Copper(II) complexes of pyridine-oxazoline (Pyox) ligands: Coordination chemistry, ligand stability, and catalysis

Article abstract of DOI:10.1016/j.ica.2015.10.032

The coordination chemistry of copper(II) complexes bearing pyridine-oxazoline ("Pyox") ligands has been studied, with an aim of investigating their catalytic ability. Interestingly, the stability of the coordinated ligands has been shown to be much less than previously assumed: hydrolysis of the ligands by fortuitous water gives rise to 2-pyridine carboxylate formation, which encapsulate the copper in a two-dimensional coordination polymer 3. The complexes [Cu(R-Pyox)(NCMe)₂(ClO₄)₂] {R = benzyl (Bn) 2a, phenyl (Ph) 2b, isopropyl (ⁱPr) 2c} have been prepared, of which the benzyl derivative has been analysed by CW EPR spectroscopy. The complex [Cu(Bn-Pyox)(NCMe)₂(ClO₄)₂] and the afore-mentioned coordination polymer have been crystallographically characterised. The performance of complexes 2a-c in the asymmetric allylic oxidation of cyclohexene is described.

Full text of DOI:10.1016/j.ica.2015.10.032

Accepted Manuscript
Copper(II) complexes of pyridine-oxazoline (Pyox) ligands: Coordination
chemistry, ligand stability, and catalysis
Andrew J. Hallett, Thomas M. O’Brien, Emma Carter, Benson M. Kariuki,
Damien M. Murphy, Benjamin D. Ward
PII:
S0020-1693(15)00526-5
http://dx.doi.org/10.1016/j.ica.2015.10.032
ICA 16742
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
3 July 2015
6 October 2015
7 October 2015
Please cite this article as: A.J. Hallett, T.M. O’Brien, E. Carter, B.M. Kariuki, D.M. Murphy, B.D. Ward, Copper(II)
complexes of pyridine-oxazoline (Pyox) ligands: Coordination chemistry, ligand stability, and catalysis, Inorganica
Chimica Acta (2015), doi: http://dx.doi.org/10.1016/j.ica.2015.10.032
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Revised manuscript
Copper(II) complexes of pyridine-oxazoline (Pyox) ligands:
Coordination chemistry, ligand stability, and catalysis
Andrew J. Hallett, Thomas M. O’Brien, Emma Carter, Benson M. Kariuki, Damien M. Murphy, and
Benjamin D. Ward*
School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, UK.
Abstract
The coordination chemistry of copper(II) complexes bearing pyridine-oxazoline (“Pyox”) ligands
has been studied, with an aim of investigating their catalytic ability. Interestingly, the stability of
the coordinated ligands has been shown to be much less than previously assumed: hydrolysis of the
ligands by fortuitous water gives rise to 2-pyridine carboxylate formation, which encapsulate the
copper in a two-dimensional coordination polymer 3. The complexes [Cu(R-
Pyox)(NCMe)2(ClO4)2] {R = benzyl (Bn) 2a, phenyl (Ph) 2b, isopropyl (iPr) 2c} have been
prepared, of which the benzyl derivative has been analysed by CW EPR spectroscopy. The complex
[Cu(Bn-Pyox)(NCMe)2(ClO4)2] and the afore-mentioned coordination polymer have been
crystallographically characterised. The performance of complexes 2a–c in the asymmetric allylic
oxidation of cyclohexene is described.
Keywords: epr spectroscopy, coordination chemistry, oxazoline ligands, copper, oxidation catalysis,
X-ray crystallography
* Proofs and correspondence to Dr. B. D. Ward. Email: WardBD@Cardiff.ac.uk; Fax: +44 (0)29
208 74030
1

Highlights
ꢀ Coordination chemistry of Cu(II) complexes bearing pyridine-oxazoline ligands
ꢀ Hydrolysis of the coordinated ligand forms a coordination polymer of pyridine-2-
carboxylate
ꢀ EPR analysis of complexes
ꢀ Oxidation catalysis studied
2

1. Introduction
The continued development of metal catalysts is supported by studies into the coordination
chemistry of complexes bearing supporting ligands commonly employed in catalysis. These studies
are particularly important when complex ligands are employed, that may themselves become the
focus of chemical transformations in direct competition with the catalytic substrates. Ligand-based
(undesired) chemical transformations are numerous; common examples include C-H activation of
side-chains,[1] the epimerisation of chiral ligands,[2a] the ring-opening of cyclic ligand
architectures [2a] and the reaction of coordinated imine ligands [2b] in the presence of Lewis acidic
transition metals. A detailed understanding of these processes is crucial if catalyst performance is to
be rationalised so that catalyst performance and stability can be attained.
It is in this context that we sought to elucidate the coordination chemistry of copper supported by
pyridine-oxazoline “Pyox” ligands. Pyox ligands have been successfully employed as chiral
supporting ligands for a range of catalytically active complexes, e.g. in the rhodium-catalysed
asymmetric hydrosilylation of carbonyl compounds.[3] However, their wider application has been
somewhat less forthcoming; for example their complexes with copper(I) have been studied in the
asymmetric Kharash-Sosnovsky reaction, but the enantiomeric excesses were significantly lower
than similar ligand systems.[4] In the afore-mentioned Kharash-Sosnovsky reaction, the copper(I)
complexes were prepared in situ, and therefore there are a number of unanswered questions
pertaining to the coordination environment involving the Pyox ligand, that may offer some
explanation as to the observed activity and selectivity in such catalytic transformations.
Consequently, we set out to prepare and characterise copper complexes with Pyox ligands in order
that the stability of such complexes could be adequately assessed.
Whilst Pyox ligands have been used in copper-catalysis, such as cyclopropanation [5] and allylic
oxidation,[4] their structural coordination chemistry is much more limited. A search of the
Cambridge Structural Database provides five examples of structurally characterised copper
complexes bearing Pyox derivatives, of which three feature the five-coordinate copper centre
coordinated by two Pyox ligand fragments along with a halide coligand [6-8]. The only
crystallographically characterised copper-Pyox complexes, in which only one Pyox moiety is
coordinated to the copper, have been reported by Brunner [9] and Breit.[10] Once again, both
complexes are five-coordinate, as is common for copper(II), and both also contain halide co-
ligands. Most noticeable is the total absence of copper-Pyox complexes that do not contain halides;
this is an important omission, since the most common counterions employed in catalysis are those
3

