Effects of metal ions and ligands on transesterification: Synthesis, structures, and catalytic activities of a series of cation-anionic complexes with dipyridylamine ligands

Article abstract of DOI:10.1080/00958972.2012.704996

A series of cation-anion complexes derived by 2,2′-dipyridylamine (Hdpa) and carboxylate ligands with formulas [Ni(Hdpa)₂(CH ₃COO)]Cl(CH₃OH) (1), [Co(Hdpa)₂(CH ₃COO)]Cl(CH₃OH) (2), [Ni(Hdpa)₂(CH ₃CH₂CH₂COO)]Cl (3), [Co(Hdpa) ₂(CH₃CH₂CH₂COO)]Cl (4), [Ni(Hdpa)₂(C₆H₅COO)]Cl (5), and [Co(Hdpa) ₂(C₆H₅COO)]Cl (6), were synthesized and characterized by IR, elemental analysis, MS(ESI), TG analysis, UV-Vis, and fluorescence spectra. X-ray single crystal structural analysis showed that the coordination geometries of metal ions in these complexes are similar and they are cation-anion species. The hydrogen-bonding structures are 1-D chains through the N-H...Cl bonds. There are weak stacking interactions between pyridine rings in 1-4, while there are no stacking interactions in 5 and 6. We have investigated the transesterification of phenyl acetate with methanol catalyzed by 1-6 under mild conditions; 1-4 are homogeneous catalysts while 5 and 6 are heterogeneous catalysts due to their poor solubility in methanol. Cobalt complexes exhibit higher catalytic activities than corresponding nickel complexes. Complex 4 is the best catalyst of these six complexes.

Full text of DOI:10.1080/00958972.2012.704996

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Effects of metal ions and ligands
on transesterification: synthesis,
structures, and catalytic activities of a
series of cation–anionic complexes with
dipyridylamine ligands
a b
b
a a
b
Yuan Deng
, Ying Bai , Long-Guan Zhu
, Jian-Xiong Jiang
b
&
a
Guo-Qiao Lai
Department of Chemistry, Zhejiang University, Hangzhou 310027,
People's Republic of China
b
Key Laboratory of Organosilicon Chemistry and Material
Technology of Ministry of Education, Hangzhou Normal University,
Hangzhou 310012, People's Republic of China
Accepted author version posted online: 20 Jun 2012. Version of
record first published: 04 Jul 2012
To cite this article: Yuan Deng, Ying Bai, Long-Guan Zhu, Jian-Xiong Jiang & Guo-Qiao Lai
(2012): Effects of metal ions and ligands on transesterification: synthesis, structures, and
catalytic activities of a series of cation–anionic complexes with dipyridylamine ligands, Journal of
Coordination Chemistry, 65:16, 2793-2803
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Journal of Coordination Chemistry
Vol. 65, No. 16, 20 August 2012, 2793–2803
Effects of metal ions and ligands on transesterification:
