Structure and catalytic activity of organopalladium(II) complexes based on 4,5-dihydro-1H-imidazol-5-one derivatives

Article abstract of DOI:10.1016/j.jorganchem.2010.10.031

The paper describes preparation of a chiral bidentate ligand - 2-(2-bromophenyl)-4,5-dihydro-1H-imidazol-5-one, and a tridentate ligand - 2-bromo-1,3-bis(4,5-dihydro-1H-imidazol-5-on-2-yl)benzene, whose oxidative addition reaction with Pd(0) giving neutra

Full text of DOI:10.1016/j.jorganchem.2010.10.031

Journal of Organometallic Chemistry 696 (2011) 971e981
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Structure and catalytic activity of organopalladium(II) complexes based
on 4,5-dihydro-1H-imidazol-5-one derivatives
,
b
a
ꢀ a
Pavel Drabina a , Bretislav Broz , Zdenka Padelková , Milos Sedlák
ꢀ
ꢀ
ꢀ
*
ꢀ
a Institute of Organic Chemistry and Technology, Faculty of Chemical Technology, University of Pardubice, Studentská 573, 53210 Pardubice, Czech Republic
b Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 573, 53210 Pardubice, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
The paper describes preparation of a chiral bidentate ligand e 2-(2-bromophenyl)-4,5-dihydro-1H-
imidazol-5-one, and a tridentate ligand e 2-bromo-1,3-bis(4,5-dihydro-1H-imidazol-5-on-2-yl)benzene,
whose oxidative addition reaction with Pd(0) giving neutral organopalladium(II) complexes has been
studied. The structure of these complexes was studied by means of NMR spectroscopy and X-ray
diffraction. After transformation of the neutral organopalladium(II) complexes into the corresponding
ionic species the latter were studied as enantioselctive catalysts for asymmetric FriedeleCrafts alkylation
and Michael addition.
Received 16 September 2010
Received in revised form
8 October 2010
Accepted 18 October 2010
Available online 23 October 2010
Keywords:
Ó 2010 Elsevier B.V. All rights reserved.
4,5-Dihydro-1H-imidazol-5-one ligands
Pdepincer complexes
Asymmetric catalysis
FriedeleCrafts alkylation
Michael addition
1. Introduction
are most often amines [1e,9], imines [10], oxazolines [11] and other
nitrogen heterocycles [12]. The nitrogen “pincers” possess several
Chiral organopalladium(II) compounds have become significant
tools in dealing with various stereochemical problems. The areas
that make use of organopalladium(II) complexes particularly
include asymmetric syntheses, i.e. their application as enantiose-
lective catalysts or pre-catalysts [1]. Another field of application of
these compounds is, e.g., separation of enantiomers or spectral
determination of enantiomeric purity [2] and absolute configura-
tion [3].
One of the most frequently studied types of chiral compounds
containing covalently bound palladium are complexes of “pincer”
type, which are derived from ligands of formally bidentate type
“XC” or tridentate type “XCX”, where X is a donor atom e nitrogen,
phosphorus, sulfur or oxygen or a combination of these atoms [4].
The “pincer” complexes which proved most useful in catalytic
applications are complexes containing N- and P-donor atom.
Among another pincer ligands with wide range of possible appli-
cations belong to N-heterocyclic carbons (NHCs) [5a] bearing
especially imidazole [5b,c] and benzimidazole moiety [5def]. The
P-donors include in particular phosphins [6], phosphites [7],
phosphinites [8] and phosphoramidites [1a], while the N-donors
advantages over the phosphine types: lower price and toxicity,
easy availability, insensitivity to air oxygen. From the standpoint of
application, these complexes are very promising, though the
enantioselectivity of the “pincer” complexes described so far tends
not to be always high. However, this fact justifies further efforts
directed to designing and syntheses of new compounds of this
type.
4,5-Dihydro-1H-imidazol-5-one derivatives were studied in
earlier papers as promising catalysts of many different chemical
processes [13]. Particularly they proved useful as very efficient
catalysts in the deallylation reaction of 2-substituted-2-allylmalo-
nates [13a], alkylating ring closure reaction of 2-chloro-1,7-hepta-
diene [13b], asymmetric Henry reaction [13c] or asymmetric allyl
oxidation [13d]. This fact inspired us to the decision to prepare and
study chiral organopalladium(II) complexes containing a “CN”
bidentate ligand and “NCN” tridentate ligand on the basis of 4,5-
dihydro-1H-imidazol-5-one (Chart 1). In this way we obtained
“pincers” having the structure formally very similar to that of well-
known oxazoline (“Phebox”; “Phemox”) [11] and imidazoline
ligands (“Phebim”) [12a,14]. In addition to that, 4,5-dihy-
dro-1H-imidazol-5-ones has the advantage over oxazolines and
imidazolines in generally higher stability and resistance to race-
mization [15].
* Corresponding author. Tel.: þ420 466037010; fax: þ420 466037068.
E-mail address: pavel.drabina@upce.cz (P. Drabina).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.10.031

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P. Drabina et al. / Journal of Organometallic Chemistry 696 (2011) 971e981
ratio because the differences in chemical shifts of the individual
groups ofdiastereoisomersinthe 1HNMR spectrumwere verysmall.
On the other hand, the optically pure forms of compounds 5e7
exhibited only one set of signals in the 1H NMR spectra, which
confirmed their optical purity.
If 2-bromo-1,3-bis(4-isopropyl-4-methyl-4,5-dihydro-1H-imi-
dazol-5-on-2-yl)benzene (6) was methylated with methyl iodide
added in one portion, then mono-methylation was predominantly
observed e even when six equivalents were used. Only after
dividing the total amount of the reagent into two portions and
addition of these portions in a 4-h interval the required dimethyl
derivative 7 was obtained with practically quantitative conversion.
(S)-2-(2-Bromophenyl)-4-isopropyl-1,4-dimethyl-4,5-dihydro-1H-
imidazol-5-one ((S)-3) was characterised by means of X-ray anal-
ysis. The crystalline form suitable for this analysis was obtained by
slow evaporation of the solution of this compound in CH2Cl2. Fig. 1
represents the ORTEP diagram, in which only one of the four
independent molecules present in elementary cell is depicted. The
two planes defined by the plane of benzene nucleus and the plane
of 4,5-dihydro-1H-imidazol-5-one cycle form an angle of 68.8ꢀ.
Chart 1.
2. Results and discussion
2.1. Syntheses of ligands
The 4,5-dihydro-1H-imidazol-5-one ligands 3 and 7 were
prepared by procedures described earlier [13c,e] from easily avail-
able racemic or optically pure 2-amino-2,3-dimethylbutanamide
[16] (Scheme 1). In comparison with the earlier synthetic proce-
dures, it was necessary for the ring closure leading to formation of
4,5-dihydro-1H-imidazol-5-one derivatives 2 and 6 to prolong the
reaction time since the ortho-Br substituent in the phenyl ring
significantly slows down this reaction [17]. Side reactions were
observed in the case of ring closure reaction of N,N0-bis(2-carba-
moyl-3-methylbut-2-yl)-2-bromobenzene-1,3-dicarboxamide (5)
in the medium of methanolic solution of KOH; they probably consist
of nucleophilic aromatic substitution of the bromine atom. There-
fore, we replaced KOH with little nucleophilic tBuOK in the medium
2.2. Synthesis and structure of neutral organopalladium(II)
complexes
Ligands 3 and 7 were converted into palladium derivatives by
means of two reagents e Pd(dba)2 and Pd(PPh3)4 (Scheme 2.). The
reactions were carried out in dry degassed toluene at room
temperature under argon atmosphere. The reaction times were not
optimised; the neutral organopalladium(II) complexes 8e9 and 11
were isolated in good yields, viz. ꢁ90%, as yellow-orange crystalline
solids. Apart from the oxidative addition of Pd(0) we also verified
the possibility of bromineemagnesium exchange reaction in the
t
of BuOH, and under these conditions the side reactions were not
observed. The starting compound for synthesis of tridentate ligand 7
was the commercially available 2,6-dimethylbromobenzene, which
was oxidized to the corresponding dicarboxylic acid by a known
procedure [18], whereupon the diacid was transformed into the
respective dichloride by reactionwith a phosgene solution in CH2Cl2
(1:5 m/m) in the yield of 87%. Racemic derivatives 5e7 were isolated
as a mixture of diastereoisomers (R,R) þ (S,S) and meso-form, which
resulted in a broad melting point and doubling of some signals in the
NMR spectra. Unfortunately, it was impossible to determine their
i
case of compound 3, namely by means of PrMgCl in THF. The
obtained Grignard reagent was subsequently submitted to reaction
with carbon dioxide, and acid 4 was isolated in satisfactory yield
(44e49%) after acidification.
