An efficient approach to the ammoxidation of alcohols to nitriles and the aerobic oxidation of alcohols to aldehydes in water using Cu(ii)/pypzacac complexes as catalysts

Article abstract of DOI:10.1039/c4ra11743c

Reactions of 2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl)acetic acid (pypzacacH) ligand with Cu(OAc)₂, Cu(NO₃)₂, CuSO₄, Cu(ClO₄)₂ or CuCl₂ produced four dinuclear Cu(ii) complexes [{(MeOH)Cu(OAc)}(μ-κ²:κ¹-pypzacac)]₂·0.5H₂O (1·0.5H₂O), [{Cu(pypzacac)}(μ-κ²:κ¹-pypzacac)₂{Cu(H₂O)₂}](NO₃)·2(MeOH)_0.5·6H₂O (2·2(MeOH)_0.5·6H₂O), [{(MeOH)Cu(mpypzacac)}(μ-SO₄)]₂·2MeOH (3·2MeOH; mpypzacac = methyl 2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl)acetate), [{Cu(mpypzacac)₂}(μ-κ²:κ¹-pypzacac){Cu(mpypzacac)}](ClO₄)₃·MeOH (4·MeOH) and one polymeric Cu(ii) complex [(CuCl)(μ-κ³:κ¹-pypzacac)]_n (5), respectively. The mpypzacac ligand in 3 and 4 was in situ generated via the Cu²⁺-catalyzed dehydrative esterification of acetic acid of the pypzacacH ligand. Complexes 1-5 are characterized by elemental analysis, IR and single-crystal X-ray diffraction. Complex 1 contains two {(MeOH)Cu(OAc)} fragments that are interconnected by two μ-κ²:κ¹-pypzacac^- ligands, forming a dimeric structure. In 2, {Cu(pypzacac)} and {Cu(H₂O)₂} units are bridged by a pair of μ-κ²:κ¹-pypzacac^- ligands. In 3, two {Cu(mpypzacac)} fragments are linked by two μ-κ¹:κ¹-SO₄^2- ions to form a dinuclear structure. Complex 4 also adopts a dimeric structure in which {Cu(mpypzacac)₂} and {Cu(mpypzacac)} units are interconnected by one μ-κ³:κ¹-pypzacac^- ligand. Complex 5 contains a 1D chain in which (CuCl) fragments are interlinked by μ-κ³:κ¹-pypzacac^- ligands. Complexes 1-5 exhibited excellent catalytic performance in the ammoxidation of alcohol to nitrile and the aerobic oxidation of alcohol to aldehyde in water. The catalytic aqueous solution was easily separated and could be reused for several cycles without any obvious decay of catalytic efficiency.

Full text of DOI:10.1039/c4ra11743c

RSC Advances
View Article Online
View Journal | View Issue
PAPER
An efficient approach to the ammoxidation of
alcohols to nitriles and the aerobic oxidation of
alcohols to aldehydes in water using Cu(II)/
pypzacac complexes as catalysts†
Cite this: RSC Adv., 2014, 4, 54007
a
a
a
Jing-Bo Xie, Jia-Jing Bao, Hong-Xi Li, Da-Wei Tan,a Hai-Yan Lia
*
ab
*
and Jian-Ping Lang
Reactions of 2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl)acetic acid (pypzacacH) ligand with Cu(OAc)2, Cu(NO3)2,
CuSO4, Cu(ClO4)2 or CuCl2 produced four dinuclear Cu(II) complexes [{(MeOH)Cu(OAc)}(m-k2:k1-
pypzacac)]2$0.5H2O (1$0.5H2O), [{Cu(pypzacac)}(m-k2:k1-pypzacac)2{Cu(H2O)2}](NO3)$2(MeOH)0.5$6H2O
(2$2(MeOH)0.5$6H2O), [{(MeOH)Cu(mpypzacac)}(m-SO4)]2$2MeOH (3$2MeOH; mpypzacac ¼ methyl 2-
(3-(pyridin-2-yl)-1H-pyrazol-1-yl)acetate), [{Cu(mpypzacac)2}(m-k2:k1-pypzacac){Cu(mpypzacac)}](ClO4)3$
MeOH (4$MeOH) and one polymeric Cu(II) complex [(CuCl)(m-k3:k1-pypzacac)]n (5), respectively. The
mpypzacac ligand in 3 and 4 was in situ generated via the Cu2+-catalyzed dehydrative esterification of
acetic acid of the pypzacacH ligand. Complexes 1–5 are characterized by elemental analysis, IR and
single-crystal X-ray diffraction. Complex
1 contains two {(MeOH)Cu(OAc)} fragments that are
interconnected by two m-k2:k1-pypzacacꢀ ligands, forming a dimeric structure. In 2, {Cu(pypzacac)} and
{Cu(H2O)2} units are bridged by a pair of m-k2:k1-pypzacacꢀ ligands. In 3, two {Cu(mpypzacac)}
fragments are linked by two m-k1:k1-SO4 ions to form a dinuclear structure. Complex 4 also adopts a
2ꢀ
dimeric structure in which {Cu(mpypzacac)2} and {Cu(mpypzacac)} units are interconnected by one
m-k3:k1-pypzacacꢀ ligand. Complex 5 contains a 1D chain in which (CuCl) fragments are interlinked by
m-k3:k1-pypzacacꢀ ligands. Complexes 1–5 exhibited excellent catalytic performance in the
ammoxidation of alcohol to nitrile and the aerobic oxidation of alcohol to aldehyde in water. The
catalytic aqueous solution was easily separated and could be reused for several cycles without any
obvious decay of catalytic efficiency.
Received 2nd September 2014
Accepted 10th October 2014
DOI: 10.1039/c4ra11743c
www.rsc.org/advances
transformation of organic molecule to CNꢀ via the C–H func-
tionalization of arenes,8 and oxidative dehydrogenation of
benzylic alcohols and ammonia,9 azides10 or methyl arenes.11
Introduction
Nitriles are important building blocks of dyes, natural products,
herbicides, agrochemicals, pharmaceuticals, and various ne
chemicals.1 These derivatives can be used to construct esters,
amides, carboxylic acids, amines,2 and nitrogen-containing
heterocycles, etc.3 The approaches to nitriles include Sand-
meyer's reaction,4 transition metal-catalyzed cyanation of aryl
halides with metal cyanides via a nucleophilic pathway,5
oxidation of amines,6 dehydration of amides and aldoximes,7
These methods require the use of toxic inorganic cyanide salts,
high temperature, pressure, and stoichiometric or excess
amounts of highly reactive oxidants or expensive transition
metal catalysts. Hence, the development of concise, efficient
and safe approaches for nitrile synthesis is of general interest.
Very recently, the ammoxidation reaction of alcohols using
inexpensive copper complexes as catalysts and O2 as the oxidant
under ambient conditions has provided an economical and
efficient method.12 Huang et al. reported the synthesis of nitriles
through the dehydrogenation cascade mediated by CuI/2,20-
bipy/TEMPO (TEMPO ¼ 2,2,6,6-tetramethyl-1-piperidinyloxy)
systems in EtOH or MeCN.12a Tao and co-workers prepared
nitriles through the reactions of alcohols or aldehydes with
aqueous ammonia catalyzed by Cu(NO3)2/TEMPO system in
DMSO.12b Cook and Muldoon et al. reported that the Cu(OTf)2/
2,20-bipy in combination with TEMPO could also catalyze
synthesis of nitriles from aldehydes or alcohols with aqueous
aCollege of Chemistry, Chemical Engineering and Materials Science, Soochow
University, Suzhou 215123, People's Republic of China. E-mail: jplang@suda.edu.
cn; lihx@suda.edu.cn; Fax: +86 512 65880328; Tel: +86 512 65882865
bState Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, Shanghai 200032, People's Republic of China
† Electronic supplementary information (ESI) available: The 1H NMR spectra of
nitrile and aldehyde products. CCDC 1021990 (1$0.5H2O), 1021991
(2$2(MeOH)0.5$6H2O), 1021992 (3$2MeOH), 1021994 (4$MeOH), 1021994 (5).
