Rh(1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene) (COD) tetrafluoroborate, an unsymmetrical Rh-homoazallylcarbene: Synthesis, X-ray structure and reactivity in carbonyl arylation and hydrosilylation reactions

Article abstract of DOI:10.1016/j.jorganchem.2004.11.057

The synthesis of novel Rh(1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6- tetrahydropyrimidin-2-ylidene)(COD) tetrafluoroborate (1, COD = η⁴-1,5-cyclooctadiene) is described. The N-heterocyclic carbene acts as a bidentate ligand with the carbene coordinating to the Rh(I) center and an arene group acting as a homoazallyl ligand. 1 was used in various carbonyl arylation and hydrosilylation reactions allowing the formation of the desired products with unprecedented selectivity and efficiency. Thus, turn-over numbers (TONs) up to 2000 were achieved.

Full text of DOI:10.1016/j.jorganchem.2004.11.057

Journal of Organometallic Chemistry 690 (2005) 4433–4440
www.elsevier.com/locate/jorganchem
Rh(1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-
2-ylidene)(COD) tetrafluoroborate, an unsymmetrical
Rh-homoazallylcarbene: synthesis, X-ray structure and
reactivity in carbonyl arylation and hydrosilylation reactions q
c
a,b,
*
Nicolas Imlinger a,b, Klaus Wurst , Michael R. Buchmeiser
a
Leibniz Institut fu¨r Oberfla¨chenmodifizierung (IOM) e. V., Permoserstr. 15, D-04318 Leipzig, Germany
b
´
Technische Chemie der Polymere, Universita¨t Leipzig, Linnestr. 3, D-04103 Leipzig, Germany
Institut fu¨r Allgemeine, Anorganische und Theoretische Chemie, Leopold-Franzens-Universita¨t Innsbruck, Innrain 52 a, A-6020 Innsbruck, Austria
c
Received 26 August 2004; received in revised form 16 November 2004; accepted 16 November 2004
Available online 16 February 2005
Abstract
The synthesis of novel Rh(1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) tetrafluoroborate (1,
COD = g4-1,5-cyclooctadiene) is described. The N-heterocyclic carbene acts as a bidentate ligand with the carbene coordinating
to the Rh(I) center and an arene group acting as a homoazallyl ligand. 1 was used in various carbonyl arylation and hydrosilylation
reactions allowing the formation of the desired products with unprecedented selectivity and efficiency. Thus, turn-over numbers
(TONs) up to 2000 were achieved.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: N-heterocyclic carbenes; Rhodium; Carbonyl arylation; Hydrosilylation
1. Introduction
propyl). For carbonyl arylation and hydrosilylation
reactions the novel NHC-complexes MX(1,3-R2-
3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) (M = Rh,
Ir; X = Cl, Br; R = 2-Pr, mesityl; COD = g4-1,5-cyclo-
octadiene) have been used and were found to possess
excellent activity [20,21]. However, inspired by fruitful
discussions in course of the International Symposium
on Homogeneous Catalysis (ISHC) in Munich, 2004,
we were interested whether the corresponding cationic
complexes would allow for even enhanced reactivity
and/or selectivity in these reactions. Based on the finding
that Rh(CF3COO)(1,3-dimesityl-3,4,5,6-tetrahydropyr-
imidin-2-ylidene)(COD) (2) was the most active metal
complex in comparison to all other analogues investi-
gated, we aimed on the synthesis of Rh(1,3-bis(2,4,6-
trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene)
tetrafluoroborate (1). In the following, its synthesis,
N-heterocyclic carbenes (NHCs) [1–6] are currently
among the most intensively investigated compounds
since the corresponding transition metal complexes were
found to possess good stabilities and high activities in
various catalytic processes [7–14]. Recently, our group
[15–21] reported on novel NHC complexes of Ag (I),
Pd (II), Rh (I), Ir (I), and Ru (II) based on 1,3-R2-
3,4,5,6-tetrahydropyrimidin-2-ylidenes (R = mesityl, 2-
q
This paper was first presented at the XIVth International Confer-
ence on Homogeneous Catalysis, Munich, July 7, 2004.
