Template synthesis of ruthenium complexes with saturated and benzannulated NH,NH-stabilized N-heterocyclic carbene ligands

Article abstract of DOI:10.1021/om800964n

Reaction of [RuCl₂(p-cymene)]₂ with 2-azidoethyl isocyanide (1a) or 2-azidophenyl isocyanide (1b) leads to the isocyanide complexes [RuCl₂(p-cymene)(1a)] [2a] and [RuCl₂(p-cymene) (lb)] [2b], respectively. Compl

Full text of DOI:10.1021/om800964n

896
Organometallics 2009, 28, 896–901
Template Synthesis of Ruthenium Complexes with Saturated and
Benzannulated NH,NH-Stabilized N-Heterocyclic Carbene Ligands
Oliver Kaufhold, Aaro´n Flores-Figueroa, Tania Pape, and F. Ekkehardt Hahn*
Institut fu¨r Anorganische und Analytische Chemie, Westfa¨lische Wilhelms-UniVersita¨t Mu¨nster,
Corrensstrasse 30, D-48149 Mu¨nster, Germany
ReceiVed October 8, 2008
Reaction of [RuCl2(p-cymene)]2 with 2-azidoethyl isocyanide (1a) or 2-azidophenyl isocyanide (1b)
leads to the isocyanide complexes [RuCl2(p-cymene)(1a)] [2a] and [RuCl2(p-cymene)(1b)] [2b],
respectively. Complex [2a] reacts with triphenylphosphine to yield the complex with a phosphinimine-
substituted isocyanide ligand [3]. The attempted hydrolysis of the phosphinimine group in [3] with
HCl · Et2O produced the complex with a protonated phosphinimine ligand [4]Cl instead of the expected
complex with a 2-aminoethyl isocyanide ligand. An alternative method for the reduction of the azido
group in [2a] and [2b] using FeCl3/NaI has been applied leading to complexes with the 2-amino-substituted
isocyanide ligands, which undergo intramolecular ring closure to yield the complexes of type [RuI2(p-
cymene)(NHC)], [5a] and [5b].
Scheme 1. Template Syntheses of Cyclic Heteroatom-
Stabilized NHC Ligands
Introduction
The majority of N-heterocyclic carbenes and their metal
complexes are obtained from cyclic azolium salts.1 However,
the nucleophilic attack at the carbon atom of a coordinated
isocyanide2 constitutes an alternative method to generate metal
carbene complexes. Protic nucleophiles HX such as alcohols
and primary or secondary amines have been particularly useful
in this reaction. This carbene complex synthesis was uninten-
tionally first applied in 1925 when Tschugajeff and Skanawy-
Grigorjewa reacted tetrakis(methyl isocyanide) platinum(II) with
hydrazine.3 Only 50 years later were the reaction products
recognized as carbene complexes.4 Some interesting modifica-
tions of this reaction have been reported recently.5
While the addition of HX to coordinated isocyanides usually
leads to the formation of complexes with acyclic carbene
ligands, the use of functional isocyanides, which contain both
the isocyanide group and the nucleophile in the same molecule,
gives access to complexes with heterocyclic carbene ligands
through an intramolecular 1,2-addition across the CtN triple
bond. Fehlhammer et al. have introduced readily available and
stable 2-hydroxyalkyl isocyanides such as CtNCH2CH2OH, in
which the nucleophile and the isocyanide group are already
linked before coordination of the ligand to a metal center. If
suitably activated by coordination to transition metals in higher
oxidation states these ligands spontaneously cyclize to form
oxazolidin-2-ylidene complexes A (Scheme 1)6 allowing even
the isolation of homoleptic tetra-7a and hexacarbene comp-
lexes.7b An interesting alternative to this cyclization reaction
has been proposed by Liu et al. who reacted an amine
phosphinimine with a metal carbonyl complex. The phosphin-
imine reacts with a carbonyl group to give an isocyanide and
R3PdO. The amine-functionalized isocyanide subsequently
cyclizes to yield the complex with an NH,NH-stabilized
heterocarbene ligand B (Scheme 1).8 In addition, the metal
template controlled coupling of propargyl amine with phenyl
* Corresponding author. E-mail: fehahn@uni-muenster.de.
(1) (a) Hahn, F. E. Angew. Chem., Int. Ed. 2006, 45, 1348–1352. (b)
Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47, 3122–3172.
(c) Kaufhold, O.; Hahn, F. E. Angew. Chem., Int. Ed. 2008, 47, 4057–
4061.
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10.1021/om800964n CCC: $40.75
2009 American Chemical Society
Publication on Web 01/13/2009

