When is an imine not an imine? Unusual reactivity of a series of Cu(ii) imine-pyridine complexes and their exploitation for the Henry reaction

Article abstract of DOI:10.1039/c0dt01740j

In this paper we report the synthesis and solid-state structures for a series of pyridine based Cu(ii) complexes and preliminary data for the asymmetric Henry reaction. Interestingly, the solid-state structures indicate the incorporation of an alcohol into one of the imine groups of the ligand, forming a rare α-amino ether group. The complexes have been studied via single crystal X-ray diffraction, EPR spectroscopy and mass spectrometry. Intriguingly, it has been observed that the alcohol only adds to one of the imine moieties. Density functional theory (DFT) calculations have also been employed to rationalise the observed structures. The Cu(ii) complexes have been tested in the asymmetric Henry reaction (benzaldehyde + nitromethane or nitroethane) with ee's up to 84% being achieved as well as high conversions and modest diastereoselectivities. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c0dt01740j

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PAPER
When is an imine not an imine? Unusual reactivity of a series of Cu(II)
imine-pyridine complexes and their exploitation for the Henry reaction†
Christine J. Cooper,a Matthew D. Jones,*a Simon K. Brayshaw,a Benjamin Sonnex,a Mark L. Russell,a
Mary F. Mahona and David R. Allanb
Received 10th December 2010, Accepted 8th February 2011
DOI: 10.1039/c0dt01740j
In this paper we report the synthesis and solid-state structures for a series of pyridine based Cu(II)
complexes and preliminary data for the asymmetric Henry reaction. Interestingly, the solid-state
structures indicate the incorporation of an alcohol into one of the imine groups of the ligand, forming a
rare a-amino ether group. The complexes have been studied via single crystal X-ray diffraction, EPR
spectroscopy and mass spectrometry. Intriguingly, it has been observed that the alcohol only adds to
one of the imine moieties. Density functional theory (DFT) calculations have also been employed to
rationalise the observed structures. The Cu(II) complexes have been tested in the asymmetric Henry
reaction (benzaldehyde + nitromethane or nitroethane) with ee’s up to 84% being achieved as well as
high conversions and modest diastereoselectivities.
selective for this reaction.10 Oxazolines, imines and amine ligands
Introduction
with Cu(II) have also been exploited for this reaction.11 However,
The use of imines (C N) as ligands in coordination chemistry and
Cu(II) is by no means the only metal centre that will catalyse this
catalysis is ubiquitous.1 This is simply because imines are versatile
ligands and can bind to many metal centres. In the preparation
of such metal complexes alcohol solvents (in particular MeOH
and EtOH) are commonplace and it is generally assumed that the
solvent is innocent in terms of reactivity. However, under certain
circumstances these labile azomethine linkages can be susceptible
to attack by alcohols to generate O-alkyl hemiaminals. Such
species are believed to be short lived intermediates in the formation
of imines.2 Very recently, and for the first time, Fujita was able to
crystallographically characterise a transient hemiaminal trapped
in a porous Zn(II) network.2 However, pertinent to this study are
the very limited crystallographically characterised examples of
such ligated species. Notable examples include those of Pregosin
(Pt),3 Hoskins (Cu),4 Rybak–Akimova (Cu)5 and Mitra (Ni)6
where the coordination of the metal ion is believed to stabilise
the highly reactive a-amino ether.
process Zn(II),12 Cr(III),13 La(III)14 and Co(II)15 are active for this
transformation.
In this paper we have prepared a series of Cu(II) complexes based
on Schiff base pyridine ligands where the solvent has played a key
role in the formation of unexpected products. In some instances
the alcohol solvent has reacted with one of the imine groups of the
ligand to form an a-amino ether group. The nature of the alcohol
has been varied to study this effect in more detail.
Results and discussion
Ligand and complex preparation
As part of our on going investigations into the use of Cu(II)
complexes in asymmetric catalysis we were interested in the
coordination chemistry of ligands L1–L4, Scheme 1 and 2.11d
These ligands were readily prepared by the reaction of (1R,2R)-
diaminocyclohexane with pyridine-2-carboxaldehyde or 6-methyl-
2-pyridine carboxaldehyde and reduction with NaBH4 where
appropriate. All ligands were characterised by multi-nuclear NMR
spectroscopy and HR-MS.
Ligand L1 was reacted with one equivalent of Cu(OTf)2 in
methanol, in anticipation of generating Cu(1)(OTf)2, Scheme 2.
