Impact of ligand modification on structures and catalytic activities of chelating bis-carbene rhodium(I) complexes

Article abstract of DOI:10.1021/om1005897

A series of novel chelating N-heterocyclic bis-carbene rhodium(I) complexes based on 1,2,4-triazoles, benzimidazoles, and imidazoles with varying bridge length and N substituents has been synthesized. In addition to their structural characterization, thei

Full text of DOI:10.1021/om1005897

Organometallics 2010, 29, 5681–5692 5681
DOI: 10.1021/om1005897
Impact of Ligand Modification on Structures and Catalytic Activities
of Chelating Bis-Carbene Rhodium(I) Complexes†
Stephanie K. U. Riederer,†,‡ Peter Gigler,†,‡ Manuel P. Hogerl,†,§ Eberhardt Herdtweck,‡
€
,†,‡,§
Bettina Bechlars,‡ Wolfgang A. Herrmann,*,†,‡ and Fritz E. Kuhn*
€
§
†WACKER-Institut fu€r Siliciumchemie, ‡Chair of Inorganic Chemistry, and Molecular Catalysis,
€
€
Catalysis Research Center, Department of Chemistry, Technische Universitat Munchen,
Lichtenbergstrasse 4, 85747 Garching b. Mu€nchen, Germany
Received July 8, 2010
A seriesof novelchelating N-heterocyclicbis-carbene rhodium(I) complexes basedon 1,2,4-triazoles,
benzimidazoles, and imidazoles with varying bridge length and N substituents has been synthesized. In
addition to their structural characterization, their catalytic activity in the hydrosilylation of 4-fluoro-
acetophenone with diphenylsilane has been examined. The results reveal that selectivities and turnover
frequencies (TOFs) are influenced by bridge length, steric demand of the N substituents, and electronic
properties of the heterocycle.
Introduction
metal complexes in homogeneous catalysis is a topic of high
interest, apparent by the number of review articles and books
published in this field during the course of the past several
years.1 In addition to the strong metal-carbon bond present
in NHC metal complexes, bidentate bis-carbene ligands
enhance stability as a result of the chelate effect and therefore
offer important advantages over their monodentate analo-
gues with regard to applications in catalysis. Cavell et al.
predicted that reductive elimination, representing the most
common decomposition mechanism of NHC-based catalysts
in hydrogenation and hydroformylation, will be impeded by
using chelating bis-NHC ligands.2 In addition to bidentate
Rh complexes with donor-functionalized mono-carbene
ligands,3 there are several examples of Rh complexes with
imidazole (im),4 benzimidazole (bim),4p,5 and triazole (tri)
based biscarbene ligands.6 Some of them were successfully
tested in different catalytic applications such as transfer
hydrogenation,4a,c,d hydrosilylation,4d,f,m,5b,c,e,h hydroge-
nation,5g hydroformylation,5g oxidative kinetic resolution,5h
and intramolecular hydroamination.4b It was shown that
N-heterocyclic bis-carbene ligands allow a better control
over the coordination sphere and the fine tuning of proper-
ties such as steric hindrance, bite angles, chirality, and fluxi-
onal behavior.7 However, the influence of different types of
The chemistry of N-heterocyclic carbenes (NHCs) and
their application as strongly binding ligands of transition-
† Part of the Dietmar Seyferth Festschrift. Dedicated to Dietmar Seyferth.
*To whom correspondence should be addressed. E-mail:
wolfgangherrmann@ch.tum.de (W.A.H.); fritz.kuehn@ch.tum.de
(F.E.K.).
(1) (a) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290–1309.
(b) Nolan, S. P. N-Heterocyclic Carbenes in Synthesis; Wiley-VCH:
Weinheim, Germany, 2006. (c) Glorius, F. N-Heterocyclic Carbenes in
Transition Metal Catalysis; Springer: Berlin and Heidelberg, Germany,
2007. (d) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47, 3122–
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Commun. 2002, 32–33. (b) Burling, S.; Field, L. D.; Li, H. L.; Messerle,
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4846–4848. (i) Wanniarachchi, Y. A.; Khan, M. A.; Slaughter, L. M.
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Cronje, S.; Esterhuysen, C.; Raubenheimer, H. G. Dalton Trans. 2005,
181–192. (k) Frey, G. D.; Rentzsch, C. F.; von Preysing, D.; Scherg, T.;
M€uhlhofer, M.; Herdtweck, E.; Herrmann, W. A. J. Organomet. Chem.
2006, 691, 5725–5738. (l) Leung, C. H.; Incarvito, C. D.; Crabtree, R. H.
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2010 American Chemical Society
Published on Web 08/04/2010
pubs.acs.org/Organometallics

5682 Organometallics, Vol. 29, No. 21, 2010
Riederer et al.
1,3-dibromopropane in THF to form the bromide salts
(Scheme 1).6a,9
In order to isolate the bis-carbene complexes in high yields,
it is necessary to exclude halides or other coordinating anions
from the reaction mixture, which requires an anion exchange
of Br- to PF6- prior to the complex synthesis.4b Following
an adapted literature procedure, the metal complexes have
been prepared under mild conditions.10 [Rh(OEt)COD]2 is
obtained from [RhCl(COD)]2 with in situ generated NaOEt
for the synthesis of triazole- and imidazole-based complexes.
For the benzimidazole-based complexes, readily synthesized
[Rh(OEt)COD]2 is added as a THF solution to the reaction
mixture of the benzimidazolium salt with NaOEt in MeOH.
Subsequently, [Rh(OEt)COD]2 reacts with the azolium salts
2 to give the corresponding complexes of type 3 (Scheme 2),
which are obtained in high yields (80-98%).
Figure 1. Catalyst design and tuning parameters: electronics:
heterocycle (X = N, C); sterics, bridge length and wing substit-
uents (R = alkyl or aryl substituent).
ligand modifications on the catalytic properties has not yet
been systematically studied. Bidentate ligands of the type
depicted in Figure 1 represent ideal candidates to examine
the influence of ligand properties on structures and catalytic
activities.
Some rhodium bis-carbene complexes of the motif depicted
in Figure 1 have been reported in the literature. In contrast
to imidazole-4b,e,g,i-m and benzimidazole-based4p,5a,d,f,g sys-
tems, triazole-based systems are less investigated, only two
tetrakis-NHC rhodium complexes are known so far.6a Crab-
tree et al.6b,c recently prepared a novel bitriazole-2-ylidene
ligand and its dinuclear Rh(I) complex, with the NHC ligand
bridging two metal ions. However, to the best of our knowl-
edge, none of the published Rh(I)-NHC complexes display
the structural motif [Rh(COD)(bis-NHC)]X (NHC = 1,2,4-
triazole, X = anion).
In contrast to earlier reports,4e,g,l the formation of dinuclear
Rhspeciesis not observed. Our investigation indicates that the
formation of dinuclear species does not primarily depend on
the interplay between bridge length and wingtips,4l but rather
on the synthetic method used to prepare the complexes.4b
The stability of the complex changes significantly with
varying bridge length. Whereas all complexes with ethylene
and propylene bridges are stable to prolonged exposure to
air, water, and high temperatures (up to 200 °C; confirmed
by TG/MS measurements), the complexes with a methylene
bridge decompose in solution—depending on the hetero-
cycles—after a few minutes (imidazole- and benzimidazole-
based complexes) to several days (triazole-based complexes).
The isolated complexes were characterized by elemental
1
analysis, FAB mass spectrometry, H and 13C{1H} NMR
spectroscopy and X-ray crystallography. Evidence for the
coordination of the carbene carbon atom to the rho-
dium atom is obtained by 13C{1H} NMR spectroscopy.
A doublet resonance in the typical range of δ 178-195
ppm (1JRh-C(carbene) = 50-55 Hz) is observed for all
complexes.4g,5a,6a The 1H NMR spectrum reflects the rigidity
of the bis-carbene complexes. In the case of tri-31-Me, the 1H
NMR spectrum displays two methylene C-H resonances
with a 2JH-H coupling constant of approximately 13 Hz. The
magnetic inequivalence of the methylene protons indicates a
nonfluxional behavior at room temperature. A boat-to-boat
inversion of the six-membered metallacycle does not occur.
The rigidity of the complexes with an ethylene bridge was
also confirmed by 1H NMR spectra, as two different multi-
plets of the linker protons are present in each case, as shown
for im-32-Me in Figure 2 as a representative example.
In order to understand the intricate interplay of electronic
and steric effects, a series of analogous Rh(I) complexes of
the type [Rh(COD)(bis-NHC)]PF6 was prepared, exhibit-
ing a set of systematically varied bis-NHC ligands based
on 1,2,4-triazole, benzimidazole, and imidazole. A compara-
tive study of [RhI(CO)2(NHC)] complexes revealed that the
σ-donor ability increases in the order 1,2,4-triazole < benzi-
midazole < imidazole.6a The catalytic performance can be
modified via the σ-donor ability of a ligand. It was shown,
for example, that the donor capability of the NHC ligand
in catalysts of the type [IrX(COD)(NHC)] (X = I, COD =
cyclooctadiene) has a significant impact on the initiation
time and the reaction rates of the transfer hydrogenation of
acetophenone and acetonaphthone.8
In the present work the synthetic procedure for the
preparation of such Rh(I) complexes with novel chelating
bis-carbene NHC ligands is presented, along with their
structural characterization. The new complexes were tested
as catalysts for the hydrosilylation of 4-fluoroacetophenone
with diphenylsilane as a model reaction. The influence of
the different carbene moieties, particularly the bridge length
(n = 1-3), the heterocycle composition, and the wingtip
groups on the structure, stability, and catalytic activity of the
resulting Rh complexes is discussed.
This splitting can be explained as an AA0XX0 spin system
being caused by a fixed C1-symmetric arrangement of the
ligands. This is realized in a boat conformation of the seven-
membered metallacycle,4g as illustrated in Figu0re 3, in which
0
axial (HA and HA ) and equatorial (HX and HX ) protons are
chemically but not magnetically equivalent. This interpreta-
tion is supported by a WinDNMR simulation of multiplet A,
which matches the experimental spectrum, as can be seen in
Figure 2 (right).
Crystals suitable for X-ray analysis were obtained for a
number of complexes. The molecular structure of the catio-
nic complex tri-32-Me in the solid state is depicted as an
Results and Discussion
The preparation of the azolium salts 1 as ligand precursors
is straightforward and high-yielding. N-substituted azoles
readily react with dibromomethane, 1,2-dibromoethane, and
(9) Scherg, T.; Schneider, S. K.; Frey, G. D.; Schwarz, J.; Herdtweck,
E.; Herrmann, W. A. Synlett 2006, 2894–2907.
€
(8) Zinner, S. C.; Rentzsch, C. F.; Herdtweck, E.; Herrmann, W. A.;
Kuhn, F. E. Dalton Trans. 2009, 7055–7062.
(10) Kocher, C.; Herrmann, W. A. J. Organomet. Chem. 1997, 532,
261–265.
€

Article
Organometallics, Vol. 29, No. 21, 2010 5683
1
Figure 2. Section of the H NMR spectrum of im-32-Me showing the bridging ethylene protons (left) and the experimental (a) and
0
simulated (b) multiplet structure of A (right). WinDNMR simulation parameters: JAA = 5.24 Hz, JXX = 5.26 Hz, JAX = 14.5 Hz,
0
0
JAX = -7.10 Hz, Wa = 1.78 Hz.
Scheme 1. Synthesis of Ligand Bis-Azolium Bromide Salts 1 and Hexafluorophosphate Salts 2
Scheme 2. Synthesis of Rh(I) Complexes 3
Images of the molecular structures for the other complexes
along with selected geometrical and crystallographic details
are given in the Supporting Information.
As previously reported by Crabtree et al.,4l a distortion of
the square-planar geometry and an in-plane distortion of the
NHC moiety can be observed in complexes of this type. In
each complex, the rhodium atom is coordinated by two
carbene carbon atoms and two η2-bound olefin groups of
the cyclooctadiene ligand that form a distorted-square-pla-
nar coordination environment. The deviation from the ideal
square-planar arrangement of the ligands can be described
by the tilt angle j between plane A (through Rh1, C9, and
Figure 3. Boat conformation of the metallacycle.
example in Figure 4, and selected bond distances and bond
angles of tri-32-Me are provided in Table 1.

