Ruthenium(II) and iron(II) complexes of N-pyridyl substituted imidazolin-2-ylidenes

Article abstract of DOI:10.1016/j.jorganchem.2008.08.013

N-mesityl-N′-pyridyl-imidazolium chloride 1a and the corresponding bromide salt 1b have been deprotonated with NaH in THF giving the free N-heterocyclic carbene N-mesityl-N′-pyridyl-imidazolin-2-ylidene 2 in 80% yield (starting from 1a). Imidazolium salt 1a reacts with RuCl₃ · xH₂O to give a racemic mixture of dinuclear di-μ-chloro bridged ruthenium complexes [(κ²-2)₂Ru(μ-Cl)₂Ru(κ²-2)₂]²⁺ [3a]²⁺. The carbene carbon atoms as well as the halides are arranged in cis-positions to each other whereas the nitrogen atoms adopt a trans-configuration. The di-μ-bromo bridged derivative [(κ²-2)₂Ru(μ-Br)₂Ru(κ²-2)₂]²⁺ [3b]²⁺ was obtained from RuCl₃ · xH₂O and 1b. The bridging halide ligands can be removed by the reaction with silver or sodium salts of bidentate Lewis acids. Complex [3a]²⁺ reacts with silver pyridylcarboxylate to give a racemic mixture of the mononuclear complex [4]⁺. Reaction of [3a]²⁺ with the sodium salt of l-proline resulted in a diastereomeric mixture of complexes [5]⁺. The free N-heterocyclic carbene 2 reacts with [FeCl₂(PPh₃)₂] to give after anion exchange with NaBPh₄ cis/cis/trans coordinated [Fe(κ²-2)₂(MeCN)₂](BPh₄)₂ [6](BPh₄)₂. The molecular structures of [3b](PF₆)₂, [4]PF₆ and [6](BPh₄)₂ · H₂O are reported.

Full text of DOI:10.1016/j.jorganchem.2008.08.013

Journal of Organometallic Chemistry 693 (2008) 3435–3440
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Ruthenium(II) and iron(II) complexes of N-pyridyl substituted
imidazolin-2-ylidenes
*
Oliver Kaufhold, F. Ekkehardt Hahn , Tania Pape, Alexander Hepp
Institut für Anorganische und Analytische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 36, 48149 Münster, Germany
a r t i c l e i n f o
a b s t r a c t
N-mesityl-N0-pyridyl-imidazolium chloride 1a and the corresponding bromide salt 1b have been depro-
tonated with NaH in THF giving the free N-heterocyclic carbene N-mesityl-N0-pyridyl-imidazolin-2-yli-
dene 2 in 80% yield (starting from 1a). Imidazolium salt 1a reacts with RuCl3 ꢀ xH2O to give a racemic
Article history:
Received 27 June 2008
Received in revised form 5 August 2008
Accepted 6 August 2008
Available online 13 August 2008
mixture of dinuclear di-l-chloro bridged ruthenium complexes [(j l-Cl)2Ru(j .
2-2)2Ru( 2-2)2]2+ [3a]2+
The carbene carbon atoms as well as the halides are arranged in cis-positions to each other whereas
the nitrogen atoms adopt a trans-configuration. The di-l-bromo bridged derivative [(j l-
2-2)2Ru(
Keywords:
N-heterocyclic carbenes
Ruthenium
Br)2Ru(
j
2-2)2]2+ [3b]2+ was obtained from RuCl3 ꢀ xH2O and 1b. The bridging halide ligands can be
removed by the reaction with silver or sodium salts of bidentate Lewis acids. Complex [3a]2+ reacts with
silver pyridylcarboxylate to give a racemic mixture of the mononuclear complex [4]+. Reaction of [3a]2+
Iron
with the sodium salt of
erocyclic carbene 2 reacts with [FeCl2(PPh3)2] to give after anion exchange with NaBPh4 cis/cis/trans coor-
dinated [Fe(
2-2)2(MeCN)2](BPh4)2 [6](BPh4)2. The molecular structures of [3b](PF6)2, [4]PF6 and
[6](BPh4)2 ꢀ H2O are reported.
L
-proline resulted in a diastereomeric mixture of complexes [5]+. The free N-het-
Chelating ligands
j
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
complexes with donor-functionalized carbene ligands are also
known [7,8a,d,h,9,10].