The 1H, 13C and 31P NMR spectroscopy revealed that complex 8
contains one PPh3 molecule. Slow diffusion of n-hexane into its
saturated solution in CH2Cl2 gave a crystalline form suitable for
X-ray analysis. Fig. 2 represents the ORTEP diagram of complex
( )-8, wherefrom it was deduced that palladium does not assume
the regular square-planar arrangement, typical of Pd2þ
compounds [19], but a considerable deformation is present. The
angle formed by two imaginary planes defined by atoms
C1ePd1eN1 (the 1st plane) and P1ePd1eBr1 (the 2nd plane) has
Fig. 1. Molecular structure of (S)-3; ORTEP 50% probability level. Hydrogen atoms are
omitted for clarity. Selected interatomic distances (Å) and angles (ꢀ): Br1eC2 1.902(3),
C1eC7 1.482(3), C7eN1 1.270(3), C7eN2 1.405(3), C8eO1 1.217(3), N1eC7eN2 115.7
(2).
Scheme 1.

P. Drabina et al. / Journal of Organometallic Chemistry 696 (2011) 971e981
973
Scheme 2.
the value of 12.4ꢀ (Fig. 3A). This deviation from ideal arrangement
is caused by interaction of bulky phenyl groups of PPh3 with
hydrogen atoms of benzene cycle of ligand, which results in
atropoisomerism [20].
Interpretation of the 13C NMR spectrum showed that
compound ( )-8 is formed by a mixture of four enantiomeric pairs
(Chart 2). Apart from the asymmetry centre present in the
4,5-dihydro-1H-imidazol-5-one cycle, further configuration isom-
erism results from two different arrangements of the substituents
at the palladium atom. Besides the arrangement determined by X-
ray analysis (Fig. 2.), also an opposite arrangement can exist in
which the ligands PPh3 and Br will exist in mutually reversed
position. This isomerism is an analogy of cisetrans isomerism at
a double bond. Each of the two possible isomers, “cis” and “trans”,
can additionally exhibit atropoisomerism due to two different
arrangements of the ligands PPh3 and Br with regard to the
C1ePd1eN1 plane. On the other hand, the 1H and 31P NMR spectra
contained only two sets of signals corresponding obviously to the
respective “cis” and “trans” forms. In this case the individual
atropoisomers possess practically identical chemical shifts due to
very little differences in their structure. Fig. 4 represents the
splitting of signals of selected groups in complex ( )-8: carbonyl
group and quaternary carbon (in 13C NMR), isopropyl group (in 1H
Fig. 2. Molecular structure of complex ( )-8; ORTEP 50% probability level. Hydrogen
atoms and molecules of solvent are omitted for clarity. Only one of two independent
molecules is shown. Selected interatomic distances (Å) and angles (ꢀ): Pd1eC1 2.032
(4), Pd1eN1 2.080(4), Pd1eBr1 2.4808(7), Pd1eP1 2.2589(11), C2eC7 1.460(6), P1eC15
1.825(4), C1ePd1eN1 79.94(16), P1ePd1eBr1 91.48(3), N1eC7eN2 113.6(4).

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P. Drabina et al. / Journal of Organometallic Chemistry 696 (2011) 971e981
Fig. 3. Comparison of geometries of Pd atom in complexes 8 (A) and 9 (B). Viewed in the plane C1ePdeN1.
Chart 2. Presumed arrangement of ligands around central Pd atom.
NMR), and phosphine signal (in 31P NMR). Approximately deter-
mined ratio of the forms is 4:3.
The optically pure complex (S)-9 was prepared in crystal-
line form suitable for X-ray analysis by slow evaporation of
solvent from its saturated solution in CH2Cl2. The ORTEP diagram
(Fig. 5.) shows that compound 9 in solid state forms a dimeric
structure in which the palladium atoms of individual monomers
are connected by two bromine bridges. In this way, palladium
supplements its coordination sphere to the coordination number
4. In this structure the angle formed by two imaginary planes
defined by the atoms Br1ePd1eBr1a (the 1st plane) and
C1ePd1eN1 (the 2nd plane) is only 3.4ꢀ (Fig. 3B) and, therefore,
the palladium atom in complex (S)-9 can be defined as having
square-planar geometry.
Two comparable sets of signals were found in the 1H and 13C
NMR spectra of racemic as well as optically pure forms of
complex 9, wherefrom it can be deduced that in both cases they
are mixtures of two configurational isomers. The observed
isomerism can be explained by the existence of two different
mutual positions of the individual 4,5-dihydro-1H-imidazol-5-one
ligands in the dimer, which leads to isomerism of “cis-trans” type
(Chart 3). The probably more stable arrangement “trans” (I) was
confirmed by means of X-ray analysis. The possibility of “cis” (II)
arrangement can be presumed on the basis of the NMR spectra of
the (S)-9 form. This form e in the case of existence of only “trans”
form e would be presented by only a single set of signals, while
the racemic form ( )-9 would be presented by two sets corre-
sponding to two types of diastereoisomers. The first would
Fig. 5. Molecular structure of complex (S)-9; ORTEP 50% probability level. Hydrogen
atoms and molecules of solvents are omitted for clarity. Selected interatomic distances
(Å) and angles (ꢀ): Pd1eC1 1.990(6), Pd1eN1 2.033(4), Pd1eBr1 2.5694(7), Pd1eBr1a
2.4377(6), Pd1ePd1a 3.6834(8), C2eC7 1.461(7), C1ePd1eN1 80.3(2), Br1ePd1eBr1a
84.97(2), Pd1eBr1ePd1a 94.68(2), N1ePd1eBr1a 100.00(12), C1ePd1eBr1 94.85(16),
N1eC7eN2 113.2(5), Pd1eN1eC7 115.0(4), Pd1eC1eC2 114.8(4), C1eC2eC7 112.0(5).
involve the configurations at chiral carbon atoms of imidazoli-
nones S,S and R,R, the second would involve the combination R,S
(meso-form) (III). The existence of diastereoisomeric pairs within
each of the “cis” and “trans” forms of racemic complex ( )-9
Fig. 4. Selected peaks from 1H, 13C and 31P NMR spectra of compound ( )-8.

P. Drabina et al. / Journal of Organometallic Chemistry 696 (2011) 971e981
975
cannot be excluded, but according to NMR spectroscopy it cannot
be confirmed either.
model reactions were chosen whose realization necessitates the
presence of electrophilic species.
Chart 3. Possible configurational isomerism in dimer 9: I e (S,S) e “transoid”; II e (S,S) e “cisoid”; III e (S,R) e “transoid”.
It can be presumed that the coordination of bromine atom
towards palladium atom of the second molecule of dimer is
relatively weak and is enforced by the absence of another, better
coordinating ligand. In the presence of a well coordinating
compound (e.g., coordinating solvent or another ligand) dimer 9
would decompose into two monomeric forms. This presumption
was confirmed by an experiment in which complex 9 was
submitted to the reaction with PPh3. After one-day stirring with
stoichiometric amount of the reagent in CH2Cl2 at room
temperature the isolated product was identified as complex 8
(Scheme 2).
Palladium treatment of ligand 7 with the above-mentioned
reagents always led to formation of complex 11, even in the case of
application of Pd(PPh3)4, which is a source of strongly coordinating
triphenylphosphine. This compound is known to be able, under
certain conditions, to replace one of the N-donors in the coordi-
nation sphere of palladium [21] in NCN pincers. From the viewpoint
of stereochemistry, complex 11 is simpler than compounds 8 and 9:
the optically pure form is presented in NMR spectra by one form,
the racemic one by two forms which correspond to two forms of
diastereoisomers of the starting ligand.
