Synthesis of a ruthenium(II) complex containing an [11]ane-P 2CNHC (NHC = Imidazolidin-2-ylidene) macrocycle

Article abstract of DOI:10.1021/om900703q

Reaction of [RuCl(Cp)(PPh₃)₂] with bis[di(2-fluorophenyl)phosphino]benzene, 3, yields complex [RuCl(Cp)(3)], [4]. The chloro ligand in [4] can be exchanged for the 2-azidoethyl isocyanide ligand 2, giving complex [Ru(Cp)(2)(3)]Cl, [5

Full text of DOI:10.1021/om900703q

6362 Organometallics 2009, 28, 6362–6369
DOI: 10.1021/om900703q
Synthesis of a Ruthenium(II) Complex Containing an [11]ane-P2CNHC
(NHC = Imidazolidin-2-ylidene) Macrocycle
†
Aaron Flores-Figueroa, Oliver Kaufhold, Alexander Hepp, Roland Frohlich, and
†
†
‡
ꢀ
€
F. Ekkehardt Hahn*,†
†
€
Institut fu€r Anorganische und Analytische Chemie, Westfalische Wilhelms-Universitat Munster,
Corrensstrasse 30, D-48149 Mu€nster, Germany, and Organisch-Chemisches Institut, Westfalische
€
€
€
‡
Wilhelms-Universita€t Mu€nster, Corrensstrasse 40, D-48149 Mu€nster, Germany
Received August 9, 2009
Reaction of [RuCl(Cp)(PPh3)2] with bis[di(2-fluorophenyl)phosphino]benzene, 3, yields complex
[RuCl(Cp)(3)], [4]. The chloro ligand in [4] can be exchanged for the 2-azidoethyl isocyanide ligand 2,
giving complex [Ru(Cp)(2)(3)]Cl, [5]Cl, which reacts with NH4BF4 to give [5]BF4. The azido group
of the coordinated isocyanide ligand in [5]Cl or [5]BF4 can be reduced with Zn/NH4Cl/H2O to give
the complex with the 2-aminoethyl isocyanide ligand. This ligand is not stable but cyclizes by an
intramolecular nucleophilic attack of the amino group at the isocyanide carbon atom to give an NH,
NH-stabilized NHC ligand in complexes [6]X (X = Cl, [6]Cl; X = 0.5 ZnCl4, [6]2(ZnCl4); X = BF4,
[6]BF4). Deprotonation of the NH,NH-stabilized NHC ligands in cations of type [6]þ leads to an
intramolecular nucleophilic attack of the amido nitrogen atoms at the fluorinated phenyl groups
of the diphosphine ligand under formation of the complex with the facially coordinated macro-
cyclic [11]ane-P2CNHC ligand [1]X (X = Cl, [1]Cl; X = 0.5 ZnCl4, [1]2(ZnCl4); X = BF4, [1]BF4).
Formation of the macrocycle is facilitated by the steric pressure excerted by the cyclopentadienyl
ligand. The molecular structures of [4], [5]BF4, [6]BF4 CH2Cl2, and [1]Cl CH2Cl2 0.5H2O have been
3
3
3
determined by X-ray diffraction.
Introduction
liberate the facially coordinated P3-donor macrocycle from
the metal center4 and to coordinate it to another metal under
conservation of the all-syn conformation.4,5 The template
synthesis proved advantageous since the separation of syn
and anti ligand isomers could be avoided and the incor-
poration of different linkers within the macrocycle proved
possible.3
Most template syntheses of P3-macrocycles proceed via
radical or base-induced intramolecular hydrophosphination
of appropriately functionalized primary or secondary phos-
phines (Scheme 1, method A).3 In addition, a template
approach utilizing the nucleophilic attack of coordinated
phosphides at halogenato functionalized aryl or alkyl phos-
phines has been developed (Scheme 1, method B)6 next to
more exotic methods such as olefin metathesis for the gen-
eration of very large P3-macrocycles.7
The coordination chemistry of facially coordinated
macrocyclic tridentate N-donor ligands such as triazacyclo-
nonane (tacn) has been studied for some years,1 but their
P-donor analogues have only recently attracted attention
when efficient synthetic procedures for the preparation of
such ligands were developed. Initially, cyclic ligands with
three P-donors have been prepared as mixtures of all possible
diastereomers by a purely organic approach.2 More recently,
complexes with macrocyclic P-donor ligands in the all-syn
conformation have been obtained by metal template-con-
trolled procedures.3 In selected cases it was possible to
*Corresponding author. E-mail: fehahn@uni-muenster.de.
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pubs.acs.org/Organometallics
Published on Web 10/05/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 21, 2009 6363
Scheme 1. Template Synthesis of P3-Macrocycles
Scheme 2. Template Synthesis of [11]ane-P2CNHC Macrocycles
Due to the similarities in the coordination chemistry of
N-heterocyclic carbenes8 and phosphine ligands,9 we became
interested in the preparation of tridentate facially coordi-
nated macrocyclic ligands incorporating simultaneously
phosphine and NHC donor groups. Such ligands, if facially
coordinated to an octahedral {M(CO)3} metal center, could
lead to a discrimination in the reactivity of the carbonyl
ligands, which would be located in trans position to either an
NHC or a phosphine ligand.
