Copper complexes bearing methylthiophenyl and methylfuranyl derivatives of (R,R)-1,2-diaminocyclohexane: X-ray structures and catalytic exploitation in Henry reaction

Article abstract of DOI:10.1016/j.poly.2015.07.023

Abstract Two novel dichloro Cu(II) complexes of (R,R)-N¹,N²-bis((5-methylthiophen-2-yl)methyl)cyclohexane-1,2-diamine (MTCHD) and (R,R)-N¹,N²-bis((5-methylfuran-2-yl)methyl)cyclohexane-1,2-diamine (MFCHD) ligand

Full text of DOI:10.1016/j.poly.2015.07.023

Accepted Manuscript
Copper complexes bearing methylthiophenyl and methylfuranyl derivatives of
(R,R)-1,2-diaminocyclohexane: X-ray structures and catalytic exploitation in
Henry reaction
Jaewon Cho, Gang Ho Lee, Saira Nayab, Jong Hwa Jeong
PII:
S0277-5387(15)00378-2
DOI:
http://dx.doi.org/10.1016/j.poly.2015.07.023
POLY 11409
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
4 May 2015
8 July 2015
Please cite this article as: J. Cho, G.H. Lee, S. Nayab, J.H. Jeong, Copper complexes bearing methylthiophenyl and
methylfuranyl derivatives of (R,R)-1,2-diaminocyclohexane: X-ray structures and catalytic exploitation in Henry
reaction, Polyhedron (2015), doi: http://dx.doi.org/10.1016/j.poly.2015.07.023
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- Revised -
Copper complexes bearing methylthiophenyl and methylfuranyl
derivatives of (R,R)-1,2-diaminocyclohexane: X-ray structures and
catalytic exploitation in Henry reaction
Jaewon Choa, Gang Ho Leea, Saira Nayabb, and Jong Hwa Jeonga,*
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a Department of Chemistry and Green-Nano Materials Research Center, Kyungpook National University, 1370
Sankyuk-dong, Taegu,702-701, Republic of Korea.
b Department of Chemistry, Shaheed Benazir Bhutto University, Sheringal, Dir (Upper), Khyber Pakhtunkhwa,
Republic of Pakistan.!
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Tel. (82)-53-950-6343
Fax: (82)-53-950-6330
E-mail: jeongjh@knu.ac.kr"
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Copper complexes bearing methylthiophenyl and methylfuranyl
derivatives of (R,R)-1,2-diaminocyclohexane: X-ray structures and
catalytic exploitation in Henry reaction
Jaewon Choa, Gang Ho Leea, Saira Nayabb, and Jong Hwa Jeonga,*
"
a Department of Chemistry and Green-Nano Materials Research Center, Kyungpook National University, 1370
Sankyuk-dong, Taegu,702-701, Republic of Korea.
b Department of Chemistry, Shaheed Benazir Bhutto University, Sheringal, Dir (Upper), Khyber Pakhtunkhwa,
Republic of Pakistan.!
Abstract
Two novel dichloro Cu(II) complexes of (R,R)-N1,N2-bis((5-methylthiophen-2-
yl)methyl)cyclohexane-1,2-diamine (MTCHD) and (R,R)-N1,N2-bis((5-methylfuran-2-
yl)methyl)cyclohexane-1,2-diamine (MFCHD) ligands have been synthesised and
structurally characterised using X-ray diffraction. The geometry around the Cu(II) centres
was distorted square planner. A strong Cu…Ofuranyl interaction exists in Cu(MFCHD)Cl2 that
leads to the disappearance of original C2-symmetry of the ligand, resulting in selective R,S-
coordination of N atoms in (1R,2R)-1,2-diaminocyclohexane. Catalytic activities of dichloro
and diacetato Cu(II) complexes with 3 mol% of iPr2NEt were assessed in asymmetric Henry
reactions that resulted in moderate to high yields with an enantiomeric excess up to 92%,
without air/moisture exclusion.
