Copper(II) complexes containing chiral substituted 2-(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridine ligands: Synthesis, X-ray structural studies and asymmetric catalysis

Article abstract of DOI:10.1016/j.jorganchem.2006.01.056

New chiral N,N-bidentate ligands derived from substituted 2-(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridines have been prepared and characterised by means of ¹H, ¹³C NMR spectroscopy and optical rotation. Their Cu(II) complexes were characterized by means of elemental analysis, ¹H NMR spectroscopy and MS. By means of X-ray diffraction, molecular geometry of the complex of 2-(1-methyl-4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridine with copper(II) chloride was determined. The complex exhibits heterochiral dimeric arrangement of two square pyramids with one terminal and one bridge-forming chlorine atoms and two nitrogen atoms in the bases of the pyramids. The tops of these pyramids are formed by the remaining chlorine atoms. The complexes prepared catalyse the Henry reaction with the overall yields of 41-97% and with the maximum enantioselective excess of 19%.

Full text of DOI:10.1016/j.jorganchem.2006.01.056

Journal of Organometallic Chemistry 691 (2006) 2623–2630
www.elsevier.com/locate/jorganchem
Copper(II) complexes containing chiral substituted
2-(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridine
ligands: Synthesis, X-ray structural studies and asymmetric catalysis
a,
a
a
a
*
´
Milosˇ Sedlak , Pavel Drabina , Roman Keder , Jirı Hanusek ,
ˇ´
b
c
´
´
˚
Ivana Cısarˇova , Alesˇ Ruzˇicˇka
a
ˇ
Department of Organic Chemistry, Faculty of Chemical Technology, University of Pardubice, Na´m. Cs. legiı´ 565, 532 10 Pardubice, Czech Republic
b
Department of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 43 Prague 2, Czech Republic
c
ˇ
Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Na´m. Cs. legiı´ 565,
532 10 Pardubice, Czech Republic
Received 14 September 2005; received in revised form 9 January 2006; accepted 31 January 2006
Available online 7 March 2006
Abstract
New chiral N,N-bidentate ligands derived from substituted 2-(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridines
have been prepared and characterised by means of 1H, 13C NMR spectroscopy and optical rotation. Their Cu(II) complexes were char-
1
acterized by means of elemental analysis, H NMR spectroscopy and MS. By means of X-ray diffraction, molecular geometry of the
complex of 2-(1-methyl-4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridine with copper(II) chloride was determined.
The complex exhibits heterochiral dimeric arrangement of two square pyramids with one terminal and one bridge-forming chlorine
atoms and two nitrogen atoms in the bases of the pyramids. The tops of these pyramids are formed by the remaining chlorine atoms.
The complexes prepared catalyse the Henry reaction with the overall yields of 41–97% and with the maximum enantioselective excess of
19%.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: 4,5-Dihydro-1H-imidazol-5-one ligands; Copper complexes; Asymmetric catalysis; Henry reaction
1. Introduction
by us have the advantage in their asymmetrical carbon atom
being quaternary, which prevents racemization by splitting
off of a-hydrogen, which happens, e.g., in the oxazolines
derived from natural amino acids [7]. On the other hand,
the substituted 4,4-dialkyl-4,5-dihydro-2-phenyl-1H-imi-
dazol-5-ones derived from pyridine-2,3-dicarboxylic acid
are commercially available herbicides [8]. In the case of her-
bicide Imazapyr, its copper(II) complexes were described [9].
This paper deals with synthesis and characterisation of
new chiral substituted 2-(4-isopropyl-4-methyl-4,5-dihy-
dro-1H-imidazol-5-one-2-yl)pyridines. In contrast to the
previous paper [2], the present paper concerns the deriva-
tives only substituted at 2-position of pyridine ring; this
results in obtaining chiral N,N-bidentate ligands allowing
the metal ion to be coordinated with two nitrogen atoms.
The complex heterocyclic compounds containing a stere-
ogenous centre are particularly used as homogeneous cata-
lysts in a number of asymmetric syntheses [1]. In our
previous work [2], we placed two 2-(4-isopropyl-4-methyl-
4,5-dihydro-1H-imidazol-5-one-2-yl)pyridine cycles at 2,6-
positions of pyridine and thus prepared chiral ligands
formally similar to the well-known N,N,N-tridentate ligands
of oxazoline (‘‘Pybox’’) [3], terpyridine (‘‘Terpy’’) [4] or 2,6-
bis(imidazol-2-yl)pyridine [5] and 2,6-bis(1-methylbenzimi-
dazol-2-yl)pyridine [6]. The ligands and complexes prepared
*
Corresponding author. Tel.: +420 466 037 015; fax: +420 466 037 068.
´
E-mail address: milos.sedlak@upce.cz (M. Sedlak).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.01.056

2624
M. Sedla´k et al. / Journal of Organometallic Chemistry 691 (2006) 2623–2630
N,N-Bidentate ligands [10], such as, e.g., 2,20-bipyridine
and 1,10-phenanthroline play chief roles in key areas such
as photovoltaics [11], molecular sensors [12], DNA interca-
lation [13], molecular wires [14] and supramolecular struc-
tures (network, helical, box, etc.) [15]. The diverse
applications stem from the fact that the ligands are capable
of chelating various metal ions and the resultant complexes
possess a wide range of catalytic, magnetic, photophysical
and electrochemical properties. Besides the preparation
and structural study of the Cu(II) complexes with the newly
suggested and prepared N,N-bidentate ligands, further aim
of this work is to verify their catalytic properties using the
Henry reaction as the particular model [16].
