Investigation of the complexation behaviour and catalysis of IBiox-[(-)-menthyl]·HOTf

Article abstract of DOI:10.1016/j.tet.2012.06.039

Herein we provide an overview on the unique properties of the sterically demanding IBiox-[(-)-menthyl]HOTf ligand (such as flexibility and sterics) and an application of this ligand in Pd-catalyzed asymmetric intra- and intermolecular α-arylation reactions. Furthermore we demonstrate the synthesis of novel NHC-metal complexes and a new bifunctional NHC ligand whilst insight into the mechanistic mode of action of IBiox-[(-)-menthyl]HOTf in catalysis is provided.

Full text of DOI:10.1016/j.tet.2012.06.039

Tetrahedron 68 (2012) 7636e7644
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Investigation of the complexation behaviour and catalysis
of IBiox-[(ꢀ)-menthyl]$HOTf
a
a
b
c
a
€
€
Claudia Lohre , Corinna Nimphius , Marc Steinmetz , Sebastian Wurtz , Roland Frohlich ,
Constantin G. Daniliuc a, Stefan Grimme b, Frank Glorius a
,
*
a
€
€
€
€
Organisch-Chemisches Institut der Westfalischen Wilhelms-Universitat Munster, Corrensstrasse 40, 48149 Munster, Germany
b
c
€
€
Mulliken Center for Theoretical Chemistry, Institut fur Physikalische und Theoretische Chemie, Universitat Bonn, Beringstrasse 4, 53115 Bonn, Germany
Euticals GmbH, Industriepark Hochst, D569, 65926 Frankfurt am Main, Germany
€
a r t i c l e i n f o
a b s t r a c t
Article history:
Herein we provide an overview on the unique properties of the sterically demanding IBiox-
Received 2 March 2012
Received in revised form 29 May 2012
Accepted 8 June 2012
[(ꢀ)-menthyl]∙HOTf ligand (such as flexibility and sterics) and an application of this ligand in Pd-
catalyzed asymmetric intra- and intermolecular
a-arylation reactions. Furthermore we demonstrate
the synthesis of novel NHCemetal complexes and a new bifunctional NHC ligand whilst insight into the
mechanistic mode of action of IBiox-[(ꢀ)-menthyl]∙HOTf in catalysis is provided.
Ó 2012 Elsevier Ltd. All rights reserved.
Available online 19 June 2012
Keywords:
N-Heterocyclic carbenes
Conformation studies
Asymmetric catalysis
Palladium complex
Theoretical calculations
1. Introduction
In the last couple of years N-heterocyclic carbenes (NHCs)1,2 have
become an important class of organocatalysts3 and ligands4 in or-
ganometallic chemistry and transition-metal catalysis, due to their
electron richness, their steric demand and the high stability of the
metaleNHC bond structure.2 Their widespread application as li-
gands in catalysis demonstrates their attractive properties.1e5 We
recently reported the synthesis of an exceedingly sterically de-
manding ligand: the NHC derived from IBiox-[(ꢀ)-menthyl]∙HOTf
(1).6 The desired imidazolium salt and NHC-precursor 1 could be
obtained by starting with a Bucherer reaction from commercially
available, enantiopure (ꢀ)-menthone (Fig. 1).6
Fig. 1. Sterically demanding IBiox-[(ꢀ)menthyl]∙HOTf (1) ligand.
2. Results and discussion
At the outset of our work, we wondered if even more sterically
demanding NHC ligands would lead to new levels of reactivity of
the resulting metal complexes. Herein we provide an overview on
the physicochemical properties, such as flexibility and sterics of
IBiox-[(ꢀ)-menthyl]∙HOTf (1) and the application of this NHC li-
Based on the chair flip of the cyclohexyl rings the IBiox6 system
2 is structurally dynamic. It was shown that the least sterically
demanding conformation (2a) is preferred (Scheme 1). In the
i
(ꢀ)-menthyl-derived IBiox precursor 1 the additional Pr/Me sub-
gand in Pd-catalyzed asymmetric intra- and intermolecular a-ary-
stituents on the cyclohexyl rings shift the equilibrium towards the
most sterically demanding conformation 1c.7 The predominance of
conformation 1c was confirmed by NMR studies at ꢀ80 ꢁC and rt,
which show only one set of signals, and X-ray analysis. As a result,
ligand 1 has an enhanced steric demand compared to IBiox6.6,7 The
preferred conformations 1c of NHC-precursor 1 and 2a and 2b of
the NHC-precursor IBiox6 are also evident from DFT calculations of
lation reactions. Furthermore we present the synthesis of novel
IBiox-[(ꢀ)-menthyl] derived metal complexes, the synthesis of
a bifunctional IBiox-[(ꢀ)-menthyl]-derived ligand and mechanistic
understanding of ligand 1 in catalysis.
* Corresponding author. E-mail address: glorius@uni-muenster.de (F. Glorius).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.06.039

C. Lohre et al. / Tetrahedron 68 (2012) 7636e7644
7637
A description of the steric demand of NHC ligands in a general
way is challenging, considering the variety of N-substituents and
the anisotropic structure of NHCs. A method to calculate the steric
demand of NHC ligands was developed by Nolan, Cavallo, and co-
workers.
They demonstrated how to quantify the steric demand by means
of the ‘buried volume’ (%Vbur) of various NHCs (Table 1).2,14e16 For
numerous X-ray structures of [(NHC)AuCl], [(NHC)AgCl], and [(NHC)
CuCl] complexes the buried volume was calculated (Table 1). The
buried volume for some of the most commonly used NHCs ranges
from 36.5% to 47.0% (calculated from their AuCl complexes, Table 1,
entries 1e5).2,16,17
Scheme 1. Chair flip properties of IBiox-[(ꢀ)-menthyl]∙HOTf (1) and IBiox6∙HOTf.
