Bringing an old biological buffer to coordination chemistry: New 1D and 3D coordination polymers with [Cu4(Hbes)4] cores for mild hydrocarboxylation of alkanes

Article abstract of DOI:10.1021/ic1007999

New water-soluble 1D and 3D Cu^II/Na coordination polymers 1-3 bearing unprecedented [Cu₄(Hbes)₄] cores have been easily generated by aqueous-medium self-assembly and fully characterized, thus opening up the use of the common biological buffer H₃bes, (HO ₃SCH₂CH₂)N(CH₂CH₂OH) ₂, In synthetic coordination chemistry. Apart from representing the first isolated and structurally characterized coordination compounds derived from H₃bes, 1-3 show a remarkable promoting effect in the mild aqueous-medium hydrocarboxylatlon, by CO and H₂O, of gaseous alkanes (C₃H₈ and n-C₄H₁₀) to the corresponding carboxyllc acids, which are obtained In up to 95% yields based on the alkane

Full text of DOI:10.1021/ic1007999

6390 Inorg. Chem. 2010, 49, 6390–6392
DOI: 10.1021/ic1007999
Bringing an “Old” Biological Buffer to Coordination Chemistry:
New 1D and 3D Coordination Polymers with [Cu4(Hbes)4] Cores for Mild
Hydrocarboxylation of Alkanes
,†
†
†
†,‡
ꢀ
Alexander M. Kirillov,* Jaime A. S. Coelho, Marina V. Kirillova, M. Fatima C. Guedes da Silva,
Dmytro S. Nesterov,† Katrin R. Gruenwald,† Matti Haukka,§ and Armando J. L. Pombeiro*,†
†
´
ꢀ
Centro de Quımica Estrutural, Complexo I, Instituto Superior Tecnico, TU Lisbon, Avenida Rovisco Pais, 1049-
‡
ꢀ
001 Lisbon, Portugal, Universidade Lusofona de Humanidades e Tecnologias, ULHT Lisbon, Avenida do
§
Campo Grande 376, 1749-024 Lisbon, Portugal, and Department of Chemistry, University of Eastern Finland,
P.O. Box 111, FIN-80101 Joensuu, Finland
Received April 23, 2010
New water-soluble 1D and 3D CuII/Na coordination polymers 1-3
bearing unprecedented [Cu4(Hbes)4] cores have been easily gener-
ated by aqueous-medium self-assembly and fully characterized,
thus opening up the use of the common biological buffer H3bes,
(HO3SCH2CH2)N(CH2CH2OH)2, in synthetic coordination chemistry.
Apart from representing the first isolated and structurally characterized
coordination compounds derived from H3bes, 1-3 show a remarkable
promoting effect in the mild aqueous-medium hydrocarboxylation, by
CO and H2O, of gaseous alkanes (C3H8 and n-C4H10) to the
corresponding carboxylic acids, which are obtained in up to 95% yields
based on the alkane.
structurally characterized in the solid state. This contrasts
with the rich family of compounds with the related amino-
polyalcohol triethanolamine.3,4
Bearing these features in mind and following our interest in
the design, by aqueous-medium self-assembly with amino-
polyalcohol ligands, of catalytically active multicopper(II)
compounds,4 the main objectives of the present work consist
of (i) opening up the use of H3bes for the synthesis of novel
multicopper cores and (ii) establishing their application for the
selective oxidative functionalization of alkanes as bioinspired
catalysts relevant to particulate methane monooxygenase
(pMMO).5
Hence, we report herein the new series of water-soluble CuII/
Na coordination polymers 1-3 having the general formulas
Since the discovery by Good et al. in 1966, N,N-bis(2-
hydroxyethyl)-2-aminoethanesulfonic acid (H3bes) has be-
come a well-known low-interference buffer with a recognized
use in biochemical and biomedical research.1 However, in
spite of its commercial availability, aqueous solubility, and
interesting structure with different functional groups, the
application of H3bes as a multidentate N,O ligand in syn-
thetic coordination chemistry has remained virtually unex-
plored. Although the formation of some metal complexes
with H3bes in solution has been documented,2 searches of the
literature and the Cambridge Structural Database (CSD)3
show that there is no single example of a coordination
compound derived from H3bes that has been isolated and
[Cu4(Hbes)4(RC6H4COO){Na(H2O)x}]n ynH2O [R = 4-HO-
3
(1), H- (2), and 2-MeO- (3)], which represent the first struc-
turally characterized examples of coordination compounds
derived from H3bes (Scheme 1). We also show that their
water-soluble [Cu4(Hbes)4] cores efficiently promote mild
hydrocarboxylation, by CO and H2O, of propane and butane
to the corresponding carboxylic acids.