The utilization of N-heterocyclic carbenes (NHCs) [1] as ligands
in organometallic chemistry has attracted considerable attention
in recent years. NHCs do not only form stable complexes with tran-
sition metals in high or low oxidation states, but are increasingly
employed as spectator ligands in novel catalysts [2]. We have stud-
ied benzannulated N-heterocyclic carbenes [3] and their metal
complexes [4]. Of particular interest are NHC ligands which are
functionalized with donor groups at the nitrogen atoms of the het-
erocycle. Such ligands are capable of forming a stable M–Ccarbene
and a labile M-donor bond. A number of complexes with donor-
functionalized [5] and pincer-type [5b,6] benzimidazolin-2-yli-
dene ligands are known.
We report here on the coordination chemistry of the potentially
chelating N-pyridyl substituted carbene ligand 2 derived from the
imidazolium salts of type 1 (Scheme 1). Both mono and dinuclear
ruthenium(II) and mononuclear iron(II) complexes with ligand 2
have been synthesized and characterized by X-ray diffraction
studies.
2. Results and discussion
Besides the known N-mesityl-N0-pyridylimidazolium bromide
1b [8g], we have prepared the corresponding chloride 1a from 2-
chloropyridine and 1-mesitylimidazole using the method de-
scribed for the synthesis of 1b. The 1H NMR resonance of the NCHN
proton in 1a (d = 11.91 ppm) is shifted downfield relative to the
equivalent resonance in 1b (d = 11.45 ppm) [8g]. This observation
is consistent with previous results which describe a N2C–Hꢀ ꢀ ꢀCl
hydrogen bond in imidazolium chlorides [11] that seems to be less
distinct for the bromides.
Both imidazolium salts 1a and 1b can be deprotonated with
NaH in THF giving 2. The free carbene was isolated in 80% yield
(from 1a) (Scheme 1). Formation of 2 is indicated by absence of
the signal for the NCHN proton in the 1H NMR spectrum and the
appearance of the characteristic resonance of the carbene carbon
atom at d = 219.7 ppm in the 13C{1H} NMR spectrum. Similar
Recent reports describe imidazolin-2-ylidenes which are N-
substituted by nitrogen-donors. Among these are N-(a-picolyl)
[7] and N-(2-pyridyl) [7b–f,8] substituted NHCs as well as pincer-
ligands derived from N-substituted imidazolin-2-ylidenes [9]. A
large number of AgI, PdII, IrI, RhI, NiII, CuI and RuII complexes with
these ligands exhibiting diverse structural motifs have been de-
scribed. All of these have in common that the carbene carbon atom
is coordinated to the metal center while the additional nitrogen
donor might or might not coordinate. Di- and polynuclear
* Corresponding author. Tel.: +49 251 8333111; fax: +49 2518333108.
E-mail address: fehahn@uni-muenster.de (F.E. Hahn).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.08.013

3436
O. Kaufhold et al. / Journal of Organometallic Chemistry 693 (2008) 3435–3440
16
of complexes [3a](PF6)2/[3b](PF6)2 in acetone. The structure analy-
sis (Fig. 1) confirms the proposed composition of the complex.
The Ru–C bond distances in the [3b]2+ dication (range 1.951(7)–
1.982(6) Å) are remarkably short when compared to other octahe-
dral [8e,14,15] or even pentacoordinated trigonal–bipyramidal RuII
complexes with imidazolin-2-ylidene ligands [16]. We attribute
X
2
3
10
5
6
NaH
THF
11
12
9
4
N
N
N
N
1
7
17
14
N
N
H
13
8
15
1a: X = Cl
1b: X = Br
2
this to the trans-position of the carbene ligand to the p-donor bromo
ligand.
Scheme 1. Synthesis of ligand 2. The numbering refers to the assignment of the
NMR resonances.
Compound [3b](PF6)2 was observed as pair of
K,K/D,D enantio-
mers. The isomer as well as other possible cis/trans isomers
K,D
were not observed. The mesityl and pyridyl rings of two different
ligands coordinated to the same metal center are arranged in a
coplanar fashion. This face-to-face arrangement in combination
unsymmetrically N,N0-substituted imidazolin-2-ylidenes have
been described by Danopoulos et al. [12].
The reaction of the free carbene 2 with different RuII precursors
under varying reaction conditions applying different stoichiome-
tric ratios of reagents did not lead to uniform products. No discrete
ruthenium(II) complexes could be isolated. Mass spectroscopic
analysis of the reaction mixture obtained by treatment of the
coordinatively unsaturated phosphine complex [RuCl2(PPh3)3]
with 2 in varying stoichiometric amounts revealed the formation
of the cations [RuCl(2)2]+ and [Ru(2)3]2+ none of which could be
isolated so far. The reaction of 2 with [RuCl2(p-cymene)]2 led to
the mass spectroscopic identification of the same RuII complexes
in addition to the desired complex [RuCl(p-cymene)(2)]+ in the
reaction mixture. Again we did not succeed in separating the reac-
tion products. 1H NMR spectroscopy of the product mixture re-
with their short separation (3.44 Å) are indicative of
tions [17] between the aromatic rings. Apart from steric factors
this interaction is responsible for a restricted rotation of the
p–p interac-
p–p
mesityl rings which leads to two resonances for the o-methyl
groups (d = 1.90 and 1.30 ppm) in the 1H NMR spectrum.
