The role of the apical donor in the decomposition of copper(II) benzoate under DOW-phenol conditions

Article abstract of DOI:10.1002/1099-0682(200112)2001:12<3143::AID-EJIC3143>3.0.CO;2-U

The synthesis and characterization of copper(II) benzoates with the apical donors pyridine, 2-CH₃-pyridine, 2,4-(CH₃)₂-pyridine, 2,6-(CH₃)2-pyridine, 2-fluoropyridine, 2-chloropyridine, 2-bromopyridine, 3-bromopyridine, 2,5-dibromopyridine, 3,5-dibromopyridine, and aniline, starting from copper (II) benzoate, is reported. Single-crystal X-ray structures of the products with four apical ligands show the usual paddle-wheel structure of copper(II) carboxylates; in the case of aniline no paddle-wheel dicopper(II) benzoate could be isolated. The products of thermal decomposition of the pure copper(II) compounds were analyzed by HPLC, LC-MS, and GCFID, and the expected DOW-phenol products were found in all cases other than that of aniline. This supports the assumption that a paddle-wheel dicopper(II) benzoate is required for the DOW-phenol reaction. Generally, high orthoselectivities (to phenyl benzoate and phenol; the selectivity increases with increasing basicity) are obtained, in good agreement with earlier findings on the role of the base. Small but significant steric effects are observed in the series of methylated pyridine donors and the monohalogenated pyridine donors used as apical ligands; with the two dibromopyridine donors there are large steric effects and the DOW-phenol reaction is partially suppressed. With halogenated pyridine donors as apical ligands, a Cu^[I]-catalyzed process occurs, leading to dehalogenation.

Full text of DOI:10.1002/1099-0682(200112)2001:12<3143::AID-EJIC3143>3.0.CO;2-U

FULL PAPER
The Role of the Apical Donor in the Decomposition of Copper(II) Benzoate
under DOW-Phenol Conditions
Wim Buijs,[a] Peter Comba,*[b] Danny Corneli,[b] Ynze Mengerink,[a] Hans Pritzkow,[b] and
Martina Schickedanz[c]
Keywords: DOW-phenol process / Methylated pyridines / Halogenated pyridines / Pyrolysis / Paddle-wheel / Aniline
The synthesis and characterization of copper(II) benzoates
with the apical donors pyridine, 2-CH3-pyridine, 2,4-(CH3)2-
sumption that a paddle-wheel dicopper(II) benzoate is re-
quired for the DOW-phenol reaction. Generally, high ortho-
pyridine, 2,6-(CH3)2-pyridine, 2-fluoropyridine, 2-chloropyri- selectivities (to phenyl benzoate and phenol; the selectivity
dine, 2-bromopyridine, 3-bromopyridine, 2,5-dibromopyrid- increases with increasing basicity) are obtained, in good
ine, 3,5-dibromopyridine, and aniline, starting from cop- agreement with earlier findings on the role of the base. Small
per(II) benzoate, is reported. Single-crystal X-ray structures
of the products with four apical ligands show the usual
but significant steric effects are observed in the series of
methylated pyridine donors and the monohalogenated pyrid-
paddle-wheel structure of copper(II) carboxylates; in the case ine donors used as apical ligands; with the two dibromopyri-
of aniline no paddle-wheel dicopper(II) benzoate could be dine donors there are large steric effects and the DOW-
isolated. The products of thermal decomposition of the pure
copper(II) compounds were analyzed by HPLC, LC-MS, and
GCFID, and the expected DOW-phenol products were found
in all cases other than that of aniline. This supports the as-
phenol reaction is partially suppressed. With halogenated
pyridine donors as apical ligands, a Cu[I]-catalyzed process
occurs, leading to dehalogenation.