CCDC 1021990–1021994. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c4ra11743c
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 54007–54017 | 54007

View Article Online
RSC Advances
Paper
ammonia in aqueous MeCN.12c Although the aforementioned 43.54; H, 4.53; N, 12.12. IR (KBr disk, cmꢀ1): 2924 (m), 2853 (m),
copper catalytic systems exhibited high activity, these reactions 1598 (s), 1568 (s), 1409 (s), 1338 (m), 1261 (w), 1099 (w), 1022 (w),
were carried out in organic solvents or aqueous organic solvent 678 (m), 647 (w), 618 (w), 536 (w), 521 (w), 506 (w), 490 (w), 477
mixtures. Thus it would be a green and economic approach if (w), 462 (w), 433 (w), 419 (w).
the aerobic dehydrogenation cascade reaction could be con-
Synthesis of [{Cu(pypzacac)}(m-k2:k1-pypzacac)2{Cu(H2-
ducted in pure water. The well-dened water-soluble catalysts O)2}](NO3)$2(MeOH)0.5$6H2O (2$2(MeOH)0.5$6H2O). Blue crys-
might be an effective tool to promote organic transformations tals of 2$2(MeOH)0.5$6H2O were isolated by a similar manner to
in aqueous media. It is noted that water-soluble organic ligands that used for the isolation of 1$0.5H2O, using pypzacacH (30
could increase the hydrophilicity of the resulting catalysts.13–16 mg, 0.15 mmol) and Cu(NO3)2$2.5H2O (25 mg, 0.1 mmol) as
More importantly, the water-soluble catalyst can be easily starting materials. Yield: 27 mg (65% based on Cu). Anal. calcd
separated from the organic products and may be recycled for for C30H28Cu2N10O11: C, 43.32; H, 3.39; N, 16.84; found C, 43.57;
the repeat use. Recently, we have been interested in the H, 3.55; N, 16.59. IR (KBr disk, cmꢀ1): 2988 (w), 1633 (s), 1488
syntheses of water-soluble transition metal coordination (w), 1440 (w), 1384 (s), 1308 (w), 1174 (m), 1100 (w), 1002 (w),
complexes and their reusable catalytic properties in water.17 In 787 (s).
this manuscript, we deliberately selected a water-soluble
Synthesis of [{(MeOH)Cu(mpypzacac)}(m-SO4)]2$2MeOH
organic ligand, 2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl)acetic acid (3$2MeOH). Blue crystals of 3$2MeOH were obtained by a
(pypzacacH), to react with Cu(OAc)2, Cu(NO3)2, CuSO4, similar manner to that used for the isolation of 1$0.5H2O, using
Cu(ClO4)2 or CuCl2. Four dinuclear Cu(II) complexes [{(MeOH)- pypzacacH (20 mg, 0.1 mmol) and CuSO4$5H2O (25 mg, 0.1
Cu(OAc)}(m-pypzacac)]2$0.5H2O (1$0.5H2O), [{Cu(pypzacac)}- mmol) as starting materials. Yield: 30 mg, (74% based on Cu).
(m-k2:k1-pypzacac)2{Cu(H2O)2}](NO3)$2(MeOH)0.5$6H2O
(2$2- Anal. calcd for C24H30Cu2N6O14S2: C, 35.25; H, 3.70; N, 10.28;
(MeOH)0.5$6H2O), [{(MeOH)Cu(mpypzacac)}(m-SO4)]2$2MeOH found C, 34.81; H, 3.43; N, 9.88. IR (KBr disk, cmꢀ1): 1731 (s),
(3$2MeOH; mpypzacac ¼ methyl 2-(3-(pyridin-2-yl)-1H-pyrazol- 1616 (s), 1509 (m), 1445 (m), 1426 (w), 1384 (w), 1343 (m), 1305
1-yl)acetate), [{Cu(mpypzacac)2}(m-k2:k1-pypzacac){Cu(mpypzacac)}]- (w), 1285 (m), 1254 (m), 1173 (s), 1097 (s), 1043 (s), 1003 (m), 959
(ClO4)3$MeOH (4$MeOH) and one polymeric complex [(CuCl)- (w), 782 (m), 621 (m).
(m-k3:k1-pypzacac)]n (5) were isolated therefrom. The mpypzacac
Synthesis
of
[{Cu(mpypzacac)2}(m-k2:k1-pypzacac)
ligand in 3 and 4 was in situ formed via the Cu2+-catalyzed {Cu(mpypzacac)}](ClO4)3$MeOH (4$MeOH). Blue crystals of
esterication of acetic acid of the pypzacacH ligand. Complexes 4$MeOH were isolated by a similar manner to that used for the
1–5 are soluble in water and work as efficient catalysts for the isolation of 1$0.5H2O, using pypzacacH (40 mg, 0.2 mmol) and
ammoxidation of alcohol to nitrile and the aerobic oxidation of Cu(ClO4)2$6H2O (37 mg, 0.1 mmol) as starting materials. Yield:
alcohol to aldehyde in H2O. The catalytic system modeled by 1 45 mg (70% based on Cu). Anal. calcd for C43H41Cl3Cu2N12O20:
could be also recycled for several times. Their syntheses, crystal C, 40.37; H, 3.23; N, 13.14; found C, 40.03; H, 2.89; N, 12.88. IR
structures and catalytic properties are described below.
(KBr disk, cmꢀ1): 1621 (s), 1508 (w), 1488 (w), 1442 (m), 1396 (w),
1384 (m), 1257 (w), 1121 (s), 1108 (s), 783 (m), 705 (s), 625 (m).
Synthesis of [(CuCl)(m-k3:k1-pypzacac)]n (5). Green crystals of
5 were obtained by a similar manner to that used for the
isolation of 1$0.5H2O, using pypzacacH (20 mg, 0.1 mmol) and
Experimental section
General
All reagents were used as purchased from commercial sources CuCl (17 mg, 0.1 mmol) as starting materials. Yield: 20 mg (68%
without further purication. The ligand pypzacacH was prepared based on Cu). Anal. calcd for C10H8ClCuN3O2: C, 39.88; H, 2.68;
according to the published procedure.18 Elemental analyses for C, N, 13.95; found C, 39.59; H, 2.75; N, 13.67. IR (KBr disk, cmꢀ1):
H and N were performed on a Carlo-Erba CHNO-S microanalyzer. 3089 (w), 2988 (w), 1625 (s), 1578 (w), 1488 (w), 1450 (w), 1384
The IR spectra (KBr disc) were recorded on a Nicolet MagNa-IR550 (m), 1311 (w), 1254 (w), 1173 (m), 1002 (w), 787 (m), 619 (w).
FT-IR spectrometer (4000–400 cmꢀ1). The 1H NMR spectra in
CDCl3 were recorded at ambient temperature on a Varian
UNITYplus-400 spectrometer and the chemical shis d were
reported as parts per million (ppm) relative to, respectively, the
Typical procedure for the ammoxidation of alcohol to nitrile
and the aerobic oxidation of alcohol to aldehyde in water
TMS as the internal standard. Resonance patterns were reported A test tube equipped with a magnetic stirring bar was charged
with the notations of s (singlet), d (doublet) and m (multiplet). In with 1 (62 mg, 0.0876 mmol), TEMPO (33 mg, 0.21 mmol), TEAI
addition, coupling constants J were reported in Hertz (Hz).
(72 mg, 0.28 mmol), and K2CO3 (48 mg, 0.35 mmol). The reac-
Synthesis of [{(MeOH)Cu(OAc)}(m-k2:k1-pypzacac)]2$0.5H2O tion vessel was vacuumed and backlled with oxygen for three
(1$0.5H2O). To the MeOH (3 mL) solution of Cu(OAc)2$H2O (20 times. Benzyl alcohol (0.378 g, 3.5 mmol), H2O (3 mL), NH3 (aq,
mg, 0.1 mmol) was added the solution of pypzacacH (20 mg, 0.1 25–28% w/w, 550 mL) (for the synthesis of aldehyde, aqueous
mmol) in MeOH (3 mL). The mixture was stirred at room ammonia was not added) were added subsequently. The
temperature for 30 min and then ltered. Et2O (30 mL) was resulting deep blue solution was stirred under an oxygen
layered onto the ltrate to produce blue crystals of 1$0.5H2O in balloon at 60 ꢁC for one day. Then it was cooled to room
several days, which were collected by ltration, washed with temperature, and extracted three times with Et2O (3 ꢂ 5 mL).