synthesis, structures, and catalytic activities of a series of
cation–anionic complexes with dipyridylamine ligands
YUAN DENGyz, YING BAIz, LONG-GUAN ZHU*y, JIAN-XIONG JIANGz
and GUO-QIAO LAIz
yDepartment of Chemistry, Zhejiang University, Hangzhou 310027, People’s
Republic of China
zKey Laboratory of Organosilicon Chemistry and Material Technology of
Ministry of Education, Hangzhou Normal University, Hangzhou 310012,
People’s Republic of China
(
Received 28 February 2012; in final form 8 May 2012)
0
A series of cation–anion complexes derived by 2,2 -dipyridylamine (Hdpa) and carboxylate
ligands with formulas [Ni(Hdpa)
Cl(CH OH) (2), [Ni(Hdpa) (CH CH
4), [Ni(Hdpa) (C COO)]Cl (5), and [Co(Hdpa)
2
(CH
3
COO)]Cl(CH
COO)]Cl (3), [Co(Hdpa)
(C COO)]Cl (6), were synthesized and
3
OH) (1), [Co(Hdpa)
2
(CH
3
COO)]
3
2
3
2
CH
2
2
(CH CH CH
3
2
2
COO)]Cl
(
2
6
H
5
2
6 5
H
characterized by IR, elemental analysis, MS(ESI), TG analysis, UV-Vis, and fluorescence
spectra. X-ray single crystal structural analysis showed that the coordination geometries of
metal ions in these complexes are similar and they are cation–anion species. The hydrogen-
bonding structures are 1-D chains through the N–Hꢀ ꢀ ꢀCl bonds. There are weak stacking
interactions between pyridine rings in 1–4, while there are no stacking interactions in 5 and 6.
We have investigated the transesterification of phenyl acetate with methanol catalyzed by 1–6
under mild conditions; 1–4 are homogeneous catalysts while 5 and 6 are heterogeneous catalysts
due to their poor solubility in methanol. Cobalt complexes exhibit higher catalytic activities
than corresponding nickel complexes. Complex 4 is the best catalyst of these six complexes.
0
Keywords: 2,2 -Dipyridylamine; Catalytic activity; Transesterification
1. Introduction
Supramolecular structures based on non-covalent weak intermolecular interactions,
such as hydrogen bonds, ꢀ–ꢀ and C–Hꢀ ꢀ ꢀꢀ interactions have attracted attention due to
their potential applications as functional materials [1–6]. Transesterification is a classic
reaction in synthesizing carboxylic esters [7, 8], catalyzed by a variety of protic and
Lewis acids, organic and inorganic bases, enzymes, complexes, and antibodies [9].
Moreover, the ester-to-ester transformation is particularly useful in laboratory and
industrial applications [10].
Although many efforts have been made to design transesterification catalysts based
0
on metal ions with 2,2 -dipyridylamine (Hdpa), these complexes focus on Zn and other
*
Corresponding author. Email: chezlg@zju.edu.cn
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.704996