Introduction
180 °C with moist air and copper(II) to give phenyl benzo-
ate and CO2; the reduced copper(I) is reoxidized by dioxy-
gen; hydrolysis of the phenyl benzoate then yields the de-
sired phenol and benzoic acid [Equations (1)Ϫ(5)].[4]
The selective oxidation of hydrocarbons in the liquid
phase is a major challenge in fundamental and applied
research.[1Ϫ3] Generally, free-radical chain mechanisms
dominate, and only in a few cases (xylene and toluene deriv-
atives) is a high selectivity towards the corresponding acids
obtained. Various approaches have been proposed to over-
come these problems but, so far, these have led to only lim-
ited success. We have tried to avoid unselective free-radical
chain oxidation reactions by adopting an approach that
utilizes oligonuclear metal complexes in the oxygenation of
hydrocarbons. The starting point for our studies was the
DOW-phenol process. This converts benzoic acid into
phenol under copper(II) catalysis and this reaction may be
considered as a regioselective hydroxylation.[4] In the DOW-
phenol process (Scheme 1), benzoic acid is oxidized at T Ͼ
(1)
2 CuII ϩ 2 ArCOOH Ǟ ArCO2Ar ϩ 2 Hϩ ϩ CO2 ϩ 2 CuI
2 CuI ϩ 1/2 O2 ϩ 2 Hϩ Ǟ 2 CuII ϩ H2O
(2)
(3)
(4)
ArCO2Ar ϩ H2O Ǟ ArOH ϩ ArCOOH
Overall:
(5)
ArCOOH ϩ 1/2 O2 Ǟ ArOH ϩ CO2
The main reaction in the catalytic process (Scheme 1) is
the thermal decomposition of copper(II) benzoate to o-
benzoyloxybenzoic acid. Rapid decarboxylation leads to
phenyl benzoate [Equation (1)]. The amount of CO2 pro-
duced is directly proportional to the amount of copper(II)
involved in the stoichiometric decomposition and its quan-
tification can be used to study the kinetics of the process.
Phenyl benzoate is hydrolyzed with steam to yield phenol
[Equation (4)]. The overall reaction is sensitive to solvents.
In anhydrous benzoic acid solutions, the ortho-selectivity of
the benzoyloxybenzoic acid formation is only about 50%
(45% meta-benzoyloxybenzoic acid, 5% para-benzoyloxy-
benzoic acid).[5]
Scheme 1
[a]
DSM Research,
P. O. Box 18, 6160 MD Geleen, The Netherlands
[b]
Anorganisch-Chemisches Institut der Universität Heidelberg,
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax: (internat.) ϩ 49-(0)6221/546617
E-mail: comba@akcomba.oci.uni-heidelberg.de
[c]
Organisch-Chemisches Institut der Universität Heidelberg,
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Eur. J. Inorg. Chem. 2001, 3143Ϫ3149
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ1948/01/1212Ϫ3143 $ 17.50ϩ.50/0
3143

W. Buijs, P. Comba, D. Corneli, Y. Mengerink, H. Pritzkow, M. Schickedanz
FULL PAPER
Table 1. Overview of the results of the thermal decomposition of copper(II) benzoates with substituted pyridines and aniline at 230 °C
with various apical ligands
Apical donor
Conversion[a]
(%)
DOW Phenol product (%)[b]
Reduced
(%)[b]
Benzene
(%)[c]
ortho
meta
para
pyridine
40.9
12.4
6.6
99.9
98.5
97.8
95.7
93.9
89.2
94.8
95.1
98.1
66.7
99.2
0.1
1.3
1.8
3.5
5.2
5.6
2.7
2.5
1.3
31.0
0.8
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
4.5
1.4
14.3
3.3[f]
12.0[g]
Ϫ
Ϫ
Ϫ
1.3
4.0
8.8
Ϫ
Ϫ
Ϫ
2-CH3-pyridine
2,4-(CH3)2-pyridine
2,6-(CH3)2-pyridine
aniline
0.2
0.4
0.8
0.9
5.2
2.5
2.4
0.6
2.3
Ϫ
3.8
0.7[d]
17.7
31.4
21.5
59.3
4.1
2-F-pyridine[e]
2-Cl-pyridine
2-Br-pyridine
3-Br-pyridine
2,5-Br2-pyridine
3,5-Br2-pyridine
Ϫ
Ϫ
11.6
[a]
[b]
[c]
With respect to copper benzoate. Ϫ Reduced products in mol % copper benzoate (dimer). Ϫ mol % relative to the total benzoic
acid in the starting material. Ϫ [d] Most likely due to the salicylic acid reaction; aniline was completely converted to N-phenyl benzamide
(HPLC and LC-MS). Ϫ [e] Results obtained at 250 °C; no reaction occurred at 230 °C. Ϫ [f] Products: 2-benzoyloxypyridine, 2-hydroxypyr-
[g]
idine (approx. 1:1). Ϫ Products: pyridine, 3-benzoyloxypyridine, 3-hydroxypyridine (approx. 2:2:1.5).
dines follows the order pyridine Ͻ 2-methylpyridine Ͻ 2,4-
dimethylpyridine ഠ 2,6-dimethylpyridine, both the conver-
Results and Discussion
sion and the ortho-selectivity might have been expected to
increase, as was observed with MgII benzoate.[5] However,
the pyridine donors coordinate to CuII whereas MgII
benzoate merely acts as a simple base. The electronic effect
of the pyridine donors influences the thermal stability and
hence the reactivity: the more electron-donating the pyri-
dine donor is, the less effectively CuII will be able to abstract
electrons from benzoate. If, however, the electrophile re-
sulting from a benzoate is formed, the steric effect of the
methylated pyridine donors may slightly decrease the prob-
ability of an ortho-attack at the corresponding pyridinium
benzoate.