-
-
that are unrepresented in these studies, such as PF6 and CF3SO3 .
2. Experimental
2.1 General information
All air sensitive preparations were carried out under an atmosphere of argon or of dinitrogen using
standard glove box or Schlenk techniques. Solvents were purified by distillation from calcium
hydride (chloroform), or by passing through a column of activated alumina using an MBraun SPS-
800 solvent purification system (ethanol, acetonitrile).
Samples for NMR spectroscopy were prepared in 5 mm Wilmad NMR tubes and spectra were
measured on Bruker DPX-250 and Avance 400 NMR spectrometers. Spectra were referenced
internally to residual protio solvent resonances and are reported relative to tetramethylsilane (δ = 0
ppm). Mass spectra were measured on a Waters LCT Premier XE by the mass spectrometry service
at the Cardiff University School of Chemistry. Elemental analyses were measured by the analytical
services at London Metropolitan University.
The CW-EPR measurements were recorded on an X-band Bruker EMX spectrometer operating at
100 kHz field modulation, 10 mW microwave power and equipped with a high sensitivity cavity
(Bruker ER 4119HS). EPR computer simulations were performed using the SimEPR32 program
[11], and g values were determined using a DPPH standard. For EPR measurements, 0.5 ml of a 3 ×
10-2 M solution of 2a in MeCN was diluted with toluene (0.5 ml) and a drop of DMF added. 200 µl
of the solution was placed into an EPR tube (4mm Suprasil) under argon, and the sample frozen
immediately for the analysis. UV-vis. studies were performed on a Jasco V-570 spectrometer as 2
mmol dm-3 solutions.
2.2 Synthesis of ligands
Amino alcohols were prepared by the reduction of the corresponding amino acid. All other reagents
were obtained from commercial suppliers and used as received unless stated.
2.2.1 2-pyridinecarboxyimidate
4

Sodium metal (0.044 g, 1.91 mmol) was added to a solution of 2-cyanopyridine (2 g, 19.21 mmol)
in EtOH (30 ml) and stirred at room temperature for 24 h. Glacial acetic acid (0.12 ml, 2.09 mmol)
was then added to quench the reaction and the solvent removed under reduced pressure. The crude
product was dissolved in CH2Cl2 (50 ml), washed with water (2 × 50 ml), brine (10% w/v, 50 ml)
and dried over Na2SO4. After filtering, the solvent was removed under reduced pressure to give the
1
product as a light brown oil. Yield = 2.71 g (94%). H NMR (400.1 MHz, CDCl3, 293 K) δ = 9.03
3
3
(1H, br s, NH), 8.53 (1H, d, JHH = 5.6 Hz, pyH), 7.78 (1H, d, JHH = 7.9 Hz, pyH), 7.70 (1H, dd,
3JHH = 7.7 and 5.6 Hz, pyH), 7.27 (1H, m, pyH), 4.36 (2H, q, 3JHH = 7.1 Hz, CH2), 1.37 (3H, t, 3JHH
= 7.1 Hz, CH3) ppm.
The ligand precursors R-Pyox {R = benzyl (Bn, 1a), phenyl (Ph, 1b), isopropyl (iPr, 1c)} were
prepared using a modified literature procedure and data were consistent with reported values.[3,12]
Spectroscopic data are reported here for convenience and completeness.
2.2.2 Bn-Pyox (1a)
2-pyridinecarboxyimidate (0.523 g, 3.48 mmol) and L-phenylalaninol (0.527 g, 3.48 mmol) in
CHCl3 (15 ml) were heated at 60 °C for 16 h. The organic solution was washed with water (2 × 30
ml), brine (10% w/v, 30 ml) and dried over Na2SO4. After filtering, the solvent was removed under
1
reduced pressure to give the product as an off white solid. Yield = 0.739 g (89%). H NMR (400.1
3
MHz, CDCl3, 293 K) δ = 8.62 (1H, d, JHH = 5.9 Hz, pyH), 7.97 (1H, d, 3JHH = 7.9 Hz, pyH), 7.60
3
(1H, dd, JHH = 7.9 and 5.9 Hz, pyH), 7.30 (1H, m, pyH), 7.26-7.06 (5H, m, PhH), 4.58 (1H, m,
CHBn), 4.36 (1H, app. t, app. JHH = 9.0 Hz, CHHO), 4.13 (1H, app. t, app. JHH = 8.1 Hz, CHHO),
3.32 (1H, dd, 2JHH = 13.2 Hz, 3JHH = 5.1 Hz, CHHPh), 2.56 (1H, dd, 2JHH = 13.0 Hz, 3JHH = 5.2 Hz,
CHHPh) ppm. ES-MS: m/z (%) = 239.13 (100) [Bn-Pyox + H]+.
2.2.3 Ph-Pyox (1b)
Prepared similarly from 2-pyridinecarboxyimidate (0.508 g, 3.38 mmol) and D-phenylglycinol
1
(0.464 g, 3.38 mmol). Yield = 0.728 (96%). H NMR (400.1 MHz, CDCl3, 293 K) δ = 8.67 (1H, d,
3JHH = 6.0 Hz, pyH), 8.08 (1H, d, 3JHH = 7.9 Hz, pyH), 7.71 (1H, app. t, 3JHH = 7.9 Hz, pyH), 7.36
(1H, m, pyH), 7.30-7.18 (5H, m, PhH), 5.38 (1H, app. t, app. 3JHH = 8.6 Hz, CHPh), 4.81 (1H, app.
5

t, app. JHH = 8.6 Hz, CHHO), 4.30 (1H, app. t, app. JHH = 8.5 Hz, CHHO) ppm. ES-MS: m/z (%) =
225.10 (100) [Ph-Pyox + H]+.
2.2.4 iPr-Pyox (1c)
Prepared similarly from 2-pyridinecarboxyimidate (0.524 g, 3.49 mmol) and L-valinol (0.360 g,
1
3.49 mmol). Yield = 0.604 g (91%). H NMR (400.1 MHz, CDCl3, 293 K) δ = 8.65 (1H, d, 3JHH
=
5.8 Hz, pyH), 8.03 (1H, d, 3JHH = 7.9 Hz, pyH), 7.72 (1H, app. t, 3JHH = 7.8 Hz, pyH), 7.33 (1H, m,
pyH), 4.46 (1H, app. t, 3JHH = 8.0 Hz, CHiPr), 4.18-4.04 (2H, m, CH2O), 1.85 {1H, sept, 3JHH = 6.8
3
3
Hz, CH(CH3)2}, 1.00 {3H, d, JHH = 6.8 Hz, CH(CH3)(CH3)}, 0.89 (3H, d, JHH = 6.8 Hz,
CH(CH3)(CH3)} ppm. ES-MS: m/z (%) = 191.12 (100) [iPr-Pyox + H]+.
2.3 Synthesis of complexes
2.3.1 General procedure for the preparation of [Cu(R-Pyox)(NCMe)2(ClO4)2] (2)
To a solution of [Cu(H2O)6][ClO4]2 (74.1 mg, 0.200 mmol) [warning: perchlorates can be
dangerous – this procedure should not be scaled up without appropriate precautions] in acetonitrile
(3.0 ml) was added a solution of R-Pyox (0.200 mmol) in acetonitrile (3.0 ml). The resulting
blue/green solution was allowed to stir for 12 h under argon before removing the volatiles under
reduced pressure (Schlenk line vacuum). The solid residue was washed with diethyl ether (2 × 5
ml), extracted into acetonitrile (10 ml), filtered through celite to remove any insoluble residues, and
the solvent removed from the filtrate under reduced pressure. The solid product was dried in vacuo
for 3 h at room temperature to 1.0 × 10–2 mbar to afford the complex as a blue/green powder.
Elemental combustion analyses were consistent with the title complexes without the coordinated
acetonitrile.
2.3.2 [Cu(Bn-Pyox)(NCMe)2(ClO4)2] (2a)
IR data (KBr pellet, cm-1): 3411 (br), 3323 (m), 3247 (m), 3194 (m), 3065 (m), 3025 (m), 2963 (m),
2921 (m), 2854 (m), 2015 (w), 1891 (w), 1653 (s), 1595 (s) 1570 (m), 1497 (s), 1453 (m), 1414 (s)
1300 (m), 1261 (s), 1142 (s), 1110 (s), 1086 (s), 1023 (s), 926 (m), 799 (s), 747 (m), 703 (m), 675
(m), 623 (s), 515 (w), 492 (w), 464 (w). ES-MS: m/z (%) = 399.99 [Cu(Bn-Pyox)(ClO4)]+ (100),
6