of 2-(4-isopropyl-1,4-dimethyl-4,5-dihydro-1H-imidazol-5-
one-2-yl)pyridines 3 and 2-(1-benzyl-4-isopropyl-4-methyl-
4,5-dihydro-1H-imidazol-5-one-2-yl)pyridines 4, we pre-
pared the racemates 3 (69%) and 4 (65%) as well as the opti-
cally pure ligands 3(R) (65%), 3(S) (66%), 4(R) (73%) and
4(S) (84%). In the other cases, only the racemates were pre-
pared (5–7) in the yields of 79–92%. The alkylation, i.e.,
nucleophilic substitution of dimethyl sulphate (methyl
iodide), benzyl bromide, 2-picolyl chloride, chloracetonitrile
and ethyl bromoacetate with anion of 4,5-dihydro-1H-imi-
dazol-5-one was carried out in anhydrous dimethylformam-
t
ide (Method A: K2CO3 or Cs2CO3; Method B: BuOK)
(Scheme 1). 2-(1-Carbamoyl-4-isopropyl-4-methyl-4,5-
dihydro-1H-imidazol-5-one-2-yl)pyridine 8 (65%) was pre-
pared by partial hydrolysis of nitrile 6. The ligands prepared
2. Results and discussion
in the described way were characterised by means of 1H, 13
C
2.1. Syntheses of ligands
NMR spectroscopy, elemental analysis and melting points.
The systems suggested by us are relatively easy to synthe-
size and further modify, as the case may be. The source of
stereogenous centre is the easily accessible and optically
2.2. Synthesis and characterisation of complexes
Complexes 9–14 were prepared by reactions of cupric
chloride with the individual ligands 3–8 in ethanol, in the
yields of 60–96%. The complexes prepared (9–14) were
characterised by means of elemental analysis, mass spec-
25
pure (R)-2-amino-2,3-dimethylbutanamide, ½aꢀD ¼ þ59:4ꢁ
(c = 0.0162, THF) and (S)-2-amino-2,3-dimethylbutana-
25
mide, ½aꢀD ¼ ꢂ57:1ꢁ (c = 0.0654, THF) [8b]. In analogy with
1
the previous work [2], we used the reaction of the pyridine-2-
carbocylic acid activated with methyl chloroformate, with
racemic 2-amino-2,3-dimethylbutanamide, with (R)-2-
amino-2,3-dimethylbutanamide, and with (S)-2-amino-2,3-
dimethylbutanamide to prepare the corresponding acylated
butanamides (pyridine-2-carboxylic acid (1-carbamoyl-1,2-
dimethyl-propyl)-amides): 1 racemic (78%), 1(R) (87%),
1(S) (85%). Base catalysed ring closure of 1 gave 2 racemic
(76%) and the optically pure 2-(4-isopropyl-4-methyl-4,5-
dihydro-1H-imidazol-5-on-2-yl)pyridines 2(R) (80%) and
2(S) (82%). The subsequent alkylation of 1-nitrogen atom
in 1H-imidazol-5-one ring with various groups gave a series
of N1-substituted 2-(4-isopropyl-4-methyl-4,5-dihydro-1H-
imidazol-5-one-2-yl)pyridines 3–8 (Scheme 1). In the cases
trometry and H NMR. The mass spectrometry results of
complexes 9–14 show that each of the complexes is present
in two forms, i.e., as the monomer a and the dimer b, which
can exist in various proportions in gas phase as well as in
solution or solid phase (Scheme 2).
The monomeric form a is characterised by the presence of
molecular peak [MꢂCl]+ in the mass spectrum, while the
dimeric form b is indicated by characteristic molecular peaks
[2MꢂCl]+ and [2MꢂCuCl2ꢂ2Cl]+. With complexes 9–14
also measurement of 1H NMR spectra in DMSO-d6 was car-
ried out, but the spectra obtained only exhibit very broad sig-
nals in the region 0.8–11.5 ppm with almost no informative
value. The said broadening is most probably due to dynamic
processes produced by a coordination of the solvent (Scheme
2) to give mononuclear paramagnetic species (a). Compound
10, as the single one, dissolved sufficiently in chloroform. Its
H
H
N
N
N
NaOH/H2O
N
O
N
R
N
O
CONH2
N
O
R
Cl
Cl
N
1
2
Cu
N
N
2
O
Cl
R-X, Base/DMF
X: I or Br,Cl
N
Cu
Cu
Cl
N
Cl
Cl
O
N
N
Base: K2CO3 or Cs2CO3; tBuOK
R
R
N
3: R = CH3;
4: R = CH2Ph;
9a – 14a
9b – 14b
N
O
5: R = CH2-2-Py;
6: R = CH2CN;
N
7: R = CH2CO2C2H5;
8: R = CH2CONH2.
9: R = CH3; 10: R = CH2Ph; 11: R = CH2-2-Py;12: R = CH2CN;
13: R = CH2CO2C2H5;14: R = CH2CONH2;
3 – 8
Scheme 1.
Scheme 2.

M. Sedla´k et al. / Journal of Organometallic Chemistry 691 (2006) 2623–2630
2625
spectrum shows one set of relatively narrow signals, which
were ascribed to the respective hydrogen atoms (1H NMR,
CDCl3, d ppm: 0.005 (4H, Py); 1.00 (2H, CH2); 1.30
(1H,CH); 1.60 (9H, 3 · CH3); 3.55 (5H, Ph)), this is most
probably caused by antiferromagnetic coupling of two cop-
per nuclei and thus the formation of a dimer (10b) in this sol-
vent. In order to verify the structure of complex 9 (made from
racemic 3) in solid phase, we managed to prepare the respec-
tive single crystal, which was submitted to X-ray analysis.