The 1D (1) and 3D (2 and 3) polymers have been generated
via a facile self-assembly route that is based on the combina-
tion, in an aqueous solution and at room temperature, of cop-
per(II) nitrate (metal source) and H3bes (main ligand source),
with the corresponding benzoic acid RC6H4COOH (auxi-
liary ligand source) and sodium hydroxide (pH-regulator)
(4) (a) Kirillov, A. M.; Kopylovich, M. N.; Kirillova, M. V.; Haukka, M.;
da Silva, M. F. C. G.; Pombeiro, A. J. L. Angew. Chem., Int. Ed. 2005, 44,
4345. (b) Karabach, Y. Y.; Kirillov, A. M.; da Silva, M. F. C. G.; Kopylovich,
M. N.; Pombeiro, A. J. L. Cryst. Growth Des. 2006, 6, 2200. (c) Karabach, Y. Y.;
Kirillov, A. M.; Haukka, M.; Kopylovich, M. N.; Pombeiro, A. J. L. J. Inorg.
Biochem. 2008, 102, 1190. (d) Kirillov, A. M.; Karabach, Y. Y.; Haukka, M.; da
Silva, M. F. C. G.; Sanchiz, J.; Kopylovich, M. N.; Pombeiro, A. J. L. Inorg.
Chem. 2008, 47, 162. (e) Gruenwald, K. R.; Kirillov, A. M.; Haukka, M.; Sanchiz,
J.; Pombeiro, A. J. L. Dalton Trans. 2009, 2109.
*To whom correspondence should be addressed. E-mail: kirillov@ist.utl.
pt (A.M.K.), pombeiro@ist.utl.pt (A.J.L.P.). Phone: þ351 218419207/37.
Fax: þ351 218464455.
(1) (a) Good, N. E.; Winget, G. D.; Winter, W.; Connolly, T. N.; Izawa, S.;
Sing, R. M. M. Biochemistry 1966, 5, 467. (b) Ferguson, W. J.; Braunschweiger,
K. I.; Braunschweiger, W. R.; Smith, J. R.; McCormick, J. J.; Wasmann, C. C.; Jarvis,
N. P.; Bell, D. H.; Good, N. E. Anal. Biochem. 1980, 104, 300.
(2) (a) Fasching, R.; Kohl, F.; Urban, G. Sens. Actuators B 2003, 93, 197.
(b) Azab, H. A.; Elnady, A. M.; Elkorashy, S. A.; Hamed, M. M. A. J. Chem. Eng.
Data 1995, 40, 83. (c) Azab, H. A.; El-Nady, A. M. Monatsh. Chem. 1994, 125, 849.
(3) See the CSD (version 5.31, May 2010): Allen, F. H. Acta Crystallogr.
2002, B58, 380.
(5) (a) Lieberman, R. L.; Rosenzweig, A. C. Nature 2005, 434, 177.
(b) Chan, S. I.; Wang, V. C.-C.; Lai, J. C.-H.; Yu, S. S.-F.; Chen, P. P.-Y.; Chen,
K. H.-C.; Chen, C.-L.; Chan, M. K. Angew. Chem., Int. Ed. 2007, 46, 1992.
r
pubs.acs.org/IC
Published on Web 06/14/2010
2010 American Chemical Society

Communication
Inorganic Chemistry, Vol. 49, No. 14, 2010 6391
Figure 1. Crystal structure of
1 (partial view) representing the
[Cu4(Hbes)4(4-HO-C6H4COO)]- unit (a) and its [Cu4(μ-O)4(μ-COO)]
core (b). μ-Na(H2O)4 moieties and H atoms are omitted for clarity. Color
codes: Cu, green; O, red; N, blue; C, cyan; S, yellow. Selected bonding
Figure 2. Fragments of crystal-packing diagrams of 1 (a) and 2 (b)
(views along the c axis) showing the interlinkage of Cu4 cluster nodes into
a zigzag 1D chain (a) and a 3D metal-organic framework (b). Color
codes: Cu, green; Na, purple; O, red; N, blue; C, cyan; S, yellow. H atoms
(in 1 and 2), C6H5COO, and some CH2CH2(O) groups of Hbes (in 2) are
omitted for clarity.