2
794
Y. Deng et al.
metals have not been mentioned [11–13]. The effect of different carboxylates on
transesterification has not been reported. To find efficient catalysts to catalyze
transesterification reactions under mild conditions, we have chosen chelating Hdpa
with nickel and cobalt salts containing different carboxylates to investigate their
catalytic activity. Herein, we report the syntheses, structures, and catalytic activities
of [Ni(Hdpa) (CH COO)]Cl(CH OH) (1), [Co(Hdpa) (CH COO)]Cl(CH OH) (2),
2
3
3
2
3
3
[
[
Ni(Hdpa) (CH CH CH COO)]Cl
(3),
Ni(Hdpa) (C H COO)]Cl (5), and [Co(Hdpa) (C H COO)]Cl (6).
[Co(Hdpa) (CH CH CH COO)]Cl
2
(4),
2
3
2
2
2
3
2
2
6
5
2
6
5
2
2
. Experimental
.1. General procedures
0
Chemicals (except 2,2 -dipyridylamine) and solvents were of analytical grade
purchased from commercial sources and used as obtained without purification.
0
2
,2 -Dipyridylamine was prepared according to the literature [14]. Elemental analyses
C, H, and N) were performed on a Elementar Vario Elemental Analyzer. The infrared
(
spectrum (KBr pellet) was recorded on a Bruker VERTEX 70 spectrophotometer from
ꢁ
1
00–4000 cm . Thermal analysis was performed on a NETZSCH 409 F3 thermal
4
analyzer at a heating rate of 10 C min in flowing nitrogen from 30–800 C using Al O
ꢂ
ꢁ1
ꢂ
2
3
crucibles. MS (ESI) was determined by a Thermo LCQ Advantage MAX. The UV-Vis
spectra were recorded in methanol at room temperature with a Thermo Evolution 300
spectrophotometer. The fluorescence spectroscopic studies were carried out in methanol
at room temperature with a Hitachi F-2700 FL spectrometer. Analysis of catalytic
transesterification product was performed with a Trace 2000 GC-DSQ MS instrument
(Thermo Electron, USA). Mass spectra were acquired by electron-impact ionization
under normal conditions. Catalytic reaction conversion was monitored by an Agilent
7890A gas chromatograph with SE-30 capillary column.
2
2
.2. Synthesis
.2.1. Preparation of [Ni(Hdpa) (CH COO)]Cl(CH OH) (1).
2
A
mixture of
3
3
NiCl ꢀ 6H O (0.238 g, 1.0 mmol), anhydrous sodium acetate (0.082 g, 1.0 mmol), and
2
2
0
2
,2 -dipyridylamine (0.342 g, 2.0 mmol) was dissolved in methanol (20 mL), stirring at
room temperature for 12 h and mother liquor carefully layered with ether. After one
week, suitable purple crystals for X-ray crystal structure analysis were obtained. Calcd
for C H N O ClNi (%): C, 52.42; H, 4.75; N, 15.95. Found (%): C, 52.24; H, 4.85;
2
3
25
6
3
þ
þ
N, 15.79. MS (ESI, m/z): 459 ([Ni(Hdpa) (CH COO)] ), 399 ([Ni(Hdpa)(dpa)] ),
2
3
þ
ꢁ1
2
2
9
88([Ni(Hdpa)(CH COO)] ). IR (KBr, cm ): 3437s, 3283m, 3238w, 3179m, 3131m,
3
970s, 1639s, 1584s, 1536s, 1477s, 1364s, 1270m, 1240s, 1160s, 1058w, 1013s, 938m,
07m, 844w, 791s, 770s, 741w, 676m, 647w, 626w, 537m, 432m.
2.2.2. Preparations of 2, 3, 4, and 6. The synthetic procedures of 2, 3, 4, and 6 are very
similar to the synthesis of 1. Crystals of 2 are orange. Calcd for C H N O ClCo (%):
C, 52.32; H, 4.74; N, 15.92. Found (%): C, 52.40; H, 4.87; N, 15.82. MS (ESI, m/z):
2
3
25
6
3