Our first experiments with the template-controlled hydro-
phosphination method (Scheme 2, top) using a diallyl-func-
tionalized benzannulated carbene ligand10 did not lead to the
desired facial diphosphine-NHC complex. The free NHC
ligand is basic enough to deprotonate the coordinated diphos-
phine under formation of complexes of type C (Scheme 2).11
We have therefore developed an alternative template
synthesis starting with complexes of 2-azido-functionalized
isocyanides,12 which upon reduction of the azido function by
a Staudinger reaction followed by hydrolysis13 cyclize to
yield the complexes of type D with an NH,NH-stabilized
NHC ligand (Scheme 2, bottom).14 Subsequently, a fluori-
Scheme 3
nated diphenylphosphine was introduced, giving complexes
of type E. Deprotonation of the NHC ligand led to an attack
of the NHC nitrogen atoms at the fluorinated diphosphine
under formation of the complexes F with the [11]ane-
P2CNHC ligand (Scheme 2, bottom).15
We became particularly interested in ruthenium com-
plexes like G (Scheme 3) with an [11]ane-P2CNHC ligand
since they could find application as olefin metathesis cata-
lysts in analogy with the well-known complexes of type
[RuCl2(PCy3)(CHPh)(NHC)] (type II Grubbs catalysts).16
Dissociation of the monodentate phosphine ligand in G
would, however, generate a cationic species that might
exhibit catalytic properties different from the original
Grubbs type II catalyst. In this contribution we describe
the generation of a macrocyclic [11]ane-P2CNHC ligand at
RuII leading to complex [1]Cl (Scheme 3).
(8) (a) Arduengo, A. J., III; Bertrand, G., Eds. Chem. Rev. 2009, 109,
2309-3884, this is a themed issue dedicated to NHC chemistry. (b) Hahn,
F. E., Ed. Dalton Trans. 2009, 6893-7313, this is a themed issue dedicated
to NHC chemistry. (c) Kaufhold, O.; Hahn, F. E. Angew. Chem., Int. Ed.
2008, 47, 4057–4061. (d) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed.
2008, 47, 3122–3172. (e) Hahn, F. E. Angew. Chem., Int. Ed. 2006, 45,
1348–1352.
(9) Crabtree, R. H. J. Organomet. Chem. 2005, 690, 5451–5457.
(10) (a) Hahn, F. E.; Holtgrewe, C.; Pape, T.; Martin, M.; Sola, E.;
Oro, L. A. Organometallics 2005, 24, 2203–2209. (b) Holtgrewe, C.;
Diedrich, C.; Pape, T.; Grimme, S.; Hahn, F. E. Eur. J. Org. Chem. 2006,
€
3116–3124. (c) Hahn, F. E.; Wittenbecher, L.; Boese, R.; Blaser, D. Chem.-
Eur. J. 1999, 5, 1931–1935. (d) Hahn, F. E.; Wittenbecher, L; Le Van, D.;
€
Frohlich, R. Angew. Chem., Int. Ed. 2000, 39, 541–544.
(11) Edwards, P. G.; Hahn, F. E.; Limon, M.; Newman, P. D.;
Kariuki, B. M.; Stasch, A. Dalton Trans. 2009, 5115–5119.
(12) (a) Hahn, F. E. Angew. Chem., Int. Ed. Engl. 1993, 32, 650–665.
(b) Singleton, E.; Oosthuizen, H. E. Adv. Organomet. Chem. 1983, 22,
209–310. (c) Treichel, P. M. Adv. Organomet. Chem. 1973, 11, 21–86.
(13) Staudinger, H.; Meyer, J. Helv. Chim. Acta 1919, 2, 635–646.
Results and Discussion
€
(14) (a) Hahn, F. E.; Langenhahn, V.; Meier, N.; Lugger, T.;
Fehlhammer, W. P. Chem.-Eur. J. 2003, 9, 704–712. (b) Hahn, F. E.;
Langenhahn, V.; L€ugger, T.; Pape, T.; Le Van, D. Angew. Chem., Int. Ed.
2005, 44, 3759–3763. (c) Hahn, F. E.; García Plumed, C.; M€under, M.;
L€ugger, T. Chem.-Eur. J. 2004, 10, 6285–6293. (d) Hahn, F. E.;
Langenhahn, V.; Pape, T. Chem. Commun. 2005, 5390–5392. (e) Liu,
C.-Y.; Chen, D.-Y.; Lee, G.-H.; Peng, S.-M.; Liu, S.-T. Organometallics
1996, 15, 1055–1061. (f) Ku, R.-Z.; Chen, D.-Y.; Lee, G.-H.; Peng, S.-M.;
Liu, S.-T. Angew. Chem., Int. Ed. Engl. 1997, 36, 2631–2632. For two
reviews on the cyclization of 2-functionalized isocyanides see: (g) Tamm, M.;
Hahn, F. E. Coord. Chem. Rev. 1999, 182, 175–209. (h) Michelin, R. A.;
Pombeiro, A. J. L.; Guedes da Silva, M. F. C. Coord. Chem. Rev. 2001, 218,
75–112.
We have previously studied the cyclization of 2-azidoethyl
isocyanide 2 at a RuII template center.17 In contrast to
(15) (a) Kaufhold, O.; Stasch, A.; Edwards, P. G.; Hahn, F. E. Chem.
Commun. 2007, 1822–1824. (b) Kaufhold, O.; Stasch, A.; Pape, T.; Hepp,
A.; Edwards, P. G.; Newman, P. D.; Hahn, F. E. J. Am. Chem. Soc. 2009,
131, 306–317.
(16) Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18–29.
(17) Kaufhold, O.; Flores-Figueroa, A.; Pape, T.; Hahn, F. E.
Organometallics 2009, 28, 896–901.

6364 Organometallics, Vol. 28, No. 21, 2009
Flores-Figueroa et al.
Scheme 4. Reduction and Cyclization of 2-Azidoethyl Isocyanide
at RuII
Figure 1. Molecular structure of [4] (50% displacement ellip-
soids, hydrogen atoms have been omitted). Selected bond
lengths (A) and angles (deg): Ru-P1 2.2652(9), Ru-P2
2.2512(9), Ru-Cl 2.4454(8); P1-Ru-P2 82.97(3), Pl-Ru-C1
85.75(3), P2-Ru-C1 83.52(3).
previous observations,14 the Staudinger reaction followed by
hydrolysis at the azido group of the 2-azidoethyl isocyanide
ligand in [Ru(Cl)2(p-cymene)(2)] did not yield the complex
with the NH,NH-stabilized NHC ligand (Scheme 4).