*
Corresponding author. Tel.: +49 0 341 235 2229; fax: +49 0 341 235
2584.
E-mail address: michael.buchmeiser@iom-leipzig.de (M.R. Buch-
meiser).
0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.11.057

4434
N. Imlinger et al. / Journal of Organometallic Chemistry 690 (2005) 4433–4440
Table 1
Crystal data and structure refinement for 1
solid state structure and reactivity in carbonyl arylation
and hydrosilylation reactions is described.
1
Mol formula
fw
C30H40BF4N2Rh
618.36
2. Results and discussion
Cryst syst
Space group
orthorohombic
Pbca (No. 61)
1560.31(4)
2.1. Synthesis and X-ray structure of compound 1
a (pm)
b (pm)
1589.84(3)
4790.4(1)
1,3-Dimesityl-3,4,5,6-tetrahydropyrimidinium tetra-
fluoroborate was reacted with [RhCl(COD)]2 to yield
RhCl(1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydro-
c (pm)
Unit cell dimensions
a (°)
b (°)
90
90
pyrimidin-2-ylidene)
(COD = g4-1,5-cyclooctadiene)
c (°)
90
11.8833(5)
16
Vol (nm3)
[17,18], which was subsequently reacted with silver tetra-
fluoroborate to yield Rh(1,3-bis(2,4,6-trimethylphenyl)-
3,4,5,6-tetrahydropyrimidinium) tetrafluoroborate (1,
Scheme 1). 1 crystallizes in the orthorhombic space
group Pbca, a = 1560.31(4), b = 1589.84(3), c =
4790.4(1), a = b = c = 90°, Z = 16 with two molecules
in the asymmetric unit. These two molecules possess
basically identical conformation with only incremental
differences in the coordination of the cyclooctadienes
(Fig. 1). Relevant structural data, bond angels, and dis-
tances are summarized in Tables 1 and 2.
Z
Temp (K)
Density (calcd.) (Mg/m3)
Abs coeff (mmꢀ1
Color, habit
233(2)
1.383
0.621
)
orange prism
6016
1.020
No. of rflns with I > 2r(I)
Goodness-of-fit on F2
R indices I > 2r(I)
R1 = 0.0408
xR2 = 0.0786
The crystal structure of 1 shows some interesting fea-
tures. The distance Rh(1)–C(9) is 204.0(4) pm, some-
what shorter than the one found in 2 (206.5(8)) [21].
However, the cationic Rh-center is stabilized by a
homoazallyl bonding to the arene, as evidenced by a
comparably short distance Rh(1)–C(13) of 237.7(4)
pm. In due consequence, the angle N(1)–C(9)–Rh(1) is
reduced to 101.5(3)°, compared to 119.6(5)° in 2 [21].
The distances Rh(1)–C(5), Rh(1)–C(6), Rh(1)–C(1),
1. LiO-tertBu
BF4
2.
N
N
N
N
Rh
Cl
Cl
Cl
Rh
Rh
1/2
AgBF4
-AgCl
N
N
Table 2
Bond lengths (pm) and angles (°) for 1
Rh
BF4
Rh(1)–C(9)
Rh(1)–C(6)
Rh(1)–C(5)
Rh(1)–C(2)
Rh(1)–C(1)
Rh(1)–C(13)
204.0(4)
209.6(5)
211.9(5)
222.5(5)
223.9(5)
237.7(4)
1
Scheme 1. Synthesis of Rh-complex 1.