Keywords: Enantiopure N,N-diamines, copper complexes, R,S-coordination N,N-diamines,
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enantioselective Henry reaction.
Introduction
Chiral secondary vic-diamines, specifically those derived from enantiomerically pure (R,R)-
1,2-diaminocyclohexane and its N,N-disubstituted derivatives, are attractive ligands and
organocatalysts in many asymmetric transformations1 including Michael additions,2 aza-
Henry reactions,3 enantioselective reductions,4,5 allylation,6 and aldehyde crotylation.7
Despite the increased acidity of the N-H proton,8 these C2-type symmetrical ligand
precursors form stable metal complexes, creating chiral environments for catalytic reactions.
Coordination of the (R,R)-1,2-diaminocyclohexane ligand to metal prevents N-inversion,
and thus resulted in fixing the chirality of N atoms. 9 The resultant configurations of N
atoms; i.e. (R,R), (S,S), and (R,S), may be interesting in terms of structure and coordination
modes of the metal centre. Similarly, modification of the various groups attached to the
(R,R)-1,2-diaminocyclohexane by different small substituents can effectively tune the
electronic and steric properties of the ligands, and thus affect the coordination properties of
the resultant complexes.10 Recently, the use of chiral complexes to control stereochemical
outcomes in asymmetric Henry reactions have been described by various groups including
Jørgensen,11 Trost,12 Yamada,13 and Palomo14. The Bandini and" Skarzewski groups
independently applied chiral complexes derived from (R,R)-1,2-diaminocyclohexane as
catalysts to asymmetric Henry reactions that resulted in high enantioselectivity.15,16 Since
then, efforts have been devoted to develop novel Cu(II) complexes based on (R,R)-1,2-
diaminocyclohexane with various moieties to yield the corresponding β-nitroalcoholes with
high yield and enantioselectivities.17-20 However, the structural properties and X-ray
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diffraction characteristics of these complexes have not been well-studied. The potential
merits of (R,R)-1,2-diaminocyclohexane framework and recent results in asymmetric Henry
reaction for Cu(II) complexes supported by such ligands reported by our group encouraged
us to evaluate more broadly these C2-symmetric chiral diamines in asymmetric Henry
reaction.21 To increase our understanding of the effect of ligand architecture (S vs. O-
heterocycle) on the level of asymmetric induction, we explored structural characteristics of
these complexes and the efficiency of novel copper complexes as catalysts with an organic
base in asymmetric Henry reactions (Scheme 1).
Experimental Section
General Consideration
(R,R)-1,2-diaminoniumcyclohexane mono-(L)-(+)-tartrate salt (1) (99%), 5-methyl-2-
furaldehyde, 5-methyl-2-thiophenecarboxaldehyde, and copper(II) chloride dihydrate
CuCl2·2H2O (99%) were obtained from Aldrich chemical company. Silica gel 60 (230–400
mesh) from Merck, ethanol (99.8%) and methanol (99.9%) from Aldrich. The ligand, (R,R)-
N,N'-bis(5-methylthiophen-2-ylmethyl)cyclohexane-1,2-diamine (MTCHD) and (R,R)-N,N'-
bis(5-methylfuran-2-ylmethyl)cyclohexane-1,2-diamine (MFCHD) were obtained using
reported method.22
NMR spectra were recorded on a Bruker advance digital 400 (400 Hz)-NMR
Spectrometer at ambient temperature. FT-IR spectra were measured on Jasco FT/IR-620
spectrophotometer. Band positions in IR spectra were reported as wave number (m) in cm-1
and band intensity in semiquantitative terms (w = weak, m = medium, s = strong). Elemental
analyses were determined on EA 1108-Elemental Analyzer at the Chemical Analysis
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Laboratory of the Center of Scientific Instruments of Kyungpook National University.
