Multicomponent synthesis of N-heterocyclic carbene complexes

Article abstract of DOI:10.1021/om070168u

N-Heterocyclic carbenes (NHCs) are valuable ligands in transition metal catalysis, due to their unique electronic properties. However, only a few routes toward unsymmetrically substituted, saturated NHCs are known. We have successfully applied the multicomponent synthesis of 2H-2-imidazolines for the preparation of a range of diversely substituted imidazolidin-2-ylidene complexes under mild conditions. In the desired NHC precursors the substituents at N-1, N-3, C-4, and C-5 were varied easily and independently by choosing the appropriate amine, aldehyde, isocyanide, or halide as starting material. Subsequent formation of the imidazolium salts followed by deprotonation with KO^tBu and direct complexation of the in situ-generated NHCs at room temperature affords Rh- and Ir-NHC complexes. Properties of the resulting complexes were studied with ¹³C NMR spectroscopy and X-ray crystallography.

Full text of DOI:10.1021/om070168u

Organometallics 2007, 26, 3639-3650
3639
Articles
Multicomponent Synthesis of N-Heterocyclic Carbene Complexes
Robin S. Bon,† Frans J. J. de Kanter,† Martin Lutz,‡ Anthony L. Spek,‡ Mareike C. Jahnke,§
F. Ekkehardt Hahn,§ Marinus B. Groen,† and Romano V. A. Orru*,†
Department of Organic and Inorganic Chemistry, Faculty of Science, Vrije UniVersiteit Amsterdam,
De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
ReceiVed February 23, 2007
N-Heterocyclic carbenes (NHCs) are valuable ligands in transition metal catalysis, due to their unique
electronic properties. However, only a few routes toward unsymmetrically substituted, saturated NHCs
are known. We have successfully applied the multicomponent synthesis of 2H-2-imidazolines for the
preparation of a range of diversely substituted imidazolidin-2-ylidene complexes under mild conditions.
In the desired NHC precursors the substituents at N-1, N-3, C-4, and C-5 were varied easily and
independently by choosing the appropriate amine, aldehyde, isocyanide, or halide as starting material.
Subsequent formation of the imidazolium salts followed by deprotonation with KOtBu and direct
complexation of the in situ-generated NHCs at room temperature affords Rh- and Ir-NHC complexes.
Properties of the resulting complexes were studied with 13C NMR spectroscopy and X-ray crystallography.
functional groups, leading to easily recoverable catalysts,4
water-5 or methanol6-soluble catalysts, and catalysts containing
“flexible steric bulk”7 as well as chiral ligands8a and bidentate
and pincer ligands,1f,9 although it should be noted that the
potential of monodentate NHC complexes for asymmetric
catalysis is believed to be only modest.8b-8d
Introduction
N-Heterocyclic carbenes (NHCs) attract considerable attention
as valuable ligands in coordination chemistry and homogeneous
catalysis.1 This can be attributed to some rather unique properties
of NHC ligands, such as their stronger σ-donor ability compared
to, for example, tertiary phosphine ligands. Further, their strong
nucleophilic character and weak π back-donating ability make
NHC ligands comparable to P- or N-donating ligands rather
than to classical Fischer- or Schrock-type carbenes.2 Important
advantages of NHC metal complexes are their low sensitivity
to air (oxidation), heat, and moisture compared to the corre-
sponding phosphine complexes.3 As a result, NHC ligands serve
as good alternatives to electron-rich phosphine ligands, which
makes them increasingly popular in transition metal (TM)
catalysis.1 In addition to beneficial electronic properties robust
synthetic procedures give access to NHCs bearing additional
Figure 1. Commonly used N-heterocyclic carbenes.
NHCs derived from three-, four-, six-, and seven-membered
* Corresponding author. E-mail: orru@few.vu.nl.
† Vrije Universiteit Amsterdam. Fax: (+31) 20-598-7488. E-mail:
orru@few.vu.nl.
(4) Su¨ssner, M.; Plenio, H. Angew. Chem., Int. Ed. 2005, 44, 6885-
6888.
(5) Hong, S. H.; Grubbs, R. H. J. Am. Chem. Soc. 2006, 128, 3508-
3509.
‡ Bijvoet Center for Biomolecular Research, Crystal and Structural
Chemistry, Utrecht University, Padualaan 8, 3584 CH Utrecht, The
Netherlands.
(6) Hahn, F. E.; Paas, M.; Fro¨hlich, R. J. Organomet. Chem. 2005, 690,
5816-5821.
(7) (a) Altenhoff, G.; Goddard, R.; Lehmann, C. W.; Glorius, F. Angew.
Chem., Int. Ed. 2003, 42, 3690-3693. (b) Lavallo, V.; Canac, Y.; Pra¨sang,
C.; Donnadieu, B.; Bertrand, G. Angew. Chem., Int. Ed. 2005, 44, 5705-
5709.
(8) (a) Seiders, T. J.; Ward, D. W.; Grubbs, R. H. Org. Lett. 2001, 3,
3225-3228. (b) Rivas, F. M.; Riaz, U.; Giessert, A.; Smulik, J. A.; Diver,
S. T. Org. Lett. 2001, 3, 2673-2676. (c) Baskakov, D.; Herrmann, W. A.;
Herdtweck, E.; Hoffmann, S. D. Organometallics 2007, 26, 626-632.
(9) (a) For a recent review on bidentate carbenes see: Cabeza, J. A.; da
Silva, I.; del Rio, I.; Sanchez-Vega, M. G. Dalton Trans. 2006, 3966-
3971. For other examples, see also: (b) Hahn, F. E.; Jahnke, M. C.; Gomes-
Benitez, V.; Morales-Morales, D.; Pape, T. Organometallics 2005, 24,
6458-6463. (c) Hahn, F. E.; Jahnke, M. C.; Pape, T. Organometallics 2006,
25, 5927-5936. (d) Slootweg, J. C.; Chen, P. Organometallics 2006, 25,
5863-5869.
§ Institut fu¨r Anorganische und Analytische Chemie, Westfa¨lische
Wilhelms-Universita¨t Mu¨nster, Corrensstr. 36, D-48149 Mu¨nster, Germany.
(1) For reviews see: (a) Bourissou, D.; Guerret, O.; Gabbai, F. P.;
Bertrand, G. Chem. ReV. 2000, 100, 39-92. (b) Herrmann, W. A. Angew.
Chem., Int. Ed. 2002, 41, 1290-1309. (c) Herrmann, W. A.; Weskamp,
T.; Bo¨hm, V. P. W. AdV. Organomet. Chem. 2001, 48, 1-69. (d) Hillier,
A. C.; Grasa, G. A.; Viciu, M. S.; Lee, H. M.; Yang, C.; Nolan, S. J.
Organomet. Chem. 2002, 653, 69-82. (e) Bedford, R. B.; Cazin, C. S. J.;
Holder, D. Coord. Chem. ReV. 2004, 248, 2283-2321. (f) Trnka, T. M.;
Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18-29. (g) Peris, E.; Crabtree,
R. H. Coord. Chem. ReV. 2004, 248, 2239-2246. (h) Crabtree, R. H. J.
Organomet. Chem. 2005, 690, 5451-5457. (i) Hahn, F. E. Angew. Chem.,
Int. Ed. 2006, 45, 1348-1352.
(2) Lee, M. T.; Hu, C. H. Organometallics 2004, 23, 976-983.
(3) Herrmann, W. A.; Roesky, P. W.; Elison, M.; Artus, G. R.; O¨ fele,
K. Organometallics 1995, 14, 1085-1086.
10.1021/om070168u CCC: $37.00 © 2007 American Chemical Society
Publication on Web 06/20/2007

3640 Organometallics, Vol. 26, No. 15, 2007
Bon et al.
Scheme 2. Multicomponent Approach toward NHC
Scheme 1. Syntheses of Imidazolinium Salts
Complexes
heterocycles have been reported.10-13 However, the most
frequently used NHC ligands are the five-membered imidazolin-
2-ylidenes A, imidazolidin-2-ylidenes B, benzimidazolin-2-
ylidenes C, and triazolin-2-ylidenes D (Figure 1). A straight-
forward procedure to synthesize the “saturated” carbenes B is
by deprotonation of the corresponding imidazolinium salts
BH+X- with bases such as NaH, KH, LDA, KHMDS, or KOt-
Bu. The imidazolinium salts BH+X- can be obtained by
condensation of 1,2-diamines with triethyl orthoformate. A quick
way to generate symmetrically substituted 1,2-diamines is via
reduction of 1,2-diimines or via amination of 1,2-dibromides.14
Variation of the C-4 and C-5 side groups of carbenes of type B
can in principle be achieved by using available 1,2-diamines 1
or by alkylation of imidazolines 3 containing various R1-R5
groups (Scheme 1). However, methods for the synthesis of
NHCs containing distinct side groups in the carbon backbone
(R2-R5) are limited. In fact, the only general procedure involves
a one-pot synthesis of imidazolidin-2-thiones followed by
reduction of its thiourea moiety,15 although the harsh reaction
conditions are only compatible with nonfunctionalized alkyl
substituents.
Recently, we reported a versatile multicomponent synthesis
of 2H-2-imidazolines 7.16 The mild reaction conditions render
this multicomponent reaction (MCR) compatible with a broad
spectrum of aliphatic, aromatic, heteroaromatic, and olefinic
substituents and even with more delicate functional groups such
as amines, alcohols, esters, and primary chlorides. Because the
substituents on C-4 and C-5 of the resulting 2H-2-imidazolines
can be varied independently, we envisioned this MCR as a
valuable tool for the synthesis of unprecedented types of NHC-
transition metal complexes. In this contribution, we report a
Chart 1. Building Blocks for NHC Precursors
very short and flexible synthetic protocol for the synthesis of a
structurally diverse set of Rh- and Ir-NHC metal complexes
of type 9 (Scheme 2). All substituents R1-R5 at N-1, N-3, C-4,
and C-5 in 9 were varied easily and independently by choosing
an appropriate amine, aldehyde, isocyanide, or halide as starting
materials.
Results and Discussion
For the synthesis of a diverse set of NHC precursors 8, three
amines, three aldehydes, three isocyanides, and three halides
were chosen (Chart 1). Thus, after the synthesis of 2-imidazo-
lines 22, 25, 27, 29, and 31, which proceeds smoothly via our
three-component approach, alkylation gives the corresponding
imidazolinium halides 23, 24, 26, 28, 30, and 32 in high yields
(Table 1; entries 1-6). Although conversions are generally
quantitative, small amounts of the product are sometimes lost
during washing of the salts with ether or pentane. Quarterniza-
tion with 19 or 20 can be performed in CH2Cl2, but for the less
reactive chloride 21, more polar solvents such as DMF are
preferred (entry 2).
(10) (a) Schumann, H.; Glanz, M.; Girgsdies, F.; Hahn, F. E.; Tamm,
M.; Grzegorzewski, A. Angew. Chem., Int. Ed. 1997, 36, 2232-2234. (b)
Lavallo, V.; Canac, Y.; Donnadieu, B.; Schoeller, W. W.; Bertrand, G.
Science 2006, 312, 722-724. (c) Lavallo, V.; Ishida, Y.; Donnadieu, B.;
Bertrand, G. Angew. Chem., Int. Ed. 2006, 45, 6652-6655.
(11) (a) Despagnet-Ayoub, E.; Grubbs, R. H. J. Am. Chem. Soc. 2004,
126, 10198-10199. (b) Despagnet-Ayoub, E.; Grubbs, R. H. Organome-
tallics 2005, 24, 338-340. (c) Ishida, Y.; Donnadieu, B.; Bertrand, G. Proc.
Natl. Acad. Sci. 2006, 103, 13585-13588.
(12) (a) Alder, R. W.; Blake, M. E.; Bortolotti, C.; Butts, C. P.; Linehan,
E.; Oliva, J. M.; Orpen, A. G.; Quayle, M. J. Chem. Commuun. 1999, 241-
242. (b) Guillen, F.; Winn, C. L.; Alexakis, A. Tetrahedron: Asymmetry
2001, 12, 2083-2086. (c) Bazinet, P.; Yap, G. P. A.; Richeson, D. S. J.
Am. Chem. Soc. 2003, 125, 13314-13315.
(13) (a) Scarborough, C. C.; Grady, M. J. W.; Guzei, I. A.; Gandhi, B.
A.; Bunel, E. E.; Stahl, S. S. Angew. Chem., Int. Ed. 2005, 44, 5269-
5272. (b) Scarborough, C. C.; Popp, B. V.; Guzei, I. A.; Stahl, S. S. J.
Organomet. Chem. 2005, 690, 6143-6155.
(14) (a) Arduengo, A. J., III; Krafczyk, R.; Schmutzler, R.; Craig, H.
A.; Goerlich, J. R.; Marshall, W. J.; Unverzagt, M. Tetrahedron 1999, 55,
14523-14534. (b) Delaude, L.; Szypa, M.; Demonceau, A.; Noels, A. F.
AdV. Synth. Catal. 2002, 344, 749-756.
(15) (a) Hahn, F. E.; Paas, M.; Le Van, D.; Lu¨gger, T. Angew. Chem.,
Int. Ed. 2003, 42, 5243-5246. (b) Hahn, F. E.; Paas, M.; Fro¨hlich, R.
Chem.-Eur. J. 2005, 11, 5080-5085. (c) Hahn, F. E.; Le Van, D.; Paas,
M.; Fro¨hlich, R. Dalton Trans. 2006, 860-864.
(16) (a) Bon, R. S.; Hong, C.; Bouma, M. J.; Schmitz, R. F.; de Kanter,
F. J. J.; Lutz, M.; Spek, A. L.; Orru, R. V. A. Org. Lett. 2003, 5, 3759-
3762. (b) Bon, R. S.; van Vliet, B.; Sprenkels, N. E.; Schmitz, R. F.; de
Kanter, F. J. J.; Stevens, C. V.; Swart, M.; Bickelhaupt, F. M.; Groen, M.
B.; Orru, R. V. A. J. Org. Chem. 2005, 70, 3542-3553.
Imidazolinium salts 23 and 24 seemed useful to investigate
since it is known that free NHCs are stabilized toward
dimerization by one or two bulky N-substituents. Application
of ferrocene carboxaldehyde 15 as the aldehyde component in
our MCR gives easy access to 4-ferrocenyl-substituted 2-imi-
dazoline 27, and subsequent alkylation with MeI affords the
corresponding imidazolinium salt 28 (entry 4) as an interesting
NHC precursor. Such NHC ligands with ferrocenyl substituents
in the carbon backbone are not yet studied, although NHCs and
NHC complexes containing (remote) ferrocenyl substituents at