Generally, complexes of cupric chloride with neutral
ligands containing two or more nitrogen atoms can crystal-
lize either as monomers [17] or as dimers with trigonal
bipyramidal geometry of copper(II) central atoms [18a–d].
Another possible arrangement of these complexes is
dimeric with square pyramidal geometry (SPY) of copper
atoms which are connected by two chlorine bridges; in their
bases there are bidentate nitrogen ligands, one terminal and
one bridge-forming chlorine atoms; the remaining bridge
chlorine atoms are in alternative arrangement at the tops
of the two pyramides [18e]. Only the small variation of this
geometry was found in complexes where the distance
between the two copper atoms that is shorter than the
sum of the respective van der Waals radii [19]. As examples
of special oligomeric formations can be given complexes
with chelate-forming ligands containing a large spacer
[20a], tridentate [20b] or tetradentate ligands [20b], or a
complex with only one bridge-forming chlorine atom
[20c]. On the basis of X-ray analysis, we found out that
complex 9 is preferably separated from the solvent system
of ethanol–hexane in the form of dimer 9b (Fig. 1). The
molecular geometry 9b can best be described as a dimeric
arrangement of two square pyramids with one terminal
chlorine atom and one bridge-forming chlorine atom (Cl2
for Cu1) and two nitrogen atoms placed in the bases of
the pyramids. The tops of these pyramids are occupied by
the remaining bridge-forming chlorine atoms (Cl2a for
Cu1). This arrangement is very close to the latter structures
described in the literature [18e]. Molecule 9b is composed of
two almost planar formations that can be defined by the
nitrogen atoms of one of the ligands, the copper atom,
one bridge chlorine atom and one terminal chlorine atom
(N1, N7, Cu1, Cl1 and Cl2). The ligands are mutually in
heterochiral arrangement. The distances between the atoms
Cu and Cl in 9b considerably depend on their position (Cu1
Cl1 2.2413(5) – terminal, Cu1 Cl2 2.2917(5) – bridge-form-
ing atom in the base, Cu1 Cl2a 2.7934(5) – bridge-forming
atom at the top), which is typical of this structural motif
[18e]. Other structural parameters also agree with the liter-
ature data about this type of compounds [21].
2.3. Study of enantioselectivity in the Henry reaction
For a model we chose the nitroaldol (Henry) reaction
[16] of 4-nitrobenzaldehyde with nitromethane (Scheme
3). This reaction produces 2-nitro-1-(4-nitrophenyl)etha-
nol, i.e., a stereogenic centre is formed at carbon-1. Even
CHO
NO2
OH
OH
(S)
NO2
O2N
NO2
ligand-salt
CH3NO2
(R)
O2N
Scheme 3.
˚
Fig. 1. Molecular structure of 9b, ORTEP 40% probability level. Hydrogen atoms are omitted for clarity. Selected interatomic distances (A) and angles
(ꢁ): Cu1–N1 2.0183(14), Cu1–N7 2.0588(15), Cu1–Cl1 2.2413(5), Cu1–Cl2 2.2917(5), Cu1–Cl2a 2.7934(5), Cu1–Cu1a 3.6364(3), N1–Cu1–N7 79.38(6),
N1–Cu1–Cl1 94.58(4), N7–Cu1–Cl1 170.00(4), N1–Cu1–Cl2 169.10(4), N7–Cu1–Cl2 93.02(4), Cl1–Cu1–Cl2 91.80(1), N1–Cu1–Cl2a 98.41(4), N7–Cu1–
Cl2a 89.41(4), Cl1–Cu1–Cl2a 99.41(2), Cl2–Cu1–Cl2a 89.24(2), Cu1–Cl2–Cu1a 90.76(2).

2626
M. Sedla´k et al. / Journal of Organometallic Chemistry 691 (2006) 2623–2630
Table 1
Survey of conditions and yields of nitroaldolisation of 4-nitrobenzaldehyde with nitromethane (Method D)
Ligand
Salt
Mol% of catalyst
Time
Temperature (ꢁC)
Overall yield (%)
ee (%)
3(R)
3(R)
3(S)
3(R)
3(S)
3(S)
3(S)
3(S)
3(S)
3(S)
4(R)
4(R)
Copper(II) chloride/TEA
Copper(II) acetate
Copper(II) acetate
Copper(II) acetate
Copper(II) acetate
Copper(II) acetate
Copper(II) benzoate
Copper(II) isophthalate
Copper(II)pivaloate
Copper(II) pivaloate
Copper(II) acetate
Copper(II) acetate
5
5
5
10
20
5
5
5
5
5
6 d
27 d
14 d
14 d
14 d
19 h
23 h
29 h
6 d
ꢂ20
ꢂ20
0
59
41
75
97
96
49
79
61
56
81
63
54
8.9 (R)
18.6 (R)
14.4 (S)
13.6 (R)
14.5 (S)
10.5 (S)
11.2 (S)
9.9 (S)
4.1 (S)
3.4 (S)
11.2 (R)
10.1 (R)
0
0
25
25
25
0
25
0
21 h
10 d
26 h
5
5
25
though the Henry reaction is very similar to aldolization, in
the literature there are but few examples in which high
enantioselectivity was attained [16]. The nitroaldol reaction
is usually catalysed by a combination of a Lewis acid and a
Brønsted base, i.e., two chemically incompatible species,
for which it is necessary to optimise the reaction condi-
tions. At first, we used the experimental conditions already
optimised for the copper(II) complex derived from
(4S,4S0)-2,20-propan-2,20-diylbis(4-isopropyl-4,5-dihydro-1,
3-oxazole) [16e] (Method C). At these conditions, we
applied the method to complex 9(R), which in combination
with one equivalent of triethylamine (ꢂ20 ꢁC) will very
probably exist in the form of monomer 9a with coordinated
triethylamine [16c]. However, using this Method C, we only
achieved a yield of ca. 9% enantioselective excess, the total
(chemical) yield being 56%. Besides this application of pure
complex, we also tried a combination of the respective opti-
cally pure ligand 3 or 4 with corresponding copper(II) carb-
oxylates (Method D). The catalytic role should be played
by the complexes formed in situ; however, we did not man-
age to prepare these complexes in crystalline form. The
reactions were found to proceed with yields of 41–97%
(Table 1).