5684 Organometallics, Vol. 29, No. 21, 2010
Riederer et al.
transformation, as protected alcohols can be produced di-
rectly from carbonyl compounds. Although several com-
plexes containing phosphine ligands are known to be highly
active catalysts,13 they have some drawbacks such as low
stability and deactivation. As the presented complexes are
extremely stable to air, water, and elevated tempera-
tures, they are expected to increase the stability of the
catalytic system and do not require inert-gas conditions.
The influence of ligand modifications of the synthesized
bis-NHC rhodium complexes on activity and selectivity
was evaluated in the hydrosilylation of 4-fluoroaceto-
phenone with diphenylsilane to yield silyl ether 5, as shown
in Scheme 3.
Figure 4. Molecular structure of cationic complex in tri-32-Me
Hydrogen atoms are omitted for clarity. Thermal ellipsoids are
drawn at the 50% probability level.11
.
In agreement with previous reports,14 silyl enol ether 6
formed as a side product. 4-Fluoroacetophenone was used as
the substrate in order to conveniently monitor the reaction
progress in situ by 19F NMR spectroscopy. No spectroscopic
evidence for defluorination or side products other than 6 was
observed. The reactions were carried out with 2 mol %
catalyst at 25 °C in dichloromethane. Yields and turnover
frequencies (TOFs) were determined and are summarized in
Table 2. Some of the complexes were recovered and analyzed
after the catalytic run and thus proved their stability under
catalytic conditions.
Table 1. Selected Structural Details of the Rh(I) Bis-Carbene
Complex tri-32-Me
˚
d(Rh-Ccarbene) (A)
2.043(7), 2.052(8)
2.087, 2.101
85.0(3)
1.5(5), 0.5(6)
6.0(6)
16.9
a
˚
d(Rh-Cg) (A)
Ccarbene-Rh-Ccarbene bite angle (deg)
yaw distortion angle θ (deg)
average yaw distortion angle θav (deg)
tilt angle j (deg)
The activities of the complexes are comparable with those
of previously reported related systems. Shi et al. obtained
44% of the product in 48 h with a Rh(III) complex bearing
2,20-bis-carbene-biphenyl ligands, using 2 mol % of catalyst
in CH2Cl2 at room temperature.5c Enders et al. tested
(triazolinylidene)rhodium(I) complexes as catalysts for the
hydrosilylation of acetophenone with diphenylsilane using
1 mol % catalyst in THF and observed yields ranging from
60 to 90% within 4 h to 6 days.15
Influence of Bridge Length. The influence of the bridge
length on the activity can be seen for complexes containing
identical heterocycles and wingtips, differing only in bridge
length (Table 3).
For complexes bearing alkyl-substituted triazole-based
bis-carbenes (entries 1-3), the activity is shown to increase
with decreasing bridge length, whereas in analogous aryl-
substituted derivatives (entries 4 and 5) this tendency is
reversed. The exact opposite trend, however, is observed
for the complexes with benzimidazole-based bis-carbenes
(alkyl substituted, entries 6-9, aryl substituted, entries 10
and 11). These results indicate that the influences of two
different parameters cannot be treated separately but must
be regarded as interdependent. No clear trend is found with
regard to the selectivity.
distance of Cg to plane through
0.567, -0.176
˚
Rh and both Ccarbene (A)
a Cg is defined as the center of a CdC double bond in COD.
C11) and plane B (through Rh1, Cg1, and Cg2) and the
distances of Cg1 and Cg2 to plane A (Cg1 and Cg2 denote the
centers of the CdC double bond within the COD ligand)
(Figure 5).
In accordance with the observations made by Crabtree
et al. it was found that one of the Rh-Cg bonds is loca-
ted within or very close to plane A (shortest distance of Cg
˚
and A: 0.003-0.368 A), whereas the other bond deviates
from it more significantly (longest distance of Cg and A:
4l
˚
0.115-0.648 A). The values for j vary from 3.7 to 19.0°.
This distortion was attributed to a better overlap of the
empty CCODdCCOD π* orbital with the occupied rho-
dium dz2 orbital, as previously described for electron-rich
d8 ruthenium complexes.12,4l A correlation between the N
substituents or the bridge length and the distortion was
not observed. The distortions of the M-C-N bond angles
(R and β) are reflected in the yaw distortion angle θ (θ = 1/2-
(R - β)) shown in Figure 5.4l The values determined for θ are
summarized in the Supporting Information. With the ex-
ception of tri-33-Ph (5.9(1)°), the θ values for ethylene- and
propylene-bridged derivatives (2.9(2)-3.7(2) and 4.9(3)-
7.5(1)°) fall within the same range as previously reported
by Crabtree et al. for similar systems. The average value for θ
decreases with increasing bridge length, which was proposed
to be a consequence of the ring strain.4b It can also be seen
that in all complexes the yaw distortion mainly affects one of
the two M-NHC bonds, which appears to be energetically
favorable.
Influence of N Substituents. Depending on the steric de-
mand of the N substituents, the turnover frequencies (TOFs)
vary considerably (Table 4).
When alkyl- (entries 1-6) and aryl-substituted (entries
7-10) complexes are compared separately, the activity and
selectivity for 5 are seen to increase with steric demand of the
wingtips. This implicates that the reaction pathway to 5 is
favored in comparison to the competing pathway to the silyl
enol ether 6 by bulky substituents.
Impact of Ligand Modification on Catalysis. The hydro-
silylation of ketones or aldehydes leading to silyl ethers
is a useful and experimentally relatively straightforward
(13) (a) Reyes, C.; Prock, A.; Giering, W. P. J. Organomet. Chem.
2003, 671, 13–26. (b) Thiot, C.; Wagner, A.; Mioskowski, C. Org. Lett.
2006, 8, 5939–5942.
(14) Brunner, H.; Brandl, P. J. Organomet. Chem. 1990, 390, c81–c83.
(15) (a) Enders, D.; Gielen, H.; Breuer, K. Tetrahedron: Asymmetry
1997, 8, 3571–3574. (b) Enders, D.; Gielen, H. J. Organomet. Chem. 2001,
617-618, 70–80.
(11) Brandenburg, K. DIAMOND Version 3.1, Crystal and Molecu-
lar Structure Visualization; Bonn, Germany, 2005.
(12) Ogasawara, M.; Macgregor, S. A.; Streib, W. E.; Folting, K.;
Eisenstein, O.; Caulton, K. G. J. Am. Chem. Soc. 1996, 118, 10189–
10199.

Article
Organometallics, Vol. 29, No. 21, 2010 5685
Figure 5. Tilt angle j between planes A and B in tri-32-Me and yaw distortion angle.11
Table 4. Influence of the N Substituent: Selected Yields of Silyl
Ether 5 and Silyl Enol Ether 6 and TOFs for the Hydrosilylation
of 4-Fluoroacetophenone with Diphenylsilane
Scheme 3. Hydrosilylation of 4-Fluoroacetophenone with
Diphenylsilane using [Rh(COD)(bisNHC)]PF6 Complexes
To Yield Silyl Ether 5 and Silyl Enol Ether 6
entry
complex
yield 5/6 (%)
TOF (h-1)
1
2
3
4
5
6
7
8
tri-32-Me
tri-32-iPr
bim-33-Me
bim-33-iPr
im-32-Me
im-32-Cy
tri-32-Ph
60/40
77/23
74/26
77/23
44/56
68/32
84/16
80/20
75/25
75/25
5
56
100
140
7
38
7
25
24
199
tri-32-4-iPrPh
im-32-Ph
Table 2. Yields of Silyl Ether 5 and Silyl Enol Ether 6 and
Turnover Frequencies for the Hydrosilylation of
4-Fluoroacetophenone with Diphenylsilanea
9
10
im-32-Mes
entry
complex
yield 5/6 (%)b
TOF (h-1)c
Table 5. Influence of the Heterocycle: Selected Yields of Silyl
Ether 5 and Silyl Enol Ether 6 and TOFs for the Hydrosilylation
of 4-Fluoroacetophenone with Diphenylsilane
1
2
3
4
5
6
7
8
tri-31-iPr
tri-32-Me
tri-32-iPr
tri-32-4-iPrPh
tri-32-Ph
71/29
60/40
77/23
80/20
84/16
77/33
80/20
66/34
74/26
88/12
77/23
82/18
80/20
44/56
58/42
68/32
75/25
75/25
163
5
56
25
7
entry
complex
yield 5/6 (%)
TOF (h-1)
1
2
3
4
5
6
7
8
9
tri-32-Me
bim-32-Me
im-32-Me
tri-32-iPr
bim-32-iPr
im-32-iPr
tri-32-Ph
bim-32-Ph
im-32-Ph
60/40
66/34
44/56
77/23
88/12
58/42
84/16
82/18
75/25
5
70
7
56
68
5
7
550
24
tri-33-iPr
tri-33-Ph
2
60
70
100
68
140
550
154
7
bim-32-Me
bim-33-Me
bim-32-iPr
bim-33-iPr
bim-32-Ph
bim-33-Ph
im-32-Me
im-32-iPr
im-32-Cy
im-32-Ph
9
10
11
12
13
14
15
16
17
18
5
38
24
199
Influence of Heterocycle. In order to study the influence of
the different heterocycles, the activities and selectivities of
complexes with the same N substituents (Me, iPr, Ph) and
bridge length (n = 2) are compared. Table 5 shows the TOFs
and yields of silyl ether 5 for the three sets of complexes.
According to these data, the benzimidazole-based systems
are the most active and, except for 32-Ph, also the most
selective catalysts, whereas the imidazole-based systems are
the least selective catalysts in all cases.
im-32-Mes
a 2 mol % catalyst in CH2Cl2 at 25 °C; conversion for all experiments
>99%. b Yields determined by 19F NMR spectroscopy. No spectro-
scopic evidence was found for compounds other than 4-6 and defluor-
ination; thus, additional reaction pathways were excluded and no
internal standard was needed. c TOFs were determined at the steepest
slope of the kinetic curves.
Table 3. Influence of the Bridge Length: Selected Yields of Silyl
Ether 5 and Silyl Enol Ether 6 and Turnover Frequencies for the
Hydrosilylation of 4-Fluoroacetophenone with Diphenylsilane
It is apparent that the benzimidazole systems offer the
most favorable electronic properties for achieving high acti-
vity and selectivity.
entry
complex
yield 5/6 (%)
TOF (h-1)
Conclusion
1
2
3
4
5
6
7
8
tri-31-iPr
tri-32-iPr
tri-33-iPr
tri-32-Ph
71/29
77/23
77/33
84/16
80/20
66/34
74/26
88/12
77/23
82/18
80/20
163
56
2
7
60
70
100
68
140
550
154
In summary, synthetic routes to novel triazole-, benzimi-
dazole- and imidazole-based bis-carbene ligands and derived
rhodium(I) complexes are described. The complexes were
analyzed by elemental analysis and mass spectrometry and
structurally characterized in solution by NMR spectroscopy
and by X-ray crystallography. All compounds are shown to
be catalytically active for the hydrosilylation of 4-fluoro-
acetophenone with diphenylsilane. The systematic study of a
tri-33-Ph
bim-32-Me
bim-33-Me
bim-32-iPr
bim-33-iPr
bim-32-Ph
bim-33-Ph
9
10
11