Multicomponent Synthesis of N-Heterocyclic Carbene Complexes
Organometallics, Vol. 26, No. 15, 2007 3641
Table 1. Synthesis of Imidazol(in)ium Salts
b
c
d
a Isolated yields are reported. Conditions: Na2SO4, CH2Cl2, rt, 18 h, see also ref 16. Conditions: R-X, CH2Cl2, rt, 18 h. Conditions: R-X, DMF, rt,
e
f
18 h. Conditions: MeOH, rt, 18 h. Conditions: 8 equiv of MeI, CH2Cl2, 100 °C (microwave), 20 min. Mes ) 2,4,6-trimethylphenyl; PMB ) p-methoxybenzyl;
Fc ) ferrocenyl; PNP ) p-nitrophenyl.
the nitrogens have been reported.17 Recently, even the generation
of a metallocene-fused imidazol-2-ylidene and its mercury
complex was reported.18 An elegant application of NHCs with
redox-active ferrocenyl groups in an easily recyclable olefin
metathesis catalyst has been described by Plenio.6 In addition,
also the imidazole 3316 was used as NHC precursor in order to
compare unsymmetrically substituted imidazolidin-2-ylidenes
with their unsaturated analogues. Methylation of imidazole 33
was successful using microwave heating and an excess of MeI
and gave the corresponding salt 34 in good yield (entry 7). The
imidazol(in)ium salts were all isolated as stable but somewhat
hygroscopic solids.
Deprotonation of 23 with NaH followed by refluxing with
[Rh(cod)Cl]2 in THF provided the stable, crystalline NHC
complex 35 in 52% yield (Table 2, entry 1). Replacement of
the chloride on rhodium by the iodide that was present in 23
was confirmed by mass spectroscopy and X-ray crystallography
(Figure 2). To ensure complete substitution of chloride by iodide,
excess KI was added to the reaction mixture. Although
deprotonation of imidazolinium salts is usually faster with KOt-
Bu than with NaH, tert-butanol reacts with the resulting carbenes
to form their corresponding alcohol adducts, which can be
liberated again at elevated temperatures. Instead, a one-pot
(17) (a) Bildstein, B.; Malaun, M.; Kopacka, H.; Ongania, K.-H.; Wurst,
K. J. Organomet. Chem. 1998, 552, 45-61. (b) Bildstein, B.; Malaun, M.;
Hopacka, H.; Wurst, K.; Mitterbo¨ck, M.; Ongania, K.-H.; Opromolla, G.;
Zanello, P. Organometallics 1999, 18, 4325-4336. (c) Bolm, C.; Kessel-
gruber, M.; Raabe, G. Organometallics 2002, 21, 707-710. (d) Seo, H.;
Park, H.; Kim, B. Y.; Lee, J. H.; Son, S. U.; Chung, Y. K. Organometallics
2003, 22, 618-620.
(18) (a) Arduengo, A. J., III; Tapu, D.; Marshall, W. J. Angew. Chem.,
Int. Ed. 2005, 44, 7240-7244. (b) Arduengo, A. J., III; Tapu, D.; Marshall,
W. J. J. Am. Chem. Soc. 2005, 127, 16400-16401.

3642 Organometallics, Vol. 26, No. 15, 2007
Bon et al.
Table 2. Synthesis of Rh- and Ir-NHC Complexesa
entry
compound
method
yield
ratiob
1
2
3
4
5
6
7
8
35
35
36
36
37
37
38
38
a
b
a
b
a
b
a
b
52%
82%
55%
63%
51%
63%
51%
49%c
89:11
78:22
52:48
57:43
Figure 3. Displacement ellipsoid plot of 38a, the major, least polar
isomer of 38, drawn at the 50% probability level. Hydrogen atoms
are omitted for clarity. Selected bond lengths [Å], angles [deg],
and torsion angles [deg]: Ir1-I1 2.67288(19), Ir1-C1 2.023(2),
N1-C1 1.354(3), N2-C1 1.343(3); I1-Ir1-C1 90.11(6), Ir1-
C1-N1 121.82(15), Ir1-C1-N2 129.67(16), N1-C1-N2 108.48-
(19); I1-Ir1-C1-N1 89.20(17).
a Reagents and conditions: (a) (1) NaH, THF, rt, 18 h; (2) [Rh(cod)Cl]2,
KI (xs), reflux, 20 h; (b) KOtBu, [Rh(cod)Cl]2, KI, rt, 18 h. Isolated yields
b
c
and ratios are reported. Ratios refer to relative amounts of rotamers. This
yield could be improved by performing the reaction in refluxing THF: 57%
(67:33).
Figure 4. Displacement ellipsoid plot of 38b, the minor, most polar
isomer of 38, drawn at the 50% probability level. Hydrogen atoms
are omitted for clarity. Selected bond lengths [Å], angles [deg],
and torsion angles [deg]: Ir1-I1 2.6716(2), Ir1-C1 2.030(3), N1-
C1 1.344(3), N2-C1 1.351(3); I1-Ir1-C1 92.09(7), Ir1-C1-N1
121.34(18), Ir1-C1-N2 129.94(19), N1-C1-N2 108.2(2); I1-
Ir1-C1-N1 86.9(2).
Figure 2. Displacement ellipsoid plot of 35 drawn at the 50%
probability level. Hydrogen atoms are omitted for clarity. Selected
bond lengths [Å], angles [deg], and torsion angles [deg]: I1-Rh1
2.70624(17), Rh1-C1 2.0197(14), N1-C1 1.3481(18), N2-C1
1.3576(19); I1-Rh1-C1 86.10(4), Rh1-C1-N1 120.53(10),
Rh1-C1-N2 131.58(10), N1-C1-N2 107.88(12); I1-Rh1-C1-
N1-85.36(11).
separated using flash column chromatography.20 Ultimate proof
for the existence of the two rotational isomers was provided by
X-ray crystal structure analysis of the two products. In the major,
least polar fraction of 38, the carboxylic ester and the iodide
are on opposite sides of the NHC plane (Figure 3), while in the
minor, most polar fraction, they are on the same side (Figure
4).
Several methods exist to circumvent halogen exchange during
the formation of TM-NHC complexes. For example, an
azolium salt containing a noncoordinating anion can be used
as precursor.21 Imidazolinium hexafluorophosphate 39 can be
obtained in nearly quantitative yield from reaction of imidazo-
linium iodide 30 with AgPF6 (Scheme 3). This reaction is driven
by the precipitation of AgI from the DCM solution. Deproto-
nation of 39 and in situ complexation of the resulting carbene
reaction between 23, KOtBu, KI, and [Rh(cod)Cl]2 at room
temperature results in deprotonation of 23 followed by trapping
of the in situ-generated NHC, giving rhodium complex 35 in
82% yield (entry 2). Apparently, halogen exchange already takes
place at room temperature.
Both the two-step and the one-step method were used for
the synthesis of several rhodium and iridium complexes. The
NHC complexes 35-38 were isolated as stable, crystalline
solids. In general, the one-step deprotonation and complexation
(method b) gives higher yields (entries 1-6). The yield of Ir-
NHC complex 38 could be enhanced by performing the reaction
in refluxing THF (entry 8). Also at iridium, halogen exchange
already takes place at room temperature.
The NMR spectra of 37 and 38 show double sets of signals,
which are caused by the formation of rotamers. Rotation of the
carbene ligand around the TM-NHC axis is hindered for steric
reasons. High-temperature NMR experiments have shown that
this rotation does not occur once the complex has formed. In
the case of iridium complex 38, the rotational isomers could be
(19) Small differences in ratios depicted in Table 2 may be attributed to
small losses during chromatographic purification.
(20) Heating a solution of a single rotamer of 38 in toluene-d8 at 150 °C
(microwave) for 30 min does not provide a mixture of rotamers. At
200 °C, the product decomposes completely.
(21) Baker, M. V.; Brayshaw, S. K.; Skelton, B. W.; White, A. H. Inorg.
Chim. Acta 2004, 357, 2841-2849.

