A new stable CNHCCHCNHCN-heterocyclic dicarbene ligand: Its mono- and dinuclear Ir(i) and Ir(i)-Rh(i) complexes

Article abstract of DOI:10.1039/b902733e

The ligand [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-2-ylidene) (2) (abbreviated as ^EtC_NHCCHC_NHC with CH = central aromatic ring, = CH₂ spacer) has been synthesised, and isolated, by deprotonation of [(1,3-phenylene)bis(methylene)]bis(1-ethyl- imidazolium) dichloride, ^Et(CH_imid.CHCH _imid.)Cl₂ (1) with LiN(SiMe₃)₂. This new, remarkably stable NHC dicarbene ligand is quantitatively protonated with HBr to form [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazolium) dibromide ^Et(CH_imid.CHCH_imid.)Br₂ (3) and reprotonated slowly enough in MeOH to allow observation of the monoprotonated intermediate 4. Dicarbene 2 reacts with S₈ to give the dithione compound [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-2-thione) ^Et[(SC)CH(CS)] (6). Reaction of 2 with [IrCl(CO)(PPh ₃)₂] and [Ir(μ-Cl)(cod)]₂ yielded the mononuclear [Ir(CO)(PPh₃)₂^Et(CH _imid.CHC_NHC)(PF₆)](PF₆) (8) and [IrCl(cod)^Et(CH_imid.CHC_NHC)](PF₆) (10) complexes, respectively, and the dinuclear complexes [{Ir(CO)(PPh ₃)₂}₂^Et(μ-C_NHCCHC _NHC)](PF₆)₂ (7) and [{IrCl(cod)} ₂^Et(μ-C_NHCCHC_NHC)] (9), respectively, in which 2 acts as a bridging, non-pincer type ligand. Only one other Ir(i) complex has been reported before containing a C _NHCCHC_NHC ligand. The structures of 6 and 9 were determined by X-ray diffraction and depict different conformations of the (1,3-phenylene)bis(methylene) (or xylylene) moiety. The mononuclear Ir complex 9 reacted smoothly with [Rh(μ-Cl)(cod)]₂ and Cs₂CO ₃ to generate a rare example of a heteronuclear NHC complex, [IrRhCl₂(cod)₂^Et(μ-C_NHCCHC _NHC)] (11).

Full text of DOI:10.1039/b902733e

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A new stable CNHC∧CH∧CNHC N-heterocyclic dicarbene ligand:
its mono- and dinuclear Ir(I) and Ir(I)–Rh(I) complexes†
Matthieu Raynal,a Catherine S. J. Cazin,‡a Christophe Valle´e,b He´le`ne Olivier-Bourbigoub and
Pierre Braunstein*a
Received 10th February 2009, Accepted 27th February 2009
First published as an Advance Article on the web 30th March 2009
DOI: 10.1039/b902733e
The ligand [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-2-ylidene) (2) (abbreviated as
Et
C
NHC
∧CH∧CNHC with CH = central aromatic ring, ∧ = CH2 spacer) has been synthesised, and isolated,
by deprotonation of [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazolium) dichloride,
Et(CHimid.∧CH∧CHimid.)Cl2 (1) with LiN(SiMe3)2. This new, remarkably stable NHC dicarbene ligand is
quantitatively protonated with HBr to form [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazolium)
dibromide Et(CHimid.∧CH∧CHimid.)Br2 (3) and reprotonated slowly enough in MeOH to allow
observation of the monoprotonated intermediate 4. Dicarbene 2 reacts with S8 to give the dithione
compound [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-2-thione) Et[(S C) CH (C S)] (6).
Reaction of 2 with [IrCl(CO)(PPh3)2] and [Ir(m-Cl)(cod)]2 yielded the mononuclear [Ir(CO)(PPh3)2-
Et(CHimid.∧CH∧CNHC)(PF6)](PF6) (8) and [IrCl(cod)Et(CHimid.∧CH∧CNHC)](PF6) (10) complexes,
respectively, and the dinuclear complexes [{Ir(CO)(PPh3)2}2Et(m-CNHC∧CH∧CNHC)](PF6)2 (7) and
[{IrCl(cod)}2Et(m-CNHC∧CH∧CNHC)] (9), respectively, in which 2 acts as a bridging, non-pincer type
ligand. Only one other Ir(I) complex has been reported before containing a CNHC∧CH∧CNHC ligand. The
structures of 6 and 9 were determined by X-ray diffraction and depict different conformations of the
(1,3-phenylene)bis(methylene) (or xylylene) moiety. The mononuclear Ir complex 9 reacted smoothly
with [Rh(m-Cl)(cod)]2 and Cs2CO3 to generate a rare example of a heteronuclear NHC complex,
[IrRhCl2(cod)2Et(m-CNHC∧CH∧CNHC)] (11).
∧
∧
=
=
proved ingenious)9,10 or the reduction of thione compounds11,12
Introduction
are both suitable routes. Dicarbene metal complexes are usually
generated in situ by metallation of their imidazolium precursor.4
The drawback of this method is that undesired reactions may
occur between unreacted base and the metal precursors or the
products.13 Only few free dicarbenes have been isolated12,14–19 and
they often require storage temperatures below -15 ◦C (Scheme 1).
In particular, CNHCCHCNHC or CNHCNCNHC dicarbene ligands
have been isolated (II, III, IV and V, Scheme 1) and their
reactivity, mostly in the case of CNHCNCNHC ligands, has been
investigated towards organic reagents20 and transition metals.18,19,21
However, the dicarbene ligands containing a methylene spacer,
CNHC∧CH∧CNHC and CNHC∧N∧CNHC, have not been isolated but
generated10 and/or used in situ for the preparation of Ag,22–27
Au,28 Cu,29 Pd,23–25,27,30–36 rare-earth,37 Ir38 and Rh24 complexes,
and remain less studied than the CNHCCHCNHC and CNHCNCNHC
systems.21
In the course of the last fifteen years, N-heterocyclic carbene
(NHC) ligands have emerged as a unique class of ligands, and
their transition metal complexes have recently found impressive
applications in homogeneous catalysis.1–6 The isolation of 1,3-di-
1-adamantyl-imidazol-2-ylidene by Arduengo et al.7 in 1991 was
key to this success since free carbenes ceased to be only regarded
as highly reactive or fleeting intermediates. The kinetic stability
of a free carbene appears to be governed by both electronic
and steric parameters but remains rather difficult to anticipate.
For example, bulky groups on nitrogen are no prerequisite
for getting a “bottle-able” free carbene and e.g. tetramethyl-
imidazol-2-ylidene is stable at room temperature under N2.8 The
experimental conditions used to generate isolable free carbenes
are also critical: the deprotonation of imidazolium salts (in this
case the use of NaH in NH3–THF or NH3–CH3CN mixture
Although Ag(I),22 Au(I),28 Cu(II)29 (non-pincer type),
Pd(II),25,30,31,35,36 or rare-earth elements37 (pincer and non-
pincer type) complexes have been prepared from the well-known
salts R(CHimid.∧CH∧CHimid.)X2 containing an imidazolium or a
benzimidazolium core, only one Ir(I) complex has been reported,
[Ir(cod)i-Pr(CNHC∧CH∧CNHC)]Cl (triazolium core),38a before our
work.38b.c Its structure was suggested to contain a chelating,
non-pincer type dicarbene ligand.38a In view of potential catalytic
applications, we were interested in isolating the new, potentially
pincer dicarbene ligand EtCNHC∧CH∧CNHC (∧ is a CH2 spacer) 2 in
order to study its reactivity and coordination behaviour towards
iridium complexes.
aLaboratoire de Chimie de Coordination, Institut de Chimie, UMR 7177
CNRS, Universite´ de Strasbourg, 4 rue Blaise Pascal, F-67070, Strasbourg
Cedex, France. E-mail: braunstein@chimie.u-strasbg.fr; Fax: +33 390 241
322
bIFP-Lyon, Rond Point de l’Echangeur de Solaize, BP3, 69360, Solaize
† Electronic supplementary information (ESI) available: The formula of
ligands and complexes described in this paper, the NMR spectra of
compounds 1–11 and the CIF files for compounds 6 and 9. CCDC
reference numbers 706832 and 719957. For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/b902733e
‡ Present address: School of Chemistry, University of St Andrews, North
Haugh, St Andrews, UK KY16 9ST.