5686 Organometallics, Vol. 29, No. 21, 2010
Riederer et al.
variety of bis-carbene ligand systems reveals that the inter-
play of heterocycle, bridge length and N substituents has to
be considered when designing an appropriate catalyst for a
certain application. Sterically demanding substituents and
benzimidazole-based bis-carbene ligands with short bridge
lengths seem to be favorable for the hydrosilylation with
Rh(I) bis-carbene complexes. Additional mechanistic studies
are currently under way to allow a deeper understanding of
the observed results and the prediction of the modifications
necessary to enhance the catalyst activity and selectivity,
including applications for asymmetric hydrosilylation.
δ 1.53 (d, 3J = 6.4 Hz, 12H, CH3CH), 4.90 (sept, 3J = 6.4 Hz, 2H,
CH3CH), 6.91 (s, 2H, NCH2), 9.59 (s, 2H, NCHN), 10.69 (s, 2H,
NCHN). 13C{1H} NMR (100.5 MHz, DMSO-d6): δ 21.0 (CH3),
44.3 (NCH2), 55.1 (CH3CH), 141.5 (NCHN), 144.4 (NCHN).
1,10-Bis(4-isopropylphenyl)-4,40-ethylenedi-1,2,4-triazolium
Dibromide (tri-12-iPr). Yield: 1.52 g (54%). 1H NMR (400 MHz,
DMSO-d6): δ 1.24 (d, 3J = 6.6 Hz, 12H, CH3CH), 3.02 (sept, 2H,
3J = 6.6 Hz, CH3CH), 5.04 (s, 4H, NCH2), 7.58 (d, 4H, m-CH),
7.81 (d, 4H, o-CH), 9.46 (s, 2H, NCHN), 11.02 (s, 2H, NCHN).
13C{1H} NMR (100.5 MHz, DMSO-d6): δ 23.6 (CH3CH), 33.1
(CH3CH), 46.8 (NCH2), 120.7 (m-CH), 128.0 (o-CH), 132.8
(Cquat), 141.6 (NCHN), 145.1 (NCHN), 151.4 (Cquat).
1,10-Diphenyl-4,40-ethylenedi-1,2,4-triazolium Dibromide (tri-
1
12-Ph). Yield: 1.94 g (81%). H NMR (400 MHz, DMSO-d6):
Experimental Section
δ 5.06 (s, 4H, NCH2), 7.65 (m, 2H, p-CH), 7.73 (m, 4H, m-CH),
7.92 (m, 4H, o-CH), 9.50 (s, 2H, NCHN), 11.12 (d, 2H, NCHN).
13C{1H} NMR (100.5 MHz, DMSO-d6): δ 46.8 (NCH2),
120.6 (m-CH), 130.3 (o-CH), 130.7 (p-CH), 134.8 (Cquat),
142.0 (NCHN), 145.2 (NCHN).
General Remarks. The synthesis of the metal complexes was
carried out using standard Schlenk techniques under an argon
atmosphere. Solvents were dried and degassed by standard
methods prior to use.16 The term filtration refers to filtration
via cannula and a Whatman GF/B filter. Elemental analyses were
carried out by the Microanalytical Laboratory of the Technische
1,10-Diisopropyl-4,40-propylenedi-1,2,4-triazolium Dibromide
1
(tri-13-iPr). Yield: 2.08 g (98%). H NMR (400 MHz, DMSO-
3
d6): δ 1.54 (d, J = 6.8 Hz, 12H, CH3), 2.59 (t, 2H, NCH2-
€
€
Universitat Munchen. Mass spectra were acquired by the Tech-
3
CH2CH2N), 4.38 (t, 4H, NCH2), 4.82 (sept, J = 6.8 Hz, 2H,
€
€
nische Universitat Munchen Mass Spectrometry Laboratory
using a Finnigan MAT 90 spectrometer equipped with a FAB
ionization chamber. NMR spectra were recorded on a JEOL-
JMX-GX 400 MHz or Bruker Avance DPX 400 spectrometer.
NMR multiplicities are abbreviated as follows: s, singlet; d,
doublet; t, triplet; sept, septet; m, multiplet; br, broad signal.
Couplingconstants J are given in Hz. The spectra were referenced
to residual 1H and 13C{1H} signals of the solvents.17 If not
otherwise mentioned, all reagents were purchased from commer-
cial sources and used without further purification.
CH3CH), 9.35 (s, 2H, NCHN), 10.41 (s, 2H, NCHN). 13C{1H}
NMR (100.5 MHz, DMSO-d6): δ 21.0 (CH3), 28.3 (NCH2-
CH2CH2N), 44.3 (NCH2), 55.1 (CHCH3), 141.5 (NCHN), 144.4
(NCHN).
1,10-Diphenyl-4,40-propylenedi-1,2,4-triazolium Dibromide (tri-
1
13-Ph). Yield: 1.65 g (67%). H NMR (400 MHz, DMSO-d6):
δ 2.72 (qu, 2H, NCH2CH2CH2N), 4.52 (t, 4H, NCH2), 7.67 (m,
2H, p-CH), 7.73 (m, 4H, m-CH), 7.96 (m, 4H, o-CH), 9.54 (s, 2H,
NCHN), 11.10 (s, 2H, NCHN). 13C{1H} NMR (100.53 MHz,
DMSO-d6): δ 28.3 (NCH2CH2CH2N), 44.8 (NCH2), 120.7 (m-
CH), 130.3 (o-CH), 130.7 (p-CH), 135.0 (Cquat), 141.9 (NCHN),
145.2 (NCHN).
General Synthesis for Di-1,2,4-triazolium Bis(hexafluorophos-
phate) Salts. A solution of ditriazolium dibromide (5 mmol) in
water (15 mL) was added to a solution of potassium hexafluoro-
phosphate (10 mmol) in water (10 mL). The precipitate was
isolated by filtration, washed with diethyl ether (three times with
5 mL), and dried in vacuo overnight, yielding the colorless solid
product.
1,10-Diisopropyl-4,40-methylenedi-1,2,4-triazolium Bis(hexa-
fluorophosphate) (tri-21-iPr). Yield: 2.32 g (88%). 1H NMR (400
MHz, DMSO-d6): δ 1.53 (d, 3J = 6.6 Hz, 12H, CH3CH), 4.93
(sept, 3J = 6.6 Hz, 2H, CH3CH), 6.74 (s, 2H, NCH2), 9.36 (s,
2H, NCHN), 10.29 (s, 2H, NCHN). 13C{1H} NMR (100.5
MHz, DMSO-d6): δ 21.1 (CH3), 54.9 (NCH2), 55.6 (CH3CH),
142.2 (NCHN), 144.8 (NCHN). MS (FAB): m/z (%) 380.8
(36.7) [M þ PF6]þ, 234.9 (100) [M]2þ. Anal. Calcd for
C11H20F12N6P2 (526.10): C, 25.11: H, 3.83; N, 15.97. Found:
C, 24.99: H, 3.88; N, 15.95.
Di-1,2,4-triazolium Salts. 1-Phenyl-1H-1,2,4-triazole,18 1-(4-
isopropylphenyl)-1H-1,2,4-triazole,18 1-isopropyl-1H-1,2,4-tria-
zole,19 and 1-methyl-1H-1,2,4-triazole20 were prepared according
to previously reported literature methods. The ditriazolium
bromide and hexafluorophosphate salts were obtained by follow-
ing a previously reported procedure.4b,6a
1-(4-Isopropylphenyl)-1H-1,2,4-triazole. (4-Isopropylphenyl)-
hydrazine hydrochloride (3.44 g, 1.85 mol) was added to a
solution of s-triazine (1.0 g, 12.3 mmol) in ethanol (10 mL). The
mixture was refluxed for 12 h before the precipitating ammo-
nium chloride was removed by filtration, leaving a red filtrate.
The solvent was removed in vacuo to yield a dark brown oil
which was purified by vacuum distillation at 150 °C and 10-2
mbar. Yield: 1.91 g (72%). 1H NMR (400 MHz, CDCl3): δ 1.27
(d, 3J = 7.04 Hz, 6H, CH3CH), 2.96 (sept, 3J = 7.04 Hz, 1H,
CH3CH), 7.34 (d, 2H, m-CH), 7.57 (d, 2H, o-CH), 8.08 (s, 1H,
NCHN), 8.51 (s, 1H, NCHN). 13C{1H} NMR (100.5 MHz,
CDCl3): δ 23.9 (CH3CH), 33.8 (CH3CH), 120.2 (m-CH), 127.7
(o-CH), 134.9 (Cquart), 140.7 (NCHN), 149.3 (Cquart), 152.3
(NCHN).
1,10-Dimethyl-4,40-ethylenedi-1,2,4-triazolium Bis(hexafluoro-
phosphate) (tri-22-Me). Yield: 2.20 g (91%). 1H NMR (400 MHz,
DMSO-d6): δ 4.10 (s, 6H, CH3), 4.78 (s, 4H, NCH2), 9.06 (s, 2H,
NCHN), 9.94 (s, 2H, NCHN). 13C{1H} NMR (100.5 MHz,
DMSO-d6): δ 38.7 (CH3), 46.5 (NCH2), 143.1 (NCHN), 144.5
(NCHN). MS (FAB): m/z (%) 338.8 (17.4) [M þ PF6]þ, 191.7
(100) [M]2þ. Anal. Calcd for C8H14F12N6P2 (484.06): C, 19.85:
H, 2.91; N, 17.36. Found: C, 19.58: H, 2.92; N, 16.70.
1,10-Diisopropyl-4,40-ethylenedi-1,2,4-triazolium Bis(hexafluoro-
phosphate) (tri-22-iPr). Yield: 1.57 g (84%). 1H NMR (400 MHz,
General Procedure for the Synthesis of Di-1,2,4-triazolium
Dibromide. 1-R-1H-1,2,4-triazole (10 mmol), dibromoalkane
(5 mmol), and 2 mL of THF were heated for 12 h at 80 °C in
an ACE pressure tube with a volume of 35 mL. The precipitate
was isolated by filtration, washed three times with 5 mL of
diethyl ether, and dried under reduced pressure to obtain the
pure product in form of a colorless solid.
1,10-Diisopropyl-4,40-methylenedi-1,2,4-triazolium Dibromide
(tri-11-iPr). Yield: 1.72 g (87%), 1H NMR (400 MHz, DMSO-d6):
3
DMSO-d6): δ 1.52 (d, J = 6.6 Hz, 12H, CH3), 4.75 (s, 4H,
(16) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518–1520.
(17) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997,
62, 7512–7515.
(18) Grundmann, C.; Ratz, R. J. Org. Chem. 1956, 21, 1037–1038.
€
(19) Frey, G. D.; Schutz, J.; Herrmann, W. A. J. Organomet. Chem.
2006, 691, 2403–2408.
(20) Mirzaei, Y. R.; Twamley, B.; Shreeve, J. M. J. Org. Chem. 2002,
67, 9340–9345.
3
NCH2), 4.84 (sept, J = 6.6 Hz, 2H, CH3CH), 9.11 (s, 2H,
NCHN), 10.08 (s, 2H, NCHN). 13C{1H} NMR (100.5 MHz,
DMSO-d6): δ 21.1 (CH3), 46.5 (NCH2), 55.3 (CHCH3), 141.7
(NCHN), 144.7 (NCHN). MS (FAB): m/z (%) 394.8 (59.9)
[M þ PF6]þ, 248.9 (100) [M]2þ. Anal. Calcd for C12H22F12N6P2
(540.12): C, 26.68, H, 4.10; N, 15.56. Found: C, 26.51: H, 4.01;
N, 15.40.