2.3.1. Catalytic studies in asymmetric FriedeleCrafts alkylation
Asymmetric FriedeleCrafts alkylation belongs among signifi-
cant methods introducing a new stereogenic centre into hetero-
cyclic system. As a rule, an electron-rich heteroaromatic system
(such as substituted 1H-pyrrole or 1H-indole) is chosen as the
substrate, and the reagent is a polarized prochiral alkene [12a, 23].
The asymmetric induction is achieved with chiral complexes of
transition metals, particularly Zn(II) [23a,b,d] and Cu(I) [23c,g] or
enantioselective organocatalysts (phosphates [23e], thioureas
[23f]). In our case we studied asymmetric Friedel–Crafts alkylation
of indole with (E)-2-phenyl-1-nitroethene catalysed with 5 mol. %
organopalladium(II) complex 9-10, 12. Indole was used in consid-
erable extent (ca 5 eq.) because it underwent polymerization
during the reaction. A survey of the experiments performed,
reaction conditions and yields are summarized in Table 1. The
values of enantiomeric excess show that only complex (S)-12
exhibited a certain enantioselectivity (experiments 3 and 4), while
complexes (S)-9 and (S)-10 gave only racemic product (experi-
ments 1 and 2). Lowering of reaction temperature to 0 ꢀC did not
bring about any increase in enantioselectivity (experiment 4). In
the case of application of coordinating THF the reaction did not
proceed (experiment 5). The reason is probably in preferential
coordination of the solvent, whose concentration in the reaction
2.3. Synthesis and catalytic studies of cationic organopalladium(II)
complexes
For application to catalytic studies the neutral complexes 9 and
11 were transformed into the cationic complexes 10 and 12 by
treatment with AgBF4 in acetone with 1 % water admixture: the
yields were practically quantitative (93e97%). The free coordina-
tion positions were occupied by water molecules; therefore, the
complexes obtained are stable and have precisely defined compo-
sition. Compound 10 has substantially simpler structure as
compared with the neutral complexes 8 and 9: the palladium atom
in this case is not an asymmetric centre any more. This fact was
manifested by the presence of only one set of signals in the NMR
spectra. As water molecules are relatively small ligands, it is
possible to presume square-planar geometry of palladium in
complex 10. Water does not belong among strongly coordinating
ligands and so it can be replaced during the catalytic process by
reactants with similar or stronger coordination properties, which
results in their activation and hence execution of the catalytic
process. Generally, organopalladium(II) complexes are charac-
terised by considerable electrophilicity [22] and, therefore, such
Table 1
Survey of conditions and yields of alkylation of 1H-indole with (E)-2-phenyl-1-
nitroethene.
Entry
Catalyst
Solvent
Temp. (ꢀC)
Time (d)
Yield (%)
ee (%)
1
2
3
4
5
6
(S)-9
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
THF
20
20
20
0
20
20
10
7
7
10
12
12
50
95
98
99
0
<3
<3
10
12
e
(S)-10
(S)-12
(S)-12
(S)-12
(S)-12
(bmim)BF4
0
e

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P. Drabina et al. / Journal of Organometallic Chemistry 696 (2011) 971e981
Table 2
reagents for the syntheses were obtained from commercial sources
(SigmaeAldrich, Acros Organics e reagent grade) and were used
without further purification. Column chromatography was per-
formed using silica gel 60 (230e400 mesh) supplied by Merck. The
1H and 13C NMR spectra were recorded on a Bruker Avance 400
Survey of conditions and yields of addition of ethyl 2-oxocyclohexanecarboxylate to
methyl vinyl ketone.
spectrometer at 400.13 (1H), 125.62
( (
13C), 376.46 19F) and
161.97 MHz (31P). The 1H and 13C chemical shifts were referenced to
the central peaks of solvents e 1H: CDCl3 (
7.26), DMSO-d6 ( 2.50),
77.16), DMSO-d6 39.52),
49.00). The 19F NMR chemical shifts were uncalibrated,
d
d
CD3OD (
CD3OD (
d
d
4.87 and 3.31), 13C: CDCl3
(
d
(d
the 31P NMR data are reported relative to external 85% H3PO4. The
mass spectra were recorded on instrument set from Agilent Tech-
nologies (gas chromatograph 6890N with mass detector 5973
Network). The elemental analyses were performed on FISONS
Instruments EA 1108 CHN. The optical rotation was measured on
a PerkineElmer 341 instrument, concentration c is given in g/
100 mL. FT-IR spectra were recorded on a PerkineElmer Spectrum
BX. The optical purity of 3-(2-nitro-1-phenylethyl)-1H-indole and
ethyl 2-oxo-1-(3-oxobutyl)cyclohexane-1-carboxylate was deter-
mined by HPLC using Chiralcel OD-H or Chiralpak AS-H column
(Daicel).
Entry
Catalyst
Solvent
Time (d)
Yield (%)
ee (%)
1
2
3
(S)-10
(S)-12
(S)-12
CH2Cl2
Acetone
CH2Cl2
8
12
12
98
0
23
<3
e
<3
mixture is several orders of magnitude higher than that of the
reactants, whereby the catalyst complex becomes inactive. In the
medium of ionic liquid (bmim)BF4 (experiment 6) the reaction did
not take place either.
4.2. Syntheses of ligands
2.3.2. Catalytic studies in asymmetric Michael addition
Asymmetric Michael addition of electron-deficient alkenes to
1,3-dicarbonyl or 1,3-dicarboxylic systems belongs among the
oldest and very useful reactions creating a new CeC bond and
stereogenic centre [24]. Usually, the reaction is catalysed by
complexes of transition metals inclusive of organopalladium(II)
complexes [25]. Therefore, we decided to test our prepared orga-
nopalladium(II) complexes also as catalysts for the addition of ethyl
2-oxocyclohexanecarboxylate to methyl vinyl ketone (MVK). The
reaction was catalysed with 5 mol.% of the respective complex 10
and 12, and in order to maximize the conversion, MVK was used in
a slight excess (1.5 eq.). Reaction times and yields are summarized
in Table 2. Unfortunately, all the products obtained were isolated as
racemic mixtures only. In a coordinating solvent (acetone) the
reaction did not proceed.
4.2.1. (ꢃ)-N-(2-Carbamoyl-3-methylbut-2-yl)-2-
bromobenzenecarboxamide ((ꢃ)-1)
A mixture of (ꢃ)-2-amino-2,3-dimethylbutanamide (3.20 g;
24.6 mmol) and triethylamine (2.49 g; 3.4 mL; 24.6 mmol) in dry
CH2Cl2 (30 mL) was cooled to 0 ꢀC and treated with a solution of
2-bromobenzoylchloride (5.40 g; 3.2 mL; 24.6 mmol) in dry CH2Cl2
(15 mL). The reaction mixture was stirred for 5 h at room temper-
ature. The obtained suspension was filtered, washed with
3 ꢄ 20 mL water and dried in vacuo to give a white crystalline solid
( )-1 (5.95 g; 77% yield), m.p. 110e115 ꢀC. EI-MS: m/z 270, 254, 183
(100%), 155, 113, 105, 76. 1H NMR (DMSO-d6,
d ppm): 8.00 (bs, 1H,
CONH), 7.62 (m, 1H, PhH6), 7.40 (m, 3H, PhH3e5), 7.06 (bs, 1H,
CONH2), 7.02 (bs, 1H, CONH2), 2.15 (sp, 3J ¼ 5.6 Hz, 1H, iPrH), 1.43 (s,
i
3H, CH3), 0.93 (d, 3J ¼ 5.6 Hz, 3H, PrCH3), 0.89 (d, 3J ¼ 5.6 Hz, 3H,
iPrCH3). 13C NMR (DMSO-d6,
d ppm): 174.7, 166.9, 139.2, 132.5, 130.7,
3. Conclusion
129.1, 127.5, 118.8, 63.1, 54.9, 33.9, 17.4, 17.2, 17.0. Anal. Calc. for
C13H17BrN2O2 (313.19): C, 49.85; H, 5.47; Br, 25.51; N, 8.94. Found:
C, 49.97; H, 5.40; Br, 25.40; N, 9.09.