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Scheme 1 Isolated dicarbene ligands. *The dimer is in equilibrium with the free dicarbene in solution.12,14,39
Results and discussion
The salt [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazolium)
dichloride Et(CHimid.∧CH∧CHimid.)Cl2 (1) was prepared similarly to
its methyl analog Me(CHimid.∧CH∧CHimid.)Cl2,40 but in contrast to
the reactions of the latter with KOt-Bu or KH,22 1 was cleanly
deprotonated by two equivalents of LiN(SiMe3)2 (THF, -78 ◦C) to
yield the dicarbene ligand EtCNHC∧CH∧CNHC (2) (eqn (1), in general,
the drawings do not intend to give an exact view of the molecular
conformations).
(2)
(1)
Compound 2 was collected as a white solid at the end of the
reaction and could be stored under nitrogen at room temperature
for months without any sign of decomposition. It is scarcely
soluble in THF and aromatic solvents but soluble in more polar
1
solvents such as DMSO and MeOH. Its H NMR spectrum in
(3)
d6-DMSO confirmed the deprotonation of 1 since the resonance
of the acidic NCHN proton at d 9.82 ppm has disappeared and the
other signals were upfield shifted by 0.1 (for CH3) to 0.6 (for the
aromatic protons) ppm. Progressive degradation of 2 in DMSO
(the solution turns red after 0.5 h) and its reprotonation in alcohols
1
(see below) prevented determination of the 13C{ H} NMR chemi-
cal shift of the carbene carbon. Although reprotonation of 2 with
HBr instantly gave Et(CHimid.∧CH∧CHimid.)Br2 (3) as indicated by
the appearance of the 1H NMR resonance for the NCHN protons
at 9.48 ppm, reprotonation in MeOH was surprisingly slow
enough to allow observation of a monoprotonated intermediate
[EtCHimid.∧CH∧CNHC]OMe (4), which is suggested to have the proton
bridging between the two carbenes (eqn (2), see ESI†).41
protonation of 2 being slower than thione formation. Compound
6 could also be obtained quantitatively from 1 or 5 by reacting
them with Cs2CO3 and S8 in MeOH at room temperature.
Single crystals suitable for X-ray diffraction studies were ob-
tained by slow diffusion of pentane in a saturated dichloromethane
solution of 6 (Fig. 1, Table 1).† The unit cell contains two
crystallographically independent molecules A and B. For both
molecules, the two imidazole rings are almost orthogonal to the
Formation of the dicarbene 2 was further demonstrated by its
rapid reaction with S8 which afforded the mono- and dithione
derivatives Et[CHimid. CH (C S)]Cl (5) and [(S C) CH (C S)]
(6), in 10–15% and 85% yield, respectively (eqn (3)). The presence
of the chloride counterion in 5 suggests that it was already
present in 2, probably in the form of a LiCl adduct. Coordination
of free carbene to soluble lithium salts is commonly observed
and could explain the unexpected stability of the “deprotonated
product”.42,43 Although this reaction was carried out in MeOH,
neither formation of 1 or 4 was observed, consistent with
∧
∧
Et
∧
∧
=
=
=
=
central phenyl, and the C S moieties are placed in the same half
space defined by the aromatic ring (as represented in eqn (3)). The
=
C S distances (molecule A: C1–S1 = 1.694(2), C14–S2 = 1.678(2)
˚
˚
A; molecule B: C1–S1 = 1.686(2), C14–S2 = 1.682(2) A) are in
the range of values reported for mono-44–46, di-47–49 and trithione50
compounds. The C1–N1, C1–N2, C14–N3 and C14–N4 distances
˚
in 6 are longer by nearly 0.05 A than the corresponding distances
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Table 1 Crystal data and structure refinement for 6 and 9
6
9
Chemical formula
Mr
C18H22N4S2
358.52
Monoclinic, P21/c
173(2)
14.1399(3)
9.5935(3)
28.2325(8)
90.00
103.675(2)
90.00
3721.21(18)
8
1.280
Mo Ka
0.29
Prism, colourless
0.25 ¥ 0.15 ¥ 0.15
Kappa CCD
CCD
C34H46Cl2Ir2N4
966.05
Triclinic, P-1
173(2)
10.5520(8)
11.0660(8)
15.0870(12)
101.543(5)
98.061(4)
101.036(3)
1664.7(2)
2
1.927
Mo Ka
8.18
Cube, yellow
0.1 ¥ 0.1 ¥ 0.1
Kappa CCD
CCD
Cell setting, space group
Temperature/K
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
Dx/Mg m-3
Radiation type
m/mm-1
Crystal form, colour
Crystal size/mm
Diffractometer
Data collection method
Absorption correction
None
Multi-scan (based on symmetry-related
measurements)
0.410, 0.482
19970, 8774, 6327
I > 2s(I)
0.068
T
min, Tmax
—
No. of measured, independent and observed reflections
Criterion for observed reflections
13019, 8071, 5472
I > 2s(I)
0.027
Rint
qmax
Refinement on
◦
/
27.0
29.0
F2
F2
R[F2 > 2s(F2)], wR(F2), S
No. of reflections
No. of parameters
H-atom treatment
Weighting scheme
0.047, 0.150, 1.06
8071
437
0.045, 0.106, 1.02
8774
381
Constrained to parent site
Constrained to parent site
Calculated w = 1/[s (Fo2) + (0.0853P)2]
Calculated w = 1/[s (Fo2) + (0.0437P)2]
2
2
2
2
where P = (Fo + 2Fc2)/3
where P = (Fo + 2Fc2)/3
(D/s)max
Drmax, Drmin/e A
0.002
0.001
-3
˚
0.52, -0.32
3.50, -2.41
Although the reaction of
2 with Vaska’s complex in
ethanol at room temperature may have been anticipated to
afford a mononuclear, chelate complex, it afforded a mix-
ture of [{Ir(CO)(PPh3)2}2Et(m-CNHC∧CH∧CNHC)](PF6)2 (7) and
[Ir(CO)(PPh3)2Et(CHimid.∧CH∧CNHC)(PF6)](PF6) (8) in 24 and 18%
isolated yield, respectively, in which the metal is bound to only one
carbene function (eqn (4)).
Fig. 1 ORTEP plot of the molecular structure of the dithione derivative
Et
∧
∧
=
=
[(S C) CH (C S)] (6). Ellipsoids are represented at 50% level probability
level. Only one of the two crystallographically independent molecules
˚
is depicted (molecule A). Selected bonds distances (A) and angles
(◦): Molecule A: C1–S1 1.694(2), C1–N1 1.357(2), C1–N2 1.360(3),
C14–S2 1.678(2), C14–N3 1.365(3), C14–N4 1.354(3), N1–C1–S1 126.8(2),
N2–C1–S1 127.6(2), N3–C14–S2 127.3(2), N4–C14–S2 127.3(2); Molecule
B: C1–S1 1.686(2), C1–N1 1.363(3), C1–N2 1.358(3), C14–S2 1.682(2),
C14–N3 1.362(3), C14–N4 1.360(3), N1–C1–S1 127.3(2), N2–C1–S1
127.4(2), N3–C14–S2 126.8(2), N4–C14–S2 128.3(2).