Enantiomeric excesses (ee) were determined by HPLC with a chiralcel OD-H column and
OJ-H column using HPLC grade isopropanol (IPA) and n-hexane (n-hex) as eluting
solvents.21b
Copper Complexes
Synthesis of Cu(MTCHD)Cl2
A solution of MTCHD (1.00 g, 2.99 mmol) in CH2Cl2 (10 mL) was added dropwise to
suspension of CuCl2·2H2O (0.51 g, 2.99 mmol) in CH2Cl2 (10 mL). The mixture was stirred
overnight at ambient temperature. The solvent was removed to get light blue solid as final
product (0.89 g, 64%). Calcd. for C18H26Cl2CuN2S2: C, 46.10; H, 5.59; N, 5.97. Found: C,
46.13; H, 5.56; N, 5.99. IR (solid neat; cm-1): 3234 (w), 2940 (w), 2858 (w), 1699 (w), 1651
(w), 1541 (w), 1444 (m), 1421 (w), 1228 (w), 1150 (w), 1091 (w), 1041 (w), 977 (w), 955
(w), 920 (m), 817 (s), 801 (s).
Synthesis of Cu(MFCHD)Cl2
The analogues method to that of Cu(MTCHD)Cl2 was applied to Cu(MFCHD)Cl2 except
that (MFCHD) (0.92 g, 3.04 mmol) and CuCl2·2H2O (0.52 g, 3.04 mmol) were used.
Removal of solvent yielded dark green solid as final product (0.91 g, 69%). Calcd. for
C18H26Cl2CuN2O2 C, 49.49; H, 6.00; N, 6.41. Found C, 49.46; H, 6.03; N, 6.42. IR (solid
neat; cm-1): 3149 (w), 2935 (w), 2858 (w), 1559 (m), 1518 (w), 1438 (m), 1217 (m), 1020
(s), 999 (s), 928 (m), 785 (s), 751 (w).
X-ray Crystallography
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X-ray quality single crystals of (MFCHDA)CuCl2 and (MTCHDA)CuCl2 were obtained by
slow evaporation of 95% MeOH solutions. An X-ray quality single crystals were mounted
in a thin-walled glass capillaries on an Enraf-Noius CAD-4 diffractometer with Mo Kꢀ
radiation (( = 0.71073 Å). Unit cell parameters were determined using least-squares analysis
of 25 reflections (10° < % < 13°). Intensity data were collected in 2/2% scan mode, and three
standard reflections were monitored every hour during data collection. Empirical absorption
corrections with 1-scans were performed to the data using the ABSCALC program.23 The
structures were solved using direct methods and refined using the full-matrix least-squares
techniques on F2 using SHELXL-97 and SHELXS-97 program packages.24 Absolute
structures were confirmed using anomalous dispersion effects with Friedel pairs, which
were not merged. All non-hydrogen atoms were refined anisotropically, and all hydrogen
atoms were positioned geometrically using the riding model with fixed isotropic thermal
factors.
Typical catalytic procedure for Henry reaction
All the reactions were carried out at -20 ºC. 10 mol% of the dichloro copper complexes were
dissolved in 15 mL IPA. Then nitromethane (0.50 mL, 20 mmol) and benzaldehyde (0.50
mL, 10 mmol) were added followed by addition of 3.0 mol% or 5.0 mol% of iPr2Net as a
cocatalyst owing to its good activity.25,26 Similarly 10 mol% of the diacetato-copper
catalysts were obtained in situ by treating dichloro-complexes with Ag(OAc) in IPA and the
resultatnt solution was applied to Henry reaction under aforementioned reaction conditions.
Reactions were monitored by TLC. After stirring for specified time, reactions were
quenched with 1 mL of 1 M HCl solution and then evaporated. The products were extracted
by CH2Cl2 (3 times x 20 mL) and dried over anhydrous MgSO4, then filtered and the
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solvents were removed under reduced pressure. The crude products were purified by column
chromatography (10% EtOAc/hexane) to give a yellowish oil of 1-phenyl-2-nitroethanol.