N(2)–C(9)–Rh(1)
N(1)–C(9)–Rh(1)
C(9)–Rh(1)–C(6)
C(9)–Rh(1)–C(5)
C(6)–Rh(1)–C(5)
C(9)–Rh(1)–C(2)
C(6)–Rh(1)–C(2)
C(5)–Rh(1)–C(2)
C(9)–Rh(1)–C(1)
C(6)–Rh(1)–C(1)
C(5)–Rh(1)–C(1)
C(2)–Rh(1)–C(1)
C(9)–Rh(1)–C(13)
C(6)–Rh(1)–C(13)
C(5)–Rh(1)–C(13)
C(2)–Rh(1)–C(13)
C(1)–Rh(1)–C(13)
139.7(3)
101.5(3)
96.06(18)
102.06(19)
38.28(19)
163.7(2)
96.2(2)
81.3(2)
158.8(2)
81.4(2)
88.99(19)
35.11(19)
62.20(17)
132.82(18)
163.32(18)
115.37(19)
104.31(18)
Fig. 1. X-ray structure of compound 1.

N. Imlinger et al. / Journal of Organometallic Chemistry 690 (2005) 4433–4440
4435
Rh(1)–C(2) are 211.9(5), 209.6(5), 223.9(5) and 222.5(5)
pm, respectively, are significantly longer than the Rh–
aldehydes (Table 3, entries 1, 5 and 7). Significant
amounts of the ketone were formed in these reactions.
Apparently, the cationic, electron deficient complex 1 fa-
vors the catalytic oxidation of the corresponding sec-
ondary alcohols formed in course of the reaction.
COD distances found in
2
(208.2(8), 209.3(8),
216.6(11) and 219.5(11) pm, respectively). To the best
of our knowledge, this is the only example of an origi-
nally symmetrical carbene forming an unsymmetrical
homoazallylcarbene-complex of Rh(I) in the solid state.
2.3. Catalytic activity of compound 1 in hydrosilylation
reactions
1
In contrast to these findings, the room temperature H
and 31C NMR solution spectrum of 1, recorded either
in THF-d8 or CDCl3 does not show any further addi-
tional coordination of the arene ligand. In due conse-
quence, both mesityl groups are chemically and
magnetically equivalent. Since Herrmann et al. were
able to identify the unsymmetrical structure of
Cr(CO)4(C(N-(2-Pr)2)2) [22], we recorded a spectrum
at ꢀ60 °C in CDCl3. However, it was identical to the
one obtained at room temperature, indicating a symmet-
rical structure.
Hydrosilylation (or hydrosilation) reactions involve
the addition of inorganic or organic silicon hydrides to
multiple bonds such as alkyne, alkene, ketoxime and
carbonyl groups (Scheme 3). For hydrosilylations pro-
moted by transition metal complexes, as is the case in
the present report, the (modified) Chalk–Harrod mech-
anism [29,30] is still the generally accepted one, however,
other mechanisms have been suggested recently [31–33].
Among the various transition metals most commonly
employed in hydrosilylation reactions [33–37], Rh is cer-
tainly a prominent one. Various NHC complexes of Rh
have been used so far, however, with the exception of 2
[21], Rh-1,3-R2-imidazol-2-ylidenes (R = mesityl, etc.)
have been used almost exclusively [10,12,38–47]. In com-
parison to 2, the new cationic catalyst 1 shows some
interesting features. As can be deduced from Table 4,
entries 1–7 and 8–10, respectively, both the reactivity
and selectivity of novel 1 in the hydrosilylation of alky-
nes and 1-alkenes, respectively, is comparable to the one
of 2. However, increased reactivity is observed in the
hydrosilylation of cyclohex-2-en-1-one (Table 4, entries
11–12). TONs twice as high as found with 2, yet identi-
cal selectivity were observed. Thus, as for 2, reactions
catalyzed by 1 proceeded again selectively via 1,4-addi-
tion (C@O hydrosilylation) to produce the correspond-
ing silylethers. Finally, 1 can be used in the C@O
hydrosilylation of aldehydes and ketones (Table 4, en-
tries 13–15), resulting in the formation of the corre-
sponding silylethers.