Bidentate N,O-ligands have been employed successfully in the
preparation of ruthenium olefin metathesis catalysts. Samec and
Grubbs described an N,O-prolinate ruthenium benzylidene catalyst
which is highly active in the RCM of disubstituted dienes [18]. We
demonstrated that a ruthenium benzylidene complex with two
N,O-pyridylcarboxylato ligands shows catalytic RCM activity in
protic media [15]. We therefore decided to investigate the cleavage
of the dinuclear complex [3a]2+ by anionic N,O-ligands obtained
vealed that the introduction of ligand
2 prevents the free
from silver pyridylcarboxylate and sodium L-prolinate.
Reaction of [3a](PF6)2 with two equivalents of silver pyridyl-
carboxylate in refluxing tetrahydrofurane results in cleavage of
rotation of the p-cymene ligand in [RuCl(p-cymene)(2)]+. Four res-
onances were observed for the aromatic protons of the p-cymene
ligand in addition to two doublets for the CH3 groups of the isopro-
pyl substituent [13].
An interesting method for the generation of ruthenium(II) com-
plexes with N-pyridyl-functionalized imidazolin-2-ylidenes has
been described by Son et al. who reacted RuCl3 ꢀ xH2O with N-
methyl-N0-pyridylimidazolium iodide to obtain the octahedral tri-
carbene ruthenium(II) dication [8e]. The analogous reaction of 1a
with RuCl3 ꢀ xH2O did not yield the mononuclear trischelate but in-
stead the dinuclear complex [3a](PF6)2 with two ligands 2 coordi-
nated in the chelating
j
2-mode to each ruthenium(II) center
(Scheme 2). We assign this behavior to the larger sterical demand
of the N-mesityl substituents in 2.
N1
N7
Br2
Br1
C40
Carbene complex [3a](PF6)2 was identified by 13C{1H} NMR
spectroscopy showing a resonance at d = 191.3 ppm which is typi-
cal for ruthenium(II) complexes with imidazolin-2-ylidene ligands
[14a]. The MALDI mass spectrum (positive ions) shows a signal at
½ of the mass of [3a]2+ which is not due to the dicationic nature of
the complex but arises from ruthenium–halogen bond scission and
detection of the mononuclear complex cation. While the presence
of NHC ligands in [3a](PF6)2 was established by spectroscopic
methods no information about the stereochemistry of the ligand
coordination is available from these data.
C23
C6
Ru1
N4
Ru2
C57
N10
Treatment of RuCl3 ꢀ xH2O with 1b instead of 1a results in a
mixture of di-l-chloro and di-l-bromo diruthenium complex cat-
ions [3a]2+ and [3b]2+ (Scheme 2). In spite of the different halogen
bridges, the two complex cations give rise to essentially identical
NMR spectra. Crystals of [3b](PF6)2 suitable for an X-ray diffraction
study were grown by diffusion of pentane into a saturated solution
Fig. 1. Molecular structure of the cation [3b]2+ in [3b](PF6)2. Hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angles (°): Ru1–Br1 2.6394(9),
Ru1–Br2 2.6468(9), Ru1–N1 2.081(5), Ru1–N4 2.078(5), Ru1–C6 1.982(6), Ru1–C23
1.978(7), Ru2–Br1 2.6365(9), Ru2–Br2 2.6458(9), Ru2–N7 2.097(5), Ru2–N10
2.093(5), Ru2–C40 1.970(6), Ru2–C57 1.951(7); Br1–Ru1–Br2 82.30(3), Br1–Ru1–
N1 87.89(13), Br1–Ru1–N4 96.8(2), Br1–Ru1–C6 91.0(2), Br1–Ru1–C23 173.0(2),
Br2–Ru1–N1 96.08(13), Br2–Ru1–N4 88.32(13), Br2–Ru1–C6 171.2(2), Br2–Ru1–
C23 92.9(2), N1–Ru1–N4 174.0(2), N1–Ru1–C6 77.9(2), N1–Ru1–C23 97.7(2), N4–
Ru1–C6 98.2(2), N4–Ru1–C23 77.9(2), C6–Ru1–C23 94.3(3), Br1–Ru2–Br2 82.37(3),
Br1–Ru2–N7 96.31(13), Br1–Ru2–N10 88.42(14), Br1–Ru2–C40 171.8(2), Br1–Ru2–
C57 92.1(2), Br2–Ru2–N7 87.96(13), Br2–Ru2–N10 96.3(2), Br2–Ru2–C40 91.9(2),
Br2–Ru2–C57 170.6(2), N7–Ru2–N10 174.0(2), N7–Ru2–C40 77.6(2), N7–Ru2–C57
97.5(2), N10–Ru2–C40 98.0(2), N10–Ru2–C57 78.6(3), C40–Ru2–C57 94.1(3), Ru1–
Br1–Ru2 97.87(3), Ru1–Br2–Ru2 97.45(3).