However, this was not the case and instead methanol added across
one imine and [Cu(1-MeOH)](CF3SO3)2 was isolated, Scheme 2.
The cation is shown in Fig. 1, in-which one of the imine groups
of the ligand has reacted with MeOH to form the rare a-amino
ether moiety. Selected bond lengths for all complexes prepared are
shown in Table 1.
Cu(II) complexes have been extensively utilised in the asym-
metric Henry (nitro aldol) reaction.7 For example, Bandini et al.
have utilised a series of C2-symmetrical oligothiophene ligands
for this reaction.8 Blay and co-workers have applied C1-symmetric
camphor derived amino pyridine ligands with high ee’s being
observed.9 Sparteine Cu(II) complexes have been shown to be
aDepartment of Chemistry, University of Bath, Claverton Down, Bath., BA2
7AY, U.K. E-mail: mj205@bath.ac.uk; Fax: +44 (0)1225 386231; Tel: +44
(0)1225 384908
bDiamond Light Source, Didcot, OX11 0DE, Oxon, England
† Electronic supplementary information (ESI) available. CCDC reference
numbers 804589–804597. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt01740j
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Scheme 1 Ligands used in this study.
Fig. 1 Top: Molecular structure of the cation [Cu(1-MeOH)]2+ Bottom:
Molecular structure of the cation [Cu(1)]2+ prepared from IPA. In both
cases the triflate anions all H atoms (except H3A) have been removed for
clarity.
addition of MeOH across the imine was 100% as indicated by the
fact that this was fully occupied in the crystal structure. Whereas
for the other Cu(II) centre the occupancy of the alcohol group was
˚
40%. This is exemplified by the N(3)–C(13) distance of 1.450(7) A,
indicative of a nitrogen-carbon single bond, in the fully occupied
system. Whilst, in the partially occupied system this distance is
˚
1.358(8) A; thereby averaging a C–N and C N bond length. Also
of note was that only one Schiff base group of each ligand reacted
with the alcohol solvent.
Upon reaction with MeOH a new chiral centre was generated
at C(13), which has the S configuration. In the MS a peak at
504.0473 was observed corresponding to [Cu(1)·CF3SO3]+ and a
major peak at 536.0745 assigned as [Cu(1-MeOH)·CF3SO3]+ was
also detected, Scheme 2. In the MS there was no peak due to the
addition of MeOH to both imine moieties. As expected for an
MS run in CD3OD a mass at 539.0925 was detected, presumably
the initially formed N–D is labile and exchanges with free H+
in the mass spectrometer. Spurred on by this result the reaction
Scheme 2 Novel Cu(II) complexes prepared in this study.
In the solid-state there are two crystallographically unique
Cu(II) centres both with a square planar arrangement of nitrogen
atoms and a weakly coordinating triflate anion completing the
coordination sphere of the metal. For one of the Cu(II) centres the
Table 1 Selected bond lengths for complexes prepared in this work
Ligand
Cation
L1 (Solvent)a
L2
L3
[Cu(1-
[Cu(1-
[Cu(1-
[Cu(1-MeO- [Cu(1-CF3-
[Cu(1-C6H5-
[Cu(1)-MeOH+
(solvent)a
MeOH)]2+ EtOH)]2+ IPA)]2+
(CH2)2OH)]2+ CH2OH)]2+
CH(OH)CH3)]2+ AcOH)]2+
[Cu(2)]2+
[Cu(3·MeOH)]2+
Cu(1)–N(1) 2.054(5)
Cu(1)–N(2) 1.993(5)
Cu(1)–N(3) 2.035(5)
Cu(1)–N(4) 1.955(5)
N(3)–C(13) 1.450(7)
2.056(5)
1.994(6)
2.024(5)
1.948(6)
1.475(7)
1.251(9)
2.018(5) 2.000(8)
2.044(10)
2.047(11)
1.964(11)
1.942(10)
1.275(16)
1.276(14)
2.032(2)
1.958(2)
—
2.045(4)
1.982(4)
2.020(4)
1.943(4)
1.448(5)
1.273(6)
2.006(4)
1.995(3)
2.002(3)
1.993(3)
1.453(5)
—
2.035(4)
2.038(4)
1.940(3)
1.956(4)
1.277(5)
1.264(5)
2.036(6) 2.043(9)
1.950(5) 1.939(8)
1.965(5) 1.968(8)
1.266(8) 1.259(12)
1.268(8) 1.275(11)
—
—
N(4)–C(6)
1.284(8)
1.258(3)b
a For complexes prepared from L1 the solvent is that used to prepare and crystallise the sample, see Scheme 2. b Due to symmetry this in N(2)–C(6).