Instead, protonation of the intermediate phosphinimine-
substituted isocyanide ligand leading to complex H was
observed. The hydrolysis/cyclization reaction of the isocya-
nide ligand might be competing with the protonation
reaction. This is particularly likely when MfCNR back-
bonding deactivates the coordinated isocyanide for an
intramolecular nucleophilic attack.18
Scheme 5. Synthesis of Complex 4a
Reduction of the azido group followed by cyclization to
yield complex I was achieved with a FeCl3/NaI mixture
(Scheme 4).19 The required large excess of NaI led to an
exchange of the halogenato ligands at the ruthenium atom,
resulting in the isolation of the diiodo complex. Complex I,
however, proved unsuitable for the generation of a
macrocycle since its reaction with chelating diphosphines
led invariably to decomposition or mixtures of reaction
products.
In order to obtain a RuII complex of type E (Scheme 2)
bearing a diphosphine and the NH,NH-stabilized NHC
ligand in the facial orientation essential for a subsequent
linkage, we decided to introduce the diphosphine ligand first,
followed by generation of the carbene ligand at the metal
center. Complex [RuCl(Cp)(PPh3)2] has been shown to react
with chelating diphosphines in boiling toluene within 24 h
under substitution of the monodentate phosphine ligands.20
Reaction of [RuCl(Cp)(PPh3)2] with the less reactive fluori-
nated diphosphine 315a required 48 h but yielded complex
[RuCl(Cp)(3)], [4], in an excellent yield of 97% (Scheme 5).
The high yield observed with the fluorinated dipho-
sphine 3 contrasts the observation made when a nonfluori-
nated diphosphine such as bis(diphenylphosphino)benzene
(dppbz) was used, where after a reaction time of 24 h a
product mixture composed of [RuCl(Cp)(dppbz)] (57%) and
[Ru(Cp)(dppbz)PPh3]Cl (27%) was obtained.21 While
diphosphine 3 is less reactive than dppbz in the substitution
reaction with [RuCl(Cp)(PPh3)2], it is a better π-acceptor
a The numbering refers to the assignment of the NMR resonances.
once coordinated to the metal center, and thus ligand
scrambling was not observed.
Complex [4] was characterized by NMR spectroscopy and
X-ray diffraction. As expected, only one signal was observed
in the 31P{1H} NMR spectrum of [4] at δ = 62 ppm, while the
19F NMR spectrum exhibited two resonances, at δ = -100
and -101 ppm. The occurrence of these two resonances is
caused by the presence of two sets of fluorophenyl rings
oriented toward different parts of the pseudotetrahedral
coordination sphere.
An X-ray diffraction study confirmed the connectivity in
[4] (Figure 1). The metric parameters found in [4] fall in the
range previously observed for related ruthenium complexes.
The P-Ru-P bite angles in [4] (82.97(3)°) and in the ruthe-
nium complex with the nonfluorinated bis(diphenylpho-
sphino)benzene (dppbz) ligand [Ru(Cp)(dppbz)PPh3]Cl
(82.87(2)°) exhibit almost identical values.21
Substitution of the chloro ligand in [4] by a slight excess of
2-azidoethyl isocyanide 2 in refluxing methanol yields com-
pound [Ru(Cp)(2)(3)]Cl, [5]Cl, in excellent yield (Scheme 6).
Anion exchange with NH4BF4 in methanol gave [5]BF4.
In the 13C{1H} NMR spectrum the resonance for the iso-
cyanide carbon atom of [5]Cl was observed at δ = 151.7 ppm
(2JCP = 18 Hz), slightly downfield from the isocyanide
carbon resonance in complex [Ru(Cl)2(p-cymene) (2)] at
δ = 142.4 ppm (Scheme 4).17 Coupling between the isocya-
nide nitrogen atom and the adjacent carbon atoms, which is
typical for free alkyl isocyanides, was not observed for the
coordinated isocyanide ligand in [5]Cl.22
(18) (a) Hahn, F. E.; Tamm, M. J. Organomet. Chem. 1993, 456, C11–
C14. (b) Hahn, F. E.; Tamm, M. Organometallics 1995, 14, 2597–2600.
(c) Hahn, F. E.; Tamm, M. J. Chem. Soc., Chem. Commun. 1995, 569–570.
(d) Hahn, F. E.; Tamm, M.; L€ugger, T. Angew. Chem., Int. Ed. Engl. 1994,
33, 1356–1359. (e) Hahn, F. E.; Imhof, L. Organometallics 1997, 16, 763–
769. (f) Wanniarachchi, Y. A.; Slaughter, L. Organometallics 2008, 27,
1055–1062.
(19) Kamal, A.; Ramana, V.; Ankati, H. B.; Ramana, A. V. Tetra-
hedron Lett. 2002, 43, 6861–6863.
(20) (a) Bruce, M. I.; Windsor, N. J. Aust. J. Chem. 1977, 30, 1601–
1604. (b) Ashby, G. S.; Bruce, M. I.; Tomkins, I. B.; Wallis, R. C. Aust. J.
Chem. 1979, 32, 1003–1016.
The wavenumber of the CtN stretching frequency in the IR
spectrum of [5]Cl(ν(KBr) = 2152 cm-1) is lower than the value
recorded for [Ru(Cl)2(p-cymene)(2)] (ν(KBr) = 2199 cm-1).
(22) (a) Hahn, F. E.; Tamm, M. Angew. Chem., Int. Ed. Engl. 1991,
30, 203–205. (b) Hahn, F. E.; Tamm, M. Angew. Chem., Int. Ed. Engl. 1992,
31, 1212–1214.
(21) Guan, H.; Iimura, M.; Magee, M. P.; Norton, J. R.; Janak, K. E.
Organometallics 2003, 22, 4084–4089.

Article
Scheme 6. Synthesis of Compounds [5]Cl and [5]BF4
Organometallics, Vol. 28, No. 21, 2009 6365
Apparently, the 2-azidoethyl isocyanide ligand receives more
dfπ* back-bonding from the ruthenium atom in complex
cation [5]þ than in the neutral complex [Ru(Cl)2(p-cymene)(2)].