Multicomponent Synthesis of N-Heterocyclic Carbene Complexes
Organometallics, Vol. 26, No. 15, 2007 3643
Table 3. Synthesis of Rh-NHC Complexes
Scheme 3. Multicomponent Approach toward NHC
Complexes
gave chloro complex 40 in high yield as a mixture of rotamers.
When the same reaction sequence was applied to imidazolinium
iodide 23, an inseparable mixture of chloro complex 42 and
bis(carbene) complex Rh(cod)(NHC)2‚PF6 was isolated. Con-
sequently, complex 42 was synthesized from imidazolinium
tosylate 41, which was obtained in quantitative yield by
alkylation of imidazoline 22 with methyl tosylate. In this case,
the contaminating bis(carbene) complex, as its tosylate salt, can
be easily removed by washing with water.
Rhodium (and iridium)-NHC complexes are being increas-
ingly applied as catalysts for, among others, (asymmetric)
hydrosilylations22 and cycloaddition reactions.23 Furthermore,
an established method for determining the ligand properties of
NHCs involves studying Rh-NHC complexes.24 In order to
compare our NHCs, we decided to synthesize a broader range
of unsymmetrically substituted NHC complexes of rhodium
(Table 3). Our one-step deprotonation/complexation procedure
proved compatible with all imidazol(in)ium salts from Table 1
and provided complexes 43-47 in reasonable to high yields.
Again, chiral NHCs gave rise to mixtures of rotamers (entries
2-4). The major isomers of 44 and 46 could be obtained as
pure compounds easily by slow crystallization. Complexes 44,
46, and 47 were studied using X-ray crystal structure analysis.
Interestingly, crystals of the major isomer of complex 44
undergo a solid-solid phase transition upon cooling. The high-
temperature phase 44-I crystallizes in the centrosymmetric space
group P21/n with one independent molecule in the asymmetric
unit (Figure 5). Close to the isopropyl group there is a small
void. The low-temperature phase 44-II crystallizes in the
noncentrosymmetric space group P21, which is a subgroup of
P21/n (Figure 6). In the P21 phase there are two independent
molecules in the asymmetric unit, which differ mainly in the
conformation of the isopropyl group. Additionally, due to the
phase transition, there are significant changes of intermolecular
distances, which make the packing motif of 44-II incompatible
with P21/n. Over a wide temperature range (110-250 K) both
phases are present. The different molecular structures show only
a Isolated yields and ratios are reported. Ratios refer to relative amounts
of rotamers. Fc ) ferrocenyl.
Figure 5. Displacement ellipsoid plot of two symmetry-related
molecules in the high-temperature phase 44-I of the major isomer
of 44 (200 K), drawn at the 50% probability level. Hydrogen atoms
are omitted for clarity. Selected bond lengths [Å], angles [deg],
and torsion angles [deg]: I1-Rh1 2.6748(3), Rh1-C1 2.023(3),
N1-C1 1.351(3), N2-C1 1.342(3); I1-Rh1-C1 88.72(7), Rh1-
C1-N1 125.12(18), Rh1-C1-N2 126.67(19), N1-C1-N2 108.2-
(2); I1-Rh1-C1-N1 85.5(2), N2-C3-C23-C24-56.2(4), N2-
C3-C23-C25 176.3(3), N2-C26-C27-C28 157.8(3), C29-
C30-O1-C33 163.9(3). Symmetry operation i: 1-x, 1-y, 1-z.
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slight variations in the bond lengths and angles around the
carbene center.
The 13Ccarbene NMR chemical shifts (208-218 ppm) and Rh-
Ccarbene coupling constants (43-47 Hz) of our saturated NHC
transition metal complexes are in good agreement with values
reported for complexes of other saturated NHCs (Table 4, entries
1-11).15a,29 Furthermore, complex 47 shows a typical chemical
(28) (a) Karkhanis, D. W.; Field, L. Phosphorus Sulfur 1985, 22, 49-
57. (b) Marshall, C.; Ward, M. F.; Harrison, W. T. A. J. Organomet. Chem.
2005, 690, 3970-3975.

3644 Organometallics, Vol. 26, No. 15, 2007
Bon et al.
by the separation and X-ray crystal structure determination of
two rotamers of Ir complex 38. Also 4-(p-nitrophenyl)imida-
zoles, which are side products of reactions between amines,
aldehydes, and p-nitrobenzyl isocyanide 18, can be used in the
synthesis of NHC complexes. Data obtained from NMR
spectroscopic and X-ray crystallographic studies of the com-
plexes correspond well with earlier reported properties of NHCs.
Experimental Section
General Information. All reactions were carried out under an
inert atmosphere of argon or dry nitrogen (glovebox). Standard
syringe techniques were applied for transfer of air-sensitive reagents
and dry solvents. Melting points were measured using a Stuart
Scientific SMP3 melting point apparatus and are uncorrected.
Infrared (IR) spectra were obtained from CHCl3 films on NaCl
tablets (unless noted otherwise), using a Matteson Instruments 6030
Galaxy Series FT-IR spectrophotometer, and wavelengths (ν) are
Figure 6. Displacement ellipsoid plot of the two independent
molecules in the low-temperature phase 44-II of the major isomer
of 44 (110 K) drawn at the 50% probability level. Hydrogen atoms
are omitted for clarity. Selected bond lengths [Å], angles [deg],
and torsion angles [deg]. Values for the second molecule are given
in square brackets: I1-Rh1 2.6821(3) [2.6592(3)], Rh1-C11
2.020(3) [2.022(3)], N11-C11 1.346(4) [1.347(4)], N12-C11
1.337(4) [1.341(4)]; I1-Rh1-C11 89.01(9) [89.01(9)], Rh1-C11-
N11 125.5(2) [124.1(2)], Rh1-C11-N12 126.8(2) [126.7(2)],
N11-C11-N12 107.6(3) [109.0(3)]; I1-Rh1-C11-N11 84.4(3)
[-88.2(3)], N12-C13-C123-C124-53.8(4) [-71.7(4)], N12-
C13-C123-C125 179.3(3) [168.5(3)], N12-C126-C127-C128
159.2(3) [-165.9(3)], C129-C130-O1-C133 168.5(3) [-176.3-
(3)].
1
reported in cm-1. H and 13C nuclear magnetic resonance (NMR)
spectra were recorded on a Bruker Avance 400 (400.13 and 100.61
MHz, respectively), a Bruker Avance 250 (250.13 and 62.90 MHz,
respectively), or a Bruker Avance 200 (200.13 and 50.32 MHz,
respectively) with chemical shifts (δ) reported in ppm downfield
from tetramethylsilane. Peak assignment was also done with the
aid of gs-COSY, gs-HMQC, and gs-HMBC measurements. EIMS
and HRMS spectral data were recorded on a Finnigan Mat 900
spectrometer. ESIMS and HRMS spectra were recorded on a LTQ
XL Orbitrap spectrometer. Chromatographic purification refers to
flash chromatography using the indicated solvent (mixture) and
Baker 7024-02 silica gel (40 µm, 60 Å). Thin-layer chromatography
shift (180.0 ppm) for Rh complexes of imidazolin-2-ylidenes
A (entry 12).24,30 However, recent studies have shown that
chemical shifts of carbene carbons and the coupling constants
J(Rh-C) in 13C NMR, although usually specific for the type
of carbon, do not show systematic order for an estimation of
the σ donor strength.24
was performed using silica plates from Merck (Kieselgel 60 F254
)
on aluminum with fluorescence indicator. Compounds on TLC were
visualized by UV detection. THF and Et2O were dried and distilled
from sodium benzophenone ketyl prior to use. DCM was dried and
distilled from CaH2 prior to use. Petroleum ether (PE) with a boiling
range of 40-65 °C was distilled prior to use as eluent for
chromatography. Isocyanides 16, 17, and 18,13 [Rh(cod)Cl]2,31 and
[Ir(cod)Cl]232 as well as imidazolines 25,16a 29,16b 31,16b and 3316b
were prepared according to literature procedures. Other com-
mercially available reagents were used as purchased.
Microwave Experiments. Microwave-assisted reactions were
performed in a Discover (CEM Corporation) single-mode micro-
wave instrument producing controlled irradiation at 2450 MHz,
using standard sealed microwave glass vials. Reaction temperatures
were monitored with an IR sensor on the outside wall of the reaction
vials. Reaction times refer to hold times at the indicated temper-
atures, not to total irradiation times.
General Procedure I for the Synthesis of 2-Imidazolines.
Reactions were carried out at a concentration of 1 M amine, 1 M
aldehyde, and 0.5 M isocyanide in dry DCM, unless noted
otherwise. Na2SO4 and the aldehyde were added, at rt, to a stirred
solution of the amine. After the mixture was stirred for 2 h, the
isocyanide was added and the reaction mixture was stirred at rt for
an additional 18 h. The reaction mixture was filtered and concen-
trated in Vacuo. The crude product was purified by flash column
chromatography (PE/EtOAc/Et3N ) 2:1:0.01, gradient, unless stated
otherwise).
2-Imidazoline 22. According to General Procedure I, reaction
between tert-butylamine 10 (1.46 g, 20 mmol), p-formaldehyde 13
(600 mg, 20.0 mmol), and isocyanide 16 (2.0 g, 10.5 mmol),
followed by flash column chromatography, afforded 22 (2.58 g,
89%) as a light yellow solid. Crystallization from pentane/Et2O
affords white crystals. Mp: 95-96 °C. 1H NMR (250 MHz,
CDCl3): δ (ppm) 7.68 (d, J ) 6.9 Hz, 2H), 7.50-7.32 (m, 7H),
3.73 (s, 2H), 1.42 (s, 9H). 13C NMR (63 MHz, CDCl3): δ (ppm)
155.6 (CH), 150.6 (2×C), 140.3 (2×C), 128.7 (2×CH), 128.4
(2×CH), 124.2 (2×CH), 120.1 (2×CH), 79.1 (C), 55.6 (CH2), 53.1
The X-ray crystal structures of the NHC complexes all show
(slightly disturbed) square-planar coordination geometries, as
expected for 16e Rh and Ir complexes. The different Rh
complexes show only small differences in Rh-Ccarbene distances
(Table 5, entries 1-5). However, the saturated NHC complexes
show characteristic N1-C1-N2 angles around 108° (entries
1-4), which are 3-4° larger than that in complex 47 (entry 5),
bearing an unsaturated NHC. To accommodate the steric
requirements of tert-butyl substituents in complexes 35, 38a,
and 38b, their M-C1-N2 angles are about 10° larger than their
M-C1-N1 angles (entries 1, 6, 7). When the two nitrogen
substituents are sterically more alike, these angles are almost
equal (entries 2-5). Furthermore, the plane of the five-
membered carbene ring is almost perpendicular to the coordina-
tion plane of the complex (>85°).
Conclusion
We have successfully applied the multicomponent synthesis
of 2H-2-imidazolines in the preparation of a range of unsym-
metrically substituted imidazolidin-2-ylidene complexes under
mild conditions. Substituents at N-1, N-3, C-4, and C-5 can be
varied easily and independently by choosing the appropriate
amine, aldehyde, isocyanide, or halide in the two-step synthesis
of the NHC precursors. Deprotonation of the imidazolium salts
with KOtBu and direct complexation of the in situ-generated
NHCs at room temperature affords Rh- and Ir-NHC com-
plexes. The existence and stability of two hindered rotamers of
M(cod)X(NHC) complexes have been unambiguously proven
(29) Coleman, A. W.; Hitchcock, P. B.; Lappert, M. F.; Maskell, R. K.;
Mu¨ller, J. H. J. Organomet. Chem. 1985, 296, 173-196.
(30) Herrmann, W. A.; Ko¨cher, C.; Goossen, L. J.; Artus, G. R. J.
Chem.-Eur. J. 1996, 2, 1627-1636.