X
(PF6)2
N
Ru
N
N
Ru
N
RuCl3 xH2O
NH4PF6
N
N
C
X
C
X
C
C
N
H
[3a](PF6)2: X = Cl
[3b](PF6)2: X = Br
1a: X = Cl
1b: X = Br
Scheme 2. Synthesis of complexes of type [3](PF6)2.

O. Kaufhold et al. / Journal of Organometallic Chemistry 693 (2008) 3435–3440
3437
the dinuclear complex and formation of two equivalents of the
mononuclear complex [4]PF6 (Scheme 3). The same reaction was
observed with [3b](PF6)2. Complex [4]PF6 precipitates from the
reaction solution together with insoluble silver salts. It can be sep-
arated from these by recrystallization from chloroform.
membered chelate rings. The Ru–Ccarbene distances differ slightly
(Ru–C1 1.977(2), Ru–C21 1.948(2) Å) with the shorter Ru–C sepa-
ration observed for the carbene ligand located trans to the oxygen
atom of the pyridylcarboxylato ligand. Additional geometric
parameters for [4]+ are similar to equivalent parameters found
Complex cation [4]+ contains two different carbene carbon
atoms (trans to the oxygen and the nitrogen atoms of the pyridyl-
carboxylate, respectively). These give rise to two chemically
inequivalent carbon atoms observed in the 13C{1H} NMR spectrum
at d = 197.3 and 196.7 ppm.
for [3b]2+
.
We found that the halogen abstraction from [3a](PF6)2 does not
require the addition of a silver salt or an elevated reaction temper-
ature as applied for the synthesis of [4](PF6). The strong trans-ef-
fect [4b] of the carbene ligands in [3a]2+ allows halogen
abstraction under cleavage of the dinuclear complex at ambient
Crystals of [4]PF6 suitable for an X-ray diffraction study were
obtained by diffusion of pentane into a solution of the complex
in acetone. The structure analysis (Fig. 2) confirms the assumptions
made for the composition of [4]PF6. The ruthenium atom is coordi-
nated in a distorted octahedral fashion with small N–Ru–C and O–
Ru–N angles (range 76.21(6)–78.21(8)°) observed for the five-
temperature using sodium
with sodium -prolinate to give a mixture of the diastereomeric
complexes [5]PF6. The diastereomers, and , exhibit distinctly
L-prolinate. Complex [3a](PF6)2 reacts
L
D
L
KL
different signals in the NMR spectra. For example, the 13C{1H} NMR
spectrum exhibits four resonances for the carbene carbon atoms
(diastereomer A: d = 197.6 and 195.7 ppm; diastereomer B:
d = 197.2 and 195.8 ppm). In addition two resonances were ob-
served for the carboxylato carbon atoms (diastereomer A:
d = 182.6 ppm; diastereomer B: d = 182.8 ppm).
(PF6)2
N
Ru
N
N
Ru
N
C
X
C
X
In contrast to the non-selective reaction of the free carbene 2
with ruthenium(II) precursors, treatment of [FeCl2(PPh3)2] with 2
in acetonitrile leads after anion exchange to a discrete complex
which was isolated and characterized as [6](BPh4)2 (Scheme 4).
The characteristic resonance for the carbene carbon atoms in
[6]2+ was observed in the 13C{1H} NMR spectrum at
d = 200.2 ppm while solubility and stability problems have previ-
ously prevented recording of the 13C{1H} NMR spectra of iron(II)
imidazolin-2-ylidene complexes [19]. In addition, the MALDI mass
spectrum shows a signal at m/z = 582 corresponding to the ion
[6ꢁ2 MeCN]+.
C
C
[3a](PF6)2
O
O
OAg
N
H
ONa
N
18 19
X-ray quality crystals of [6](BPh4)2 ꢀ H2O were obtained by slow
evaporation of the solvent from an acetonitrile solution of the
compound. The structure analysis revealed an iron atom coordi-
19
PF6
20
21
N
N
Ru
N
PF6
18
H
20
N
N
C
C
Ru
21
22
C
C
O
O
22
N
O
O
[4]PF6
[5]PF6
(BPh4)2
N
Fe
N
N
N
[FeCl2(PPh3)2]
NaBPh4
NCCH3
NCCH3
C
Scheme 3. Cleavage of complex [3a](PF6)2 by Lewis bases. The numbering refers to
the assignment of the NMR resonances.