2.2. Catalytic activity of compound 1 in carbonyl
arylation reactions
Excellent summaries on both the synthesis and use of
transition metal NHC complexes have been given else-
where [7,8,10,23,24]. In terms of carbonyl arylation
reactions (Scheme 2), originally reported by Miyaura
et al. [25,26], Rh (III) (NHC) complexes have been used
by Furstner [27], the use of Rh (I) (NHC) complexes has
¨
been reported by our group [20].
As already briefly mentioned particularly the use of 2
gave raise to arylation reactions with TONs up to 1200
[20]. With one exception (Table 3, entry 5), the use of 1
under conditions identical to the ones reported previ-
ously gave raise to enhanced turn-over numbers, exceed-
ing the previously reported ones up to a factor of 3.
Important enough, the reactivity of 1 is by far higher
than the one observed with other cationic Rh (I) and Rh
(III) complexes, respectively [28]. In terms of product
selectivity, no changes were observed in the reaction of
2-hydroxybenzeneboronic acid with an aldehyde, result-
ing exclusively in the formation of the thermodynami-
cally favored 2-hydroxy-ketone. The same accounts for
the reaction of arylboronic acids with cyclohex-2-en-1-
one, proceeding exclusively via 1,4-addition to yield
the corresponding ketone. However, different selectivity
was observed in reactions involving electron-poor aryl
3. Experimental
All manipulations were performed under a nitrogen
atmosphere in a glove box (MBraun LabMaster 130)
or by standard Schlenk techniques. Purchased starting
materials were used without any further purification.
Pentane and tetrahydrofurane (THF) were distilled from
sodium benzophenone ketyl under nitrogen. Methylene
chloride was distilled from calcium hydride.
NMR data were obtained at 300.13 MHz for proton
and 75.74 MHz for carbon in the indicated solvent at
25 °C on a Bruker Spectrospin 300 and are listed in parts
per million downfield from tetramethylsilane for proton
and carbon. Coupling constants are listed in Hz. IR
spectra were recorded on a Mattson Instruments Galaxy
Series FT-IR 3000. Elemental analyses were carried out
Scheme 2. Carbonyl arylations reactions.

4436
N. Imlinger et al. / Journal of Organometallic Chemistry 690 (2005) 4433–4440
Table 3
Arylation of carbonyl compounds with Rh(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) BF4
#
Educt
Product
Mol% cat. (yield) TONa
Alcohol:Ketonea
12:88 (71:29)
1
4-F-Benzaldehyde/2-Thienylboronic acid
0.05 (52)
1040 (760)
2
4-F-Benzaldehyde/4-MeO-Benzeneboronic acid
0.05 (65)
1300 (950)
99:1 (100:0)
3
2-OH-Benzaldyde/4-MeO-Benzeneboronic acid
0.05 (35)b
700 (375)
0:100 (0:100)
4
Cyclohex-2-en-1-one/4-MeO-Benzeneboronic acid
0.05 (33)b
660 (590)
0:100 (0:100)
5
4-F-Benzaldehyde/4-Me-Benzeneboronic acid
0.05 (40)
800 (1230)
0:100 (100:0)
6
2-OH-Benzaldehyde/4-Methylbenzeboronic acid
0.05 (30)b
600 (420)
0:100 (0:100)
7
4-F-Benzaldehyde/4-Vinylbenzeneboronic acid
0.05 (68)
1360 (1230) 77:23 (100:0)
8
9
2-OH-Benzaldehyde/4-Vinylbenzeboronic acid
Benzaldehyde/4-Methoxybenzeneboronic acid
0.05 (53)b
1060 (340)
0:100 (0:100)
0.05 (50)
1000
98:2
Reaction time: 8 h, T = 80 °C.
Values in brackets are the one reported for 2 [20].
a
b
Reaction time: 20 h.