(4)
-
Exchange of the chloride counterion with PF6 facilitated the
separation of these cationic complexes by column chromato-
1
in the parent imidazolium salt,40 which parallels the decreased p
delocalization in the dithione compound.4
graphy. The 31P{ H} NMR spectrum of 7 contained a singlet
1
at 21.0 ppm for the equivalent trans PPh3 ligands and the H
The molecular structure indicated a C1 symmetry for 6 in
the solid state, but only one set of NMR signals was observed,
in agreement with an average C2 symmetry of the molecule
NMR spectrum in CD2Cl2 showed a shielding of all the protons
compared to 1 and the spacer CH2 protons gave rise to a singlet
at d 4.30 ppm. The two equivalent carbene carbons gave rise to
1
1
in solution. The 13C{ H} NMR signal at 161.2 ppm for 6 is
a triplet in 13C{ H} NMR at d 174.1 ppm (2J(CP) = 13.7 Hz), a
characteristic of the C2 thione carbon.4
value comparable to those for cationic NHC Ir(I) complexes.51–54
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The presence of the CO ligands is confirmed by the n(CO)
1
vibration at 1991 cm-1 and by the triplet observed in the 13C{ H}
NMR spectrum (d 184.6 ppm). The 1H NMR spectrum of 8
shows a strong shielding of the coordinated arm in contrast to
the imidazolium “non-coordinated” arm of the molecule. The
NCHN imidazolium proton gave a characteristic broad singlet
1
at d 8.66 ppm in the H NMR spectrum and the carbene and
Scheme 2 Differing conformations of the “xylylene” moiety in 6 and 9
based on their solid-state structure.
1
carbonyl carbons showed 13C{ H} NMR signals almost identical
to those of 7. Displacement of a chloride anion instead of a
neutral PPh3 ligand in eqn (4) could result from facilitated chloride
decoordination from the Ir(I) centre in a polar solvent.55
systems for the hydrogen atoms of the CH2 spacers and the 13C
NMR spectrum contains two signals for the carbene carbon at d
180.1 and 180.2 ppm. This could be explained by the presence in
solution of a single diastereoisomer with a conformation similar
to that observed in the solid-state or by the coexistence of two
different diastereoisomers in a 1 : 1 ratio resulting from different
orientations for the CH2 spacers and the imidazole rings (see
ESI†). On the basis of these X-ray structures, one could suggest
that if the imidazole rings in 2 remain in solution far away
from the C12–H12 bond, formation of pincer complexes will be
disfavoured, as indeed observed.
The reaction of 2 with [Ir(m-Cl)(cod)]2 afforded similarly the
dinuclear complex [{IrCl(cod)}2Et(m-CNHC∧CH∧CNHC)] (9) and the
mono-NHC complex [IrCl(cod)Et(CHimid.∧CH∧CNHC)](PF6) (10)
(eqn (4)). No pincer-type complex was observed under these
conditions or even upon heating the reaction mixture in acetoni-
trile at 60 ◦C. The selective precipitation of 10 from CH2Cl2–
Et2O facilitated the separation of these two Ir(I) complexes. The
molecular structure of 9, determined by X-ray diffraction,† has
no symmetry element (Fig. 2, Table 1) and the Ir(cod) fragments
occupy positions that minimize steric repulsion.
1
As expected, the H NMR spectrum of 10 in CD2Cl2 showed
the characteristic NCHN proton resonance at 8.76 ppm. The CH2
spacer hydrogen atoms gave rise to two doublets for the coordi-
nated arm and to an AB spin system for the imidazolium “non-
coordinated” arm of the molecule, which highlights a restricted
rotation of the imidazole ring, probably due to the adjacent iridium
moiety. HMBC analysis of 10 allows the differentiation between
the two arms of the molecule. Other NMR signals, in particular the
1
13C-{ H} NMR resonance at d 179.9 ppm for the carbene carbon,
are in the range reported for other NHC–Ir(I) complexes.38,53
The reactivity of 10 towards bases was studied with the aim to
metalate the second arm of the ligand. Whereas 10 did not react
with Ag2O in CH2Cl2, the use of n-BuLi led to decomposition of
the complex. However, 10 reacted smoothly with one equivalent
of the Ir(I) precursor in the presence of Cs2CO3 to form 9, which
emphasizes the critical importance of the choice of the base.
Replacement of Ir(I) with Rh(I) led selectively (1H NMR data,
including 1J(RhC) couplings, and mass spectrometry evidence) to
the heterobimetallic complex 11 in 89% yield (Scheme 3).
Fig. 2 ORTEP plot of the molecular structure of 9. Hydrogen atoms
omitted for clarity. Ellipsoids are represented at 50% level probability
◦
˚
level. Selected bonds distances (A) and angles ( ): Ir1–C1 2.035(6),
In solution, 11 is present as a 1 : 1 mixture of two diastereoiso-
mers, as indicated by the observation in the H NMR spectrum
Ir1–C19 2.184(7), Ir1–C20 2.191(6), Ir1–C23 2.034(8), Ir1–C24 2.126(6),
Ir2–C14 2.045(6), C27–C28 1.405(8), C31–C32 1.386(8); C1–Ir1–C19
158.0(3), C1–Ir1–C20 164.6(3), C1–Ir1–C23 91.2(3), C1–Ir1–C24 91.5(3),
C1–Ir1–Cl1 90.3(2), C14–Ir2–Cl 2 89.7(2).
1
of four AB spin systems for the spacer CH2 protons and in
1
13C{ H} NMR by two distinct doublets for the rhodium-bound
carbene carbons. This is consistent with the lack of symmetry
element relating the two metal centres, which are now chemically
different, in contrast to 9. To the best of our knowledge, only
two other heterodinuclear NHC complexes have been reported to
date, also with the Ir–Rh couple.58,59 Further reactivity studies are
in progress.
In [{RhCl(cod)}2n-Bu(m-CNHC∧N∧CNHC)],24 the metal–metal sep-
˚
˚
aration (6.333(2) A) is shorter that in 9 (7.0817(5) A). Another
important difference between these two structures concerns the
orientation of the chloride ligands: in 9 the ligand Cl1 is directed
˚
towards the hydrogen atom H12 of the central aryl (2.944(2) A)
whereas Cl2 in [{RhCl(cod)}2n-Bu(m-CNHC∧N∧CNHC)] is further away
In conclusion, we have isolated the new, stable dicarbene
ligand 2, and structurally characterised its dithione derivative. The
dicarbene ligand readily forms dinuclear Ir(I) complexes and, in a
stepwise manner, heterodinuclear Ir(I)–Rh(I) complexes. This step-
wise method appears promising and could be used to prepare other
types of heteronuclear systems. A “bottle-able” dicarbene ligand
offers specific synthetic advantages when the in situ preparation of
the metal complexes from the bis(imidazolium) carbene precursors
affords lower yields or would fail. This approach also offers the
advantage of avoiding the use of additional bases, required for
˚
from the central nitrogen atom (5.77(2) A), probably to avoid
electronic repulsion between their lone pairs. In 9, the Ir1–C19
and Ir1–C20 distances are longer than Ir1–C23 and Ir1–C24,
and C31–C32 is shorter than C27–C28, which reflects the larger
trans influence of the carbene ligand compared to chloride. This
is consistent with data on other NHC–Ir(I) complexes.38,56,57
A comparison of the crystal structures of 6 and 9 reveals a
different orientation of the CH2 spacer and of the imidazole
1
rings (Scheme 2). The H NMR spectrum of 9 contains two AB
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Scheme 3 Stepwise synthesis of homo- and heterodinuclear carbene complexes.
the in situ syntheses, which can be detrimental to the stability
of the metal complexes. The fact that ligands such as 2 may
act as bridges rather than chelates is important to keep in mind
when attempting to prepare “pincer-type” complexes requiring a
chelating behaviour of the ligand. It is suggested that conformation
effects explain the lack of formation of pincer complexes with 2
and its unusual bridging behaviour.
received from commercial suppliers. Yields of the metal complexes
are based on iridium. In the assignment of the spectroscopic
data, the abbreviation “coord.” corresponds to the values for
the coordinated arm of the ligand when an imidazolium moiety
remains non-coordinated.