Article
Organometallics, Vol. 29, No. 21, 2010 5687
1,10-Bis(4-isopropylphenyl)-4,40-ethylenedi-1,2,4-triazolium
δ 4.16 (s, 6H, CH3), 7.55 (s, 2H, NCH2N), 7.76 (m, 4H, CHarom),
8.09 (d, 2H, CHarom), 8.44 (d, 2H, CHarom), 10.41 (s, 2H, NCHN).
13C{1H} NMR (100 MHz, DMSO-d6): δ 34.6 (CH3), 55.4
(NCH2N), 114.3, 114.7, 127.7, 128.0 (CHarom), 130.8, 132.3
(Ctert), 144.8 (NCHN). HPLC-MS (ESI): m/z (%) 356.8 (7) [M -
Br]þ, 277.2 (100) [M - Br2] þ, 173.1 (16) [M - C8H9Br2N2]þ, 153.2
Bis(hexafluorophosphate) (tri-22-4-iPrPh). Yield: 2.60 g (96%).
1H NMR (400 MHz, DMSO-d6): δ 1.24 (d, 3J = 6.6 Hz, 12H,
CH3CH), 3.02 (sept, 2H, J = 6.6 Hz, CH3CH), 5.02 (s, 4H,
3
NCH2), 7.59 (m, 4H, m-CH), 7.81 (m, 4H, o-CH), 9.44 (s, 2H,
NCHN), 10.97 (s, 2H, NCHN). 13C{1H} NMR (100.5 MHz,
DMSO-d6): δ 23.6 (CH3CH), 33.1 (CH3CH), 46.8 (NCH2),
120.7 (m-CH), 128.0 (o-CH), 132.8 (Cquat), 141.6 (NCHN),
145.1 (NCHN), 151.4 (Cquat). MS (FAB): m/z (%) 547.1 (5.9)
[M þ PF6]þ, 401.0 (100) [M]2þ. Anal. Calcd for C24H30F12N6P2
(692.18): C, 41.63: H, 4.37; N, 12.14. Found: C, 41.54: H, 4.55;
N, 12.20.
1,10-Diphenyl-4,40-ethylenedi-1,2,4-triazolium Bis(hexafluoro-
phosphate) (tri-22-Ph). Yield: 2.37 g (78%). 1H NMR (400 MHz,
DMSO-d6): δ 4.99 (s, 4H, NCH2), 7.67 (m, 2H, p-CH), 7.74
(m, 4H, m-CH), 7.90 (m, 4H, o-CH), 9.42 (s, 2H, NCHN), 10.92
(s, 2H, NCHN). 13C{1H} NMR (100.5 MHz, DMSO-d6): δ 46.8
(NCH2), 120.5 (m-CH), 130.2 (o-CH), 130.7 (p-CH), 134.7
(Cquat), 141.9 (NCHN), 145.2 (NCHN). MS (FAB): m/z (%)
459.8 (100) [M þ PF6]þ. Anal. Calcd for C18H18F12N6P2
(608.09): C, 35.54: H, 2.98; N, 13.82. Found: C, 35.85: H,
2.84; N, 13.53.
(100) [M - Br]2þ
.
1,10-Dimethyl-3,30-ethylenedibenzimidazolium Dibromide
(bim-12-Me). Yield: 3.38 g (75%). 1H NMR (400 MHz,
DMSO-d6): δ 4.10 (s, 6H, CH3), 5.15 (s, 4H, CH2CH2), 7.62 (t,
2H, CHarom), 7.67 (t, 2H, CHarom), 7.93 (d, 2H, CHarom), 8.03 (d,
2H, CHarom), 9.88 (s, 2H, NCHN). 13C{1H} NMR (100 MHz,
DMSO-d6): δ 34.0 (CH3), 46.1 (CH2CH2), 113.6, 114.3, 127.2,
127.3 (CHarom), 131.4, 132.3 (Ctert), 144.0 (NCHN). HPLC-MS
(ESI):m/z (%) 371.0(7) [M - Br]þ, 291.1(100) [M - Br2] þ, 173.1
(16) [M - C8H9Br2N2]þ, 153.2 (100) [M - Br]2þ
.
1,10-Dimethyl-3,30-propylenedibenzimidazolium Dibromide
(bim-13-Me). Yield: 4.52 g (97%). 1H NMR (400 MHz, DMSO-
d6): δ 2.61 (q, 2H, NCH2CH2CH2N), 4.09 (s, 6H, CH3), 4.72 (t,
J = 7.1, 4H, NCH2CH2CH2N), 7.78-7.62 (m, 4H, CHarom), 8.08
(dd, J = 8.3, 33.2, 4H, CHarom), 9.90 (s, 2H, NCHN). 13C{1H}
NMR (100 MHz, DMSO-d6): δ 28.7 (CH2CH2CH2), 33.9 (CH3),
44.5 (CH2CH2CH2), 114.2, 127.0, 127.1 (CHarom), 131.5, 132.4
(Ctert), 143.5 (NCHN). HPLC-MS (ESI): m/z (%) 385.0 (12)
[M - Br]þ, 305.0 (15) [M - Br2] þ, 173.1 (16) [M - C8H9Br2N2]þ,
153.2 (100) [M - Br]2þ. Anal. Calcd for C19H22Br2N4: C, 48.95;
H, 4.76; N, 12.02. Found: C, 48.90; H, 5.00; N, 11.81.
1,10-Diisopropyl-4,40-propylenedi-1,2,4-triazolium Bis(hexa-
fluorophosphate) (tri-23-iPr). Yield: 2.69 g (97%). 1H NMR
(400 MHz, DMSO-d6): δ 1.57 (d, 3J = 6.6 Hz, 12H, CH3), 2.53
(t, 2H, NCH2CH2CH2N), 4.34 (t, 4H, NCH2), 4.86 (sept, 3J =
6.6 Hz, 2H, CH3CH), 9.24 (s, 2H, NCHN), 10.16(s, 2H, NCHN).
13C{1H} NMR (100.5 MHz, DMSO-d6):
δ 21.1 (CH3),
1,10-Diisopropyl-3,30-methylenedibenzimidazolium Dibromide
(bim-11-iPr). Yield: 2.66 g (54%). 1H NMR (400 MHz, DMSO-
d6): δ 1.68 (d, 12H, CH(CH3)2), 5.13 (sept, 2H, CH(CH3)2),
7.78-7.22 (m, 4H, CHarom), 8.21 (d,2H, CHarom), 8.46 (d,2H,
CHarom), 10.70 (s, 2H, NCHN). 13C{1H} NMR (100 MHz,
DMSO-d6): δ 22.1 (CH(CH3)2), 45.6 (NCH2N), 51.8 (CH-
(CH3)2), 114.2, 115.1, 127.6, 128.1 (CHarom), 131.0, 131.4
(Ctert), 143.5 (NCHN). HPLC-MS (ESI): m/z (%) 419.1 (15)
and 427.1 (17) [M - Br]þ, 348.2 (22) and 347.2 (5) [M - 2Br -
H]þ, 174.2 (100) [M - 2Br]2þ. Anal. Calcd for C21H26Br2N4: C,
51.03; H, 5.30; N, 11.34. Found: C, 51.04; H, 5.28; N, 10.98.
1,10-Diisopropyl-3,30-ethylenedibenzimidazolium Dibromide
(bim-12-iPr). Yield: 3.88 g (77%). 1H NMR (400 MHz, DMSO-
d6): δ 1.53 (d, 12H, CH(CH3)2), 5.07 (sept, 2H, CH(CH3)2),
7.66-7.59 (m, 4H, CHarom), 7.79 (d, 2H, CHarom), 8.10 (d, 2H,
CHarom), 9.84 (s, 2H, NCHN). 13C{1H} NMR (100 MHz,
DMSO-d6): δ 22.0 (CH(CH3)2), 45.4 (NCH2CH2N), 51.8
(CH(CH3)2), 114.2, 115.2, 127.6, 128.0 (CHarom), 131.1, 131.6
(Ctert), 141.5 (NCHN). HPLC-MS (ESI): m/z (%) 427.0 (17) and
429.0 (16) [M - Br]þ, 347.1 (28) [M - Br2 - H]þ, 305.2 (100) and
306.2 (20) [M - Br2 - C3H7]þ, 263.2 (33) [M - Br2 - (C3H7) þ
28.3 (NCH2CH2CH2N), 44.3 (NCH2), 55.1 (CHCH3), 141.3
(NCHN), 144.5 (NCHN). MS (FAB): m/z (%) 408.8 (46.9)
[M þ PF6]þ, 262.9 (100) [M]2þ. Anal. Calcd for C13H24F12N6P2
(554.14): C, 28.17: H, 4.36; N, 15.16. Found: C, 27.98; H, 4.37;
N, 15.03.
1,10-Diphenyl-4,40-propylenedi-1,2,4-triazolium Bis(hexafluoro-
phosphate) (tri-23-Ph). Yield: 2.55 g (82%). 1H NMR (400 MHz,
DMSO-d6): δ 2.65 (t, 2H, NCH2CH2CH2N), 4.48 (t, 4H, NCH2),
7.68 (t, 2H, p-CH), 7.75 (t, 4H, m-CH), 7.94 (d, 4H, o-CH), 9.46
(s, 2H, NCH), 10.94 (s, 2H, NCH). 13C{1H} NMR (100.53 MHz,
DMSO-d6): δ 28.1 (NCH2CH2CH2N), 44.5 (NCH2), 120.5 (m-
CH), 130.2 (o-CH), 130.6 (p-CH), 134.8 (Cquat), 141.7 (NCHN),
145.0 (NCHN). MS (FAB): m/z (%) 476.8 (69.3) [M þ PF6]þ,
330.9 (100) [M]2þ. Anal. Calcd for C19H20F12N6P2 (622.11): C,
36.67: H, 3.24; N, 13.50. Found: C, 36.82; H, 2.99; N, 13.28.
Dibenzimidazolium Salts. Methylbenzimidazole was synthe-
sized according to the literature procedure21 or was obtained from
a commercial source and sublimated (90 °C @ 10-2 mbar) prior
to use. Isopropylbenzimidazole5a and phenylbenzimidazole22 were
synthesized according to literature procedures. Isopropylbenzi-
midazole was distilled (bp 136-137 °C @ 2.0 mbar, 106 °C @ 0.2
mbar) to yield a colorless oil. Phenylbenzimidazole was purified by
extraction with hot pentane to yield a white solid.
H], 174.1 (53) [M - Br]2þ
.
1,10-Diisopropyl-3,30-propylenedibenzimidazolium Dibromide
(bim-13-iPr). Yield: 3.64 g (70%). 1H NMR (400 MHz, DMSO-
d6): δ 1.41 (d, 12H, CH(CH3)2), 3.35 (q, 2H, CH2CH2CH2), 4.53
(t, 4H, CH2CH2CH2), 4.85 (sept, 2H, CH(CH3)2), 7.49 (m, 4H,
CHarom), 7.96 (m, 4H, CHarom), 9.92 (s, 2H, NCHN). 13C{1H}
NMR (100 MHz, DMSO-d6): δ 22.1 (CH(CH3)2), 28.5
(CH2CH2CH2), 44.7 (CH2CH2CH2), 51.2 (CH(CH3)2), 114.2,
114.7, 127.2, 127.3 (CHarom), 131.1, 131.9 (Ctert), 141.3
(NCHN). HPLC-MS (ESI): m/z (%) 443.1 (23) and 441.0 (21)
General Synthesis for 1,10-Disubstituted 3,30-Alkyl-Bridged
Dibenzimidazolium Salts9. To a solution of the N-substituted
benzimidazole (20 mmol) in 5 mL of THF in an ACE pressure
tube was added dibromoalkane (10 mmol), and the mixture was
heated for 72 h at 120 °C. The solution was filtered off, and the
precipitate was washed with 2 ꢀ 5 mL of THF, recrystallized
from methanol, and dried in vacuo to yield a white powder.
-
Thereafter, an exchange of the anion from Br- to PF6 was
[M - Br] þ, 181.2 (100) [M - Br - H]2þ
.
1,10-Diphenyl-3,30-methylenedibenzimidazolium Dibromide
(bim-11-Ph). Yield: 1.17 g (21%). 1H NMR (400 MHz, DMSO-
d6): δ 7.71 (s, 2H, NCH2N), 7.76-7.92 (m, 16H, CHarom), 8.65 (d,
2H, CHarom), 10.88 (s, 1H, NCHN). 13C{1H} NMR (100 MHz,
DMSO-d6): δ 55.1 (NCH2N), 113.9, 114.1, 125.1, 127.9, 128.0,
130.6, 130.7 (CHarom), 130.8 (Ctert), 131.0 (CHarom), 132.8 (Ctert),
144.7 (NCHN). HPLC-MS (ESI): m/z (%) 481.1 (2) [M - Br]þ,
401.4 and 402.4 (17) [M - Br2 - H]þ.
performed.
1,10-Dimethyl-3,30-methylenedibenzimidazolium Dibromide
(bim-11-Me). Yield: 4.29 (89%). 1H NMR (400 MHz, DMSO-d6):
(21) (a) Claramunt, R. M. J. Heterocycl. Chem. 1983, 20, 1245–1249.
(b) Pilarski, B. Liebigs Ann. Chem. 1983, 1078–1080.
(22) (a) Kuil, M.; Bekedam, E. K.; Visser, G. M.; van den Hoogen-
band, A.; Terpstra, J. W.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.;
van Strijdonck, G. P. F. Tetrahedron Lett. 2005, 46, 2405–2409.
(b) Zhang, Z.; Mao, J.; Zhu, D.; Wu, F.; Chen, H.; Wan, B. Tetrahedron
2006, 62, 4435–4443. (c) Zhu, L.; Cheng, L.; Zhang, Y.; Xie, R.; You, J.
J. Org. Chem. 2007, 72, 2737–2743.
1,10-Diphenyl-3,30-ethylenedibenzimidazolium Dibromide (bim-
1
12-Ph). Yield: 3.80 g (64%). H NMR (400 MHz, DMSO-d6):
δ 5.37 (s, 4H, CH2CH2), 7.73-7.89 (m, 16H, CHarom), 8.16