The halogenated pyridine donors constitute another in-
teresting series. Unfortunately, their conversion cannot be
compared directly with that of the methylated pyridine
donors because they are also subject to reduction, which
produces additional CuII.[6] This reaction seems to be com-
parable to the reduction of halogenated hydrocarbons.[7]
The scope and limitations of the catalytic reduction are re-
ported separately.[6]
Thermal Decomposition of Copper(II) Benzoate with
Substituted Pyridine Donors or Aniline at the Apical Sites
of the Paddle-Wheel Dicopper(II) Compounds
The influence of substituted pyridine donors bearing
electron-withdrawing or electron-donating groups was
studied to investigate the role of the donors at the apical
sites of the paddle-wheel dicopper(II) complexes in the
DOW-phenol process (see Scheme 2). Copper(II) benzoate
with various pyridine donors (different substitution pat-
terns) and with aniline was pyrolyzed in a sealed silica tube
(stoichiometric reaction; see Exp. Sect.). Table 1 summar-
izes the identified DOW-phenol products recovered follow-
ing the pyrolyses of the copper(II) compounds.
The use of 2-fluoropyridine did not lead to any reaction
at 230 °C. However, at 250 °C a fast substitution reaction
of benzoate on the fluoride was observed prior to the
DOW-phenol reaction. The resulting ortho-selectivity of ap-
proximately 89% cannot be assigned to 2-fluoropyridine,
but mainly to 2-benzoyloxypyridine and HF instead.[6]
The other halogenated pyridine donors show ortho-select-
ivities of 66.7% (2,5-dibromopyridine), 94.8% (2-chloropyr-
Scheme 2
An important observation is that all the apical donors idine), 95.1% (2-bromopyridine), 98.1% (3-bromopyridine),
studied show high ortho-selectivities, except for 2,5-di- and 99.2% (3,5-dibromopyridine). We believe that in these
bromopyridine. This is in line with earlier observations on cases, both electronic and steric effects play a similar role
the effect of base in the DOW-phenol reaction.[5] In the to that observed with the methylated pyridine donors, albeit
series pyridine, 2-methylpyridine, 2,4-dimethylpyridine, and to a less pronounced extent. Despite the increasing size of
2,6-dimethylpyridine, both the conversion and the ortho-se- the substituents, a chloro or a bromo substituent in the 2-
lectivity decrease, from 40.9% to 3.8% and from 99.9% to position of the pyridine has a similar effect on the ortho-
95.7%, respectively. Since the basicity in this series of pyri- selectivity as two methyl groups in the 2,6-positions. This
3144
Eur. J. Inorg. Chem. 2001, 3143Ϫ3149

Decomposition of Copper(II) Benzoate under DOW-Phenol Conditions
FULL PAPER
might be due to the fact that only one side of the benzoate
in a pyridinium benzoate is accessible for the coupling reac-
tion. Moreover, a bromo substituent in the 3-position of
pyridine has a similar effect as a methyl group in the 2-
position. Comparing the pyridine donors with two bromo
substituents in the 2,5- and 3,5-positions, a large steric ef-
fect on the ortho-selectivity due to the second bromine in
the 2-position is evident.
For the series of monohalogenated pyridine donors, the
relative amount of reduced material (given as mol % of ad-
ditional copper benzoate; see Table 1) is comparatively
small with respect to the observed conversion, but it is high
for the dibromopyridine donors. For the latter, this correl-
ates with the observed conversion ratios. The total conver-
sion may therefore be interpreted as follows. The steric de-
mand of dibromo-substituted pyridine donors in the apical
positions leads to a slow DOW-phenol reaction; the re-
sulting Cu[I] leads to a comparably high reduction and sub-
stitution rate to yield reduced and substituted pyridine
donors and CuII; the DOW-phenol reaction then also pro-
ceeds with pyridine and benzoate-substituted pyridines. The
observed selectivities for the two dibromopyridine ligands
support this. With 3,5-dibromopyridine, a comparatively
large amount of pyridine is formed and the observed ortho-
selectivity is 99.2%, similar to that seen with pyridine itself.
With 2,5-dibromopyridine, the major product is a pyridine
substituted at the 2-position and reduced at the 5-position.