Synthesis of [(1,3-phenylene)bis(methylene)]bis
(1-ethyl-imidazolium) dichloride, Et(CHimid.∧CH∧CHimid.)Cl2 (1)
Experimental
The procedure published for [(1,3-phenylene)bis(methylene)]bis(1-
methyl-imidazolium) dichloride, Me(CHimid.∧CH∧CHimid.)Cl2,40 was
General procedures
slightly modified as follows.
A mixture of solid 1,3-bis
All operations were carried out using standard Schlenk techniques
under inert atmosphere. The synthesis of the imidazolium salts
was conducted under nitrogen, whereas that of the complexes
was performed under argon. Solvents were dried, degassed,
and freshly distilled prior to use. THF and Et2O were dried
over sodium–benzophenone. The solvents CH2Cl2 and CH3CN
were distilled from CaH2 and d6-DMSO and CD3CN were
(chloromethyl)benzene (8.790 g, 49.2 mmol) and pure 1-ethyl-
imidazole (9.650 g, 100.4 mmol) was stirred and heated to 135 ◦C
for 10 min. The solid obtained was then allowed to cool to room
temperature, washed with THF (2 ¥ 20 mL), which dissolves the
reagents but not the product, yielding 1 as a hygroscopic colourless
solid in 98% yield (17.71 g, 48.2 mmol). 1H NMR (d6-DMSO): d
1.43 (t, 3J(HH) = 7.3 Hz, 6H, CH3), 4.25 (q, 3J(HH) = 7.3 Hz, 4H,
CH3CH2), 5.49 (s, 4H, CH2), 7.45–7.50 (m, 3H, CH arom.), 7.76
˚
degassed and stored over 4 A molecular sieves. CD2Cl2 was
4
(s, 1H, CH arom.), 7.89 (pseudo t, 3J(HH) = J(HH) = 1.6 Hz, 2H,
˚
dried over 4 A molecular sieves, degassed by freeze–pump–thaw
3
4
cycles and stored under argon. NMR spectra were recorded at
room temperature on a Bruker AVANCE 300 spectrometer (1H,
300 MHz; 13C, 75.47 MHz) and referenced using the residual
proton solvent (1H) or solvent (13C) resonance. Assignments are
based on 1H, 1H-COSY, 1H, 13C-HMQC and 1H, 13C-HMBC
experiments. IR spectra were recorded in the region 4000–100 cm-1
on a Nicolet 6700 FT-IR spectrometer (ATR mode, diamond
crystal). Elemental analyses were performed by the “Service de
microanalyses”, Universite´ de Strasbourg and the “Service Central
d’Analyses”, USR-59/CNRS, Solaize. Electrospray Mass Spectra
(ESI-MS) were recorded on a microTOF (Bruker Daltonics,
Bremen, Germany) instrument using nitrogen as drying agent and
nebulising gas and Maldi-TOF analyses were carried out on a
Bruker AutiflexII TOF/TOF (Bruker Daltonics, Bremen, Ger-
many), using dithranol (1,8,9-trihydroxyanthracene) as a matrix.
Potassium imidazolide (KC3H3N2) was obtained in quantitative
yield by mixing imidazole and KOt-Bu in toluene and heating to
110 ◦C. 1-Ethylimidazole was prepared by reaction of potassium
imidazolide with ethyl iodide in THF at room temperature and was
isolated as a colourless oil in 70% yield after filtration, evaporation
and distillation (bp 97–98 ◦C at 27 mmHg) of the reaction mixture
(for analytical data, see ref. 60). All other reagents were used as
CH imid.), 7.97 (pseudo t, J(HH) = J(HH) = 1.6 Hz, 2H, CH
4
1
imid.), 9.82 (pseudo t, J(HH) = 1.6 Hz, 2H, NCHN). 13C{ H}
NMR (d6-DMSO): d 15.0 (CH3), 44.3 (CH3CH2), 51.4 (CH2),
122.4 (CH imid.), 122.5 (CH imid.), 128.6 (CH arom.), 128.7 (CH
arom.), 129.6 (CH arom.), 135.7 (C arom.), 136.2 (NCHN). ESI-
MS (CH3OH, 10 V, m/z): 331.2 [M - Cl]+, 295.2 [M - 2Cl - H]+.
HRMS (ESI) [M - Cl]+: 331.1712 calcd for C18H24ClN4: 331.1684.
Anal. Calc. for C18H24Cl2N4 (367.32): C, 58.86; H, 6.59; N, 15.25.
Found: C, 57.69; H, 7.25; N, 14.68%. Despite several attempts,
better elemental analyses could not be obtained owing to the
strongly hygroscopic properties of this compound. IR (pure,
diamond orbit): 3365 wbr, 3129 w, 3043 mbr, 2970 mbr, 2869 wbr,
1612 w, 1557 s, 1491 w, 1446 s, 1352 m, 1321 m, 1254 w, 1154 vs,
1093 m, 1021 m, 975 w, 955 w, 752 s, 729 vs cm-1.
Synthesis of [(1,3-phenylene)bis(methylene)]bis
(1-ethyl-imidazol-2-ylidene), EtCNHC∧CH∧CNHC (2)
Solid lithium bis(trimethylsilyl)amide (0.192 g, 1.26 mmol) and
[(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazolium) dichlo-
ride (1, 0.210 g, 0.57 mmol) were mixed and cooled to -78 ◦C
and THF (10 mL) was added dropwise. The reaction mixture was
3828 | Dalton Trans., 2009, 3824–3832
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warmed to room temperature and stirred for 15 h. The solvent
was then removed in vacuo and the crude product was washed
with THF (6 mL) yielding 0.134 g of 2 as a white solid, which
corresponds to 80% yield (0.46 mmol based on free NHC), 62%
yield (0.35 mmol based on NHC·2LiCl) or 70% yield (0.40 mmol
based on NHC·LiCl). 1H NMR (d6-DMSO): d 1.34 (t, 3J(HH) =
Observation of [(1,3-phenylene)bis(methylene)]-(1-ethyl-
imidazolium)-(3-ethyl-imidazol-2-thione) chloride,
Et[CHimid. CH (C S)]Cl (5)
∧
∧
=
This compound was observed in the crude product during the
synthesis of [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-
2-thione) 6 but was not isolated pure. Selected data assigned to 5:
1H NMR (d6-DMSO): d 1.23 (t, 3J(HH) = 7.2 Hz, 3H, CH3), 1.43
3
7.3 Hz, 6H, CH3), 4.02 (q, J(HH) = 7.3 Hz, 4H, CH3CH2),
5.20 (s, 4H, CH2), 7.20–7.34 (m, 8H, 4 CH arom. and 4 CH
imid.). Anal. Calc. for C18H22N4·5LiCl: C, 42.70; H, 4.38; N, 11.06.
Found: C, 45.72; H, 6.39; N, 10.92%. There is uncertainty about
the amount of LiCl present in the sample, but the atomic C : N
ratio found to be 4.88 is satisfactory. IR (pure, diamond orbit):
3053 br, 2974 br, 2866 wbr, 1612 w, 1554 s, 1449 m, 1353 w, 1257 w,
1240 w, 1159 vs, 1093 w, 1065 w, 1018 w, 955 w, 824 mbr, 756 sh,
733 vs cm-1.