3678 | Dalton Trans., 2011, 40, 3677–3682
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Table 2 Energies calculated from DFTa
was repeated in EtOH and again it was observed that the solvent
had added to only one of the imine moieties. The structure is
analogous to that formed in MeOH, with two crystallographically
unique Cu(II) centres-one with a fully occupied alcohol group
and another with a partially occupied alcohol moiety. Again the
Cu(II) centres have a square planar arrangement of nitrogen atoms
and a weakly coordinating anion. In the MS the a-amino ether
species was observed at 550.0919. As with the previous case a
new chiral centre was observed at C(13) which is again the S
form. If isopropanol (IPA) was employed then no a-amino ether
product was observed in the solid state and Cu(1)(CF3SO3)2 was
isolated (Fig. 1 and Scheme 2). However, a small peak for the
ether was observed in the MS. Interestingly, if a racemic form
of 1-phenyl ethanol was utilised as the solvent then no a-amino
ether was detected. However, is it noteworthy that the crystal was
chirally enriched, with the solvent of crystallisation being 75%
S enantiomer and 25% R enantiomer. This lack of formation of
the a-amino ether species is presumably due to the extra steric
bulk of these alcohols hindering its formation. The reaction was
repeated with the electron withdrawing alcohols MeO(CH2)2OH
and CF3CH2OH, which are more acidic but less nucleophilic,
in an attempt to shed additional light on the reactivity. It was
hypothesised that there are two possible mechanisms of attack i)
the alcohol dissociates in solution and the anion (RO-) then attacks
the carbon of the imine or ii) the alcohol first pre-coordinates to
the metal centre and then attacks the imine. When more acidic
alcohol solvents were employed no a-amino ether product was
observed which indicates that pre-coordination of the alcohol is
potentially involved. In an attempt to form the structure in which
both alcohols are fully occupied in the solid state the complexation
was also performed in a MeOH/acetic acid mixture (9 : 1). As
before there were two crystallogaphically unique Cu(II) centres.
The occupancy of the added alcohol was now 100% for both Cu(II)
cations. In this case the N(3)–C(13) bond length was 1.448(5) and
Cation
DE/kJ mol-1
DH/kJ mol-1
DG/kJ mol-1
[Cu(1)]2+
0
0
0
[Cu(1-MeOH)]2+
[Cu(1-MeOH)]2+,b
[Cu(1-MeOH2)]2+,c
[Cu(1-EtOH)]2+
[Cu(1-iPrOH)]2+
-88.6
-62.7
-152.5
-69.8
-62.2
-73.1
-50.0
-126.1
-56.2
-46.7
-11.3
+11.6
-15.9
+0.6
+9.8
a See supporting information for full details of the analysis. b Energy for
the other diastereoisomer-R at C(13). c Energy for the double addition of
MeOH.
with no trace being observed in the mass spectrum. Therefore, it
is assumed that this species is kinetically not favourable.
Unsurprisingly, with the reduced ligand L2 Cu(2)(CF3SO3)2 was
formed, Scheme 2. In this case the Cu(II) centre has a square planar
arrangement of nitrogen atoms and a weakly coordinating anion.
In an attempt to gain more of an understanding into the methanol
addition process the Cu(II) complex of ligand L3 was prepared in
MeOH, Fig. 2:
Fig. 2 Molecular structure of the cation [Cu(3·MeOH)]2+ the triflate
˚
in the other Cu(II) cation the analogous length was 1.431(6) A.
anions have been removed for clarity. This was recrystallised in MeOH.
The Cu(II) complexes formed with L1 were analysed via EPR
spectroscopy in MeOH, EtOH and IPA which all showed similar g
and A values to eachother and analogous Cu(II) complexes in the
literature.16 Elemental analysis was consistent with the addition
of MeOH being the bulk crystallised product and the MS of the
solution after crystallisation and the crystals were identical. A
pXRD of the crude product (before recrystallisation) is analogous
to that determined from the crystal data, implying that methanol
addition is occurring on a significant scale, with this ligand system.