The chiral CN and NCN pincer ligands derived from 4,5-dihydro-
1H-imidazol-5-ones 3 and 7 were submitted to oxidative addition
of Pd(0) to give the respective complexes 8, 9, and 11, whose
structure was studied by means of NMR and IR spectroscopy and
X-ray diffraction. While in complexes 9 and 11 the palladium atom
assumes the typical square-planar geometry, in complex 8 this
arrangement is somewhat deformed due to the interaction of tri-
phenylphosphine with CN pincer ligand. The neutral organo-
palladium(II) complexes were converted into cationic complexes 10
and 12, which were studied as enantioselective catalysts for
asymmetric FriedeleCrafts alkylation and asymmetric Michael
addition. In many cases products of these reactions were obtained
in high chemical yield (ꢂ99%) but with only a low enantiose-
lectivity (ꢂ12% ee).
4.2.2. (S)-N-(2-Carbamoyl-3-methylbut-2-yl)-2-
bromobenzenecarboxamide ((S)-1)
In a similar manner, the compound (S)-1 was isolated as
a colorless oil (81% yield). 1H NMR (CDCl3,
d ppm): 8.24 (bs, 1H,
CONH), 7.58 (m, 1H, PhH), 7.51 (m, 1H, PhH), 7.36 (m, 1H, PhH), 7.28
(m, 1H, PhH), 6.97 (bs, 1H, CONH2), 6.77 (bs, 1H, CONH2), 2.40 (sp,
3J ¼ 6.9 Hz, 1H, iPrH), 1.61 (s, 3H, CH3), 1.05 (d, 3J ¼ 6.9 Hz, 3H,
iPrCH3), 1.00 (d, 3J ¼ 6.9 Hz, 3H, iPrCH3). ½a 2D0
ꢅ
¼ þ34:3ꢀ (c ¼ 1.02 in
MeOH). Anal. Calc. for C13H17BrN2O2 (313.19): C, 49.85; H, 5.47; Br,
25.51; N, 8.94. Found: C, 49.83; H, 5.62; Br, 25.38; N, 9.01.
4.2.3. (ꢃ)-2-(2-Bromophenyl)-4-isopropyl-4-methyl-4,5-dihydro-
1H-imidazol-5-one ((ꢃ)-2)
4. Experimental
A mixture of ( )-1 (5.64 g; 18.0 mmol) and KOH (6.0 g;
110 mmol) in MeOH (25 mL) was stirred for 10 days at room
temperature, then neutralized with glacial acetic acid to pH w6 and
concentrated in vacuo. The residue was treated with water (50 mL)
and suspension formed was extracted with CH2Cl2 (4 ꢄ 50 mL). The
organic solution was dried over Na2SO4 and evaporated under
reduced pressure to give white crystals of ( )-2 (4.88 g; 92% yield),
m.p. 124e126 ꢀC. EI-MS: m/z 296 (Mþ), 252 (100%), 184, 102, 76. 1H
4.1. General
The reactions, as is mentioned below, were performed under
argon atmosphere by using standard Schlenk techniques. Solvents
were dried using standard procedures. The racemic and enantio-
merically pure S-2-amino-2,3-dimethylbutanamide was prepared
according to the method reported by Weplo [16]. The other
NMR (DMSO-d6,
d
ppm): 11.14 (bs, 1H, CONH), 7.75 (d, 3J ¼ 6.4 Hz,

P. Drabina et al. / Journal of Organometallic Chemistry 696 (2011) 971e981
977
1H, PhH6), 7.49 (m, 3H, PhH3e5), 1.94 (sp, 3J ¼ 5.2 Hz, 1H, iPrH), 1.24
(s, 3H, CH3), 1.00 (d, 3J ¼ 5.2 Hz, 3H, iPrCH3), 0.84 (d, 3J ¼ 5.2 Hz, 3H,
pH w3 and concentrated to 1/3 of volume. After cooling in ice bath,
a formed solid was filtered, washed with small amount of cold
water and dried in vacuo to give white needles of ( )-4 (182 mg;
iPrCH3). 13C NMR (DMSO-d6,
d ppm): 187.0, 158.9, 133.1, 132.1, 132.0,
130.8, 127.9, 120.6, 74.0, 33.9, 21.0, 20.9, 17.0, 16.7. Anal. Calc. for
C13H15BrN2O (295.18): C, 52.90; H, 5.12; Br, 27.07; N, 9.49. Found: C,
53.06; H, 5.25; Br, 27.26; N, 9.68.
44% yield), m.p. 244e246 ꢀC. 1H NMR (CD3OD,
d ppm): 8.37 (m, 1H,
PhH6), 8.00 (m, 2H, PhH4,5), 7.83 (m, 1H, PhH3), 3.04 (s, 3H, NCH3),
2.33 (sp, 1H, 3J ¼ 6.8 Hz, iPrH), 1.67 (s, 3H, CH3), 1.17 (d, 3H,
3J ¼ 6.8 Hz, iPrCH3), 1.09 (d, 3H, 3J ¼ 6.8 Hz, iPrCH3). 13C NMR
4.2.4. (S)-2-(2-Bromophenyl)-4-isopropyl-4-methyl-4,5-dihydro-
1H-imidazol-5-one ((S)-2)
(CD3OD, d ppm): 178.1, 174.8, 167.5, 135.2, 135.1, 132.8, 131.3, 130.7,
124.9, 71.6, 35.8, 28.1, 19.3, 17.4, 16.7. Anal. Calc. for C15H18N2O3
(274.32): C, 65.68; H, 6.61; N, 10.21. Found: C, 65.46; H, 6.60; N,
10.01.
In a similar manner, the compound (S)-2 was prepared as
a white crystalline solid (90% yield), m.p. 130e133 ꢀC. 1H NMR
(CDCl3, d ppm): 9.17 (bs, 1H, CONH), 7.63 (m, 2H, PhH), 7.36 (m, 2H,
PhH), 2.06 (sp, 3J ¼ 6.9 Hz, 1H, iPrH), 1.37 (s, 3H, CH3), 1.05 (d,
4.2.8. (S)-2-(4-Isopropyl-1,4-dimethyl-4,5-dihydro-1H-imidazol-5-
on-2-yl)benzoic acid ((S)-4)
3J ¼ 6.9 Hz, 3H, iPrCH3), 0.90 (d, 3J ¼ 6.9 Hz, 3H, iPrCH3).
½
a 2D0
ꢅ
¼ ꢆ45:7ꢀ (c ¼ 0.99 in MeOH). Anal. Calc. for C13H15BrN2O
In a similar manner, the compound (S)-4 was obtained as a white
(295.18): C, 52.90; H, 5.12; Br, 27.07; N, 9.49. Found: C, 52.87; H,
5.34; Br, 26.93; N, 9.56.
crystalline solid (49% yield), m.p. 119e121 ꢀC. 1H NMR (CD3OD,
d
ppm): 8.36 (m, 1H, PhH6), 7.97 (m, 2H, PhH4,5), 7.77 (m, 1H, PhH3),
i
3.03 (s, 3H, NCH3), 2.33 (sp, 1H, 3J ¼ 6.8 Hz, PrH), 1.65 (s, 3H, CH3),
i
i
4.2.5. (ꢃ)-2-(2-Bromophenyl)-4-isopropyl-1,4-dimethyl-4,5-
dihydro-1H-imidazol-5-one ((ꢃ)-3)
1.16 (d, 3H, 3J ¼ 6.8 Hz, PrCH3), 1.08 (d, 3H, 3J ¼ 6.8 Hz, PrCH3).