441.02 [Cu(Bn-Pyox)(MeCN)(ClO4)]+ (97), 423.06 [Cu(Bn-Pyox)(2-Py-CO2)]+ (24), 269.57
[Cu(Bn-Pyox)2]2+ (16); HR ES-MS for [Cu(Bn-Pyox)(MeCN)(ClO4)]+: m/z = 441.0144 (calcd for
C17H17ClCuN3O5: 441.0153). UV-vis (MeCN): λmax (ε dm-3 mol-1 cm-1) = 694 nm (40.9). Anal.
Calcd for C15H14Cl2CuN2O9: C, 35.98; H, 2.82; N, 5.59. Found: C, 35.91; H, 2.99; N, 5.88.
2.3.3 [Cu(Ph-Pyox)(NCMe)2(ClO4)2] (2b)
IR data (KBr pellet, cm-1): 3407 (br), 3326 (m), 3260 (m) 3195 (m), 3070 (m), 2929 (m), 2250 (w),
2019 (w), 1893 (m), 1828 (w), 1652 (s), 1591 (s), 1571 (m), 1496 (m), 1456 (m), 1405 (s), 1330
(w), 1300 (m), 1265 (m), 1149 (s), 1109 (s), 1084 (s), 1028 (m), 928 (m), 797 (m), 752 (s), 702 (s),
671 (s), 621 (s), 546 (m), 480 (w). ES-MS: m/z (%) = 427.01 [Cu(Ph-Pyox)(MeCN)(ClO4)]+ (100),
409.05 [Cu(Ph-Pyox)(2-Py-CO2)]+ (24), 385.98 [Cu(Ph-Pyox)(ClO4)]+ (13); HR ES-MS for
[Cu(Ph-Pyox)(MeCN)(ClO4)]+: m/z = 426.9985 calcd for C16H15ClCuN3O5: 426.9996). UV-vis
(MeCN): λmax (ε dm-3 mol-1 cm-1) = 695 nm (46.9). Anal. Calcd for C14H12Cl2CuN2O9: C, 34.55; H,
2.49; N, 5.76. Found: C, 34.79; H, 2.69; N, 5.77.
2.3.4 [Cu(iPr-Pyox)(NCMe)2(ClO4)2] (2c)
IR data (KBr pellet, cm-1): 3411 (br), 3326 (m), 3260 (m), 3195 (m), 3069 (m), 2964 (m), 2924 (w),
2869 (w), 2069 (w), 2019 (w), 1652 (s), 1596 (s), 1571 (m), 1501 (w), 1471 (w), 1415 (m), 1300
(w), 1260 (m), 1144 (s), 1109 (s), 1093 (s), 1018 (m), 927 (m), 802 (m), 757 (w), 666 (w), 625 (s),
475 (w). ES-MS: m/z (%) = 393.02 [Cu(iPr-Pyox)(MeCN)(ClO4)]+ (100), 375.07 [Cu(iPr-Pyox)(2-
Py-CO2)]+ (71), 542.10 [Cu(iPr-Pyox)2(ClO4)]+ (32), 351.99 [Cu(iPr-Pyox)(ClO4)]+ (29); HR ES-
MS for [Cu(iPr-Pyox)(MeCN)(ClO4)]+: m/z = 393.0163 calcd for C13H17ClCuN3O5: 393.0153).
UV-vis (MeCN): λmax (ε dm-3 mol-1 cm-1) = 693 nm (49.6). Anal. Calcd for C11H14Cl2CuN2O9: C,
29.19; H, 3.12; N, 6.19. Found: C, 29.05; H, 3.35; H, 6.48.
2.4 Oxidation catalysis
A solution of the ligand (0.05 mmol) and Cu salt (0.04 mmol) in dry acetonitrile (3 ml) were stirred
at room temperature for 1 h to ensure formation of the copper complex. Cyclohexene (5 mmol) was
then added. A solution of tert-butyl peroxybenzoate (0.85 mmol) in acetonitrile (2 ml) was added.
7

After the reaction was judged to be complete (TLC: disappearance of the peroxyester) the solvent
was removed under reduced pressure and the residue dissolved in dichloromethane (20 ml). The
solution was washed successively with 10% aqueous NaHCO3, brine, and water, and dried over
Na2SO4. Evaporation of the volatiles and purification by flash chromatography (silica, hexane/ethyl
acetate 50:1) afforded the allylic benzoate. The enantiopurities were determined by chiral HPLC
using a Chiracell OJ column [hexane; flow rate 0.35 ml.min–1; t1 = 36.2 min (R), 38.9 min (S)].
2.5 Crystallographic studies
Crystals of 2a suitable for X-ray diffraction were grown by the slow evaporation of a saturated
acetonitrile solution (50 mg in 10 ml) over a period of 7 days. During the crystallisation, crystals of
3 were formed alongside those of 2a. Diffraction data, using Mo-Kα radiation, were collected at
low temperature on a Nonius Kappa-CCD diffractometer. A semi-empirical absorption correction
was applied. The structures were solved by direct methods and refined using full matrix least
squares methods. Hydrogen atoms were input at calculated positions and refined with the riding
model. The calculations were performed using SIR92,[13] SIR97,[14] CRYSTALS [15] and
SHELX.[16] Crystal and experimental data are provided in Table 1. The crystals of both 2a and 3
were poorly diffracting and therefore show low completeness values, although the data : parameter
ratios were acceptable. Structure solution and refinement proceeded without any adverse effects
and gave reliable molecular information. Complex 3 has been previously prepared by an alternative
route, as discussed below.
Table 1 X-ray experimental data of 2a and 3
8