This assumption, however, is easily explained by the presence of
two strongly donating ligands in the complex cation [5]þ, while
the neutral complex contains much weaker donor ligands.
Strong back-bonding to the isocyanide is undesirable, as it
deactivates the isocyanide carbon atom for a nucleophilic
attack.
Figure 2. Molecular structure of the cation [5]þ in [5]BF4 (50%
displacement ellipsoids, hydrogen atoms have been omitted).
The asymmetric unit contains one-half of the cation, related to
the other half by a crystallographic mirror plane. Selected bond
lengths (A) and angles (deg): Ru-P1 2.2803(14), Ru-C4
1.942(9), N1-C4 1.169(11), N1-C5 1.381(14), N2-C6
1.24(2), N2-N3 1.26(2), N3-N4 1.13(2); P1-Ru-P1*
84.83(7), P1-Ru-C4 87.6(2), Ru-C4-N1 174.4(7),
C4-N1-C5 169.3(10), C6-N2-N3 134(2), N2-N3-N4
176(2).
The trend in the IR data appears to contradict the trend
observed for the 13C{1H} NMR data, which show a down-
field shift for the resonance of the isocyanide carbon atom in
[5]Cl (δ = 151.7 ppm) relative to the equivalent resonance
in [Ru(Cl)2(p-cymene)(2)] (δ = 142.4 ppm), while the IR
spectra indicate an enhanced back-bonding in [5]Cl relative
to [Ru(Cl)2(p-cymene)(2)]. The ligand sets in the two RuII
isocyanide complexes are different, and it appears that the
isocyanide carbon atom in [5]Cl reaches into the deshielding
region of the phenylene rings, while such a long-range
interaction does not exist for [Ru(Cl)2(p-cymene)(2)].
While numerous recrystallization attempts with com-
pound [5]Cl did not yield crystals suitable for an X-ray
diffraction study, such crystals could be obtained from a
methanol solution of [5]BF4. The monoclinic unit cell of
[5]BF4 contains two formula units located on crystallo-
graphic mirror planes (Figure 2). Substitution of the chloro
ligand in [4] for the isocyanide ligand in [5]BF4 does not lead
to significantly different metric parameters for the ruthe-
nium complexes. The bite angle of the diphosphine ligand
(84.83(7)°) in [5]BF4 is only marginally enlarged compared
to [4] (82.97(3)°). Only the Ru-P distance in the cationic
complex [5]þ (2.2803(14) A) is slightly longer than the
corresponding bond lengths in the neutral complex [4]
(2.2652(9) and 2.2512(9) A).
reaction followed by hydrolysis of the intermediate phosphi-
nimine can be used for the conversion of the azido function
into a primary amine,14 although this method has failed in
selected cases.17 Alternatively, azide reduction was achieved
with FeCl3/NaI followed by an aqueous workup.17 We have
recently carried out a systematic study regarding the conver-
sion of coordinated 2-azido-substituted isocyanides into
2-amino isocyanides at {Ru(Cp)(PR3)2}þ templates.24 From
this study a mixture of Zn/NH4Cl/H2O emerged as a suitable
reducing agent.25
Reaction of [5]Cl with 1.3 equiv of Zn dust, 2.3 equiv of
NH4Cl, and a small amount of water in boiling methanol for
24 h gave complex cation [6]þ as a mixture of the salts [6]Cl
and [6]2[ZnCl4]. The reaction can be followed by mass
spectroscopy showing the disappearance of the peak for
[5]þ (m/e = 781) and the appearance of a new peak at
m/e = 755. This latter peak is caused by the intermediate
complex cation with the 2-aminoethyl isocyanide ligand or
by the isomeric carbene complex cation [6]þ. The actual
nature of the reaction product was established spectroscopi-
cally. The IR spectrum of the reaction product shows no
absorptions due to the N3 and CtN groups in [5]þ. The
resonance for the isocyanide carbon atom of [5]þ at
δ = 151.7 ppm (2JCP = 18 Hz) was also absent in the
13C{1H} NMR spectrum of the reaction product, and a new
resonance at δ = 199.7 ppm (2JCP = 15.2 Hz) typical for the
carbene carbon atom in RuII NHC complexes17,24 was
detected instead. In addition, the typical resonance for the
NH protons of the carbene ligand was found in the 1H NMR
spectrum at δ = 6.26 ppm. The spectroscopic data indicate
immediate cyclization of the 2-aminoethyl isocyanide upon
reduction of the azido function in [5]Cl. No indication for an
equilibrium between the isocyanide and the NHC complex
was found. Such equilibria have previously been observed in
the template-controlled cyclization of 2-hydroxyphenyl iso-
cyanides18a-e and during the synthesis of complexes with
acyclic diaminocarbene ligands.18f
The isocyanide C-N-C angle in [5]þ (169.8(10)°) is
smaller than the corresponding angle in [Ru(Cl)2(p-cymene)-
(2)] (175.7(5)°).17 Like the wavenumbers for the CtN
stretching vibration, this indicates an increased dfπ*
back-bonding to the isocyanide ligand in the cationic com-
plex [5]þ in comparison to [Ru(Cl)2(p-cymene)(2)].
The next step in the preparation of the [11]ane-P2CNHC
macrocycle is the reduction of the azido function of the
coordinated 2-azidoethyl isocyanide in [5]þ to a primary
amine, which is supposed to cyclize to the NH,NH-stabilized
carbene ligand in [6]þ (Scheme 7). Various methods for the
reduction azide f primary amine in organic compounds
have been reported.23 The situation is more complicated for
an azide that is part of a coordinated ligand, as in complexes
with 2-azidoethyl isocyanide, as the azide reduction must not
affect the metal complex. We have shown that the Staudinger
(24) Flores-Figueroa, A.; Kaufhold, O.; Feldmann, K.-O.; Hahn,
F. E. Dalton Trans., in press, DOI: 10.1039/b915033a.
(25) Lin, W.; Zhang, X.; He, Z.; Jin, Y.; Gong, L.; Mi, A. Synth.