Et2O and dried in air. Yield: 28 mg (79% based on Cu). Anal. The combined organic layer was washed with brine (20 mL) and
calcd for C26H30Cu2N6O10: C, 43.76; H, 4.24; N, 11.78; found C, dried over anhydrous Na2SO4 and concentrated under reduced
54008 | RSC Adv., 2014, 4, 54007–54017
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
pressure. The crude product was puried by ash column uncoordinated H2O molecule was rened to one-fourth-
chromatography using petroleum ether and ethyl acetate as the occupancy to give an acceptable thermal parameter. For
eluent. All nitrile and aldehyde products synthesized in this 2$2(MeOH)0.5$6H2O, three O atoms of three lattice H2O mole-
work are known and conrmed by comparing their 1H NMR cules were rened to be disordered over two positions with an
spectra with those found in the literatures.
occupancy factor of 0.50/0.50 for O(15)/O(15A), O(18)/O(18A)
and O(19)/O(19A). For 3$2MeOH, one C atom of the coordi-
nated MeOH molecule and one O and one C atom from the
uncoordinated MeOH molecule were rened to be disordered
over two positions with an occupancy factor of 0.50/0.50 for
C(12)/C(12A), O(8)/O(8A) and C(13)/C(13A). For 4$MeOH, one C
atom of one pypzacac ligand and one C atom of the uncoordi-
nated MeOH molecule were rened to be disordered over two
positions with an occupancy factor of 0.50/0.50 for C(11)/C(11A)
X-ray crystallography
Single crystals of 1$0.5H2O, 2$2(MeOH)0.5$6H2O, 3$2MeOH,
4$MeOH, and 5 suitable for X-ray analysis were obtained
directly from the above preparations. Each single crystal was
mounted on a glass ber with grease and cooled in a liquid
nitrogen stream at 153 K (1$0.5H2O, 2$2(MeOH)0.5$6H2O and 5)
or 223 K (3$2MeOH, 4$MeOH). Crystallographic measurements
ꢀ
and C(44)/C(44A). One O atom of ClO4 was rened to be
disordered over two positions with an occupancy factor of 0.25/
0.25 for O(18)/O(18A). Except for one O atom of H2O molecule in
1$0.5H2O, three disordered O atoms of H2O molecules in
2$2(MeOH)0.5$6H2O, one C atom of the coordinated MeOH
molecule and one O atom and one C atom from the uncoordi-
nated MeOH molecule in 3$2MeOH, one Cl atom from one
ClO4ꢀ, six O atoms from two ClO4ꢀ, one C atom from the pyp-
zacac ligand, and one C atom from MeOH molecule in 4$MeOH,
all other non-hydrogen atoms were rened anisotropically. The
hydrogen atoms of O(6) from the H2O molecule in 1$0.5H2O,
the hydrogen atoms of O(17), C(32), O(16), C(31), O(15), O(18)
and O(19) from the uncoordinated MeOH and H2O molecules in
2$2(MeOH)0.5$6H2O, O(25) and C(44) atoms from MeOH
molecule in 4$MeOH were not located. The hydrogen of O(5)
atom from the coordinated MeOH molecule in 1$0.5H2O, the
hydrogen atoms of O(7), O(8), O(12), O(13) and O(14) atoms from
were made on
2$2(MeOH)0.5$6H2O and 5), or an Xcalibur Atlas Gemini
(3$2MeOH, 4$MeOH) diffractometer by using a graphite-
a
Bruker APEX-II CCD (1$0.5H2O,
˚
monochromated Mo-Ka (l ¼ 0.71070 A) radiation. Diffraction
data were collected at a u mode with a detector distance of 35
mm to the crystal. The collected data were reduced by using the
program Bruker APEX2 or CrysAlisPro, Agilent Technologies (Cry-
sAlis171.NET, Version 1.171.36.28) and an absorption correc-
tion (multi-scan) was applied. The reection data were also
corrected for Lorentz and polarization effects.
The crystal structures of 1$0.5H2O, 2$2(MeOH)0.5$6H2O,
3$2MeOH, 4$MeOH and 5 were solved by direct methods and
rened on F2 by full-matrix least-squares techniques with
SHELXTL-97 program.19 For 1$0.5H2O, one O atom of OAcꢀ was
rened to be disordered over two positions with an occupancy
factor of 0.80/0.20 for O(4)/O(4A). The O(6) atom of
Table 1 Crystal data and structure refinement parameters for 1$0.5H2O, 2$2(MeOH)0.5$6H2O, 3$2MeOH, 4$MeOH, and 5
1$0.5H2O
26H31Cu2N6O10.5
2$2(MeOH)0.5$6H2O
3$2MeOH
4$MeOH
5
Emperical formula
Formula mass
C
C31H44Cu2N10O18
971.84
C26H38Cu2N6O16S2
881.82
C44H45Cl3Cu2N12O21
1311.35
C10H8ClCuN3O2
301.18
722.65
Crystal system
Orthorhombic
Pbcn
0.40 ꢂ 0.12 ꢂ 0.08
12.5992(6)
7.8436(4)
Triclinic
P1
Triclinic
P1
Triclinic
P1
Monoclinic
P21/c
ꢀ
ꢀ
ꢀ
Space group
Crystal dimension (mm3)
0.50 ꢂ 0.08 ꢂ 0.04
10.9883(4)
12.4084(5)
16.1803(6)
75.070(2)
85.468(2)
72.003(2)
2027.37(13)
2
0.30 ꢂ 0.20 ꢂ 0.15
9.9313(5)
10.6591(8)
10.9968(6)
112.268(6)
114.296(6)
96.811(5)
928.42(10)
1
0.50 ꢂ 0.40 ꢂ 0.30
13.2169(3)
14.6198(5)
15.9990(3)
75.840(3)
79.165(2)
78.964(2)
2766.38(15)
2
0.35 ꢂ 0.18 ꢂ 0.10
˚
a (A)
9.1736(5)
˚
b (A)
6.8909(4)
16.9201(9)
˚
c (A)
30.4801(13)
a (ꢁ)
b (ꢁ)
g (ꢁ)
103.292(2)
3
˚
V (A )
3012.1(2)
4
1.594
1484
1040.94(10)
4
1.922
604
Z
Dcalc (g cmꢀ3
F(000)
)
1.592
1004
1.137
1.577
454
1.334
1.574
1340
3.044
m (mmꢀ1
)
1.479
2.345
Total no. of rens
No. of unique rens
No. of obsd rens
No. of variables
37 222
24 423
8269
24 860
16 640
2761 (Rint ¼ 0.0371)
2220 (I > 2.00s(I))
215
7548 (Rint ¼ 0.1058)
5247 (I > 2.00s(I))
572
3449 (Rint ¼ 0.0318)
2917 (I > 2.00s(I))
240
9869 (Rint ¼ 0.0332)
8585 (I > 2.00s(I))
757
2361 (Rint ¼ 0.0416)
2079 (I > 2.00s(I))
154
Transmission factor
0.5892–0.8909
0.0330
0.0772
0.6002–0.9559
0.0707
0.1589
0.6904–0.8250
0.0373
0.0867
0.3134–0.4642
0.0723
0.2191
0.4941/0.7993
0.0245
0.0584
a
R1
wR2
b
GOFc
1.088
1.129
1.038
1.048
1.073
a
2
c
2
R1 ¼ S||F0| ꢀ |Fc||/S|F0|. b wR2 ¼ {Sw(F0 ꢀ Fc2)2/Sw(F02)2}1/2
.