5688 Organometallics, Vol. 29, No. 21, 2010
Riederer et al.
(d, 2H, CHarom), 10.47 (s, 2H, NCHN). 13C{1H} NMR (100
MHz, DMSO-d6): δ 45.7 (CH2CH2), 113.5, 113.7, 125.0, 127.2,
127.8, 130.5, 130.7 (CHarom), 130.9 (Ctert), 131.1 (Ctert), 132.9
(Ctert,Ph), 143.4 (NCHN). HPLC-MS (ESI): m/z (%) 417 (100)
and 418 (30) and 419 (12) [M - 2Br - H]þ.
(CHarom), 130.9, 131.8 (Ctert), 141.9 (NCHN). HPLC-MS (ESI):
m/z (%) 493.2 (90) and 494.2 (23) and 495.2 (2) [M - PF6]þ, 347.2
(28) and 348.2 (8) [M - 2PF6 - H]þ, 305.3 (50) and 306.2 (10)) [M
- 2PF6 - (C3H7)], 174.2 (100) [M - 2PF6]2þ. Anal. Calcd for
C22H28F12N4P2: C, 41.39; H, 4.42; N, 8.78. Found: C, 41.49; H,
4.45; N, 8.54.
1,10-Diisopropyl-3,30-propylenedibenzimidazolium Bis(hexa-
fluorophosphate) (bim-23-iPr). Yield: 4.89 g (75%). 1H NMR
(400 MHz, DMSO-d6): δ 1.62 (d, 12H, CH(CH3)2), 2.78 (q, 2H,
CH2CH2CH2), 4.65 (s, 4H, CH2CH2CH2), 5.06 (sept, 2H, CH-
(CH3)2), 7.70-7.74 (m, 4H, CHarom), 8.09 (d, 2H, CHarom), 8.15
(d, 2H, CHarom), 9.78 (s, 2H, NCHN). 13C{1H} NMR (100 MHz,
DMSO-d6): δ 22.0 (CH(CH3)2), 28.5 (CH2CH2CH2), 44.7
(CH2CH2CH2), 51.2 (CH(CH3)2), 114.2, 114.7, 127.2, 127.3
(CHarom), 131.1, 131.9 (Ctert), 141.3 (NCHN). HPLC-MS
(ESI): m/z (%) 507.1 (94) and 508.1 (27) [M - PF6]þ, 361.1
(49) and 362.1 (11) [M - 2PF6 - H]þ, 319.3 (58) and 320.2 (11)
[M - 2PF6 - (C3H7)], 181.2 (100) [M - 2PF6]2þ. Anal. Calcd for
C23H30F12N4P2: C, 42.34; H, 4.63; N, 8.59. Found: C, 42.30; H,
4.56; N, 8.72.
1,10-Diphenyl-3,30-propylenedibenzimidazolium Dibromide
(bim-13-Ph). Yield: 5.47 g (93%). 1H NMR (400 MHz, DMSO-
d6): δ 2.85 (q, 2H, CH2CH2CH2), 4.89 (t, 4H, CH2CH2CH2),
7.72-7.80 (m, 16H, CHarom), 8.30 (m, 2H, CHarom), 10.38 (s, 2H,
NCHN). 13C{1H} NMR (100 MHz, DMSO-d6): δ 27.7
(CH2CH2CH2), 44.3 (CH2CH2CH2), 113.6, 114.1, 125.2, 127.0,
127.6, 130.4, 130.5 (CHarom), 131.1, 131.3 (Ctert), 133.1 (Ctert,Ph),
142.7 (NCHN). HPLC-MS (ESI): m/z (%) 509.0 (17) and 511.0
(4) [M - Br]þ, 429.1 (28) [M - Br2 - H] þ
.
General Synthesis for 1,10-Substituted 3,30-Alkyl-Bridged Di-
benzimidazolium Hexafluorophosphate Salts. The azolium bro-
mide salt (10 mmol) was dissolved in 10 mL of warm water and
transferred via cannula to a solution of KPF6 (20 mmol) in 5 mL
of water, and a white precipitate formed. The mixture was
cooled for 5 h at 4 °C and filtered off. The residue was dried in
vacuo to yield a white powder.
1,10-Diphenyl-3,30-methylenedibenzimidazolium Bis(hexafluoro-
phosphate) (bim-21-Ph). Yield: 6.44 g (93%). 1H NMR (400 MHz,
DMSO-d6): δ 7.67 (s, 2H, NCH2N), 7.67 (s, 2H, NCH2N),
7.80-7.93 (m, 16H, CHarom), 8.63 (d, 2H, CHarom), 10.81 (s,
2H, NCHN). 13C{1H} NMR (100 MHz, DMSO-d6): δ 55.6
(NCH2N), 114.6, 118.1, 125.7, 128.6, 128.7, 130.7, 131.7
(CHarom), 132.7 (Ctert), 133.3 (CHarom), 135.3 (Ctert), 145.1
(NCHN). HPLC-MS (ESI): m/z (%) 494.9 (17) and 496.9
(15) [M - PF6]þ, 415.1 (94) and 416.1 (34) [M - 2PF6 - H]þ,
339.3 (39) [M - 2PF6 - C6H5]þ, 221.2 (100) [M - 2PF6 -
1,10-Dimethyl-3,30-methylenedibenzimidazolium Bis(hexa-
fluorophosphate) (bim-21-Me). Yield: 3.52 (62%). 1H NMR
(400 MHz, DMSO-d6): δ 4.14 (s, 6H, CH3), 7.40 (s, 2H, CH2),
7.75 (m, 4H, CHarom), 8.08 (d, 2H, CHarom), 8.34 (d, 2H, CHarom),
10.12 (s, 2H, NCHN). 13C{1H} NMR (100 MHz, DMSO-d6):
δ 34.3 (CH3), 55.4 (CH2), 114.1, 114.6, 127.7, 128.1 (CHarom),
130.8, 132.4 (Ctert), 144.8 (NCHN). HPLC-MS (ESI): m/z (%)
422.9 (49) and 424.0 (12) [M - PF6]þ, 277.1 (100) [M - 2PF6 -
H]þ. Anal. Calcd for C17H18F12N4P2: C, 35.93; H, 3.19; N, 9.86.
Found: C, 36.20; H, 3.23; N, 9.69.
1,10-Dimethyl-3,30-ethylenedibenzimidazolium Bis(hexafluoro-
phosphate) (bim-22-Me). Yield: 3.55 g (61%). 1H NMR (400
MHz, DMSO-d6): δ 4.05 (s, 6H, CH3), 5.08 (s, 4H, NCH2-
CH2N), 7.71 (m, 4H, CHarom), 7.90 (d, 2H, CHarom), 8.04 (d, 2H,
CHarom), 9.57 (s, 2H, NCHN). 13C{1H} NMR (100 MHz,
DMSO-d6): δ 33.9 (CH3), 46.1 (CH2CH2), 113.5, 114.3, 127.3,
127.4 (CHarom), 131.4, 132.3 (Ctert), 143.9 (NCHN). HPLC-MS
(ESI): m/z (%) 437.1 (42) and 438.1 (8) [M - PF6]þ, 291.2 (35)
and 292.2 (7) [M - 2PF6 - H]þ, 146.2 [M - 2PF6]2þ. Anal.
Calcd for C18H20F12N4P2: C, 37.13; H, 3.46; N, 9.62. Found: C,
37.47; H, 3.42; N, 9.51.
1,10-Dimethyl-3,30-propylenedibenzimidazolium Bis(hexafluoro-
phosphate) (bim-23-Me). Yield: 4.30 g (72%). 1H NMR (400 MHz,
DMSO-d6): δ 2.60 (q, 2H, J = 7.2), 4.66 (t, 4H, J = 7.2), 4.08 (s,
6H), 7.62-7.83 (m, 4H, CHarom), 7.95-8.15 (m, 4H, CHarom),
9.68 (s, 2H, NCHN). 13C{1H} NMR (100 MHz, DMSO-d6):
δ 28.6 (CH2CH2CH2), 33.9 (CH3), 44.4 (CH2CH2CH2), 114.0,
114.2, 127.1, 127.2 (CHarom), 131.4, 132.4 (Ctert), 143.4 (NCHN).
HPLC-MS(ESI):m/z (%) 451.9(28) [M - PF6]þ, 305.1 (22) [M -
2PF6 - H] þ. Anal. Calcd for C19H22F12N4P2: C, 38.27; H, 3.72;
N, 9.40. Found: C, 37.95; H, 3.52; N, 9.60.
C
13H11N2]þ. Anal. Calcd for C27H22F12N4P2: C, 46.83; H,
3.20; N, 8.09. Found: C, 46.43; H, 3.12; N, 7.86.
1,10-Diphenyl-3,30-ethylenedibenzimidazolium Bis(hexafluoro-
phosphate) (bim-22-Ph). Yield: 5.44 g (77%). 1H NMR (400 MHz,
DMSO-d6): δ 5.26 (s, 4H, CH2CH2), 7.73-7.90 (m, 16H,
CHarom), 8.11 (d, 2H, CHarom), 10.19 (s, 2H, NCHN). 13C{1H}
NMR (100 MHz, DMSO-d6): δ 46.3 (CH2CH2), 114.0, 114.4,
125.5, 127.9, 128.4, (CHarom), 131.1 (Ctert), 131.4 (CHarom),
131.6 (Ctert), 133.5 (Ctert,Ph), 144.0 (NCHN). HPLC-MS (ESI):
m/z (%) 417 (100) and 418 (30) and 419 (12) [M - 2PF6 - H]þ.
Anal. Calcd for C28H28F12P2N4: C, 47.60; H, 3.42; N, 7.93.
Found: C, 47.28; H, 3.38; N, 7.90.
1,10-Diphenyl-3,30-propylenedibenzimidazolium Bis(hexa-
1
fluorophosphate) (bim-23-Ph). Yield: 4.97 g (69%). H NMR
(400 MHz, DMSO-d6): δ 2.81 (q, 2H, CH2CH2CH2), 4.81 (t, 4H,
CH2CH2CH2), 7.74-7.92 (m, 16H, CHarom), 8.23 (m, 2H,
CHarom), 10.20 (s, 2H, NCHN). 13C{1H} NMR (100 MHz,
DMSO-d6): δ 28.0 (CH2CH2CH2), 44.8 (CH2CH2CH2), 114.2,
114.5, 125.7, 127.7, 128.2, 131.0, 131.2 (CHarom), 131.7, 131.8
(Ctert), 133.7 (Ctert,Ph), 143.3 (NCHN). HPLC-MS (ESI): m/z (%)
575.0 (35) [M - PF6]þ, 430 (8) [M - 2PF6]þ, 430 (19) [M - 2PF6
- H]þ, 215 (100) [M - 2PF6]2þ. Anal. Calcd for C29H26F12P2N4:
C, 48.34; H, 3.64; N, 7.78. Found: C, 47.98; H, 3.48; N, 7.69.
Diimidazolium Salts. The N-substituted imidazoles and the
imidazolium salts im-12-Me and im-32-iPr were synthesized ac-
cording to known literature procedures.23,9
General Synthesis of the Diimidazolium Bromides. A mixture
of the N-substituted imidazole (50 mmol), 1,2-dibromoethane
(25 mmol), and THF (5 mL) was heated in an ACE pressure tube
(35 mL) at 120 °C for 48 h. The resulting colorless precipitate
was collected by filtration, washed with THF (3 ꢀ 5 mL), and
dried in vacuo.
1,10-Dicyclohexyl-3,30-ethylenediimidazolium Dibromide (im-
12-Cy). Yield: 88%. 1H NMR (DMSO-d6): δ 1.16-1.23 (m, 2H,
cy-H), 1.33-1.42 (m, 4H, cy-H), 1.60-1.82 (m, 10H, cy-H), 2.05
1,10-Diisopropyl-3,30-methylenedibenzimidazolium Bis(hexa-
fluorophosphate) (bim-21-iPr). Yield: 2.81 g (45%). 1H NMR (400
MHz, DMSO-d6): δ 1.68 (d, 12H, CH(CH3)2), 5.13 (sept, 2H,
CH(CH3)2), 7.29 (s, 2H, NCH2N), 7.76-7.85 (m, 4H, CHarom),
8.20 (d, 2H, CHarom), 8.41 (d, 2H, CHarom), 10.31(s, 2H, NCHN).
13C{1H} NMR (100 MHz, DMSO-d6): δ 22.0 (CH(CH3)2), 51.9
(NCH2N), 55.7 (CH(CH3)2), 114.1, 115.1, 127.7, 128.2 (CHarom),
131.0, 131.4 (Ctert), 143.3 (NCHN). HPLC-MS (ESI): m/z (%)
479.0 (47) and 480.0 (8) and481.0 (2) [M - PF6]þ, 333.2 (100) and
334.2 (24) and 335.4 (3) [M - PF6 - H]þ, 291.1 (34) and 292.2 (4)
[M - PF6 - C3H7]þ.
1,10-Diisopropyl-3,30-ethylenedibenzimidazolium Bis(hexafluoro-
phosphate) (bim-22-iPr). Yield: 4.00 g (63%). 1H NMR (400 MHz,
DMSO-d6): δ 1.54 (d, 12H, CH(CH3)2), 5.02 (sept, 2H, CH-
(CH3)2), 5.06 (s, 4H, NCH2CH2N), 7.60-7.66 (m, 4H, CHarom),
7.79 (d, 2H, CHarom), 8.10 (d, 2H, CHarom), 9.79 (s, 2H, NCHN).
13C{1H} NMR (100 MHz, DMSO-d6): δ 22.0 (CH(CH3)2, 46.4
(NCH2CH2N), 51.2 (CH(CH3)2), 113.3, 114.7, 127.3, 127.4
(23) (a) Gridnev, A. A.; Mihaltseva, I. M. Synth. Commun. 1994, 24,
1547–1555. (b) Liu, J.; Chen, J.; Zhao, J.; Zhao, Y.; Li, L.; Zhang, H.
Synthesis 2003, 2661–2666. (c) Lu, C. Y.; Chen, C. Y.; Chen, W. L.; Lin,
H. C.; Chin, P. L.; Chen, P. Y. Tetrahedron 2004, 60, 5807–5825.