2a
C38H40Cl4Cu2N8O18
1165.68
0.20 × 0.15 × 0.15
0.71073
3
empirical formula
formula weight
crystal size (mm)
Wavelength [Å]
crystal system
space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C18H14ClCu2N3O11
610.85
0.10 × 0.03 × 0.03
0.71073
Triclinic
P1
Triclinic
ꢁ
ꢀ1
8.828(2)
10.076(2)
14.925(3)
76.39(3)
78.81(3)
66.84(3)
1178.7(5)
1
8.562(2)
10.268(2)
12.907(3)
101.62(3)
100.94(3)
98.19(3)
1071.8(4)
2
γ [°]
V [Å3]
Z
ρcalcd [Mgm-3]
1.642
1.211
1.893
2.178
µ [mm-1]
max., min. trans.
index ranges, h, k, l
θ [°]
0.83, 0.83
0.938, 0.812
-11≤h≤11, -13≤k≤13, -19≤l≤13 -9≤h≤9, -11≤k≤11, -14≤l≤14
4 – 27
2 – 24
T [K]
150
150
F(000)
594
612
refl. collected
refl. indep. [Rint]
data/rest./par.
GOF on F2
7469
5363
7469 [0.036]
7446 / 99 / 632
0.9905
3203 [0.082]
3203 / 0 / 319
0.992
final R indices [I>2σ(I)] R1, wR1
R indices (all data) R1, wR1
abs. structural par.
largest res. [e Å-3]
0.0578, 0.1376
0.0669, 0.1464
0.08(2)
0.0716, 0.1672
0.1217, 0.2111
n.d.
1.33 and -1.38
1.272 and -0.764
2.6 DFT calculations
DFT calculations were carried out using the Gaussian 09 package.[17] Geometry optimisations of
both singlet ground and triplet excited states were performed at the B3LYP level,[18,19] with the 6-
31+G(d,p) basis set on all atoms.[20-23] Time-dependent DFT (TD-DFT) calculations also
employed B3LYP. As shown by Vlček et al.,[24] solvent effects can be crucial for obtaining
satisfactory agreement between experiment and TD-DFT. Solvent was therefore modelled using
the polarisable continuum model,[25] with the molecular cavity defined by a united atom model
that incorporates hydrogen into the parent heavy atom, and included in both geometry optimisations
and TD-DFT calculations. Triplet states were confirmed not to suffer from significant spin
contamination via the expectation value of the S2 operator, which in all cases were less than 0.76.
Thus, effects of spin-contamination on energy differences and optimised structures are expected to
be negligible.
9

3. Results and discussion
3.1 Synthesis and characterisation
i
The pyridine-oxazoline ligands R-Pyox (R = Bn 1a, Ph 1b, Pr 1c) were prepared by coupling
amino alcohols with 2-cyanopyridine via a Pinner reaction (Scheme 1), following the method of
Brunner and Obermann.[3] Since our interests are concerned with the catalytic applications of these
ligands with copper, the Cu(II) complexes [Cu(R-Pyox)(NCMe)2(ClO4)2] (R = Bn 2a, Ph 2b and iPr
2c) were prepared by reacting the appropriate ligand with [Cu(H2O)6][ClO4]2 in acetonitrile solution
(Scheme 1). The copper complexes 2a – c were obtained as pale blue solids upon concentration of
the reaction mixture. The complexes were characterised by IR and UV-vis spectroscopies, mass
spectrometry (including HR), along with X-ray crystallography and EPR spectroscopy for complex
2a.
O3Cl
O
O
N
MeCN
N
(i)
(iii)
R
R'
H
Ph
H
O
Cu
O
N
CN
1a/2a Bn
MeCN
R'
(ii)
1b/2b
H
R
N
N
R
1c/2c iPr
R'
O3Cl
(1a-c)
(2a-c)
Scheme 1. Preparation of pyridine oxazoline (Pyox) ligands and complexes. Reagents: (i)
EtOH/Na; (ii) H2NCH(R)CH2OH, CH2Cl2, (iii) Cu(ClO4)2, MeCN.
The UV/vis spectra of complexes 2a–c exhibited only a slight variation in maxima and molar
absorption coefficient with alterations in stereodirecting group. Given that the TD-DFT
calculations suggest little contribution of this group to the principal excited states (vide infra), this
is expected, and consistent with a common coordination chemistry for each of the three ligand
derivatives. Contrary to expectations, the infrared spectra of the bulk material, isolated by removal
of the volatiles under reduced pressure, did not display the expected ν(C≡N) stretches. Furthermore,
no identifiable ions could be detected in the electrospray mass spectra, when using the isolated
material, which was dissolved in acetonitrile immediately prior to data collection. Mass spectra
measurements using the in situ prepared samples (i.e. using the reaction mixture without prior
removal of the volatiles), gave spectra in which the ions attributed to [Cu(R-Pyox)(NCMe)n(ClO4)]+
10

(n = 0 or 1) were clearly visible, and upon which accurate mass data were obtained. Spectra
recorded using the isolated material, and which had been dissolved in acetonitrile for several hours
before data acquisition, showed identical signals to those observed in the in situ prepared samples.
These data suggest that the coordinated acetonitrile is highly labile, and is easily removed in vacuo.
The precise nature of the resulting coordination complex is unclear, but we note that there was no
evidence of homoleptic complex formation (e.g. [Cu(R-Pyox)2(ClO4)2]); more detailed analysis of
these species was not possible, since the acetonitrile-free species were found to be insoluble in all
solvents except for acetonitrile, which necessarily re-formed [Cu(R-Pyox)(NCMe)2(ClO4)2] over
time. Combustion elemental analysis data were irreproducible, and were consistent with a varying,
non-stoichiometric amount of acetonitrile, unless the samples were dried in vacuo for an extended
period of time to a vacuum of 1 × 10-2 mbar. In such cases, elemental analyses were consistent with
the expected complex but without the coordinated acetonitrile, i.e. [Cu(R-Pyox)][ClO4]2. Attempts
to prepare complexes bearing two Pyox ligands, [Cu(R-Pyox)2(ClO4)2], by adding an excess of the
Pyox ligands to the reaction mixtures, yielded only complexes 2a–c.
3.2 X-ray crystallography
The structure of the complexes was confirmed by single crystal X-ray analysis of [Cu(Bn-
Pyox)(NCMe)2(ClO4)2] 2a. The perchlorate anion was utilised in order to aid crystallisation. The
molecular structure is depicted in Fig. 1, with principal bond lengths and angles provided in Table 2.
Fig. 1. Molecular structure of 2a. Ellipsoids are drawn at 25% probability and H atoms are omitted
for clarity
11