GOF ¼ {Sw((Fo ꢀ Fc2)2)/(n ꢀ p)}1/2, where n ¼ number of reections and p ¼ total
numbers of parameters rened.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 54007–54017 | 54009

View Article Online
RSC Advances
Paper
Table 2 Selected bond lengths (A˚) and angles (ꢁ) for 1$0.5H2O, Table 3 Selected bond lengths (A˚) and angles (ꢁ) for 4$MeOH and 5a
2$2(MeOH)0.5$6H2O and 3$2MeOHa
Compound 4$MeOH
Compound 1$0.5H2O
Cu(1)–O(2A)
Cu(1)–N(3)
Cu(1)–O(5)
1.9515(19) Cu(1)–N(3)
1.971(3)
2.003(4)
2.178(4)
1.993(3)
Cu(1)–N(6)
Cu(1)–N(1)
Cu(2)–N(10)
Cu(2)–N(9)
1.999(4)
2.089(4)
1.929(3)
1.994(4)
1.9507(18)
2.021(2)
2.405(2)
91.80(8)
93.43(9)
158.14(9)
94.30(7)
86.08(8)
Cu(1)–O(3)
Cu(1)–N(2)
Cu(1)/O(4)
O(2A)Cu(1)–N(3)
O(2A)–Cu(1)–N(2)
N(3)–Cu(1)–N(2)
O(3)–Cu(1)–O(5)
N(2)–Cu(1)–O(5)
2.025(2)
2.642
Cu(1)–N(4)
Cu(2)–O(6)
Cu(2)–N(12)
Cu(1)–O(5)
O(2A)–Cu(1)–O(3)
O(3)–Cu(1)–N(3)
O(3)–Cu(1)–N(2)
O(2A)–Cu(1)–O(5)
N(3)–Cu(1)–O(5)
174.67(8)
94.84(8)
79.91(9)
96.83(8)
103.40(8)
2.069(4)
Cu(2)–N(7)
2.210(4)
O(5)–Cu(1)–N(6)
N(6)–Cu(1)–N(3)
N(6)–Cu(1)–N(1)
O(5)–Cu(1)–N(4)
N(3)–Cu(1)–N(4)
N(10)–Cu(2)–O(6)
O(6)–Cu(2)–N(9)
O(6)–Cu(2)–N(12)
N(10)–Cu(2)–N(7)
N(9)–Cu(2)–N(7)
90.00(14)
179.40(17)
100.04(16)
121.44(13)
101.32(15)
88.43(13)
96.63(13)
161.89(14)
105.84(15)
78.53(15)
O(5)–Cu(1)–N(3)
O(5)–Cu(1)–N(1)
N(3)–Cu(1)–N(1)
N(6)–Cu(1)–N(4)
N(1)–Cu(1)–N(4)
N(10)–Cu(2)–N(9)
N(10)–Cu(2)–N(12)
N(9)–Cu(2)–N(12)
O(6)–Cu(2)–N(7)
N(12)–Cu(2)–N(7)
90.36(14)
143.47(14)
79.39(16)
78.90(16)
95.02(15)
172.81(15)
79.39(15)
94.47(15)
98.53(14)
97.67(15)
Compound 2$2(MeOH)0.5$6H2O
Cu(1)–O(8)
Cu(1)–N(1)
Cu(1)–O(7)
Cu(2)–N(7)
Cu(2)–N(9)
O(8)–Cu(1)–O(5)
O(5)–Cu(1)–N(1)
O(5)–Cu(1)–N(3)
O(8)–Cu(1)–O(7)
N(1)–Cu(1)–O(7)
O(1)–Cu(2)–N(7)
N(7)–Cu(2)–N(6)
N(7)–Cu(2)–N(9)
O(1)–Cu(2)–N(4)
N(6)–Cu(2)–N(4)
1.955(5)
2.005(5)
2.239(5)
1.999(5)
2.051(5)
90.29(18)
96.61(18)
166.41(19)
93.60(19)
92.82(19)
97.07(19)
172.7(2)
80.0(2)
Cu(1)–O(5)
Cu(1)–N(3)
Cu(2)–O(1)
Cu(2)–N(6)
1.960(4)
2.018(5)
1.961(4)
2.004(5)
2.241(5)
170.1(2)
91.2(2)
Cu(2)–N(4)
O(8)–Cu(1)–N(1)
O(8)–Cu(1)–N(3)
N(1)–Cu(1)–N(3)
O(5)–Cu(1)–O(7)
N(3)–Cu(1)–O(7)
O(1)–Cu(2)–N(6)
O(1)–Cu(2)–N(9)
N(6)–Cu(2)–N(9)
N(7)–Cu(2)–N(4)
N(9)–Cu(2)–N(4)
Compound 5
Cu(1)–N(1)
Cu(1)–N(3)
Cu(1)–Cl(1)
N(1)–Cu(1)–O(1)
O(1)–Cu(1)–N(3)
1.9355(16)
2.0632(16)
2.2383(5)
87.88(6)
160.57(6)
101.72(6)
158.76(5)
94.33(5)
Cu(1)–O(1)
Cu(1)–O(2A)
1.9962(14)
2.2083(15)
80.5(2)
95.09(18)
98.29(19)
89.87(19)
N(1)–Cu(1)–N(3)
N(1)–Cu(1)–O(2A)
N(3)–Cu(1)–O(2A)
O(1)–Cu(1)–Cl(1)
O(2A)–Cu(1)–Cl(1)
78.51(7)
102.68(6)
94.81(6)
93.48(4)
97.80(5)
159.33(19) O(1)–Cu(1)–O(2A)
94.2(2)
97.6(2)
93.9(2)
N(1)–Cu(1)–Cl(1)
N(3)–Cu(1)–Cl(1)
106.69(18)
78.2(2)
a
Symmetry code: (A) 1 ꢀ x, y + 1/2, ꢀz + 1/2 for 4.
Compound 3$2MeOH
Cu(1)–O(6A)
Cu(1)–N(1)
1.930(2)
2.008(2)
2.207(2)
93.97(9)
164.82(8)
91.20(9)
95.65(11)
98.31(9)
Cu(1)–O(4)
Cu(1)–N(3)
1.9376(19)
2.022(2)
Cu(1)–O(3)
binuclear copper complex 1$0.5H2O in 79% yield. In this reac-
tion, the acetates in Cu(OAc)2$H2O were partially protonated by
pypzacacH to form HOAc, which might be due to the fact that
the acidity of pypzacacH is stronger than that of HOAc. The
dinuclear Cu(II) complex 2$2(MeOH)0.5$6H2O was obtained by
the treatment of pypzacacH with Cu(NO3)2 in MeOH. All the
NO3ꢀ anions in Cu(NO3)2 were removed and replaced by two N
atoms of the pyridyl and pyrazolyl groups and one O atom of the
carboxylate group of the pypzacacꢀ ligand. Similar reactions of
pypzacacH with CuSO4$5H2O or Cu(ClO4)2$6H2O yielded
another two dinuclear Cu(II) complexes 3$2MeOH and 4$MeOH,
respectively. However, all (in 3) or partial (in 4) COOH groups of
pypzacacH were esteried into COOMe group, thereby forming
a new ligand, mpypzacac. It was assumed that the Cu2+ ion may
initialize such an esterication, which was similar to the
dehydrative condensation of carboxylic acid with alcohol cata-
lyzed by Lewis acids such as HfCl4, Sc(OTf)3, MoO2Cl2, Bi(OTf)3
and FeCl3.20 But the aforementioned esterication was different
from the hydrolysis of the ether from ethyl[3-(pyridin-2-yl)-1H-
pyrazol-1-yl]acetate (epypzacac) ligand to the parent acetate
pypzacacꢀ and ethanol in hydrothermal reaction of [MoO2-
O(6A)–Cu(1)–O(4)
O(4)–Cu(1)–N(1)
O(4)–Cu(1)–N(3)
O(6A)–Cu(1)–O(3)
N(1)–Cu(1)–O(3)
O(6A)–Cu(1)–N(1)
O(6A)–Cu(1)–N(3)
N(1)–Cu(1)–N(3)
O(4)–Cu(1)–O(3)
N(3)–Cu(1)–O(3)
91.72(9)
163.61(9)
79.69(9)
95.11(9)
99.36(11)
a
Symmetry code: (A) ꢀx + 5/2, ꢀy + 1/2, z + 1/2 for 1. (A) ꢀx, 1 ꢀ y, ꢀz
for 2.
the uncoordinated H2O molecules in 2$2(MeOH)0.5$6H2O, the
hydrogen atoms of O(3) and O(8) atoms from the MeOH mole-
cules in 3$2MeOH were rstly located from Fourier maps and
˚
subsequently the O–H bond was xed to be 0.86 A. All other H
atoms introduced at the calculated positions and included in the
structure-factor calculations. All the calculations were performed
on a Dell workstation using the CrystalStructure crystallographic
soware package (Rigaku and MSC, Ver.3.60, 2004). Crystal data
along with data collection and renement parameters for
1$0.5H2O, 2$2(MeOH)0.5$6H2O, 3$2MeOH, 4$MeOH and 5 were
summarized in Table 1. The selected bond distances and angles of
1$0.5H2O, 2$2(MeOH)0.5$6H2O and 3$2MeOH, are listed in Table 2
and the selected bond distances and angles of 4$MeOH and 5 are
listed in Table 3.
2ꢀ
Cl2(epypzacac)].21 Two SO4 anions in 3 worked as bridging
ꢀ
ligands to link two Cu2+ centers, while two ClO4 anions in 4
remained intact. In the case of CuCl2, its reactions with pyp-
zacacH gave one polymeric complex [(CuCl) (m-k3:k1-pypzacac)]n
(5). In this reaction, half of the chlorides of CuCl2 was replaced
by pypzacacꢀ ligands. In 1–5, the pypzacacꢀ ligand showed
three coordination modes: chelating bidentate mode
h1(N),h1(N0) (2) and chelating/bridging coordination fashion
Results and discussion
Synthesis and structural characterization of 1–5
As shown Scheme 1, reactions of Cu(OAc)2$H2O with one equiv.
of pypzacacH in MeOH at room temperature, afforded one
54010 | RSC Adv., 2014, 4, 54007–54017
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
centers. Each pypzacacꢀ ligand takes a m-k2(N,N0):k1(O) mode to
bind two Cu centers via two Cu–N bonds and one Cu–O bond.
Cu(1) or Cu(1A) in 1 can be described as having a square pyra-
midal coordination geometry in which O(2A), N(2), N(3), and
O(5) atoms (or O(2), N(2A), N(3A), and O(5A) atoms) sit on the
basal plane while O(3) atom (or O(3A) atom) from the MeOH
molecule occupies the ꢀapical position. In 1, the mean
Cu–O(AcOꢀ and CH2COO ) bond length (1.9515(19) A) (Table 2)
˚
˚
is much shorter than the Cu–O(MeOH) bond length (2.405(2) A),
but is comparable to those observed in [{Cu2(m-OAc)2}2-
22a
˚
(m-dcmpz)2(m-OAc)2] (1.948(3) A).