Article
Organometallics, Vol. 29, No. 21, 2010 5689
(m, 4H, cy-H), 4.30 (m, 2H, cy-H), 4.76 (s, 4H, NCH2), 7.70 (s,
2H, NCH), 7.93 (s, 2H, NCH), 9.40 (s, 2H, NCHN). 13C{1H}
NMR (DMSO-d6): δ 24.3 (s, cy-C3/C4/C5), 32.3 (s, cy-C2/C6),
48.4 (s, cy-C1), 58.7 (s, NCH2), 121.2 (s, NCH), 122.5 (s, NCH),
135.5 (s, NCHN). MS (FAB): m/z (%) 407 (16) [M þ Br]þ, 327
1,10-Diphenyl-3,30-ethylenediimidazolium Dibromide (im-12-Ph).
Yield: 78%. 1H NMR (DMSO-d6): δ 4.98 (s, 4H, NCH2), 7.60
(t, 3JHH = 7.7 Hz, 2H, ar-H4), 7.67 (t, 3JHH = 7.7 Hz, 4H, ar-H3/
H5), 7.82 (d, 3JHH = 7.7 Hz, 4H, ar-H2/H6), 8.04 (s, 2H, NCH),
8.38 (s, 2H, NCH), 10.13 (s, 2H, NCHN) . 13C{1H} NMR
(DMSO-d6): δ 48.7 (s, NCH2), 121.2 (s, NCH), 121.8 (s, ar-C2/
C6), 123.5 (s, NCH), 129.8 (s, ar-C4), 130.1 (s, ar-C3/C5), 134.7
(s, ar-C1), 136.3 (s, NCHN).
(s, ar-C4), 140.5 (s, NCHN). 31P{1H} NMR (DMSO-d6):
δ -144.0 (sp, 1JPF = 709.2 Hz, PF6). MS (FAB): m/z (%) 545
(9) [M þ PF6]þ, 399 (15) [M]2þ, 213 (100) [M - mesityl-
imidazole]2þ. Anal. Calcd for C26H32F12N4P2 (690.49): C,
45.23; H, 4.67; N, 8.11. Found: C, 45.87; H, 5.00; N, 8.11.
General Synthesis for 1,2,4-Triazolium-Based Rhodium
Complexes.10. NaH (12.16 mg, 0.51 mmol) was dissolved in
ethanol (5 mL) and slowly added to a suspension of [RhCl-
(COD)]2 (50.0 mg, 0.10 mmol) in ethanol (5 mL). The reaction
mixture was stirred for 30 min at room temperature before the
di-1,2,4-triazolium bis(hexafluorophosphate) salt (0.21 mmol)
was added. After the mixture was stirred for 16 h at 40 °C, the
solvent was reduced in vacuo. The remaining solid was dissolved
in dichloromethane, this solution was filtered, and then the
solvent was removed under reduced pressure to obtain the pure
product. Crystals suitable for X-ray diffraction were obtained
by slow diffusion of pentane into a solution of the corresponding
complex in dichloromethane.
(21) [M]2þ, 177 (100) [M - cyclohexylimidazole]2þ
.
1,10-Dimesityl-3,30-ethylenediimidazolium Dibromide (im-12-Mes).
Yield: 86%. 1H NMR (DMSO-d6): δ1.99 (s, 12H, ar-CH3), 2.33 (s,
6H, ar-CH3), 5.05 (s, 4H, NCH2), 7.15 (s, 4H, ar-H3/H5), 8.01 (s,
2H, NCH), 8.13 (s, 2H, NCH), 9.65 (s, 2H, NCHN). 13C{1H}
NMR (DMSO-d6): δ 17.0 (s, ar-CH3), 20.6 (s, ar-CH3), 48.5 (s,
NCH2), 123.3 (s, NCH), 124.2 (s, NCH), 129.3 (s, ar-C3/C5), 130.9
(s, ar-C1), 134.2 (s, ar-C2/C6), 138.1 (s, ar-C4), 140.4 (s, NCHN).
MS (FAB): m/z (%) 479 (11) [M þ Br]þ, 399 (20) [M]2þ, 213 (100)
(η4-1,5-Cyclooctadiene)(1,10-diisopropyl-4,40-methyleneditria-
zoline-5,50-diylidene)rhodium(I) Hexafluorophosphate (tri-31-iPr).
Yield: 101.4 mg (86%). 1H NMR (400 MHz, DCM): δ 1.38, 1.46
(d, 3J = 6.6 Hz, 6H, CH3), 2.10 (m, 4H, CODallyl), 2.34 (m, 2H,
CODallyl), 2.56 (br, 2H, CODallyl), 4.75 (sept, 3J = 6.6 Hz, 2H,
CH3CH), 4.86 (br, 4H, CODvinyl), 6.37, 6.55 (d, 2J = 13.1 Hz, 4H,
NCH2N), 8.44 (s, 2H, NCHN). 13C{1H} NMR (100.5 MHz,
DCM): δ 22.8, 23.1 (CH3), 30.8, 30.9 (CODallyl), 55.0 (CH3CH),
[M - mesitylimidazole]2þ
.
Synthesis of the Diimidazolium Bis(hexafluorophosphates).4b
A solution of diimidazolium dibromide (7.7 mmol) in water
(15 mL) was added to a solution of potassium hexafluoropho-
sphate (2.9 g, 15 mmol) in water (50 mL). The resulting pre-
cipitate was isolated by filtration, washed with diethyl ether (3 ꢀ
5 mL), and dried in vacuo overnight to yield im-22-R in the form
of a colorless solid.
1
59.1 (NCH2), 89.7 (d, JRh-C = 7.6 Hz, CODvinyl), 94.3 (d,
1JRh-C = 8.4 Hz, CODvinyl), 142.3 (NCHN), 179.8 (d, 1JRh-C
=
51.2 Hz, carbene). 31P NMR (161.8 MHz, DCM): δ -143.6
(sept). MS (FAB): m/z (%) 444.7 (8.2) [M]þ, 336.7 (100) [M -
COD]þ. Anal. Calcd for C19H30F6N6PRh (590.35): C, 38.66: H,
5.12; N, 14.24. Found: C, 38.55: H, 5.27; N, 14.31.
1,10-Diisopropyl-3,30-ethylenediimidazolium Bis(hexafluoro-
phosphate) (im-22-iPr). Yield: 80%. 1H NMR (DMSO-d6): δ
3
3
(η4-1,5-Cyclooctadiene)(1,10-dimethyl-4,40-ethyleneditriazo-
line-5,50-diylidene)rhodium(I) Hexafluorophosphate (tri-32-Me).
Yield: 101.2 mg (91%). 1H NMR (400 MHz, DCM): δ 2.25 (m,
2H, CODallyl), 2.36 (m, 4H, CODallyl), 2.52 (m, 2H, CODallyl),
3.98 (s, 6H, CH3), 4.68-4.80 (m, 6H, NCH2, CODvinyl), 5.42 (m,
2H, NCH2), 8.11 (s, 2H, NCHN). 13C{1H} NMR (100.5 MHz,
DCM): δ 30.8, 30.9 (CODallyl), 40.5 (CH3), 45.6 (NCH2), 90.6
1.61 (d, JHH = 6.8 Hz, 12H, CHCH3), 4.81 (sp, JHH = 6.8
Hz, 2H, CHCH3), 5.02 (s, 4H, NCH2), 7.74 (s, 2H, NCH), 7.90
(s, 2H, NCH), 9.29 (s, 2H, NCHN). 13C{1H} NMR (DMSO-
d6): δ 22.8 (s, CHCH3), 49.8 (s, NCH2), 54.5 (s, CHCH3), 122.4
(s, NCH), 123.9 (s, NCH), 136.5 (s, NCHN). 31P{1H} NMR
(acetone-d6): δ -143.6 (sp, 1JPF = 707.4 Hz, PF6). MS (FAB):
m/z (%) 393 (100) [M þ PF6]þ, 247 (68) [M]2þ. Anal. Calcd for
C14H24F12N4P2 (538.30): C, 31.24; H, 4.49; N, 10.41. Found:
C, 31.13; H, 4.43; N, 9.84.
1
1
(d, JRh-C = 7.6 Hz, CODvinyl), 93.1 (d, JRh-C = 7.6 Hz,
CODvinyl), 144.3 (NCHN), 181.9 (d, 1JRh-C = 51.2 Hz, carbene).
31P NMR (161.8 MHz, DCM): δ -143.8 (sept). MS (FAB): m/z
(%) 402.5 (100) [M]þ, 294.6 (35.0) [M - COD]þ. Anal. Calcd for
C16H24F6N6PRh (548.29): C, 35.05: H, 4.41; N, 15.33. Found: C,
34.81: H, 4.68; N, 15.52.
1,10-Diphenyl-3,30-ethylenediimidazolium Bis(hexafluorophos-
phate) (im-22-Ph). Yield: 91%. 1H NMR (DMSO-d6): δ 4.83 (s,
4H, NCH2), 7.61 (t, 3JHH = 7.7 Hz, 2H, ar-H4), 7.69 (t, 3JHH
=
7.7 Hz, 4H, ar-H3/H5), 7.83 (d, 3JHH = 7.7 Hz, 4H, ar-H2/H6),
7.90 (s, 2H, NCH), 8.35 (s, 2H, NCH), 9.80 (s, 2H, NCHN) .
13C{1H} NMR (DMSO-d6): δ 48.9 (s, NCH2), 121.5 (s, NCH),
121.8 (s, ar-C2/C6), 123.4 (s, NCH), 130.0 (s, ar-C4), 130.2 (s, ar-
C3/C5), 134.6 (s, ar-C1), 136.1 (s, NCHN). 31P{1H} NMR
(DMSO-d6): δ -143.5 (sp, 1JPF = 710.9 Hz, PF6). Anal. Calcd
for C20H20F12N4P2 (606.33): C, 39.62; H, 3.32; N, 9.24. Found:
C, 39.26; H, 2.99; N, 8.95.
(η4-1,5-Cyclooctadiene)(1,10-diisopropyl-4,40-ethyleneditriazo-
line-5,50-diylidene)rhodium(I) Hexafluorophosphate (tri-32-iPr).
Yield: 109.4 mg (89%). 1H NMR (400 MHz, DCM): δ 1.36 (d,
6H, CH3), 1.47 (d, 6H, CH3), 2.21-2.56 (m, 8H, CODallyl), 4.62
(br, 2H, CODvinyl), 4.73 (m, 4H, NCH2, CODvinyl), 4.97 (sept,
2H, CH3CH), 5.45 (m, 2H, NCH2), 8.14 (s, 2H, NCHN). 13C-
{1H} NMR (100.5 MHz, DCM): δ 23.0 (CH3), 30.9 (CODallyl),
1
1,10-Dicyclohexyl-3,30-ethylenediimidazolium Bis(hexafluoro-
phosphate) (im-22-Cy). Yield: 72%. 1H NMR (acetone-d6): δ
1.23-1.34 (m, 2H, cy-H), 1.43-1.54 (m, 4H, cy-H), 1.70-1.92
(m, 10H, cy-H), 2.24 (m, 4H, cy-H), 4.45 (m, 2H, cy-H), 4.99 (s,
4H, NCH2), 7.69 (s, 2H, NCH), 7.90 (s, 2H, NCH), 9.02 (s, 2H,
NCHN). 13C{1H} NMR (acetone-d6): δ 25.4 (s, cy-C4), 25.6 (s,
cy-C3/C5), 33.7 (s, cy-C2/C6), 50.0 (s, cy-C1), 61.0 (s, NCH2),
122.7 (s, NCH), 123.7 (s, NCH), 136.1 (s, NCHN). 31P{1H}
45.7 (NCH2), 55.6 (CH3CH), 90.0 (d, JRh-C = 6.9 Hz,
CODvinyl), 92.8 (d, JRh-C = 8.4 Hz, CODvinyl), 144.5
1
1
(NCHN), 180.0 (d, JRh-C = 50.5 Hz, carbene). 31P NMR
(161.8 MHz, DCM): δ -143.7 (sept). MS (FAB): m/z (%) 458.6
(100) [M]þ, 350.6 (68.1) [M - COD]þ Anal. Calcd for
C20H32F6N6PRh (604.38): C, 39.75: H, 5.34; N, 13.91. Found:
C, 40.13: H, 5.43; N, 13.42.
(η4-1,5-Cyclooctadiene)(1,10-bis(4-isopropylphenyl)-4,40-ethyl-
eneditriazoline-5,50-diylidene)rhodium(I) Hexafluorophosphate
(tri-32-4-iPrPh). Yield: 122.0 mg (80%). 1H NMR (400 MHz,
DCM): δ 1.34 (d, 3J = 7.04 Hz, 12H, CH3), 1.93 (br, 8H,
CODallyl), 3.06 (sept, 3J = 7.04 Hz, 2H, CH3CH), 3.77 (br, 2H,
CODvinyl), 4.53 (br, 2H, CODvinyl), 4.90 (m, 2H, NCH2), 5.71
(m, 2H, NCH2), 7.41-8.00 (m, 8H, aryl), 8.39 (s, 2H, NCHN).
1
NMR (acetone-d6): δ -143.6 (sp, JPF = 709.2 Hz, PF6). MS
(FAB): m/z (%) 473 (29) [M þ PF6]þ, 327 (27) [M]2þ, 177 (100)
[M - cyclohexylimidazole]2þ
.
1,10-Dimesityl-3,30-ethylenediimidazolium Bis(hexafluorophos-
phate) (im-22-Mes). Yield: 91%. H NMR (acetone-d6): δ 1.98
1
(s, 12H, ar-CH3), 2.33 (s, 6H, ar-CH3), 4.97 (s, 4H, NCH2), 7.15
(s, 4H, ar-H3/H5), 8.00 (s, 2H, NCH), 8.05 (s, 2H, NCH), 9.49 (s,
2H, NCHN). 13C{1H} NMR(DMSO-d6): δ17.0 (s, ar-CH3), 20.6
(s, ar-CH3), 48.7 (s, NCH2), 123.3 (s, NCH), 124.4 (s, NCH),
129.4 (s, ar-C3/C5), 130.9 (s, ar-C1), 134.2 (s, ar-C2/C6), 138.0
13C{1H} NMR (100.5 MHz, DCM): δ 24.1 (CH3), 30.4, 30.8
1
(CODallyl), 34.4 (CH3CH), 46.8 (NCH2), 90.9 (d, JRh-C
7.7 Hz, CODvinyl), 93.0 (d, JRh-C = 8.4 Hz, CODvinyl),
124.3, 127.4, 137.2, 144.5 (aryl), 151.4 (NCHN), 181.5 (d,
=
1