½
a 2D0
ꢅ
¼ ꢆ26:3ꢀ (c ¼ 0.51 in DMF). Anal. Calc. for C15H18N2O3
A mixture of ( )-2 (3.27 g; 11.1 mmol) and tBuOK (2.52 g;
22.4 mmol; 2 eq.) in extra dry DMF (10 mL) under argon atmo-
sphere was cooled to 0 ꢀC and then MeI (3.19 g; 1.4 mL; 22.4 mmol;
2 eq.) was added drop by drop. The reaction mixture was stirred for
24 h at room temperature. The solvent was evaporated in vacuo
until dry, the residue was dissolved in AcOEt (10 mL), filtered
through plug of silica gel (5 cm) and washed with additional AcOEt
(100 mL). The filtrate was evaporated to dryness to give the crude
product which was treated with 2 M HCl (10 mL) and obtained
solution extracted with ether (2 ꢄ 15 mL). The water layer was
neutralized with concd. NH3 to pH w9 and suspension formed was
extracted with CH2Cl2 (2 ꢄ 20 mL). The combined extracts were
dried over Na2SO4 and after distilling off of solvent under reduced
pressure was isolated a yellowish oily product ( )-3 (2.42 g; 71%
yield) which crystallized within several weeks, m.p. 78e81 ꢀC. EI-
MS: m/z 308 (Mþ), 266 (100%), 196, 184, 155, 117, 102, 89, 76. 1H
(274.32): C, 65.68; H, 6.61; N, 10.21. Found: C, 65.55; H, 6.83; N,
10.06.
4.2.9. (ꢃ)-N,N0-bis(2-carbamoyl-3-methylbut-2-yl)-
2ebromobenzene-1,3-dicarboxamide ((ꢃ)-5)
A mixture of (ꢃ)-2-amino-2,3-dimethylbutanamide (7.81 g;
60.0 mmol) and triethylamine (6.10 g; 8.4 mL; 60.0 mmol) in
dry CH2Cl2 (80 mL) was cooled to 0 ꢀC and treated with a solu-
tion 2-bromobenzene-1,3-dicarboxylic acid dichloride (8.46 g;
30.0 mmol) in dry CH2Cl2 (30 mL). After 12 h stirring at room
temperature, the suspension formed was filtered off, washed with
several portion of water an dried in vacuo to give a white crystalline
product ( )-5 (12.20 g; 87% yield) as a mixture of two diastereo-
mers, m.p. 233e242 ꢀC. 1H NMR (DMSO-d6,
d ppm): 8.01 (d,
3J ¼ 7.4 Hz, 2H, CONH), 7.45 (m, 3H, PhH4e6), 7.09 (m, 4H, CONH2),
2.15 (m, 2H, iPrH), 1.46 (s, 6H, CH3), 0.91 (m, 12H, iPrCH3). 13C NMR
NMR (DMSO-d6,
d
ppm): 7.81 (m, 1H, PhH6), 7.54 (m, 3H, PhH3e5),
(DMSO-d6, d ppm): 174.7, 166.8, 140.3, 128.9, 127.4, 115.8, 63.2, 34.1,
17.5, 17.3, 17.2. Anal. Calc. for C20H29BrN4O4 (469.37): C, 51.18; H,
6.23; Br, 17.02; N, 11.94. Found: C, 51.45; H, 6.41; Br, 16.79; N, 11.66.
i
2.76 (s, 3H, NCH3), 1.97 (sp, 1H, 3J ¼ 6.8 Hz, PrH), 1.26 (s, 3H, CH3),
0.99 (d, 3H, 3J ¼ 6.8 Hz, iPrCH3), 0.84 (d, 3H, 3J ¼ 6.8 Hz, iPrCH3). 13
C
NMR (DMSO-d6,
d ppm): 184.9, 160.4, 132.8, 132.3, 131.5, 131.1,
128.2, 121.0, 73.4, 33.9, 26.7, 20.9, 17.1, 16.7. Anal. Calc. for
C14H17BrN2O (309.20): C, 54.38; H, 5.54; Br, 25.84; N, 9.06. Found: C,
54.36; H, 5.60; Br, 25.82; N, 9.01.
4.2.10. (S,S)-N,N0-bis(2-carbamoyl-3-methylbut-2-yl)-
2ebromobenzene-1,3-dicarboxamide ((S)-5)
In a similar manner, the compound (S)-5 was isolated as a white
crystalline solid (91% yield), m.p. 254e257 ꢀC. 1H NMR (DMSO-d6,
4.2.6. (S)-2-(2-Bromophenyl)-4-isopropyl-1,4-dimethyl-4,5-
dihydro-1H-imidazol-5-one ((S)-3)
d ppm): 7.98 (bs, 2H, NH), 7.45 (m, 3H, PhH4e6), 7.08 (bs, 2H,
CONH2), 7.04 (bs, 2H, CONH2), 2.15 (sp, 3J ¼ 6.8 Hz, 2H, iPrH), 1.46 (s,
i
In a similar manner, the compound (S)-3 was isolated as a white
6H, CH3), 0.92 (d, 3J ¼ 6.8 Hz, 6H, PrCH3), 0.89 (d, 3J ¼ 6.8 Hz, 6H,
crystalline solid (76% yield), m.p. 93e96 ꢀC. 1H NMR (CDCl3,
iPrCH3).
½
a 2D0
ꢅ
¼ þ48:2ꢀ (c ¼ 1.02 in MeOH). Anal. Calc. for
d
ppm): 7.67 (m, 1H, PhH6), 7.41 (m, 3H, PhH3e5), 2.91 (s, 3H, NCH3),
C20H29BrN4O4 (469.37): C, 51.18; H, 6.23; Br, 17.02; N, 11.94. Found:
C, 51.23; H, 6.22; Br, 16.84; N, 12.01.
2.13 (sp, 1H, 3J ¼ 6.9 Hz, iPrH), 1.41 (s, 3H, CH3), 1.09 (d, 3H,
3J ¼ 6.9 Hz, iPrCH3), 0.92 (d, 3H, 3J ¼ 6.9 Hz, iPrCH3). ½a 2D0
ꢅ
¼ ꢆ24:2ꢀ
(c ¼ 0.99 in MeOH). Anal. Calc. for C14H17BrN2O (309.20): C, 54.38;
H, 5.54; Br, 25.84; N, 9.06. Found: C, 54.19; H, 5.71; Br, 25.72; N,
9.28.
4.2.11. (ꢃ)-2-Bromo-1,3-bis(4-isopropyl-4-methyl-4,5-dihydro-1H-
imidazol-5-on-2-yl)benzene ((ꢃ)-6)
t
A suspension of ( )-5 (11.73 g; 25 mmol) and BuOK (14.03 g;
125 mmol; 5 eq.) in tBuOH (130 mL) was stirred for 14 days at room
temperature. After neutralization with glacial acetic acid to pH w6,
the mixture was concentrated and treated with water (100 mL).
The suspension was extracted with CH2Cl2 (4 ꢄ100 mL), combined
organic layers was washed with saturated aqueous solution
NaHCO3 (60 mL) and dried over Na2SO4. The solvents were evap-
orated under reduced pressure to dryness to give a white crystalline
product ( )-6 (7.70 g; 71% yield) as a mixture of two diastereomers,
m.p. 149e155 ꢀC. EI-MS: m/z 434 (Mþ), 392 (100%), 349, 320, 278,
4.2.7. (ꢃ)-2-(4-Isopropyl-1,4-dimethyl-4,5-dihydro-1H-imidazol-
5-on-2-yl)benzoic acid ((ꢃ)-4)
Compound ( )-3 (461 mg; 1.5 mmol) was dissolved in extra dry
THF (5 mL) under argon atmosphere and was cooled to 0 ꢀC,
whereupon the solution of 2 M isopropylmagnesium chloride in
ether (3 mL; 6 mmol) was added. The solution was stirred for
30 min and then was poured on the mixture of freshly crushed dry
ice (100 g) and ether (50 mL). The temperature was allowed to rise
to room temperature and the suspension was extracted with water
(3 ꢄ 20 mL). Combined water layers was acidified with 35% HCl to
207, 128, 102, 86, 69. 1H NMR (CDCl3,
d ppm): 10.36 (bs, 2H, NH),
i
7.42 (m, 3H, PhH4e6), 2.08 (m, 2H, PrH), 1.39 (d, 6H, 3J ¼ 10.9 Hz,

978
P. Drabina et al. / Journal of Organometallic Chemistry 696 (2011) 971e981
CH3), 1.05 (m, 6H, iPrCH3), 0.91 (m, 6H, iPrCH3). 13C NMR (DMSO-d6,
ppm): 187.0, 159.0, 133.7, 132.3, 128.2, 119.9, 74.2, 34.0, 20.9, 17.2,
16.8. Anal. Calc. for C20H25BrN4O2 (433.34): C, 55.43; H, 5.81; Br,
18.44; N, 12.93. Found: C, 55.35; H, 5.49; Br, 18.57; N, 12.90.