Cation–anionic complexes
2795
þ
þ
þ
460 ([Co(Hdpa) (CH COO)] ), 400 ([Co(Hdpa)(dpa)] ), 289 ([Co(Hdpa)(CH COO)] ).
IR (KBr, cm ): 3428s, 3285w, 3181w, 3066m, 2968m, 1640s, 1582s, 1530s, 1477s,
2
1
3
3
ꢁ
1
5
437w, 1421w, 1371m, 1269w, 1238s, 1160s, 1057w, 1010s, 907w, 791s, 772s, 674m,
35m, 426m.
Crystals of 3 are purple. Calcd for C H N O ClNi (%): C, 55.12; H, 4.78; N, 16.08.
2
4
25
6
2
Found (%): C, 55.24; H, 4.85; N, 16.15. MS (ESI, m/z): 487 ([Ni(Hdpa)
þ
2
þ
þ
(CH CH CH COO)] ), 399 ([Ni(Hdpa)(dpa)] ), 316 ([Ni(Hdpa)(CH CH CH COO)] ).
IR (KBr, cm ): 3434s, 3283w, 3179w, 3128w, 3062m, 2965s, 2932w, 1640s, 1583s,
3
2
2
3
2
2
ꢁ
1
1
9
524s, 1477s, 1434m, 1417m, 1369m, 1315w, 1270w, 1238m, 1158m, 1059w, 1012m,
34w, 907w, 879w, 838w, 785m, 773m, 670w, 646w, 666w, 536w, 433w.
Crystals of 4 are orange. Calcd for C H N O ClCo (%): C, 55.01; H, 4.78;
2
4
25
6
2
N, 16.05. Found (%): C, 55.11; H, 4.70; N, 15.96. MS (ESI, m/z):
þ þ
88 ([Co(Hdpa) (CH CH CH COO)] ), 400 ([Co(Hdpa)(dpa)] ), 317 ([Co(Hdpa)
2 3 2 2
4
(
þ ꢁ1
CH CH CH COO)] ). IR(KBr, cm ): 3447m, 3281w, 3235w, 3177w, 3127w,
3 2 2
3
1
8
061m, 2960s, 2931w, 2901w, 2871w, 1639s, 1593s, 1581s, 1527s, 1476s, 1433m,
417m, 1370m, 1314w, 1268w, 1237s, 1170w, 1158m, 1058w, 1008m, 933w, 906w, 880w,
32w, 785m, 775m, 670w, 645w, 605w, 533w, 421w.
Crystals of 6 are orange. Calcd for C H N O ClCo (%): C, 58.12; H, 4.13;
2
7
23
6
2
N, 15.07. Found (%): C, 58.10; H, 4.16; N, 15.13. MS (ESI, m/z): 522 ([Co(Hdpa)
2
þ þ þ
C H COO)] ), 400 ([Co(Hdpa)(dpa)] ), 351 ([Co(Hdpa)(C H COO)] ). IR (KBr,
6 5 6 5
(
ꢁ
1
cm ): 3436s, 3289w, 3241w, 3180w, 3131w, 3064m, 2987s, 2926m, 2855w, 1643s, 1596s,
1
8
583s, 1531s, 1480s, 1419s, 1376m, 1327m, 1267w, 1238s, 1160s, 1056w, 1009s, 907w,
72w, 800s, 774s, 726s, 681w, 645m, 605w, 532m, 425m.
2
.2.3. Preparation of [Ni(Hdpa) (C H COO)]Cl (5). A mixture of NiCl ꢀ 6H O
2
6
5
2
2
0
(0.238 g, 1.0 mmol), sodium benzoate (0.144 g, 1.0 mmol), and 2,2 -dipyridylamine
(0.342 g, 2.0 mmol) was dissolved in methanol/H O (10 mL/10 mL) solution. The
2
ꢂ
resulting mixture was sealed in a 25 mL Teflon-lined autoclave and heated to 150 C
for 48 h, then cooled to room temperature. Suitable purple crystals for X-ray crystal
structure analysis were obtained. Calcd for C H N O ClNi (%): C, 58.22; H, 4.13;
2
7
23
6
2
N, 15.09. Found (%): C, 58.14; H, 4.21; N, 15.15. MS(ESI, m/z): 521 ([Ni(Hdpa)
(
2
þ þ þ ꢁ1
C H COO)] ), 399 ([Ni(Hdpa)(dpa)] ), 350 ([Ni(Hdpa)(C H COO)] ). IR (KBr, cm ):
6 5 6 5
3
1
9
436m, 3287w, 3240w, 3179w, 3130w, 3065m, 2985w, 2924m, 2854m, 1643s, 1584s,
529s, 1479s, 1420s, 1373m, 1326w, 1268w, 1240s, 1160s, 1122w, 1107w, 1057w, 1013s,
07m, 883w, 856 m, 800s, 772s, 727s, 682w, 647m, 605w, 534m, 432m.
2
.3. X-ray crystallographic determination
Crystallographic data were collected on a Bruker Apex DUO diffractometer at 296 K
˚
using graphite monochromated Mo-Ka radiation (ꢁ ¼ 0.71073 A). The frames were
integrated with Bruker SAINT Software package [15] and the data were corrected for
absorption using SADABS [16]. The structures were solved by direct methods using
SHELXS-97 [17]. All non-hydrogen atoms were refined with anisotropic thermal
2
parameters by full-matrix least-squares on F using SHELXS-97. Hydrogen atoms were
0
placed in idealized positions except NH of 2,2 -dipyridylamine. Details of crystal data
and structure refinements for the six complexes are listed in table 1.