To the best of our knowledge the chiral IBiox[(ꢀ)-menthyl],
CAAC, as well as the achiral IPr* (1,3-bis[2,6-bis(diphenyl-methyl)-
4-methylphenyl] imidazol-2-ylidene) and the most shielding li-
the different conformations of 1 and 2 at 193 K, 298 K (shown) and
373 K (see Supplementary data). The calculations were performed
with two different dispersion corrected density functionals,8,9,11,12
which yield qualitatively the same picture. However, for the dis-
gand
IPr**
(1,3-bis[2,6-bis[(4-tert-butylphenyl)-methyl]-4-
ethylphenyl]imidazol-2-ylidene)14 are among the most sterically
demanding monodentate carbene ligands with a buried volume
range from 47.7% to 53%.2,15b,15c,15i,17 The buried volume (%Vbur) for
the NHC ligand derived from imidazolinium salt 6 determined
from its X-ray data was found to be 37%.
cussion only the
D D
G298 corrected (Figs. 2 and 4) and the G323
corrected results at the B2PLYP-D3/QZVPP//TPSS-D3/TZVP (Figs. 2
and 3) and B2PLYP-D3/TZVPP//TPSS/TZVP (Fig. 4) were used.8e12
Furthermore, different NHCemetal complexes from IBiox-
[(ꢀ)-menthyl]$HOTf (1) were synthesized with coinage metals
(Scheme 4). First, deprotonation of IBiox-[(ꢀ)-menthyl]$HOTf (1)
with NaOtBu in THF or CH2Cl2 for the free carbene formation fol-
lowed by addition of the desired metal salt, stirring overnight at
room temperature yielded, after column-chromatography, the de-
sired NHCemetal complexes in good to excellent yields (Scheme
4).6,18 We could obtain X-ray structures of all new NHCemetal
complexes, which exhibit a linear conformation (Scheme 5). The
calculation of the buried volume of the newly obtained complexes
IBiox-[(ꢀ)-menthyl]eCuCl, IBiox-[(ꢀ)-menthyl]eAgBr and IBiox-
[(ꢀ)-menthyl]eAuCl showed the well-defined dependency of the
steric demand on the inserted metal species (Table 2). The results
are in analogy to the results of other NHCs, where a similar decrease
of the steric demand from the Cu to Ag to Au can be found.
In previous work we could already show the successful appli-
cation of IBiox[(ꢀ)-menthyl]$HOTf (1) in the Pd-catalyzed asym-
metric intramolecular a-arylation of aryl chlorides for the synthesis
Fig. 2. Calculated relative free enthalpies of the different conformations of 1 and 2 at
of 3,3-disubstituted oxindoles.4,6,19e24 Remarkably, in the case of
sterically more demanding substrates IBiox[(ꢀ)-menthyl]$HOTf (1)
generally leads to the formation of the corresponding oxindoles
with increased enantioselectivities. With synthetically more ver-
satile N-benzyl-substituted substrates higher enantioselectivities
are obtained compared to the N-methyl-substituted substrates.
Even at higher temperatures (100 ꢁC) we observed for sterically
demanding substrates, good yields with remarkably high ee. This
finding is another indication for the high level of rigidity of the
novel NHC ligand 1. This enables the conversion of less reactive
substrates at higher temperature without significant loss of enan-
tioselectivity (Scheme 6).
298 K and the corresponding equilibrium populations.
The free carbene 3 was formed by in situ deprotonation in THF-
d8 using NaOtBu as base. The indicative and characteristic signal of
the carbene carbon at
d
¼194.6 in the 13C NMR spectrum provides
evidence for the formation of the free carbene and makes com-
plexation of a metal possible. Therefore ligand precursor 1 should
be able to provide interesting complexes (Scheme 2).6
Furthermore, the palladium catalyzed
a-arylation of ketones
has become an established synthetic method. Whereas chiral
bisphosphine ligands have been very successfully employed in
intermolecular asymmetric
monodentate NHC ligands in these reactions is still in its in-
fancy.25 In 2005, the intermolecular
-arylation of ketones using
a-arylation reactions, the use of chiral
Scheme 2. Synthesis of the free carbene of 1.6
a
an achiral NHCepalladium complex was reported by Nolan, but
still, the formation of quaternary centres failed.26 Recently we
In addition, we synthesized a bifunctional NHC-ligand derived
from (ꢀ)-menthone to obtain the saturated imidazolinium salt 6
(Scheme 3). Starting from the chiral aminoalcohol 4, the imidazo-
linium tetrafluoroborate salt 6 was synthesized by a standard
procedure whereas the ring closure of diamine 5 was carried out
with NH4BF4 and triethyl orthoformate to obtain the desired
product in 41% yield.13
published on the enantioselective Pd/cinchona alkaloid catalyzed a-
arylation between cyclic ketones and arylhalides under phosphine-
free conditions.27 We were also pleased to find that IBiox
[(ꢀ)-menthyl]$HOTf (1) provides the reactivity needed to enable the
Pd-catalyzed intermolecular
a-arylation of 2-methyl-1-tetralone
giving products containing a quaternary stereocenter (Scheme 7).
Moreover, these products are formed with significant levels of

7638
C. Lohre et al. / Tetrahedron 68 (2012) 7636e7644
Scheme 3. Synthesis of a new chiral NHC ligand 6.
Cl]2, 1 and NaOtBu in THF at room temperature in good yield
Table 1
%Vbur for some of the most commonly used NHCs
(Scheme 8).29
The structure of the isolated IBiox[(e)-menthyl]ePd(allyl)Cl-
complex (13) and its different conformations at 50 ꢁC were de-
termined by DFT calculations (Fig. 3). The calculated population of
conformation 13c is above 99%. These results are in line with the
ones obtained by crystal structure analysis of complex 13 (not
shown),28 showing that the more sterically demanding conforma-
tion is locked. The existence of conformation 13c is promoted by
(an)agostic interactions that stabilize this conformation.
Despite the high steric demand of the IBiox[(ꢀ)-menthyl]$HOTf
ligand, the corresponding unsaturated Pd species can undergo di-
merization. The dimeric complex 14 was synthesized from
Pd(OAc)2, 1 and LiCl in THF at 100 ꢁC. A crystal suitable for X-ray
analysis could be obtained (Scheme 9). The PdeCeNHC bond
Entry
NHC
%Vbur (Au)
1
2
3
4
5
ICy
27.4
36.5
36.9
44.5
47.0
IMes
SIMes
IPr
SIPr
Determined from X-ray structure from the NHCeAu complex (parameter: r¼3.5 A,
d¼2.0 A, Bondi radii scaled by 1.17).
ꢀ
ꢀ
lengths obtained are 1.958 A and 1.951 A.
Finally, attention was turned to the aryl chloride substrates and
DFT calculations revealed the mode of asymmetric induction in the
a-arylation of amides. The mechanism of this reaction follows the
general coupling pathway. The ligand of choice demonstrates the
importance of the bulky menthyl groups. Chiral induction from this
intermediate could occur during the PdeOeenolate to
PdeCeenolate rearrangement or during reductive elimination. Both
the steric and electronic properties of the ligands are important.
Sterically hindered ligands render the reductive elimination more
facile.18 The B2PLYP-D3/TZVPP calculations showed that the S-con-
figuraton of the PdeCeenolate complex is preferred over the R-
configuration by 7.5 kcal/mol, stabilized by (an)agostic interactions
with the methyl group (Scheme 10; Fig. 4). New chiral NHC ligands,
which provided excellent results in Pd-catalyzed
a-arylation of
€
amides reported by Kundig group revealed a diminished role of the
bulkiness of their ligands for the chiral induction because the %Vbur
for their best and less bulky ligand was 37.4%.24
Scheme 4. Synthesis of the the IBiox[(ꢀ)-menthyl]eCu/Ag/Au-complexes.18
enantioselectivity. Arguably, this represents a further successful
3. Conclusion
application of the chiral NHC 1 in an intermolecular
a-arylation
reaction.