N. Imlinger et al. / Journal of Organometallic Chemistry 690 (2005) 4433–4440
4437
Table 4
Hydrosilylation of unsaturated compounds with Rh(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) BF4
#
Educt
Product
Mol% cat. (yield) b-trans (%)b b-cis (%)b a (%)a,b TONb
1
Diphenylacetylene/Triethylsilane
0.05 (69)
0.05 (30)
0.05 (18)
0.05 (38)
0.05 (53)
0.05 (9)
–
–
–
1380 (780)
2
3
4
5
6
7
8
9
Phenylacetylene/Triethylsilan
Trimethylsilylacetylene/Trimethoxysilane
Phenylacetylen/Dichlormethylsilan
1-Hexyne/Triethylsilane
62
11
27
600
77 (77)
0 (0)
23 (23)
360 (210)
760 (810)
1060 (890)
180 (340)
720 (900)
800 (460)
720 (180)
240(100)
2000(1000)
900(310)
53 (46)
28 (38)
19 (16)
56 (61)
8 (11)
36 (27)
1-Hexyne/Triphenylsilane
0 (0)
92 (99)
8 (1)
1-Hexyne/Dichlormethylsilane
Styrene/Triethylsilane
0.05 (36)
0.05 (40)
0.05 (36)
0.05 (12)
0.05 (100)
0.04 (36)
100 (100)
0 (0)
0 (0)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
1-Hexene/Triethylsilane
10 1-Octene/Triethylsilane
11 Cyclohex-2-en-1-one/Triethylsilane
12 Cyclohex-2-en-1-one/Triphenylsilane
(continued on next page)

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N. Imlinger et al. / Journal of Organometallic Chemistry 690 (2005) 4433–4440
Table 4 (continued)
#
Educt
Product
Mol% cat.
(yield)
b-trans
b-cis
a (%)a,b
TONb
(%)b
(%)b
13
4-Chloroacetyldehyde/
Triethylsilane
0.05 (17)
–
–
–
340(300)
14
15
Benzaldehyde/Triethylsilane
0.05 (17)
0.05 (37)
–
–
–
–
–
–
340
740
4-F-Benzaldehyde/Triethylsilane
Reaction time: 12 h, T = 80 °C.
Different positional numbers for the substituents according to Scheme 2 apply.
a
b
Values in brackets are the one reported for 2 [21].
2884 (m), 2831 (w), 1603 (w), 1537 (s), 1480 (s), 1456
(w), 1435 (w), 1380 (w), 1336 (m), 1308 (m), 1207 (w),
1
1085 (s), 1058 (s), 963 (w), 862 (w), 519 cmꢀ1 (w); H-
NMR (CDCl3) d 6.93 (br s, 4H, aromatic H), 3.37 (t,
4H, NCH2, 3J(H,H) = 5.71), 3.34 (m, 2H, CHCOD),
2.67 (m, 2H, CHCOD), 2.49 (br s, 12H, mesityl-ortho-
3
CH3), 2.35 (quint, 2H, CH2, J(H,H) = 5.71), 2.27 (br
s, 6H, mesityl-para-CH3), 2.17–1.88 (m, 4H, CH2
COD), 1.69–1.53 ppm (m, 4H, CH2COD); 31C NMR
1
(CDCl3) d 174.4 (d, NCN, J(103Rh,31C) = 35.3), 141.6,
137.2, 131.0, 127.9 (s, aromatic C), 99.7 (d, CHCOD
,
,
1J(103Rh,31C) = 7), 70.7 (d, CHCOD 1J(103Rh,31C) =
15), 49.2 (s, NCH2), 33.6 (s), 27.6 (s), 21.5 (br), 21.2
(br) (CH2, mesityl-CH3), 18.8 (br, CH2 COD). Elemental
Anal. Cald. for C30H40BF4N2Rh: C, 58.27; H, 6.52; N,
4.53. Found: C, 57.71; H, 6.38; N, 4.37%.
Scheme 3. Hydrosilylation reactions.
at the Mikroanalytisches Labor, Anorganisch-Chemis-
ches Institut, TU Munchen, Germany.