of a heterochiral dimer of two square pyramids with one ter-
minal chlorine atom and one bridge-forming chlorine atom
and two nitrogen atoms in the bases of each pyramid. The
tops of the pyramids are occupied by the remaining bridge-
forming chlorine atoms. When studying the Henry nitroal-
dol reaction, we achieved high chemical yields (97%) but only
low enantioselectivity (19% at the most).
4. Experimental
4.1. NMR measurements
1
The H and 13C NMR spectra were recorded on a Bru-
ker Avance spectrometer at 500.13 (1H) and 125.76 MHz
1
(13C) in DMSO-d6. The H and 13C chemical shifts were
referenced to the central peaks of solvent (d = 2.55 and
39.60, respectively). All 2D experiments (gradient-selected
gs-COSY, gs-HSQC, gs-HMBC) were performed using
the manufacturer’s software (XWINNMR 3.1). The pro-
ton-proton connectivities were found using gs-COSY.
(The protonated carbons were assigned by gs-HSQC and
the quaternary carbons by gs-HMBC spectra.)
It is well known that optical yield is significantly affected
by temperature, which can also be seen from Table 1. Fur-
ther decrease in temperature would probably lead to some-
what higher optical yield than 18.6%; however, at the same
time the reaction would be unacceptably prolonged to as
much as several months. We did not succeed in increasing
the optical yield even by using bulky anions (benzoate,
pivaloate and isophtalate) either. Also increased concentra-
tion of catalyst did not affect enantioselectivity (Table 1).
4.2. MS measurements
Mass spectra of complexes were measured on a VG Plat-
form II mass spectrometer (Micromass, Manchester, UK)
with chemical ionisation at atmospheric pressure (APCI)
and quadrupole analyser (0–3000 Da).
4.3. Optical rotatory power determination
Optical rotation was measured on a Perkin–Elmer 341
3. Conclusion
instrument, concentration c is given in g/100 mL.
Substituted
2-(4-isopropyl-4-methyl-4,5-dihydro-1H-
4.4. HPLC analyses
imidazol-5-one-2-yl)pyridines form complexes with cop-
per(II) chloride, and these complexes exist in the monomer
and dimer forms that are in equilibrium in solution. On the
basis of X-ray analysis, we found out that the complex of
2-(1-methyl-4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-
5-one-2-yl)pyridine separated from the solution in the form
The optical purity of 2-nitro-1-(4-nitrophenyl)ethanol
was determined by means of HPLC using a Chiralcel OD–
H column (85:15 hexane: propane-2-ol, 0.8 mL/min,
220 nm; (R)-isomer: tR = 20.3 min, (S)-isomer: tR = 25.4
min).

M. Sedla´k et al. / Journal of Organometallic Chemistry 691 (2006) 2623–2630
2627
4.5. X-ray crystallography
150.4, 148.4, 138.0, 126.5, 121.4, 62.5, 34.6, 18.2, 17.6,
17.5. Anal. Calc. for C12H17N3O2: C, 61.26; H, 7.28; N,
17.86. Found: C, 61.10; H, 7.25; N, 17.83%.
The single crystals of 9 were grown from ca. 10% solution
into which ethanol–hexane was charged via slow vapour dif-
fusion. The relevant crystallographic parameters and proce-
dures are: Data for colourless crystal were collected at
150(2) K on a Nonius KappaCCD diffractometer using
4.6.2. (R)-2-[N-(2-Aminocarbonyl-2,3-
dimethylbutyl)aminocarbonyl]pyridine (1(R))
In a similar manner, the compound 1(R) was prepared
as white crystals in a yield of 87%, m.p. 135–136 ꢁC,
˚
Mo Ka radiation (k = 0.71073 A), a graphite monochroma-
25
tor, the structure was solved by direct methods (SIR-92 [22a]).
All reflections were used in the structure refinement based on
F2 by full-matrix least-squares technique (SHELXL-97 [22b]).
The hydrogen atoms were mostly localised on a difference
Fourier map, however, to ensure uniformity of treatment
of all crystals, all hydrogen atoms were recalculated into
idealised positions (riding model) and assigned temperature
factors Hiso(H) = 1.2 Ueq (pivot atom) or of 1.5Ueq for the
methyl moiety. The absorption corrections were carried
out using either multi-scan procedure (PLATON [22c] or
SORTAV [22d]) or Gaussian integration from crystal shape
(Coppens [22e]). Empirical formula: C26H34Cl4Cu2N6O2;
formula weight: 731.47; crystal system: triclinic; space
½aꢀD ¼ ꢂ39:1ꢁ (c = 1.0, CH3OH). The elemental analysis
1
is comparable with that of 1, and the H and 13C NMR
spectra are identical with those of 1.
4.6.3. (S)-2-[N-(2-Aminocarbonyl-2,3-
dimethylbutyl)aminocarbonyl]pyridine (1(S))
In a similar manner, the compound 1(S) was prepared as
white crystals in a yield of 85%, m.p. 136–138 ꢁC,
25
½aꢀD ¼ þ38:4ꢁ (c = 0.9, CH3OH). The elemental analysis
1
is comparable with that of 1, and the H and 13C NMR
spectra are identical with those of 1.