Commun. 2002, 32, 3279–3284.
€
(23) Brase, S.; Gil, C.; Knepper, K.; Zimmermann, V. Angew. Chem.,
Int. Ed. 2005, 44, 5188–5240.

6366 Organometallics, Vol. 28, No. 21, 2009
Flores-Figueroa et al.
Scheme 7. Reduction of the Azido Group in [5]þ followed by Cyclization to Give Cation [6]þ and Synthesis of Complex Cation [1]þ Bearing
the Macrocyclic [11]ane-P2CNHC Ligand
The spectroscopic features of [6]þ parallel those of the
rhenium(I) complex cation E (Scheme 2), both containing
the NH,NH-stabilized NHC ligand and the fluorinated
diphosphine.15 In both, the chemical shifts of the resonances
for the diphosphine ligand are essentially identical in the 1H,
13C{1H} NMR, and 19F NMR spectra. The resonances in the
31P{1H} NMR spectra, however, differ somewhat (δ = 22
ppm for E (M = Re),15a δ = 72 ppm for [6]þ).
macrocycle F,15 the nucleophilic aromatic substitution of
fluoride has been shown to be an efficient method for
template-controlled macrocycle formation (Scheme 2). The
same reaction also worked for the macrocycle formation in
complex cation [6]þ. Deprotonation of the NHC nitrogen
atoms in [6]Cl/[6]2[ZnCl4] with 2 equiv of KOtBu in THF at
room temperature yielded complex cation [1]þ with the
[11]ane-P2CNHC macrocycle after a reaction time of 24 h
(Scheme 7). Use of less than 2 equiv of KOtBu gave a mixture
of complexes with only one new Ncarbene-Cphenyl bond
(formal elimination of 1 equiv of HF, m/z = 735) and two
new Ncarbene-Cphenyl bonds (formal elimination of 2 equiv of
HF, m/z = 715). The complex cation [1]þ can also be
obtained by the same reaction starting from [6]BF4. As was
previously observed for complexes of type F (Scheme 2),
formation of the macrocycle in [1]þ leads to an upfield shift
to δ = 62 ppm in the 31P{1H} NMR spectrum (δ = 72 ppm
in [6]þ), and two resonances are observed for the CH2
protons of the carbene ring due to their locked position in
the complex cation.
The formation of cation [6]þ under the given reaction
conditions proceeded under formation of salts containing
two different anions ([6]Cl and [6]2[ZnCl4], Scheme 7), which
were difficult to separate. The mixture of salts was also
difficult to crystallize. We therefore studied the azide reduc-
tion with [5]BF4 as the starting material, hoping that the
presence of the tetrafluoroborate anion would lead to com-
pound [6]BF4, which we believed would be easier to crystal-
lize. Reaction of [5]BF4 with Zn/NH4Cl/H2O under the same
conditions used for the reduction of [5]Cl led as expected to
the formation of [6]BF4. The yield, however, was signifi-
cantly lower, and unreacted [5]BF4 was identified by NMR
spectroscopy in the reaction mixture after 24 h. Apparently,
the azide reduction is sensitive to the type of counterion
present in [5]X. The reasons for this behavior have not been
investigated yet. In spite of the low yield, compound [6]BF4
could be crystallized from dichloromethane. It can also be
obtained by anion exchange with NH4BF4 from the salt
mixture [6]Cl/[6]2[ZnCl4]2.
Crystals of [1]Cl CH2Cl2 0.5H2O were grown from a
3
3
mixture of salts [1]Cl/[1]2[ZnCl] in dichloromethane.
The X-ray structure analysis confirms the formation of the
complex cation [1]þ with the macrocyclic ligand at the
ruthenium(II) template atom (Figure 4).
Upon formation of the macrocycle, the Ru-Ccarbene bond
shortens slightly from 2.032(4) A in [6]þ to 1.996(5) A in [1]þ,
while the P1-Ru-P2 angle expands slightly. Additional
metric parameters in [6]þ and [1]þ are essentially identical,
indicating a stress-free formation of the macrocycle.
The relatively short reaction time for the formation of the
macrocycle in [1]þ (24 h) compared to the analogous
rhenium(I) complex (E in Scheme 2, 5 days)15 is remarkable.
We attribute this behavior to the influence of the ancillary
ligands in the two complexes. In the template-controlled
formation of [12]ane-P3 macrocycles from trisphosphine
complexes the additional ligands at the template metal
played an important role. It was argued that at the
Crystals of [6]BF4 CH2Cl2 were investigated by X-ray
3
diffraction methods. The molecular structure of the cation
[6]þ is depicted in Figure 3. Transformation of the
2-azidoethyl isocyanide ligand in [5]þ to the NH,NH-stabi-
lized NHC ligand in [6]þ does not significantly change the
other metric parameters in the cations. The Ru-C62 bond
lengths of 2.032(4) A compare well with the value found
for the Ru-Ccarbene separation of 2.031(4) A in [Ru(I)2-
(p-cymene)(NH,NH-NHC)].17
As demonstrated for the formation of triphosphamacro-
cycles6 and for the first complexes with the [11]ane-P2CNHC

Article
Organometallics, Vol. 28, No. 21, 2009 6367
metal center and reacts with a o-fluorinated bis(diphe-
nylphosphino)benzene at the RuII template to give the air-
and water-stable complex [1]Cl with the macrocyclic [11]ane-
P2CNHC ligand. Complexes of type [1]þ have been prepared
in our search for new olefin metathesis catalysts of type
[Ru([11]ane-P2CNHC)(CHPh)PR3]2þ. While the RuII-tem-
plate-controlled formation of the macrocycle is possible,
the substitution of the cyclopentadienyl ligand in [1]þ for
an alkylidene and a phosphine has not been achieved yet. We
are currently studying the formation of the [11]ane-P2CNHC
macrocycle at {Ru(indenyl)}þ and {Ru(pentadienyl)}þ tem-
plates, where the removal of the π-perimeters is more easily
achieved.
