [56–63] have
been performed using MOF-based catalysts. Iron-based metal-
organic frameworks were previously synthesized and employed
as heterogeneous catalysts for organic transformations [64–68].
In this paper, we would like to present the direct alkenylation of
Dichloromethane (3 × 10 ml) was used for solvent exchange at
◦
room temperature. The Fe-MOF was then heated at 150 C for 6 h
under vacuum, yielding 0.428 g of the Fe O(BPDC) as orange crys-
3
3
ꢀ
tals (71% based on biphenyl-4,4 -dicarboxylic acid).
2.3. Catalytic studies
2
-substituted azaarenes with carbonyls via C H bond activation
to produce 2-alkenylazaarenes using the iron-based metal-organic
framework Fe O(BPDC) as a recyclable heterogeneous catalyst.
To the best of our knowledge, 2-alkenylazaarenes was not previ-
ously synthesized via the direct alkenylation transformation using
heterogeneous catalysts.
In a typical experiment, Fe O(BPDC) catalyst (0.012 g, 10 mol%)
3
3
3
3
was added to the 10 ml vial containing
a solution of 2-
methylquinoline (0.057 g, 0.4 mmol), acetic acid (0.002 g, 10 mol%),
benzaldehyde (0.064 g, 0.6 mmol) and diphenyl ether (0.068 g,
.4 mmol) as an internal standard in toluene (1 ml). The catalyst
0
amount was calculated with respect to the iron/2-methylquinoline
molar ratio and the measured AAS value of Fe3O(BPDC)3 (See Sup-
porting Information). Then reaction mixture was filled with argon
2
. Experimental
◦
2.1. Materials and instrumentation
and magnetically stirred for 24 h at 120 C. Reaction yield was
monitored by withdrawing aliquots from the reaction mixture,
quenching with Na2CO3 solution (1 ml). The organic components
were then extracted into ethyl acetate (3 ml), dried over anhy-
drous Na2SO4, and analyzed by GC with reference to diphenyl ether.
The combined organic layers were concentrated under reduced
pressure. The resulting residue was purified by recrystalization
in ethanol and water to afford (E)-2-styrylquinoline. The product
identity was further confirmed by GC–MS, 1H NMR, and C NMR.
To investigate the recyclability of the Fe3O(BPDC)3, the catalyst
was separated from the reaction mixture by simple centrifugation,
washed with copious amounts of toluene, dichloromethane, then
All organic and inorganic chemicals were purchased from
Sigma–Aldrich, Acros/Fisher Scientific, and Merck, and were used
as received. X-ray powder diffraction (XRD) analysis were per-
formed using a D8 Advance Bruker powder diffractometer with a
Cu K␣ radiation source. Surface areas and pore size distribution
of the Fe O(BPDC) catalyst were achieved via nitrogen physisorp-
3
3
13
tion measurements on a Micromeritics 2020 volumetric adsorption
analyzer system. Fe-MOF samples were heated under vacuum at
◦
1
50 C for 5 h prior to the measurement. Thermogravimetric anal-
ysis (TGA) was carried out on a Netzsch Thermoanalyzer STA
◦
◦
4
09 with a heating rate of 10 C/min under a nitrogen atmo-
activated under vacuum at 150 C for 3 h, and reused under identical
sphere. Elemental analysis of the Fe-MOF was conducted on an
AA-6800 Shimadzu using atomic absorption spectrophotometry
conditions.
(
(
AAS) method. A Hitachi S-4800 Scanning Electron Microscope
SEM) was used to achieve SEM images. A JEOL JEM 1400 Trans-
3. Results and discussion
mission Electron Microscope (TEM) was employed to obtain TEM
image. A Nicolet 6700 was used for Fourier transform infrared (FT-
IR) analysis, with samples being dispersed on potassium bromide
pallets.