4.6.4. ( )-2-(4-Isopropyl-4-methyl-4,5-dihydro-1H-
imidazol-5-one-2-yl)pyridine (2)
˚
ꢀ
group: P1; unit cell dimensions: a, b, c, a, b, c (A, ꢁ):
6.91100(10), 9.4370(3), 12.2190(4), 102.6140(13), 93.269(2),
A mixture of 1 (2.1 mmol) and 20 mL 1 M NaOH
(20 mmol) was stirred at room temperature. After 5 h, the
mixture was neutralised with concd. HCl to pH ꢃ 7 and
extracted with 4 · 25 mL CH2Cl2. The solution was evapo-
rated until dry to give the product as white crystals in a
yield of 76%, m.p. 88–91 ꢁC; 1H NMR (DMSO-d6, d
ppm): 11.43 (s, 1H, NH), 8.73 (d, 1H, PyH6), 8.22 (d,
1H, PyH5), 8.03 (m, 1H, PyH3), 7.64 (m, 1H, PyH4), 1.97
(m, 1H, i-PrCH), 1.29 (s, 3H, CH3), 1.01 (d, 3H, i-PrCH3),
0.80 (d, 3H, i-PrCH3). 13C NMR (DMSO-d6, d ppm):
187.0, 159.2, 149.3, 147.4, 137.6, 126.4, 121.7, 74.7, 34.2,
21.3, 16.9, 16.8. Anal. Calc. for C12H15N3O: C, 66.34; H,
6.96; N, 19.34. Found: C, 66.12; H, 6.92; N, 19.10%.
3
104.8110(18); volume (A ) 746.44(4); Z = 1; Dcalc (Mg/m3):
˚
1.627; absorption coefficient (mmꢂ1): 1.819; F(000) 374;
crystal size (mm): 0.3 · 0.2 · 0.075; h range for data collec-
tion: 1.0–27.5; h range ꢂ8 ! 8; k ꢂ12 ! 12; l ꢂ15 ! 15;
reflections collected: 12184; Tmin, Tmax: 0.672, 0.937; inde-
pendent/observed reflections: (I > 2d(I)) 3089/3409; Rint
P
P
ðRint
¼
P
jF 2o ꢂ F 2o;mean
j
F 2oÞ 0.034; absorption corrected
multi-scans (SORTAV) number of parameters 186; S all data
2
1=2
ðS ¼ ½ ðwðF 2o ꢂ F c2Þ Þ=ðNdiffrs ꢂ NparamsÞꢀ Þ: 1.071; R1,
P
P
wR2 [I > 2d(I)] (R(F) = iFo| ꢂ |Fci |Fo|, wRðF 2Þ ¼
P
P
2
2
1=2
½
ðwðF 2o ꢂ F 2cÞ Þð wðF o2Þ Þꢀ Þ 0.026, 0.061; R1, wR2 (all
3
˚
data): 0.031, 0.064; Dqmax, Dqmin (e/A ): 0.366, ꢂ0.477;
CCCD deposition No. 278396.
4.6.5. (R)-2-(4-Isopropyl-4-methyl-4,5-dihydro-1H-
imidazol-5-one-2-yl)pyridine (2(R))
4.6. Synthesis of ligands
In a similar manner, the compound 2(R) was prepared
25
4.6.1. ( )-2-[N-(2-Aminocarbonyl-2,3-dimethylbutyl)-
aminocarbonyl]pyridine (1)
as pure colourless oil in a yield of 80%, ½aꢀD ¼ þ19:0ꢁ
(c = 2.4, CH3OH). The elemental analysis is comparable
1
A mixture of picolinic acid (15 mmol) and triethylamine
(15 mmol) in 50 mL dry THF was treated with a solution
of ethyl chloroformate (15 mmol) in 15 mL dry THF added
drop by drop. After 30 min, 2-amino-2,3-dimethylbutana-
mide (15 mmol) in 20 mL THF was added to the suspen-
sion formed, and the mixture was stirred 3 h. The
triethylammonium chloride formed was removed by filtra-
tion and washed with 10 mL THF. The removal of THF by
means of distillation left a yellowish crude product. This
was recrystallized from toluene to give white crystalline
substance 1 in the yield of 78%, m.p.189–190 ꢁC.
with that of 2, and the H and 13C NMR spectra are iden-
tical with those of 2.
4.6.6. (S)-2-(4-Isopropyl-4-methyl-4,5-dihydro-1H-
imidazol-5-one-2-yl)pyridine (2(S))
In a similar manner, compound 2(S) was prepared as
25
pure colourless oil in a yield of 82%, ½aꢀD ¼ ꢂ18:0ꢁ
(c = 2.0, CH3OH). The elemental analysis is comparable
with that of 2, and the H and 13C NMR spectra are iden-
1
tical with those of 2.
1H NMR (DMSO-d6, d ppm): 8.97 (s, 1H, NH), 8.71 (m,
1H, PyH6), 8.06 (m, 2H, PyH3, H5), 7.65 (m, 1H, PyH4),
7.40 (s, 1H, NH2), 7.26 (s, 1H, NH2), 2.35 (m, 1H, i-PrCH),
1.65 (s, 3H, CH3), 0.98 (d, 3H, i-PrCH3), 0.95 (d, 3H, i-
PrCH3). 13C NMR (DMSO-d6, d ppm): 174.7, 162.4,
4.6.7. Procedures of N-alkylation of 2-(4-isopropyl-4-
methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridine (2)
Method A: A mixture of compound 2 (10 mmol) and
potassium or cesium carbonate (15 mmol) in 10 mL dry
DMF kept under argon atmosphere was treated with the

2628
M. Sedla´k et al. / Journal of Organometallic Chemistry 691 (2006) 2623–2630
respective alkylation agent (12 mmol) (the alkylation agent
in the synthesis of 3: dimethylsufate; 4: benzyl bromide; 5:
picolyl chloride; 6: chloroacetonitrile; 7: ethyl bromoace-
tate). The reaction mixture was heated at 160 or 90 ꢁC
for a period of 48 or 24 h, respectively. The inorganic salts
formed were removed by filtration, DMF was distilled off,
and the crude product was dissolved in ethyl acetate and
filtered through a 1 cm silica gel layer. After distilling off
of ethyl acetate, products 3–7 were obtained.