3
3
(t, J(HH) = 7.3 Hz, 3H, CH3 imidazolium), 3.98 (q, J(HH) =
7.2 Hz, 2H, CH3CH2 partly masked by signals of 6), 4.22 (q,
3J(HH) = 7.3 Hz, 2H, CH3CH2 imidazolium), 5.20 (s, 2H, CH2),
5.45 (s, 2H, CH2 imidazolium), 7.13–7.18 (m, 4H, 2 CH arom.
and 2 CH imid. partly masked by signals of 6), 7.32–7.50 (m, 2H,
CH arom. partly masked by signals of 6), 7.90 (pseudo t, 3J(HH) =
4J(HH) = 1.6 Hz, 1H, CH imidazolium), 7.92 (pseudo t, 3J(HH) =
4J(HH) = 1.6 Hz, 1H, CH imidazolium), 9.76 (pseudo t, 4J(HH) =
1.6 Hz, 1H, NCHN). ESI-MS (CH3OH, 10 V, m/z): 327.2
[M - Cl]+.
Synthesis of [(1,3-phenylene)bis(methylene)]bis(1-ethyl-
imidazolium) dibromide, Et(CHimid.∧CH∧CHimid.)Br2 (3)
In a NMR tube two drops of pure HBr were added to a fresh
solution of [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-2-
ylidene) 2 (0.010 g, 0.034 mmol) in d6-DMSO (0.25 mL). The tube
was closed and shaken. NMR analysis of the colourless solution
indicated quantitative formation of 3 (the signal at 5.89 ppm
corresponds to excess HBr). 1H NMR (d6-DMSO): d 1.34 (t,
Synthesis of [(1,3-phenylene)bis(methylene)]bis(1-ethyl-
∧
∧
imidazol-2-thione), Et[(S C) CH (C S)] (6)
=
=
(a) From 2. A solution of [(1,3-phenylene)bis(methylene)]
bis(1-ethyl-imidazol-2-ylidene) 2 (0.844 g, 2.21 mmol) in MeOH
(10 mL) was quickly added to a suspension of flowers of sulfur
(0.142 g, 4.42 mmol) in MeOH (40 mL) and the mixture was
stirred at room temperature for 12 h. The solvent was then removed
in vacuo and the crude product was purified by chromatography
on silica gel with MeOH as eluant. The orange solid obtained
after removal of the solvent in vacuo was triturated with water
(2 ¥ 10 mL) and dried under vacuum overnight. Recrystallisation
from dichloromethane–pentane gave 6 as a white solid in 70%
yield (0.555 g, 1.55 mmol). Single crystals suitable for X-ray
diffraction were obtained by slow diffusion of pentane into a
3
3J(HH) = 7.3 Hz, 6H, CH3), 4.17 (q, J(HH) = 7.3 Hz, 4H,
CH3CH2), 5.42 (s, 4H, CH2), 7.33–7.47 (m, 3H, CH arom.), 7.63
3
4
(s, 1H, CH arom.), 7.77 (pseudo t, J(HH) = J(HH) = 1.6 Hz,
3
4
2H, CH imid.), 7.80 (pseudo t, J(HH) = J(HH) = 1.6 Hz, 2H,
CH imid.), 9.48 (br s, 2H, NCHN).
Observation of the monoprotonated compound
[EtCHimid.∧CH∧CNHC]OMe (4)
(a) From the reaction between 1 and 2 in d6-DMSO. In a NMR
tube, a solution of 2 (0.005 g, 0.017 mmol) in d6-DMSO (0.10 mL)
was added to a solution of 1 (0.006 g, 0.017 mmol) in d6-DMSO
1
saturated dichloromethane solution of 6. H NMR (d6-DMSO):
d 1.24 (t, 3J(HH) = 7.2 Hz, 6H, CH3), 3.98 (q, 3J(HH) = 7.2 Hz,
4H, CH3CH2), 5.18 (s, 4H, CH2), 7.13 and 7.19 (AB spin system,
3J(HH) = 2.4 Hz, 4H, CH imid.), 7.14–7.18 (m, 2H, CH arom.),
1
(0.10 mL). The tube was closed and shaken. H NMR analysis
1
of the solution indicated quantitative formation of 4. H NMR
(d6-DMSO): d 1.43 (t, 3J(HH) = 7.3 Hz, 6H, CH3), 4.23 (q,
3J(HH) = 7.3 Hz, 4H, CH3CH2), 5.46 (s, 4H, CH2), 7.45 (br s,
3H, CH arom.), 7.67 (br s, 1H, CH arom.), 7.84 and 7.88 (AB spin
system, 3J(HH) = 1.8 Hz, 4H, CH imid.), 8.70–10.70 (vbr s, 1H,
NCHN). The solution became orange-red after 1 h, preventing
determination of the 13C NMR chemical shift of the NCN carbon
atoms.
1
7.26–7.32 (m, 2H, CH arom.). 13C{ H} NMR (d6-DMSO): d 14.1
(CH3), 42.1 (CH3CH2), 49.5 (CH2), 117.2 (CH imid.), 117.4 (CH
imid.), 126.8 (CH arom.), 127.1 (CH arom.), 128.7 (CH arom.),
137.3 (C arom.), 161.2 (N(C=S)N). ESI-MS (CH3OH, 43 V, m/z):
397.1 [M + K]+, 381.1 [M + Na]+, 365.1 [M + Li]+, 359.1 [M + H]+.
Anal. Calc. for C18H22N4S2 (358.52): C, 60.30; H, 6.18; N, 15.63.
Found: C, 60.13; H, 6.47; N, 15.87%. IR (pure, diamond orbit):
3150 w, 3121 w, 3092 w, 2921 wbr, 2849 w, 1440 m, 1409 s, 1306 m,
1267 s, 1235 vs, 1193 s, 1137 sbr, 983 m, 802 w, 770 m, 754 m,
722 m, 678 m cm-1.
(b) From protonation of 2 in MeOH. Compound 2 (0.010 g,
0.034 mmol) was dissolved in MeOH and stirred for 15 h at room
temperature. The solvent was then removed in vacuo and the crude
product was analysed by 1H NMR, which indicated the formation
of 4.
We suggest that the anion associated with the cationic part of 4
is MeO-, although the presence of OH- cannot be ruled out when
water is present.
Even if these reactions demonstrated that 2 is reprotonated in
MeOH (and alcohols in general), the limited solubility of 2 in
other organic solvents limited the study of its reactivity in these
solvents.
(b) From 1 and/or 5. Compounds 1 and 5 could be converted
almost quantitatively in 6 by reaction with Cs2CO3 and S8 in
MeOH at room temperature for 15 h. The resulting suspension
was filtered and the solvent was then removed in vacuo. The orange
solid obtained was triturated with water and dried under vacuum
for overnight. Recrystallisation from dichloromethane–pentane
gave 6 as a white solid.