Multicomponent Synthesis of N-Heterocyclic Carbene Complexes
Organometallics, Vol. 26, No. 15, 2007 3645
Table 4. 13C NMR Chemical Shifts δ of M(cod)X(NHC) Complexes and Rh-Ccarbene Coupling Constants J of Rh(cod)X(NHC)
Complexesa
entry
complex
M
X
δ Ccarbene (ppm)
J(Rh-Ccarbene) (Hz)
1
2
3
4
5
6
7
8
35
36
Rh
Ir
Rh
Ir
I
I
I
I
213.3
209.0
213.3
208.8
209.2
213.8
214.0
217.8
217.8
216.4
213.7
180.0
43.5
37b
38a
38b
40b
42
43.8
Ir
I
Rh
Rh
Rh
Rh
Rh
Rh
Rh
Cl
Cl
Cl
I
I
I
45.9
45.6
46.2
45.6
44.7
44.5
48.8
43
9
44b
45b
46b
47
10
11
12
I
b
a Spectra were recorded in CDCl3. Chemical shifts and coupling constants of main isomer are reported.
Table 5. Selected Bond Distances (Å), Bond Angles (deg), and Torsion Angles (deg) for M(cod)I(NHC) Complexes
entry
complex
M
M-C1
N1-C1-N2
M-C1-N1
M-C1-N2
I-M-C1-N1
1
2
3
35
Rh
Rh
Rh
2.0197(14)
2.023(3)
2.020(3)
2.022(3)
2.0183(15)
2.028(2)
2.023(2)
2.030(3)
107.88(12)
108.2(2)
107.6(3)
120.53(10)
125.12(18)
125.5(2)
131.58(10)
126.67(19)
126.8(2)
-85.36(11)
85.5(2)
84.4(3)
-88.2(3)
88.22(13)
90.56(18)
89.20(17)
86.9(2)
44I
44-IIa
109.0(3)
124.1(2)
126.7(2)
4
5
6
7
46
47
38a
38b
Rh
Rh
Ir
108.57(13)
104.84(17)
108.48(19)
108.2(2)
125.59(11)
128.43(15)
121.82(15)
121.34(18)
125.78(10)
126.72(14)
129.69(16)
129.94(19)
Ir
a Values of both molecules in the asymmetric unit are reported.
Figure 8. Displacement ellipsoid plot of 47 drawn at the 50%
probability level. Hydrogen atoms are omitted for clarity. Selected
bond lengths [Å], angles [deg], and torsion angles [deg]: I1-Rh1
2.6652(2), Rh1-C1 2.028(2), N1-C1 1.348(3), N2-C1 1.360(3);
I1-Rh1-C1 87.58(6), Rh1-C1-N1 128.43(15), Rh1-C1-N2
126.72(14), N1-C1-N2 104.84(17); I1-Rh1-C1-N1 90.56(18).
Figure 7. Displacement ellipsoid plot of the major isomer of 46
drawn at the 50% probability level. Hydrogen atoms and disordered
solvent molecules are omitted for clarity. Selected bond lengths
[Å], angles [deg], and torsion angles [deg]: I1-Rh1 2.68360(17),
Rh1-C1 2.0183(15), N1-C1 1.3473(18), N2-C1 1.339(2); I1-
Rh1-C1 88.86(4), Rh1-C1-N1 125.59(11), Rh1-C1-N2 125.78-
(10), N1-C1-N2 108.57(13); I1-Rh1-C1-N1 88.22(13).
+
(m), 1307 (m), 1269 (m). HRMS (ESI): calcd for C20H23N2
(cation) 291.1856, found 276.1856.
(C), 28.9 (3×CH3). IR (neat): 2973 (s), 1674 (m), 1585 (s), 1450
(s), 1236 (s). HRMS (EI, 70 eV): calcd for C19H20N2 (M+)
276.1626, found 276.1617. Anal. Calcd for C19H20N2 (%): C 82.57,
H 7.29, N 10.14. Found: C 82.42, H 7.44, N 10.06.
2-Imidazolinium Iodide 24. According to General Procedure
II, alkylation of imidazoline 22 (770 mg, 2.8 mmol) with 2,4,6-
trimethylbenzyl chloride 21 (475 mg, 2.8 mmol) in DMF (15 mL),
followed by washing with pentane, afforded 24 (1.04 g, 84%) as a
white solid. 1H NMR (250 MHz, CDCl3): δ (ppm) 10.44 (s, 1H),
7.60 (d, J ) 7.5 Hz, 2H), 7.52 (d, J ) 7.6 Hz, 2H), 7.45-7.38 (m,
2H), 7.28-7.23 (m, 2H), 6.45 (s, 2H), 4.78 (s, 2H), 4.23 (s, 2H),
2.09 (s, 3H), 1.92 (s, 6H), 1.67 (s, 9H); 13C NMR (63 MHz,
CDCl3): δ (ppm) 158.6 (CH), 142.2 (2×C), 139.9 (2×C), 137.9
(C), 137.6 (2×C), 130.5 (2×CH), 129.1 (2×CH), 128.9 (2×CH),
126.3 (C), 124.0 (2×CH), 120.4 (2×CH), 74.5 (C), 58.0 (CH2),
57.8 (C), 44.6 (CH2), 28.3 (3×CH3), 20.7 (CH3), 19.7 (2×CH3).
IR (neat): 1626 (s), 1450 (m), 1217 (m). HRMS (ESI): calcd for
General Procedure II for the Synthesis of 2-Imidazolinium
Salts. Reactions were carried out at a concentration of 0.15-0.25
M of imidazoline in dry DCM, unless noted otherwise. The halide
was added to a stirred solution of the imidazoline, and the reaction
mixture was stirred at rt for 18 h. Then, the reaction mixture was
concentrated in Vacuo. The crude product was washed with pentane
or Et2O.
2-Imidazolinium Iodide 23. According to General Procedure
II, alkylation of imidazoline 22 (1.99 g, 7.2 mmol) with methyl
iodide 19 (1.08 g, 7.6 mmol) followed by washing with Et2O
afforded salt 23 as a white solid (2.95 g, 98%). 1H NMR (250 MHz,
CDCl3): δ (ppm) 7.75-7.70 (m, 4H), 7.57-7.43 (m, 4H), 4.26 (s,
2H), 2.91 (s, 3H), 1.69 (s, 9H). 13C NMR (50 MHz, CDCl3): δ
(ppm) 157.2 (CH), 141.7 (2×C), 140.2 (2×C), 131.1 (2×CH),
129.4 (2×CH), 124.3 (2×CH), 120.7 (2×CH), 74.8 (C), 57.9 (C),
56.6 (CH2), 30.7 (CH3), 28.2 (3×CH3). IR (neat): 1633 (s), 1450
+
C29H33N2 (cation) 409.2638, found 409.2631.
2-Imidazolinium Bromide 26. According to General Procedure
II, alkylation of imidazoline 25 (1.4 g, 3.7 mmol) with benzyl
bromide 20 (751 mg, 4.4 mmol), followed by washing with cold
Et2O, afforded 26 (1.9 g, 93%) as a white solid. H NMR (250
MHz, CDCl3): δ (ppm) 10.50 (s, 1H), 7.71 (d, J ) 7.5 Hz, 1H),
7.62 (d, J ) 7.6 Hz, 1H), 7.56-7.35 (m, 5H), 7.29-7.20 (m, 1H),
1