In conclusion, we have investigated the behaviour of the sterically
demanding, C2-symmetric NHC-ligand derived from IBiox
[(ꢀ)-menthyl]$HOTf (1). The successful synthesis of a new bi-
functional IBiox[(ꢀ)-menthyl] derived NHC precursor 6 could be
demonstrated. Furthermore the successful application of IBiox
[(ꢀ)-menthyl]$HOTf (1) in Pd-catalyzed asymmetric intra- and
i
The role of the bulky menthyl group with the Pr/Me group is
demonstrated in the crystal structure of the Pd-complex. The lo-
cation and orientation of the cyclohexyl ring is fixed by confor-
mational locking of the iPr/Me group that enables optimal transfer
of chiral information. The complex was synthesized from [Pd(allyl)

C. Lohre et al. / Tetrahedron 68 (2012) 7636e7644
7639
Scheme 5. X-ray structures of the [(IBiox-[(ꢀ)-menthyl])eCuCl], [(IBiox-[(ꢀ)-menthyl])eCuI], [(IBiox-[(ꢀ)-menthyl])eAgBr]6 and the [(IBiox-[(ꢀ)-menthyl])eAuCl]-complexes.
Table 2
%Vbur for the IBiox[(ꢀ)-menthyl]eCu/Ag/Au-complexes
Scheme 7. Intermolecular a-arylation of 2-methyl-1-tetralone.
Entry
Complex
Metal
%Vbur
1
2
3
7
9
10
Cu
Ag
Au
51.0
49.4
47.7
Determination of the X-ray structures from the NHCemetal-complexes (Parameter:
ꢀ
ꢀ
r¼3.5 A, d¼2.0 A, Bondi radii scaled by 1.17).
Scheme 8. Synthesis of the IBiox[(e)-menthyl]ePd(allyl)Cl-complex.
Scheme 6. Intramolecular a-arylation of aryl chlorides.
intermolecular a-arylation reactions to obtain high levels of enan-
tioselectivity could be illustrated, revealing the unique reactivity and
selectivity of this ligand system. Novel NHCemetal complexes were
synthesized and DFT calculations confirmed that the asymmetric in-
duction of the metaleligand system is strongly linked to the presence
Fig. 3. Calculated relative free enthalpies of the IBiox[(e)-menthyl]ePd(allyl)Cl-com-
plex (13) at 50 ꢁC (323 K) and the corresponding Boltzmann distributions.

7640
C. Lohre et al. / Tetrahedron 68 (2012) 7636e7644
Scheme 9. Synthesis of the dimeric IBiox-[(ꢀ)-menthyl]ePdCl-complex 14.
Fig. 4. PdeCeenolate complex I (0.0 kcal/mol) and ent-I (7.5 kcal/mol) obtained by
DFT calculations.
4. Experimental
4.1. General
Unless otherwise noted, all reactions were carried out under an
atmosphere of argon in flame-dried glassware. The solvents used
were purified by distillation over the drying agents indicated in
parentheses and were transferred under argon: n-hexane, CH2Cl2,
Toluene (CaH2), THF (Naebenzophenone). Anhydrous DME was
purchased from Acros Organics and stored over molecular sieves
under argon. Commercially available chemicals were obtained from
Acros Organics, Aldrich Chemical Co., Strem Chemicals, Alfa Aesar,
ABCR and TCI Europe and used as received unless otherwise stated.
Scheme 10. Mechanistic studies based on Hartwig’s proposed catalytic cycle.
i
of the bulky Pr/Me groups connected at the cyclohexyl rings and
agostic interactions for stabilization effects. Further development of
chiral bifunctional NHC ligands, their application in organometallic
catalysis, and additional mechanistic studies are in progress.

C. Lohre et al. / Tetrahedron 68 (2012) 7636e7644
7641
NMR-spectra were recorded on a Bruker ARX-300, AV-300 or AV-
400 MHz 1H and 13C NMR spectra were recorded in CDCl3 or in the
solvent indicated. Chemical shifts (d) are quoted in parts per million
downfield of tetramethylsilane and were referenced to the residual
chloroform and CDCl3, 1H NMR: 7.26 ppm, 13C NMR: 77.00 ppm,
respectively; likewise for other solvents where applicable as in-
26.1 (CH2), 30.1 (CH), 33.8 (CH), 45.8 (CH2), 50.7 (CH), 67.5 (Cq), 87.8
(CH2), 126.6 (Cq), 155.9 (Cq); ESI-MS: calculated for
[C25H40N2O2CuINa]þ: 613.1323, found: 613.1326; ATR-FTIR (cmꢀ1):
2952, 2853, 2349, 2154, 1753, 1475, 1434, 1390, 1369, 1299, 1274,
1204, 1155, 1105, 1022, 1002, 987, 975, 936, 924, 880, 851, 813, 685,
641; ½a 2D0
ꢃ ¼þ63 (c¼1.11 in CHCl3). The structure was determined by
ternal standard on the
Hertz. Infrared spectra were recorded on a Varian Associated FTIR
3100 Excalibur with ATR unit. The wave numbers ( ) of recorded IR-
d
scale. Coupling constants (J) are quoted in
X-ray analysis.