1H-NMR (400 Hz, CDCl3): δ 7.30 (5H, m, Ar-H), 5.38 (1H, dd, -CH), 4.51(1H, dd, CH2),
4.41 (1H, dd, -CH2), 2.89 (1H, br,s, -OH). Enantiomeric excess (ee) was determined using
HPLC on Chiracel OD-H column (n-Hex: isopropanol = 95:5; flow rate = 1.5 mL/min; k =
215 nm); (R) enantiomer tr = 15.63 min, (S) enantiomer tr = 19.52 min (Table 3).21b
Results and Discussion
Synthesis of Cu(MTCHD)Cl2 and Cu(MFCHD)Cl2
Complexes Cu(MTCHD)Cl2 and Cu(MFCHD)Cl2 were obtained in good yields (up to 89%)
by treating MTCHD and MFCHD22 ligands at a 1:1 ratio with CuCl2.2H2O in CH2Cl2 at
ambient temperatures (Scheme 2). These complexes were structurally characterised using IR,
elemental analysis, and X-ray diffraction studies. A comparison of the IR spectra of ligands
with that of the complexes was performed, specifically in the N-H region. The characteristic
broad N-H peaks for MTCHD and MFCHD ligands in the IR spectra were observed at 3300
and 3302 cm-1, while in Cu(II) complexes the N-H absorption band appeared at 3234 and
3149 cm-1 for Cu(MTCHD)Cl2 and Cu(MFCHD)Cl2, respectively. Blue crystals of
complexes suitable for single-crystal X-ray crystallography were obtained by slow
evaporation of concentrated MeOH solution.
Description of X-ray crystal structures of Cu(MTCD)Cl2 and Cu(MFCD)Cl2
The molecular structures of the synthesised complexes, Cu(MTCHD)Cl2 and
Cu(MFCD)CuCl2, have been determined based on X-ray diffraction studies. The
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crystallographic data and refinements are summarised in Table 1. The crystal systems were
trigonal with space group P31 for Cu(MTCHD)Cl2•H2O and orthorhombic with space group
P212121 for (MFCHD)CuCl2. The expected distorted square planner geometry of Cu(II) was
observed in both complexes (Fig. 1 and Fig. 2). Selected bond lengths and angles are
presented in Table 2 for both complexes. However, a strong Cu…Ofuranyl interaction with a
distance of 2.704(2) Å was observed in Cu(MFCHD)Cl2 (Fig. 2), which is longer compared
to similar reported complexes21b where exocyclic oxygen strongly interacts with the Cu(II)
centre, having an average distance of 2.45(3) Å. The Cu-N and Cu-Cl bond lengths in both
complexes do not vary from similar reported complexes.21a,15a However, the Cl1–Cu–Cl2
angle of 103.10(4)° was larger in Cu(MTCHD)Cl2 compared to 96.20(2)° in
Cu(MFCHD)Cl2, which may be due to the Cu…Ofuranyl interaction in the latter case.
Similarly, N1–Cu–N2 angles in Cu(MTCHD)Cl2 and Cu(MFCHD)Cl2 are 85.1° and 83.71°,
respectively and illustrative of the distortion from ideal geometry.
Complexation of the metal to ligand framework with stereogenic centres RC, RC in the
carbon skeleton derived from (R,R)-1,2-cyclohexadiamine fragment leads to a 5-membered
metalla-heterocyclic ring that blocks the nitrogen (increases the N-inversion barrier), and
thus induces chirality provided there is nonequivalence"of the nitrogen substituents. It is
clear from crystal structures that both nitrogens are in the RN configuration in
Cu(MTCHD)Cl221b,27, while RN and SN configurations exist in Cu(MFCHD)Cl2, which is
consistent with the reported Pd complex.28 In addition, upon coordination to the Cu(II)
centre, the original C2-symmetry of MFCHD ligand is lost, which may be due to one of the
furanyl moieties that shows hindered free rotation due to the Cu...Ofuranyl interaction. It has
been shown in Fig. 2 that both furanyl moieties are on the same side of the
cyclohexadiamine plane and opposite to the metal; i.e. the furanyl moiety at the nitrogen is
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pseudo-axial at one and pseudo equatorial at the other nitrogen. One of the factors for this
selective R,S-coordination of N atoms of (R,R)-1,2-diaminocyclohexane to the Cu(II) centre
in Cu(MFCHD)Cl2 may be the Cu…Ofuranyl interaction (Fig. 3). Hydrogen atoms of the
chiral carbons and nitrogens are found to be in head-to-tail conformation in Cu(MTCHD)Cl2
and in head-to-head conformation in Cu(MFCHD)Cl2 (Fig. 3). Furthermore, the resultant
five membered chelate rings Cu-N-C-C-N in both complexes were solely in λ
conformations.