Figure 3. Molecular structure of the cation [6]þ in [6]BF4
Experimental Section
3
CH2Cl2 (50% displacement ellipsoids, hydrogen atoms have
been omitted except for those bound to the NHC nitrogen
atoms). Selected bond lengths (A) and angles (deg): Ru-P1
2.2601(8), Ru-P2 2.2584(8), Ru-C62 2.032(4); P1-Ru-P2
83.77(3), P1-Ru-C62 84.53(10), P2-Ru-C62 96.34(10),
N61-C62-N63 106.0(3).
General Comments. Caution! Aliphatic azides are high-energy
density materials. Vigorous heating of 2-azidoethyl isocyanide can
cause an explosive decomposition, and appropriate care is advised
when handling organic azides. All preparations were carried out
under an argon atmosphere using conventional Schlenk techni-
ques. Solvents were dried and degassed by standard methods
prior to use. The preparation of isocyanide 2,17 diphos-
phine 3,15a and [RuCl(Cp)(PPh3)2]26 has been described. NMR
spectra were recorded with a Bruker Avance I 400 NMR
spectrometer. IR spectra were measured with a Bruker Vector
22 spectrometer. MALDI mass spectra were obtained with a
Varian MAT 212 spectrometer. Consistent microanalytical data
were difficult to obtain due to the presence of fluoride in all
complexes. MALDI and ESI HRMS data are provided instead.
In addition H, 13C{1H}, 31P{1H}, and 19F NMR spectra are
1
provided for all compounds in the Supporting Information.
[RuCl(Cp)(3)], [4]. A solution of [RuCl(Cp)(PPh3)2] (280 mg,
0.39 mmol) and diphosphine 3 (400 mg, 0.77 mmol) in toluene
(20 mL) was heated under reflux for 48 h. The solvent was
removed under reduced pressure, and the solid obtained was
washed with diethyl ether (2 ꢀ 10 mL) to give a yellow solid.
Yield: 270 mg, (0.38 mmol, 97%). For assignment of the
1
resonances in the NMR spectra see Scheme 5. H NMR (400
Figure 4. Molecular structure of the cation [1]þ in [1]Cl
CH2Cl2 0.5H2O (50% displacement ellipsoids, hydrogen atoms
omitted). Selected bond lengths (A) and angles (deg): Ru-P1
2.2221(12), Ru-P2 2.2257(12), Ru-C62 1.996(5), C62-N61
1.370(6), C62-N63 1.356(6); P1-Ru-P2 84.89(4), P1-
Ru-C62 83.76(12), P2-Ru-C62 82.98(13), N61-C62-N63
107.1(4).
MHz, CDCl3): δ 8.15 (m, 2H, Ar-H15), 8.03 (m, 2H, Ar-H2),
7.47 (m, 2H, Ar-H3), 7.43 (m, Ar-H13), 7.25 (m, 2H, Ar-H7),
7.20 (m, 2H, Ar-H14), 7.07 (m, 2H, Ar-H12), 6.97 (m, 2H,
Ar-H6), 6.60 (m, 2H, Ar-H8), 6.17 (m, 2H, Ar-H9), 4.79
(s, 5H, Cp). 13C{1H} NMR (100 MHz, CDCl3): δ 163.2 (d,
3
3
1
1JCF = 247 Hz, C11), 162.3 (d, JCF = 248 Hz, C5), 142.5
(pseudo-t, 1JCP = 42.7 Hz, 2JCP = 42.7 Hz, C1), 137.0 (m, C15),
3
134.2 (m, C9), 132.7 (m, C2), 132.2 (d, JCF = 8.4 Hz, C13),
131.6 (d, 3JCF = 8.4 Hz, C7), 130.8 (C3), 126.2 (m, C4), 123.6
(m, C14), 123.4 (m, C8), 121.4 (m, C10), 115.6 (d, 2JCF = 23.8
Hz, C6), 115.2 (d, 2JCF = 23.8, C12), 81.6 (Cp). 31P{1H} NMR
(162 MHz, CDCl3): δ 62. 19F NMR (376 MHz, CDCl3): δ -100,
-101. MS (MALDI) m/z (%): 720 (100) [M - Cl]þ.
{CpFe}þ template, in contrast to {M(CO)3} templates (M =
Cr, Mo), the cyclopentadienyl ligand exerts a certain amount
of steric pressure, favoring an orientation of the phosphines
that is suitable for the subsequent linkage.4b The same
appears to be true for [6]þ, where the cyclopentadienyl ligand
favors the orientation of the NH,NH-stabilized NHC ligand
in an orientation suitable for its subsequent linkage to the
phenyl groups of the phosphine.
[Ru(Cp)(2)(3)]Cl, [5]Cl. A mixture of [4] (250 mg, 0.35 mmol)
and 2-azidoethyl isocyanide 2 (44 mg, 0.46 mmol) in methanol
(10 mL) was heated under reflux for 3 h. The solvent was
removed under reduced pressure and the colorless solid washed
with diethyl ether (2 ꢀ 10 mL). Yield: 270 mg (0.33 mmol, 92%).