˚
parameters (A): Cu-OHbes 1.918(2)-1.931(2), Cu-OCOO 2.012(2),
Cu1 Cu2 3.0563(5), Cu1 Cu3 3.3510(7), Cu3 Cu4 5.9013(9).
3 3 3
3 3 3
3 3 3
Scheme 1. Aqueous-Medium Self-Assembly Synthesis of 1-3
atoms. The geometries around the pentacoordinated Cu
atoms can be described as square pyramids fused via com-
mon vertexes into the [Cu4(μ-O)4(μ-COO)] cores, wherein the
Cu centers are located almost in one plane, with the shortest
and longest Cu Cu separations in 1 of 3.0563(5) and
3 3 3
˚
5.9013(9) A, respectively. Such a relative planarity of the
Cu atoms in 1-3 is very unusual for tetracopper(II)
compounds, as confirmed by a search in the CSD.3
In spite of bearing similar tetracopper cores (cluster
nodes), the main architectural distinctive features of 1-3
arise from the different coordination modes of the sulfonate
groups in the Hbes moieties. In 1, only two of four sulfonate
groups connect to the aqua-sodium linkers, thus giving rise
to 1D zigzag metal-organic chains (Figure 2a). In contrast,
all four sulfonate groups within the Cu cluster node in 2
coordinate to the neighboring Na atoms, generating an
infinite 3D metal-organic framework (Figure 2b). A similar
3D architecture is also observed in the structure of 3 (Figure
S9 in the Supporting Information).
(Scheme 1). The crucial role in defining the dimensionality of
the obtained networks is eventually played by the type of
auxiliary benzenecarboxylate ligand. The obtained products
have been isolated as air-stable crystalline solids and char-
acterized by IR spectroscopy, electrospray ionization mass
spectrometry (ESI-MS), elemental analyses, and X-ray
crystallography.6
The X-ray crystal structures of all of the compounds bear
structurally similar tetracopper(II) [Cu4(Hbes)4(carboxy-
late)]- blocks (as a typical example, see Figure 1) that are
further assembled, via the charge-balancing sodium moieties
and the sulfonate groups of Hbes, into the different 1D or 3D
coordination networks (Figure 2). In all compounds, the
tetracopper(II) cores are composed of four μ-O bridging
Hbes ligands (acting in different N,O2- and N,O3-coordina-
tion modes) and one μ-COO carboxylate ligand, which
provides an additional interlinkage of the “central” Cu
All of the compounds 1-3 represent rare examples4b,7 of
water-soluble copper-containing coordination polymers, with
solubilities (S25 °C in H2O) ranging from 15 (1 and 3) to 130 (2)
mg mL-1. In aqueous solution, they eventually dissociate into
ionic species upon decoordination of the carboxylate ligands,
in accordance with detection of the [Cu4(Hbes)4Na]þ and
[Cu4(Hbes)3(bes)]- fragments at m/z 1122 and 1098, respec-
tively, in the ESI-MS(() spectra of 1-3. An important feature
of the highly soluble compound 2 consists of its ability to
recrystallize from a H2O solution in the original form, as
confirmed by IR spectroscopy and elemental analysis.
The water solubility of 1-3 and the significance of their labile
tetracopper cores in terms of the active site of pMMO (a multi-
copper cluster with a N,O environment)5 suggest the potential
application of these compounds for oxidative functionalization,
in an aqueous medium, of inert gaseous alkanes. Although
numerous examples of bioinspired copper complexes have been
reported,8 the aqueous-medium transformations of gaseous
alkanes with water-soluble catalysts remain rather scant.