Catalytic activities of Cu(II) complexes in Henry reactions
As a part of our ongoing investigations towards the application of versatile enantiopure
copper initiators in asymmetric Henry reactions, the association of benzaldehyde and
nitromethane was examined using synthesised complexes as catalysts with varying amounts
of iPr2NEt. The results are summarised in Table 3. The diacetato derivatives generated in
situ by treating dichloro Cu(II) complexes with Ag(OAc) were also subjected to asymmetric
Henry reactions. No product formation was observed in the absence of iPr2NEt for dichloro
and diacetato derivatives of both catalytic systems (Table 3, entries 1,4,7,10). The recent
concept of double catalytic activation i.e. transition metal complexes as a Lewis acid are not
powerful enough to form bonds through single activation of nucleophiles; thus,
deprotonation of a nucleophile precursor with an amine base is required to activate the
reaction.29 Therefore, in the presence of 3 mol % iPr2NEt as a promoter, the best results in
terms of yield (70%), and enantioselectivity (92%) of corresponding β-nitroalcohol was
achieved with (MTCHD)Cu(OAc)2. With increasing amounts of iPr2NEt to 5 mol %, the
product yield was increased with loss of ee, which may be due to the interaction of achiral
amine with Cu(II) complexes. Chloro derivatives were less active (required longer reaction
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times with lower conversion yields) than their diacetato counterparts under the same
experimental conditions for both catalytic systems (Table 3).21a,30 With dichloro catalytic
species using 3 mol% iPr2NEt, reactions took longer and the corresponding product was
obtained at a lower yield, although the ee was quite high (91%) (Table 3, entries 2 and 8).
Thus, enantiopure Lewis acid complex/amine promoter ratio strongly influences the reaction
outcomes. Blank reactions without the use of chiral complex resulted in higher conversion
but low selectivity. The catalytic reaction with Cu(II) complexes containing MTCHD
resulted in higher yields compared to MFCHD containing complexes, and this decrease in
yield may be due to the Cu…Ofuranyl interaction that hinders substrate approach (Table 3,
entries 5 and 11). However, the enantiomeric excess was comparable for Cu(II) complexes
of both ligands under the same experimental conditions. A plausible mechanism can be
represented by a transition state model shown in Fig. 4. We assume that the favorable
positioning of the reactants taking into account the steric and electronic considerations is
where the carbonyl oxygen atom is coordinated at one of the equatorial positions, and the
oxygen atom of nitromethane approaches the metal center from the axial side. Thus, after
deprotonation by the external base, the resulting nitronate ion approaches the aldehydes
from the Re face to give corresponding β-nitroalcohols with an (S)-conformation. Other
possibilities seem to be restricted by the unfavorable steric interactions of the phenyl group
of benzaldehyde and aromatic moieties of the ligand framework.31,32 Hence, this study
provides a combination of complementary synthetic, structural, and catalytic studies, and
increases our understanding on the chemistry of Cu(II) complexes and their application in
the Henry reactions.
Conclusion
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In conclusion, Cu(II) complexes bearing methylthiophenyl and methylfuranyl derivatives of
(R,R)-1,2-diaminocyclohexane have been synthesised and characterised. The C2-symmetry
of the MFCHD ligand was lost upon coordination to the metal centre and resulted solely in
R,S-configurations at nitrogen atoms. The dichloro and diacetato complexes bearing the
MTCHD ligand function as efficient catalyst precursors for the asymmetric nitroaldol
reaction of benzaldehydes and nitromethane to yield corresponding !-nitroalcohols (up to 92%
ee) with 3 mol% iPr2NEt, whereas MFCHD ligand-containing complexes show a modest
catalytic activity with comparable ee (90%). In general, the dichloro derivatives were less
active than their diacetato counterparts under the same experimental conditions for both
catalytic systems.