The a-amino ether species were probed via DFT calculations,
see Table 2 and Supporting Information for details on the LUMOs
and HOMOs for the respective Cu(II) species. The calculations
clearly showed that the addition of MeOH was energetically
favourable. The addition of EtOH was seen to be energetically
neutral, but given it is present in large excess this addition can
be observed. From the calculations it is seen that addition of
iPrOH to the imine is unfavourable, supporting our empirical
observations. In all cases the new chiral centre at C(13) is S.
From DFT calculations the formation of the R diastereoisomer
is much higher in energy (+22.9 kJ mol-1) and this is presumably
why only one form is detected in the solid-state. However, the
addition of a methoxy group to both imine groups is predicted
to be thermodynamically feasible. However, even under reflux
conditions we were unable to assist the production of this species
In this case the solid-state product included a coordinated
MeOH moiety and the imine was left intact. Analysis of the
product via MS indicated there was only a trace amount of the
a-amino ether species present. This is presumably related to the
extra degree of steric bulk caused by the addition of the ortho
methyl group on the pyridine ring.
Catalysis
The complexes described, together with Cu(II) complexes formed
with ligands shown in Scheme 3 were tested for the asymmetric
Henry reaction with benzaldehyde and either nitromethane or
nitroethane. The results of which are shown in Tables 3 and 4.
As a direct comparison we have prepared Cu(II) complexes of
related ligands, Scheme 3.7h,8 Complexes based on L9 have been
shown by Bandini to be very effective catalysts for this reaction.
Interestingly, they observed that the unsaturated version of the
ligand afforded no enantioselectivity.8 Ligands L6 and L8 have
been shown to form supramolecular arrays with Cu(II) in the
solid state with bridging pyridine moieties.7h However, the related
furan ligand, L10, has not been previously exploited for this
reaction.
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Table 3 Catalytic results for the Henry reaction with nitromethanea
Catalyst prepared fromb
Solvent
T/◦C
Con/%c
eed
L1
L1
L1
L1
L2
L3
L4
L5
L6
L7
L8
L9
L9
L10
L10
MeOH
MeOH
EtOH
20
0
50
34
40
27
98
18
44
82
95
74
96
94
94
96
95
42
34
33
19
4
2
5
26
26
1
46
37
80
57
84
20
20
20
20
20
20
20
20
20
20
0
IPA
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
20
0
a Catalyst:benzaldehyde:Nitromethane molar ratio employed was
0.05 : 1 : 10, b see Scheme 2 and 3; c conversion as determined by 1H NMR
spectroscopic analysis, d determined by chiral HPLC.
Table 4 Catalytic results for the Henry reaction with nitroethanea
Catalyst prepared fromb Solvent T/◦C Con/%c Anti:Synd eed
L1
L1
L1
L1
L2
L2
L3
L4
L5
L6
L6
L7
L8
L9
L9
L10
MeOH 20
MeOH
EtOH 20
IPA 20
MeOH 20
MeOH
MeOH 20
MeOH 20
MeOH 20
MeOH 20
80
38
31
61
97
86
73
99
99
95
72
96
95
87
77
90
59 : 41
58 : 42
60 : 40
62 : 38
68 : 32
79 : 21
61 : 36
73 : 27
58 : 42
59 : 41
33 : 67
60 : 40
41 : 59
57 : 43
30 : 70
46 : 54
33, 34
18, 21
10, 9
11, 16
32, 25
52,12
13, 7
36, 41
10, 12
7, 38
46, 30
5, 18
0
0
MeOH
0
MeOH 20
MeOH 20
MeOH 20
10, 37
20, 50
46, 29
33, 8
Scheme 3 Top: Henry reaction studied in this work. Bottom: extra ligands
employed for comparison.
MeOH
0
MeOH 20
Experimental
a Catalyst:benzaldehyde:Nitroethane molar ratio employed was
0.05 : 1 : 10, b see Scheme 2 and 3; c conversion as determined by 1H
NMR spectroscopic analysis, d determined by chiral HPLC.
1
1H and 13C{ H}are NMR spectra were recorded on a Bruker
300 or 250 MHz spectrometer, and referenced to residual sol-
vent peaks (CDCl3). Coupling constants are given in Hertz.
Elemental analysis was performed by Mr. A. K. Carver at
the Department of Chemistry, University of Bath. (1R,2R)-1,2-
diaminocyclohexane was resolved from the commercially available
trans-1,2-diaminocyclohexane by the method of Jacobson.