3646 Organometallics, Vol. 26, No. 15, 2007
Bon et al.
7.18-6.97 (m, 7H), 6.90-6.87 (m, 2H), 5.37 (d, J ) 14.4 Hz,
1H), 4.72 (d, J ) 14.4 Hz, 1H), 4.32 (d, J ) 5.3 Hz, 1H), 4.30 (d,
J ) 14.4 Hz, 1H) , 4.06 (d, J ) 14.4 Hz, 1H), 3.86 (s, 3H), 2.19-
2.13 (m, 1H), 0.77 (d, J ) 6.9 Hz, 3H), 0.60 (d, J ) 7.0 Hz, 3H).
13C NMR (63 MHz, CDCl3): δ (ppm) 160.9 (CH), 160.1 (C), 143.1
(C), 141.5 (C), 140.1 (C), 137.9 (C), 133.2 (C), 131.0 (CH), 130.6
(CH), 130.4 (2×CH), 129.1 (2×CH), 129.0 (CH), 128.5 (2×CH),
128.4 (CH), 127.9 (CH), 127.4 (CH), 125.3 (CH), 124.6 (C), 120.7
(CH), 120.2 (CH), 114.7 (2×CH), 79.2 (C), 74.2 (CH), 55.4 (CH3),
51.8 (CH2), 49.3 (CH2), 28.0 (CH), 19.3 (CH3), 18.6 (CH3). IR
(neat): 1626 (s), 1514 (m), 1452 (m), 1252 (m). HRMS (ESI):
calcd for C33H33N2O+ (cation) 473.2587, found 473.2581.
(C), 144.5 (C), 128.7 (2×CH), 124.4 (2×CH), 72.4 (CH), 63.4
(CH), 47.7 (CH), 32.6 (CH3), 27.4 (CH), 21.2 (CH3), 20.7 (CH3),-
16.7 (CH3),13.8 (CH3). IR (KBr): 1743 (s), 1633 (s), 1265 (m),
1230 (m), 1196 (m). HRMS (ESI): calcd for C16H24N3O2+ (cation)
290.1863, found 290.1863.
2-Imidazolium Iodide 34. Methyl iodide 19 (988 mg, 7.0 mmol)
was added to a solution of imidazole 33 (238 mg, 2.8 mmol) in
DCM (4 mL) in a microwave vessel. The reaction mixture was
heated in the microwave at 100 °C for 20 min. After cooling, the
reaction mixture was concentrated in Vacuo. After washing with
Et2O, salt 34 (253 mg, 70%) was isolated as a white solid. 1H NMR
(250 MHz, CDCl3): δ (ppm) 10.38 (s, 1H), 8.41 (d, J ) 8.6 Hz,
2H), 7.80 (d, J ) 8.6 Hz, 2H), 4.68-4.62 (m, 1H), 3.82 (s, 3H),
3.15-3.11 (m, 1H), 1.82 (d, J ) 6.7 Hz, 6H), 1.22 (d, J ) 7.1 Hz,
6H). 13C NMR (63 MHz, CDCl3): δ (ppm) 149.2 (C), 136.5 (C),
135.7 (CH), 132.9 (2×CH), 132.4 (C), 128.3 (C), 124.2 (2×CH),
51.1 (CH), 35.2 (CH3), 24.7 (CH), 24.0 (2×CH3), 22.1 (2×CH3).
2-Imidazoline 27. According to General Procedure I, reaction
between p-methoxybenzylamine 11 (685 mg, 5.0 mmol), ferrocen-
ecarboxaldehyde 15 (1.07 g, 5.0 mmol), and isocyanide 16 (500
mg, 2.6 mmol) in MeOH (15 mL), followed by flash column
chromatography, afforded 27 (936 mg 69%) as an orange solid.
1H NMR (250 MHz, CDCl3): δ (ppm) 7.67-7.63 (m, 1H), 7.54-
7.31 (m, 7H), 7.23-7.17 (m, 1H), 7.11-6.96 (m, 4H), 4.98 (d, J
) 14.5 Hz, 1H), 4.95 (s, 1H), 4.50 (d, J ) 14.5 Hz, 1H), 4.14 (br
s, 1H), 3.95 (br s, 1H), 3.92 (s, 3H), 3.90 (s, 5H), 3.77 (br s, 1H),
3.13 (d, J ) 1.1 Hz, 1H). 13C NMR (63 MHz, CDCl3): δ (ppm)
159.3 (C), 159.1 (CH), 149.6 (C), 145.7 (C), 141.4 (C), 139.9 (C),
129.2 (2×CH), 129.1 (C), 128.5 (CH), 128.0 (CH), 127.7 (CH),
126.7 (CH), 126.0 (CH), 124.4 (CH), 119.5 (CH), 119.1 (CH), 114.5
(2×CH), 85.0 (C), 84.1 (C), 69.4 (CH), 66.5 (5×CH), 67.8 (CH),
66.9 (CH), 66.3 (CH), 65.1 (CH), 55.4 (CH3), 50.2 (CH2). IR
(neat): 1599 (s), 1512 (s), 1448 (m), 1248 (s). HRMS (EI, 70 eV):
calcd for C33H28FeN2O (M+) 524.1551, found 524.1533.
+
IR (neat): 1522 (s), 1348 (s). HRMS (ESI): calcd for C16H22N3O2
(cation) 288.1707, found 288.1707.
General Procedure III for the Synthesis of M(cod)X(NHC)
Complexes. In a glovebox, NaH (12 mg, 0.5 mmol) was added to
a solution of imidazolinium halide (0.5 mmol) in THF (5-8 mL).
After stirring the reaction mixture at rt for 18 h, the reaction mixture
was filtered and the filtrate transferred to a Schlenk tube containing
[Rh(cod)Cl]2 or [Ir(cod)Cl]2 (0.23-0.24 mmol). THF (10 mL) was
added, and the reaction mixture was stirred at reflux for 18 h. After
cooling, the mixture was filtered through a pad of Celite, concen-
trated in Vacuo, and purified using flash column chromatography
(pentane/DCM ) 4:1, gradient).
2-Imidazolinium Iodide 28. According to General Procedure
II, alkylation of imidazoline 27 (380 mg, 0.73 mmol) with methyl
iodide 19 (109 mg, 0.77 mmol) followed by washing with pentane
General Procedure IV for the Synthesis of M(cod)X(NHC)
Complexes. Reactions were carried out at a concentration of 0.04
M of imdazol(in)ium salt in dry THF. A Schlenk tube was charged
with imidazol(in)ium salt (1 equiv), KOtBu (1 equiv), [Rh(cod)-
Cl]2 or [Ir(cod)Cl]2 (0.95 equiv), and KI (3 equiv). THF was added
and the reaction mixture was stirred at rt for 18 h. Then, the mixture
was filtered through a pad of Celite, concentrated in Vacuo, and
purified using flash column chromatography (pentane/DCM ) 4:1,
gradient).
Rh-NHC Complex 35. Method A. According to General
Procedure III, reaction between imidazolinium iodide 23 (209 mg,
0.5 mmol), NaH (12 mg, 0.5 mmol), [Rh(cod)Cl]2 (113 mg, 0.23
mmol), and KI (249 mg, 1.5 mmol), followed by flash column
chromatography, afforded 35 (150 mg, 52%) as an orange-yellow
solid.
Method B. According to General Procedure IV, reaction between
imidazolinium iodide 23 (209 mg, 0.5 mmol), KOtBu (56 mg, 0.5
mmol), [Rh(cod)Cl]2 (113 mg, 0.23 mmol), and KI (249 mg, 1.5
mmol), followed by flash column chromatography, afforded 35 (238
mg, 82%) as an orange-yellow solid. 1H NMR (250 MHz,
CDCl3): δ (ppm) 7.86-7.83 (m, 1H), 7.71-7.66 (m, 2H), 7.47-
7.23 (m, 5H), 5.22 (br s, 2H), 4.08 (d, J ) 10.8 Hz, 1H), 3.96 (d,
J ) 10.8 Hz, 1H), 3.65 (br s, 2H), 3.19 (s, 3H), 2.37-2.21 (m,
3H), 2.15-2.07 (m, 2H), 1.90 (s, 9H), 1.82-1.73 (m, 3H). 13C
NMR (63 MHz, CDCl3): δ (ppm) 213.3 (d, J ) 43.5 Hz, C), 145.7
(C), 145.1 (C), 140.5 (C), 139.4 (C), 129.5 (CH), 129.4 (CH), 129.0
(CH), 128.3 (CH), 125.0 (CH), 122.8 (CH), 120.3 (CH), 120.0 (CH),
95.2 (d, J ) 6.9 Hz, CH), 93.5 (d, J ) 6.7 Hz, CH), 74.2 (C), 74.0
(d, J ) 15.4 Hz, CH), 70.4 (d, J ) 14.0 Hz, CH), 59.7 (CH2), 56.6
(C), 35.3 (CH3), 33.9 (CH2), 30.9 (CH2), 30.2 (3×CH3), 30.2 (CH2),
27.9 (CH2). IR (neat): 1475 (s), 1433 (s). HRMS (EI, 70 eV): calcd
for C28H34IN2Rh (M+) 628.0822, found 628.0820. Crystals suitable
for X-ray crystal structure determination were obtained by the slow
diffusion of pentane into a saturated solution of 75 in DCM. Mp:
230-233 °C.
1
afforded salt 28 (481 mg, 99%) as a light brown solid. H NMR
(250 MHz, CDCl3): δ (ppm) 9.10 (s, 1H), 8.23-8.20 (m, 1H),
7.69 (d, J ) 8.6 Hz, 2H), 7.68-7.37 (m, 6H), 7.20-7.09 (m, 1H),
7.06 (d, J ) 8.6 Hz, 2H), 5.65 (s, 1H), 5.21 (d, J ) 13.6 Hz, 1H),
5.17 (d, J ) 13.8 Hz, 1H), 4.26-4.25 (m, 1H), 4.17-4.16 (m,
1H), 3.96-3.94 (m, 1H), 3.92 (s, 5H), 3.89 (s, 3H), 3.21-3.20
(m, 1H), 2.70 (s, 3H). 13C NMR (63 MHz, CDCl3): δ (ppm) 160.2
(C), 159.3 (CH), 141.4 (C), 141.2 (C), 140.9 (C), 138.3 (C), 131.2
(CH), 131.0 (2×CH), 130.8 (CH), 129.5 (CH), 127.7 (CH), 126.5
(CH), 126.0 (CH), 125.4 (C), 120.4 (CH), 120.3 (CH), 114.9
(2×CH), 80.0 (C), 78.3 (C), 72.3 (CH), 69.2 (5×CH), 68.5 (CH),
68.2 (CH), 68.1 (CH), 66.0 (CH), 55.4 (CH3) 50.3 (CH2), 31.3
(CH3). IR (neat): 1639 (s), 1514 (m), 1250 (s). HRMS (ESI): calcd
for C34H31FeN2O+ (cation) 539.1780, found 539.1772.
2-Imidazolinium Iodide 30. According to General Procedure
II, alkylation of imidazoline 29 (1.28 g, 4.9 mmol) with methyl
iodide 19 (734 mg, 5.17 mmol) followed by washing with pentane
afforded salt 30 (1.8 g, 93%) as a white solid. 1H NMR (400 MHz,
CDCl3): δ (ppm) 9.73 (s, 1H), 7.51-7.46 (m, 3H,), 7.37-7.36
(m, 2H), 4.80 (d, J ) 12.2 Hz, 1H), 4.01 (s, 3H), 3.94 (d, J ) 12.2
Hz, 1H), 3.43 (s, 3H), 1.58 (s, 9H). 13C NMR (101 MHz, CDCl3):
δ (ppm) 168.9 (C), 156.6 (CH), 134.0 (C), 130.1 (CH), 129.8
(2×CH), 126.4 (2×CH), 75.9 (C), 58.1 (C), 57.7 (CH2), 54.1 (CH3),
33.8 (CH3), 28.1 (3×CH3). IR (neat): 2974 (s), 1743 (s), 1633 (s),
+
1265 (s), 1230 (s), 1196 (s). HRMS (ESI): calcd for C16H23N2O2
(cation) 275.1754, found 275.1754.
2-Imidazolinium Iodide 32. According to General Procedure
II, alkylation of imidazoline 31 (500 mg, 1.8 mmol) with methyl
iodide 19 (284 mg, 2.0 mmol) followed by washing with Et2O
1
afforded salt 32 (656 mg, 86%) as a white solid. H NMR (250
MHz, DMSO-d6): δ (ppm) 8.77 (s, 1H), 8.34 (d, J ) 8.2 Hz, 2H),
7.73 (d, J ) 8.3 Hz, 2H), 5.34 (d, J ) 4.6 Hz, 1H), 4.26-4.11 (m,
1H), 3.64-3.53 (m, 1H), 2.94 (s, 3H), 2.60-2.39 (m, 1H), 1.43
(d, J ) 4.8 Hz, 3H), 1.27 (d, J ) 4.7 Hz, 3H), 0.92 (d, J ) 4.4 Hz,
6H). 13C NMR (63 MHz, DMSO-d6): δ (ppm) 156.3 (CH), 147.9
Ir-NHC Complex 36. Method A. According to General
Procedure III, reaction between imidazolinium iodide 23 (209 mg,
0.5 mmol), NaH (12 mg, 0.5 mmol), [Ir(cod)Cl]2 (154 mg, 0.23