Acknowledgements
This research was supported by Basic Science Research Program through the National
Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and
Technology (NRF-2011-0023197).
Appendix A. Supplementary data
CCDC 1049315 & 1049316 contain the supplementary crystallographic data for
(MTCD)CuCl2 and (MFCD)CuCl2. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
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OH
NO2
O
OH
Chiral Catalyst
H
+
CH3NO2
+
NO2
Base
"
Scheme 1. Formation of β-nitroalcohols by Henry reaction
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Het
Het
NH
NH
Cl
Cl
NH
NH
CuCl2.2H2O
CH2Cl2, 12 h
Cu
Het
Het
Het =
H3C
H3C
S
O
MFCD
MTCD
Scheme 2. Synthesis of Cu(MTCHD)Cl2 and Cu(MFCHD)Cl2.
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Table 1 Crystallographic data and structure refinements for Cu(MTCHD)Cl2 H2O and
#
Cu(MFCHD)Cl2
Cu(MFCHD)Cl2
Cu(MTCHD)Cl2 H2O
#
Empirical formula
Formula weight
C18 H26 Cl2 Cu N2 S2^H2O
C18 H26 Cl2 Cu N2 O2
436.85
486.98
Trigonal
P31
Crystal system
Orthorhombic
P212121
Space group
Unit cell dimensions
a (Å)
10.0522(6)
10.0522(5)
18.5907(16)
120
9.4594(7)
14.3118(9)
15.1239(8)
b (Å)
c (Å)
γ (°)
Volume (Å3), Z
1626.85(19),
1.491
3
2047.5(2), 4
Density (calcd.) (Mg/m3)
Absorption coefficient (mm-1)
Reflections collected
Independent reflections
Reflections observed (>2σ)
Data/ restraints/ parameters
Final R indices [I>2σ(I)]
R indices (all data)
Absolute structure parameter
Largest diff. peak and hole (e/ Å3)
1.417
1.456
1.341
6832
4517
4034 [R(int) = 0.0374]
3598
3808 [R(int) = 0.0138]
3307
4034 / 1 / 237
3808 / 0 / 228
R1 = 0.0342
wR2 = 0.0848
R1 = 0.0232
wR2 = 0.0594
R1 = 0.0410 wR2 = 0.0866
0.002(12)
R1 = 0.0338 wR2 = 0.0614
0.001(10)
0.477 and -0.404
0.169 and -0.163
#'"
"

Table 2 Selected bond lengths (Å) and bond angles (°) of Cu(MTCHD)Cl2 H2O and
#
Cu(MFCHD)Cl2.