(6) Crystal data for 1: C31H64Cu4N4NaO27S4, MW = 1331.26, monoclinic,
˚
˚
˚
space group P21/c, a = 17.502(3) A, b = 21.080(3) A, c = 13.7686(9) A, β =
106.664(7)°, V = 4866.5(11) A , T = 120(2) K, Z = 4, Dcalcd = 1.817 Mg m-3
,
3
˚
μ = 1.999 mm-1, F(000) = 2744, θ = 1.93-27.5°, GOF = 1.061, 85 491 reflns
measured, 11 162 unique (Rint = 0.0565), R1 = 0.0351, wR2 = 0.0628. Crystal
data for 2: C31H57Cu4N4NaO22S4, MW = 1243.20, monoclinic, space group C2/
˚
˚
˚
c, a = 18.0367(13) A, b = 21.0944(15) A, c = 14.0941(10) A, β = 116.122(3)°,
V = 4814.7(6) A , T = 292(2) K, Z = 4, Dcalcd = 1.715 Mg m-3, μ = 2.006
3
˚
mm-1, F(000) = 2552, θ = 1.93-27.10°, GOF = 0.913, 18 403 reflns measured,
5291 unique (Rint = 0.0780), R1 = 0.0518, wR2 = 0.1250. Crystal data for 3:
C32H59Cu4N4NaO26S4, MW = 1321.22, monoclinic, space group C2/c, a =
(7) (a) Friese, V. A.; Kurth, D. G. Coord. Chem. Rev. 2008, 252, 199.
(b) Gasnier, A.; Barbe, J.-M.; Bucher, C.; Duboc, C.; Moutet, J.-C.; Saint-Aman,
E.; Terech, P.; Royal, G. Inorg. Chem. 2010, 49, 2592.
(8) (a) Que, L., Jr.; Tolman, W. B. Nature 2008, 455, 333. (b) Lewis, E. A.;
Tolman, W. B. Chem. Rev. 2004, 104, 1047. (c) Gamez, P.; Aubel, P. G.; Driessen,
W. L.; Reedijk, J. Chem. Soc. Rev. 2001, 30, 376.
˚
˚
˚
18.6049(12) A, b = 21.0872(11) A, c = 14.0954(9) A, β = 118.396(2)°, V =
4864.6(5) A , T = 150(2) K, Z = 4, Dcalc = 1.804 Mg m-3, μ = 1.997 mm-1
,
3
˚
F(000) = 2712, θ = 2.49-26.41°, GOF = 1.041, 19293 reflns measured, 5001
unique (Rint = 0.0415), R1 = 0.0624, wR2 = 0.1549.

6392 Inorganic Chemistry, Vol. 49, No. 14, 2010
Kirillov et al.
Scheme 2. Copper-Promoted Hydrocarboxylation of Propane and
n-Butane to Carboxylic Acidsa
exceptionally mild and acid-solvent-free reaction conditions
and operation in an aqueous medium with a rare hydroxylat-
ing role of water and with high selectivities to carboxylic
acids. These represent some of the mildest methods so far
reported for the efficient oxidative functionalization of gas-
eous alkanes. In this regard, one should mention that,
because of the high inertness of gaseous alkanes, most of
the state-of-the-art systems for their relatively mild
transformations11 require the use of strongly acidic reaction
media (concentrated trifluoroacetic or sulfuric acid or a
superacid).12
In summary, this study has opened up the use, for the first
time, of the common biological buffer H3bes in synthetic
coordination chemistry, resulting in the self-assembly gen-
eration and isolation of the unprecedented Cu/Na coordina-
tion polymers 1-3, which represent the first structurally
characterized coordination compounds derived from
H3bes. They feature a rare type of water-soluble tetra-
copper(II) core, capable of efficiently promoting mild and
selective hydrocarboxylations of propane andn-butane to the
corresponding carboxylic acids. Besides, this work provides a
contribution to the sweeping area of crystal engineering,13
namely, toward the development of aqueous-medium pro-
cesses and the synthesis of rare water-soluble coordination
polymers. Further research toward the exploration of H3bes
in the design of metal-organic materials and the search for
their diverse applications is currently underway in our group.
a The molar percent yields are based on alkane.