With nitromethane modest conversions and selectivities were
achieved with Cu(II) complexes prepared from L1–L4. The highest
ee was achieved with the furan system, L9. In most cases with
nitroethane the anti form of the product was prevalent and modest
ee’s were achieved; the highest being 50% ee for the syn isomer with
the Cu(II) complexes from L9 and 52% for the anti isomer with
[Cu(2)]2+.
Metal complexes
Cu(OTf)2 (0.20 g, 0.55 mmol) was dissolved in methanol (30 ml)
under argon, and L1 (0.16 g, 0.55 mmol) added. The reaction
mixture was stirred for 72 h at room temperature before the
solvent was removed by rotary evaporation. The product was
recrystallised from the minimum amount of methanol. Calcd.
C20.7H22.8N4O6.70F6S2Cu1 C, 36.75; H, 3.40; N, 8.28. Found C, 36.8;
H, 3.33; N, 8.25. IR 2945 w, 2868 w (C–H), 1663 m (C N), 1607
m, 1481 m, 1451 m (C N, C C pyridine), 1293 m, 1278 m, 1149 s,
1027 s, 784 m, 634 s. Analytical data for EtOH solvent preparation:
Calcd. C21.7H25.1N4O6.85F6S2Cu1 C, 37.60; H, 3.65; N, 8.08. Found
C, 37.4; H, 3.56; N, 7.98. IR 2950 w, 1668 m (C N), 1607 m,
Conclusions
In summary a series of Cu(II) Schiff base complexes have been
prepared and structurally characterised. The complexes have been
shown to react with the solvent to generate an a-amino ether
group. This should act as warning that in all cases when imines are
complexed in alcohol solvents all may not be what is seems. The
complexes, and related ligand systems, were tested for the Henry
reaction.
3680 | Dalton Trans., 2011, 40, 3677–3682
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Table 5 X-Ray crystallographic data
Cation
[Cu(1-MeOH)]2+
MeOH
[Cu(1-EtOH)]2+
EtOH
[Cu(1)]2+
IPA
[Cu(1)]2+
MeO(CH2)2OH
[Cu(1)]2+
CF3CH2OH
Solventa
Empirical formula
Formula weight
Crystal system
Space group
C20.7H22.8CuF6N4O6.7S2
676.49
Triclinic
C21.7H25.1CuF6N4O6.85S2
693.22
Triclinic
C23H28CuF6N4O7S2
714.15
Triclinic
P1
9.5699(3)
11.4168(3)
13.9033(4)
76.376(2)
82.061(1)
88.308(1)
1462.14(7)
2
1.622
0.977
27768
3.54–27.49
0.022(13)
12531, 0.0391
1.029
0.0528, 0.1213
0.0754, 0.1343
1.459, -0.518
C21H22.5CuF6N4O6.5S2 C22H21CuF9N4O7S2
676.59
Triclinic
P1
752.09
Triclinic
P1
P1
P1
˚
a/A
8.8600(5)
11.2890(5)
14.6510(7)
80.751(3)
86.603(2)
69.248(3)
1352.51(12)
2
8.8420(3)
11.6520(4)
14.8430(5)
98.123(2)
93.505(2)
111.186(2)
1401.10(8)
2
8.8900(2)
11.4790(3)
15.4820(5)
111.620(1)
101.199(1)
93.665(1)
1424.80(7)
2
9.5450(8)
11.4260(10)
13.6980(12)
78.636(6)
83.184(5)
88.992(5)
1454.3(2)
2
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
Volume/A
Z
D
calc/g cm-3
1.661
1.050
25918
3.57–27.48
0.027(13)
11526, 0.0452
1.018
0.0533, 0.1296
0.0815, 0.1481
0.681, -0.600
1.643
1.016
18888
4.20–27.48
0.017(15)
10538, 0.0570
1.033
0.0575, 0.1340
0.0725, 0.1449
0.736, -0.822
1.577
1.718
m/mm-1
0.996
26438
1.001
10765
Refns collected
q range/◦
3.56–27.47
0.02(2)
12251, 0.0496
1.036
4.16–24.16
-0.05(2)
7741, 0.0629
1.048
Flack parameter
Indep. refns(Rint)
Goodness-of-fit
R1, wR2 [I > 2s(I)]
R1, wR2 [all data]
0.0585, 0.1375
0.0922, 0.1559
1.219, -0.504
0.0548, 0.1137
0.0869, 0.1313
0.419, -0.447
-3
˚
Max, min difference/e A
Cation
[Cu(1)]2+
C6H5CH(OH)CH3
C36H40CuF6N4O8S2
898.38
Tetragonal