Template Synthesis of Ruthenium Complexes
Organometallics, Vol. 28, No. 3, 2009 897
isocyanide14 (Scheme 2) or 2-nitrophenyl isocyanide15 was used
as synthon for the unstable 2-aminophenyl isocyanide. Again
the ring nitrogen atom can be alkylated leading to complexes
of type D, which in one case allowed the preparation of a cyclic
tetracarbene ligand at a platinum(II) center.14b The metal
template controlled cyclization of 2-aminophenyl isocyanides
followed by N,N′-alkylation provides an alternative route to
complexes with benzannulated N-heterocyclic carbenes, which
is particularly useful for the preparation of complexes with NHC
ligands, which are difficult to stabilize in the free state.16
Ruthenium(II) complexes of type [RuCl2(PCy3)(NHC)-
(CHPh)] (type II Grubbs catalysts) bearing saturated NHC
ligands are important catalysts for olefin metathesis. These
complexes are normally generated from ruthenium(II) precursors
like [RuCl2(PR3)2(CHPh)] (type I Grubbs catalysts) and an NHC
ligand.17 We searched for alternative methods for the synthesis
of ruthenium(II) olefin metathesis catalysts employing the
cyclization of 2-functionalized isocyanides for the generation
of an NHC ligand at the ruthenium center instead of the
substitution of a ligand at ruthenium(II) for a stable NHC. Here
we describe the addition and intramolecular cyclization of
2-azidoethyl isocyanide 1a and 2-azidophenyl isocyanide 1b at
RuII templates.
Scheme 2. Template Syntheses of Complexes with
Benzannulated NHC Ligands
Results and Discussion
We have previously described the cyclization of 2-azidophe-
nyl isocyanide 1b at different template metals (Scheme 2).14
Recently we succeeded in the preparation of 2-azidoethyl
isocyanide 1a, which after coordination to tungsten(0)18 or
rhenium(I)19 can be intramolecularly cyclized to yield complexes
with an NH,NH-stabilized saturated NHC ligand. The prepara-
tion of 1a, for example, by formylation of 2-azidoethyl amine
and subsequent dehydration with diphosgene18 proceeds with
low yield (2 steps, 16%), and the workup is tedious. Alterna-
tively, both 1a and 1b can be prepared in high yields (47% and
57%) from 2-azidoethylamine or 2-azidoaniline, respectively,
using CHCl3/NaOH under standard phase transfer catalysis
(PTC) conditions.
isocyanide to yield an NH,NPh-stabilized NHC ligand has also
been reported.9
We have used ꢀ-functionalized aryl isocyanides where the
electrophilic isocyanide and the nucleophilic substituent are not
only linked together but also suitably oriented in one plane for
an intramolecular cycloaddition reaction. Contrary to aliphatic
2-hydroxyethyl isocyanide,6,7 free 2-hydroxyphenyl isocyanide
is not stable and cyclizes to give benzoxazole.10 However,
lithiation of benzoxazole and subsequent reaction with Me3SiCl
yields 2-(trimethylsiloxy)phenyl isocyanide,11 a synthon for
2-hydroxyphenyl isocyanide. Coordination of 2-(trimethylsi-
loxy)phenyl isocyanide to a transition metal and subsequent
hydrolysis of the Me3Si-O bond has yielded a number of NHC
complexes C with the benzoxazolin-2-ylidene ligand, which is
easily alkylated at the ring nitrogen atom (Scheme 2).12 The
cyclization of 2-functionalized phenyl isocyanides can also be
employed for the generation of complexes bearing benzannu-
lated cyclic diaminocarbenes.13 In this case 2-azidophenyl
Reaction of the dinuclear complex [RuCl2(p-cymene)]2 with
a slight excess of 1a gives the monomeric isocyanide complex
[RuCl2(p-cymene)(1a)] [2a] (complexes are written in brackets
throughout the manuscript) in nearly quantitative yield (Scheme
3). The resonance for the isocyanide carbon atom was observed
in the 13C{1H} NMR spectrum at δ ) 142.4 ppm. This
1
resonance lacks the typical JC,N coupling found for the free
ligand 1a and related aliphatic isocyanides.2a,20 In contrast to
(9) (a) Ruiz, J.; Garc´ıa, G.; Mosquera, M. E. G.; Perandones, B. F.;
Gonzalo, M. P.; Vivanco, M. J. Am. Chem. Soc. 2005, 127, 8584–8585.
(b) Ruiz, J.; Perandones, B. F.; Garc´ıa, G.; Mosquera, M. E. G. Organo-
metallics 2007, 26, 5687–5695.
(10) Ferris, J. P.; Antonucci, F. R.; Trimmer, R. W. J. Am. Chem. Soc.
1973, 95, 919–920.
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mer, W. P. Chem.sEur. J. 2003, 9, 704–712. (b) Hahn, F. E.; Langenhahn,
V.; Lu¨gger, T.; Pape, T.; Le Van, D. Angew. Chem., Int. Ed. 2005, 44,
3759–3763.
(15) Hahn, F. E.; Garc´ıa Plumed, C.; Mu¨nder, M.; Lu¨gger, T.
Chem.sEur. J. 2004, 10, 6285–6293.
(16) (a) Holtgrewe, C.; Diedrich, C.; Pape, T.; Grimme, S.; Hahn, F. E.
Eur. J. Org. Chem. 2006, 3116–3124. (b) Hahn, F. E.; Holtgrewe, C.; Pape,
T.; Martin, M.; Sola, E.; Oro, L. A. Organometallics 2005, 24, 2203–2209.
(17) (a) Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18–29.
(b) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett. 1999, 1,
953–956.
(18) Hahn, F. E.; Langenhahn, V.; Pape, T. Chem. Commun. 2005, 5390–
5392.
(19) (a) Kaufhold, O.; Stasch, P.; 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, G. E. J. Am. Chem. Soc. 2009,
131, 306–317.
(20) (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.
(11) Jutzi, P.; Gilge, U. J. Organomet. Chem. 1983, 246, 159–162.
(12) (a) Hahn, F. E.; Tamm, M. J. Organomet. Chem. 1993, 456, C11–
C14. (b) Kernbach, U.; Lu¨gger, T.; Hahn, F. E.; Fehlhammer, W. P. J.
Organomet. Chem. 1997, 541, 51–55. (c) Tamm, M.; Lu¨gger, T.; Hahn,
F. E. Organometallics 1996, 15, 1251–1256. (d) Hahn, F. E.; Tamm, M.
Organometallics 1995, 14, 2597–2600. (e) Hahn, F. E.; Tamm, M. J. Chem.
Soc., Chem. Commun. 1993, 842–844. (f) Hahn, F. E.; Tamm, M. J. Chem.
Soc., Chem. Commun. 1995, 569–570. (g) Hahn, F. E.; Tamm, M.; Lu¨gger,
T. Angew. Chem., Int. Ed. Engl. 1994, 33, 1356–1359. (h) Hahn, F. E.;
Imhof, L. Organometallics 1997, 16, 763–769. For two reviews on the
cyclization of functionalized isocyanides, see: (i) Tamm, M.; Hahn, F. E.
Coord. Chem. ReV. 1999, 182, 175–209. (j) Michelin, R. A.; Pombeiro,
A. J. L.; Guedes da Silva, M. F. C. Coord. Chem. ReV. 2001, 218, 75–112.
(13) (a) Hahn, F. E.; Wittenbecher, L.; Boese, R.; Bla¨ser, D. Chem.sEur.
J. 1999, 5, 1931–1935. (b) Hahn, F. E.; Wittenbecher, L.; Le Van, D.;
Fro¨hlich, R. Angew. Chem., Int. Ed. 2000, 39, 541–544.