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The Royal Society of Chemistry 2009
Dalton Trans., 2009, 3824–3832 | 3829
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Synthesis of [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-
2-ylidene)-bis[trans-carbonylbis(triphenylphosphine)iridium(I)]
dihexafluorophosphate, [{Ir(CO)(PPh3)2}2Et(l-CNHC∧CH∧CNHC)]
(PF6)2 (7)
Solubilisation of the complex in dichloromethane followed by
filtration allows the elimination of excess KPF6. Recrystallisation
from dichloromethane–pentane yielded pure 8 in 18% yield
1
3
(0.158 g, 0.12 mmol). H NMR (CD2Cl2): d 0.53 (t, J(HH) =
7.4 Hz, 3H, coord. CH3), 1.58 (t, 3J(HH) = 7.4 Hz, 3H, CH3), 3.23
A solution of compound 2 (0.300 g, 0.72 mmol) in ethanol (15 mL)
was rapidly added to a suspension of trans-[IrCl(CO)(PPh3)2]
(0.516 g, 0.66 mmol) in ethanol (20 mL). The reaction mixture
was stirred at room temperature for 15 h and the solvent
was removed in vacuo. The crude product was dissolved in
dichloromethane (5 mL), the solution was filtered and washed
with deionised water saturated with KPF6 (10 mL). The organic
layer was then washed with deionised water (3 ¥ 10 mL),
collected, dried over MgSO4, filtered and the solvent was removed
in vacuo. The crude product was purified by chromatography on
silica gel (dichloromethane : acetone 9 : 1 and KPF6) yielding 7
as a yellow solid. Elution with a more polar solvent mixture
(dichloromethane : acetone 7 : 3 and KPF6) yielded 8 (see below).
Solubilisation of the complex in dichloromethane followed by
filtration allows the elimination of excess KPF6. Recrystallisation
from CH2Cl2–pentane yielded pure 7 in 24% yield (0.165 g,
3
3
(q, J(HH) = 7.4 Hz, 2H, coord. CH2CH3), 4.26 (q, J(HH) =
7.4 Hz, 2H, CH2CH3), 4.34 (s, 2H, coord. CH2), 5.22 (s, 2H,
CH2), 6.34 (br d, 3J(HH) = 7.7 Hz, 1H, C–CH–CH xylene), 6.67
3
and 6.75 (AB spin system, J(HH) = 2.0 Hz, 2H, CH imid.),
3
6.90 (s, 1H, C–CH–C xylene), 6.94 (t, J(HH) = 7.7 Hz, 1H,
CH–CH–CH xylene), 7.23 (br d, 3J(HH) = 7.7 Hz, 1H, C–CH–
CH xylene), 7.29–7.59 (m, 32H, PPh3 and 2 ¥ CH imidazolium),
8.66 (br s, 4J(HH) = 1.8 Hz, 1H, NCHN). 13C{ H} NMR
1
(CD2Cl2): d 13.9 (CH3), 15.4 (CH3), 46.0 (CH2CH3), 46.1 (coord.
CH2CH3), 53.5 (CH2), 54.5 (coord. CH2), 121.8 (CH imid.), 122.8
(CH imidazolium), 123.2 (CH imidazolium), 123.3 (CH imid.),
129.6 (virtual t, 3+5J(CP) = 10.0 Hz, PPh3) and one CH arom.
masked by this triplet, 130.3 (CH arom.), 130.5 (CH arom.), 130.7
(CH arom.), 132.1 (s, para-C PPh3), 132.2 (virtual t, 1+3J(CP) =
54.4 Hz, ipso-C PPh3), 134.1 (C arom.), 134.3 (virtual t, 2+4J(CP) =
12.2 Hz, ortho-C PPh3), 135.1 (C arom.), 135.6 (NCHN), 174.3 (t,
1
3
0.08 mmol). H NMR (CD2Cl2): d 0.54 (t, J(HH) = 7.4 Hz,
1
2J(CP) = 13.7 Hz, C–Ir), 184.7 (t, 2J(CP) = 11.7 Hz, CO). 19F{ H}
6H, CH3), 3.22 (q, 3J(HH) = 7.4 Hz, 4H, CH2CH3), 4.30 (s, 4H,
1
1
NMR (CD2Cl2): d -72.8 (d, J(FP) = 711.3 Hz). 31P{ H} NMR
(CD2Cl2): d -143.1 (sept, 1J(PF) = 711.3 Hz, PF6), 21.2 (s, PPh3).
MALDI TOF-MS (CH3CN, m/z): 1185.2 [M - PF6]+. Anal. Calc.
for C55H53F12IrN4P4O (1330.13): C, 49.66; H, 4.02; N, 4.21. Found:
C, 48.99; H, 4.34; N, 4.09%. IR (pure, diamond orbit): 3154 w,
3051 w, 2958 wbr, 1985 s (nCO), 1564 w, 1480 w, 1435 m, 1350 w,
1260 w, 1220 w, 1154 w, 1095 m, 1027 w, 826 vs, 740 s, 692 vs, 555
sbr, 515 sbr, 499 sh, 455 w, 421 m cm-1.
3
CH2), 6.06 (br d, J(HH) = 7.7 Hz, 2H, CH–CH–CH xylene),
3
6.28 (br s, 1H, C–CH–C xylene), 6.33 (t, J(HH) = 7.7 Hz, 1H,
CH–CH–CH xylene), 6.53 (d, 3J(HH) = 1.5 Hz, 2H, CH imid.),
3
6.78 (d, J(HH) = 1.5 Hz, 2H, CH imid.), 7.37–7.58 (m, 60H,
PPh3). 13C{ H} NMR (CD2Cl2): d 13.8 (CH3), 46.1 (CH3CH2),
1
54.6 (CH2), 122.3 (CH imid.), 122.8 (CH imid.), 129.6 (virtual
t, 3+5J(CP) = 10.0 Hz, meta-C PPh3), 130.0 (CH arom.), 130.2
(CH arom.), 130.8 (CH arom.), 132.0 (s, para-C PPh3), 132.2
(virtual t, 1+3J(CP) = 54.4 Hz, ipso-C PPh3), 134.3 (virtual t,
2+4J(CP) = 12.2 Hz, ortho-C PPh3), 134.6 (C arom.), 174.1 (t,
2J(CP) = 13.7 Hz, C–Ir), 184.6 (t, 2J(CP) = 11.7 Hz, CO). 19F{ H}
1
Synthesis of [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-
2-ylidene)-bis[(g4-1,5-cyclooctadiene)iridium(I)chloride],
[{IrCl(cod)}2Et(l-CNHC∧CH∧CNHC)] (9)
NMR (CD2Cl2): d -73.4 (d, J(FP) = 711.3 Hz). 31P{ H} NMR
(CD2Cl2): d -143.2 (sept, 1J(PF) = 711.3 Hz, PF6), 21.0 (s, PPh3).
MALDI TOF-MS (CH3CN, m/z): 1927.3 [M - PF6]+. Anal. Calc.
for C92H82F12Ir2N4P6O2 (2073.92): C, 53.28; H, 3.99; N, 2.70.
Found: C, 53.00; H, 4.25; N, 2.47%. IR (pure, diamond orbit):
3178 w, 3136 w, 3054 wbr, 2946 w, 1983 s (nCO), 1570 w, 1480 m,
1434 m, 1310 w, 1260 w, 1220 w, 1184 w, 1094 m, 1027 w, 999 w,
831 vs, 742 s, 691 vs, 556 s, 514 s, 496 s, 455 w, 418 m cm-1.
1
1
Compound 2 (0.800 g, 1.90 mmol) in ethanol (15 mL) was rapidly
added to a suspension of [Ir(m-Cl)(cod)]2 (0.639 g, 0.95 mmol)
in ethanol (10 mL). The reaction mixture was stirred at room
temperature for 15 h and the solvent was removed in vacuo. The
crude product was dissolved in dichloromethane (15 mL), the
solution was filtered and washed with deionised water saturated
with KPF6 (15 mL). The aqueous layer was extracted with
CH2Cl2 (3 ¥ 15 mL). The combined organic extracts were dried
over MgSO4, filtered and addition of Et2O (50 mL) led to the
precipitation of 10 (see below) which was separated by filtration.