The Cu(1)–O(4) and
˚
Cu(1)–O(5)(MeOH) bond lengths are relatively long (2.642(2) A,
˚
2.405(2) A), indicating that the O(4) and O(5) atoms interact
weakly with the Cu(1) center. The mean Cu–N bond length
˚
(2.023(2) A) is longer than that observed in [{Cu(m-dcmpz)}2-
Scheme 1 Syntheses of complexes 1–5.
22a
˚
(m-OMe)2]3 (1.978(2) A), but close to that in [CuCl2(bppyH2)]
(2.009(11) A; bppyH2 ¼ 2,6-bis(pyrazol-3-yl)pyridine).22b The
˚
m-h1(N),h1(N0)-h1(O) (1 and 2) and m-h1(N),h1(N0),h1(O)-h1(O0) (4
and 5). Thus, we assumed that the above ve anions in cop-
per(II) salts might play an important role in the coordination
modes of pypzacacꢀ ligand, and the formation of 1–5 (Scheme
1). Compounds 1–5 were stable toward oxygen and moisture,
and readily soluble in H2O, DMF, DMSO, MeOH, EtOH and
MeCN, but insoluble in toluene, Et2O, CH2Cl2 and n-hexane.
Their elemental analyses were consistent with their chemical
formula. In the FT-IR spectra of 1–5, the strong peaks at 1598
cmꢀ1 (1), 1633 cmꢀ1 (2), 1731/1616 cmꢀ1 (3), 1621 cmꢀ1 (4),
1625 cmꢀ1 (5) were assigned as the C]O stretching vibrations
of pypzacacꢀ or/and mpypzacac ligand. Their identities were
nally conrmed by X-ray crystallography.
˚
Cu/Cu distance is 6.220 A, which excludes any metal–metal
interaction.
Crystal structure of 2$2(MeOH)0.5$6H2O
Complex 2$MeOH$6H2O crystallizes in the triclinic space group
ꢀ
P1, and its asymmetric unit contains one [ꢀ{Cu(pypzacac)}(m-
k2:k1-pypzacac)2{Cu(H2O)2}]+ cation, one NO3 ion, two halves
of MeOH and six H2O solvent molecules. In 2, one {Cu(pypza-
cac)} fragment and one {Cu(H2O)2} fragment are bridged by a
pair of m-k2:k1-pypzacac ligands, forming an asymmetric
dimeric structure (Fig. 2). Cu(1) or Cu(2) center in 2 also adopts
a square pyramidal coordination geometry in which O(5), N(1),
N(3), and O(8) atoms (or O(1), N(7), N(9), and N(7) atoms) sit on
the basal plane while O(7) atom (or N(4) atom) occupies the
Crystal structure of 1$0.5H2O
˚
apical position. The Cu(1)–O(7) (2.239(5) A) or Cu(2)–N(4)
Compound 1$0.5H2O crystallizes in the orthorhombic space
group Pbcn, and its asymmetric unit contains half a discrete
molecule [{(MeOH)Cu(OAc)}(m-k2:k1-pypzacac)]2 and one-fourth
of a H2O molecule. Complex 1 has a dimeric structure in which
two {(MeOH)Cu(OAc)} moieties are symmetrically bridged by a
pair of m-k2:k1-pypzacacꢀ ligands (Fig. 1). A crystallographic
inversion center is located on the midpoint of the two Cu
˚
(2.241(5) A) distance on the apical line is longer than the Cu–O
(1.955(5)–1.961(4) A) and Cu–N lengths (2.004(5)–2.051(5) A) on
the basal plane (Table 2). The Cu(1)–O(5)(COO) (1.960(4) A) and
Cu(2)–O(1)(COO) (1.961(4) A) bond lengths are comparable to
˚
˚
˚
˚
those of the corresponding ones in 1.
Fig. 2 View of the [{Cu(pypzacac)}(m-pypzacac)2{Cu(H2O)2}]+ cation
Fig. 1 View of the molecular structure of 1 with a labeling scheme and of 2 with a labeling scheme and 50% thermal ellipsoids. All hydrogen
50% thermal ellipsoids. All hydrogen atoms were omitted for clarity.
atoms and NO3ꢀ were omitted for clarity.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 54007–54017 | 54011

View Article Online
RSC Advances
Paper
Crystal structure of 3$2MeOH
ꢀ
Complex 3$2MeOH crystallizes in the triclinic space group P1,
and its asymmetric unit contains half a discrete [{(MeOH)
Cu(mpypzacac)}(m-SO4)]2 molecule and one MeOH solvent
molecule. In 3, two {(MeOH)Cu(mpypzacac)} moieties are
2ꢀ
symmetrically bridged by a pair of m-SO4
ions to form a
dimeric structure with a crystallographic center of symmetry
lying at the midpoint of Cu(1) and Cu(1A) centers (Fig. 3). Each
Cu(II) center is coordinated by two N atoms from mpypzacac,
two O atoms from two m-SO42ꢀ anions and one O atom from the
coordinated MeOH molecule to form a distorted square pyra-
midal coordination geometry. The pseudo-equatorial plane is
dened by two N atoms and two O atoms of m-SO42ꢀ, while the
O(3) atom from the MeOH molecule occupies the apical posi-
Fig. 4 View of the [{Cu(mpypzacac)2}(m-k2:k1-pypzacac){Cu(mpyp-
zacac)}]3+ trication of 4 with a labeling scheme and 50% thermal
ellipsoids. All hydrogen atoms and three ClO4ꢀ ions were omitted for
clarity.
˚
tion. The Cu(1)–N(1)(pz) bond distance of 2.008(2) A (Table 2) is
˚
slightly shorter than the Cu(1)–N(3)(py) bond length (2.022(2) A)
˚
and the Cu(1)–N(2)(pz) bond length (2.025(2) A) in 1. In 3, the
2ꢀ
˚
˚
Cu–O(SO4 ) bond lengths (1.930(2) A and 1.9376(19) A) are
much shorter than the Cu–O(3)(MeOH) bond length (2.207(2)
˚
˚
lengths (2.089(4) A, 2.178(4) A) on the equatorial plane (Table 3).
While Cu(2) center displays a square pyramidal coordination
geometry in which O(6), N(9), N(10), and N(12) atoms sit on the
basal plane while N(7) atom occupies the apical position. The
Cu(2)-N(7) bond distance of 2.210(4) is longer than other
˚
A). This Cu–O(3)(MeOH) bond length is shorter that that of the
corresponding one in 1 (2.642(2) A).
˚
˚
˚
˚
Cu(2)–N bond lengths (1.929(3) A, 1.994(4) A and 2.069(4) A) on
Crystal structure of 4$MeOH
˚
the equatorial plane. The Cu(1)–O(5) bond length of 1.971(3) A
is longer than the Cu(2)–O(6) bond distance (1.993(3) A), which
may be due to the different coordination geometry of Cu
ꢀ
Complex 4$MeOH crystallizes in the triclinic space group P1,
˚
and its asymmetric unit contains [{Cu(mpypzacac)2}(m-k3:k1-
pypzacac){Cu(mpypzacac)}]3+ trication, three ClO4ꢀ anions and
one MeOH solvent molecule. The pypzacac ligand in 4 takes a m-
k3(N,N0,O):k1(O0) coordination mode to coordinate to two Cu
centers via two Cu–N bonds and two Cu–O bonds (Fig. 4). In 4,
Cu(1) is coordinated by four N atoms from two mpypzacac
ligands and one O atom from the bridging pypzacacꢀ ligand to
form a distorted trigonal bipyramidal geometry. The N(4), N(1)
and O(5) atoms surrounding Cu(1) sit on the equatorial plane
while N(3) and N(6) atoms are located on the equatorial posi-
centers.
˚
tions. The Cu(1)–N(3)/N(6) bond distances (2.003(4) A, 1.999(4)
˚
A) on the equatorial plane is shorter than the Cu(1)–N bond
Fig. 5 View of the [{Cu(mpypzacac)2}(m-k2:k1-pypzacac){Cu(mpyp-
zacac)}]3+ trication of 4 with a labeling scheme and 50% thermal
Fig. 3 View of the molecular structure of 3 with a labeling scheme and ellipsoids. All hydrogen atoms and three ClO4ꢀ ions were omitted for
50% thermal ellipsoids. All hydrogen atoms were omitted for clarity.
clarity.
54012 | RSC Adv., 2014, 4, 54007–54017
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
ammonia in water. Firstly, we carried out the reaction of phe-
nylmethanol (6a) (3.5 mmol) with 1 (2.5 mol%), K2CO3 (10
mol%), TEMPO (6 mol%) and 550 mL aqueous ammonia with
H2O (3 mL) as a solvent under 1 atm O2 at 60 ꢁC. Aer 24 hours,
the desired product benzonitrile (7a) could be isolated in 71%
yield coupled with benzaldehyde (8a) (8% yield) (Table 4, entry
1). This preliminary result implied that 1 might initialize the
aerobic dehydrogenation cascade reaction of alcohol into
nitrile. For a variety of bases (e.g., K2CO3, K3PO4, KOH and
NaOH), K2CO3 is the best one for this reaction in H2O (entry 1).