3J ¼ 6.9 Hz, 3H, iPrCH3). 13C NMR (CDCl3,
d ppm): 182.9, 182.8, 182.6,
d
182.5, 171.3, 171.2, 170.7, 170.6, 158.5, 158.5, 157.4, 157.3, 140.0, 139.9,
139.5,139.4,138.2,138.1,138.0,138.0,135.7,135.7,135.6,135.5,132.1,
131.6,131.4,130.9,130.8,130.8,130.7,130.7,130.6,128.2,128.2,128.1,
128.0,128.0,126.0,126.0,123.9,123.8, 74.6, 74.6, 74.4, 74.3, 53.6, 33.8,
33.6, 28.8, 28.8, 22.4, 22.0, 17.2, 17.1, 15.5, 15.5. 31P NMR (CDCl3,
4.2.12. (S,S)-2-Bromo-1,3-bis(4-isopropyl-4-methyl-4,5-dihydro-
1H-imidazol-5-on-2-yl)benzene ((S)-6)
d
ppm): 45.2, 44.7. FT-IR (y; thin film): 3060 (CeH),1744 (C]O),1590
In a similar manner, the compound (S)-6 was isolated as a white
(C]N), 1479 (CeN), 744 (CeP), 692 (CeP) cmꢆ1. Anal. Calc. for
C32H32BrN2OPPd (677.91): C, 56.70; H, 4.76; Br,11.79; N, 4.13. Found:
C, 56.58; H, 4.88; Br, 11.42; N, 4.09.
crystalline solid (82% yield), m.p. 151e154 ꢀC. 1H NMR (CDCl3,
d
ppm): 9.66 (bs, 2H, NH), 7.57 (m, 2H, PhH3,5), 7,45 (m, 1H, PhH4),
2.13 (sp, 3J ¼ 6.8 Hz, 2H, iPrH), 1.43 (s, 6H, CH3), 1.07 (d, 6H,
3J ¼ 6.8 Hz, iPrCH3), 0.94 (d, 6H, 3J ¼ 6.8 Hz, iPrCH3). ½a 2D0
ꢅ
¼ ꢆ34:4ꢀ
4.3.2. (ꢃ)-Di-
dihydro-1H-imidazol-5-on-2-yl)phenyl]dipalladium(II) ((ꢃ)-9)
mixture of ( )-3 (38.7 mg; 0.125 mmol) and Pd(dba)2
m-bromobis[2-(4-isopropyl-1,4-dimethyl-4,5-
(c ¼ 1.00 in MeOH). Anal. Calc. for C20H25BrN4O2 (433.34): C, 55.43;
H, 5.81; Br,18.44; N,12.93. Found: C, 55.19; H, 5.63; Br,18.28; N,12.87.
A
(79.3 mg; 0.137 mmol; 1.1 eq.) in dry degassed toluene (5 mL)
under argon atmosphere was stirred for 7 days at room tempera-
ture. Two drops of triethylamine were added for removal of Pd(0),
and the mixture was filtered through CeliteÒ. The filtrate was
evaporated under reduced pressure and the residue was purified by
column chromatography (silica gel; AcOEt/n-hexane (1:4); Rf 0.11)
to give a yellow-orange solid ( )-9 (48.3 mg; 93% yield), m.p. >
4.2.13. (ꢃ)-2-Bromo-1,3-bis(4-isopropyl-1,4-dimethyl-4,5-dihydro-
1H-imidazol-5-on-2-yl)benzene ((ꢃ)-7)
A mixture of ( )-6 (1.73 g; 4.0 mmol) and tBuOK (1.35 g;
12 mmol; 3 eq.) in extra dry DMF (10 mL) under argon atmosphere
was cooled to 0 ꢀC and then MeI (1.70 g; 0.75 mL; 12 mmol; 3 eq.)
was added drop by drop. The reaction mixture was stirred for 4 h at
t
room temperature, whereupon another portion of BuOK (1.35 g;
265 ꢀC (decomp.). 1H NMR (CDCl3,
(m, 2H, PhH), 7.14 (m, 4H, PhH), 3.52 (s, 6H, NCH3), 2.66 (m, 2H,
iPrH),1.62 (m, 6H, CH3),1.18 (m, 6H, iPrCH3), 0.81 (m, 6H, iPrCH3). 13
NMR (CDCl3, ppm): 180.6, 170.6, 153.6, 136.1, 135.7, 135.6, 131.5,
126.1, 124.7, 73.3, 73.2, 73.0, 34.8, 34.6, 34.4, 28.2, 28.1, 22.1, 22.0,
d ppm): 7.77 (m, 2H, PhH), 7.53
3 eq.) was slowly added and subsequently MeI (0.75 mL; 3 eq.).
After 20 h, the solvent was removed in vacuo until dry, the residue
was dissolved in acetone (10 mL), filtered through plug of silica gel
(5 cm) and washed with additional acetone (100 mL). The filtrate
was evaporated under reduced pressure to give a white solid ( )-7
(1.30 g; 72% yield) as a mixture of two diastereomers, m.p.
154e172 ꢀC. EI-MS: m/z 462 (Mþ), 418 (100 %), 376, 348, 307, 260,
C
d
17.1, 15.5. FT-IR (y; thin film): 2922 (CeH), 1741 (C]O), 1590 (C]N),
1484 (CeN) cmꢆ1. Anal. Calc. for C28H34Br2N4O2Pd2 (831.24): C,
40.46; H, 4.12, Br; 19.23; N, 6.74. Found: C, 40.52; H, 4.27; Br, 19.38;
N, 6.52.
293, 223, 143, 116, 69. 1H NMR (CDCl3,
d ppm): 7.58 (m, 3H, PhH4e6),
2.88 (s, 6H, NCH3), 2.12 (sp, 3J ¼ 6.9 Hz, 2H, iPrH), 1.38 (m, 6H, CH3),
i
i
1.07 (d, 6H, 3J ¼ 6.9 Hz, PrCH3), 0.92 (m, 6H, PrCH3). 13C NMR
4.3.3. (S,S)-Di-m-bromobis[2-(4-isopropyl-1,4-dimethyl-4,5-
(CDCl3,
d
ppm): 185.6, 160.7, 133.5, 132.8, 128.9, 74.5, 34.7, 27.3, 21.4,
dihydro-1H-imidazol-5-on-2-yl)phenyl]dipalladium(II) ((S)-9)
In a similar manner, the compound (S)-9 was isolated as
17.4,16.9. Anal. Calc. for C22H29BrN4O2 (461.40): C, 57.27; H, 6.34; Br,
17.32; N, 12.14. Found: C, 57.28; H, 6.43; Br, 17.06; N, 11.85.
a yellow-orange solid (96% yield). 1H NMR (CDCl3,
d ppm): 7.77 (m,
2H, PhH), 7.57 (m, 2H, PhH), 7.14 (m, 4H, PhH), 3.52 (m, 6H, NCH3),
4.2.14. (S,S)-2-Bromo-1,3-bis(4-isopropyl-1,4-dimethyl-4,5-
dihydro-1H-imidazol-5-on-2-yl)benzene ((S)-7)
2.68 (m, 2H, iPrH), 1.64 (m, 6H, CH3), 1.20 (m, 6H, iPrCH3), 0.84 (m,
i
20
6H, PrCH3). ½
a
ꢅ
¼ þ113:2ꢀ (c ¼ 1.01 in acetone). Anal. Calc. for
546
In a similar manner, the compound ( )-7 was isolated as a white
C28H34Br2N4O2Pd2 (831.24): C, 40.46; H, 4.12, Br; 19.23; N, 6.74.
Found: C, 40.27; H, 4.23; Br, 19.50; N, 6.84.
solid (80% yield). M.p. 246e248 ꢀC. 1H NMR (CDCl3,
d ppm): 7.59 (m,
3H, PhH4e6), 2.91 (s, 6H, NCH3), 2.08 (sp, 3J ¼ 6.8 Hz, 2H, iPrH), 1.42
(s, 6H, CH3), 1.10 (d, 6H, 3J ¼ 6.8 Hz, iPrCH3), 0.92 (d, 6H, 3J ¼ 6.8 Hz,
4.3.4. (ꢃ)-[2-(4-Isopropyl-1,4-dimethyl-4,5-dihydro-1H-imidazol-
5-on-2-yl)phenyl]palladium(II) tetrafluoroborate-diaqua complex
((ꢃ)-10)
iPrCH3).