The solvent was removed in vacuo yielding 9 as a light orange solid
in 33% yield (0.300 g, 0.31 mmol). Single crystals suitable for X-ray
diffraction studies were obtained by slow diffusion of diisopropyl
ether in a saturated acetonitrile solution of the complex. 1H NMR
Synthesis of [(1,3-phenylene)bis(methylene)]-(1-ethyl-imida-
zolium)-(3-ethyl-imidazol-2-ylidene)-hexafluorophosphate-[trans-
carbonylbis(triphenylphosphine)iridium(I)] hexafluorophosphate,
[IrCO(PPh3)2Et(CHimid.∧CH∧CNHC)(PF6)](PF6) (8)
Compound 2 (0.300 g, 0.72 mmol) in ethanol (15 mL) was
rapidly added to a suspension of trans-[IrCl(CO)(PPh3)2] (0.516 g,
0.66 mmol) in ethanol (20 mL). The reaction mixture was stirred
at room temperature for 15 h and the solvent was removed
in vacuo. The crude product was dissolved in dichloromethane
(5 mL), the solution was filtered and washed with deionised
water saturated with KPF6 (10 mL). The organic layer was
then washed with deionised water (3 ¥ 10 mL), collected, dried
over MgSO4, filtered and the solvent was removed in vacuo.
The crude product was purified by chromatography on silica gel
(dichloromethane : acetone 7 : 3 and KPF6) to yield a yellow solid.
3
(CD2Cl2): d 1.50 (t, J(HH) = 7.3 Hz, 6H, CH3), 1.45–1.86 (m,
8H, CH2 cod), 2.00–2.41 (m, 8H, CH2 cod), 2.84–2.92 (m, 2H, CH
cod), 2.97–3.01 (m, 2H, CH cod), 4.31–4.66 (m, 8H, 2 CH3CH2
and 4 CH cod), 5.37 and 5.96 (AB spin system, 2J(HH) = 14.9 Hz,
2
2H, CH2), 5.46 and 5.86 (AB spin system, J(HH) = 14.8 Hz,
3
2H, CH2), 6.81 (d, J(HH) = 2.0 Hz, 1H, CH imid.), 6.82 (d,
3
3J(HH) = 2.0 Hz, 1H, CH imid.), 6.93 (d, J(HH) = 2.0 Hz,
1
2H, CH imid.), 7.29–7.51 (m, 4H, CH arom.). 13C{ H} NMR
(CDCl3): d 16.4 (CH3), 29.3 (CH2 cod), 29.4 (CH2 cod), 29.9 (CH2
3830 | Dalton Trans., 2009, 3824–3832
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©

View Article Online
cod), 30.0 (CH2 cod), 33.4 (CH2 cod), 33.5 (CH2 cod), 34.0 (CH2
cod), 34.1 (CH2 cod), 45.5 (CH3CH2), 51.7 (CH cod), 51.8 (CH
cod), 52.0 (CH cod), 52.1 (CH cod), 54.1 (CH2), 84.4 (CH cod),
84.8 (CH cod), 85.0 (CH cod), 120.0 (CH imid.), 120.1 (CH imid.),
120.5 (CH imid.), 120.6 (CH imid.), 128.0 (CH arom.), 128.1 (CH
arom.), 128.2 (CH arom.), 128.3 (CH arom.), 129.4 (CH arom.),
129.5 (CH arom.), 137.2 (C arom.), 137.3 (C arom.), 180.1 (C–Ir),
180.2 (C–Ir). MALDI TOF-MS (CH3CN, m/z): 931.2 [M - Cl]+.
Anal. Calc. for C34H46Cl2Ir2N4 (966.1): C, 42.27; H, 4.80; N, 5.80.
Found: C, 42.18; H, 4.69; N, 5.38%. IR (pure, diamond orbit):
3171 w, 3096 w, 2927 m, 2872 m, 2827 m, 1721 w, 1610 w, 1491 w,
1449 m, 1406 s, 1325 m, 1258 s, 1222 s, 1181 m, 1076 m, 1037 m,
996 m, 968 m, 841 s, 802 s, 739 s, 705 vs, 689 vs, 557 w, 521 w,
506 w, 472 w, 433 w, 375 w, 289 s (nIr–Cl), 255 m, 141 m, 105 m,
98 m, 78 s, 60 s cm-1.
Synthesis of [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-2-
ylidene)-bis(g4-1,5-cyclooctadiene)iridium(I)rhodium(I)dichloride,
[IrRhCl2(cod)2Et(l-CNHC∧CH∧CNHC)] (11)
Solid 10 (0.050 g, 0.06 mmol), [Rh(m-Cl)(cod)]2 (0.016 g,
0.03 mmol) and Cs2CO3 (0.026 g, 0.08 mmol) were stirred in
acetonitrile (7 mL) at room temperature for 15 h. The suspension
was then filtered and the solvent was removed in vacuo. The orange
solid was dissolved in dichloromethane (15 mL), the solution was
filtered and addition of Et2O (15 mL) led to the precipitation
of a solid which was discarded by filtration. The solvent was
removed in vacuo yielding 11 as an orange solid in 89% yield
(0.050 g, 0.05 mmol) as a mixture of two diastereoisomers in
a 1 : 1 ratio. 1H NMR (CDCl3): d 1.48 (t, 3J(HH) = 7.7 Hz,
3
6H, CH3), 1.53 (t, J(HH) = 7.7 Hz, 6H, CH3), 1.60–1.80 (m,
8H, CH2 cod), 1.85–2.00 (m, 8H, CH2 cod), 2.07–2.49 (m, 16H,
CH2 cod), 2.83–2.90 (m, 2H, CH cod), 2.95–3.01 (m, 2H, CH
cod), 3.21–3.28 (m, 2H, CH cod), 3.31–3.38 (m, 2H, CH cod),
4.36–4.75 (m, 12H, 4 CH3CH2 and 4 CH cod), 5.02 (br s, 4H,
2
Synthesis of [(1,3-phenylene)bis(methylene)]-(1-ethyl-imida-
CH cod), 5.28 and 6.00 (AB spin system, J(HH) = 14.7 Hz,
zolium)-(3-ethyl-imidazol-2-ylidene)-hexafluorophosphate(g4-1,
2
2H, CH2), 5.43 and 5.86 (AB spin system, J(HH) = 14.8 Hz,
5-cyclooctadiene)iridium(I)chloride, [IrCl(cod)Et(CHimid.
CH∧CNHC)](PF6) (10)
-
∧
2
2H, CH2), 5.43 and 6.11 (AB spin system, J(HH) = 14.8 Hz,
2
2H, CH2), 5.56 and 5.98 (AB spin system, J(HH) = 14.8 Hz,
3
2H, CH2), 6.70 (d, J(HH) = 2.0 Hz, 1H, CH imid.), 6.72 (d,
Compound 2 (0.800 g, 1.90 mmol) in ethanol (15 mL) was rapidly
added to a suspension of [Ir(m-Cl)(cod)]2 (0.639 g, 0.95 mmol)
in ethanol (10 mL). The reaction mixture was stirred at room
temperature for 15 h and then the solvent was removed in vacuo.