¨
3.2. Standard procedure for the reaction of an arylboronic
acid with a carbonyl compound
3.1. Rh(1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-
tetrahydropyrimidinium)(COD) tetrafluoroborate (1)
The catalyst (for the amount refer to Table 3) and
arylboronic acid (0.53 mmol) were dissolved in DME
(2.2 mL). Tetradecane (0.7 equiv. with respect to the
arylboronic acid) as an internal standard as well as the
carbonyl compound (1 equiv. with respect to the arylbo-
ronic acid), sodium hydroxide (2 equiv. with respect to
the arylboronic acid) and water (0.6 mL) were added.
The mixture was stirred at 80 °C until no further conver-
sion was monitored by GC–MS. Yields and turn over
numbers (TONs) were determined by GC–MS using
both the conversion of the educts and the peak areas
of standard solutions of the products. Isolation and
properties of the products is described elsewhere [20,21].
RhCl(1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahy-
dropyrimidinium)(COD) (40.6 mg, 72 lmol) was dis-
solved in 1 mL of THF, the solution was cooled and
silver tetrafluoroborate (14.0 mg, 72 lmol), dissolved
in 3 mL of THF, was added slowly. The mixture was
stirred at room temperature for 1 h. The mixture was fil-
tered through celite, which was washed twice with THF
(0.5 mL each). The solution was dried in vacuo yielding
an orange-yellow powder (quantitative conversion). A
crystal of 1 suitable for X-ray analysis was obtained
by cooling a concentrated THF solution to ꢀ40 °C for
several days. FT-IR (KBr, cmꢀ1): 2938 (m), 2919 (m),

N. Imlinger et al. / Journal of Organometallic Chemistry 690 (2005) 4433–4440
4439
3.3. Standard procedure for hydrosilylation reactions
(I) catalysts based on the same N-heterocyclic carbene
in activity up to a factor of 3. In addition, different selec-
tivities are observed. Particularly in hydrosilylation
reactions of a, b-unsaturated ketones, one can now
perform chemo- and regioslelective reactions with both
the new catalyst 1 and the parent compound 2.
The catalyst (for the amount refer to Table 4) was
dissolved in DME (2 mL). Tetradecane (100 lL) was
added as an internal standard followed by the silane
(0.50 mmol) and the unsaturated compound (alkyne-,
alkene- or carbonyl compound, 0.50 mmol). The mix-
ture was stirred at 80 °C until no further conversion
was monitored by GC–MS. Yields and turn over num-
bers (TONs) were determined by GC–MS using both
the conversion of the educts and the peak areas of stan-
dard solutions of the products. Isolation and properties
of the products is described elsewhere [20,21]. For the al-
kyne compounds the ratio of the product isomers was
determined by integration of the GC–MS peaks. These
were correlated with the results taken from NMR-
measurements.
For NMR-measurements, the solvent of the reaction
mixture was removed in vacuo and the residue was ta-
ken up in CDCl3. Integration of the olefinic region pro-
vided the ratio of the product isomers of the reaction of
an alkyne compound with a silane. Concerning the reac-
tion of the a,b-unsaturated carbonyl compound with a
silane, the 1,4-addition was confirmed by NMR, the lack
of olefinic proton-signals and the appearance of a sing-
lett around 5 ppm.
Acknowledgement
Our work was supported by a grant of the Austrian
Science Fund (START Y-158).
Appendix A. Supplementary data
The crystallographic data for 1 have been deposited
with the CCDC-No. 248426, and on the Cambridge
Crystallographic Data Centre. The coordinates can be
obtained, on request, from the Director, Cambridge
Crystallographic Data Centre, 12 Union Road, Cam-
bridge, CB2 1EZ, UK (fax: +44 1223 336033; e-mail: de-
posit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.
ac.uk). Supplementary data associated with this article
can be found, in the online version at doi:10.1016/
j.jorganchem.2004.11.057.
