Inorganic Chemistry
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diversity of Cu-containing enzymes with a well-recognized
was used for running ESI-MS(±) spectra (typically, diluted solutions
2
−4
−3
of 1−4 were used, < 10 M). EA (elemental analyses) were carried
catalytic function.
Within the different copper enzymes, the
out on a PerkinElmer PE 2400 Series II analyzer (Laboratory of
Analyses, IST). In catalytic studies, GC (gas chromatography)
analyses were performed on an Agilent Technologies 7820A series
gas chromatograph (carrier gas, helium; detector, flame ionization;
capillary column, BP20/SGE, 30m × 0.22 mm × 0.25 μm). A detailed
description of experimental procedures for oxidation and carbox-
particulate methane monooxygenase contains multicopper
active sites and represents an especially interesting example
given its ability to catalyze the hydroxylation of virtually inert
19,20
substrates such as methane and other alkanes.
On the other hand, saturated hydrocarbons constitute the
main components of petroleum and natural gas, but their
direct, selective, and efficient transformation to value-added
oxidation products (e.g., alcohols, ketones, carboxylic acids) is
General Synthetic Procedure for 1−4. An aqueous solution of
21−23
Cu(NO ) ·3H O (1 mmol, 0.1 M, 10 mL) was mixed with N,N-bis(2-
limited owing to their exceptional inertness.
However, the
3
2
2
hydroxyethyl)-2-aminoethanesulfonic acid (H bes, 1 mmol, 213 mg)
3
use of appropriate copper-based catalytic systems and oxidizing
agents along with well-tuned reaction parameters can provide
attractive and efficient protocols for the functionalization of
under stirring in air at room temperature, producing the reaction
solution A. In a small glass vial, benzenecarboxylic acid [4-
methoxybenzoic acid for 1 and 3 (Hfmba, 1 mmol, 138 mg) or 4-
chlorobenzoic acid for 2 and 4 (Hfcba, 1 mmol, 157 mg)] was
1
3,14,24,25
alkanes under mild conditions.
Despite intensive
research on the design and catalytic application of biomimetic
or bioinspired copper coordination compounds for hydro-
carbon functionalization, the majority of reported catalytic
systems still represent a number of limitations, either from the
activity, selectivity, sustainability, and substrate scope view-
point or they require the synthesis of expensive ligands and the
dissolved in an aqueous NH OH [25% m/m, 6 mmol for 1 and 3, 4
4
mmol for 2 and 4] to produce the reaction solution B. Then, B was
slowly added to A under constant stirring to give the reaction mixture
C. This mixture was stirred for an additional 25 min and then filtered
off and left in an open glass vial to slowly evaporate in the air. Blue
crystals of 1 and 2 were formed in ∼1 week after partial evaporation
of the filtrate. These were isolated manually after decanting the
reaction solution and dried in air to give the products 1 and 2 (first
product in each reaction; ∼30% yield based on copper(II) nitrate).
The remaining mother liquors were left in other glass vials for further
evaporation, producing green crystals of 3 and 4 in 1−2 weeks. These
were isolated manually and dried in the air to furnish the products 3
and 4 (second product of each reaction; ∼40% yield based on
copper(II) nitrate). In each reaction, the total yields of 1 + 3 or 2 + 4
were ∼70% based on copper(II) nitrate. The bulk samples of 3 and 4
were not washed to preserve crystallinity and thus may contain a
26−28
use of unfavorable reaction conditions.
On the basis of the above discussion and following our main
research interest in the design and catalytic application of new
copper(II) coordination compounds derived from simple,
commercially available and low-cost organic building
2
9−31
blocks,
in the present study we have focused our attention
2
+
on a multicomponent reaction system composed of Cu ions,
a main aminoalcohol building block (H bes) and a supporting
3
benzenecarboxylic acid ligand. N,N-bis(2-hydroxyethyl)-2-
minor amount of absorbed NH OH. In all cases, the obtained
4
aminoethanesulfonic acid (H bes) is a popular biological
3
3
2,33
products included single crystals, the portions of which were not dried
biobuffer
but remains poorly explored as a ligand in
and subjected to X-ray diffraction.
coordination chemistry despite its water solubility and the
−1
[
Cu (μ -OH) (μ-fmba) (fmba) (H O) ] (1). IR (KBr, cm ):
3
3
2
2
2
2
2 n
presence of three different types of sites for potential
3
238 (m br) ν(OH/H O), 2961 (w) ν(CH), 1603 (s) δ(OH/H O),
2
2
3
4
coordination (−N/−OH/−SO H). Thus, the two principal
1590 (vs) ν (COO), 1532 (s) ν (COO), 904 (m), 851 (m), 828 (w),
3
a
s
s
objectives of this study have been (1) the synthesis and
characterization of new copper(II) coordination compounds
from a Cu −H bes−benzenecarboxylic acid−NH OH−H O
782 (m), 733 (m), 668 (w). Anal. Calcd for 1, Cu C H O (MW
3 32 34 16
865.2): C, 44.42%; H, 3.96%. Found: C, 44.40%; H, 3.97%. ESI−
2
+
MS(±) (H O), selected fragments with relative abundance >5%,
2
3
4
2
+
MS(+), m/z: 145 (100%) [Cu (OH)] . MS(−), m/z: 418 (60%)
2
system and (2) the application of the synthesized products as
catalysts for the oxidative transformation of saturated hydro-
carbons under mild conditions to obtain different types of
important products such as carboxylic acids, ketones, and
alcohols.