Table 2 Selected bond lengths (Å) and angles (°) for 2a. Values for the second
crystallographically independent molecule are provided in parentheses
Cu(1)-O(2)
Cu(1)-O(6)
Cu(1)-N(1)
2.487(7) [2.510(5)]
2.426(5) [2.433(6)]
1.995(8) [1.975(7)]
Cu(1)-N(2)
Cu(1)-N(3)
Cu(1)-N(4)
2.019(7) [1.964(7)]
2.021(6) [2.023(6)]
1.972(7) [1.972(6)]
N(1)-Cu(1)-N(2) 90.8(3) [91.0(3)] O(2)-Cu(1)-O(6) 173.5(3) [175.3(2)]
N(1)-Cu(1)-N(3) 92.6(3) [92.4(3)] Cu(1)-N(1)-C(1) 165.4(8) [167.3(6)]
N(2)-Cu(1)-N(4) 94.9(3) [95.2(3)] Cu(1)-N(2)-C(3) 174.8(7) [166.1(7)]
N(3)-Cu(1)-N(4) 81.6(3) [81.4(3)]
The asymmetric unit of the structure contains two symmetry independent molecules that are related
by a pseudocentre of inversion; the difference between the two molecules is manifested in the
relative orientation of the perchlorate anions relative to the Pyox and acetonitrile ligands. A
comparison of the two structures is provided in Fig. S1 in the supplementary information. The
equivalent metric parameters show no significant differences. The copper assumes a distorted
octahedral geometry, with two acetonitrile ligands coordinated in a mutually cis arrangement,
forming an approximate square plane with the Pyox ligand {sum of angles subtended at Cu in the
equatorial plane: 359.9(12) °}. Two perchlorate ligands occupy the axial positions, and exhibit
elongated Cu-O bond lengths, as expected for the Jahn-Teller distorted d9 copper centre. The Cu-
Operchlorate bond lengths of 2.426(5) and 2.487(7) are well within the sum of the van der Waals radii
(2.92 Å),[26] and are comparable with copper-coordinated perchlorate ligands in the Cambridge
Structural Database (mean Cu-O distance: 2.53 Å).[27] The bond lengths associated with the Pyox
ligand and acetonitrile ligands are unremarkable. Interestingly, the coordination of the acetonitrile
ligands deviate significantly from the expected linear arrangement: the angle subtended at N(1) and
N(2) being 165.4(8) ° and 174.8(7) ° respectively. It is noteworthy that the greatest deviation from
linear occurs in the acetonitrile furthest away from the Pyox stereodirecting group, which may be
expected to be closer to 180 ° based upon steric arguments. We note however that the difference is
negligible in the crystallographically independent molecule {167.3(6) and 166.1(7) respectively},
and that deviations from linear coordination of nitriles is not uncommon, with the Cu-N-C angle in
the structurally related [Cu(bpy)(NCMe)2(ClO4)2] being 169.7 ° [28] and the mean M-N-C angle in
the Cambridge Structural Database being 169.8 ° (5052 examples of transition metal-nitrile
complexes). Given that the spectroscopic data are consistent across the series of complexes, we
propose that the molecular structure of 2a shown in Fig. 1 is likely to be similar to the structures of
2b and 2c.
12

Alongside the crystals of 2a, several distinctly different crystals were formed. The serendipitous
formation of these crystals provides a clear insight into the stability of these Pyox ligands in the
coordination sphere of copper(II).
Scheme 2. Copper-catalysed ligand hydrolysis
This second species, 3, is a supramolecular array of copper, ligated by 2-pyridinecarboxylate
ligands. The pyridine carboxylate moieties are presumably formed by the in situ hydrolysis of the
Pyox ligands (Scheme 2) in the presence of Cu(II). This structure has previously been reported from
the reaction of Cu(II) salts with picolinic acid;[30] its formation in this instance is interesting
because it implicates ligand stability in an assessment of catalytically active complexes. The
hydrolysis of bis(hydroxymethyl) substituted Pyox ligands (affording pyridine-2-carboxylate and
the corresponding amino alcohol) has been reported by Segl’a and co-workers,[29] although only in
aqueous solution under forcing conditions; complex 3 is interesting in that it was formed under
much milder conditions, presumably with water arising from the use of a hydrated copper
perchlorate salt. A fragment of the asymmetric unit is depicted in Fig. 2, with principal bond lengths
and angles given in Table 3, although the full details of the supramolecular structure are best
appreciated from the extended structure shown in Fig. 3.
13

Fig. 2. Molecular structure of 3. Probability ellipsoids are drawn at 25%. H atoms (other than
those associated with the coordinated water molecule) and perchlorate counterion are omitted for
clarity. Only one copper environment is shown.
Fig. 3. Packing diagram of 3. H atoms (other than those associated with the coordinated water
molecule) are omitted for clarity. § = Cu(1), † = Cu(2), ◊ = Cu(3)
14

Table 3 Principal bond lengths (Å) and angles (°) for 3. Atoms labelled with suffixes A–E are
related by symmetry elements as follows: A = –x, y, 1–z; B = x, y–1, z; C = x–1, y, z; D = 1–x, –1–y,
1-z; E = 1–x, –y, 1–z
Cu(1)-O(7A)
Cu(1)-O(7B)
Cu(1)-O(2C)
Cu(1)-O(2D)
Cu(1)-O(1)
Cu(3)-N(3A)
Cu(3)-N(3)
Cu(3)-O(6)
1.940(7)
1.940(7)
1.957(7)
1.957(7)
2.644(7)
1.978(8)
1.978(8)
1.989(7)
1.989(7)
Cu(2)-O(4)
Cu(2)-O(3)
Cu(2)-N(1)
Cu(2)-N(2)
Cu(2)-O(1)
Cu(2)-O(5E)
Cu(3)-O(5)
Cu(3)-O(5A)
1.942(7)
1.982(7)
1.984(9)
1.987(9)
2.368(7)
2.735(7)
2.332(7)
2.332(7)
Cu(3)-O(6A)
O(7)-Cu(1)-O(7B) 180.0 O(2C)-Cu(1)-O(2D) 180.0
O(7A)-Cu(1)-O(2C) 95.9(3) O(7A)-Cu(1)-O(1) 102.2(3)
O(7B)-Cu(1)-O(2C) 84.1(3) O(7B)-Cu(1)-O(1) 77.8(3)
O(7A)-Cu(1)-O(2D) 84.1(3) O(2C)-Cu(1)-O(1) 97.6(3)
O(7B)-Cu(1)-O(2D) 95.9(3) O(2D)-Cu(1)-O(1) 82.4(3)
O(4)-Cu(2)-N(1) 97.0(3) O(4)-Cu(2)-N(2)
O(3)-Cu(2)-N(1) 82.6(3) O(3)-Cu(2)-N(2)
83.9(3)
95.8(3)
N(1)-Cu(2)-N(2) 175.56(3) O(4)-Cu(2)-O(5E) 77.5(3)
O(3)-Cu(2)-O(4) 170.6(3) O(3)-Cu(2)-O(5E) 93.2(3)
O(1)-Cu(2)-O(4) 88.9(3) N(1)-Cu(2)-O(5E) 77.1(3)
O(1)-Cu(2)-O(3) 100.5(3) N(2)-Cu(2)-O(5E) 98.8(3)
N(1)-Cu(2)-O(1) 93.4(3) O(3)-Cu(2)-O(5E) 162.2(2)
N(2)-Cu(2)-O(1) 91.1(3) N(3A)-Cu(3)-N(3)
180.0
N(3A)-Cu(3)-O(6) 96.8(3) O(6)-Cu(3)-O(5)
91.4(3)
N(3)-Cu(3)-O(6) 83.2(3) O(6A)-Cu(3)-O(5) 88.6(3)
N(3A)-Cu(3)-O(6A) 83.2(3) N(3A)-Cu(3)-O(5A) 88.1(3)
N(A)-Cu(3)-O(6A) 96.8(3) N(3)-Cu(3)-O(5A) 91.9(3)
O(6)-Cu(3)-O(6A) 180.0 O(6)-Cu(3)-O(5A) 88.6(3)
N(3A)-Cu(3)-O(5) 91.9(3) O(6A)-Cu(3)-O(5A) 91.4(3)
N(3)-Cu(3)-O(5) 88.1(3) O(5)-Cu(3)-O(5A)
180.0
Each copper(II) ion occupies an octahedral coordination geometry. There are three distinct copper
environments, with two of the copper centres – Cu(2) and Cu(3) – bound by two bidentate 2-
pyridylcarboxylate ligands which coordinate via the pyridyl nitrogen and one of the carboxylate
oxygens; the remaining carboxylate oxygen coordinates to a different copper centre, which gives
rise to the observed two-dimensional polymeric structure. Cu(1) and Cu(2) are bridged by a water
molecule; this water molecule partakes in hydrogen bonding to the perchlorate anion {O(1)-
H(11)...O(9)} which are located in a regular array on either side of the sheet structure. The
coordination geometry about Cu(1) is more significantly distorted from ideal octahedral, compared
to Cu(2) and Cu(3).
15