3.4. X-ray measurement and structure determination of 1
References
Data collection was performed on a Nonius Kappa
CCD equipped with graphite-monochromatized Mo
[1] H.-W. Wanzlick, E. Schikora, Chem. Ber. 94 (1961) 2389.
[2] H.-W. Wanzlick, H.-J. Kleiner, Angew. Chem. 73 (1961)
493.
˚
Ka-radiation (k = 0.71073 A) and a nominal crystal to
area detector distance of 55 mm. Intensities were inte-
grated using DENZO and scaled with SCALEPACK
[48]. Several scans in / and x direction were made to in-
crease the number of redundant reflections, which were
averaged in the refinement cycles. This procedure re-
places in a good approximation an empirical absorption
correction. The structures were solved with direct meth-
ods SHELXS86 and refined against F2 SHELX97 [49].
[3] H.-W. Wanzlick, Angew. Chem. 74 (1962) 129.
[4] A.J. Arduengo III, R.L. Harlow, M. Kline, J. Am. Chem. Soc.
113 (1991) 361.
[5] A.J. Arduengo III, H.V. Rasika Dias, R.L. Harlow, M. Kline, J.
Am. Chem. Soc. 114 (1992) 5530.
[6] M. Regitz, Angew. Chem. 108 (1996) 791.
[7] W.A. Herrmann, M. Elison, J. Fischer, C. Ko¨cher, G.R.J. Artus,
Angew. Chem. 107 (1995) 2602.
[8] W.A. Herrmann, M. Elison, J. Fischer, C. Ko¨cher, G.R.J. Artus,
Chem. Eur. J. 2 (1996) 772.
2
The function minimized was R½wðF 2o ꢀ F c2Þ ꢁ with the
2
weight defined as wꢀ1 ¼ ½r2ðF 2oÞ þ ðxPÞ þ yPꢁ and
[9] W.A. Herrmann, B. Cornils, Angew. Chem. 109 (1997) 1074.
[10] W.A. Herrmann, C. Ko¨cher, Angew. Chem. 109 (1997) 2256.
[11] A.H. Cowley, J. Organomet. Chem. 617–618 (2001) 105.
[12] W.A. Herrmann, Angew. Chem. 114 (2002) 1342.
[13] M. Muehlhofer, T. Strassner, W.A. Herrmann, Angew. Chem.
114 (2002) 1817.
P ¼ ðF 2o þ 2F 2cÞ=3. All non-hydrogen atoms were refined
with anisotropic displacement parameters. Positions of
hydrogen atoms were calculated except for those at the
double bonds of COD, which were refined isotropically
˚
[14] V.P.W. Bo¨hm, C.W.K. Gsto¨ttmayr, T. Weskamp, W.A. Herr-
mann, Angew. Chem. 113 (2001) 3500.
with bond restraints (d = 0.95 A).
[15] J.O. Krause, M.T. Zarka, U. Anders, R. Weberskirch, O.
Nuyken, M.R. Buchmeiser, Angew. Chem. 115 (2003) 6147.
[16] M. Mayr, M.R. Buchmeiser, Macromol. Rapid. Commun. 25
(2004) 231.
4. Summary
[17] M. Mayr, K. Wurst, K.-H. Ongania, M.R. Buchmeiser, Chem.
Eur. J. 10 (2004) 1256.
In summary, we have developed a new cationic Rh (I)
catalyst based on a novel N-heterocyclic carbene (1,3-
dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene), suitable
for carbonyl arylation and hydrosilylation reactions.
The new cationic compound exceeds other active Rh
[18] M. Mayr, K. Wurst, K.-H. Ongania, M.R. Buchmeiser, Chem.
Eur. J. 10 (2004) 2622.
[19] L. Yang, M. Mayr, K. Wurst, M.R. Buchmeiser, Chem. Eur. J.
10 (2004) 5761.