N
C
[6](BPh4)2
2
Scheme 4. Synthesis of complex [6](BPh4)2.
C1
C21
N3
C27
N2
N6
Ru
N6
Fe
N1
N7
O1
N3
C10
O2
Fig. 2. Molecular structure of the cation [4]+ in [4](PF6). Hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angles (°): Ru–O1 2.1585(15), Ru–
N3 2.074(2), Ru–N6 2.058(2), Ru–N7 2.124(2), Ru–C1 1.977(2), Ru–C21 1.948(2);
O1–Ru–N3 82.80(6), O1–Ru–N6 97.90(7), O1–Ru–N7 76.26(6), O1–Ru–C1 92.55(7),
O1–Ru–C21 175.56(7), N3–Ru–N6 178.44(7), N3–Ru–N7 95.14(7), N3–Ru–C1
78.21(8), N3–Ru–C21 101.24(8), N6–Ru–N7 86.38(7), N6–Ru–C1 100.35(8), N6–
Ru–C21 78.10(8), N7–Ru–C1 167.73(8), N7–Ru–C21 101.41(8), C1–Ru–C21
90.08(9).
Fig. 3. Molecular structure of the cation [6]+ in [6](BPh4)2 ꢀ H2O. Hydrogen atoms
are omitted for clarity. Selected bond lengths (Å) and angles (°): Fe–N1 1.980(8), Fe–
N2 1.982(8), Fe–N3 1.956(8), Fe–N6 1.963(8), Fe–C10 1.917(10), Fe–C27 1.912(10);
N1–Fe–N2 90.6(3), N1–Fe–N3 88.5(3), N1–Fe–N6 93.0(4), N1–Fe–C10 89.0(3), N1–
Fe–C27 173.7(5), N2–Fe–N3 93.9(4), N2–Fe–N6 87.3(3), N2–Fe–C10 175.2(5), N2–
Fe–C27 92.1(3), N3–Fe–N6 178.0(5), N3–Fe–C10 81.3(6), N3–Fe–C27 96.9(5), N6–
Fe–C10 97.4(5), N6–Fe–C27 81.4(5), C10–Fe–C27 88.8(4).

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O. Kaufhold et al. / Journal of Organometallic Chemistry 693 (2008) 3435–3440
nated in a distorted octahedral fashion (Fig. 3). Both the
K
and
D
washed with little water. The precipitate was redissolved in dichlo-
romethane. This solution was dried with MgSO4 and then concen-
trated to 5 mL and added to diethyl ether (70 mL). A yellow
precipitate of compound [3a](PF6)2 formed which was isolated by
filtration and dried in vacuo. Yield: 460 mg (0.28 mmol, 95%). For
assignment of the resonances see Scheme 1. 1H NMR (400.1 MHz,
acetone-d6): d 8.41 (d, J = 2.3 Hz, 4H, H3), 8.23 (m, 4H, H8), 7.84
(m, 4H, H5), 7.78 (m, 4H, H6), 7.06 (d, J = 2.3 Hz, 4H, H2), 6.64 (s,
4H, H13), 6.37 (s, 4H, H11), 6.27 (m, 4H, H7), 2.15 (s, 12H, H17),
1.90 (s, 12H, H15), 1.30 (s, 12H, H16). 13C{1H} NMR (100.6 MHz,
acetone-d6): d 191.3 (C1), 154.1 (C4), 152.9 (C8), 139.9 (C12),
137.1 (C6), 136.3 (C14), 135.2 (C9), 134.3 (C10), 130.3 (C13),
130.0 (C11), 126.3 (C2), 123.0 (C7), 117.9 (C3), 111.0 (C5), 20.8
(C17), 17.9 (C15), 17.0 (C16). MS (MALDI): m/z (%): 663 (100)
[½M]+.
isomer coexist in the centrosymmetric unit cell. Short Fe–Ccarbene
bond lengths (1.917(10) and 1.912(10) Å) are found in [6]2+ which
are significantly shorter than the equivalent Fe–C separations in
octahedral FeIII hexa(imidazolin-2-ylidene) complexes [20]. How-
ever, the observed Fe–C bond lengths in [6]2+ compare well with
the values found for FeII imidazolin-2-ylidene complexes [19]
and even to those observed for dinitrogen complexes of iron(0) sta-
bilized by a tridentate pincer dicarbene ligand [21].