For assignment of the resonances in the NMR spectra see
Scheme 5. 1H NMR (400 MHz, CDCl3): δ 7.65 (m, 2H, Ar-H2),
7.60(m, 2H, Ar-H3), 7.581 (m, 2H, Ar-H15), 7.45 (m, 2H,
Ar-H9), 7.27 (m, 2H, Ar-H14), 7.21 (m, 2H, Ar-H12), 7.06
(m, 2H, Ar-H13), 7.05 (m, 2H, Ar-H8), 7.05 (m, 2H, Ar-H6),
7.02 (m, 2H, Ar-H7), 4.98 (s, 5H, Cp), 3.04 (s br,
4H, CNCH2CH2N3). 13C{1H} NMR (100 MHz, CDCl3):
Conclusion
We have demonstrated that an NH,NH-stabilized NHC
ligand can be generated at a RuII center bearing the
2-azidoethyl isocyanide ligand by reduction of the azido
function with Zn/NH4Cl/H2O. The template-controlled
cyclization of the intermediate 2-aminoethyl isocyanide oc-
curs in spite of the presence of strongly electron donating
ligands at the metal center. The reactive NH,NH-stabilized
NHC ligand can be deprotonated while coordinated to the
1
1
δ 162.8 (d, JCF = 248.8, C11), 162.2 (dd, JCF = 259.9 Hz,
(26) Bruce, M. I.; Hameister, C.; Swincer, A. G.; Wallis, R. C. Inorg.
Synth. 1982, 21, 78–84.

6368 Organometallics, Vol. 28, No. 21, 2009
Flores-Figueroa et al.
Table 1. Crystallographic Data for the Complexes [4], [5]BF4, [6]BF4 CH2Cl2, and [1]Cl CH2Cl2 0.5H2O
3
3
3
parameter
[4]
[5]BF4
[6]BF4 CH2Cl2
3
[1]Cl CH2Cl2 0.5H2O
3
3
formula
C
35H25ClF4P2Ru
C38H29N4BF8P2Ru
0.25 ꢀ 0.15 ꢀ 0.05
867.47
10.0935(7)
16.0492(12)
10.9204(9)
90.0
93.071(5)
90.0
1766.5(2)
2
P21/m
C39H33N2BCl2F8P2Ru
0.30 ꢀ 0.08 ꢀ 0.05
926.39
9.7875(3)
26.0823(8)
15.3468(5)
90.0
105.080(2)
90.0
3782.8(2)
4
P21/n
C39H32N2Cl3F2O0.5P2Ru
0.20 ꢀ 0.20 ꢀ 0.08
844.01
20.0186(5)
22.1164(7)
18.4397(7)
90.0
107.580(2)
90.0
7782.7(4)
8
C2/c
cryst size [mm]
Mr
a [A]
b [A]
c [A]
R [deg]
β [deg]
γ [deg]
V [A3]
Z
0.20 ꢀ 0.10 ꢀ 0.05
720.01
14.5918(2)
11.0255(2)
19.0144(3)
90
98.439(1)
90
3025.95(8)
4
P21/n
1.580
0.762
space group
calcd [g cm-3
F
]
1.631
5.142
1.627
6.095
1.437
6.270
μ [mm-1
]
2θ range [deg]
data collected
no. unique data, Rint
no. obsd data [I g 2σ(I)]
R
3.3-55.9
20 093
7184, 0.066
4678
0.0455
8.1-134.9
15 792
3205, 0.079
2850
0.0609
6.9-135.8
32 583
6711, 0.064
6109
0.0426
6.1-135.8
30 499
6859, 0.064
5711
0.0522
wR
no. of variables
0.0951
388
0.1538
262
0.1103
502
0.01469
450
2
2JCP = 8.4 Hz, C5), 151.7 (t, JCP = 18 Hz, CtN), 141.5
KOtBu (47 mg, 0.42 mmol) in THF (20 mL) was stirred for 24 h.
After solvent removal, the residue was extracted with dichlor-
omethane. Removal of the solvent afforded a mixture of [1]Cl
and [1]2[ZnCl4] as a yellow solid. Yield: 110 mg (0.147 mmol,
70% relative to [1]Cl, 0.134 mmol, 64% relative to [1]2[ZnCl4];
the real value lies in between these two extremes). 1H NMR (400
MHz, CDCl3): δ 7.50 (m, 2H, Ar-H15), 7.44 (m, 4H, Ar-H2
and Ar-H3), 7.39 (m, 4H, Ar-H12 and Ar-H7), 7.31 (m, 2H,
Ar-H13), 7.15 (m, 2H, Ar-H14), 7.14 (m, 2H, Ar-H6), 7.01
(m, 2H, Ar-H8), 6.66 (br, 2H, Ar-H9), 4.96 (m, 2H,
NCHH-CHHN), 4.71 (s, 5H, Cp), 3.39 (m, 2H,
NCHH-CHHN). 13C{1H} NMR (100 MHz, CDCl3): δ 204.3
2
(m, C1), 134.2 (d, JCP = 8.6 Hz, C15), 133.9 (m, C9), 133.1
(m, C2 and C7), 132.3 (d, 3JCP = 3.5 Hz, C3), 131.5 (C13), 125.3
(m, C14), 124.7 (C8), 121.8 (m, C4), 121.2 (m, C10), 116.7
(d, 2JCF = 22.6 Hz, C6), 116.7 (d, 2JCF = 22.0 Hz, C12), 86.2
(Cp), 49.6 (CH2N3), 44.3 (CH2NC). 31P{1H} NMR (162 MHz,
CDCl3): δ 61. 19F NMR (376 MHz, CDCl3): δ -97, -98. IR
(KBr): ν 2152 (s, CN), 2136 (sh, N3), 2099 (s, N3). MS (MALDI)
m/z (%): 781 (100) [M - Cl]þ. MS (ESI HRMS) m/z (%):
781.0855 (100) [5]þ (calcd for [5]þ 781.0852).
[Ru(Cp)(2)(3)]BF4, [5]BF4. The tetrafluoroborate salt was
obtained by anion exchange with NH4BF4. The H, 13C, and
1
31P NMR are not affected by the anion exchange.
(br, NCN), 162.9 (dd, JCF = 249.5 Hz, JCP = 2.3 Hz, C5),
145.0 (d, 2JCP = 12.8 Hz, C11), 133.9 (d, 3JCF = 8.0, C7), 132.8
(br, C15), 132.7 (C3), 132.3 (br, C9), 132.2 (br, C1), 131.5 (m,
C2), 128.9 (C13), 125.1 (dd, 4JCF = 8.5 Hz, 3JCP = 3.0 Hz, C8),
1
2
[Ru(Cp)(3)(NH,NH-NHC)]Cl, [6]Cl. A suspension of [5]Cl
(180 mg, 0.22 mmol), zinc dust (19 mg, 0.29 mmol), and NH4Cl
(27 mg, 0.29 mmol, 2.3 equiv) in methanol (20 mL) was treated
with 0.1 mL of degassed water. The mixture was subsequently
heated under reflux for 24 h. The solvent was removed and the
solid residue was extracted with dichloromethane (20 mL).