n
4.2.3. IBiox[(e)-menthyl]eAgBr (9). A Schlenk flask was charged
with IBiox[(e)-menthyl]∙HOTf (1) (150 mg, 0.27 mmol, 1.0 equiv),
Ag2O (63 mg, 0.27 mmol, 1.0 equiv), NaBr (37 mg, 0.36 mmol,
1.35 equiv) and CH2Cl2 (6 mL) was added. The resulting solution
was stirred in the dark at rt for 12 h. The resulting precipitate was
filtered over Celite and washed with CH2Cl2 (3ꢂ20 mL). The com-
bined filtrates were collected, and the solvent was reduced under
pressure. After crystallization with CH2Cl2/n-hexane the pure
product was obtained as colourless crystals (151 mg, 0.26 mmol,
96%); Rf (CH2Cl2/MeOH¼10:1): 0.87; 1H NMR (400 MHz, CDCl3):
signals are quoted in cmꢀ1. ESI mass spectra were recorded on
a Bruker Daltonics MicroTof. Specific rotation was measured on
a Perkin Elmer 341 polarimeter at 20 ꢁC using a quartz glass cell
(100 mm path length). HPLC analysis was performed on an Agilent
Technologies 1200 series HPLC with a Daicel Chemical Industries
LTD chiral AD-H column. Analytical thin layer chromatography was
performed on Polygram SIL G/UV254 plates. Visualization was ac-
complished with short wave UV light and/or KMnO4 staining so-
lution followed by gentle heating. Flash column chromatography
was performed on Merck silica gel (40e63 mesh) by using standard
laboratory techniques. Solvents used for flash column chromatog-
raphy were distilled before use. GC/MS Spectra were recorded with
an Agilent Technologies 7890A GC-system with Agilent 5975C VL
MSD or 5975 inert Mass Selective Detector and a HP-5MS column
d
¼0.30 (d, J¼6.8 Hz, 6H, 2ꢂCH3), 0.95e0.93 (m, 14H), 1.39e1.21 (m,
4H), 1.73e1.67 (m, 2H), 1.95e1.89 (m, 2H), 2.15e2.03 (m, 4H),
2.35e2.20 (m, 2H), 3.32e3.16 (m, 2H, CH2), 4.42 (d, J¼9.4 Hz, 2H,
CH2), 4.65 (d, J¼9.4 Hz, 2H, CH2); 13C NMR (100 MHz, CDCl3):
d
¼16.6 (CH3), 22.7 (CH3), 22.8 (CH2), 24.4 (CH3), 26.2 (CH), 30.5 (d,
(0.25 mmꢂ30 m, Film: 0.25
mm).
J¼3.3 Hz, CH), 34.1 (CH2), 45.8 (CH2), 51.5 (CH), 67.8 (Cq), 88.3 (CH2),
127.5 (d, 3J (13C, 109Ag)¼6.6 Hz, Cq), 156.9 (dd, J (13C, 109Ag)¼
275.9 Hz, J (13C, 107Ag)¼240.2 Hz Cq); ESI-MS: calculated for
[C25H40N2O2AgBrNa]þ: 609.1216, found: 609.1215; Element. Anal.
calcd for C25H40AgBrN2O2: C, 51.03; H, 6.85; N, 4.76; found: C, 51.01;
H, 6.92; N, 4.82; ATR-FTIR (cmꢀ1): 2958, 2924, 2857, 1754, 1433,
4.2. Preparation of the IBiox[(e)-menthyl]emetal complexes
4.2.1. IBiox[(e)-menthyl]eCuCl (7). A Schlenk flask was charged
with IBiox[(e)-menthyl]∙HOTf (1) (500 mg, 0.91 mmol, 1.0 equiv),
NaOtBu (87 mg, 0.91 mmol,1.0 equiv) and THF (20 mL). The mixture
was stirred for 10 min and then CuCl (99 mg,1.0 mmol,1.1 equiv) was
added. The resulting solution was stirred at room temperature for
12 h. The resulting mixture was filtered over Celite and washed with
CH2Cl2 (3ꢂ20 mL). The combined filtrates were collected, and the
solvent was evaporated under reduced pressure. After purification
by flash chromatography (silica, CH2Cl2/MeOH¼90:1) the pure
product was obtained as a white solid (515 mg, 0.86 mmol, 95%); Rf
1297, 976, 937, 806, 741, 686, 655, 602, 596; ½a D20
ꢃ ¼þ71 (c¼0.28 in
CHCl3). The structure was determined by X-ray analysis.
4.2.4. IBiox[(e)-menthyl]eAuCl (10). A Schlenk flask was charged
with IBiox[(e)-menthyl]∙HOTf (1) (198 mg, 0.36 mmol, 1.0 equiv),
NaOtBu (35 mg, 0.36 mmol, 1.0 equiv) and THF (4 mL). The mixture
was stirred for 10 min and then Au(I)Cl (93 mg, 0.40 mmol,1.1 equiv)
was added. The resulting solution was stirred at room temperature
for 12 h. The resulting mixture was filtered over Celite and washed
with CH2Cl2 (3ꢂ5 mL). The combined filtrates were collected, and
the solvent was evaporated under reduced pressure. After purifi-
cation by short flash chromatography (silica, CH2Cl2) the pure
product was obtained as a white solid (97 mg, 0.15 mmol, 42%); Rf
(CH2Cl2/MeOH¼10:1): 0.82; 1H NMR (300 MHz, CDCl3):
¼0.30 (d,
d
J¼6.7 Hz, 6H, 2ꢂCH3), 0.99e0.93 (m, 14H), 1.38e1.23 (m, 4H),
1.75e1.67 (m, 2H), 1.92e1.85 (m, 2H), 2.19e2.00 (m, 4H), 2.51e2.38
(m, 2H), 3.52e3.46 (m, 2H, CH2), 4.41 (d, J¼8.9 Hz, 2H, CH2), 4.66 (d,
J¼8.9 Hz, 2H, CH2); 13C NMR (75 MHz, CDCl3):
¼16.4 (CH3), 22.4
d
(CH3), 22.6 (CH2), 24.2 (CH3), 26.1 (CH2), 30.1 (CH), 34.1 (CH), 45.9
(CH2), 51.0 (CH), 67.3 (Cq), 87.8 (CH2), 126.7 (Cq), 154.1 (Cq); ESI-MS:
calculated for [C25H40N2O2ClCuNa]þ: 521.1967, found: 521.1954;
Element. Anal. calcd for C25H40ClCuN2O2: C, 60.10; H, 8.07; N, 5.61;
found: C, 59.97; H, 8.12; N, 5.79; ATR-FTIR (cmꢀ1): 2955, 2929, 2871,
(CH2Cl2/MeOH¼10:1): 0.90; 1H NMR (300 MHz, CD2Cl2):
¼0.39 (d,
d
J¼6.7 Hz, 6H, 2ꢂCH3), 0.97e0.91 (m, 14H), 1.25e1.16 (m, 2H),
1.46e1.40 (m, 2H), 1.73e1.68 (m, 2H), 2.09e1.94 (m, 6H), 2.84e2.70
(m, 2H), 3.92e3.84 (m, 2H), 4.44 (d, J¼8.9 Hz, 2H, CH2), 4.65 (d,
J¼8.9 Hz, 2H, CH2), 13C NMR (100 MHz, CD2Cl2):
¼16.9 (CH3); 22.5
d
1748, 1476, 1431, 1300, 1202, 976, 937, 851, 687, 568; ½a D20
ꢃ
[þ85
(CH3), 22.9 (CH2), 24.5 (CH3), 26.7 (CH2), 29.6 (CH), 34.8 (CH), 45.7
(CH2), 52.1 (CH), 69.6 (Cq), 89.1 (CH2), 127.6 (Cq), 148.8 (Cq), ESI-MS:
calculated for [C25H40N2O2AuClNa]þ: 655.2336, found: 655.2335;
Element. Anal. calcd for C25H40N2O2AuCl: C, 47.43; H, 6.37; N, 4.43;
(c¼0.99 in CHCl3). The structure was determined by X-ray analysis.