This secondary ligand still leads to substantial steric hind-
rance, and the resulting ortho-selectivity of 66.7% is close
to that observed for CuII benzoate in the absence of base
and water.[5]
Figure 1. ORTEP[12] plot of [Cu2(µ-O2CϪC6H5)4(3,5-BrϪ
C5H3N)2] (compound 1)
case of 2-fluoropyridine, the elevated temperature might be
the most important factor.
Molecular Structures of Copper(II) Benzoates with Apical
Donors
For all the apical donors studied, except for aniline, di-
copper(II) species with stoichiometries in agreement with
the expected paddle-wheel structures were isolated. The X-
ray crystal structures of the four structurally characterized
dicopper(II) benzoates (see Figure 1, Table 2) are essentially
identical and, as expected for copper(II), do indeed repres-
ent paddle-wheel compounds. They consist of centrosym-
metric dicopper(II) units, in which each copper(II) ion is
coordinated by four oxygen atoms of the four bridging
carboxylate groups (see Figure 1, Scheme 2, and Table 2).
The apical donor aniline blocks the DOW-phenol reac-
tion completely. Phenyl benzoate was not detected. Instead,
the quantitative formation of N-phenyl benzamide was ob-
served. Since this co-elutes with phenyl benzoate in the
HPLC procedure used, LC-MS, including a peak purity
check, was applied to enable a quantitative determination.
On adding pyridine donors to a CuII benzoate solution in
acetone, the paddle-wheel structure remained intact,
whereas with aniline a distinct color change was observed
and no paddle-wheel dicopper(II) compound could be isol-
ated. The failure to observe DOW-phenol chemistry with
aniline supports the interpretation that paddle-wheel struc-
tures of copper(II) benzoate are a requirement for the
DOW-phenol reaction.[5]
˚
The copperϪcopper distances range from 2.626 A to 2.678
˚
A. The angle between the two planes through the two cop-
per(II) centers and two benzoates ranges from 88.92° to
89.80°. The two pyridine rings are parallel, except in com-
pound 2, where their ring planes intersect at an angle of
79.23°. No paddle-wheel-type copper(II) benzoate could be
isolated with aniline. Aniline seems to destroy the cop-
per(II) benzoate fragment and this leads to the formation
of unidentified mononuclear copper(II) species.
CO2 Measurements
With three donors, namely 2,6-dimethylpyridine, aniline,
and 2-fluoropyridine, benzene was detected as an additional
The pyrolyses of copper(II) benzoate in sealed silica tubes
product of the stoichiometric DOW-phenol reactions. Ben- in the absence of oxygen, with all the pyridine derivatives
zene is a common by-product in the DOW-phenol process, used in this study, produce CO2. The cumulative formation
but its formation is generally attributed to Cu[I], reaction at of CO2 as a function of time with copper(II) benzoate alone
the reactor wall, and high temperatures (Ն 250 °C). How- reaches a constant value of approximately 66% with respect
ever, in the three cases where benzene was found (Table 1), to the stoichiometrically expected amount (Figure 2; ap-
[Cu[I]] is low and no metal reactor wall was present. With proximately 50% o-selectivity in the formation of the
2,6-dimethylpyridine and aniline, the reaction temperature benzoyloxybenzoic acid, see above[5]). With the methylated
was as low as 230 °C. Therefore, apart from in the case of and halogenated pyridine donors, the production of CO2
2-fluoropyridine, our interpretation of the benzene produc- increases significantly [see Figure 2; with pyridine 109% and
tion is that a relatively strong base must be present.[8] In the with 3-bromopyridine 108% was obtained; 100% CO2
Eur. J. Inorg. Chem. 2001, 3143Ϫ3149
3145

W. Buijs, P. Comba, D. Corneli, Y. Mengerink, H. Pritzkow, M. Schickedanz
FULL PAPER
˚
Table 2. Selected distances [A] and angles [deg.] for tetrakis(benzoato-µ-O,OЈ)bis(3,5-dibromopyridine)dicopper(II) (compound 1),
tetrakis(benzoato-µ-O,OЈ)bis(3-bromopyridine)dicopper(II) (compound 2), tetrakis(benzoato-µ-O,OЈ)bis(2,5-dibromopyridine)dicop-
per(II) (compound 3), and tetrakis(benzoato-µ-O,OЈ)bis(2-chloropyridine)dicopper(II) (compound 4)
corresponds to the stoichiometric amount of copper(I) gen- dine leads to an even larger excess of CO2, although no
erated in one reduction cycle (see Scheme 1)].
elemental copper could be found after the reaction. This
There are various explanations for this behavior. An im- may be related to the detection of reduced pyridines by
portant observation is that after the pyrolysis with pyridine, HPLC. After the usual decomposition of copper(II) benzo-
elemental copper is found in the reaction vessel. This indic- ate, copper(I) is re-oxidized to copper(II) by the halopyrid-
ates that copper(I), formed during the reduction of the hal- ines [Equation (7)]. The complete reduction of halogenated
ogenated pyridines and the ensuing DOW-phenol process, pyridine derivatives in a catalytic reaction is prohibited by
undergoes disproportionation to copper(0) and copper(II) the precipitation of copper(I) halides.[7] These processes are
[Equation (6)]. The resulting copper(II) leads to additional described in detail in a separate publication.[6]
CO2 production [Equation (1) and Scheme 1].
