Q. Wang et al. / Catalysis Communications 14 (2011) 92–95
93
of components was performed by using acetophenone as an internal
standard.
ν(C=N) 1608 (s), ν(C-N) 1339 (s), ν(Cu-N) 547 (s). m/z (%): 485
(20, M+-1), 275 (49, M+- L4), 212 (100, L4). UV (λ, nm): 270,
312, 585.
2.2. Synthesis and characterization of ligands and complexes
L5
Red oil (yield 89%). Anal. Calc. (%): C 59.71, H 6.83, N 18.99;
found: C 59.65, H 6.77, N 19.04. IR (cm−1): ν(C=N)1621 (s),
ν(C-N) 1347 (s). 1H NMR (d-DMSO, ppm): 2.23 (s, 6H, CH3);
2.74 (t, 2H); 3.56 (t, 2H); 7.80 (d, 1H); 8.09 (d, 1H); 8.22 (s,
1H). UV (λ, nm): 281, 324.
All ligands were synthesized by condensation reaction of N,N-
dimethylethylenediamine and the corresponding aldehydes [26,27].
Two equivalent ligand (typically, 1.76 g L1) reacted with CuBr2
(1.12 g) in 10 mL CH3CN under refluxing for 3 h to give the deposited
corresponding Cu complex, which was collected by filtration, washed
by ether, and then vacuum dried. They were characterized by 1H NMR,
IR, Elemental analyses, MS and UV, respectively, and were presented
in Fig. 1 where the ligands were described as typified by L1, and the
complexes as Cu(L1)2, respectively.
Cu(L5)2 Blue solid (yield 86%). Mp 127–128 °C. Anal. Calc. (%): C
39.68, H 4.54, N 12.62; found: C 39.81, H 4.53, N 12.57. IR
(cm−1): ν(C = N) 1614 (s), ν(C-N) 1342 (s), ν(Cu-N) 549(s).
m/z (%): 506 (20, M+-1), 285 (47, M+- L5), 222 (100, L5).
UV (λ, nm): 282, 320, 600.
L1
Brown oil (yield 90%). Anal. Calc. (%): C 74.96, H 9.15, N 15.89;
found: C 74.86, H 9.23, N 15.92. IR (cm−1): ν(C = N) 1628 (s),
ν(C-N) 1332 (s). 1H NMR (d-DMSO, ppm): 2.26 (s, 6H, CH3);
3.39 (t, 2H); 3.63 (t, 2H); 7.29 (d, 1H); 7.61(d, 1H); 8.27 (s,
1H). UV (λ, nm): 267, 321.
2.3. Oxidation experiments
Typically, benzyl alcohol (3 mmol), TEMPO (0.09 mmol), CuBr2
(0.06 mmol), L1 (0.12 mmol) and CH3CN/H2O (v/v=1/1, 6 mL) were
added into a 70-mL Teflon-lined stainless-steel reactor. After the air
was replaced with O2 for three times, the reactor was heated to 80 °C
under stirring, and then charged by 0.2 MPa O2. After reaction ended,
the reaction mixture was cooled to room temperature, and extracted
with ethyl acetate. The organic phase was measured by GC analysis.
Cu(L1)2 Blue solid (yield 87%). Mp 151–152 °C. Anal. Calc. (%): C 45.88,
H 5.60, N 9.73; found: C 45.92, H 5.71, N 9.66. IR (cm−1):
ν
(C=N) 1604 (s), ν(C-N) 1328 (s) , ν(Cu-N) 533 (s). m/z (%): 416
(20, M+-1), 239 (48, M+- L1), 176 (100, L1). UV (λ, nm): 265,
310, 571.
L2
Yellow oil (yield 86%). Anal. Calc. (%): C 69.87, H 8.80, N 13.58;
found: C 69.53, H 8.98, N 13.43. IR (cm−1): ν(C = N) 1638 (s),
ν(C-N) 1342 (s). 1H NMR (d-DMSO, ppm): 2.18 (s, 6H, CH3);
3.71 (s, 3H, CH3); 2.72 (t, 2H); 3.64 (t, 2H); 6.92 (d, 1H); 7.61
(d, 1H); 8.12 (s, 1H). UV (λ, nm): 270, 324.