3. Conclusions
The N-pyridyl-N0-mesityl substituted imidazolin-2-ylidene 2 has
beenprepared. Its parentimidazoliumsalts 1a,breact withRuCl3 ꢀ x-
H2O under formation of dinuclear complexes of type [Ru(2)2(l-X)]2
(X = Cl, Br). The dinuclear complexes are cleaved by bidentate mono-
anionic Lewis bases (N–O) to yield monodentate complexes
[Ru(2)2(N–O)]PF6. Direct reaction of the carbene ligand 2 with
[FeCl2(PPh3)2] in acetonitrile yields the iron complex [Fe(2)2
(NCCH3)2](BPh4)2. The mononuclear RuII and FeII complexes are
promising starting materials for functionalization with an alkyl-
idene ligand which could lead to novel complexes for olefin
metathesis.
4.5. Complex [4]PF6
A solution of [3a](PF6)2 (280 mg, 0.17 mmol) and silver pyridyl-
carboxylate (80 mg, 0.35 mmol) in THF (20 mL) was heated under
reflux for 8 h. The precipitate was filtered off and dissolved in chlo-
roform. After an additional filtration the solvent was removed in va-
cuo. Yield: 200 mg (0.22 mmol, 65%). For assignment of the
resonances see Scheme 3. 1H NMR (400.1 MHz, acetone-d6): d 8.50
(d, J = 2.4 Hz, 1H, H3), 8.43 (d, J = 2.4 Hz, 1H, H30), 8.09 (m, 1H,
H21), 8.07 (m, 1H, H18), 7.98 (m, 1H, H20), 7.87 (m, 2H, H5), 7.81
(m, 3H, H6, H8, H60), 7.70 (m, 1H, H50), 7.48 (m, 1H H19), 7.43 (m,
1H, H80), 7.36 (d, J = 2.4 Hz, 1H, H2), 7.34 (d, J = 2.4 Hz, 1H, H20),
6.93 (m, 1H, H70), 6.86 (m, 2H, H7, H130), 6.67 (s, 1H, H11), 6.54 (s,
1H, H13), 6.43(s, 1H, H110), 2.19 (s, 3H, H170), 2.16 (s, 3H, H17),
2.13 (s, 3H, H150), 2.10 (s, 3H, H15), 1.60 (s, 3H, H160), 1.58 (s, 3H,
4. Experimental
4.1. General methods
All reactions were carried out under an argon atmosphere. Sol-
vents were dried and degassed by standard methods. The imidazo-
lium salts 1b [8g] and [FeCl2(PPh3)2] [22] were prepared according
to literature procedures. NMR spectra were recorded on Bruker AC
200 (200 MHz), Bruker Avance I 400 (400 MHz) or Varin Unity Plus
600 (600 MHz) spectrometers. Mass spectra were obtained with a
Bruker Reflex IV mass spectrometer.
13
H16). C{1H} NMR (100.6 MHz, acetone-d6): d 197.3 (C10), 196.7
(C1), 170.9 (C23), 155.0 (C40), 154.3 (C22), 153.8 (C4), 152.5 (C18),
150.7 (C80), 150.2 (C8), 140.0 (C120), 139.9 (C12), 138.7 (C20),
137.7 (C60), 137.7 (C140), 137.5 (C6), 135.7 (C14), 135.7 (C90), 135.2
(C9), 135.2 (C10), 134.3 (C100), 130.5 (C130), 130.1 (C13), 129.8
(C11), 129.5 (C110), 128.2 (C19), 127.4 (C21), 126.2 (C2), 125.9
(C20), 122.7 (C70), 122.3 (C7), 118.1 (C30), 117.7 (C3), 111.7 (C50),
111.0 (C5), 20.9 (C170), 20.8 (C17), 18.8 (C15), 18.0 (C150), 17.9
(C160), 17.5 (C16). MS (MALDI): m/z (%): 750 (100) [M]+.
4.2. Spectroscopic parameters for 1a
1H NMR (200.1 MHz, CDCl3): d 11.91 (t, J = 1.5 Hz, 1H, H1), 9.37
(d, J = 8.4 Hz, 1H, H5), 8.89 (m, 1H, H3), 8.53 (dm, J = 4.8 Hz, 1H,
H8), 8.12 (m, 1H, H6), 7.48 (dd, J = 7.3 Hz, J = 4.8 Hz, 1H, H7), 7.30
(m, 1H, H2), 7.05 (s, 2H, H11 and H13), 2.35 (s, 3H, H17), 2.20 (s,
6H, H15 and H16).