2 CuI Ǟ Cu0 ϩ CuII
(6)
(7)
Moreover, pyridine catalyzes the decarboxylation of aro-
matic acids.[8] The copper(II) compound with 3-bromopyri-
3146
Eur. J. Inorg. Chem. 2001, 3143Ϫ3149

Decomposition of Copper(II) Benzoate under DOW-Phenol Conditions
FULL PAPER
ate (3.71 g, 5.72 mmol) in dry acetone (100 mL). The reaction mix-
ture was heated at 60 °C for 24 h. The solvent was then removed
under reduced pressure, and the residue was washed with petroleum
ether (30 mL) and dried in vacuo. Yield: 2.46 g (51.25%). Ϫ IR
˜
(KBr): ν ϭ 3062 [ν(CϪH)], 1626 [ν(CϭN)], 1616 [ν(CϭC)], 1572
[νasym. (CϭO, COOϪ)], 1406 [νsym. (CϭO, COOϪ)], 1270 [ν(aryl-
Cl)] cmϪ1. Ϫ C38H28Cu2Cl2N2O8 (838.65): calcd. C 54.42, H 3.37,
N 3.34; found C 54.48, H 3.50, N 3.13.
[Cu2(µ2-O2C؊C6H5)4(2-Br؊C5H4N)2]: 2-Bromopyridine (2.70 g,
17.09 mmol) was added to a solution of copper(II) benzoate
(5.00 g, 7.72 mmol) in dry acetone (100 mL). The reaction mixture
was heated to 60 °C for 24 h. The solvent was then removed under
reduced pressure, and the residue was washed with petroleum ether
(30 mL) and dried in vacuo. Yield: 4.7 g (65.64%). Ϫ IR (KBr):
ν ϭ 3063 [ν(CϪH)], 1625 [ν(CϭN)], 1600 [ν(CϭC) ϭ ], 1570 [νasym.
(CϭO, COOϪ)], 1410 [νsym. (CϭO, COOϪ)], 1070 [ν(aryl-Br)] ϭ
cmϪ1. Ϫ C33H24BrCu2NO8 (769.55): calcd. C 51.50, H 3.14, N
1.82, Br 10.38; found C 51.52, H 3.46, N 1.84, Br 10.11.
˜
Figure 2. Cumulative CO2 formation during the pyrolysis of vari-
ous copper(II) benzoates with apical donors (stoichiometric reac-
tion under argon; for conditions, see Exp. Sect.)
[Cu2(µ2-O2C؊C6H5)4(2-F؊C5H4N)2]: 2-Fluoropyridine (1.00 g,
10.30 mmol) was added to a solution of copper(II) benzoate
(2.34 g, 5.16 mmol) in dry acetone (50 mL). The reaction mixture
was heated at 60 °C for 24 h. The solvent was then removed under
reduced pressure, and the residue was washed with petroleum ether
(30 mL) and dried in vacuo. Yield: 2.53 g (53.73%). Ϫ IR (KBr):
ν˜ ϭ 3070 [ν(CϪH)], 1628 [ν(CϭN)], 1610 [ν(CϭC)], 1574 [νasym.
Experimental Section
Materials: Copper(II) benzoate was obtained from DSM and was
used without purification. All other compounds were purchased
from Sigma or Aldrich and were used without further purification.
The purity ranges were 97Ϫ99%.
(CϭO, COOϪ)], 1404 [νsym. (CϭO, COOϪ)], 1270 [ν(aryl-F)] cmϪ1
.
Ϫ C38H28Cu2F2N2O8 (805.74): calcd. C 56.64, H 3.50, N 3.48;
found C 56.58, H 3.87, N 3.10.