3. Results and discussion
3.1. Comparison of the activities of catalysts
The oxidation of benzyl alcohol in CH3CN/H2O (v/v=1/1) was
chosen as a model reaction to test initially the catalytic potential of the
Cu(L)2 s (Table 1). As could be seen, all of pre-made Cu(L)2 s in
combination with TEMPO gave above 83% conversions in 2 h, and
benzaldehyde was the sole product (entries 1–5). In particular, Cu
(L1)2 realized a complete transformation. Since the Cu(L)2 s could be
easily prepared just by heating CuBr2 and Ls, CuBr2 and Ls were
directly employed in the oxidation, which realized approximate
conversions to those of the pre-made Cu(L)2 s under the same
conditions (entries 6–10). It was reasonably thought that Cu(L)2 s
could be in situ formed during the oxidations when CuBr2 and Ls were
used directly.
Cu(L2)2 Blue solid (yield 89%). Mp 160–161 °C. Anal. Calc. (%): C 45.33,
H 5.71, N 8.81; found: C 45.23, H 5.78, N 8.43. IR (cm−1):
ν
(C=N) 1624 (s), ν(C-N) 1334 (s), ν(Cu-N) 542 (s). m/z (%): 477
(22, M+-1), 269 (47, M+- L2), 206 (100, L2). UV (λ, nm): 269,
315, 582.
L3
Yellow oil (yield 88%). Anal. Calc. (%): C 75.74, H 9.53, N 14.72;
found: C 75.58, H 9.68, N 14.41. IR (cm−1): ν(C = N) 1634 (s),
ν(C-N) 1336 (s). 1H NMR (d-DMSO, ppm): 2.17 (s, 6H, CH3);
2.33 (s, 3H, CH3); 3.39 (t, 2H); 3.63 (t, 2H); 7.24 (d, 1H); 7.61
(d, 1H); 8.28 (s, 1H). UV (λ, nm): 268, 323.
Cu(L3)2 Blue solid (yield 84%). Mp 159–160 °C. Anal. Calc.: C 47.73; H
6.01; N 9.28; found: C 47.52, H 6.23, N 9.41. IR (cm−1):ν(C=N)
1623 (s), ν(C-N) 1328 (s), ν(Cu-N) 538 (s). m/z (%): 444 (20,
M+-1), 253 (50, M+- L3), 190 (100, L3). UV (λ, nm): 267, 314,
580.
Table 1
a
Oxidation of benzyl alcohol using different Cu catalysts
.
L4
Yellowish oil (yield 84%). Anal. Calc. (%): C 62.70, H 7.18, N
13.30; found: C 62.82, H 7.03, N 13.55. IR (cm−1): ν(C=N)
1619 (s), ν(C-N) 1347(s). 1H NMR (d-DMSO, ppm): 2.18(s, 6H,
CH3); 2.72 (t, 2H); 3.53 (t, 2H); 7.30 (d, 1H); 7.56 (d, 1H); 8.15
(s, 1H). UV (λ, nm): 272, 326.
Entry
Catalyst
Conv. (%)
1
2
3
4
5
6
7
8
Cu(L1)2
100
86
99
93
83
100
95
99
94
85
Cu(L2)2
Cu(L3)2
Cu(L4)2
Cu(L5)2
Cu(L4)2 Blue solid (yield 86%). Mp 135–136 °C. Anal. Calc. (%): C 40.98,
CuBr2 +L1
CuBr2 +L2
CuBr2 +L3
CuBr2 +L4
CuBr2 +L5
CuBr2
H 4.69, N 8.69; found: C 40.82, H 4.53, N 8.85. IR (cm−1):
9
R
10
11
12
13b
14b
15c
16d
b1
2
4
L1
CuBr2 +L1
Cu(L1)2
L1: R = H
b1
98
N
N
N
N
L2: R = CH3O
CuBr2 +L1
CuBr2 +L1
Cu
35, 100e
_
L3: R = CH3
L4: R = C1
L5: R = NO2
2Br
a
Reaction conditions: 3 mmol benzyl alcohol, 3 mol% TEMPO, 2 mol% Cu(L)2 or the
combination of 2 mol% CuBr2 and 4 mol%L, 3 mL CH3CN, 3 mL H2O, 80 °C, 0.2 MPa O2,
2 h.
b
TEMPO-free.
with 2 mmol K2CO3.
Air instead of O2.
for 12 h.
c
R
d
e
Fig. 1. Schematic structures of Cu(L)2 complexes.