In the presence of benzyltrimethylammonium chloride
(TMBAC, 8% mol), the yield of desired product was increased
from 71% to 85% (entry 5). Almost complete conversion of 6a
into 7a was achieved when tetraethylammonium iodide (TEAI)
was added into the reaction (entry 6). In the absence of base, 1
exhibited very low activity at 60 ꢁC (entry 7). The reaction
temperature exerted great impact on the ammoxidation reac-
tion of alcohol. When the temperature was raised from 30 ꢁC to
Crystal structure of 5
Complex 5 crystallizes in the monoclinic space group P21/c, and
its asymmetric unit contains one discrete [(CuCl)(m-k3:k1-pyp-
zacac)] molecule. Compound 5 has a 1D a spiral array (extend-
ing along the b axis) in which each {(CuCl)(pypzacac)} unit is
interlinked by carboxyl groups of pypzacac ligands (Fig. 5). Each
pypzacac ligand in 5 also takes a m-k3(N,N0,O):k1(O0) mode to
bind two Cu centers via two Cu–N and two Cu–O bonds. Each
Cu center is coordinated by two N atoms from one pypzacac and
two O atoms from two pypzacac ligand and one Cl atom,
forming a distorted square pyramidal coordination geometry.
˚
The Cu(1)–Cl(1) bond distance of 2.2383(5) A (Table 3) is shorter
than that found in [CuCl2(bppyH2)] (2.391(10) A).22b The Cu(1)–
N(1)(pz) bond distance of 1.9355(16) A is shorter than the Cu(1)–
N(3)(py) bond length (2.0632(16) A) and the Cu(1)–N(2) bond
˚
˚
˚
˚
distance (2.025(2) A) in 1. The Cu(1)–O(1) bond length of
˚
1.9962(14) A is shorter than the Cu(1)–O(2A) bond distance
˚
(2.2083(15) A).
ꢁ
ꢁ
40 C to 50 C, the yields of the benzonitrile product could be
increased from 23% to 42% and 72%, respectively (entries 8–
10). However, the benzonitrile yield was decreased from 99% to
89% when the reaction temperature was increased from 60 ꢁC to
Ammoxidation of alcohol to nitrile and aerobic oxidation of
alcohol into aldehyde catalyzed by 1–5
Complexes 1–5 hold good solubility in water and the Cu(II) 70 ꢁC (entries 8 and 11). The TEMPO loading greatly affected the
centers in 1–5 are coordinatively unsaturated or weakly- catalytic activity. The product yield was gradually increased
coordinated by H2O or MeOH molecule. Thus complexes 1–5 from 59% to 99% when the TEMPO loading was changed from
may possess catalytic activity towards some organic trans- 2% mol to 6% mol at 60 ꢁC (Table 4, entries 6, 12 and 13). The
formations. We attempted these compounds as catalysts for the relatively higher TEMPO loading (10% mol) for this reaction
double dehydrogenation reactions of alcohols with aqueous
Table 4 Optimizing reaction conditions for the ammoxidation reaction of benzyl alcohol
Entrya
Cat.
TEMPO (%)
Base
Additive
T (ꢁC)
Time (h)
Yieldb (%) 7a
Yieldb (%) 8a
1
2
3
4
5
6
7
8
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
3
4
5
10
6
6
6
6
6
6
6
6
6
6
6
2
4
10
6
6
6
6
6
6
6
K2CO3
KOH
—
—
—
60
60
60
60
60
60
60
50
40
30
70
60
60
60
60
60
60
60
60
60
60
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
71
52
68
48
85
99
30
72
42
23
89
59
90
98
87
44
98
86
99
88
76
8
7
K3PO4
NaOH
K2CO3
K2CO3
—
Trace
Trace
11
—
Trace
7
TMBAC
TEAI
TEAI
TEAI
TEAI
TEAI
TEAI
TEAI
TEAI
TEAI
TEAI
TEAI
TEAI
TEAI
TEAI
TEAI
TEAI
TEAI
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
9
9
10
11
12
13
14
15
16
17
18
19
20
21c
18
Trace
35
2
—
12
37
—
5
—
4
8
a
3.5 mmol benzyl alcohol and 550 mL aqueous ammonia, 10 mol% base, 5 mol% [Cu] in 3 mL H2O. TMBAC ¼ benzyltrimethylammonium chloride
(8 mol%); TEAI ¼ tetraethylammonium iodide (8 mol%). b GC yield. c 10 ¼ Cu(NO3)2/2,20-bipyridine.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 54007–54017 | 54013

View Article Online
RSC Advances
Paper
Table 5 Ammoxidation of alcohol to nitrile and aerobic oxidation of alcohol to aldehyde catalyzed by 1
Ar–CH2OH + NH3 / Ar–CN
Ar–CH2OH / Ar–CHO
Entry
Alcohol
Nitrilea
Yieldb (%)
Aldehyded
Yieldb (%)
1
2
94
89
95
97
3
91
95
4
5
92
85
91
98
6
7
93
94
94
92
8
95
98
9
45c
70c
22/70c
71
10
11
85
41
85
67
12
a
Reaction conditions: alcohol (3.5 mmol), 550 mL aqueous ammonia, 6 mol% TEMPO, 8 mol% TEAI, 10 mol% K2CO3, 1 atm O2, and catalyst loading
¼ 5 mol% [Cu] at 60 ꢁC for 24 hours. b Isolated yield. c Reaction temperature ¼ 80 ꢁC. d Reaction conditions: alcohol (3.5 mmol), 1 atm O2, 5 mol%
[Cu], 6 mol% TEMPO, 8 mol% TEAI, 10 mol% K2CO3 in 3 mL H2O at 40 ꢁC for 24 hours.
seemed not to affect the product yields (entries 14). According to of aromatic functional groups including electron donating
the aforementioned optimization experiments, the optimal groups such as methoxyl and methyl, aryl chloride, nitro groups
reaction conditions were identied as follows: catalyst loading and aromatic heterocyclic molecules. It appeared that the
([Cu] ¼ 5 mol%), 8 mol% TEAI loading, 6 mol% TEMPO electronic nature of substituents on benzyl alcohols had some
loading, 10 mol% K2CO3 loading and H2O (as a solvent) with a effect on the catalytic activity towards the transformation from
reaction temperature of 60 ꢁC. With these optimized condi- benzylic alcohol to aryl nitrile. Commercially available methyl-,
tions, the catalytic performances of 2–5 were also investigated. and methoxy-substituted benzyl alcohols gave the respective
These complexes exhibited highly catalytic activity for the nitriles in 85–95% yield (Table 5, entries 1–8). For the double
ammoxidation of phenylmethanol to benzaldehyde (entries 17– dehydrogenation reactions of electron-withdrawing chloride-
20). The catalytic activities of 1, 2 and 4 were higher than those and nitryl-substituted benzamides, higher reaction temperature
of 3 and 5. Comparative runs with Cu(NO3)2/2,20-bipyridine (80 ꢁC) was needed for the moderate yields (entries 9 and 10). It
(76%) catalytic system under the same reaction conditions seemed that the o-, m-substituted groups on phenyl rings of
indicated that 1–5 exhibited better catalytic perforꢀmance and benzyl alcohols promote rather than hamper the double dehy-
higher selectivity (entry 21). The hydrophilic –CO2 group on drogenation reactions. Substrates with substituents at the meta
the pypzacac ligand did play an important role in controlling and ortho positions (entries 3, 4, 6 and 7) were more reactive
the active catalytic species in water.
than para-substituted substrates (entries 2 and 5). Notably,
heteroatom-containing alcohols including nitrogen and sulfur
atoms such as pyridin-3-ylmethanol, thiophen-2-ylmethanol
were well tolerated under the reaction conditions and high
yields of the desired nitriles were obtained (entries 11 and 12).