The crude product was dissolved in dichloromethane (15 mL), the
solution was filtered and washed with deionised water saturated
with KPF6 (15 mL). The aqueous layer was extracted with
CH2Cl2 (3 ¥ 15 mL). The combined organic extracts were dried
over MgSO4, filtered and addition of Et2O (50 mL) led to the
precipitation of a solid which was collected by filtration. Two
recrystallisations from THF–pentane yielded 10 as an orange solid
in 36% yield (0.530 g, 0.68 mmol). 1H NMR (CD2Cl2): d 1.50 (t,
3J(HH) = 2.0 Hz, 1H, CH imid.), 6.74 and 6.76 (AB spin system,
3
3J(HH) = 2.0 Hz, 2H, CH imid.), 6.84 (d, J(HH) = 2.0 Hz,
1
4H, CH imid.), 7.26–7.45 (m, 8H, CH arom.). 13C{ H} NMR
(CDCl3): d 16.4 (CH3), 28.8, 28.9, 29.2, 29.3, 29.4, 29.5, 29.9,
30.0, 32.8, 32.9, 33.3, 33.4, 33.5, 34.0, 34.1 (CH2 cod), 45.5, 45.8
(CH3CH2), 51.7, 51.8, 52.0, 52.1 (CH cod), 54.1, 54.5 (CH2), 68.1,
68.2, 68.3, 68.4, 68.5 (CH cod), 84.4 (CH cod), 84.8 (d, J(RhC) =
12.5 Hz, CH cod), 98.5, 98.6, 98.7, 98.8 (CH cod), 120.0, 120.1,
120.3, 120.4, 120.6, 120.9 (CH imid.), 128.1, 128.2, 128.3, 129.4,
129.6 (CH arom.), 137.3, 137.4 (C arom.), 180.1, 180.2 (C–Ir),
182.3 (d, 1J(CRh). = 51.1 Hz, C–Rh), 182.4 (d, 1J(CRh). =
50.3 Hz, C–Rh). MALDI TOF-MS (CH3CN, m/z): 841.2 [M -
Cl]+. ESI-MS (CH3CN, 10 V, m/z): 841.2 [M - Cl]+. HRMS (ESI)
[M - Cl]+: 841.2028 calcd for C34H46Cl1IrRhN4: 841.2083. Anal.
Calc. for C34H46Cl2IrRhN4 (876.8): C, 46.58; H, 5.29; N, 6.39.
Found: C, 42.83; H, 5.59; N, 6.39%. IR (pure, diamond orbit):
3124 w, 3082 w, 2961 w, 2912 w, 2873 w, 2827 w, 1568 w, 1449 w,
1405 m, 1353 w, 1328 w, 1259 s, 1221 s, 1180 m, 1153 m, 1089 s,
1019 s, 956 m, 842 s, 799 vs, 730 s, 698 s, 556 w, 385 m, 285 mbr
(nIr–Cl), 256 mbr, 142 wbr, 108 w, 98 m, 80 w, 75 m, 66 m, 58 s cm-1.
3
3J(HH) = 7.4 Hz, 3H, coord. CH3), 1.55 (t, J(HH) = 7.4 Hz,
3H, CH3), 1.58–1.88 (m, 4H, CH2 cod), 2.10–2.37 (m, 4H, CH2
cod), 2.91–3.00 (m, 1H, CH cod), 3.03–3.11 (m, 1H, CH cod),
3
4.21 (q, J(HH) = 7.4 Hz, 2H, CH3CH2), 4.35–4.59 (m, 4H, 2 ¥
2
CH cod and coord. CH3CH2), 5.11 (d, J(HH) = 14.9 Hz, 1H,
coord. CH2), 5.25 and 5.28 (AB spin system, 2J(HH) = 14.5 Hz,
2H, CH2), 6.26 (d, 2J(HH) = 14.9 Hz, 1H, coord. CH2), 6.84 and
3
6.98 (AB spin system, J(HH) = 2.0 Hz, 2H, CH imid.), 7.28
(br s, 1H, CH imidazolium), 7.35–7.51 (m, 4H, CH arom.), 7.55
1
(br s, 1H, CH imidazolium), 8.76 (br s, 1H, NCHN). 13C{ H}
NMR (CDCl3): d 15.1 (CH3), 16.4 (coord. CH3), 29.4, 30.0, 33.4,
33.9 (CH2 cod), 45.5 (coord. CH3CH2), 45.6 (CH3CH2), 52.1, 52.6
(CH cod), 53.5 (coord. CH2), 53.6 (CH2), 84.7, 84.9 (CH cod),
120.7, 120.8 (CH imid.), 121.8, 122.9 (CH imidazolium), 128.7,
128.9, 129.2, 129.8 (CH arom.), 133.6 (C arom.), 135.5 (NCHN),
X-Ray crystal structure determinations of 6 and 9†
The relevant details of the crystals, data collection and structure
refinement are given in Table 1. The intensity data were col-
lected at 173(2) K on a Kappa CCD diffractometer61 (graphite
1
138.3 (C arom.), 179.9 (C–Ir). 19F{ H} NMR (CD2Cl2): d -72.9
monochromated Mo Ka radiation, l = 0.71073 A). The structures
˚
1
(d, 1J(FP) = 711.3 Hz). 31P{ H} NMR (CD2Cl2): d -143.1 (sept,
were solved by direct methods (SHELXS-97) and refined by full-
matrix least-squares procedures (based on F2, SHELXL-97)62
with anisotropic thermal parameters for all the non-hydrogen
atoms. The hydrogen atoms were introduced into the geometrically
calculated positions (SHELXS-97 procedures) and refined riding
on the corresponding parent atoms. For complex 9, absorption
correction: MULTI-SCAN,63 Tmax = 0.482, Tmin = 0.410. Despite
this correction, significant residual electron density was found.
1J(PF) = 711.3 Hz). MALDI TOF-MS (CH3CN, m/z): 631.2 [M -
PF6]+. Anal. Calc. for C26H35ClF6IrN4P·CH2Cl2 (861.15): C, 37.66;
H, 4.33; N, 6.51. Found: C, 37.69; H, 4.50; N, 6.73%. IR (pure,
diamond orbit): 3160 w, 3097 w, 2961 w, 2923 w, 2873 w, 2823 w,
1563 w, 1449 m, 1408 m, 1350 w, 1328 w, 1260 m, 1225 m, 1154 m,
1095 m, 1024 m, 825 vs, 732 s, 706 s, 555 vs, 377 wbr, 286 mbr
(nIr–Cl), 104 s, 93 sh, 76 vs, 64 vs cm-1.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 3824–3832 | 3831
©

View Article Online
-3
˚
31 S. Gru¨ndemann, M. Albrecht, J. A. Loch, J. W. Faller and R. H.
Crabtree, Organometallics, 2001, 20, 5485.
32 A. A. D. Tulloch, A. A. Danopoulos, G. J. Tizzard, S. J. Coles, M. B.
Hursthouse, R. S. Hay-Motherwell and W. B. Motherwell, Chem.
Commun., 2001, 1270.
33 J. R. Miecznikowski, S. Gru¨ndemann, M. Albrecht, C. Megret, E. Clot,
J. W. Faller, O. Eisenstein and R. H. Crabtree, Dalton Trans., 2003,
831.
34 F. E. Hahn, M. C. Jahnke, V. Gomez-Benitez, D. Morales-Morales and
T. Pape, Organometallics, 2005, 24, 6458.
The highest peaks (i.e.: maximum 3.5 e A ) are located at less
than 1 A from the metal centres.
˚
Acknowledgements
We are grateful to Dr Roberto Pattacini for the refinement of the
X-ray structures and to the CNRS, the Ministe`re de la Recherche
(Paris) and the IFP for funding.
35 F. E. Hahn, M. C. Jahnke and T. Pape, Organometallics, 2007, 26, 150.
36 S. K. Schneider, J. Schwarz, G. D. Frey, E. Herdtweck and W. A.
Herrmann, J. Organomet. Chem., 2007, 692, 4560.
37 K. Lv and D. Cui, Organometallics, 2008, 27, 5438.
38 (a) W. A. Herrmann, J. Schu¨tz, G. D. Frey and E. Herdtweck,
Organometallics, 2006, 25, 2437; (b) M. Raynal, C. S. J. Cazin, C. Valle´e,
H. Olivier-Bourbigou and P. Braunstein, Chem. Commun., 2008, 3983;
(c) M. Raynal, C. S. J. Cazin, C. Valle´e, H. Olivier-Bourbigou and P.
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3832 | Dalton Trans., 2009, 3824–3832
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The Royal Society of Chemistry 2009
©