½
a 2D0
ꢅ
¼ ꢆ28:2ꢀ (c ¼ 1.00 in MeOH). Anal. Calc. for
C22H29BrN4O2 (461.40): C, 57.27; H, 6.34; Br, 17.32; N, 12.14. Found:
C, 57.04; H, 6.32; Br, 17.25; N, 11.91.
A mixture of ( )-9 (83.1 mg; 0.100 mmol) and AgBF4 (50.2 mg;
0.258 mmol; 1.3 eq.) was stirred in “wet” acetone (10 mL; acetone
/water e 99:1) for 2 days at room temperature. The reaction vessel
was covered with an aluminium foil (protection from light). The
suspension formed was filtered through CeliteÒ and the filtrate was
evaporated in vacuo to give a yellow solid ( )-10 (86.0 mg; 94%
4.3. Syntheses of organopalladium(II) complexes
4.3.1. (ꢃ)-[2-(4-Isopropyl-1,4-dimethyl-4,5-dihydro-1H-imidazol-
5-on-2-yl)phenyl]palladium(II) bromide-triphenylphosphine
complex ((ꢃ)-8)
yield), m.p. >130 ꢀC (decomp.). 1H NMR (CDCl3,
d ppm): 7.49 (m, 1H,
i
A mixture of ligand ( )-3 (38.7 mg; 0.125 mmol) and Pd(PPh3)4
(158.3 mg; 0.137 mmol; 1.1 eq.) in dry degassed toluene (5 mL)
under argon atmosphere was stirredfor 4 days at room temperature.
Two drops of triethylamine were added for removal of Pd(0), and the
mixture was filtered through CeliteÒ. The filtrate was evaporated
under reduced pressure and the residue was purified by column
chromatography (silica gel; AcOEt/n-hexane (1:2); Rf 0.22) to give an
orange solid ( )-8 (76.2 mg; 90% yield), m.p. >265 ꢀC (decomp.). 1H
PhH6), 7.15 (m, 3H, PhH3e5), 3.51 (s, 3H, NCH3), 2.15 (m, 1H, PrH),
1.46 (s, 3H, CH3), 1.13 (d, 3J ¼ 6.9 Hz, 3H, iPrCH3), 0.87 (d, 3J ¼ 6.9 Hz,
i
3H, PrCH3). 13C NMR (CD3OD,
d ppm): 181.0, 173.0, 149.3, 136.8,
132.7, 132.1, 128.2, 126.7, 72.8, 35.5, 28.2, 21.0, 17.1, 15.7. 19F NMR
(CD3OD,
(H2O), 2967 (CeH), 1740 (C]O), 1592 (C]N), 1486 (CeN), 1012
(BeF) cmꢆ1. Anal. Calc. for C14H21BF4N2O3Pd (458.55): C, 36.67; H,
4.62; N, 6.11. Found: C, 36.52; H, 4.68; N, 6.13.
d
ppm): ꢆ150.3 (BFꢆ4 ). FT-IR (
y; thin film): 3644e3081
NMR (CDCl3,
d
ppm): 7.77 (m,12H, PhH), 7.68 (d, 3J ¼ 7.8 Hz,1H, PhH),
7.67 (d, 3J ¼ 8.1 Hz, 1H, PhH), 7.43 (m, 6H, PhH), 7.36 (m, 12H, PhH),
6.97 (m, 4H, PhH), 6.62 (m, 2H, PhH), 3.58 (3H, NCH3), 3.57 (3H,
NCH3), 3.42 (sp, 3J ¼ 6.9 Hz, 1H, iPrH), 3.31 (sp, 3J ¼ 6.9 Hz, 1H, iPrH),
1.85 (s, 3H, CH3),1.81 (s, 3H, CH3),1.17 (d, 3J ¼ 7.0 Hz, 3H, iPrCH3),1.15
(d, 3J ¼ 6.9 Hz, 3H, iPrCH3), 0.86 (d, 3J ¼ 6.9 Hz, 3H, iPrCH3), 0.85 (d,
4.3.5. (S,S)-[2-(4-Isopropyl-1,4-dimethyl-4,5-dihydro-1H-imidazol-
5-on-2-yl)phenyl]palladium(II) tetrafluoroborate-diaqua complex
((S)-10)
In a similar manner, the compound (S)-10 was isolated as
a yellow solid (96% yield), m.p. >135 ꢀC (decomp.). 1H NMR (CDCl3,

P. Drabina et al. / Journal of Organometallic Chemistry 696 (2011) 971e981
979
d
ppm): 7,47 (m, 1H, PhH6), 7.15 (bs, 3H, PhH3e5), 3.52 (s, 3H, NCH3),
4.3.8. (ꢃ)-[2,6-Bis(4-isopropyl-1,4-dimethyl-4,5-dihydro-1H-
imidazol-5-on-2-yl)phenyl]palladium(II) tetrafluoroborate-aqua
complex ((ꢃ)-12)
2.63 (bs, 1H, iPrH), 1.54 (m, 3H, CH3), 1.15 (bs, 3H, iPrCH3), 0.86 (bs,
20
546
3H, iPrCH3). 19F NMR (CDCl3,
d
ppm): ꢆ150.8 (BFꢆ4 ). ½
a
ꢅ
¼ þ80:1ꢀ
(c ¼ 1.01 in acetone). Anal. Calc. for C14H21BF4N2O3Pd (458.55): C,
A mixture of ( )-11 (152.0 mg; 0.268 mmol) and AgBF4 (67.3 mg;
0.346 mmol; 1.3 eq.) was stirred in “wet” acetone (10 mL; acetone/
water e 99:1) for 5 days at room temperature. The reaction vessel
was covered with an aluminium foil (protection from light). The
suspension formed was filtered through plug of silica gel (1 cm),
washed with additional acetone (20 mL) and the filtrate was
evaporated in vacuo to give a yellow solid ( )-12 (152.2 mg; 97%
36.67; H, 4.62; N, 6.11. Found: C, 36.80; H, 4.91; N, 6.07.
4.3.6. (ꢃ)-[2,6-Bis(4-isopropyl-1,4-dimethyl-4,5-dihydro-1H-
imidazol-5-on-2-yl)phenyl]palladium(II) bromide ((ꢃ)-11)
A
mixture of ( )-7 (92.3 mg; 0.20 mmol) and Pd(dba)2
(126.5 mg; 0.22 mmol; 1.1 eq.) or Pd(PPh3)4 (254.2 mg;
0.22 mmol; 1.1 eq.) in dry degassed toluene (5 mL) under argon
atmosphere was stirred for 7 days at room temperature. Two
drops of triethylamine were added for removal of Pd(0), and the
mixture was filtered through CeliteÒ. The filtrate was evaporated
under reduced pressure and the residue was purified by column
chromatography (silica gel; AcOEt; Rf 0.25) to give an orange solid
( )-11 (107.9 mg; 95% yield), m.p. >265 ꢀC (decomp.). 1H NMR
yield), m.p. >135 ꢀC (decomp.). 1H NMR (CD3OD,
d ppm): 7.91 (d,
3J ¼ 7.9 Hz, 2H, PhH3,5), 7.46 (t, 3J ¼ 7.9 Hz, 1H, PhH4), 3.57 (s, 6H,
i
NCH3), 2.20 (m, 2H, PrH), 1.51 (s, 6H, CH3), 1.19 (d, 3J ¼ 7.0 Hz, 6H,
iPrCH3), 0.87 (m, 6H, iPrCH3). 13C NMR (CD3OD,
d ppm): 181.2, 172.2,
136.3, 129.7, 126.7, 73.1, 36.2, 28.0, 21.4, 17.3, 15.8. 19F NMR (CD3OD,
d
ppm): ꢆ154.4 (BFꢆ4 ). FT-IR (
y; thin film): 3654e3120 (H2O), 2924
(CeH), 1745 (C]O), 1595 (C]N), 1493 (CeN), 1014 (BeF) cmꢆ1
.