Multicomponent Synthesis of N-Heterocyclic Carbene Complexes
Organometallics, Vol. 26, No. 15, 2007 3647
mmol), and KI (249 mg, 1.5 mmol), followed by flash column
chromatography, afforded 36 (182 mg, 55%) as an orange solid.
4.64 (m, 2H), 4.40 (d, J ) 11.3 Hz, 1H), 3.84 (s, 3H), 3.72 (d, J
) 11.3 Hz, 1H), 3.43 (s, 3H), 3.17-3.14 (m, 1H), 2.90-2.88 (m,
1H), 2.19-1.82 (m, 5H), 1.64 (s, 9H), 1.56-1.35 (m, 2H), 1.22-
1.20 (m, 1H). 13C NMR (63 MHz, CDCl3): δ (ppm) 208.8 (C),
171.2 (C), 137.7 (C), 129.1 (2×CH), 128.7 (CH), 126.7 (2×CH),
80.7 (CH), 79.9 (CH), 74.9 (C), 61.3 (CH2), 57.1 (C), 56.9 (CH),
54.7 (CH), 52.9 (CH3), 37.6 (CH3), 34.4 (CH2), 31.5 (CH2), 30.6
(CH2), 30.5 (3×CH3), 28.5 (CH2). IR (neat) 1738 (s), 1238 (m).
HRMS (EI, 70 eV) calcd for C24H34IIrN2O2 (M+) 702.1294, found
702.1289. Crystals suitable for X-ray crystal structure determination
were obtained by the slow diffusion of pentane into a saturated
solution of 38a in dichloromethane (DCM). Mp 177-179 °C.
38b: 1H NMR (250 MHz, CDCl3): δ (ppm) 7.38-7.30 (m, 3H),
7.16-7.13 (m, 2H), 4.70 (br s, 2H), 4.54 (d, J ) 11.1 Hz, 1H),
3.86 (s, 3H), 3.54 (d, J ) 11.1 Hz, 1H), 3.42 (s, 3H), 3.12-3.10
(m, 1H), 3.03-3.00 (m, 1H), 2.18-1.80 (m, 5H), 1.63 (s, 9H),
1.39-1.20 (m, 3H); 13C NMR (101 MHz, CDCl3): δ (ppm) 209.2
(C), 170.6 (C), 137.4 (C), 129.0 (2×CH), 128.6 (CH), 126.2
(2×CH), 80.9 (CH), 79.7 (CH), 75.6 (C), 60.9 (CH2), 56.9 (C),
56.0 (CH), 54.5 (CH), 52.9 (CH3), 37.8 (CH3), 34.1 (CH2), 31.11
(CH2), 31.06 (CH2), 30.6 (3×CH3), 28.9 (CH2); IR (neat) 1736
(s), 1217 (m); HRMS (EI, 70 eV) calcd for C24H34IIrN2O2 (M+)
702.1294, found 702.1276. Crystals suitable for X-ray crystal
structure determination were obtained by the slow diffusion of
pentane into a saturated solution of 38b in DCM. Mp 178-
180 °C.
Method B. According to General Procedure IV, reaction between
imidazolinium iodide 23 (209 mg, 0.5 mmol), KOtBu (56 mg, 0.5
mmol), [Ir(cod)Cl]2 (154 mg, 0.23 mmol), and KI (249 mg, 1.5
mmol), followed by flash column chromatography, afforded 36 (209
mg, 63%) as an orange solid, which could be recrystallized by the
slow diffusion of pentane into a saturated solution of the complex
1
in DCM. Mp: 236-238 °C (dec). H NMR (250 MHz, CDCl3):
δ (ppm) 7.88-7.85 (m, 1H), 7.72-7.67 (m, 2H), 7.49-7.29 (m,
5H), 4.83-4.72 (m, 2H), 4.13 (d, J ) 10.9 Hz, 1H), 4.04 (d, J )
10.9 Hz, 1H), 3.25-3.13 (m, 2H), 3.02 (s, 3H), 2.34-2.24 (m,
1H), 2.18-1.84 (m, 4H), 1.81 (s, 9H), 1.56-1.29 (m, 3H). 13C
NMR (101 MHz, CDCl3): δ (ppm) 209.0 (C), 145.7 (C), 145.1
(C), 140.5 (C), 139.6 (C), 129.53 (CH), 129.50 (CH), 129.0 (CH),
128.4 (CH), 124.8 (CH), 122.9 (CH), 120.9 (CH), 120.0 (CH), 80.5
(CH), 79.7 (CH), 74.4 (C), 60.1 (CH2), 56.94 (C), 56.93 (CH), 54.3
(CH), 35.0 (CH3), 34.4 (CH2), 31.5 (CH2), 30.8 (CH2), 30.6
(3×CH3), 28.6 (CH2). IR (neat) 1473 (s), 1448 (s), 1429 (s), 1304
(s). HRMS (EI, 70 eV) calcd for C28H34IIrN2 (M+) 718.1396, found
718.1370. Anal. Calcd for C28H34IIrN2 (%): C 46.86, H 4.77, N
3.90. Found: C 46.62, H 4.78, N 3.87.
Rh-NHC Complex 37. Method A. According to General
Procedure III, reaction between imidazolinium iodide 30 (201 mg,
0.5 mmol), NaH (12 mg, 0.5 mmol), [Rh(cod)Cl]2 (113 mg, 0.23
mmol), and KI (249 mg, 1.5 mmol), followed by flash column
chromatography, afforded 37 (143 mg, 51%) as a 89:11 mixture
of rotamers as an orange-yellow solid.
2-Imidazolinium Hexafluorophosphate 39. AgPF6 (384 mg,
1.52 mmol) was added to a solution of imidazolinium iodide 30
(612 mg, 1.52 mmol) in DCM (12 mL). While stirring the reaction
mixture at rt, a yellow precipitate was formed. After 15 min, the
suspension was filtered and the filtrate concentrated in Vacuo and
washed with pentane to afford salt 39 as a white solid (611 mg,
96%). 1H NMR (250 MHz, CDCl3): δ (ppm) 8.75 (s, 1H), 7.51-
7.46 (m, 3H), 7.29-7.27 (m, 2H), 4.83 (d, J ) 12.2 Hz, 1H), 4.02
(s, 3H), 3.96 (d, J ) 12.2 Hz, 1H), 3.29 (s, 3H), 1.50 (s, 9H). 13C
NMR (101 MHz, CDCl3): δ (ppm) 168.9 (C), 156.9 (CH),
134.0 (C), 130.1 (CH), 129.9 (2×CH), 126.1 (2×CH), 75.9 (C),
57.83 (C), 57.79 (CH2), 54.0 (CH3), 33.1 (CH3), 27.5 (3×CH3).
IR (neat) 1747 (s), 1641 (s), 1267 (m), 839 (s). HRMS (EI, 70
Method B. According to General Procedure IV, reaction between
imidazolinium iodide 30 (300 mg, 0.75 mmol), KOtBu (84 mg,
0.75 mmol), [Rh(cod)Cl]2 (176 mg, 0.35 mmol), and KI (374 mg,
2.25 mmol), followed by flash column chromatography, afforded
37 (271 mg, 63%) as a 78:22 mixture of rotamers as a yellow solid.
Main isomer: 1H NMR (250 MHz, CDCl3): δ (ppm) 7.47-7.33
(m, 5H), 5.22-5.19 (m, 2H), 4.41 (d, J ) 11.3 Hz, 1H), 3.92 (s,
3H), 3.78 (d, J ) 11.3 Hz, 1H), 3.72-3.60 (m, 1H), 3.69 (s, 3H),
3.48-3.41 (m, 1H), 2.55-2.37 (m, 2H), 2.29-2.04 (m, 3H), 1.94-
1.88 (m, 1H), 1.82 (s, 9H), 1.77-1.64 (m, 2H). 13C NMR (63 MHz,
CDCl3): δ (ppm) 213.3 (d, J ) 43.8 Hz, C), 171.7 (C), 137.8 (C),
129.1 (2×CH), 128.6 (CH), 126.7 (2×CH), 95.3 (d, J ) 7.0 Hz,
CH), 93.4 (d, J ) 6.7 Hz, CH), 74.9 (C), 73.9 (d, J ) 15.3 Hz,
CH), 70.8 (d, J ) 14.0 Hz, CH), 60.9 (CH2), 56.8 (C), 52.8 (CH3),
37.8 (CH3), 33.9 (CH2), 30.9 (CH2), 30.1 (3×CH3), 30.0 (CH2),
27.9 (CH2). IR (neat): 1739 (s), 1475 (m), 1433 (s), 1221 (s).
HRMS (EI, 70 eV): calcd for C24H34IN2O2Rh (M+) 612.0720,
found 612.0739. Anal. Calcd for C24H34IN2O2Rh (%): C 47.07, H
5.60, N 4.57. Found: C 46.46, H 5.45, N 4.63.
Ir-NHC Complex 38. Method A. According to General
Procedure III, reaction between imidazolinium iodide 30 (201 mg,
0.5 mmol), NaH (12 mg, 0.5 mmol), [Ir(cod)Cl]2 (154 mg, 0.23
mmol), and KI (249 mg, 1.5 mmol), followed by flash column
chromatography, afforded two rotamers of 38 (least polar fraction
38a: 88 mg, 27%; most polar fraction 38b: 81 mg, 25%) as orange
solids.
Method B. According to General Procedure IV, reaction between
imidazolinium iodide 30 (201 mg, 0.5 mmol), KOtBu (56 mg, 0.5
mmol), [Ir(cod)Cl]2 (154 mg, 0.23 mmol), and KI (249 mg, 1.5
mmol), followed by flash column chromatography, afforded two
rotamers of 38 (least polar fraction 38a: 91 mg, 28%; most polar
fraction 38b: 67 mg, 21%) as orange solids.
+
eV): calcd for C16H23N2O2 (cation) 275.1754, found 275.1745.
Rh-NHC Complex 40. A Schlenk tube was charged with
imidazolinium salt 39 (210 mg, 0.5 mmol), KOtBu (56 mg, 0.5
mmol), [Rh(cod)Cl]2 (106 mg, 0.215 mmol), and tetraethylammo-
nium chloride (248 mg, 1.5 mmol). THF (10 mL) was added, and
the reaction mixture was stirred at rt for 18 h. Then, the mixture
was filtered through a pad of Celite, concentrated in Vacuo, and
purified using flash column chromatography (pentane/DCM ) 1:2,
DCM, DCM/EtOAc ) 8:1) to afford 40 (175 mg, 79%) as a 78:22
mixture of rotamers as a yellow-orange solid. Main isomer: 1H
NMR (250 MHz, CDCl3): δ (ppm) 7.36-7.19 (m, 5H), 4.89 (br
s, 2H), 4.29 (d, J ) 11.3 Hz, 1H), 3.82 (s, 3H), 3.74 (s, 3H), 3.63
(d, J ) 11.3 Hz, 1H), 3.49-3.38 (m, 1H), 3.23-3.17 (m, 1H),
2.47-2.13 (m, 4H), 1.94-1.83 (m, 2H), 1.74 (s, 9H), 1.73-1.63
(m, 2H). 13C NMR (63 MHz, CDCl3): δ (ppm) 213.8 (d, J ) 45.9
Hz, C), 171.5 (C), 137.7 (C), 129.1 (2×CH), 128.6 (CH), 126.3
(2×CH), 97.4 (d, J ) 7.0 Hz, CH), 95.1 (d, J ) 6.2 Hz, CH), 75.0
(C), 70.9 (d, J ) 15.5 Hz, CH), 67.3 (d, J ) 14.5 Hz, CH), 60.6
(CH2), 56.8 (C), 52.8 (CH3), 37.3 (CH3), 33.5 (CH2), 31.3 (CH2),
30.3 (3×CH3), 29.4 (CH2), 27.9 (CH2). IR (neat): 1739 (s), 1475
(m), 1435 (m), 1223 (m). HRMS (EI, 70 eV): calcd for C24H34-
ClN2O2Rh (M+) 520.1364, found 520.1375.
Method C. According to General Procedure IV, reaction between
imidazolinium iodide 30 (201 mg, 0.5 mmol), KOtBu (56 mg, 0.5
mmol), [Ir(cod)Cl]2 (154 mg, 0.23 mmol), and KI (249 mg, 1.5
mmol) in refluxing THF, followed by flash column chromatography,
afforded two rotamers of 38 (least polar fraction 38a: 122 mg,
38%; most polar fraction 38b: 60 mg, 19%) as orange solids. 38a:
1H NMR (250 MHz, CDCl3): δ (ppm) 7.39-7.27 (m, 5H), 4.70-
2-Imidazolinium Tosylate 41. According to General Procedure
II, alkylation of imidazoline 22 (203 mg, 0.74 mmol) with methyl
tosylate (141 mg, 0.74 mmol), followed by washing with pentane,
1
afforded salt 41 (336 mg, 99%) as a white solid. H NMR (250
MHz, CDCl3): δ (ppm) 9.70 (s, 1H), 7.75 (d, J ) 8.1 Hz, 2H),
7.64 (d, J ) 7.4 Hz, 2H), 7.54-7.33 (m, 6H), 7.06 (d, J ) 8.0 Hz,