Method B: Compound 2(R) or 2(S) (3.6 mmol) kept
under argon atmosphere was treated with potassium tert-
butoxide (5.4 mmol). The mixture was stirred at room tem-
perature, and after 1 h, t-butyl alcohol was distilled off. The
evaporation residue was dissolved in 10 mL dry DMF, the
solution was cooled to r.t., and methyl iodide (6 mmol) was
added thereto under argon atmosphere. The suspension
formed was stirred at r.t. for a period of 3 h. After distilling
off DMF, the evaporation residue was mixed with water,
and the emulsion formed was extracted with 2 · 30 mL
ether. The removal of ether by distillation left product
3(R) or 3(S), respectively.
4.6.7.5. (R)-2-(1-Benzyl-4-isopropyl-4-methyl-4,5-dihydro-
1H-imidazol-5-one-2-yl)pyridine (4(R)). Method A:
25
White crystals; yield 73%, m.p. 39–42 ꢁC, ½aꢀD ¼ þ19:4ꢁ
(c = 1.0, CH2Cl2). The elemental analysis is comparable
1
with that of 4, and the H and 13C NMR spectra are iden-
tical with those of racemic compound 4.
4.6.7.6. (S)-2-(1-Benzyl-4-isopropyl-4-methyl-4,5-dihydro-
1H-imidazol-5-one-2-yl)pyridine (4(S)). Method A: Yel-
25
lowish oil; yield 84%, ½aꢀD ¼ ꢂ20:1ꢁ (c = 1.1, CH2Cl2).
The elemental analysis is comparable with that of 4, and
1
the H and 13C NMR spectra are identical with those of
racemic compound 4.
4.6.7.7. ( )-2-(1-(2-Picolyl)-4-isopropyl-4-methyl-4,5-di-
hydro-1H-imidazol-5-one-2-yl)pyridine (5). Method A:
1
Yellowish crystals; yield 82%, m.p. 100–102 ꢁC; H NMR
(DMSO-d6, d ppm): 8.55 (d, 1H, PyH6), 8.34 (d, 1H, Py),
8.05 (d, 1H, PyH3), 7.92 (m, 1H, PyH5), 7.66 (m, 1H, Py),
7.50 (m, 1H, PyH4), 7.17–7.18 (m, 2H, Py), 5.36 (dd, 2H,
CH2), 2.06 (m, 1H, i-PrCH), 1.37 (s, 3H, CH3), 1.05 (d,
3H, i-PrCH3), 0.86 (d, 3H, i-PrCH3). 13C NMR (DMSO-
d6, d ppm): 186.1, 158.8, 155.6, 149.2, 148.9, 148.5, 137.8,
137.5, 136.6, 125.7, 123.6, 122.1, 121.0, 73.1, 46.0, 34.3,
21.3, 17.1, 16.9. Anal. Calc. for C18H20N4O: C, 70.11; H,
6.54; N, 18.17. Found: C, 70.29; H, 6.64; N, 18.26%.
4.6.7.1. ( )-2-(1-Methyl-4-isopropyl-4-methyl-4,5-dihydro-
1H-imidazol-5-one-2-yl)pyridine (3). Method A: Yellow-
1
ish oil, yield 69%; H NMR (DMSO-d6, d ppm): 8.70 (d,
1H, PyH6), 8.04 (d, 1H, PyH3), 7.99 (m, 1H, PyH5), 7.60
(m, 1H, PyH4), 3.27 (s, 3H, NCH3), 1.94 (m, 1H, i-PrCH),
1.24 (s, 3H, CH3), 0.95 (d, 3H, i-PrCH3), 0.73 (d, 3H, i-
PrCH3). 13C NMR (DMSO-d6, d ppm): 186.0, 159.2,
149.1, 149.0, 137.7, 126.0, 124.0, 73.0, 34.4, 29.0, 21.3,
16.9, 16.7. Anal. Calc. for C13H17N3O: C, 67.51; H, 7.41;
N, 18.17. Found: C, 67.44; H, 7.52; N, 18.28%.
4.6.7.8. ( )-2-(1-Cyanomethyl-4-isopropyl-4-methyl-4,5-di-
hydro-1H-imidazol-5-one-2-yl) pyridine (6). Method A:
1
Yellowish oil; yield 92%. H NMR (DMSO-d6, d ppm):
8.79 (d, 1H, PyH6), 8.23 (d, 1H, PyH3), 8.08 (m, 1H,
PyH5), 7.70 (m, 1H, PyH4), 5.10 (dd, 2H, CH2), 2.05 (m,
1H, i-PrCH), 1.34 (s, 3H, CH3), 1.00 (d, 3H, i-PrCH3), 0.81
(d, 3H, i-PrCH3). 13C NMR (DMSO-d6, d ppm): 185.0,
155.9, 149.0, 147.9, 138.2, 126.7, 123.7, 116.5, 73.2, 34.7,
31.2, 20.8, 16.7, 16.7. Anal. Calc. for C14H16N4O: C, 65.61;
H, 6.29; N, 21.86. Found: C, 65.85; H, 6.42; N, 21.73%.