4.6. Complex [5]PF6
A mixture of L-proline (46 mg, 0.39 mmol) and NaOH (16 mg,
0.40 mmol) in methanol (5 mL) was stirred for 1 h at room temper-
ature. After addition of solid [3a](PF6)2 (330 mg, 0.20 mmol) the
suspension was left stirring for 4 h. The clear solution was dropped
into diethyl ether (100 mL). After filtration, the precipitate was
washed with diethyl ether (20 mL) and dried in vacuo. Yield:
315 mg (0.36 mmol, 87%). For assignment of the resonances see
Scheme 3. Diastereomer A: 1H NMR (400.1 MHz, acetone-d6): d
8.70 (H8), 8.43 (H3), 8.40 (H30), 8.30 (H80), 7.84 (H60), 7.83 (H5),
7.78 (H6), 7.78 (H50), 7.19 (H20), 7.11 (H2), 7.04 (H70), 6.80 (H7),
6.77 (H130), 6.68 (H13), 6.54 (H11), 6.38 (H110), 5.06 (NH), 3.92
(H21), 2.47 (H18a), 2.19 (H17), 2.12 (H20a), 2.15 (H170), 2.05
(H15), 2.03 (H150), 1.65 (H20b), 1.63 (H19a), 1.52 (H16), 1.43
(H160), 1.18 (H19b), 1.18 (H18b). 13C{1H} NMR (100.6 MHz, ace-
tone-d6): d 197.6 (C10), 195.7 (C1), 182.6 (C22), 154.6 (C40), 154.4
(C4), 152.6 (C8), 150.1 (C80), 139.8 (C12), 139.7 (C120), 137.3 (C6),
137.2 (C60), 136.9 (C140), 136.4 (C14), 135.6 (C9), 135.4 (C90),
134.7 (C100), 134.3 (C10), 130.5 (C13), 130.3 (C130), 129.7 (C11),
129.6 (C110), 125.8 (C2), 125.6 (C20), 122.3 (C70), 122.2 (C7),
117.8 (C3), 117.5 (C30), 111.4 (C5), 111.3 (C50), 63.1 (C21), 49.7
(C18), 31.4 (C20), 27.4 (C19), 21.0 (C170), 20.9 (C17), 18.2 (C15),
18.1 (C150), 17.3 (C160), 17.3 (C16). Diastereomer B: 1H NMR
(400.1 MHz, acetone-d6): d 8.50 (H3), 8.37 (H30), 8.19 (H8), 8.12
4.3. Synthesis of carbene 2
A suspension of 1a (1.00 g, 2.90 mmol) and NaH (77 mg,
3.20 mmol) in THF (15 mL) was stirred for 12 h at room tempera-
ture. The precipitate was removed by filtration and the solution
was brought to dryness in vacuo. Yield: 610 mg (2.30 mmol, 80%).
For assignment of the resonances see Scheme 1. 1H NMR
(599.7 MHz, THF-d8): d 8.45 (m, 1H, H5), 8.38 (m, 1H, H8), 8.21
(m, 1H, H3), 7.76 (m, 1H, H6), 7.18 (m, 1H, H7), 7.03 (m, 1H, H2),
6.97 (s, 2H, H11 and H13), 2.32 (s, 3H, H17), 2.05 (s, 6H, H15 and
H16). 13C{1H} NMR (150.8 MHz, THF-d8): d 219.7 (C1), 154.8 (C4),
148.4 (C8), 139.4 (C9), 138.6 (C6), 137.9 (C12), 135.6 (C10 and
C14), 129.3 (C11 and C13), 122.3 (C2), 121.8 (C7), 116.7 (C3),
114.7 (C5), 21.0 (C17), 17.9 (C15 and C16).