Following our recently developed method for the mild
transformation of Cn alkanes to Cnþ1 carboxylic acids in an
aqueous medium,9 we have tested the promoting behavior of
1-3 in such hydrocarboxylation reactions using propane and
n-butane as substrates (Scheme 2).10 These transformations
were undertaken by reacting, at low temperature (50-60 °C)
in a neutral H2O/MeCN medium, an alkane with CO, H2O,
and potassium peroxodisulfate.
Compounds 1-3 were found to exhibit a remarkable
promoting behavior. Thus, the branched i-butyric and
2-methylbutyric acids were respectively obtained as the main
products (63-91% yield) during carboxylation of C3H8 and
n-C4H10, whereas the corresponding linear butyric and
valeric acids were generated in minor amounts (5-8% yield).
The structural resemblance of the [Cu4(Hbes)4] cores in 1-3
explains their somehow similar activity. However, the highest
total yields of carboxylic acids (78 and 95% in reactions with
C3H8 and n-C4H10, respectively) were obtained in the pre-
sence of 2 (Scheme 2). These yields are superior to those of
23 and 38% previously reported for the metal-free hydro-
carboxylations or promoted by the tetracopper(II) trietha-
nolaminate complex, respectively.9a
Acknowledgment. This work was supported by the
FCT, Portugal, its PPCDT (FEDER funded), and
“Science 2007” programs. We thank Dr. M. C. Oliveira
for ESI-MS (IST-node of RNEM/FCT).
Supporting Information Available: Synthetic procedures, full
experimental details, additional structural representations
(Figures S1-S9) and bonding parameters (Tables S1-S6) for
1-3, the proposed mechanism for hydrocarboxylation (Scheme
S1), and crystallographic files in CIF format. This material is
available free of charge via the Internet at http://pubs.acs.org.
On the basis of the previous background9 on the hydro-
carboxylation of alkanes RH, a free-radical mechanistic cycle
can be proposed (Scheme S1 in the Supporting Information).
Its main steps involve the (i) generation of alkyl radicals R•
(H abstraction by sulfate radicals derived from K2S2O8),
(ii) carbonylation of R• by CO to acyl radicals RCO•, (iii)
oxidation of RCO• by copper(II) species (via the CuII/CuI
redox couple) to acyl cations RCOþ, and (iv) hydrolysis of
RCOþ to furnish carboxylic acid products.9 The latter step
was previously confirmed by us on the basis of experiments
with 18O-labeled H2O and theoretical calculations.9a
(11) For reviews, see: (a) Shul’pin, G. B. Mini-rev. Org. Chem. 2009, 6, 95.
(b) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507. (c) Fokin, A. A.;
Schreiner, P. R. Chem. Rev. 2002, 102, 1551. (d) Sen, A. Acc. Chem. Res. 1998,
31, 550. (e) Crabtree, R. H. J. Organomet. Chem. 2004, 689, 4083. (f) Shilov,
A. E.; Shul'pin, G. B. Chem. Rev. 1997, 97, 2879.
(12) (a) Jia, C.; Kitamura, T.; Fujiwara, Y. Acc. Chem. Res. 2001, 34, 633.
(b) Kirillova, M. V.; Kirillov, A. M.; Reis, P. M.; Silva, J. A. L.; Fraꢀusto da Silva,
J. J. R.; Pombeiro, A. J. L. J. Catal. 2007, 248, 130. (c) Periana, R. A.; Mironov,
O.; Taube, D.; Bhalla, G.; Jones, C. J. Science 2003, 301, 814. (d) Olah, G. A.;
Apart from high product yields, important features of the
present copper-promoted hydrocarboxylations include the
ꢀ
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2010, 12, 22. (b) Perry, J. J., IV; Perman, J. A.; Zaworotko, M. J. Chem. Soc. Rev.
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(10) Reaction conditions: p(alkane) = 1.0 atm, p(CO) = 10 atm (1 atm =
0.266 mmol), K2S2O8 (1.0 mmol), H2O (2 mL)/MeCN (4 mL), copper promoters
1-3 (4.0 μmol), 50 °C (for n-C4H10) or 60 °C (for C3H8), 6 h in an autoclave
(13.0 mL), followed by workup and gas chromatographic analyses.