4.6.7.2. (R)-2-(1-Methyl-4-isopropyl-4-methyl-4,5-dihydro-
1H-imidazol-5-one-2-yl)pyridine (3(R)). Method B: Yel-
25
lowish oil, yield 65%, ½aꢀD ¼ þ28:6ꢁ (c = 0.61, CH2Cl2).
The elemental analysis is comparable with that of 3, and
1
the H and 13C NMR spectra are identical with those of
racemic compound 3.
4.6.7.9. ( )-2-(1-Ethoxycarbonylmethyl-4-isopropyl-4-
methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridine (7).
Method A: Yellowish oil; yield 79%; H NMR (DMSO-d6,
1
4.6.7.3. (S)-2-(1-Methyl-4-isopropyl-4-methyl-4,5-dihydro-
1H-imidazol-5-one-2-yl)pyridine (3(S)). Method B: Yel-
d ppm): 8.58 (d, 1H, PyH6), 8.17 (d, 1H, PyH3), 7.98 (m,
1H, PyH5), 7.56 (m, 1H, PyH4), 4.02 (q, 2H, OCH2CH3),
4.70 (dd, 2H, CH2), 2.00 (m, 1H, i-PrCH), 1.28 (s, 3H,
CH3), 1.07 (t, 3H, OCH2CH3), 0.99 (d, 3H, i-PrCH3),
0.79 (d, 3H, i-PrCH3). 13C NMR (DMSO-d6, d ppm):
185.3, 168.4, 157.1, 148.4, 148.3, 137.6, 126.0, 123.2, 73.1,
60.7, 34.3, 34.2, 21.0, 16.8, 16.6, 13.9. Anal. Calc. for
C16H21N3O3: C, 63.35; H, 6.98; N, 13.85. Found: C,
63.41; H, 6.91; N, 13.84%.
25
lowish oil, yield 66%, ½aꢀD ¼ ꢂ27:8ꢁ (c = 0.51, CH2Cl2).
The elemental analysis is comparable with that of 3, and
the 1H and 13C NMR spectra are identical with those of 3.
4.6.7.4. ( )-2-(1-Benzyl-4-isopropyl-4-methyl-4,5-dihydro-
1H-imidazol-5-one-2-yl)pyridine (4). Method A: White
crystals, yield 65%, m.p. 46–49 ꢁC; 1H NMR (DMSO-d6, d
ppm): 8.71 (d, 1H, PyH6), 8.00 (d, 1H, PyH3), 7.96 (m, 1H,
PyH5), 7.59 (m, 1H, PyH4), 7.08–7.25 (m, 5H, Ph), 5.23
(dd, 2H, CH2), 2.05 (m, 1H, i-PrCH), 1.34 (s, 3H, CH3),
1.01 (d, 3H, i-PrCH3), 0.80 (d, 3H, i-PrCH3). 13C NMR
(DMSO-d6, d ppm): 186.0, 158.3, 148.9, 148.8, 137.8,
137.7, 128.4, 127.2, 127.1, 126.0, 123.8, 72.9, 44.4, 34.4,
21.3, 16.9, 16.8. Anal. Calc. for C19H21N3O: C, 74.24; H,
6.89; N, 13.67. Found: C, 74.31; H, 6.78; N, 13.56%.
4.6.8. ( )-2-(1-Carbamoylmethyl-4-isopropyl-4-methyl-4,5-
dihydro-1H-imidazo-5-one-2-yl)pyridine (8)
A mixture of 1 M aqueous NaOH (40 mmol) and solution
of compound 7 (3.6 mmol) in 10 mL methanol was stirred at
r.t. for a period of 5 h. After adjusting pH ꢃ 7 (conc. HCl),
the mixture was extracted with 3 · 30 mL CHCl3. The com-

M. Sedla´k et al. / Journal of Organometallic Chemistry 691 (2006) 2623–2630
2629
bined extracts were filtered with charcoal, the solvent was
4.7.6. Complex 14
Complex 14 was prepared from ligand
evaporated, and product 8 was obtained as white crystalline
solid in a yield of 65%, m.p. 136–138 ꢁC; 1H NMR (DMSO-
d6, d ppm): 8.66 (d, 1H, PyH6), 8.13 (d, 1H, PyH3), 8.00 (m,
1H, PyH5), 7.59 (m, 1H, PyH4), 7.55 and 6.98 (2 · s, 2H,
NH2), 4.68 (dd, 2H, CH2), 2.02 (m, 1H, i-PrCH), 1.32 (s,
3H, CH3), 1.04 (d, 3H, i-PrCH3), 0.84 (d, 3H, i-PrCH3).
13C NMR (DMSO-d6, d ppm): 186.0, 169.2, 158.6, 149.3,
148.6, 137.6, 125.8, 123.5, 73.1, 43.8, 34.3, 21.2, 17.2, 16.9.
Anal. Calc. for C14H18N4O2: C, 61.30; H, 6.61; N, 20.42.
Found: C, 61.18; H, 6.56; N, 20.57%.
8
and
CuCl2 Æ 2H2O as light green powder in a yield of 89%,
m.p. 224–228 ꢁC. Anal. Calc. for C14H18Cl2CuN4O2: C,
41.14; H, 4.44; N, 13.71. Found: C, 41.18; H, 4.53; N,
13.43%. ESI-MS (M = 407): [MꢂCl]+ m/z 371.9,
[2MꢂCuCl2ꢂCl]+ m/z 647.3, [2MꢂCl]+ m/z 779.0.