5690 Organometallics, Vol. 29, No. 21, 2010
Riederer et al.
1JRh-C = 51.2 Hz, carbene); 31P NMR (161.8 MHz, DCM): δ
-143.7 (sept). MS (FAB): m/z (%) 610.7 (35.1) [M]þ, 502.7 (100)
[M - COD]þ. Anal. Calcd for C32H40F6N6PRh (756.57): C,
50.80: H, 5.33; N, 11.11. Found: C, 50.57: H, 5.42; N, 10.93.
(η4-1,5-Cyclooctadiene)(1,10-diphenyl-4,40-ethyleneditriazoline-
5,50-diylidene)rhodium(I) Hexafluorophosphate (tri-32-Ph). Yield:
127.6 mg (94%). 1H NMR (400 MHz, DCM): δ 1.96 (m,
4H, CODallyl), 2.03-2.12 (m, 2H, CODallyl), 2.33-2.26 (m, 2H,
CODallyl), 3.81 (br, 2H, CODvinyl), 4.57 (br, 2H, CODvinyl), 4.92
(m, 2H, NCH2), 5.74 (m, 2H, NCH2), 7.59 (m, 6H, aryl),
8.14-8.17 (m, 4H, aryl), 8.42 (s, 2H, NCHN). 13C{1H} NMR
(100.5 MHz, DCM): δ 30.4, 30.7 (CODallyl), 46.8 (NCH2),
(η4-1,5-Cyclooctadiene)(1,10-dimethyl-3,30-ethylenedibenzimi-
dazoline-2,20-diylidene)rhodium(I) Hexafluorophosphate (bim-
3
2-Me). Yield: 290.9 mg (90%). 1H NMR (400 MHz, DCM-d2):
δ 2.35 (dm, 4H, CODallyl), 2.53 (dm, 4H, CODallyl), 4.08 (s, 6H,
CH3), 4.81 (br, 4H, CODvinyl), 4.88 (m, 2H, CH2), 5.88 (m, 2H,
CH2), 7.28 (m, 6H, CHarom), 7.44 (m, 2H, CHarom). 13C{1H}
NMR (100 MHz, DCM-d2): δ 30.5, 31.1 (CODallyl), 50.8
(CH2CH2) 54.5 (CH3), 90.6, 90.7, 93.0, 93.1 (CODvinyl),
109.6, 109.9, 123.4, 123.6 (CHarom), 134.7, 135.1 (Ctert), 192.0
(NCN, d, 1JRh-C = 51.5 Hz). HPLC-MS (ESI): m/z (%) 501.2
(58) and 502.2 (20) and 503.2 (2) [M - PF6]þ, 393.3 (26) and
394.4 (6) [M - PF6 - COD]þ . MS (FAB): m/z (%) 500.5
(100.0), 501.5 (31.4), 502.5 (4.4), 392.5 (45.4). Anal. Calcd for
C26H30F6N4PRh: C, 48.31; H, 4.68; N, 8.67. Found: C, 44.92;
H, 4.39; N, 8.39.
1
91.0 (d, JRh-C = 6.9 Hz, CODvinyl), 93.4 (1JRh-C = 8.5 Hz,
CODvinyl), 124.2, 129.5, 130.0, 139.4 (aryl), 144.6 (NCHN), 181.7
1
(d, JRh-C = 52 Hz, carbene). 31P NMR (161.8 MHz, DCM):
δ -143.7 (sept). MS (FAB): m/z (%) 526.5 (100) [M]þ, 418.5
(87.3) [M - COD]þ. Anal. Calcd for C26H28F6N6PRh (672.42):
C, 46.44; H, 4.20; N, 12.50. Found: C, 46.01: H, 4.67; N, 12.12.
(η4-1,5-Cyclooctadiene)(1,10-diisopropyl-4,40-propyleneditria-
zoline-5,50-diylidene)rhodium(I) Hexafluorophosphate (tri-33-iPr).
Yield: 122.5 mg (98%). 1H NMR (400 MHz, DCM): δ 1.47 (d,
12H, CH3), 2.25-2.36 (m, 5H, CODallyl, NCH2CH2CH2N),
2.42-2.54 (m, 4H, CODallyl), 2.62 (m, 1H, NCH2CH2CH2N),
4.48-4.60 (m, 6H, NCH2, CODvinyl), 4.86 (m, 2H, NCH2), 5.10
(sept, 2H, CH3CH), 8.05 (s, 2H, NCHN). 13C{1H} NMR (100.5
MHz, DCM): δ 22.6, 24.2 (CH3), 30.8, 31.0 (CODallyl),
33.1 (NCH2CH2CH2N), 50.3 (NCH2), 55.3 (CH3CH), 91.0
(η4-1,5-Cyclooctadiene)(1,10-dimethyl-3,30-propylenedibenzimi-
dazoline-2,20-diylidene)rhodium(I) Hexafluorophosphate (bim-33-Me).
1
Yield: 290.6 mg (88%). H NMR (400 MHz, DCM-d2): δ 2.38
(m, 4H, CODallyl), 2.64 (m, 4H, CODallyl), 4.20 (s, 6H, CH3), 4.74
(br, 4H, CODvinyl), 4.78 (m, 2H, CH2CH2CH2), 5.30 (m, 4H,
CH2CH2CH2), 7.22-7.29 (m, 8H, CHarom). 13C{1H} NMR (100
MHz, DCM-d2): δ 23.6 (CH3) 30.5, 30.7, (CODallyl), 36.3
(CH2CH2CH2), 45.3 (CH2CH2CH2), 49.5 (CH3), 91.5, 92.0,
92.1, 92.3 (CODvinyl), 109.3, 109.9, 123.0, 123.2 (CHarom),
134.5, 135.0 (Ctert), 194.6 (NCN, d, 1JRh-C = 52.3 Hz). HPLC-
MS (ESI): m/z (%) 515.3 (100) and 516.3 (29) and 517.3 (4) [M -
PF6]þ, 407.3 (38) [M - PF6 - C8H12]þ. MS(FAB): m/z (%) 514.6
(100.0), 515.6 (31.6), 516.5 (4.5), 406.6 (26.6), 274.7 (27.8). Anal.
Calcd: C, 49.10; H, 4.88; N, 8.48. Found: C, 48.81; H, 4.91;
N, 8.39.
1
1
(d, JRh-C = 7.7 Hz, CODvinyl), 92.4 (d, JRh-C = 7.7 Hz,
CODvinyl), 144.6 (NCHN), 182.6 (d, 1JRh-C = 52.0 Hz, carbene).
31P NMR (161.8 MHz, DCM): δ -143.8 (sept). MS (FAB): m/z
(%) 474.7 (100) [M]þ, 364.7 (48.8) [M - COD]þ. Anal. Calcd for
C21H34F6N6PRh (618.42): C, 40.79: H, 5.54; N, 13.59. Found: C,
40.74: H, 6.00; N, 13.10.
(η4-1,5-Cyclooctadiene)(1,10-diisopropyl-3,30-ethylenedibenzi-
midazoline-2,20-diylidene)rhodium(I) Hexafluorophosphate (bim-
32-iPr). Yield: 298.6 mg (85%). 1H NMR (400 MHz, DCM-d2):
δ 2.31 (dm, 4H, CODallyl), 2.52 (dm, 4H, CODallyl), 4.67 (br, 2H,
CODvinyl), 4.81 (br, 2H, CODvinyl), 4.90 (m, 2H, CH2), 5.54
(sept, 2H, CH(CH3)2), 5.94 (m, 2H, CH2), 7.24 (m, 4H, CHarom),
7.49 (m, 4H, CHarom). 13C{1H} NMR (100 MHz, DCM-d2):
δ 21.4, 21.9 (CH3), 30.2, 30.5 (CODallyl), 44.5 (CH2CH2), 51.0
(CH(CH3)2), 89.6, 89.8, 92.7, 92.8 (CODvinyl), 110.2, 112.2,
123.4, 123.0, 123.4 (CHarom), 132.1, 136.2 (Ctert), 190.2 (NCN,
d, 1JRh-C = 52.3 Hz). HPLC-MS (ESI): m/z (%) 557.1 (20) and
558.2 (7) and 559.1(1) [M - PF6]þ, 449.3 (100) and 450.3 (23)
and 451.2 (3) [M - PF6 - COD]þ. MS (FAB): m/z (%) 556.5
(100.0), 557.6 (34.4), 558.6 (5.6), 448.6 (72.2), 364.5 (17.2). Anal.
Calcd: C, 51.29; H, 5.45; N, 7.98. Found: C, 50.98; H, 5.24;
N, 7.64.
(η4-1,5-Cyclooctadiene)(1,10-phenyl-4,40-propyleneditriazoline-
5,50-diylidene)rhodium(I) Hexafluorophosphate (tri-33-Ph). Yield:
138.1 mg (99.2%). 1H NMR (400 MHz, DCM): δ 2.13-2.28 (m,
7H, CODallyl, NCH2CH2CH2N), 2.56 (br, 2H, CODallyl), 2.83 (br,
1H, NCH2CH2CH2N), 4.36 (br, 2H, CODvinyl), 4.63 (br, 2H,
CODvinyl), 4.71(m, 2H, NCH2), 5.18 (m, 2H, NCH2), 7.26 (m, 4H,
aryl), 7.40 (m, 2H, aryl), 7.82 (m, 4H, aryl), 8.27 (s, 2H, NCHN).
13C{1H} NMR (100.5 MHz, DCM): δ 30.4, 31.0 (CODallyl), 33.3
1
(NCH2CH2CH2N), 51.1 (NCH2), 91.2 (d, JRh-C = 7.7 Hz,
1
CODvinyl), 93.3 (d, JRh-C = 8.4 Hz, CODvinyl), 123.8, 129.4,
129.5, 138.8 (aryl), 144.4 (NCHN), 185.1 (d, 1JRh-C = 51.2 Hz,
carbene). 31P NMR (161.8 MHz, DCM): δ -143.8 (sept). MS
(FAB): m/z (%) 540.3 (100) [M]þ, 432.4 (73.7) [M - COD]þ.
Anal. Calcd for C27H30F6N6PRh (686.45): C, 47.24: H, 4.41; N,
12.24. Found: C, 47.33: H, 4.33; N, 11.68.
(η4-1,5-Cyclooctadiene)(1,10-diisopropyl-3,30-propylenedibenzi-
midazoline-2,20-diylidene)rhodium(I) Hexafluorophosphate
(bim-33-iPr). Yield: 315.2 mg (88%). 1H NMR (400 MHz,
DCM-d2): δ 2.07-2.87 (m, 8H, CODallyl), 4.67 (br, 4H, CODvinyl),
4.78 (m, 2H, CH2), 5.32 (m, 2H, CH2), 5.63 (sept, 2H, CH(CH3)2),
7.22 (m, 4H, CHarom), 7.29 (m, 2H, CHarom), 7.49 (m, 2H,
CHarom). 13C{1H} NMR (100 MHz, DCM-d2): δ 22.3, 22.8
(CH3), 30.4, 30.7 (CODallyl), 37.1 (CH2CH2CH2) 50.8 (CH-
(CH3)2), 54.5, (CH2CH2CH2), 90.15, 90.22, 92.0, 92.12
(CODvinyl), 122.65, 112.40, 122.65, 123.15 (CHarom), 132.1, 136.4
(Ctert), 193.2 (NCN, d, 1JRh-C = 53.8 Hz). HPLC-MS (ESI): m/z
(%) 571 (18) and 572 (5) [M - PF6]þ, 463 (100) [M - PF6 -
C8H12]þ. MS (FAB): m/z (%) 570.5 (100.0), 571.5 (36.4), 572.5
(6.0), 462.5 (88.1), 302.6 (56.6). Anal. Calcd: C, 51.96; H, 5.63; N,
7.82; F, 15.91; P, 4.32; Rh, 14.36. Found: C, 51.46; H, 5.74; N, 7.75.
(η4-1,5-Cyclooctadiene)(1,10-diphenyl-3,30-ethylenedibenzimi-
dazoline-2,20-diylidene)rhodium(I) Hexafluorophosphate (bim-
32-Ph). Yield: 377.5 mg (98%). 1H NMR (400 MHz, DCM-d2):
δ 1.46, 1.74, 2.00, 2.32 each (m, 2H, CODallyl), 3.71 (br, 2H,
CODvinyl), 4.70 (br, 2H, CODvinyl), 5.11 (m, 2H, CH2CH2), 6.13
(m, 2H, CH2CH2), 7.20 (m, 2H, Ph-CHarom), 7.28 (m, 2H,
Ph-CHarom), 7.44 (m, 2H, Ph-CHarom), 7.62 (m, 4H, bim-
CHarom), 7.66 (m, 4H, Ph-CHarom), 7.73 (m, 4H, bim-CHarom).
13C{1H} NMR (100 MHz, DCM-d2): δ 30.3, 31.0 (CODallyl),
Cyclooctadiene Rhodium Ethoxide Dimer [Rh(COD)OEt]2.
[Rh(COD)Cl]2 (1 g) was stirred in a 1 M solution of NaOEt in
MeOH at room temperature overnight. The color of the pre-
cipitate changed from orange to yellow. The reaction mixture
was filtered and the remaining residue washed with cold MeOH
and Et2O. Yield: 98%.
General Synthesis of Benzimidazole-Based Rhodium Comp-
lexes.10,4b. The dibenzimidazolium salt (0.50 mmol) was stirred
for approximately 30 min with 1 mL of a 1 M solution of NaOEt
in MeOH. [Rh(COD)OEt]2 (0.25 mmol) was dissolved in 5 mL of
THF and the clear, yellow solution added via a Teflon cannula to
the dibenzimidazolium salt mixture. The mixture was stirred for
2-5 h at room temperature, while a color change of the reaction
mixture from the white dibenzimidazolium salt to a yellow
complex was observed. The solvent was removed in vacuo, and
the yellow residue was extracted several times with dichloro-
methane until a white residue remained. To the extract was added
8 mL of ethanol, and the solvent was reduced in vacuo to a
volume of about 1-2 mL to furnish a yellow precipitate. The
mixture was cooled to -35 °C for 2-3 h and the remaining
solvent filtered off. The yellow precipitate was washed with cold
Et2O (2-3 mL) and dried in vacuo.