(CDCl3,
d
ppm): 7.67 (m, 2H, PhH3,5), 7.31 (m, 1H, PhH4), 3.56 (m,
Anal. Calc. for C22H31BF4N4O3Pd (592.73): C, 44.58; H, 5.27; N, 9.45.
Found: C, 44.76; H, 5.09; N, 9.16.
i
i
6H, NCH3), 3.05 (m, 2H, PrH), 2.90 (m, 1H, PrH), 1.71 (m, 6H,
CH3), 1.18 (m, 6H, PrCH3), 0.74 (m, 6H, PrCH3). 13C NMR (CDCl3,
ppm): 180.6, 179.5, 169.8, 169.5, 135.1, 135.0, 126.9, 126.7, 124.3,
124.2, 73.8, 73.4, 34.2, 34.1, 27.6, 27.5, 21.9, 21.6, 17.1, 17.0, 15.4,
i
i
d
4.3.9. (S,S)-[2,6-bis(4-isopropyl-1,4-dimethyl-4,5-dihydro-1H-
imidazol-5-on-2-yl)phenyl]palladium(II) tetrafluoroborate-aqua
complex ((S)-12)
15.3. FT-IR (y; thin film): 2968 (CeH), 1741 (C]O), 1592 (C]N),
1488 (CeN) cmꢆ1. Anal. Calc. for C22H29BrN4O2Pd (567.82): C,
46.54; H, 5.15; Br, 14.07; N, 9.87. Found: C, 46.55; H, 5.44; Br,
14.14; N, 9.87.
In a similar manner, the compound (S)-12 was isolated as
a yellow solid (93% yield), m.p. >140 ꢀC (decomp.). 1H NMR (CD3OD,
d
ppm): 7.90 (d, 3J ¼ 7.9 Hz, 2H, PhH3,5), 7.45 (t, 3J ¼ 7.9 Hz, 1H,
i
PhH4), 3.57 (s, 6H, NCH3), 2.23 (bs, 2H, PrH), 1.52 (s, 6H, CH3), 1.18
4.3.7. (S,S)-[2,6-Bis(4-isopropyl-1,4-dimethyl-4,5-dihydro-1H-
imidazol-5-on-2-yl)phenyl]palladium(II) bromide ((S)-11)
In a similar manner, the compound (S)-11 was isolated as an
(d, 3J ¼ 7.0 Hz, 6H, iPrCH3), 0.85 (d, 3J ¼ 7.0 Hz, 6H, iPrCH3). 19F NMR
20
(CD3OD,
d
ppm): ꢆ154.8 (BFꢆ4 ). ½
a
ꢅ
¼ þ129:3ꢀ (c ¼ 0.68 in
546
MeOH). Anal. Calc. for C22H31BF4N4O3Pd (592.73): C, 44.58; H, 5.27;
N, 9.45. Found: C, 44.34; H, 5.51; N, 9.38.
orange solid (96% yield), m.p. >265 ꢀC. 1H NMR (CDCl3,
d ppm): 7.68
(d, 3J ¼ 7.9 Hz, 2H, PhH3,5), 7.31 (t, 3J ¼ 7.9 Hz, 1H, PhH4), 3.55 (s, 6H,
NCH3), 3.46 (s, 6H, NCH3), 3.05 (sp, 3J ¼ 6.9 Hz, 2H, iPrH), 1.69 (s, 6H,
4.4. Asymmetric FriedeleCrafts reaction of 1H-indole with (E)-2-
phenyl-1-nitroethene
CH3),1.16 (d, 3J ¼ 6.9 Hz, 6H, iPrCH3), 0.71 (d, 3J ¼ 6.9 Hz, 6H, iPrCH3).
20
½
a
ꢅ
¼ þ134:3ꢀ (c ¼ 0.99 in MeOH). Anal. Calc. for
546
C22H29BrN4O2Pd (567.82): C, 46.54; H, 5.15; Br, 14.07; N, 9.87.
Found: C, 46.42; H, 5.16; Br, 13.96; N, 9.73.
A. Typical procedure: a solution of (E)-2-phenyl-1-nitroethene
(44.8 mg; 0.30 mmol), 1H-indole (176.1 mg; 1.5 mmol; 5 eq.) and
Table 3
Crystallographic data collection and structure refinement for (S)-3, ( )-8 and (S)-9
Compound
(S)-9
( )-8
(S)-3
Empirical formula
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C28H34Br2N4O2Pd2 2(CH2Cl2)
Monoclinic
C2
22.1218(7)
7.4212(12)
10.8481(13)
90
95.46(1)
90
C32H32BrN2OPPdCH2Cl2
Triclinic
P-1
9.8721(4)
10.6458(8)
15.7882(8)
93.203(6)
103.800(4)
90.576(4)
2
C14H17BrN2O
Orthorhombic
P 21 21 210
9.8039(7)
11.0691(4)
12.8370(5)
90
90
90
4
a
b
g
Z
(ꢀ)
(ꢀ)
(ꢀ)
2
V (Å3)
1772.8(4)
1.875
1608.39(16)
1.575
1393.08(12)
1.474
Dc/g cmꢆ3
Crystal size (mm)
Crystal shape
0.40 ꢄ 0.27 ꢄ 0.23
0.45 ꢄ 0.36 ꢄ 0.26
0.46 ꢄ 0.42 ꢄ 0.30
Block
Block
Block
m
(mmꢆ1
)
3.609
2.064
2.941
F(000)
h; k; l range
range/ꢀ
Reflections measured
984
768
632
ꢆ26,28; ꢆ8,9; ꢆ13,14
1.85e27.49
5648
3447 (0.0399)
3279
ꢆ12,12; ꢆ13,13; ꢆ20,20
1.92e27.50
31,266
7298 (0.0232)
6648
ꢆ12, 10; ꢆ14, 13; ꢆ16,16
2.43e27.50
15,390
3136 (0.0465)
2906
q
a
Independent (Rint
Observed [I > 2 (I)]
Parameters refined
)
s
199
370
163
Max/min
s
/eÅꢆ3
1.169/ꢆ1.844
1.806/ꢆ2.130
0.228/ꢆ0.430
GOFb
1.106
0.972
1.114
Rc/wRc
0.0405/0.1030
0.0535/0.1474
0.0293/0.0616
a
Rint ¼ SjF2o ꢆ F2o,meanj/SF2o.
b
c
S ¼ [S(w(F2o ꢆ F2c)2)/(Ndiffrs ꢆ Nparams)]1/2
.
Weighting scheme: w ¼ [
s
2(F2o) þ (w1P)2 þ w2P]ꢆ1, where P ¼ [max(F2o) þ 2F2c], R(F) ¼ SkFoj ꢆ jFck/SjFoj, wR(F2) ¼ [S(w(Fo2 ꢆ Fc2)2)/(Sw(F2o)2)]1/2
.

980
P. Drabina et al. / Journal of Organometallic Chemistry 696 (2011) 971e981
catalyst (S)-10 (6.9 mg; 15
mmol; 5 mol%) in dry CH2Cl2 (4 mL)
Appendix A. Supplementary data
under argon atmosphere was stirred for 7 days at room tempera-
ture. The progress of the reaction was monitored by TLC. The
mixture was evaporated under reduced pressure and the residue
was separated by column chromatography (silica gel; AcOEt/n-
hexane (1:2); Rf 0.23) to give 3-(2-nitro-1-phenylethyl)-1H-indole
as an yellowish oil (95% yield). Enantiomeric purity of the product
was determined by chiral HPLC (Chiralcel OD-H, n-hexane/iPrOH
(70:30), 254 nm, 0.7 mL/min, tR1 ¼34.4 min, tR2 ¼ 44.5 min). EI-MS:
m/z 266 (Mþ), 219 (100 %), 206, 178, 143, 132, 115, 102, 89, 77.
A full list of crystallographic data and parameters including frac-
tional coordinates is deposited at the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK [fax: int. code
þ44 1223 336 033; e-mail: deposit@ccdc.cam.ac.uk.
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GOF ¼ [S(w(Fo2 ꢆ Fc2)2)/(Ndiffrs ꢆ Npar-
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Crystallographic data for structural analysis have been depos-
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Copies of this information may be obtained free of charge from The
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