P43212
21.106(5)
21.106(5)
8.547(3)
90
[Cu(1)]2+
MeOH+AcOH
C21H24CuF6N4O7S2
686.10
Triclinic
P1
8.8590(2)
11.2530(3)
14.7790(5)
80.180(1)
86.856(1)
68.960(1)
1354.92(7)
2
1.682
1.050
19858
3.83–27.46
-0.025(10)
10511, 0.0355
1.023
0.0416, 0.1024
0.0490, 0.1080
0.600, -0.566
[Cu(2)]2+
MeOH
C20H24CuF6N4O6S2
658.09
Monoclinic
P21
9.5520(2)
27.0250(10)
10.1510(4)
90
97.143(2)
90
2600.07(15)
4
1.681
1.088
[Cu(3·MeOH)]2+
Solventa
MeOH
Empirical formula
Formula weight
Crystal system
Space group
C23H28CuF6N4O7S2
714.15
Triclinic
P1
˚
a/A
9.6290(3)
11.7880(5)
13.8240(5)
99.918(2)
105.773(2)
96.220(1)
1467.40(9)
2
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
90
90
3
˚
Volume/A
3807.5(16)
4
1.567
0.770
37331
2.65–26.74
0.101(14)
4433, 0.0419
1.139
0.0413, 0.0940
0.0435, 0.0958
0.280, -0.484
Z
D
calc/g cm-3
1.616
0.973
29086
3.56–27.55
0.004(8)
12630, 0.0335
1.042
0.0341, 0.0774
0.0438, 0.0830
0.302, -0.521
m/mm-1
Refns collected
34132
q range/◦
3.86–27.50
-0.005(9)
11316, 0.0568
1.039
0.0462, 0.1061
0.0711, 0.1061
0.401, -0.665
Flack parameter
Indep. refns (Rint)
Goodness-of-fit
R1, wR2 [I > 2s(I)]
R1, wR2 [all data]
-3
˚
Max, min difference/e A
a Solvent used for the recrystallisation, see Scheme 2 for further details.
1482 m, 1450 m (C N, C C pyridine), 1293 m, 1278 m, 1239,
1143 s, 1027 s, 773 m, 630 s. Analytical data for IPA solvent
preparation C20H20N4O6F6S2Cu1 C, 36.73; H, 3.08; N, 8.57. Found
C, 36.5; H, 2.81; N, 8.50. IR 2945 w, 2869 w (C–H), 1663 m (C N),
1607 m, 1481 m, 1451 m (C N, C C pyridine), 1293 m, 1239 s,
1278 m, 1149 s, 1027 s, 784 m, 634 s.
F2 data using the SHELXL-97 suite of programs, see Table 5 for
full crystallographic parameters.17 Hydrogen atoms were included
in idealised positions and refined using the riding model, except
for an OH group in [Cu(3·MeOH)]2+. Refinements were generally
straightforward with the following exceptions and points of
note. In [Cu(1)]2+ crystallised in IPA one molecule of solvent
was disordered over two positions in a 75 : 25 ratio and refined
isotropically. For the complexes recrystallised in CF3CH2OH and
1-phenyl ethanol the hydrogens of the alcohol OH group were
placed in calculated positions. For Cu(3·MeOH)(CF3SO3)2 the
alcohol hydrogen was found from analysis of the final difference
Fourier map and freely refined. For the complex crystallised in 1-
phenyl ethanol the solvent of crystallisation was 75% S enantiomer
and 25% R. As the compounds contain optically pure (1R,2R)-
diaminocyclohexane moieties, PLATON checks suggesting the
X-Ray crystallography†
All data were collected on a Nonius Kappa CCD diffractometer
˚
using Mo-Ka radiation (l = 0.71073 A) at a temperature of
150(2) K except 1-C6H5CH(OH)CH3 which were recorded at
station I19 Diamond light source using Synchrotron radiation
˚
(l = 0.68890 A), due to their small size {0.03 ¥ 0.03 ¥ 0.07 mm}.
All structures were solved by direct methods and refined on all
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The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 3677–3682 | 3681
©

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approximate presence of inversion centres in these structures can
immediately be disregarded.