4.2.2. IBiox[(e)-menthyl]eCuI (8). A Schlenk flask was charged
with IBiox[(e)-menthyl]∙HOTf (1) (1.0 g, 1.82 mmol, 1.0 equiv),
NaOtBu (210.0 mg, 2.18 mmol, 1.2 equiv) and THF (40 mL). The
mixture was stirred for 10 min and then CuI (415 mg, 2.18 mmol,
1.2 equiv) was added. The resulting solution was stirred at room
temperature for 12 h. The resulting mixture was filtered over Celite
and washed with CH2Cl2 (3ꢂ40 mL). The combined filtrates were
collected, and the solvent was evaporated under reduced pressure.
After purification by flash chromatography (silica, CH2Cl2/
MeOH¼90:1) the pure product was obtained as a white solid
(1.011 g, 1.71 mmol, 94%); Rf (CH2Cl2/MeOH¼10:1): 0.78; 1H NMR
found: C, 47.52; H, 6.45; N, 4.24; ½a D20
ꢃ ¼þ80 (c¼0.98 in CHCl3). The
structure was determined by X-ray analysis. (Moisture- and air
sensitive compound was handled under an argon atmosphere).
4.2.5. IBiox[(e)-menthyl]ePd(allyl)Cl (13). A Schlenk flask was
charged with IBiox[(e)-menthyl]∙HOTf (1) (250 mg, 0.45 mmol,
1.0 equiv), NaOtBu (48 mg, 0.50 mmol, 1.1 equiv), [Pd(allyl)Cl]2
(83 mg, 0.23 mmol, 0.50 equiv) and THF (4.7 mL). After stirring
overnight at room temperature the resulting mixture was filtered
over Celite and washed with CH2Cl2 (3ꢂ10 mL). The combined fil-
trates were collected, and the solvent was evaporated under re-
duced pressure. After purification by flash chromatography (silica,
CH2Cl2/MeOH¼100:1/50:1) the pure product was obtained as
a yellow solid (186 mg, 0.32 mmol, 71%); Rf (CH2Cl2/MeOH¼10:1):
0.76; ESI-MS: calculated for [C28H45N2O2Pd]þ: 547.2521, found:
(300 MHz, CDCl3):
d
¼0.32 (d, J¼6.9 Hz, 6H, 2ꢂCH3), 0.95e0.86 (m,
14H), 1.37e1.24 (m, 4H), 1.72e1.66 (m, 2H), 1.91e1.84 (m, 2H),
2.17e2.00 (m, 4H), 2.45e2.35 (m, 2H), 3.52e3.47 (m, 2H, CH2), 4.43
(d, J¼8.7 Hz, 2H, CH2), 4.68 (d, J¼8.7 Hz, 2H, CH2); 13C NMR
(75 MHz, CDCl3):
d
¼16.4 (CH3), 22.0 (CH3), 22.3 (CH2), 24.2 (CH3),

7642
C. Lohre et al. / Tetrahedron 68 (2012) 7636e7644
547.2523; ATR-FTIR (cmꢀ1): 2948, 2868, 1782, 1459, 1421, 1390,
1368, 1336, 1310, 1291, 1229, 1200, 1190, 1151, 1108, 1040, 978, 935,
(58 mg, 0.6 mmol, 2 equiv) was combined in a pressure vessel and
suspended in toluene (3 mL). After addition of the arylhalide
(0.6 mmol, 2.0 equiv), the 2-methyl-1-tetralone (48 mg, 0.3 mmol,
1.0 equiv) was added and the resulting mixture stirred at 80 ꢁC for
12e16 h until all starting material was consumed (GC/MS). After
completion the mixture was filtered through a short plug of silica,
diluted with EtOAc (50 mL) and the solvents were evaporated. The
crude material was dissolved in a small amount of CH2Cl2, adsorbed
on silica and purified by flash chromatography (silica, pentane/EtOAc).
879, 842, 806, 765, 687, 667; ½a D20
ꢃ ¼þ77 (c¼0.77 in CHCl3). The
strucutre of 13 was confirmed by single-crystal X-ray analysis but
the X-ray data were not good enough for publication.
4.2.6. Imidazolinium tetrafluoroborate salt (6). ((1S,2S,5R)-1-
Amino-2-isopropyl-5-methylcyclohexyl)methanol
14,6 mmol, 2.0 equiv) was mixed in a pressure vessel with 1,2-
dibromoethane (625
L, 7.3 mmol, 1.0 equiv) and stirred at 100 ꢁC
(2.7
g,
m
overnight under argon. The resulting solid was taken up with
aqueous NaOH (1 M) and CH2Cl2 and the aqueous phase was
extracted with CH2Cl2 (3ꢂ30 mL). The combined organic layers
were dried over Na2SO4 and concentrated in vacuo. The resulting
diamine (1.76 g, redebrownish oil) was used without further pu-
rification. To the diamine (1.7 g, 4.4 mmol, 1.0 equiv) NH4BF4
4.3.2. Characterization of the products.
4.3.2.1. 2-Methyl-2-phenyl-3,4-dihydronaphthalen-1(2H)-one
(12a). Following the general procedure, 2-methyl-1-tetralone
(48 mg, 0.3 mmol, 1.0 equiv) was reacted with bromobenzene
(63 mL, 0.6 mmol, 2.0 equiv) to obtain the title compound after flash
(461 mg, 4.4 mmol, 1.0 equiv) and triethyl orthoformate (750
m
L,
chromatography (silica, pentane/EtOAc¼50:1) as pale yellow oil
4.4 mmol, 1.0 equiv) were added and the mixture was stirred at
120 ꢁC overnight. After cooling to room temperature and removal of
EtOH the crude product was purified by flash chromatograghy
(silica, CH2Cl2/MeOH¼40:1). The pure product was obtained as
a white solid (1.79 mmol, 41% for both steps); Rf (CH2Cl2/
(62 mg, 0.24 mmol, 87%); Rf (pentane/EtOAc¼10:1): 0.70; 1H NMR
(400 MHz, CDCl3):
d
¼1.53 (s, 3H), 2.23e2.30 (m, 1H), 2.62 (td,
J¼4.0 Hz, J¼14.0 Hz, 1H), 2.81e2.85 (m, 2H), 7.11 (d, J¼7.6 Hz, 1H),
7.17e7.23 (m, 3H), 7.25e7.33 (m, 3H), 7.42 (dt, J¼1.5 Hz, J¼7.5 Hz,1H),
8.15 (dd, J¼1.2 Hz, J¼7.8 Hz, 1H); 13C NMR (100 MHz, CDCl3):
¼26.1,
d
MeOH¼10:1): 0.61; 1H NMR (300 MHz, CDCl3):
d
¼0.86 (d, J¼6.8 Hz,
27.0, 36.2, 50.5, 126.3, 2ꢂ126.6, 127.9, 128.5, 128.6, 132.7, 133.1, 142.0,
143.5, 201.3; GCeMS tR (method 50_40): 9.2 min; MS-EI: m/z(%)¼236
(41), 221 (5), 131 (17), 118 (100), 90 (26); 57% ee (Chiracel AD-H col-
umn, n-hexane/i-PrOH¼99:1, 1.0 mL/min, 254 nm; tR¼8.92 min and
6H, CH3), 0.95 (dd, J¼6.2 Hz, J¼14.0 Hz, 14H), 1.10e1.28 (m, 4H),
1.32e1.49 (m, 4H), 1.72e1.78 (m, 2H), 1.85e1.89 (m, 2H), 1.95e2.05
(m, 2H), 2.26e2.31 (m, 2H), 3.43 (d, J¼11.8 Hz, 2H), 3.57 (brs, 2H,
OH), 4.08e4.13 (m, 6H), 7.79 (s, 1H, NHCN); 13C NMR (75 MHz,
10.19 min (major)); ½a D20
ꢃ ¼þ136 (c¼0.635 in CHCl3).