3.3 EPR spectroscopy
To gain further information on the structure and coordination of the complex, the low temperature
(140 K) CW-EPR spectrum of 2a was recorded (Fig. 4). The spectrum was simulated using a quasi-
axial g tensor (g1 = 2.075 0.005, g2 = 2.078 0.005, g3 = 2.328 0.005), with 63,65Cu hyperfine
determined from the simulation as CuA1=30 7MHz, CuA2=30 7MHz and CuA3=409 4MHz. The
spectrum is considerably broadened, particularly in the g1,2 region, presumably due to the
underlying 14N superhyperfine couplings from the Pyox ligand,. There is also some evidence of g/A
strain in the spectrum (particularly in the mCu=-3/2 line). The hyperfine couplings were determined
N
from the simulation as CuA1=30 7MHz, CuA2=30 7MHz, CuA3=409 4MHz, and A1=30 7MHz,
N
N
NA2=30 7MHz, A3=38 4MHz based on two equivalent 14N nuclei. Although the A hyperfine
values cannot be resolved, the expected coupling magnitude of ~ 30 MHz (as limited by the
measured EPR linewidth) is consistent with those expected for Cu(II) complexes coordinated to N4,
N2O2 and N2 bearing ligands (i.e., in porphyrins, [31] salens, [32] bis-oxazolines [33]). [34] To
date, there are no detailed EPR studies reported for Cu(II)-Pyox complexes. However Bolm et al.,
described the EPR, ENDOR and HYSCORE analysis of a series of Cu(II) bis-sulfoxime complexes,
whereby the bidentate ligand coordinated to Cu(II) via the two nitrogens, and both solvent
molecules and counterions were also involved in the copper coordination sphere. The reported g/A
values [35] are similar for 2a. The coordinated acetonitrile and perchlorate are not directly evident
from the EPR measurements, but the g and CuA values are typical of those expected for a distorted
6-coordination mode for the Cu(II) ion, and thus consistent with the structure reported in Fig. 1.
The interactions with the two Pyox nitrogen nuclei, and potentially the coordinated acetonitrile
ligand, could be further probed via high-frequency ENDOR measurements (data unavailable).
16

Fig. 4. X-band CW EPR spectrum (140K) of 2a. a) experimental, b) simulation.
3.4 DFT calculations
Fig. 5. Calculated structure of [Cu(Bn-PyOx)(NCMe)2(ClO4)2]
As a representative example, the structure of 2a was calculated using density functional methods.
The calculated structure is provided in Fig. 5; the metric parameters are in reasonable agreement
with those obtained from the X-ray structure (vide infra). The Cu–N bond lengths are around 2 Å,
which are similar to those in 2a, whilst the Cu–Operchlorate distances are 2.503 and 2.255, in which
the latter is somewhat underestimated and the former is in excellent agreement with the
experimental data. Interestingly, a calculated structure that reproduced the perchlorate coordination
was only obtained upon using diffuse functions to the basis set (6-31+G(d,p)); varying the
functional to B3PW91 or M06, or the basis set to 6-311+G(d,p) or aug-cc-pVDZ did not
significantly alter the Cu–Operchlorate distances. Equivalent calculations performed employing the 6-
31G(d,p) basis set gave 5-coordinate structures in which one perchlorate was de-coordinated from
the metal.
17

Fig. 6 Principal β-MOs involved in TD-DFT computed absorption (HOMO-11→SOMO)
TD-DFT calculations were performed on the optimised structure, and indicated excited state
absorptions at 709 and 693 nm, in agreement with the observed spectral absorption at 694 nm.
These absorptions correspond largely to transitions between the HOMO-11 and the SOMO (Fig. 6),
and contain both LMCT and d-d character.
3.5 Oxidation catalysis
The use of pyridine-oxazoline ligands in the copper-catalysed allylic oxidation of cyclic alkenes
was reported by Clark,[4] who employed [CuI(NCMe)4][PF6] as the copper source and several
ligand motifs, including 1b. It was reported that the oxidation reaction was sluggish at room
temperature, an observation supported by others with copper bisoxazoline complexes.[36] Out of
the various pyridine-oxazoline ligand types employed by Clark, those containing the pyridine
directly bound to the oxazoline moiety were found to give the lowest enantioselectivities (17% and
28% for Ph and iBu stereodirecting groups respectively).
Copper Pyox complexes were probed for their effectiveness in the copper-catalysed allylic
oxidation of cyclohexene with tert-butyl peroxybenzoate, using 5 mol% catalyst (Scheme 3).
[37,38] Owing to the ambiguity of the coordination chemistry (specifically in the formation of 3),
we prepared samples for catalytic studies in situ, immediately prior to adding the catalytic
substrates. The catalyst performances are summarised in Table 4.
Ph
O
O
O
O
Ph
O
tBu
CuX2, ligand
18