Syntheses of the Copper(II) Compounds
[Cu(µ2-O2C؊C6H5)2(H2N؊C6H5)]n: To a suspension of copper(II)
benzoate (1.00 g, 1.54 mmol) in petroleum ether (30 mL) was added
aniline (0.29 g, 3.11 mmol). After 24 h, the green precipitate was
collected by filtration, washed with Et2O, and dried in vacuo. Yield:
[Cu2(µ2-O2C؊C6H5)4(3,5-Br؊C5H3N)2] (1): 3,5-Dibromopyridine
(1.00 g, 4.22 mmol) was added to a solution of copper(II) benzoate
(1.37 g, 2.12 mmol) in dry acetone (50 mL). After 24 h, the tur-
quoise-green precipitate was collected by filtration, washed with
˜
1.10 g (80.65%). Ϫ IR (KBr): ν ϭ 3312 [ν(NϪH)], 3066 [ν(CϪH)],
1596 [ν(CϭC)], 1548 [νasym. (CϭO, COOϪ)], 1490 [νsym. (CϭO,
COOϪ)] cmϪ1. Ϫ C40H34Cu2N2O8 (797.81): calcd. C 60.22, H 4.30,
N 3.51; found C 59.16, H 4.59, N 3.72.
˜
Et2O, and dried in vacuo. Yield: 1.55 g (67.4%). Ϫ IR (KBr): ν ϭ
3060 [ν(CϪH)], 1626 [ν(CϭN)], 1600 [ν(CϭC)], 1574 [νasym. (Cϭ
O, COOϪ)], 1406 [νsym. (CϭO, COOϪ)], 1022 [ν(aryl-Br)] cmϪ1. Ϫ
C38H26Br4Cu2N2O8 (1085.34): calcd. C 42.03, H 2.41, N 2.58;
found C 42.09, H 2.61, N 2.51.
[Cu2(µ2-O2C؊C6H5)4(C5H5N)2]: Pyridine (1.22 g, 15.42 mmol) was
added to a solution of copper(II) benzoate (5.00 g, 7.72 mmol) in
dry acetone (100 mL). The reaction mixture was heated at 60 °C
for 24 h. The green precipitate was then collected by filtration,
washed with EtOH, and dried in vacuo. Yield: 3.6 g (60.60%). Ϫ
[Cu2(µ2-O2C؊C6H5)4(3-Br؊C5H4N)2]
(2):
3-Bromopyridine
(1.50 g, 9.81 mmol) was added to a solution of copper(II) benzoate
(2.05 g, 3.17 mmol) in dry acetone (50 mL). The reaction mixture
was heated at 60 °C for 24 h. The turquoise-green precipitate was
then collected by filtration, washed with Et2O, and dried in vacuo.
Yield: 2.13 g (72.4%). Ϫ IR (KBr): ν˜ ϭ 3066 [ν(CϪH)], 1628 [ν(Cϭ
N)], 1616 [ν(CϭC)], 1572 [νasym. (CϭO, COOϪ)], 1402 [νsym. (Cϭ
O, COOϪ)], 1028 [ν(aryl-F)] cmϪ1. Ϫ C38H28Cu2Br2N2O8 (927.54):
calcd. C 49.21, H 3.04, N 3.02, Br 17.23; found C 49.19, H 3.37,
N 2.87, Br 16.47.
˜
IR (KBr): ν ϭ 3063 [ν(CϪH)], 1628 [ν(CϭN)], 1600 [ν(CϭC)],
1572 [νasym. (CϭO, COOϪ)], 1405 [νsym. (CϭO, COOϪ)] cmϪ1. Ϫ
C38H30Cu2N2O8 (769.76): calcd. C 59.29, H 3.93, N 3.64; found C
59.05, H 4.01, N 3.43.
[Cu2(µ2-O2C؊C6H5)4(2-CH3؊C5H4N)2]: 2-Methylpyridine (1.44 g,
15.44 mmol) was added to a solution of copper(II) benzoate
(5.00 g, 7.72 mmol) in dry acetone (100 mL). The reaction mixture
was heated at 60 °C for 24 h. The green precipitate was then col-
lected by filtration, washed with Et2O, and dried in vacuo. Yield:
3.55 g (57.63%). Ϫ IR (KBr): ν˜ ϭ 3066 [ν(CϪH)], 2932 [ν(CϪH,
CH3)], 1630 [ν(CϭN)], 1600 [ν(CϭC)], 1574 [νasym. (CϭO,
COOϪ)], 1404 [νsym. (CϭO, COOϪ)] cmϪ1. Ϫ C40H34Cu2N2O8
(797.81): calcd. C 60.22, H 4.30, N 3.51; found C 60.27, H 4.38,
N 3.46.