2
796
Y. Deng et al.

Cation–anionic complexes
.4. Catalytic activity of the complexes
2797
2
The catalyst (7.5 ꢃ 10ꢁ2 mmol) was added to a solution of phenyl acetate (1.0 mmol)
dissolved in methanol (2.0 mL), then the mixture was stirred at room temperature.
Catalytic reaction conversion was monitored by an Agilent 7890A gas chromatograph
with a SE-30 capillary column. A solution of the sample (50 mL) from the reaction
mixture dissolved in CH OH (1 mL) was injected directly into the GC inlet for analysis.
ꢁ
3
1
Hydrogen (499.999%) was used as carrier gas at a constant flow of 1.0 mL min .
The column temperature was maintained at 70 C for 1 min then programmed from
ꢂ
ꢂ
ꢁ1
ꢂ
ꢂ
2
0 C min
to 300 C. The GC inlet temperature was 250 C and the detector
ꢂ
temperature was 260 C. The conversion yield was calculated by area normalization
based on phenyl acetate and formation of the phenol.
3
3
. Results and discussion
.1. Crystal structures of six complexes
Six complexes are cation–anion species with similar structures (figure 1), therefore
only the structure of
1 is analyzed in detail. Compound 1 consists of
Ni(Hdpa) (CH COO)] , a chloride and a methanol (figure 1a). Ni(II) is octahedral
þ
[
with four N donors from two Hdpa and two oxygen atoms from acetate, very
2
3
þ
different from that of [Cu(Hdpa) (CH COO)] [18]. Pyridine rings of Hdpa form
2
3
ꢂ
ꢂ
dihedral angles of 29.77(7) and 21.93(7) . The cation and anion form hydrogen
˚
bonds through N–Hꢀ ꢀ ꢀCl (with Dꢀ ꢀ ꢀA of 3.1638(19) A, Supplementary material),
resulting in a 1-D chain (figure 2). The ꢀ–ꢀ stacking interactions are observed
between pyridine rings of Hdpa with a Cg1ꢀ ꢀ ꢀCg1* (2 ꢁ x, 1 ꢁ y, 1 ꢁ z) separation of
˚
˚
3
.9335(15) A and a Cg2ꢀ ꢀ ꢀCg2* (2 ꢁ x, ꢁ y, 1 ꢁ z) separation of 3.6441(16) A (where
Cg1 and Cg2 are centroids of the N6/C16-C20 and N1/C1-C5 rings) (Supplementary
material).
Although these six structures are similar, the bond distances are somewhat different
between corresponding Ni and Co complexes (Supplementary material). The aromatic
ꢀꢁꢀ interactions in 2–4 are listed in ‘‘Supplementary material.’’ There are no ꢀ–ꢀ
interactions in 5 and 6.
3
.2. Thermal analysis
ꢂ
Complexes 1 and 2 contain methanol which is from room temperature to 280 C and
ꢂ
room temperature to 182 C, respectively. The weight losses are 6.17% and 5.71%,
respectively, consistent with calculated values of 6.07% and 6.06%. Decomposition
ꢂ
ꢂ
temperatures are 281 C and 182 C for 1 and 2. Complexes 3–6 have no solvent
ꢂ
ꢂ
ꢂ
ꢂ
molecules and their decomposition temperatures are 287 C, 217 C, 320 C, and 249 C,
respectively. The detailed information is shown in ‘‘Supplementary material.’’ The
DTAꢁTG analysis reveals that the decomposition temperatures of Ni complexes are
higher than those of corresponding cobalt complexes.

2
798
Y. Deng et al.
Figure 1. Molecular structures of six complexes with numbering schemes. Thermal ellipsoids are drawn at the
0% probability level.
3

Cation–anionic complexes
2799
Figure 1. Continued.

2
800
Y. Deng et al.
Figure 2. The 1-D hydrogen-bonding chain for 1.
Figure 3. Fluorescence spectra of the six complexes in methanol.
3.3. UV-Vis spectra
UV-Vis spectra of the complexes show similar patterns in methanol with concentration
ꢁ
5
ꢁ1
of 1.0 ꢃ 10 mol L and detailed data are listed in ‘‘Supplementary material.’’ Three
absorptions at about 205, 260, and 314 nm are assigned to the intraligand transitions of
Hdpa [19, 20]. Complex 5 has the strongest absorptions, while 6 has relatively weak
absorptions, indicating carboxylates with benzene ring and the metal ions are the main
factors for absorption strength. Pons and co-workers reported Co(II) and Ni(II)
ꢁ
3
ꢁ1
complexes have d–d transitions at 500–700 nm with concentration of 10 mol L
[
ꢁ ꢁ1
3
21, 22]. We performed all complexes at 10 mol L in methanol (Supplementary
material), but no d–d absorption was observed. Lin and Liu point out that the d–d
transitions for Co(II) complexes in general are weak and in some cases could not be
observed [23].
3
.4. Fluorescence spectra
ꢁ
5
ꢁ1
Fluorescence spectra were measured in CH OH at 1.0 ꢃ 10 mol L
at 298 K
ꢁ ¼ 310 nm). The six complexes together with the ligand have similar fluorescence
3
(
ex
emissions (figure 3). Emission peaks are at 350 nm for 1, 353 nm for 2, 350 nm for 3,
52 nm for 4, 351 nm for 5, and 352 nm for 6. These emissions are from N-donor
3