4440
N. Imlinger et al. / Journal of Organometallic Chemistry 690 (2005) 4433–4440
[20] N. Imlinger, M. Mayr, D. Wang, K. Wurst, M.R. Buchmeiser,
Adv. Synth. Catal. 346 (2004) 1836.
[37] R. Skoda-Fo¨ldes, L. Kollar, B. Heil, J. Organomet. Chem. 408
(1991) 297.
[21] N. Imlinger, K. Wurst, M.R. Buchmeiser, Monatsh. Chem. 136
(2005) 47.
[38] I.E. Marko, S.S.O. Buisine, G. Mignani, P. Branlard, B. Tinant,
J.-P. Declercq, Science 298 (2002) 204.
¨
[22] W.A. Herrmann, K. Ofele, D.v. Preysing, E. Herdtweck, J.
Organomet. Chem 684 (2003) 235.
¨
[23] K. Ofele, W.A. Herrmann, D. Mihalios, M. Elison, E. Herdtweck,
[39] J.W. Sprengers, M.J. Mars, M.A. Duin, K.J.B. Cavell, C.J.
Elsevier, J. Organomet. Chem 679 (2003) 149.
[40] W.L. Duan, M. Shi, G.B. Rong, Chem. Commun. (2003)
2916.
T. Priermeier, P. Kiprof, J. Organomet. Chem. 498 (1995) 1.
[24] C. Ko¨cher, W.A. Herrmann, J. Organomet. Chem 532 (1997) 261.
[25] M. Sakai, H. Hayashi, N. Miyaura, Organometallics 16 (1997)
4229.
[41] V.K. Dioumaev, M. Bullock, Nature 424 (2003) 530.
[42] K.H. Park, S.Y. Kim, S.U. Son, Y.K. Chung, Eur. J. Org. Chem.
(2003) 4341.
´
´
[43] M. Poyatos, E. Mas-Marza, J.A. Mata, M. Sanau, E. Peris, Eur.
[26] M. Sakai, M. Ueda, N. Miyaura, Angew. Chem. 110 (1998) 3475.
[27] A. Furstner, H. Krause, Adv. Synth. Catal. 343 (2001) 343.
¨
J. Inorg. Chem. (2003) 1215.
[44] W.A. Herrmann, L.J. Gooßen, C. Ko¨cher, G.R.J. Artus, Angew.
Chem. 108 (1996) 2980.
[28] C. Moreau, C. Hague, A.S. Weller, G. Frost, Tetrahedron Lett.
42 (2001) 6957.
´
´
[45] E. Mas-Marza, M. Poyatos, M. Sanau, E. Peris, Inorg. Chem. 43
[29] A.J. Chalk, J.F. Harrod, J. Am. Chem. Soc. 87 (1965) 16.
[30] M.A. Schroeder, M.S. Wrighton, J. Organomet. Chem 128 (1977)
345.
(2004) 2213.
[46] H. Kaur, F. Kauer Zinn, E.D. Stevens, S.P. Nolan, Organomet-
allics 23 (2004) 1157.
[31] P.B. Glaser, T.D. Tilley, J. Am. Chem. Soc. 125 (2003) 13640.
[32] H. Brunner, Angew. Chem. 116 (2004) 2805.
[33] B. Marciniec, Silicon Chem. 1 (2002) 155.
[34] M.L. Clarke, Polyhedron 20 (2001) 151.
[35] J.L. Speier, Adv. Organomet. Chem. 17 (1979) 407.
[36] M. Itoh, K. Iwata, R. Takeuchi, M. Kobayashi, J. Organomet.
Chem. 420 (1991) C5.
´
[47] V. Cesar, S. Bellemin-Laponnaz, L.H. Gade, Angew. Chem. 116
(2004) 1036.
[48] Z. Otwinowski, W. Minor, Methods in Enzymology, Academic
Press, New York, 1997.
[49] G.M. Sheldrick, Program Package SHELXTL V.5.1, Bruker
Analytical X-Ray Instruments Inc, Madison, USA, 1997.