The iron-based metal-organicframework Fe O(BPDC) was syn-
3
3
thesized according to a slightly modified literature procedure [69],
and was characterized by several techniques, including XRD, SEM,
TEM, TGA, FT-IR, AAS, and nitrogen physisorption measurements
Reaction yield was monitored by gas chromatographic (GC)
(
Figs. S1–S5) (Fig. 1).
analysis on an FID Shimadzu GC 2010-Plus with
a SPB-5
The Fe O(BPDC)3 was assessed for its catalytic activity in the
3
column (length = 30 m, inner diameter = 0.25 mm, and film thick-
ness = 0.25 m). In the GC temperature program, the sample of the
direct alkenylation of 2-methylquinoline with benzaldehyde via
H bond activation to form (E)-2-styrylquinoline as the principal
product (Scheme 1). Initial studies addressed the effect of temper-
ature on the yield of (E)-2-styrylquinoline. The direct alkenylation
reaction was carried out in toluene under argon for 24 h, in the
C
◦
◦
◦
reaction was held at 120 C for 0.5 min; heated from 120 to 130 C
◦
◦
at 40 C/min; held at 130 C for 1 min; heated from 130 to 280 C
◦
◦
at 40 C/min; and finally held at 280 C for 4.5 min. Reaction yield
was calculated based on a series of (E)-2-styrylquinoline standard
solutions, using diphenyl ether as an internal standard. A Shimadzu
GCMS-QP2010Ultra with a ZB-5MS column (length = 30 m, inner
diameter = 0.25 mm, and film thickness = 0.25 m) was used for
GC–MS analysis. In the GC–MS temperature program, the sample
presence of 10 mol% Fe O(BPDC)3 catalyst, with 10 mol% acetic
3
acid as co-catalyst, at 2-methylquinoline concentration of 0.4 M,
using 2-methylquinoline:benzaldehyde molar ratio of 1:1.5, at
◦
◦
◦
◦
◦
room temperature, 60 C, 90 C, 100 C, 110 C, and 120 C, respec-
tively. It was found that no reaction occurred at temperature lower
◦
◦
was held samples at 50 C for 2 min; heated from 50 to 280 C at
◦
than 60 C, with no trace amount of (E)-2-styrylquinoline being
◦
◦
1
0 C/min and held at 280 C for 10 min. A Bruker AV-500 spec-
detected after 24 h. The transformation occurred with difficulty at
1
13
trometer was employed for H NMR and C NMR analysis
◦
9
0 C, affording only 16% yield. As expected, increasing the reaction
temperature led to a significant enhancement in the yield of (E)-2-
◦
2
.2. Synthesis of the metal-organic framework Fe O(BPDC)
styrylquinoline. The reaction carried out at 100 C could proceed to
2
3
3
◦
6% yield while 41% yield was observed for the case of 110 C. It was
The Fe O(BPDC) was synthesized from the reaction of
found that the yield of (E)-2-styrylquinoline could be improved to
3
3
ꢀ
◦
biphenyl-4,4 -dicarboxylic acid and iron(III) chloride hexahydrate
by a solvothermal method in the presence of acetic acid. In a typi-
cal synthesis, a mixture of FeCl ·6H O (1.08 g, 4.0 mmol), H BPDC
58% for the reaction carried out at 120 C (Fig. 2). Indeed, in the first
3
example of the C(sp )-H functionalization of methyl azaarenes with
carbonyl compounds to form 2-alkenylazaarenes using iron acetate
and trifluoroacetic acid as catalyst system, Zou and co-workers also
3
2
2
ꢀ
(
H BPDC = biphenyl-4,4 -dicarboxylic acid; 0.48 g, 2.0 mmol) was
dissolved in DMF (DMF = N,N -dimethylformamide; 114 ml) con-
2
ꢀ
◦
performed the transformation at 120 C [15].
taing acetic acid (CH COOH; 2.4 ml, 42 mmol). The solution was
Another factor that should be addressed for the Fe O(BPDC) -
3
3
3
then distributed in twenty four 20-ml vials. The vials were tightly
capped and heated at 120 C in an isothermal oven for 48 h. After
unassisted cooling the vials to room temperature, the crystals
were separated by decantation, and washed with DMF (3 × 10 ml).
catalyzed direct alkenylation of 2-methylquinoline with benzalde-
hyde via C H bond activation to form (E)-2-styrylquinoline is the
catalyst concentration. The direct alkenylation reaction was carried
◦
◦
out at 120 C in toluene under argon for 24 h, at 2-methylquinoline