4.4. Complex [3a](PF6)2
A solution of RuCl3 ꢀ xH2O (125 mg, 0.60 mmol) and 1a (360 mg,
1.20 mmol) in ethylene glycole was heated under reflux for 4 h and
was after cooling treated with aqueous NH4PF6 (500 mg in 5 mL
H2O). A precipitate formed which was separated by filtration and

O. Kaufhold et al. / Journal of Organometallic Chemistry 693 (2008) 3435–3440
3439
Table 1
Crystal data and data collection details for [3b](PF6)2, [4]PF6 and [6](BPh4)2 ꢀ H2O
[3b](PF6)2
[4]PF6
[6](BPh4)2 ꢀ H2O
Chemical formula
Formula weight (amu)
Space group
C
68H68N12Br2F12P2Ru
C40H38N7F6O2PRu
894.81
P1
C86H82N8B2FeO
1321.07
P21/c
1705.25
P21/n
ꢀ
Z
4
2
4
T (K)
153(2)
1.277
1.343
153(2)
1.525
0.518
293(2)
1.185
2.029
q
l
(g cmꢁ3
)
(mmꢁ1
)
a (Å)
b (Å)
c (Å)
16.120(3)
20.765(3)
27.564(4)
90
105.937(3)
90
11.987(2)
12.182(2)
15.684(3)
103.138(3)
95.916(3)
116.085(3)
1948.5(5)
14.0475(7)
12.9485(7)
42.307(2)
90
105.795(3)
90
a
(°)
b (°)
c
(°)
V (Å3)
k (Å)
8872(2)
7404.8(6)
Cu Ka, 1.54178
Mo K
a, 0.71073
Mo K
a, 0.71073
Data collected
Unique data
Observed data [I > 2
70094
15618
9147
22505
11170
9481
17355
4713
3146
r(I)]
R, Rw [I > 2r(I)]
0.086, 0.1925
0.0435, 0.0936
0.0667, 0.1632
(H80), 7.90 (H5), 7.84 (H6), 7.82 (H60), 7.76 (H50), 7.17 (H20), 7.09
(H2), 6.95 (H70), 6.94 (H7), 6.85 (H130), 6.73 (H13), 6.50 (H11),
6.39 (H110), 4.59 (NH), 3.52 (H21), 3.18 (H18a), 2.92 (H18b), 2.20
(H170), 2.19 (H17), 2.10 (H150), 2.05 (H20a), 2.02 (H15), 1.92
(H20b), 1.83 (H19a), 1.55 (H19b), 1.48 (H16), 1.40 (H160). 13C{1H}
NMR (100.6 MHz, acetone-d6): d 197.2 (C10), 195.8 (C1), 182.8
(C22), 155.4 (C40), 154.6 (C4), 152.6 (C8), 150.3 (C80), 139.8
(C120), 139.8 (C12), 137.7 (C6), 137.3 (C60), 136.4 (C14), 136.0
(C140), 135.7 (C9), 135.5 (C90), 135.0 (C100), 134.3 (C10), 130.6
(C13), 130.1 (C130), 129.8 (C110), 129.8 (C11), 126.3 (C2), 125.9
(C20), 122.2 (C70), 122.0 (C7), 117.9 (C3), 117.4 (C30), 111.6 (C5),
111.5 (C50), 62.9 (C21), 52.9 (C18), 30.2 (C20), 27.6 (C19), 20.9
(C170), 20.9 (C17), 18.2 (C150), 18.2 (C15), 17.4 (C16), 17.3 (C160).
MS (MALDI): m/z (%): 742 (100) [M]+.
Bruker SMART [23] program package. Structure solutions were found
with the SHELXS-97 [24] package using the heavy-atom method and
were refined with SHELXL-97 [25] against |F2| using first isotropic
and later anisotropic thermal parameters for all non-hydrogen
atoms. Hydrogen atoms were added to the structure models on cal-
culated positions. Additional data collection and refinement
parameters are given in Table 1.
Appendix A. Supplementary material
CCDC 693197, 693198 and 693199 contains the supplementary
crystallographic data for [3a](PF6)2, [4]PF6 and [6](BPh4)2 ꢀ H2O.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif. Supplementary data associated with this article can be
4.7. Complex [6](BPh4)2
found,
in
the
online
version,
at
doi:10.1016/
j.jorganchem.2008.08.013.
To a solution of [FeCl2(PPh3)2] (800 mg, 1.25 mmol) in THF
(25 mL) was added a solution of 2 (330 mg, 1.25 mmol) in THF
(10 mL) at ꢁ78 °C. This mixture was stirred at ambient temperature
for 12 h. A precipitate formed during this time which was separated
by filtration, washed with diethyl ether (10 mL) and suspended in
acetonitrile(10 mL). To this suspensionwas added a solutionof NaB-
Ph4 (427 mg, 1.25 mmol) in acetonitrile (10 mL). After stirring for
12 h, the resulting suspension was filtered and the filtrate was con-
centrated to 5 mL. Addition of diethyl ether (30 mL) causes precipi-
tation of complex [6](BPh4)2. Yield: 299 mg (0.45 mmol, 36%). For
assignment of the resonances see Scheme 1. 1H NMR (400.1 MHz,
acetonitrile-d3): d 8.12 (m, 4H, H3, H8), 7.71 (m, 2H, H6), 7.37 (m,
2H, H5), 7.28 (m, 16H, o-H BPh4), 7.10 (d, J = 2.2 Hz, 1H, H2), 6.99
(m, 16H, m-H BPh4), 6.84 (m, 8H, p-H BPh4), 6.82 (m, 2H, H7), 6.67
(s, 2H, H13), 6.53 (s, 2H, H11), 2.18 (s, 6H, H17), 1.96 (s, 6H, H15),
1.43 (s, 6H, H16). 13C{1H} NMR (100.6 MHz, acetonitrile-d3): d
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