Cation–anionic complexes
2801
O
O
catalysts
OCCH3
+
HOCH3
OH + CH COCH
3
3
Scheme 1. The transesterification of methanol with phenyl acetate. The products were determined by GC
and GC-MS.
Table 2. Effects of metal on transesterification of phenyl acetate with methanol.
Conversion (%)
Catalyst
2 h
6 h
1d
2d
3d
4d
1
2
3
4
5
6
1.84
14.6
5.6
21.6
1.6
4.23
29.2
10.5
36.1
2.5
7.75
62.6
29.8
71.7
7.5
13.72
78.5
56.8
90.7
12.9
77.5
19.30
87.6
61.2
96.8
18.5
85.5
24.12
92.6
69.5
98.5
23.8
90.5
11.5
26.8
61.1
ligands, ligand-centered ꢀ–ꢀ* transition, and electron transfer from ligands to metal.
Complex 4 has the strongest emission and emission peaks of cobalt complexes are
stronger than those of nickel complexes. The ligand shows stronger absorption than
those of complexes, indicating that coordination does not enhance emission.
3
.5. Catalytic activity of the complexes
Transesterification of methanol with phenyl acetate (scheme 1) catalyzed by 1–6 under
mild conditions were investigated and the results are listed in table 2. Complexes 1–4 are
soluble in methanol and these complexes can be employed as homogeneous catalysts,
while 5 and 6 were heterogeneous catalysts due to their poor solubility in methanol.
Catalytic data show that the catalytic activities of Ni complexes are lower than those
of corresponding Co complexes (table 2), indicating that metal ions have impact on the
reaction, which was reported by Kim et al. [24]. We also find that carboxylates influence
the reaction conversion. The metal butanoate complexes have higher catalytic activities
than those of metal acetates or benzoates and 4 is the best catalyst. We further studied
the effect of quantity of the catalyst on the reaction for 4. Reaction rate increased with
ꢁ
2
ꢁ2
increase of the amount of 4. When 3.75 ꢃ 10 mmol, 7.50 ꢃ 10 mmol, and
ꢁ
2
11.25 ꢃ 10 mmol of 4 were used, the conversion is 29.1%, 36.1%, and 40.3%,
respectively, after 6 h; the conversions were all above 95% after 4 days (figure 4).
Previous report [6] showed that [Zn(Hdpa)(I )] has lower activity than cation–anion
2
species, such as [Zn(Hdpa) (NO )](NO ), but in previous work the neutral catalyst was
3
2
3
insoluble in methanol and a heterogeneous catalyst. Our complexes are all cation–anion
species. The difference of catalytic activities of 4 and 6 is small, although they are
homogeneous and heterogeneous catalysts, respectively. For Ni, the difference of the
catalytic activities between 3 and 5 are large. These results further illustrate that
the metal ion, carboxylates, and form all influence the reaction.

2
802
Y. Deng et al.
100
80
60
40
20
0
-
2
3
7
1
.75×10 mmol
-
2
.50×10 mmol
-
2
1.25×10 mmol
0
20
40
Time/h
60
80
100
Figure 4. The effect of quantity of 4 on the reaction.
4. Conclusion
Six cation–anion complexes have been synthesized and characterized. Hydrogen bonds
(
N–Hꢀ ꢀ ꢀCl) extend these complexes into 1-D chains. M–O and M–N bond lengths of Ni
complexes are systematically shorter than those of corresponding cobalt complexes.
There are ꢀ–ꢀ interactions between pyridine rings in 1–4 while there is no such
interaction in 5 and 6. The complexes were studied as catalysts in transesterification of
phenyl acetate with methanol under mild conditions. Complexes 1–4 are homogeneous
catalysts while 5 and 6 are heterogeneous due to their poor solubility in methanol.
Cobalt complexes systematically exhibit higher catalytic activities than corresponding
nickel complexes and 4 is the best catalyst. Carboxylates and metal play important roles
in the transesterification.
Supplementary material
CCDC 869286-869291 for 1–6 contain supplementary crystallographic data for this
article. These data can be obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif
Acknowledgments
This work was financially supported by the National Natural Science Foundation of
China (No. 21073157).

Cation–anionic complexes
2803
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