4.8. Nitroaldol (Henry) reaction of 4-nitrobenzaldehyde
with nitromethane
Method C: A solution of complex 9(R) (mol% are
given in Table 1) in 5 mL CH2Cl2 was added at a temper-
ature of ꢂ40 ꢁC to a mixture of 4-nitrobenzaldehyde
(2 mmol), nitromethane (20 mmol) and triethylamine
(0.1 mmol), and the reaction mixture was stirred at the
chosen temperature (see Table 1). The reaction course
was monitored by means of TLC (Merck silica gel plates
(60), ethyl acetate/hexane 1/4). The mixture was evapo-
rated under reduced pressure, and the evaporation residue
was mixed with ether and filtered through a 1 cm silica gel
layer. The filtrate was extracted with aqueous solution of
sodium hydrogensulphite (1 g in 50 mL H2O). After evap-
oration of the ether, the product 2-nitro-1-(4-nitro-
phenyl)ethanol was obtained as a crystalline solid (m.p.
4.7. Synthesis of the copper(II) complexes
A solution of racemic ligand 3 or 4–8 (0.2 mmol) and
CuCl2 Æ 2H2O (0.2 mmol) in 10 mL ethanol was stirred at
r.t. for ca. 20 min. The resulting solution was evaporated
until dry, and product 9 or 10–14, respectively, was mixed
with 10 mL ether, filtered and dried in a dessiccator.
4.7.1. Complex 9
Complex
9
was prepared from ligand
3
and
CuCl2 Æ 2H2O as light green powder in a yield of 73%,
m.p. 249–259 ꢁC. Anal. Calc. for C13H17Cl2CuN3O: C,
42.69; H, 4.68; N, 11.49. Found: C, 42.77; H, 4.79; N,
11.35%. ESI-MS (M = 364): [MꢂCl]+ m/z 328.9,
[2MꢂCuCl2ꢂCl]+ m/z 560.0, [2MꢂCl]+ m/z 694.9.
1
79–82 ꢁC; H NMR (CDCl3, d ppm): 8.21 (d, 2H, H3,5),
7.61 (d, 2H, H2,6), 5.60 (dd, 1H, CH), 4.59–4.57 (m,
2H, CH2), 3.58 (s, 1H, OH). Anal. Calc. for C8H8N2O5:
C, 45.29; H, 3.80; N, 13.20. Found: C, 45.31; H, 3.96;
N, 13.36%). The optical yields given in Table 1 were
determined by measuring the optical rotatory power of
product [16a]. The results obtained in the described way
were subsequently verified by means of HPLC of the
crude reaction mixture.
4.7.2. Complex 10
Complex 10 was prepared from ligand
4 and
CuCl2 Æ 2H2O as light green powder in a yield of 78%,
m.p. 258–264 ꢁC. Anal. Calc. for C19H21Cl2CuN3O: C,
51.65; H, 4.79; N, 9.51. Found: C, 51.60; H, 4.86; N,
9.69%. ESI-MS (M = 440): [MꢂCl]+ m/z 405.0,
[2MꢂCuCl2ꢂ2Cl]+ m/z 677.2, [2MꢂCl]+ m/z 846.9.
Method D: A mixture of ligand 3(S) or 4(R) (mol% are
given in Table 1) and cupric salt (0.01 mmol) (acetate, ben-
zoate, isophthalate or pivaloate) in 3 mL absolute ethanol
was stirred for a period of 30 min. The clear solution
obtained was treated with nitromethane (20 mmol) and 4-
nitrobenzaldehyde (2 mmol), and the reaction mixture
was stirred at 25 or 0 ꢁC, respectively. After the reaction,
the mixture was processed and analysed in the same way
as in the preceding Method C.
4.7.3. Complex 11
Complex 11 was prepared from ligand
5 and
CuCl2 Æ 2H2O as light green powder in a yield of 79%,
m.p. 170–172 ꢁC. Anal. Calc. for C18H20Cl2CuN4O: C,
48.82; H, 4.55; N, 12.65. Found: C, 48.76; H, 4.51; N,
12.72%. ESI-MS (M = 441): [M-Cl]+ m/z 406.0, [2M-
CuCl2-Cl]+ m/z 714.2, [2M-Cl]+ m/z 848.9.
4.7.4. Complex 12
5. Supplementary data
Complex 12 was prepared from ligand 6 and CuCl2 Æ
2H2O as light green powder in yield 85%, m.p. 204–210 ꢁC.
Anal. Calc. for C14H16Cl2CuN4O: C, 43.03; H, 4.13; N,
14.34. Found: C, 43.07; H, 4.15; N, 14.46%. ESI-MS
(M = 389): [MꢂCl]+ m/z 353.9, [2MꢂCl]+ m/z 744.9.
A full list of crystallographic data and parameters
including fractional coordinates is deposited at the Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK [fax: int. code +44 1223 336
033; e-mail: deposit@ccdc.cam.ac.uk].
4.7.5. Complex 13
Complex 13 was prepared from ligand
7 and
CuCl2 Æ 2H2O as light green powder in a yield of 76%,
m.p. 188–194 ꢁC. Anal. Calc. for C16H21Cl2CuN3O3: C,
43.90; H, 4.83; N, 9.60. Found: C, 43.94; H, 4.81; N,
9.41%. ESI-MS (M = 436): [MꢂCl]+ m/z 401.0,
[2MꢂCuCl2ꢂCl]+ m/z 704.2, [2MꢂCl]+ m/z 839.1.
Acknowledgements
The authors acknowledge the financial support the
MSM 0021627501 and the Science Foundation of the
Czech Republic (Grant No. 203/04/0646).

2630
M. Sedla´k et al. / Journal of Organometallic Chemistry 691 (2006) 2623–2630
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