Scheme 3. Asymmetric allylic oxidation of cyclohexene
When Cu(II) complexes bearing Pyox ligands (triflate analogues of 2a-c) were employed as
catalysts, acetonitrile was consistently found to be the most suitable solvent, as is consistent with
several other reports. Previous studies of Cu(II) catalysed oxidation reactions with bis(oxazoline)
ligands have shown very little variation in catalytic activity and stereodirection with differing
counter ions.[39] When acetone was used as the solvent, no stereoinduction was found with any of
the three pre-catalysts. Table 3 includes isolated yields, however for each entry the catalytic
reaction was allowed to run until the complete disappearance of the peroxyester. It is noteworthy
that this took significantly longer when compared to most other ligand systems, i.e. 6 weeks at
ambient temperature, compared to typically 1 week for bisoxazoline complexes [36] and 2 weeks
when no chiral ligand was added (entries 10 and 11). Given the propensity for lower
enantioselectivities at elevated temperatures, higher reaction temperatures were not employed, but it
was noted that cooling the reaction to 0 °C completely suppressed the reaction, with no conversion
being observed after 6 weeks. The iPr (2c) complex was found to give the highest selectivity (37%,
entry 3), with the benzyl congener (2a) giving 29% (entry 1). Adding phenylhydrazine has
previously been shown to increase the rates, yields and selectivities in previous studies on
bisoxazoline and chiral bipyridyl complexes [40] by reducing the Cu(II) to Cu(I) in situ. Here, the
reaction rate was increased but the reaction was still found to be slow and enantioselectivities were
lower (entries 12 – 14). Interestingly, whilst using acetone as a solvent gave no enantioselectivity
when only Cu(II) was employed (entries 7 – 9), reactions in acetone were found to give modest
enantioselectivities when phenylhydrazine was added (entries 15 – 17).
Table 4 Asymmetric allylic oxidation of cyclohexene using PhCO3-tBu as oxidant
19

Entry Ligand Cu salt T/°C Solvent
Timea Conv % ee (%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Cu(OTf)2 20 MeCN
Cu(OTf)2 20 MeCN
Cu(OTf)2 20 MeCN
6 weeks
6 weeks
6 weeks
6 weeks
6 weeks
6 weeks
6 weeks
6 weeks
6 weeks
2 weeks
6 weeks
3 weeks
3 weeks
3 weeks
99
99
99
0c
29
15
37
-
-
-
<5
<5
<5
<2
<2
25
16
26
18
10
12
30
15
35
1a
1b
1c
1a
1b
1c
1a
1b
1c
-
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
0
0
0
MeCN
MeCN
MeCN
0 c
0 c
23
99
54
99
99
45
64
40
30
31
60
53
41
65
Cu(OTf)2 20 Acetone
Cu(OTf)2 20 Acetone
Cu(OTf)2
0
Acetone
Cu(OTf)2 20 MeCN
-
Cu(OTf)2
0
MeCN
Cu(OTf)2 20 MeCNd
Cu(OTf)2 20 MeCNd
Cu(OTf)2 20 MeCNd
1a
1b
1c
1a
1b
1c
1a
1b
1c
Cu(OTf)2 20 Acetoned 3 weeks
Cu(BF4)2 20 Acetoned 3 weeks
Cu(OTf)2 20 Acetoned 3 weeks
Cu(OTf)2 20 MeCNe
Cu(OTf)2 20 MeCNe
Cu(OTf)2 20 MeCNe
4 weeks
4 weeks
4 weeks
a Reactions were run until judged complete by TLC (disappearance of the peroxyester). b the R
enantiomer is predominant except for values in italics, for which the S enantiomer is predominant,
based upon previous reports.[39] c No reaction was observed under these conditions. d 1 eq. of
phenylhydrazine added. e Catalysis performed under argon in anhydrous solvent.
Given that the complexes 2a–c are pure (by elemental analysis) when first formed, the afore-
mentioned ligand hydrolysis reactions are likely to lead to a gradual increase in the quantity of 3
present in the reaction mixture. It is a reasonable supposition that the 2-pyridine-carboxylate
coordinated copper centres may be able to catalyse the reaction, albeit in a non-stereoselective
manner. In order to probe this hypothesis, the catalysis studies were repeated using strictly
anhydrous conditions (other than drying the peroxyester for safety reasons). In these cases, no
alteration in enantioselectivity was observed (entries 18 – 20); this suggests that the copper-
promoted ligand hydrolysis, whilst forming an achiral copper species, does not degrade the
enantioselectivity. This suggests that the copper centres incorporated into the coordination polymer
are subsequently unavailable for catalytic activity, a conclusion which is qualitatively supported by
the observation that the peroxyester was consumed in 4 weeks, rather than 6 weeks under aerobic
conditions.
20

4. Conclusions
Copper complexes of pyridine-oxazoline (Pyox) ligands have been prepared and are suitable
catalysts for the allylic oxidation of cyclohexene. However, in the coordination sphere of copper,
these ligands show a propensity to undergo hydrolysis, affording 2-pyridine carboxylate ligands,
which were isolated as part of a coordination polymer with the copper(II) ions. This observation is
suggestive in that this process may be an important contributor in other systems containing
oxazoline ligands; ligand stability during catalysis is often neglected and an understanding of these
processes will be beneficial in the rational design of catalytically active, functional metal
complexes.
Acknowledgements
Financial support from the EPSRC (EP/H012109: postdoctoral fellowship to A.J.H.) and the Royal
Society is gratefully acknowledged.
Appendix A. Supplementary material
Molecular structures of both symmetry independent molecules of 2a, details of the excited states of
2a, and a text file of computed coordinates in a format for convenient visualisation. Supplementary
information associated with this article can be found in the online version. Crystallographic data
can be obtained from the Cambridge Crystallographic Data Centre, CCDC 886430 and 886431.
References
[1]
(a)
(b)
[2]
For examples see
R. Choukroun, F. Wolff, C. Lorber, B. Donnadieu, Organometallics, 22 (2003) 2245;
S. Harder, Angew. Chem. Int. Ed., 42 (2003) 3430.
(a) B.D. Ward, H. Risler, K. Weitershaus, S. Bellemin-Laponnaz, H. Wadepohl, L. H. Gade,
Inorg. Chem., 45 (2006) 7777;
(b)
C.J. Cooper, M.D. Jones, S.K. Brayshaw, B. Sonnex, M.L. Russell, M.F. Mahon, D.R.
Allan, Dalton Trans., 40 (2011) 3677.
21