During the ammoxidation reaction of alcohol, aldehyde was
supposed to form initially. Thus, we evaluated the 1/O2/TEMPO
catalytic system in the direct transformation of alcohol into
aldehyde. The aerobic oxidation of alcohols could afford
The aerobic oxidation of alcohols catalyzed by 1
Once the optimization had been performed, we examined the
substrate scope of the ammoxidation reaction with 1. As
depicted in Table 5, catalyst 1 exhibited a wide applicability
towards a broad array of alcohols, affording the corresponding
nitriles in high yields. The reaction could tolerate a wide range
54014 | RSC Adv., 2014, 4, 54007–54017
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
Table 6 Reuse of 1-catalyzed the oxidation of phenylmethanol and
the aerobic double dehydrogenation
Cycle
Benzonitrilea
Benzaldehydeb
1
2
3
4
5
94
90
86
82
78
95
95
94
91
92
Scheme 2 The coordination modes of pzpypzꢀ ligand in 1–5.
coordination modes for pypzacac, h1(N),h1(N0) chelating
bidentate mode (1), m-h1(N),h1(N0)-h1(O0) (1 and 2) and m-
h1(N),h1(N0),h1(O)-h1(O0) (4 and 5) chelating/bridging coordi-
nation fashion (Scheme 2). Complexes 1–5 displayed high
catalytic activity towards the ammoxidation of alcohol to nitrile
and the aerobic oxidation of alcohol to aldehyde in water.
Furthermore, catalyst 1 was easily recovered by extracting the
organic products with ether and could be reused several times
without loss of its catalytic activity, especially towards the
aerobic oxidation of alcohol to aldehyde. It is anticipated that
other polar sulfonate and ammonium groups may be employed
to functionalize the pyrzaolate ligands to achieve better catalytic
performance in H2O. Studies on these respects are currently
underway.
a
Reaction conditions: alcohol (3.5 mmol), 550 mL aqueous ammonia, 6
mol% TEMPO, 8 mol% TEAI, 10 mol% K2CO3, 1 atm O2, and catalyst
b
loading ¼ 5 mol% [Cu] at 60 ꢁC for 24 hours. Reaction conditions:
alcohol (3.5 mmol), 1 atm O2, 5 mol% [Cu], 6 mol% TEMPO, 8 mol%
TEAI, 10 mol% K2CO3 in 3 mL H2O at 40 ꢁC for 24 hours.
smoothly the corresponding nitriles in excellent yields even at
lower temperature (40 ꢁC) in water. Notably, the presence or
absence of an electron-donating group did not signicantly
affect the yield. Over 90% isolated yields were obtained
uniformly. While the result was relatively worse while using 4-
nitrobenzyl alcohol as substrates (22%). Elevating the reaction
temperature up to 80 ꢁC resulted in the higher yield (70%) of 4-
nitrobenzaldehyde. For the heteroaromatic benzylic alcohols
such as pyridin-3-ylmethanol and thiophen-2-ylmethanol, the
corresponding nitriles were obtained in 85% and 67% isolated
yield.
Acknowledgements
The authors are grateful for nancial supports from the
National Natural Science Foundation of China (21171124,
21171125 and 21371126) and State Key Laboratory of Organo-
metallic Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences (201201006). J. P. Lang also highly
appreciates the nancial supports from the Qin-Lan Project and
the “333” Project of Jiangsu Province, the Priority Academic
Program Development of Jiangsu Higher Education Institu-
tions, and the “SooChow Scholar” Program of Soochow
University.
Reusability of the catalyst
A further advantage of such a water-soluble catalytic system was
its reusability. The ammoxidation of phenylmethanol with 550
mL aqueous ammonia, 6 mol% TEMPO, 8 mol% TEAI and 10
mol% K2CO3 was performed using a 2.5 mol% catalyst 1 in
order to examine the feasibility of this approach. Aer 24 h and
cooling to room temperature, the organic product, benzonitrile,
was readily separated from the aqueous phase by simple
extraction with Et2O, and the residual aqueous solution was
then subjected to the next reaction run, charged with phenyl-
methanol, TEMPO and aqueous ammonia. The residual
aqueous solution containing 1 still worked and the conversion
steadily decreased during ve runs, from ca. 95–78% (Table 6).
For the aerobic oxidation of alcohol, the catalytic system could
also be reused several cycles. No obvious loss of catalytic activity
is observed aer the catalytic solution is used ve times.
References
1 (a) T. M. Harris, C. M. Harris, T. A. Oster, L. E. Brown and
J. Y. C. Lee, J. Am. Chem. Soc., 1988, 110, 6180–6186; (b)
V. V. Grushin and H. Alper, Chem. Rev., 1994, 94, 1047–1062.
2 (a) K. Yamaguchi, M. Matsushita and N. Mizuno, Angew.
Chem., Int. Ed., 2004, 43, 1576–1580; (b) A. V. Gulevich,
A. S. Dudnik, N. Chernyak and V. Gevorgyan, Chem. Rev.,
´
´
2013, 113, 3084–3213; (c) R. Garcıa-Alvarez, P. Crochet and
V. Cadierno, Green Chem., 2013, 15, 46–66; (d) R. E. Khidre
and B. F. Abdel-Wahab, Curr. Org. Chem., 2013, 17, 430–
445; (e) G. Abbiati, E. M. Beccalli and E. Rossi, Top.
Organomet. Chem., 2013, 43, 231–290.
3 (a) D. C. McCutcheon, M. A. Paley, R. C. Steinhardt and
J. A. Prescher, J. Am. Chem. Soc., 2012, 134, 7604–7607; (b)
S. Ueda and H. Nagasawa, J. Am. Chem. Soc., 2009, 131,
15080–15081; (c) M. Nasr-Esfahani, M. Montazerozohori
and S. Mehrizi, J. Heterocycl. Chem., 2011, 48, 249–254; (d)
X. N. Li, B. Y. Zhou, J. Zhang, M. Y. She, S. J. An, H. X. Ge,
C. Li, B. Yin, J. L. Li and Z. Shi, Eur. J. Org. Chem., 2012,
1626–1632; (e) F. Himo, Z. P. Demko, L. Noodleman and
Conclusions
In summary, we have demonstrated that reactions of pypzacacH
consisting of pyridinyl, pyrazolyl and carboxylate groups with
Cu(OAc)2, Cu(NO3)2, CuSO4, Cu(ClO4)2 or CuCl2 produced four
dinuclear Cu(II) complexes 1–4, and onꢀe polymeric complex 5.
The anions (OAcꢀ, NO3ꢀ, SO42ꢀ, ClO4 and Clꢀ) are the key
parameter for controlling the coordination modes of the pyp-
zacac ligand and the structural variations of the resulting
complexes. The mpypzacac ligands in 3 and 4 were in situ
produced via the Cu2+-catalyzed dehydrative esterication of
acetic acid of the pypzacac ligand. In 1–5, there are three
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 54007–54017 | 54015

View Article Online
RSC Advances
Paper
¨
K. Barry Sharpless, J. Am. Chem. Soc., 2003, 125, 9983–9987;
(f) W. X. Wang, H. L. Cai and R. G. Xiong, Chin. Chem.
Lett., 2013, 24, 783–785; (g) X. M. Chen and M. L. Tong,
Acc. Chem. Res., 2007, 40, 162–170.
4 T. Sandmeyer, Ber. Dtsch. Chem. Ges., 1885, 18, 1492–1496.
5 (a) P. Anbarasan, T. Schareina and M. Beller, Chem. Soc. Rev.,
2011, 40, 5049–5067; (b) G. B. Yan, J. Yu and L. Zhang, Chin. J.
Org. Chem., 2012, 32, 294–303; (c) G. A. Ellis and
T. M. Romney-Alexander, Chem. Rev., 1987, 87, 779–794; (d)
T. Schareina, A. Zapf and M. Beller, Chem. Commun., 2004,
1388–1389.
C. Fleckenstein, S. Roy, S. Leuthauber and H. Plenio,
Chem. Commun., 2007, 2870–2872; (c) C. Dupuis, K. Adiey,
L. Charruault, V. Michelet, M. Savignac and J.-P. Genet,
ˆ
Tetrahedron Lett., 2001, 42, 6523–6526; (d) P. Machnitzki,
M. Tepper, K. Wenz, O. Stelzer and E. Herdtweck, J.
Organomet. Chem., 2000, 602, 158–169; (e) L. R. Moore and
K. H. Shaughnessy, Org. Lett., 2004, 6, 225–228; (f)
L. R. Moore, E. C. Western, R. Craciun, J. M. Spruell,
D. A. Dixon, K. P. O'Halloran and K. H. Shaughnessy,
Organometallics, 2008, 27, 576–693; (g) C. Fleckenstein and
H. Plenio, J. Org. Chem., 2008, 73, 3236–3245; (h)
C. A. Fleckenstein and H. Plenio, Chem.–Eur. J., 2008, 14,
4267–4279; (i) J. Pschierer and H. Plenio, Eur. J. Org.
Chem., 2010, 2934–2937.
¨
6 (a) M. T. Schumperli, C. Hammond and I. Hermans, ACS
Catal., 2012, 2, 1108–1117; (b) Y. Zhang, K. L. Xu,
X. R. Chen, T. J. Hu, Y. P. Yu, J. L. Zhang and J. Huang,
´
Catal. Commun., 2010, 11, 951–954; (c) K. Yamaguchi and 14 (a) B. Ines, R. SanMartin, M. Moure and E. Domingueza, Adv.