3 A. Albinati, C. Arz and P. S. Pregosin, Inorg. Chem., 1988, 27, 2015–
2016.
4 B. F. Hoskins and F. D. Whillans, Journal of the Chemical Society
a -Inorganic Physical Theoretical, 1970, 123.
5 A. M. Herrera, G. V. Kalayda, J. S. Disch, R. P. Wikstrom, I. V.
Korendovych, R. J. Staples, C. F. Campana, A. Y. Nazarenko, T. E.
Haas and E. V. Rybak-Akimova, Dalton Trans., 2003, 4482–4492.
6 S. K. Dey, N. Mondal, M. S. El Fallah, R. Vicente, A. Escuer, X. Solans,
M. Font-Bardia, T. Matsushita, V. Gramlich and S. Mitra, Inorg. Chem.,
2004, 43, 2427–2434.
7 (a) H. H. Xu and C. Wolf, Chem. Commun., 2010, 46, 8026–8028;
(b) M. Luo and B. Yan, Tetrahedron Lett., 2010, 51, 5577–5580; (c) K.
Lang, J. Park and S. Hong, J. Org. Chem., 2010, 75, 6424–6435; (d) V. J.
Mayani, S. H. R. Abdi, R. I. Kureshy, N. U. H. Khan, A. Das and H. C.
Bajaj, J. Org. Chem., 2010, 75, 6191–6195; (e) A. Noole, K. Lippur, A.
Metsala, M. Lopp and T. Kanger, J. Org. Chem., 2010, 75, 1313–1316;
(f) E. C. Constable, G. Q. Zhang, C. E. Housecroft, M. Neuburger,
S. Schaffner, W. Woggon and J. A. Zampese, New J. Chem., 2009, 33,
2166–2173; (g) E. C. Constable, G. Q. Zhang, C. E. Housecroft, M.
Neuburger, S. Schaffner and W. D. Woggon, New J. Chem., 2009, 33,
1064–1069; (h) G. Q. Zhang, E. Yashima and W. D. Woggon, Adv.
Synth. Catal., 2009, 351, 1255–1262; (i) M. Bandini, M. Benaglia, R.
Sinisi, S. Tommasi and A. Umani-Ronchi, Org. Lett., 2007, 9, 2151–
2153; (j) G. Blay, E. Climent, I. Fernandez, V. Hernandez-Olmos and
J. R. Pedro, Tetrahedron: Asymmetry, 2006, 17, 2046–2049; (k) G.
Blay, E. Climent, I. Fernandez, V. Hernandez-Olmos and J. R. Pedro,
Tetrahedron: Asymmetry, 2007, 18, 1603–1612.
Typical catalytic procedure
Under nitrogen the solvent (10 ml) was added to a Schlenk flask,
to this the Cu(II) catalyst was added (0.05 mmol) and the solution
stirred. Benzaldehyde (0.1 ml, 1 mmol), nitromethane (0.55 ml,
10 mmol) and NEt3 (35 ml, 0.25 mmol) were added and the
solution stirred for the appropriate amount of time. After the
desired time the reaction was filtered through a plug of silica and
1
the solvents were removed in vacuo. H NMR spectroscopy was
used to determine the conversion by analysis of the 1H integral
for the PhCHO of benzaldehyde at 9.94 ppm to the 1H integral
of PhCH(OH)CH2NO2 at 5.45 ppm. The enantiomeric excess was
determined by HPLC using an Agilent Compact 1120 LC with UV
detection (230 nm). A flow rate of IPA:hexane (1 : 9) at 1 ml min-1
was used with a OD-H column, the retention times were 16.6 and
20.5 min for the two enantiomers. For nitroethane two doublets at
5.40 ppm (anti) and 5.00 ppm (syn) were observed. In the HPLC
(OD-H, 2 : 98 IPA/hexane at 1 ml min-1, UV = 210 nm) four peaks
at 34.3, 52.4 for the anti isomer and 44.4 and 56.7 for the syn
isomer were observed.
8 M. Bandini, F. Piccinelli, S. Tommasi, A. Umani-Ronchi and C.
Ventrici, Chem. Commun., 2007, 616–618.
9 G. Blay, L. R. Domingo, V. Hernandez-Olmos and J. R. Pedro, Chem.–
Eur. J., 2008, 14, 4725–4730.