Removal of the solvent gave a yellow solid. This solid consisted
of the salts [6]Cl and [6]2[ZnCl4], which could not be separated.
Yield: 160 mg (94% for pure [6]Cl or 87% for pure[6]2[ZnCl4];
the real value lies in between these two extremes). For assign-
ment of the resonances in the NMR spectra see Scheme 5.
1H NMR (400 MHz, DMSO-d6): δ 8.09 (m, 2H, Ar-H15),
7.80 (m, 2H, Ar-H2), 7.64 (m, 2H, Ar-H3), 7.47 (m, 2H,
Ar-H13), 7.43 (2H, Ar-H7), 7.33 (m, 2H, Ar-H12), 7.31 (m,
2H, Ar-H14), 7.20 (m, 2H, Ar-H6), 6.91 (m, 2H, Ar-H8), 6.36
(m, 2H, Ar-H9), 6.26 (s br, 2H, NH), 4.96 (s, 5H, Cp), 2.76
(s, 4H, NCH2CH2N). 13C{1H} NMR (100 MHz, DMSO-d6): δ
124.9 (m, C4), 124.6 (d, 3JCP = 7.6 Hz, C14), 121.9 (d, 3JCP
6.8 Hz, C12), 121.2 (m, C10), 116.8 (dd, 2JCF = 22.9 Hz, 3JCP
=
=
3.2 Hz, C6), 84.6 (Cp), 50.2 (NCH2CH2N). 31P{1H} NMR (162
MHz, CDCl3): δ 62. 19F NMR (376 MHz, CDCl3): δ -96. MS
(MALDI) m/z (%): 715 (100) [M - Cl]þ. MS (ESI HRMS)
m/z (%): 715.0808 (100) [1]þ (calcd for [1]þ 715.0822).
X-ray Diffraction Studies. X-ray diffraction data for [4],
[5]BF4, [6]BF4 CH2Cl2, and [1]Cl CH2Cl2 0.5H2O were col-
3
3
3
lected with a Bruker AXS APEX CCD diffractometer equipped
with a rotation anode at 223(2) K using graphite-monochro-
mated Mo KR radiation (λ = 0.71073 A) for [4] or Cu- KR
radiation (λ = 1.54178 A) for [5]BF4, [6]BF4 CH2Cl2, and
[1]Cl CH2Cl2 0.5H2O. Diffraction data were collected over
3
3
3
the full sphere and were corrected for absorption. The data
reduction was performed with the Bruker SMART27 program
package. For further crystal and data collection details see
Table 1. Structure solutions were found with the SHELXS-
9728 package using the heavy-atom method and were refined
with SHELXL-9729 against F2 using first isotropic and later
anisotropic thermal parameters for all non-hydrogen atoms.
Hydrogen atoms were added to the structure models on calcu-
lated positions.
2
1
199.7 (t, JCP = 15.2 Hz, NCN), 162.6 (d, JCF = 246.1 Hz,
C11), 161.4 (d, 1JCF = 247.1 Hz, C5), 141.3 (m, C1), 134.5 (m,
C15), 133.5 (m, C9 and C2), 133.4 (d, 3JCF = 9.7 Hz, C13), 133.1
(d, 3JCF = 8.6 Hz, C7), 132.3 (C3), 124.8 (m, C4), 124.2 (m, C8
and C14), 121.0 (m, C10), 116.0 (d, 2JCF = 23.4 Hz, C6), 115.2
(d, JCF = 22.9 Hz, C12), 86.2 (Cp), 44.0 (NCH2CH2N). 31P-
2
{1H} NMR (162 MHz, CDCl3): δ 72. 19F NMR (376 MHz,
CDCl3): δ -99, -101. MS (MALDI) m/z (%): 755 (100) [M -
Cl]þ. MS (ESI HRMS) m/z (%): 755.0916 (100) [6]þ (calcd for
[6]þ 755.0947).
Acknowledgment. The authors thank the Deutsche
Forschungsgemeinschaft and the Fonds der Chemischen
[Ru(Cp)(3)(NH,NH-NHC)]Cl, [6]BF4. The salt [6]BF4 was
obtained by azide reduction of [5]BF4 using the reaction condi-
tions employed for the reduction of the azido function in
[5]Cl/[5]2[ZnCl4]. It can also be obtained by anion exchange in
[6]Cl/[6]2[ZnCl4] using NH4BF4.
(27) SMART; Bruker AXS, 2000.
(28) Sheldrick, G. M. SHELXS-97; Acta Crystallogr. 1990, A46, 467–
473.
(29) Sheldrick, G. M. SHELXL-97; Acta Crystallogr. 2008, A64,
112–122.
[Ru(Cp)([11]ane-P2CNHC)]Cl, [1]Cl. A suspension of [6]X
(X = Cl or 0.5 ZnCl4) (165 mg, 0.21 mmol for pure [6]Cl) and

Article
Organometallics, Vol. 28, No. 21, 2009 6369
Industrie for financial support. O.K. thanks the
International Research Training Group (IRTG 1444)
for a predoctoral grant, and A.F.-F. thanks the NRW
€
Graduate School of Chemistry Munster and the DGRI-
SEP, Mexico, for predoctoral grants.
Supporting Information Available: X-ray crystallographic
files for complexes [4], [5]BF4, [6]BF4 CH2Cl2, and [1]Cl
3
3
CH2Cl2 0.5H2O in CIF format and 1H, 13C{1H}, 31P{1H},
3
and 19F NMR spectra for all compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.