CDCl3):
d
¼19.0, 22.1, 24.0, 25.8, 26.6, 27.7, 35.1, 42.3, 47.8, 49.1, 66.0,
66.6, 158.4 (NHCN); ESI-MS: calculated for [C25H47N2O2]þ:
407.3632, found: 407.3640; ATR-FTIR (cmꢀ1):¼2951, 2869, 2396,
1613, 1459, 1367, 1279, 1205, 1156, 1049, 999, 899, 760, 649, 594,
4.3.2.2. 2-(3-Methoxyphenyl)-2-methyl-3,4-dihydronaphthalen-
1(2H)-one (12b). Following the general procedure, 2-methyl-1-
tetralone (48 mg, 0.3 mmol, 1.0 equiv) was reacted with 3-
552, 523, 515, 496; ½a D20
ꢃ
¼þ17.4 (c¼0.975 in CHCl3). The structure
bromoanisole (75 mL, 0.6 mmol, 2.0 equiv) to obtain the title
was determined by X-ray analysis.
compound after flash chromatography (silica, pentane/
EtOAc¼50:1) as pale yellow oil (61 mg, 0.23 mmol, 76%); Rf (pen-
4.2.7. IBiox[(e)menthyl]2ePdCl-complex (14). A Young TeflonÒ tube
was charged under argonwith IBiox[(e)menthyl]∙HOTf (1) (500 mg,
0.91 mmol, 1.0 equiv), Pd(OAc)2 (204 mg, 0.91 mmol, 1.0 equiv), LiCl
(77 mg, 1.82 mmol, 2.0 equiv) and THF (5 mL). The solution was
stirred overnight at 100 ꢁC. After cooling to room temperature the
residue was taken up with CH2Cl2 (30 mL) and washed with water
(1ꢂ15 mL). The aqueous layer was extracted with CH2Cl2 (2ꢂ10 mL)
and the combined organic layers were washed with water
(1ꢂ15 mL), dried over Na2SO4 and concentrated in vacuo. The crude
product was purified by flash chromatography (silica, CH2Cl2/
MeOH¼40:1). The product was obtained as an orange solid
(0.49 mmol, 54%); Rf (CH2Cl2/MeOH 10:1)¼0.84; 1H NMR (400 MHz,
tane/EtOAc¼10:1): 0.47; 1H NMR (400 MHz, CDCl3):
¼1.52 (s, 3H),
d
2.22e2.29 (m, 1H), 2.59 (td, J¼4.1 Hz, J¼14.0 Hz, 1H), 2.77e2.91 (m,
2H), 3.74 (s, 3H), 6.72e6.80 (m, 3H), 7.11 (d, J¼7.6 Hz, 1H), 7.19 (t,
J¼8.0 Hz, 1H), 7.30 (t, J¼7.5 Hz, 1H), 7.41 (dt, J¼1.5 Hz, J¼7.5 Hz, 1H),
8.14 (dd, J¼1.2 Hz, J¼7.8 Hz,1H); 13C NMR (100 MHz, CDCl3):
¼26.1,
d
27.0, 36.2, 50.5, 55.1, 111.4, 112.9, 118.8, 126.5, 127.9, 128.6, 129.5,
132.7, 133.1, 143.6, 143.7, 159.7, 201.1; GCeMS tR (method 50_40):
9.8 min; MS-EI: m/z(%)¼266 (50), 251 (8), 131 (21), 118 (100), 90
(39); ESI-MS: calculated for: [C18H18O2Na]þ: 289.1199, found:
289.1198; 61% ee (Chiracel AD-H column, n-hexane/i-PrOH¼99:1,
1.0 mL/min, 254 nm; tR¼14.08 min and 15.02 min (major));
½
a 2D0
ꢃ
¼þ147 (c¼0.695 in CHCl3); ATR-FTIR (cmꢀ1):¼3065, 2928,
CD2Cl2):
d
¼0.22 (d, J¼6.6 Hz, 6H, 2ꢂCH3), 0.38 (d, J¼6.8 Hz, 6H,
2836, 1680, 1600, 1487, 1454, 1289, 1260, 1221, 1046, 748, 702.
2ꢂCH3), 0.93e1.30 (m, 32H), 1.48e1.57 (m, 4H), 1.73e1.90 (m, 4H),
2.17e2.75 (m,14H), 3.14e3.23 (m, 2H), 4.27e4.55 (m, 8H), 4.85e4.87
4.3.2.3. 2-(3-(1,3-Dioxolan-2-yl)phenyl)-2-methyl-3,4-dihydro-
naphthalen-1(2H)-one (12c). Following the general procedure, 2-
methyl-1-tetralone (48 mg, 0.3 mmol, 1.0 equiv) was reacted with
3-bromobenzaldehyde- ethylenacetal (137 mg, 0.6 mmol, 2 equiv)
to obtain the title compound after flash chromatography (silica,
pentane/EtOAc¼5:1) as yellowish oil (52 mg, 0.17 mmol, 56%); Rf
(m, 2H), 5.32e5.33 (m, 2H). 13C NMR (100 MHz, CDCl3):
d¼130.64 (s,
Cq), 129.80 (s, Cq), 114.81 (s, 2 x Cq), 88.87 (s, CH2), 88.83 (s, CH2),
71.95 (s, Cq), 71.18 (s, Cq), 55.51 (s, CH), 43.10 (s, CH2), 41.63 (s, CH2),
35.96 (s, CH2), 35.49 (s, CH2), 31.78 (s, CH), 31.12 (s, CH), 26.21 (s, CH),
26.19 (s, CH), 24.61 (s, CH3), 24.55 (s, CH3), 23.19 (s, CH2), 23.13 (s,
CH3), 22.81 (s, CH3), 22.06 (s, CH2), 17.97 (s, CH3), 17.51 (s, CH3); ESI-
MS: calculated for [C25H40N2O2Cl2PdNa]þ: 601.1396, found:
601.1383, Element. Anal. calcd for C50H80N4O4Cl4Pd2 ∙CH2Cl2: C
49.37, H 6.66, N 4.52, found: C 49.65, H 6.75, N 4.46; ATR-FTIR
(cmꢀ1):¼2362, 2339, 1461, 980, 935, 878, 853, 686, 668, 589, 569,
561, 528, 512, 499. The structure was determined by X-ray analysis.