3648 Organometallics, Vol. 26, No. 15, 2007
Bon et al.
2H), 4.17 (s, 2H), 2.75 (s, 3H), 2.26 (s, 3H), 1.54 (s, 9H). 13C NMR
(63 MHz, CDCl3): δ (ppm) 158.8 (CH), 143.9 (C), 141.9 (2×C),
140.2 (2×C), 138.9 (C), 131.0 (2×CH), 129.4 (2×CH), 128.5
(2×CH), 126.0 (2×CH), 124.1 (2×CH), 120.7 (2×CH), 74.8 (C),
57.6 (C), 56.7 (CH2), 30.5 (CH3), 28.0 (3×CH3), 21.2 (CH3). IR
140.7 (C), 138.6 (C), 135.7 (2×C), 130.5 (2×CH), 129.8 (2×CH),
129.5 (CH), 128.5 (CH), 127.9 (CH), 127.2 (2×CH), 127.1 (CH),
126.9 (CH), 126.5 (CH), 125.4 (CH), 120.2 (CH), 119.1 (CH), 113.8
(2×CH), 97.5 (d, J ) 6.4 Hz, 2×CH), 79.3 (C), 73.6 (CH), 73.1
(d, J ) 14.2 Hz, CH), 71.9 (d, J ) 14.1 Hz, CH), 55.3 (CH3), 53.5
(CH2), 52.8 (CH2), 32.5 (CH2), 32.1 (CH2), 29.39 (CH2), 29.36
(CH2), 28.7 (CH), 19.9 (CH3), 18.0 (CH3). IR (neat): 1512 (s),
1450 (s), 1248 (s). HRMS (EI, 70 eV): calcd for C33H32N2ORh
(M - (I + cod)+) 575.1570, found 575.1564 (the molecular ion is
hardly detectable in the mass spectrometer). Crystals suitable for
X-ray crystal structure determination were obtained by the slow
diffusion of pentane into a saturated solution of 44 in DCM. Mp:
186-187 °C.
+
(neat): 1475 (s), 1433 (s). HRMS (EI, 70 eV): calcd for C20H23N2
(cation) 291.1856, found 291.1849.
Rh-NHC Complex 42. A Schlenk tube was charged with
imidazolinium salt 41 (231 mg, 0.5 mmol), KOtBu (56 mg, 0.5
mmol), [Rh(cod)Cl]2 (123 mg, 0.25 mmol), and LiCl (64 mg, 1.5
mmol). THF (10 mL) was added and the reaction mixture was
stirred at rt for 18 h. Then, the mixture was filtered through a pad
of Celite and concentrated in Vacuo. The residue was taken into
DCM, washed with water, dried with Na2SO4, concentrated in
Vacuo, and purified using flash column chromatography (DCM,
DCM/EtOAc ) 20:1, gradient) to afford 40 (75 mg, 27%) as a
yellow-orange solid. 1H NMR (400 MHz, CDCl3): δ (ppm) 7.68-
7.63 (m, 3H), 7.42-7.29 (m, 4H), 7.20 (d, J ) 7.4 Hz, 1H), 4.99-
4.94 (m, 2H), 4.01 (d, J ) 10.8 Hz, 1H), 3.89 (d, J ) 10.8 Hz,
1H), 3.44-3.40 (m, 2H), 3.28 (s, 3H), 2.45-2.33 (m, 3H), 2.23-
2.20 (m, 1H), 1.97-1.91 (m, 2H), 1.88 (s, 9H), 1.86-1.75 (m,
2H). 13C NMR (63 MHz, CDCl3): δ (ppm) 214.0 (d, J ) 45.6 Hz,
C), 145.5 (C), 145.0 (C), 140.5 (C), 139.4 (C), 129.47 (CH), 129.45
(CH), 129.0 (CH), 128.3 (CH), 124.6 (CH), 122.8 (CH), 120.3 (CH),
120.0 (CH), 97.4 (d, J ) 7.2 Hz, CH), 94.9 (d, J ) 7.0 Hz, CH),
74.4 (C), 70.7 (d, J ) 15.7 Hz, CH), 67.0 (d, J ) 14.5 Hz, CH),
59.6 (CH2), 56.7 (C), 34.6 (CH3), 33.5 (CH2), 31.5 (CH2), 30.4
(3×CH3), 29.4 (CH2),28.0 (CH2). IR (neat): 1473 (s), 1450 (s),
1435 (s). HRMS (EI, 70 eV): calcd for C28H34ClN2Rh (M+)
536.1466, found 536.1473.
Rh-NHC Complex 45. According to General Procedure IV,
reaction between imidazolinium iodide 28 (166 mg, 0.25 mmol),
KOtBu (28 mg, 0.25 mmol), [Rh(cod)Cl]2 (59 mg, 0.12 mmol),
and KI (125 mg, 0.75 mmol), followed by flash column chroma-
tography, afforded 45 (173 mg, 82%) as a 58:42 mixture of rotamers
as an orange-yellow solid. 1H NMR (400 MHz, CDCl3): δ (ppm)
7.87-7.85 (m, 1HB), 7.67-7.62 (m, 1HA+2HB), 7.55-7.34 (m,
7HA+4HB), 7.26-7.21 (m, 1HB), 7.11-7.06 (m, 1HB), 6.99-6.92
(m, 3HA+1HB), 6.91-6.88 (m, 1HA+1HB), 6.81 (d, J ) 7.6 Hz,
1HB), 6.54 (d, J ) 16.9 Hz, 1HA), 5.90 (d, J ) 15.3 Hz, 1HB),
5.81 (d, J ) 17.0 Hz, 1HA), 5.32 (s, 1HA), 5.31-5.26 (m, 1HB),
5.27 (d, J ) 15.2 Hz, 1HB), 5.23-5.13 (m, 2HA+1HB), 5.09 (s,
1HB), 4.74 (br s, 1HA), 4.14 (br s, 1HA), 3.94 (br s, 1HB), 3.83 (s,
3HA), 3.81 (s, 3HB), 3.76 (s, 5HA), 3.77-3.75 (m, 1HB), 3.75-
3.72 (m, 1HA), 3.68-3.59 (m, 2HA+1HB), 3.60 (s, 5HB), 3.58-
3.50 (m, 2HB), 3.03 (br s, 1HA), 3.01 (br s, 1HB), 2.94 (s, 3HA),
2.93 (s, 3HB), 2.37-2.22 (m, 2HA+1HB), 2.21-2.12 (m, 3HB),
2.06-1.92 (m, 1HA+1HB), 1.87-1.74 (m, 4HA+2HB), 1.56-1.47
(m, 1HB). 13C NMR (101 MHz, CDCl3): δ (ppm) 216.6 (d, J )
45.0 Hz, CB), 216.4 (d, J ) 44.7 Hz, CA), 158.8 (CB), 158.5 (CA),
147.0 (CA), 145.2 (CB), 141.9 (CB), 141.0 (CB), 140.9 (CA), 140.7
(CB), 140.3 (CA), 139.9 (CA), 131.8 (CA+CB), 129.8 (CHB), 129.6
(CHA), 129.5 (CHB), 129.2 (2×CHB), 129.0 (CHA), 128.70 (CHB),
128.66 (CHA), 128.2 (CHA), 127.2 (CHA), 127.0 (CHB), 126.9
(2×CHA), 125.9 (CHB), 124.9 (CHB), 122.2 (CHA), 120.3 (CHA),
120.1 (CHB), 119.9 (CHB), 119.3 (CHA), 114.3 (2×CHA), 113.6
(2×CHB), 97.4 (d, J ) 6.2 Hz, CHB), 97.3 (d, J ) 6.6 Hz, CHB),
97.2 (d, J ) 6.5 Hz, CHA), 96.8 (d, J ) 6.5 Hz, CHA), 84.4 (CA),
82.2 (CA), 81.4 (CB), 80.4 (CB), 72.7 (d, J ) 14.2 Hz, CHA), 72.3
(d, J ) 14.4 Hz, CHB), 71.9 (d, J ) 13.9 Hz, CHA), 71.7 (d, J )
14.2 Hz, CHB), 70.7 (CHA), 70.2 (CHB), 68.78 (CHB), 68.75 (CHA),
68.6 (5×CHB), 68.5 (5×CHA), 68.4 (CHB), 67.9 (CHA), 67.6 (CHA),
Rh-NHC Complex 43. A Schlenk tube was charged with
imidazolinium chloride 24 (222 mg, 0.5 mmol), KOtBu (56 mg,
0.5 mmol), and [Rh(cod)Cl]2 (118 mg, 0.24 mmol). THF (10 mL)
was added, and the reaction mixture was stirred at rt for 18 h. Then,
the mixture was filtered through a pad of Celite, concentrated in
Vacuo, and purified using flash column chromatography (DCM,
DCM/EtOAc ) 3:1) to afford 43 (170 mg, 54%) as a yellow-orange
solid. 1H NMR (250 MHz, CDCl3): δ (ppm) 7.55 (d, J ) 7.8 Hz,
1H), 7.41 (d, J ) 7.4 Hz, 1H), 7.35-7.17 (m, 5H), 7.10-7.02 (m,
1H), 6.32 (br s, 1H), 6.19 (d, J ) 14.3 Hz, 1H), 6.09 (br s, 1H),
5.31 (d, J ) 14.2 Hz, 1H), 5.12-5.02 (m, 2H), 3.91 (d, J ) 10.7
Hz, 1H), 3.78-3.73 (m, 2H), 3.77 (d, J ) 10.7 Hz, 1H), 2.54-
2.19 (m, 5H), 1.98 (s, 6H), 1.96 (s, 9H), 1.96 (br s, 3H), 1.70-
1.64 (m, 3H). 13C NMR (101 MHz, CDCl3): δ (ppm) 217.8 (d, J
) 46.2 Hz, C), 145.1 (C), 144.5 (C), 140.2 (C), 139.7 (C), 139.0
(C), 137.1 (C), 136.7 (C), 128.7 (CH), 128.4 (CH), 128.1 (C), 128.0
(CH), 127.5 (CH), 124.5 (CH), 123.7 (CH), 122.4 (CH), 119.9 (CH),
119.6 (CH), 119.3 (CH), 97.2 (d, J ) 7.4 Hz, CH), 94.7 (d, J )
6.9 Hz, CH), 73.8 (C), 69.2 (d, J ) 14.7 Hz, CH), 68.8 (d, J )
15.2 Hz, CH), 61.2 (CH2), 57.3 (C), 50.4 (CH2), 32.6 (CH2), 32.3
(CH2), 30.5 (3×CH3), 28.7 (CH2), 28.4 (CH2), 27.4 (CH3), 20.4
(CH3), p-CH3 of mesityl group could not be observed. IR (neat):
1691 (m), 1450 (s), 1200 (s). HRMS (EI, 70 eV): calcd for C37H44-
ClN2Rh (M+) 654.2248, found 654.2250.
B
67.0 (CHB), 66.6 (CHB), 66.4 (CHA), 55.3 (CH3A+CH3 ), 52.0
B
B
B
(CH2 ), 51.5 (CH2A), 33.4 (CH3 ), 33.2 (CH2 ), 33.1 (CH3A), 32.9
A
A
B
B
A
A
(CH2 ), 31.3 (CH2 +CH2 ), 30.2 (CH2 ), 30.0 (CH2 ), 28.7 (CH2 ),
B
28.5 (CH2 ). IR (neat): 1612 (m), 1512 (s), 1489 (m), 1450 (s),
1246 (s). HRMS (EI, 70 eV): calcd for C42H42FeIN2ORh (M+)
876.0746, found 876.0768.
Rh-NHC Complex 46. According to General Procedure IV,
reaction between imidazolinium iodide 32 (208 mg, 0.5 mmol),
KOtBu (56 mg, 0.5 mmol), [Rh(cod)Cl]2 (118 mg, 0.24 mmol),
and KI (249 mg, 1.5 mmol), followed by flash column chroma-
tography, afforded 46 (238 mg, 79%) as a 82:18 mixture of rotamers
as an orange-yellow solid. Main isomer: 1H NMR (250 MHz,
CDCl3): δ (ppm) 8.18 (d, J ) 8.7 Hz, 2H), 7.68 (d, J ) 8.7 Hz,
2H), 5.65-5.50 (m, 1H), 5.15-5.03 (m, 2H), 4.34 (d, J ) 3.9 Hz,
1H), 3.74-3.65 (m, 1H), 3.60-3.42 (m, 2H), 3.25 (s, 3H), 2.28-
2.11 (m, 4H), 2.05-1.69 (m, 5H), 1.31 (d, J ) 7.0 Hz, 3H), 1.19
(d, J ) 6.7 Hz, 3H), 0.89 (d, J ) 6.9 Hz, 3H), 0.71 (d, J ) 6.7 Hz,
3H). 13C NMR (63 MHz, CDCl3): δ (ppm) 213.7 (d, J ) 44.5 Hz,
C), 147.8 (C), 147.3 (C), 128.1 (2×CH), 124.5 (2×CH), 97.7 (d,
J ) 6.4 Hz, CH), 97.1 (d, J ) 6.3 Hz, CH), 72.1 (d, J ) 18.5 Hz,
CH), 71.2 (d, J ) 15.8 Hz, CH), 71.0 (CH), 66.3 (CH), 51.5 (CH),
35.9 (CH3), 32.3 (CH2), 32.2 (CH2), 30.7 (CH), 29.4 (CH2), 29.3
Rh-NHC Complex 44. According to General Procedure IV,
reaction between imidazolinium bromide 26 (553 mg, 0.5 mmol),
KOtBu (56 mg, 0.5 mmol), [Rh(cod)Cl]2 (118 mg, 0.24 mmol),
and KI (249 mg, 1.5 mmol), followed by flash column chroma-
tography, afforded 44 (314 mg, 81%) as a 80:20 mixture of rotamers
as a yellow solid. Main isomer: 1H NMR (250 MHz, CDCl3): δ
(ppm) 7.78 (d, J ) 8.6 Hz, 2H), 7.54 (d, J ) 7.5 Hz, 1H), 7.49-
6.65 (m, 14H), 5.70 (d, J ) 14.1 Hz, 1H), 5.37-5.22 (m, 2H),
4.74 (d, J ) 14.7 Hz, 1H), 4.46 (d, J ) 14.2 Hz, 1H), 4.04-3.93
(m, 1H), 3.92 (d, J ) 4.1 Hz, 1H), 3.86-3.78 (m, 2H), 3.84 (s,
3H), 2.52-2.17 (m, 4H), 2.08-1.69 (m, 5H), 0.64 (d, J ) 7.2 Hz,
3H), 0.48 (d, J ) 7.0 Hz, 3H). 13C NMR (63 MHz, CDCl3): δ
(ppm) 217.8 (d, J ) 45.6 Hz, C), 159.2 (C), 147.2 (C), 142.0 (C),