10 H. Maheswaran, K. L. Prasanth, G. G. Krishna, K. Ravikumar,
B. Sridhar and M. L. Kantam, Chem. Commun., 2006, 4066–
4068.
11 (a) D. M. Du, S. F. Lu, T. Fang and J. X. Xu, J. Org. Chem., 2005, 70,
3712–3715; (b) D. A. Evans, D. Seidel, M. Rueping, H. W. Lam, J. T.
Shaw and C. W. Downey, J. Am. Chem. Soc., 2003, 125, 12692–12693;
(c) C. Palomo, M. Oiarbide and A. Laso, Eur. J. Org. Chem., 2007,
2561–2574; (d) M. D. Jones, C. J. Cooper, M. F. Mahon, P. R. Raithby,
D. Apperley, J. Wolowska and D. Collison, J. Mol. Catal. A: Chem.,
2010, 325, 8–14.
Acknowledgements
MDJ acknowledges the EPSRC (EP/F037864) for funding his
first grant and for a PhD studentship to CJC. We also thank the
EPSRC EPR service centre Manchester. We also thank the referees
for useful discussions during the reviewing process.
Notes and references
12 (a) B. M. Trost and V. S. C. Yeh, Angew. Chem. Int. Ed. Engl., 2002, 41,
861; (b) B. M. Trost, V. S. C. Yeh, H. Ito and N. Bremeyer, Org. Lett.,
2002, 4, 2621–2623.
1 (a) D. J. H. Emslie, W. E. Piers, M. Parvez and R. McDonald,
Organometallics, 2002, 21, 4226–4240; (b) E. Q. Gao, W. M. Bu, G. M.
Yang, D. Z. Liao, Z. H. Jiang, S. P. Yan and G. L. Wang, J. Chem.
Soc., Dalton Trans., 2000, 9, 1431–1436; (c) A. D. Garnovskii, I. S.
Vasilchenko, D. A. Garnovskii and B. I. Kharisov, J. Coord. Chem.,
2009, 62, 151–204; (d) V. C. Gibson and S. K. Spitzmesser, Chem. Rev.,
2003, 103, 283–315; (e) K. C. Gupta and A. K. Sutar, Coord. Chem. Rev.,
2008, 252, 1420–1450; (f) S. Matsui, M. Mitani, J. Saito, Y. Tohi, H.
Makio, N. Matsukawa, Y. Takagi, K. Tsuru, M. Nitabaru, T. Nakano,
H. Tanaka, N. Kashiwa and T. Fujita, J. Am. Chem. Soc., 2001, 123,
6847–6856; (g) M. Mitani, R. Furuyama, J. Mohri, J. Saito, S. Ishii, H.
Terao, T. Nakano, H. Tanaka and T. Fujita, J. Am. Chem. Soc., 2003,
125, 4293–4305; (h) Y. Yoshida, J. Mohri, S. Ishii, M. Mitani, J. Saito,
S. Matsui, H. Makio, T. Nakano, H. Tanaka, M. Onda, Y. Yamamoto,
A. Mizuno and T. Fujita, J. Am. Chem. Soc., 2004, 126, 12023–12032.
2 T. Kawamichi, T. Haneda, M. Kawano and M. Fujita, Nature, 2009,
461, 633–635.
13 A. Zulauf, M. Mellah and E. Schulz, J. Org. Chem., 2009, 74, 2242–
2245.
14 (a) A. P. Bhatt, K. Pathak, R. V. Jasra, R. I. Kureshy, N. U. H. Khan and
S. H. R. Abdi, J. Mol. Catal. A: Chem., 2006, 244, 110–117; (b) J. M.
Saa, F. Tur, J. Gonzalez and M. Vega, Tetrahedron: Asymmetry, 2006,
17, 99–106.
15 J. Park, K. Lang, K. A. Abboud and S. Hong, J. Am. Chem. Soc., 2008,
130, 16484.
16 (a) S. Abry, A. Thibon, B. Albela, P. Delichere, F. Banse and L.
Bonneviot, New J. Chem., 2009, 33, 484–496; (b) M. Becker, F. W.
Heinemann, F. Knoch, W. Donaubauer, G. Liehr, S. Schindler, G.
Golub, H. Cohen and D. Meyerstein, Eur. J. Inorg. Chem., 2000, 719–
726.
17 G. M. Sheldrick, Acta. Cryst., 2008, A64, 112.
3682 | Dalton Trans., 2011, 40, 3677–3682
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