[Cu2(µ2-O2C؊C6H5)4(2,5-Br؊C5H3N)2] (3): 2,5-Dibromopyridine
(2.00 g, 8.44 mmol) was added to a solution of copper(II) benzoate
(2.74 g, 4.43 mmol) in dry acetone (50 mL). The reaction mixture
was heated at 60 °C for 24 h. The solvent was then removed under
reduced pressure, and the residue was washed with petroleum ether
(30 mL) and dried in vacuo. Yield: 2.59 g (56.3%). Ϫ IR (KBr):
˜
ν ϭ 3063 [ν(CϪH)], 1625 [ν(CϭN)], 1600 [ν(CϭC)], 1570 [νasym.
(CϭO, COOϪ)], 1410 [νsym. (CϭO, COOϪ)], 1070 [ν(aryl-Br)]
cmϪ1. Ϫ C38H26Br4Cu2N2O8 (1085.34): calcd. C 42.03, H 2.41, N
2.58, Br 29.45; found C 42.48, H 2.72, N 2.57, Br 28.50.
[Cu2(µ2-O2C؊C6H5)4{2,4-(CH3)2؊C5H3N}2]: 2,4-Dimethylpyrid-
ine (1.65 g, 15.44 mmol) was added to a solution of copper(II)
benzoate (5.00 g, 7.72 mmol) in dry acetone (100 mL). The reaction
[Cu2(µ2-O2C؊C6H5)4(2-Cl؊C5H4N)2]
(4):
2-Chloropyridine mixture was heated at 60 °C for 24 h. The green precipitate was
(2.00 g, 17.61 mmol) was added to a solution of copper(II) benzo- then collected by filtration, washed with Et2O, and dried in vacuo.
Eur. J. Inorg. Chem. 2001, 3143Ϫ3149
3147

W. Buijs, P. Comba, D. Corneli, Y. Mengerink, H. Pritzkow, M. Schickedanz
FULL PAPER
Table 3. Crystallographic data for tetrakis(benzoato-µ-O,OЈ)bis(3,5-dibromopyridine)dicopper(II) (compound 1), tetrakis(benzoato-µ-
O,OЈ)bis(3-bromopyridine)dicopper(II) (compound 2), tetrakis(benzoato-µ-O,OЈ)bis(2,5-dibromopyridine)dicopper(II) (compound 3),
and tetrakis(benzoato-µ-O,OЈ)bis(2-chloropyridine)dicopper(II) (compound 4)
˜
Yield: 2.60 g (40.76%). Ϫ IR (KBr): ν ϭ 3062 [ν(CϪH)], 2928 For reversed-phase HPLC, the black solids produced were dis-
[ν(CϪH, CH3)], 1632 [ν(CϭN)], 1598 [ν(CϭC)], 1574 [νasym. (Cϭ
solved in acetonitrile (2 mL) and then injected into an HP 1090
O, COOϪ)], 1402 [νsym. (CϭO, COOϪ)] cmϪ1. Ϫ C42H38Cu2N2O8 chromatograph with a Nucleosil 120Ϫ5 C18 column (500 ϫ 4 mm)
(825.86): calcd. C 61.08, H 4.64, N 3.39; found C 60.97, H 4.62, at 50 °C. The products were eluted with a gradient made up of
N 3.24.
different mixtures of eluents A and B [eluent A: 1  H3PO4
(45 mL), conc. acetic acid (2 mL), and 1  NaOH (35 mL) were
added to water (1500 mL) and the pH of the solution was adjusted
to 3.2 with 1  NaOH; after the addition of acetonitrile (200 mL),
the mixture was made up with water to give 2000 mL of eluent A;
eluent B: 1  H3PO4 (20 mL), conc. acetic acid (2 mL), and 1 
NaOH (60 mL) were added to water (60 mL) and the pH of the
solution was adjusted to 6.6 with 1  NaOH; after the addition of
acetonitrile (1200 mL), the mixture was made up with water to give
2000 mL of eluent B]. A DAD (L-3000 Hitachi) was used for detec-
tion at 254 nm.
[Cu2(µ2-O2C؊C6H5)4{2,6-(CH3)2؊C5H3N}2]: 2,6-Dimethylpyrid-
ine (1.65 g, 15.44 mmol) was added to a solution of copper(II)
benzoate (5.00 g, 7.72 mmol) in dry acetone (100 mL). The reaction
mixture was heated at 60 °C for 24 h. The solvent was then removed
under reduced pressure, and the residue was washed with petroleum
ether (30 mL) and dried in vacuo. Yield: 3.24 g (58.38%). Ϫ IR
˜
(KBr): ν ϭ 3062 [ν(CϪH)], 2928 [ν(CϪH, CH3)], 1632 [ν(CϭN)],
1598 [ν(CϭC)], 1574 [νasym. (CϭO, COOϪ)], 1402 [νsym. (CϭO,
COOϪ)] cmϪ1. Ϫ C35H29Cu2NO8 (718.52): calcd. C 58.50, H 4.68,
N 1.95; found C 58.69, H 4.63, N 1.98.