Article
Organometallics, Vol. 29, No. 21, 2010 5691
45.8 (CH2CH2), 90.6, 90.7, 92.1, 92.2 (CODvinyl), 110.6, 111.5,
124.5, 124.9, 127.2, 130.3, 130.5, 135.1, 136.2, 138.2 (CHarom),
191.2 (NCN, d, JRh-C = 53.4 Hz). HPLC-MS (ESI): m/z
(η4-1,5-Cyclooctadiene)(1,10-dicyclohexyl-3,30-ethylenediimi-
dazoline-2,20-diylidene)rhodium(I) Hexafluorophosphate (im-
3
1
2-Cy). Yield: 97%. H NMR (CD2Cl2): δ 1.40-1.50 (m, 8H,
1
(%) 625.2 (30) and 626.2 (12) and 627.3 (3) [M - PF6]þ, 557.9
(100) and 558.8 (28) [M - PF6 - COD þ H3CCN]•þ, 517.6 (30)
and 518.5 (9) [M - PF6 - COD]þ . MS (FAB): m/z (%) 624.3
(62.1), 625.4 (25.5), 626.4 (5.17), 516.4 (100), 321.5 (9.5). Anal.
Calcd: C, 56.11; H, 4.45; N, 7.27. Found: C, 55.14; H, 4.42;
N, 7.34.
cy-H), 1.71-1.79 (m, 4H, cy-H), 1.87-1.96 (m, 8H, cy-H),
2.12-2.19 (m, 2H, COD-CH2), 2.25-2.31 (m, 2H, COD-CH2),
2.33-2.40 (m, 2H, COD-CH2), 2.43-2.51 (m, 2H, COD-CH2),
4.40-4.47 (m, 4H, COD-CH/NCHH), 4.53-4.62 (m, 4H, COD-
3
CH/cy-H), 5.53 (m, 2H, NCHH), 6.86 (d, JHH = 1.9 Hz, 2H,
3
NCH), 7.02 (d, JHH = 1.9 Hz, 2H, NCH). 13C{1H} NMR
(η4-1,5-Cyclooctadiene)(1,10-diphenyl-3,30-propylenedibenzi-
midazoline-2,20-diylidene)rhodium(I) Hexafluorophosphate
(bim-33-Ph). Yield: 306.0 mg (78%). 1H NMR (400 MHz,
DCM-d2): δ 1.87 (m, 2H, CODallyl), 1.97 (m, 2H, CODallyl),
2.20 (m, 2H, CODallyl), 2.55 (m, 2H, CODallyl), 4.10 (s, 2H,
CODvinyl), 4.69 (s, 2H, CODvinyl), 4.97 (m, 2H, CH2CH2CH2),
5.56 (m, 4H, CH2CH2CH2), 7.14 (m, 2H, CHarom), 7.21 (m, 2H,
CHarom), 7.32 (m, 2H, CHarom), 7.45 (m, 10H, CHarom), 7.56 (m,
2H, CH). 13C{1H} NMR (100 MHz, DCM-d2): δ 29.2, 29.8, 30.3
(CODallyl), 39.6 (CH2CH2CH2), 54.3 (CH2CH2CH2), 90.2, 90.3,
(CD2Cl2): δ 25.4 (s, cy-C), 26.1 (s, cy-C), 26.4 (s, cy-C), 31.0 (s,
COD-CH2), 31.1 (s, COD-CH2), 34.9 (s, cy-C), 35.3 (s, cy-C),
48.2 (s, cy-C), 61.6 (s, NCH2), 87.6 (d, JRhC = 7.7 Hz, COD-
1
CH), 90.6 (d, 1JRhC = 8.5 Hz, COD-CH), 118.1 (s, NCH), 123.3
1
(s, NCH), 178.6 (d, JRhC = 52.3 Hz, NCN). 31P{1H} NMR
(CD2Cl2): δ -143.8 (sp, 1JPF = 710.9 Hz, PF6). MS (FAB): m/z
(%) 537 (84) [M]þ, 427 (100) [M - COD]þ. Anal. Calcd for
C28H42F6N4PRh (682.53): C, 49.27; H, 6.20; N, 8.21. Found: C,
48.97; H, 6.37; N, 8.06.
(η4-1,5-Cyclooctadiene)(1,10-diphenyl-3,30-ethylenediimidazo-
line-2,20-diylidene)rhodium(I) Hexafluorophosphate (im-32-Ph).
91.7, 91.8 (CODvinyl), 109.8, 111.5, 123.6, 124.0, 126.6, 129.5,
129.8, 134.8, 135.8, 137.0 (CHarom), 195.2 (NCN, d, JRh-C =
1
1
Yield: 95%. H NMR (CD2Cl2): δ 1.55-1.74 (m, 4H, COD-
CH2), 1.90-1.96 (m, 2H, COD-CH2), 2.19-2.28 (m, 2H, COD-
CH2), 3.47 (s, 2H, COD-CH), 4.42 (s, 2H, COD-CH), 4.65 (m,
2H, NCHH), 5.79 (m, 2H, NCHH), 7.24 (d, 3JHH = 1.7 Hz, 2H,
NCH), 7.28 (d, 3JHH = 1.7 Hz, 2H, NCH), 7.51-7.56 (m, 6H,
ar-H), 7.79-7.82 (m, 4H, ar-H). 13C{1H} NMR (CD2Cl2): δ
30.3 (s, COD-CH2), 30.9 (s, COD-CH2), 49.2 (s, NCH2), 88.2
(d, 1JRhC = 7.7 Hz, COD-CH), 90.4 (d, 1JRhC = 9.2 Hz, COD-
CH), 123.1 (s, NCH), 123.4 (s, NCH), 125.2 (s, ar-C), 129.5
55.3 Hz). HPLC-MS (ESI): m/z (%) 639.1 (33) and 640.1 (13) and
641.1 (2) [M - PF6]þ, 571.6 (62) [M - PF6 - COD þ H3CCN]þ,
531.3 (100) and 532.3 (27) and 533.2 (4) [M - PF6 - COD]þ. MS
(FAB): m/z (%) 638.4 (80.7), 639.4 (35.2), 640.4 (7.0), 530.5 (100),
336.6 (33.1). Anal. Calcd: C, 56.64; H, 4.62; N, 7.14. Found: C,
55.21; H, 4.68; N, 6.72.
Imidazole-Based Rhodium Complexes. A solution of sodium
hydride (12.7 mg, 0.51 mmol) in ethanol (5 mL) was slowly
added to a suspension of [RhCl(COD)]2 (50.0 mg, 0.10 mmol) in
ethanol (5 mL). The reaction mixture was stirred for 30 min at
room temperature before im-22-R (0.20 mmol) was added. After
(s, ar-C), 129.6 (s, ar-C), 140.1 (s, ar-C), 179.6 (d, 1JRhC = 52.3
1
Hz, NCN). 31P{1H} NMR (CD2Cl2): δ -143.8 (sp, JPF
=
710.9 Hz, PF6). MS (FAB): m/z (%) 524 (80) [M]þ, 416 (100)
[M - COD]þ.
the mixture was stirred for 72 h in the case of im-32-Me, im-32-iPr
,
(η4-1,5-Cyclooctadiene)(1,10-dimesityl-3,30-ethylenediimidazo-
line-2,20-diylidene)rhodium(I) Hexafluorophosphate (im-32-Mes).
and im-32-Cy and 16 h in the case of im-32-Ph and im-32-Mes at
50 °C, the solvent was removed under reduced pressure. The
product was extracted with dichloromethane (3 ꢀ 5 mL). The
obtained solutions were combined and filtered, and the solvent
was removed in vacuo. The solid residue was washed with
pentane (3 ꢀ 5 mL) and dried under reduced pressure to obtain
im-32-R in the form of a yellow solid.
1
Yield: 96%. H NMR (CD2Cl2): δ 1.51 (m, 2H, COD-CH2),
1.69 (m, 2H, COD-CH2), 1.83 (s, 6H, ar-CH3), 1.86 (s, 6H,
ar-CH3), 2.18 (m, 2H, COD-CH2), 2.33 (s, 6H, ar-CH3), 2.36 (m,
2H, COD-CH2), 3.61 (s, 2H, COD-CH), 4.48 (s, 2H, COD-CH),
4.66 (m, 2H, NCHH), 5.82 (m, 2H, NCHH), 6.85 (d, 3JHH = 1.7
Hz, 2H, NCH), 6.91 (s, 2H, ar-H), 6.93 (s, 2H, ar-H), 7.28 (d,
3JHH = 1.7 Hz, 2H, NCH). 13C{1H} NMR (CD2Cl2): δ 17.8 (s,
ar-CH3), 19.7 (s, ar-CH3), 21.1 (s, ar-CH3), 30.7 (s, COD-CH2),
(η4-1,5-Cyclooctadiene)(1,10-dimethyl-3,30-ethylenediimidazo-
line-2,20-diylidene)rhodium(I) Hexafluorophosphate (im-32-Me).
1
Yield: 95%. H NMR (CD2Cl2): δ 2.14-2.20 (m, 2H, COD-
1
31.2 (s, COD-CH2), 49.7 (s, NCH2), 86.9 (d, JRhC = 7.7 Hz,
COD-CH), 89.2 (d, JRhC = 9.2 Hz, COD-CH), 122.7 (s,
CH2), 2.22-2.28 (m, 2H, COD-CH2), 2.34-2.37 (m, 2H, COD-
CH2), 2.43-2.50 (m, 2H, COD-CH2), 3.82 (s, 6H, NCH3), 4.41
(m, 2H, NCHH), 4.61 (s, 4H, COD-CH), 5.51 (m, 2H, NCHH),
6.83 (d, 3JHH = 2.1 Hz, 2H, NCH), 6.97 (d, 3JHH = 2.1 Hz, 2H,
NCH). 13C{1H} NMR (acetone-d6): δ 31.1 (s, COD-CH2), 31.3
1
NCH), 125.3 (s, NCH), 129.3 (s, ar-C), 129.4 (s, ar-C), 135.6
(s, ar-C), 136.3 (s, ar-C), 136.5 (s, ar-C), 139.8 (s, ar-C), 179.1
(d, 1JRhC = 53.0 Hz, NCN). 31P{1H} NMR (CD2Cl2): δ -143.8
(sp, 1JPF = 710.9 Hz, PF6). MS (FAB): m/z (%) 609 (68) [M]þ,
501 (100) [M - COD]þ. Anal. Calcd for C34H42F6N4PRh
(754.59): C, 54.12; H, 5.61; N, 7.42. Found: C, 54.46; H,
5.81; N, 7.00.
(s, COD-CH2), 38.5 (s, NCH3), 48.5 (s, NCH2), 88.0 (d, 1JRhC
=
8.5 Hz, COD-CH), 90.5 (d, 1JRhC = 8.5 Hz, COD-CH), 123.6
1
(s, NCH), 180.8 (d, JRhC = 52.3 Hz, NCN). 31P{1H} NMR
(acetone-d6): δ -143.6 (sp, 1JPF = 707.4 Hz, PF6). MS (FAB):
m/z (%) 401 (100) [M]þ.
€
Acknowledgment. Dr. Karl Ofele, Prof. Dr. Peter
(η4-1,5-Cyclooctadiene)(1,10-diisopropyl-3,30-ethylenediimida-
zoline-2,20-diylidene)rhodium(I) Hexafluorophosphate (im-32-iPr).
Yield: 95%. 1H NMR (CD2Cl2): δ 1.31 (d, 3JHH = 7.1 Hz, 6H,
€
Harter, and Dr. Evangeline Tosh are gratefully acknowl-
edged for helpful discussions. This work was generously
supported by the Margarete Ammon Stiftung (Ph.D.
grant for S.K.U.R.) and the Wacker AG (Ph.D. grant
for P.G. and M.P.H.). S.K.U.R., P.G., and M.P.H.
performed the majority of the experiments and data
analysis. E.H. and B.B. collected and analyzed the
X-ray data. F.E.K. and W.A.H. designed and supervised
the research. The paper was written by S.K.U.R., P.G.,
M.H., B.B., and F.E.K., and all authors discussed the
results and commented on the paper.
3
CHCH3), 1.42 (d, JHH = 7.1 Hz, 6H, CHCH3), 2.12-2.18
(m, 2H, COD-CH2), 2.21-2.27 (m, 2H, COD-CH2), 2.33-2.40
(m, 2H, COD-CH2), 2.42-2.51 (m, 2H, COD-CH2), 4.40-4.48
(m, 4H, NCHH/COD-CH), 4.62 (s, 2H, COD-CH), 4.97 (sp,
3JHH = 7.1 Hz, 2H, CHCH3), 5.56 (m, 2H, NCHH), 6.89 (d,
3JHH =1.6 Hz, 2H, NCH), 7.04 (d, 3JHH = 1.6 Hz, 2H, NCH).
13C{1H} NMR (CD2Cl2): δ 24.0 (s, CHCH3), 24.1 (s, CHCH3),
30.9 (s, COD-CH2), 31.0 (s, COD-CH2), 48.2 (s, NCH2), 50.6 (s,
CHCH3), 87.5 (d, 1JRhC = 7.7 Hz, COD-CH), 90.6 (d, 1JRhC
=
8.5 Hz, COD-CH), 117.4 (s, NCH), 123.6 (s, NCH), 178.5 (d,
1JRhC = 52.3 Hz, NCN). 31P{1H} NMR (CD2Cl2): δ -143.8 (sp,
1JPF = 710.9 Hz, PF6). MS (FAB): m/z (%) 457 (100) [M]þ, 349
(87) [M - COD]þ. Anal. Calcd for C22H34F6N4PRh (602.40): C,
43.86; H, 5.69; N, 9.30. Found: C, 44.22; H, 5.86; N, 8.76.
Supporting Information Available: Tables and figures giving
crystallographic details and Diamond plots of all crystal structures
and CIF files giving crystallographic data for all X-ray studies.

5692 Organometallics, Vol. 29, No. 21, 2010
Riederer et al.
This material is available free of charge via the Internet at
http://pubs.acs.org. Crystallographic data (excluding struc-
ture factors) for all structures reported in this paper have
also been deposited with the Cambridge Crystallographic Data
Centre as Supplementary Publication Nos. CCDC-776289
(tri-32-Me), CCDC-776288 (tri-32-4-iPrPh), CCDC-776290 (tri-
CCDC-776280 (bim-32-Me), CCDC-776282 (bim-32-iPr), CCDC-
776281 (bim-32-Ph), CCDC-776285 (im-32-Me), CCDC-776284
(im-32-Cy), CCDC-776287 (im-32-Ph), and CCDC-776286 (im-
32-Mes). Copies of the data can be obtained free of charge
on application to the CCDC, 12 Union Road, Cambridge
CB2 1EZ, U.K. (fax, (þ44)1223-336-033; e-mail, deposit@
ccdc.cam.ac.uk).
3
2-Ph), CCDC-776292 (tri-33-iPr), CCDC-776291 (tri-33-Ph),