[3]
H. Brunner, U. Obermann, Chem. Ber., 122 (1989) 499.
[4]
J.S. Clark, K.F. Tolhurst, M. Taylor, S. Swallow, J. Chem. Soc., Perkin Trans. 1, (1998)
1167.
[5]
A. Cornejo, J.M. Fraile, J.I. García, M.J. Gil, C.I. Herrerías, G. Legarreta, V. Martínez-
Merino, J.A. Mayoral, J. Mol. Catal. A: Chem., 196 (2003) 101.
[6]
[7]
[8]
[9]
P. Segl’a, M. Jaminsky, M. Koman, T. Glowiak, Polyhedron, 17 (1998) 2765.
M. Koman, P. Segl’a, M. Jaminsky, T. Glowiak, Acta Cryst., C56 (2000) 554.
P. Segl’a, M. Koman, T. Glowiak, J. Coord. Chem., 50 (2000) 105.
H. Brunner, C. Zettler, M. Zabel, Monatsh. Chem., 134 (2003) 1253.
[10] A.C. Laungani, M. Keller, B. Breit, Acta Cryst., E64 (2008) m24.
[11] T.P.P. Spalek, Z. Sojka, J. Chem. Inf. Model, 45 (2005) 18.
[12] D.W. Dodd, H.E. Toews, M.J. Trevail, M.C. Jennings, R.H.E. Hudson, N.D. Jones, Can. J.
Chem., 87 (2009) 321.
[13] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M.C. Burla, G. Polidori, M.
Camalli, J. Appl. Cryst., 27 (1994) 435.
[14] A. Altomare, M. C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, A. Guagliardi, A.G.G.
Moliterni, G. Polidori, R. Spagna, J. Appl. Cryst., 32 (1999) 115.
[15] P.W. Betteridge, J.R. Carruthers, R.I. Cooper, K. Prout, D. J. Watkin, J. Appl. Cryst., 36
(2003) 1487.
[16] G.M. Sheldrick, Acta Cryst., A64 (2008) 112.
[17] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P.
Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R.
Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A.
Montgomery Jr, J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N.
Staroverov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S.
Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken,
22

C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C.
Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J.
J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski
and D. J. Fox, in Gaussian 09, Revision D.01, Gaussian Inc., Wallingford CT, 2010.
[18] A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
[19] C. T. Lee, W. T. Yang, and R. G. Parr, Physical Review B, 37 (1988) 785.
[20] D. Andrae, U. Haussermann, M. Dolg, H. Stoll, and H. Preuss, Theor. Chim. Acta, 77
(1990) 123.
[21] W. J. Hehre, R. Ditchfie, and J. A. Pople, J. Chem. Phys., 56 (1972) 2257.
[22]. M. M. Francl, W. J. Pietro, W. J. Hehre, J. S. Binkley, M. S. Gordon, D. J. Defrees, and J. A.
Pople, J. Chem. Phys., 77 (1982) 3654.
[23]. T. Clark, J. Chandrasekhar, G. W. Spitznagel, and P. V. Schleyer, J. Comput. Chem., 4
(1983) 294.
[24]. A. Vlček and S. Zalis, Coord. Chem. Rev., 251 (2007) 258.
[25] J. Tomasi, B. Mennucci, and R. Cammi, Chem. Rev., 105 (2005) 2999.
[26] A. Bondi, J. Phys. Chem., 68 (1964) 441.
[27] F.H. Allen, Acta Cryst., B58 (2002) 380 (The UK Chemical Database Service: CSD version
5.36 updated November 2014).
[28] K.N. Lazarou, V. Psycharis, S.P. Perlepes, C.P. Raptopoulou, Polyhedron, 28 (2009) 1085.
[29] P. Segl’a, M. Jamnický, M. Koman, J. Šima, T. Glowiak, Polyhedron, 17 (1998) 4525.
[30] C. Biswas, P. Mukherjee, M.G.B. Drew, C. J. Gómez-García, J.M. Clemente-Juan, A.
Ghosh, Inorg. Chem., 46 (2007) 10771.
[31] C. Finazzo, C. Cale, S. Stoll, S. Van Dorslaer, A. Schweiger, Phys. Chem. Chem. Phys., 8
(2006) 1942.
[32] D.M. Murphy, I. Carretti, E. Carter, I.A. Fallis, M.C. Göbel, J. Landon, S. Van Doorslaer,
D.J. Willock, Inorg. Chem., 50 (2011) 6944.
[33] M.E. Owen, E. Carter, G.J. Hutchings, B.D. Ward, D.M. Murphy, Dalton Trans., 41 (2012),
11085.
23

[34] Transition Ion Electron Paramagnetic Resonance, J.R. Pilbrow, Oxford Science
Publications, 1990.
[35] C. Bolm, M. Martin, G. Gescheidt, C. Palivan, T. Stanoeva, H. Bertagnolli, M. Feth, A.
Schweiger, G. Mitrikas, J. Harmer, Chem. Eur. J., 13 (2007) 1842.
[36] (a) A.S. Gokhale, A.B.E. Minindis, A. Pfaltz, Tetrahedron Lett., 36 (1995) 1831;
(b) M.B. Andrus, A.B. Agrade, X. Chen, M.G. Pamment, Tetrahedron Lett., 36 (1995) 2945;
(c) K. Kawasaki, S. Tsumura, T. Katsuki, Synlett, (1995) 1245;
(d) A. Levina, J. Muzart, Tetrahedron: Asymmetry, 6 (1995) 147.
[37] (a) M.S. Kharasch, G. Sosnovsky, J. Am. Chem. Soc., 80 (1958) 756;
(b) M.S. Kharasch, G. Sosnovsky, J. Am. Chem. Soc., 81 (1959) 5819;
(c) A.L. Beckwith, A.A. Zavitsas, J. Am. Chem. Soc., 108 (1986) 8230.
[38] For reviews of allylic oxidation of cyclic olefins with peresters see:
(a) M.B. Andrus, J.C. Lashley, Tetrahedron, 58 (2002) 845;
(b) J. Eames, M. Watkinson, Angew. Chem. Int. Ed., 40 (2001) 3567.
[39] M. Seitz, C. Capacchione, S. Bellemin-Laponnaz, H. Wadepohl, B.D. Ward, L.H. Gade,
Dalton Trans., (2006) 193.
[40] (a) G. Sekar, A.DattaGupta, V.K. Singh, J. Org. Chem., 63 (1998) 2961.
(b) M.P.A. Lyle, P.D. Wilson, Org. Biomol. Chem., 4 (2006) 41.
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Graphical abstract
The coordination chemistry of copper bearing chiral pyridine-oxazoline ligands, and their role
in oxidation catalysis, is presented. The coordinated ligands undergo hydrolysis by fortuitous
water, affording a coordination polymer consisting of copper coordinated by pyridine-2-
carboxylate ligands.
25

Highlights:
ꢀ Coordination chemistry of Cu(II) complexes bearing pyridine-oxazoline ligands
ꢀ Hydrolysis of the coordinated ligand forms a coordination polymer of pyridine-2-
carboxylate
ꢀ EPR analysis of complexes
ꢀ Oxidation catalysis studied
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