GC analyses were performed using a HewlettϪPackard series 5890
gas chromatograph, equipped with a 30 m fused silica Megabore
column (G. & W. Scientific) with a 5 µm DBI stationary phase. The
products were identified with an FID detector; nitrogen was used
as the carrier gas. Ϫ Elemental analyses were obtained from the
microanalytical laboratory of the chemical institutes of the Univer-
sity of Heidelberg. Infrared spectra (KBr pellets) were measured
with a PerkinϪElmer 16PC FT-IR instrument.
Pyrolyses: The pure copper(II) benzoate salts with the apical
donors (150 mg in each case) were heated for 7 h at 230 °C in sealed
silica tubes. The tubes were filled under argon. Since in the case of
copper(II) benzoate with 2-fluoropyridine no reaction occurred at
230 °C, this experiment was repeated at 250 °C. After cooling to
ambient temperature, the tubes were opened and the products were
analyzed by HPLC. In the case of the halogenated pyridines, the
products were also analysed by LC-MS.
X-ray Crystallography: Crystallographic data are presented in
Table 3; all structural data have been deposited with the Cambridge
Crystallographic Data Centre (CCDC) as supplementary publica-
tion nos. CCDC-152937Ϫ152940. Copies of the data can be ob-
tained free of charge on application to The Director, CCDC, 12
Positive-ion ESI-MS data were obtained on an HP1100 quadrupole
LC-MS system (Agilent Technologies, Waldbronn, Germany).
Mass spectra were obtained in full scan mode from m/z ϭ 50Ϫ1000
amu at a fragmentor voltage of 70 V and a capillary voltage of
3000 V. The drying gas flow was 10 L/min and the drying gas tem- Union Road, Cambridge CB2 1EZ, U.K. [Fax: (internat.) ϩ44
perature was 350 °C.
(1223) 336-033; E-mail: deposit@ccdc.cam.ac.uk]. Crystal data
3148
Eur. J. Inorg. Chem. 2001, 3143Ϫ3149

Decomposition of Copper(II) Benzoate under DOW-Phenol Conditions
FULL PAPER
B. Meunier (Ed.), Metal-Oxo and Metal-Peroxo Species in
Catalytic Oxidations, Structure and Bonding, Vol. 97, Springer-
Verlag, Berlin/Heidelberg, 1999.
W.W. Kaeding, A. T. Shulgin, J. Org. Chem. 1962, 27, 3551.
W. Buijs, J. Mol. Cat. A: Chem. 1999, 146, 237.
W. Buijs, P. Comba, D. Corneli, Y. Mengerink, R. Peters, Eur.
J. Inorg. Chem. 2001, 3151Ϫ3154, see following article in this
issue.
[3]
were collected on a Bruker AXS SMART 1000 diffractometer with
a CCD area detector (Mo-Kα radiation, graphite monochromator,
[7]
˚
λ ϭ 0.71073 A) at Ϫ100 °C, using the SMART suite of programs.
The reflection intensities were integrated using SAINT and cor-
rected for absorption using SADABS.[9,10] The structures were
solved by direct methods and refined by full-matrix least-squares
methods based on F2 with all reflections, using the SHELXTL pro-
grams.[11]
[4]
[5]
[6]
[7]
[8]
[9]
W. Buijs, Cat. Today 1996, 27, 159.
L. Artok, H. H. Schobert, J. Anal. Appl. Pyr. 2000, 54, 215.
SMART and SAINT NT V5.0, Area control and integration
software, Bruker AXS, Madison, Wisconsin, 1999.
G. M. Sheldrick, SADABS, Program for scaling and correcting
of area detector data, University of Köln, 1998.
G. M. Sheldrick, SHELXTL V5.1, Bruker AXS, Madison,
USA, 1998.
Acknowledgments
Financial support by DSM Research, Geleen, The Netherlands is
gratefully acknowledged.
[10]
[11]
[12]
[1]
R. A. Sheldon, J. K. Kochi, Metal-Catalyzed Oxidations of Or-
C. K. Johnson, ORTEP: A Thermal Ellipsoid Plotting Program,
Oak Ridge National Laboratory, 1965.
ganic Compounds, Academic Press, New York, 1981.
B. Cornils, W. A. Hermann, Applied Homogeneous Catalysis
[2]
with Organometallic Compounds, Wiley-VCH, Weinheim, New
York, 2000.
Received August 1, 2001
[I01296]
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3149