"
Cu(MTCHD)Cl2
•
H2O
Cu(MFCHD)Cl2
Cu1- N2
Cu1- N1
Cu1- N1
Cu1- N2
Cu1- Cl1
Cu1- Cl2
Cu1•••• O2
2.014(3)
2.015(3)
2.019(2)
2.056(2)
2.225(6)
2.278(7)
2.704(2)
Cu1- Cl1
Cu1- Cl2
2.232(1)
2.234(1)
N1- Cu1- N2
N1- Cu1- Cl1
N2- Cu1- Cl2
N1- Cu1- N2
N1- Cu1- Cl1
N2- Cu1- Cl2
Cl1- Cu1- Cl2
N1- Cu1••• O2
N2- Cu1••• O2
85.10(1)
149.12(9)
149.15(9)
83.71(7)
169.05(5)
148.34(6)
96.20(2)
Cl1- Cu1- Cl2 103.10(4)
C11- S1- C8
93.20(2)
93.20(2)
74.89(6)
C14- S2- C17
122.24(7)
"
#("
"

Table 3 Enantioselective Henry reaction of Ph-CHO and MeNO2 promoted by enantiopure
Cu(II) catalysts a
Entry
Catalyst
Time (days) iPr2NEt (mol %)
Conv. (%)b
ee(%)c
1
(MTCD)CuCl2
14
14
14
3
0
3
5
0
3
5
0
3
5
0
3
5
0
6
0
2
(MTCD)CuCl2
91(S)
86(S)
84(S)
92(S)
89(S)
0
3
(MTCD)CuCl2
28
19
70
81
0
4
(MTCD)Cu(OAc)2
(MTCD)Cu(OAc)2
(MTCD)Cu(OAc)2
(MFCD)CuCl2
5
3
6
3
7
14
14
14
3
8
(MFCD)CuCl2
6
88(S)
87(S)
90(S)
85(S)
84(S)
9
(MFCD)CuCl2
47
7
10
11
(MFCD)Cu(OAc)2
(MFCD)Cu(OAc)2
(MFCD)Cu(OAc)2
3
43
57
12
3
a
Reaction condition: Molar ratio employed were 0.1: 1: 2 of Catalyst: Benzaldehyde: Nitromethane, Solvent (IPA), Temp (-20
ºC). b Conversion determined by 1H-NMR spectroscopic analysis. c The enantiomeric excess (ee) was determined by HPLC
analysis using OD-H column (Hexane: IPA = 95:05; flow rate = 1.5 mL/min; λ = 215 nm, R enantiomer tr = 18.4 min, S
enantiomer tr = 22.3 min) as reported in our earlier work. 21b
#)"
"

C4
C3
C5
C2
C1
C6
S1
S2
C12
C18
C7
C13
C8
C9
C14
C15
N2
N1
C11
Cu1
C17
C10
C16
Cl2
Cl1
Fig. 1. An ORTEP drawing of Cu(MTCHD)Cl2.H2O with the numbering scheme at 30%
probability level.
#*"
"

C4
C3
C5
C2
C1
C6
C7
N1
N2
Cu1
Cl2
C8
Cl1
C13
C9
C14
O1
C10
C15
O2
C11
C12
C17
C16
C18
Fig. 2. An ORTEP drawing of Cu(MFCHD)Cl2 with the numbering scheme at 30%
probability level.
#+"
"

Fig. 3 Comparative view of X-ray structures of Cu(MFCHD)Cl2 and Cu(MTCHD)Cl2
demonstrating the configurations for N atoms of enantiopure ligands. All hydrogen atoms
were omitted except those at the chiral atoms for clarity.
"
$!"
"

Me
X
H
O
OH
N
NH
NO2
(S)
O
H
H
N
Cu
OAc
O
X
H
Me
"
Fig. 4. Transition state model explaining the observed stereochemical outcomes.
$$"
"

Copper complexes bearing methylthiophenyl and methylfuranyl
derivatives of (R,R)-1,2-diaminocyclohexane: X-ray structures and
catalytic exploitation in Henry reaction
Jaewon Choa, Gang Ho Leea, Saira Nayabb, and Jong Hwa Jeong*a
Novel Cu complexes ligated to methylthiophenyl and methylfuranyl derivatives of (R,R)-
1,2-diaminocyclohexane were synthesized and characterized by X-ray diffraction. The
original C2-symmetry was lost upon complexation to Cu(II) centre and resulted in selective
R,S-coordination of N atoms in case of furanyl containing ligand. The dichloro and diacetato
derivatives proved to be active catalysts in asymmetric Henry reaction with moderate yields
and enantioselectivities up to 92 %.
"
$%"
"

Copper complexes bearing methylthiophenyl and methylfuranyl
derivatives of (R,R)-1,2-diaminocyclohexane: X-ray structures and
catalytic exploitation in Henry reaction
Jaewon Choa, Gang Ho Leea, Saira Nayabb, and Jong Hwa Jeong*a
"
"
"
$&"
"