Multicomponent Synthesis of N-Heterocyclic Carbene Complexes
Organometallics, Vol. 26, No. 15, 2007 3649

3650 Organometallics, Vol. 26, No. 15, 2007
Bon et al.
(CH2), 23.1 (CH3), 20.3 (CH3), 18.3 (CH3), 13.6 (CH3). IR (neat):
1523 (s), 1446 (m), 1346 (s), 1188 (m). HRMS (EI, 70 eV): calcd
for C24H35IN3O2Rh (M+) 627.0829, found 627.0803. Crystals
suitable for X-ray crystal structure determination were obtained by
the slow diffusion of pentane into a saturated solution of 46 in
DCM. Mp: 136-139 °C.
riding model. In 38a and 38b the H atoms at C3 and at the cod
double bonds were refined freely with isotropic displacement
parameters; all other H atoms were refined with a riding model.
Data sets for 44-I and 44-II were measured on the same crystal at
different temperatures. While over a wide temperature range (110-
250 K) both phases are present, at 200 K the P21/n phase (44-I)
has higher intensity and at 110 K the P21 phase (44-II). Only these
major components were integrated using the HKL2000 software.36
44-II was refined in a nonstandard setting of space group P21 with
an origin shift of (0.25, 0, 0.25) to obtain consistent coordinates
with respect to the high-temperature phase P21/n of 44-I (group/
subgroup relationship of the phase transition). In 44-I the H atoms
at C3 and at the cod double bonds were refined freely with isotropic
displacement parameters; all other H atoms were refined with a
riding model. In 44-II all H atoms were refined with a riding model.
44-II was refined as an inversion twin resulting in a Flack parameter
x ) 0.183(9).37 The crystal structure of 46 contains large voids
(596.4 Å3/unit cell) filled with disordered solvent molecules. Their
contribution to the structure factors was secured by back-Fourier
transformation using the SQUEEZE routine of the program PLA-
TON,35 accounting for 137 electrons/unit cell. The H atoms at the
cod double bonds were refined freely with isotropic displacement
parameters; all other H atoms were refined with a riding model. In
47 the H atoms at the cod double bonds were refined freely with
isotropic displacement parameters; all other H atoms were refined
with a riding model. For crystallographic data see also CCDC
612936 (35), 612937 (38a), 612938 (38b), 612939 (44-I), 612940
(44-II), 612941 (46), and 612942 (47).
Rh-NHC Complex 47. According to General Procedure IV,
reaction between imidazolium iodide 34 (112 mg, 0.27 mmol), KOt-
Bu (31 mg, 0.28 mmol), [Rh(cod)Cl]2 (67 mg, 0.135 mmol), and
KI (135 mg, 0.81 mmol), followed by flash column chromatogra-
phy, afforded 47 (80 mg, 46%) as an orange-yellow solid. 1H NMR
(250 MHz, CDCl3): δ (ppm) 8.25 (d, J ) 7.5 Hz, 2H), 7.43 (d, J
) 7.4 Hz, 2H), 6.19-5.96 (m, 1H), 5.23-5.04 (m, 2H), 3.55 (s,
3H), 3.52-3.40 (m, 2H), 3.29-3.08 (m, 1H), 2.36-2.11 (m, 4H),
1.95-1.63 (m, 4H), 1.62 (d, J ) 7.9 Hz, 3H), 1.58 (d, J ) 9.6 Hz,
3H), 1.04-0.83 (m, 6H). 13C NMR (63 MHz, CDCl3): δ (ppm)
180.0 (d, J ) 48.8 Hz, C), 148.3 (C), 137.1 (C), 137.0 (C), 132.6
(2×CH), 129.3 (C), 123.7 (2×CH), 96.2 (d, J ) 6.8 Hz, CH), 95.7
(d, J ) 6.8 Hz, CH), 71.5 (d, J ) 14.4 Hz, CH), 70.8 (d, J ) 14.0
Hz, CH), 54.0 (CH), 35.9 (CH3), 32.4 (CH2), 32.1 (CH2), 29.7
(CH2), 29.4 (CH2), 25.4 (CH), 23.1 (CH3), 22.8 (CH3), 22.6 (CH3),
21.8 (CH3). IR (neat): 1522 (s), 1342 (s). HRMS (EI, 70 eV): calcd
for C24H33IN3O2Rh (M+) 625.0672, found 625.0653. Crystals
suitable for X-ray crystal structure determination were obtained by
the slow diffusion of pentane into a saturated solution of 47 in
DCM. Mp: 223-225 °C (dec).
Crystal Structure Determinations. X-ray intensities were
measured on a Nonius KappaCCD diffractometer with rotating
anode (graphite monochromator, λ ) 0.71073 Å) up to a resolution
of (sin θ/λ)max ) 0.65 Å-1. The structures were solved with
automated Patterson methods33 and refined with SHELXL-9734
against F2 of all reflections. Non hydrogen atoms were refined with
anisotropic displacement parameters. Hydrogen atoms were intro-
duced in calculated positions (44-II) or located in the difference
Fourier map (all other structures). Geometry calculations and
checking for higher symmetry was performed with the PLATON
program.35 Further experimental details are given in Table 6. In 35
the H atoms of the cod ligand were refined freely with isotropic
displacement parameters; all other H atoms were refined with a
Acknowledgment. Dr. Marek Smoluch (Vrije Universiteit
Amsterdam) is gratefully acknowledged for conducting EI-(HR)-
MS measurements. Andreas Brockmeyer (Max Planck Institute
for Molecular Physiology, Dortmund) is kindly thanked for
conducting ESI-(HR)MS measurements. Elemental analyses
have been measured at the Westfa¨lischen Wilhelms-Universita¨t
Mu¨nster. This work was partially supported (M.L., A.L.S.) by
the Council for Chemical Sciences of Netherlands Organization
for Scientific Research (CW-NWO).
Supporting Information Available: Full crystallographic data
for compounds 35, 38a, 38b, 44-I, 44-II, 46, and 47 are available
as CIF files. This material is available free of charge via the Internet
at http://pubs.acs.org.
(31) Schenck, T. G.; Downes, J. M.; Milne, C. R. C.; Mackenzie, P. B.;
Boucher, H.; Whelan, J.; Bosnich, B. Inorg. Chem. 1985, 24, 2334-2337.
(32) Wehman-Ooyevaar, I. C. M.; Drenth, W.; Grove, D.; van Koten,
G. Inorg. Chem. 1993, 32, 3347-3356.
(33) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C. The
DIRDIF99 program system, Technical Report of the Crystallography
Laboratory; University of Nijmegen: The Netherlands, 1999.
(34) Sheldrick, G. M. SHELXL-97, Program for crystal structure refine-
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(36) Otwinowski, Z.; Minor, W. Methods in Enzymology; Carter, C. W.,
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