(pentane/EtOAc¼10:3): 0.48; 1H NMR (400 MHz, CDCl3):
¼1.53 (s,
d
3H), 2.22e2.30 (m, 1H), 2.64 (td, J¼4.0 Hz, J¼14.0 Hz, 1H),
2.81e2.85 (m, 2H), 3.98e4.04 (m, 2H), 4.05e4.11 (m, 2H), 5.75 (s,
1H), 7.10 (d, J¼7.6 Hz,1H), 7.18 (td, J¼1.7 Hz, J¼7.8 Hz,1H), 7.25e7.34
(m, 3H), 7.37e7.43 (m, 2H), 8.14 (dd, J¼1.1 Hz, J¼7.8 Hz, 1H); 13C
NMR (100 MHz, CDCl3):
d
¼26.0, 27.0, 36.0, 50.4, 2ꢂ 65.2, 103.6,
124.4, 124.8, 126.5, 127.4, 127.9, 2ꢂ128.6, 132.6, 133.1, 138.1, 142.2,
143.5, 201.1; GCeMS tR (method 50_40): 11.1 min; MS-EI: m/z(%)¼
308 (15), 162 (22), 149 (30), 118 (100), 90 (48), 73 (25); 60% ee
(Chiracel AD-H column, n-hexane/i-PrOH¼99:1, 1.0 mL/min,
4.3. Intermolecular a-arylation of 2-methyl-1-tetralone
4.3.1. General procedure for the synthesis of 2-aryl-2-methyl-1-
tetralones. [Pd(allyl)Cl]2 (2.7 mg, 7.5$10ꢀ4 mmol, 2.5 mol %), IBiox
[(e)-menthyl]∙HOTf (1) (8 mg, 1.5$10ꢀ3 mmol, 5 mol %), NaOtBu
254 nm; tR¼29.55 min and 37.21 min (major)); ½a D20
ꢃ ¼þ138 (c¼0.48
in CHCl3).

C. Lohre et al. / Tetrahedron 68 (2012) 7636e7644
7643
ꢀ
4.4. Computational details
l
¼0.71,073 A, T¼223(2) K,
u
q
and 4 scans, 17,065 reflections col-
ꢀꢀ1
lected (ꢅh, ꢅk, ꢅl), [(sin
)/l]¼0.60
A
,
5860 independent
(I)], 286 refined
All calculations were carried out with the TURBOMOLE 6.3
program package.30 The optimizations were performed with the
(Rint¼0.059) and 5070 observed reflections [I>2
s
parameters, R¼0.033, wR2¼0.079, max. (min.) residual electron
TPSS9 density functional together with the Ahlrichs’ type triple-
z
density 0.36 (ꢀ0.32) e A , hydrogen atoms calculated and refined
ꢀꢀ3
basis set def2-TZVP.10 For the single-point calculations the double
hybrid functional B2PLYP,8 the triple- basis set def2-TZVPP10 (for
the R- and S-configuration of the PdeOeenolate) and the large
quadruple-
basis set def2-QZVPP10 (in all other cases) were
as riding atoms. Flack parameter was refined to ꢀ0.006(9).
X-ray crystal structure analysis of 8: formula C25H40CuIN2O2,
M¼591.03, colourless crystal, 0.27ꢂ0.15ꢂ0.14 mm, a¼10.6305
z
3
ꢀ
ꢀ
z
(1), b¼12.9892(2), c¼18.7584(3) A, V¼2590.19(6) A , rcalcd¼1.516
employed. In the case of the TPSS calculations the resolution of
identity (RI-J) approximation31 were applied. For the DFT part of
B2PLYP the RI-JK approximation32 was adapted and for the per-
turbative part the RI approximation33 was used as well. All auxiliary
basis sets were taken from the TURBOMOLE basis set library.34 In all
calculations the recently developed DFT-D311 together with the
BeckeeJohnson (BJ) damping function12 was added, as indicated by
the appended ’-D3’ to the functional name. Furthermore, to simu-
late solvent effects, COSMO was used in all calculations with a di-
electric constant of ε¼2.37 (toluene). The harmonic vibrational
frequencies were obtained as numerical derivatives of analytically
calculated gradients employing a modified version of the program
g
cmꢀ3
,
m
¼2.058 mmꢀ1
,
empirical absorption correction
(0.606ꢄTꢄ0.761), Z¼4, orthorhombic, space group P212121 (No. 19),
ꢀ
l
¼0.71,073 A, T¼223(2) K,
u
q
and 4 scans, 21,337 reflections col-
ꢀꢀ1
lected (ꢅh, ꢅk, ꢅl), [(sin
)/
l]¼0.60
A
,
6206 independent
(I)], 286 refined
(Rint¼0.053) and 5973 observed reflections [I>2
s
parameters, R¼0.032, wR2¼0.078, max. (min.) residual electron
ꢀꢀ3
density 0.36 (ꢀ0.45) e A , hydrogen atoms calculated and refined
as riding atoms. Flack parameter was refined to ꢀ0.027(16).
X-ray crystal structure analysis of 10: formula C25H40AuClN2O2,
M¼663.01, colourless crystal, 0.45ꢂ0.30ꢂ0.25 mm, a¼10.8960
3
ꢀ
ꢀ
(1), b¼12.9531(2), c¼18.2371(2) A, V¼2573.93(5) A , rcalcd¼1.634
g cmꢀ3
,
m
¼5.842 mmꢀ1, empirical absorption correction (0.178
SNF11.35 This was done at the TPSS level only and the derived
(structures 1 and 2) as well as the
D
G298
ꢄTꢄ0.323), Z¼4, orthorhombic, space group P212121 (No. 19),
ꢀ
DG
323 (structure 13) values were
l
¼0.71,073 A, T¼223(2) K,
u
q
and 4 scans, 27,524 reflections col-
ꢀꢀ1
also used for B2PLYP. For structure 13a and the R-configuration we
obtained one imaginary vibrational frequency of i13 cmꢀ1 and
i9 cmꢀ1, respectively. Inspection of the corresponding normal
modes indicates them as a typical numerical artefact of the nu-
merical quadrature of the exchange-correlation energy in DFT.