−
−
[
[
Cu(fmba) (OH)(H O) ] , 365 (40%) [Cu(fmba) ] , 329 (85%)
2 2 2 2
−
−
Cu (fmba) (OH) (H O)] , 151 (10%) [fmba] .
2
2
2
2
−1
[
Cu (μ-OH) (μ-fcba) ] (2). IR (KBr, cm ): 3216 (m br) ν(OH/
2 2 2 n
H O), 2879 (w) ν(CH), 1600 (s) δ(OH/H O), 1587 (vs)
2
2
ν (COO), 1540 (s) ν (COO), 1012 (m), 904 (m), 878 (w), 849
as
s
We thus report the self-assembly formation, characterization,
crystal structures, and catalytic use of four new copper(II)
products, namely, the 1D coordination polymers [Cu (μ -
(m), 827 (m), 785 (w), 762 (w), 668 (w). Anal. Calcd for 2,
Cu C H O Cl (MW 472.2): C, 35.61%; H, 2.13%; found: C,
2
14 10
6
2
35.59%; H, 2.14%. ESI−MS(±) (H
O), selected fragments with
2
3
3
relative abundance >5%, MS(+), m/z: 750 (100%) [Cu (fcba) +
OH) (μ-fmba) (fmba) (H O) ] (1) and [Cu (μ-OH) (μ-
2
4
2
2
2
2
2 n
2
2
+
+
+
H] , 535 (24%) [Cu (OH) (fcba) ] , 300 (16%) [Cu (OH)(fcba)] .
3
2
2
2
fcba) ] (2) as well as the discrete tetracopper(II) rings
2
n
−
MS(−), m/z: 618 (22%) [Cu (fcba) (OH) + H O] , 593 (38%)
4
2
2
2
[
Cu (μ-Hbes) (μ-H bes)(μ-fmba)]·2H O (3) and [Cu (μ-
4 3 2 2 4
−
−
−
[
Cu (fcba) ] , 281 (30%) [Cu (fcba)] , 155 (22%) [fcba] .
2 3 2
Hbes) (μ-H bes)(μ-fcba)]·4H O (4). These products were
easily assembled in an aqueous medium and applied as efficient
−1
3
2
2
[
Cu (μ-Hbes) (μ-H bes)(μ-fmba)]·2H O (3). IR (KBr, cm ):
4 3 2 2
3
057 (m br) ν(OH/H O), 2900 (w) ν(CH), 1607 (s) δ(OH/H O),
2
2
catalysts for the oxidation and carboxylation of gaseous
1
591 (vs) ν (COO), 1569 (s) ν (COO), 1307 (s) ν(C−C), 1198
as
s
(
propane) and liquid (C −C cycloalkanes) saturated hydro-
(vs) ν(C−N), 1041 (vs) ν(C−S), 934 (m), 893 (m), 884 (w), 824
(m), 769 (w), 720 (m), 696 (w), 682 (w). Anal. Calcd for 3 +
5
8
carbons.
1
5
.5NH OH, Cu C H N O26.5S4 (MW 1339.9): C, 28.68%; H,
4 4 32 71.5 5.5
.38%; N, 5.75%; S, 9.57%. Found: C, 28.49%; H, 5.03%; N, 5.69%; S,
EXPERIMENTAL SECTION
■
9.81%. ESI−MS(±) (H O), selected fragments with relative
abundance >5%, MS(+), m/z: 1311 (5%) [Cu (Hbes) (H bes) +
H] , 1099 (20%) [Cu (Hbes)
[Cu (Hbes) (H bes) + H] , 977 (55%) [Cu (H bes) + H] , 825
(30%) [Cu (Hbes) + H] , 762 (90%) [Cu (H bes) (Hbes) + H] ,
701 (100%) [Cu(H bes) (H bes) + H] , 551 (37%) [Cu (Hbes) +
H] , 488 (86%) [Cu(H bes) + H] , 427 (50%) [Cu(H bes)(fmba)
+ H] , 214 (45%) [H bes + H] . MS(−), m/z: 699 (15%)
2
Reagents, Equipment, and Methods. All reagents were
obtained from commercial sources. Synthesis of 1−4 was performed
at room temperature (∼25 °C) in the air. IR (infrared) spectra were
recorded on a Shimadzu IRAffinity-1S or a JASCO FT/IR-4100 Type
4
4
2
+
+
+ H] , 1037 (60%)
4
4
+
+
3
3
2
2
2
4
+
+
3
3
2
2
2
−
1
+
A apparatus (KBr, 4000−400 cm ; abbreviations: vs, very strong; s,
strong; m, medium; w, weak; br, broad; sh, shoulder). LCQ Fleet
apparatus with an electrospray (ESI) ion source (Thermo Scientific)
2 2 3 2 2
+
+
2
2
2
+
+
3
B
Inorg. Chem. XXXX, XXX, XXX−XXX