N. Mizuno, Angew. Chem., Int. Ed., 2003, 42, 1480–1483; (d)
J. Kim and S. S. Stahl, ACS Catal., 2013, 3, 1652–1656.
Synth. Catal., 2009, 351, 2124–2132; (b) F. Churruca,
´
R. SanMartin, B. Ines, I. Tellitu and E. Domingueza, Adv.
7 (a) S. Enthaler, Chem.–Eur. J., 2011, 17, 9316–9319; (b)
S. Sueoka, T. Mitsudome, T. Mizugaki, K. Jitsukawa and
K. Kaneda, Chem. Commun., 2010, 46, 8243–8245; (c)
S. L. Zhou, D. Addis, S. Das, K. Junge and M. Beller, Chem.
Commun., 2009, 4883–4885; (d) K. Yamaguchi, H. Fujiwara,
Synth. Catal., 2006, 348, 1836–1840; (c) R. Amengual,
ˆ
E. Genin, V. Michelet, M. Savignac and J.-P. Genet, Adv.
Synth. Catal., 2002, 344, 393–398; (d) H. Hattori,
K.-i. Fujita, T. Muraki and A. Sakaba, Tetrahedron Lett.,
2007, 48, 6817–6820.
Y. Ogasawara, M. Kotani and N. Mizuno, Angew. Chem., Int. 15 (a) O. Adidou, C. Goux-Henry, M. Sa, M. Souaoui and
Ed., 2007, 46, 3922–3925; (e) K. Ishihara, Y. Furuya and
H. Yamamoto, Angew. Chem., Int. Ed., 2002, 41, 2983–2986.
8 (a) S. T. Ding and N. Jiao, J. Am. Chem. Soc., 2011, 133, 12374–
12377; (b) X. Chen, X. S. Hao, C. E. Goodhue and J. Q. Yu, J.
Am. Chem. Soc., 2006, 128, 6790–6791; (c) J. Kim and
E. Framery, Tetrahedron Lett., 2008, 49, 7217–7219; (b)
W. P. Mai and L. X. Gao, Synlett, 2006, 2553–2558; (c)
M. van der Heiden and H. Plenio, Chem.–Eur. J., 2004, 10,
1789–1797; (d) L. Zhang, J. L. Wu, L. J. Shi, C. G. Xia and
F. W. Li, Tetrahedron Lett., 2011, 52, 3897–3901.
S. Chang, J. Am. Chem. Soc., 2010, 132, 10272–10274; (d) 16 (a) S. N. Chen, W. Y. Wu and F. Y. Tsai, Green Chem., 2009,
X. Y. Ren, J. B. Chen, F. Chen and J. Cheng, Chem.
Commun., 2011, 47, 6725–6727.
11, 269–274; (b) W. Y. Wu, S. N. Chen and F. Y. Tsai,
Tetrahedron Lett., 2006, 47, 9267–9270; (c) C. S. Zhou,
J. Y. Wang, L. Y. Li, R. H. Wang and M. C. Hong, Green
Chem., 2011, 13, 2100–2106; (d) D. J. M. Snelders,
R. Kreiter, J. Firet, G. van Koten and R. J. M. K. Gebbink,
Adv. Synth. Catal., 2008, 350, 262–266; (e) R. B. DeVasher,
L. R. Moore and K. H. Shaughnessy, J. Org. Chem., 2004,
69, 7919–7927; (f) D. J. M. Snelders, C. van der Burg,
M. Lutz, A. L. Spek, G. van Koten and R. J. M. Klein
Gebbink, ChemCatChem, 2010, 2, 1425–1437; (g)
D. J. M. Snelders, G. van Koten and R. J. M. Klein Gebbink,
J. Am. Chem. Soc., 2009, 131, 11407–11416.
9 (a) S. Yamazaki and Y. Yamazaki, Chem. Lett., 1990, 571–572;
(b) F. E. Chen, Y. Y. Li, M. Xu and H. Q. Jia, Synthesis, 2002,
1804–1806; (c) G. D. McAllister, C. D. Wilfred and
R. J. K. Taylor, Synlett, 2002, 1291–1295; (d) S. Iida and
H. Togo, Tetrahedron, 2007, 63, 8274–8281; (e)
B. V. Rokade, S. K. Malekar and K. Ramaiah Prabhu, Chem.
Commun., 2012, 48, 5506–5508; (f) Y. Sasano, S. Nagasawa,
M. Yamazaki, M. Shibuya, J. Park and Y. Iwabuchi, Angew.
Chem., Int. Ed., 2014, 53, 3236–3240; (g) K. R. Reddy,
C. U. Maheswari, M. Venkateshwar, S. Prashanthi and
M. L. Kantam, Tetrahedron Lett., 2009, 50, 2050–2053.
10 (a) W. Zhou, J. J. Xu, L. G. Zhang and N. Jiao, Org. Lett., 2010,
12, 2888–2891; (b) M. Lamani and K. R. Prabhu, Angew.
Chem., Int. Ed., 2010, 49, 6622–6625; (c) B. V. Rokade,
S. K. Malekar and K. R. Prabhu, Chem. Commun., 2012, 48,
5506–5508.
17 (a) L. M. Wan, H. X. Li, W. Zhao, H. Y. Ding, Y. Y. Fang,
P. H. Ni and J. P. Lang, J. Polym. Sci., Part A: Polym. Chem.,
2012, 50, 4864–4870; (b) D. X. Liu, W. J. Gong, H. X. Li,
J. Gao, F. L. Li and J. P. Lang, Tetrahedron, 2014, 70, 3385–
3389; (c) L. L. Liu, H. X. Li, L. M. Wan, Z. G. Ren,
H. F. Wang and J. P. Lang, Chem. Commun., 2011, 47,
11146–11148.
18 (a) F. Einberg, J. Org. Chem., 1970, 35, 3978–3980; (b) J. Yang,
L. Shen, G. W. Yang, Q. Y. Li, L. L. Zhu, W. Shen, C. Ji and
X. F. Shen, Inorg. Chim. Acta, 2012, 392, 25–29; (c) H. Cai,
Y. Guo and J. G. Li, Inorg. Chem. Commun., 2013, 37, 178–181.
11 W. Zhou, L. G. Zhang and N. Jiao, Angew. Chem., Int. Ed.,
2009, 48, 7094–7097.
12 (a) W. Y. Yin, C. M. Wang and Y. Huang, Org. Lett., 2013, 15,
1850–1853; (b) C. Z. Tao, F. Liu, Y. M. Zhu, W. W. Liu and
Z. L. Cao, Org. Biomol. Chem., 2013, 11, 3349–3354; (c)
L. M. Dornan, Q. Cao, J. C. A. Flanagan, J. J. Crawford, 19 (a) G. M. Sheldrick, SHELXS-97, Program for Solution of
¨
M. J. Cook and M. J. Muldoon, Chem. Commun., 2013, 49,
6030–6032.
Crystal Structures, University of Gottingen, Germany, 1997;
(b) G. M. Sheldrick, SHELXL-97, Program for Renement of
¨
13 (a) M. Mifsud, K. V. Parkhomenko, I. W. C. E. Arends and
R. A. Sheldon, Tetrahedron, 2010, 66, 1040–1044; (b)
Crystal Structures, University of Gottingen, Germany, 1997.
54016 | RSC Adv., 2014, 4, 54007–54017
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
20 (a) K. Ishihara, S. Ohara and H. Yamamoto, Science, 2000, 21 S. Figueiredo, A. C. Gomes, P. Neves, T. R. Amarante,
290, 1140–1142; (b) K. Ishihara, M. Kubota, H. Kurihara
and H. Yamamoto, J. Am. Chem. Soc., 1995, 117, 4413–
4414; (c) C.-T. Chen, J.-H. Kuo, V. D. Pawar, Y. S. Munot,
F. A. Almeida Paz, R. Soares, A. D. Lopes, A. A. Valente,
M. Pillinger and I. S. Gonçalves, Inorg. Chem., 2012, 51,
8629–8635.
S.-S. Weng, C.-H. Ku and C.-Y. Liu, J. Org. Chem., 2005, 70, 22 (a) L. Wang, B. Guo, H. X. Li, Q. Li, H. Y. Li and J. P. Lang,
1188–1197; (d) A. Orita, C. Tanahashi, A. Kakuda and
J. Otera, J. Org. Chem., 2001, 66, 8926–8934; (e) N. Ieda,
K. Mantri, Y. Miyata, A. Ozaki, K. Komura and Y. Sugi, Ind.
Eng. Chem. Res., 2008, 47, 8631–8638.
Dalton Trans., 2013, 42, 15570–15580; (b) P. Gamez,
R. H. Steensma, W. L. Driessen and J. Reedijk, Inorg. Chim.
Acta, 2002, 333, 51–56.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 54007–54017 | 54017