These vibrational frequencies were not considered in the statistical
thermochemistry calculations.
lected (ꢅh, ꢅk, ꢅl), [(sin
)/l]¼0.60
A
,
7785 independent
(I)], 287 refined
(Rint¼0.059) and 7056 observed reflections [I>2
s
parameters, R¼0.028, wR2¼0.060, max. (min.) residual electron
ꢀꢀ3
density 0.97 (ꢀ0.95) e A , hydrogen atoms calculated and refined
as riding atoms. Flack parameter was refined to ꢀ0.014(13).
X-ray crystal structure analysis of 14: formula C51H82Cl6N4O4Pd2,
M¼1240.71, yellow crystal, 0.30ꢂ0.20ꢂ0.17 mm, a¼11.7442(1),
b¼15.4845(2), c¼31.3452(5) A, V¼5700.22(13) A , rcalcd¼1.446 g cmꢀ3
,
3
ꢀ
ꢀ
4.5. X-ray data
m
¼0.957 mmꢀ1, empirical absorption correction (0.762ꢄTꢄ0.854),
ꢀ
Z¼4, orthorhombic, space group P212121 (No. 19),
l
¼0.71,073 A,
X-ray diffraction: Data sets were collected with a Nonius Kap-
paCCD diffractometer. Programs used: data collection, COLLECT
(Nonius B.V., 1998); data reduction Denzo-SMN (Z. Otwinowski, W.
Minor, Methods Enzymol. 1997, 276, 307e326); absorption correc-
tion, Denzo (Z. Otwinowski, D. Borek, W. Majewski, W. Minor, Acta
Crystallogr. 2003, A59, 228e234); structure solution SHELXS-97 (G.
M. Sheldrick, Acta Crystallogr. 1990, A46, 467e473); structure re-
finement SHELXL-97 (G. M. Sheldrick, Acta Crystallogr. 2008, A64,
112e122) and graphics, XP (BrukerAXS, 2000). R-values are given
for observed reflections, and wR2 values are given for all reflections.
Exceptions and special features: Compound 6 crystallized with
two independent molecules per asymmetric unit. For the BF4 an-
ions in compound 6 several restraints (ISOR and SADI) were used in
order to improve refinement stability. Compound 14 present a dis-
ordered over two positions dichloromethane molecule. Several
restraints (SADI, SIMU and SAME) were used in order to improve
refinement stability.
T¼223(2) K,
u
and 4 scans, 32,618 reflections collected (ꢅh, ꢅk, ꢅl),
ꢀꢀ1
]¼0.60 A , 12,851 independent (Rint¼0.064) and 12,004 ob-
[(sinq)/l
served reflections [I>2 (I)], 629 refined parameters, R¼0.052,
s
2
ꢀꢀ3
wR ¼0.116, max. (min.) residual electron density 0.91 (ꢀ0.84) e A
,
hydrogen atoms calculated and refined as riding atoms. Flack param-
eter was refined to ꢀ0.1(3).
Acknowledgements
This paper is dedicated to Prof. Manfred T. Reetz on the occasion
of receiving the Tetrahedron Award 2011. We thank Dr. Thomas
Droge and Cornelia Weitkamp for experimental support and dis-
cussions and Dr. Klaus Bergander for excellent NMR support (all
WWU Munster). The Deutsche Forschungsgemeinschaft (GL 349 1-
€
€
€
4 and the IRTG Munster-Nagoya) is gratefully acknowledged for
financial support. The research of F.G. was supported by the Alfried
Krupp Prize for Young University Teachers of the Alfried Krupp von
Bohlen und Halbach Foundation.
X-ray crystal structure analysis of 6: formula C25H47BF4N2O2,
M¼494.46, colourless crystal, 0.30
x
0.12
x
b
0.03 mm,
¼111.909(4)ꢁ,
ꢀ
a¼25.0708(19), b¼8.0756(9), c¼29.3808(9) A,
Supplementary data
3
V¼5518.9(8) A , rcalcd¼1.190 g cmꢀ3
,
m
¼0.763 mmꢀ1, empirical
ꢀ
absorption correction (0.803ꢄTꢄ0.977), Z¼8, monoclinic, space
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tet.2012.06.039.
ꢀ
group C2 (No. 5),
l
¼1.54,178 A, T¼223(2) K,
u
and 4 scans, 22,371
ꢀꢀ1
reflections collected (ꢅh, ꢅk, ꢅl), [(sin
q)/
l
]¼0.60 A , 8361 in-
References and notes
dependent (Rint¼0.073) and 5994 observed reflections [I>2
s(I)],
631 refined parameters, R¼0.103, wR2¼0.309, max. (min.) residual
1. (a) Arduengo, A. J., III. Acc. Chem. Res. 1999, 32, 913e921; (b) Bourissou, D.;
Guerret, O.; Gabbai, F. P.; Bertrand, G. Chem. Rev. 2000, 100, 39e92; (c) Hahn, F.
E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47, 3122e3172.
2. For a review on the physicochemical properties of NHCs, see: Droge, T.; Glorius,
F. Angew. Chem., Int. Ed. 2010, 49, 6940e6953.
ꢀꢀ3
electron density 1.11 (ꢀ0.57) e A , hydrogen atoms calculated and
refined as riding atoms. Flack parameter was refined to 0.4 (5).
X-ray crystal structure analysis of 7: formula C25H40ClCuN2O2,
€
3. (a) Enders, D.; Niemeier, O.; Henseler, A. Chem. Rev. 2007, 107, 5606e5655; (b)
Phillips, E. M.; Chan, A.; Scheidt, K. A. Aldrichimica Acta 2009, 42, 55e66; (c)
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2011, 40, 786e791; (f) Nair, V.; Menon, R. S.; Biju, A. T.; Sinu, C. R.; Paul, R. R.;
M¼499.58, colourless crystal, 0.30ꢂ0.25ꢂ0.25 mm, a¼10.8800
3
ꢀ
ꢀ
(2), b¼13.1868(3), c¼17.6268(2) A, V¼2528.96(8) A , rcalcd¼1.312
g
cmꢀ3
,
m
¼0.992 mmꢀ1
,
empirical absorption correction
(0.755ꢄTꢄ0.789), Z¼4, orthorhombic, space group P212121 (No. 19),

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