898 Organometallics, Vol. 28, No. 3, 2009
Kaufhold et al.
Scheme 3. Reactions of 1a and 1b with [RuCl2(p-cymene)]2
Followed by Intramolecular Cyclization of the Isocyanide
Ligands
Figure 1. Molecular structure of complex [2a] (50% displacement
ellipsoids; hydrogen atoms have been omitted). Selected bond
lengths (Å) and angles (deg): Ru-C1 1.969(5), Ru-Cl1 2.3979(13),
Ru-Cl2 2.4060(13), N1-C1 1.148(6), N1-C2 1.441(6), N2-C3
1.482(7), N2-N3 1.213(6), N3-N4 1.135(6); Ru-C1-N1 176.7(4),
C1-N1-C2 175.7(5), N2-N3-N4 171.6(5).
reveals a broad signal at δ ) 15.1 ppm typical for the
phosphinimine group.14a Formation of the phosphinimine is also
corroborated by two resonances for the methylene groups of
1
the isocyanide in the H NMR spectrum at δ ) 3.86 ppm (t)
3
and δ ) 3.43 ppm (dt), the latter one being split by JH,H (6.6
3
Hz) and JH,P (15.2 Hz) coupling.
In the next step, it was intended to cleave the phosphinimine
in [3] hydrolytically using water and a catalytic amount of acid
to produce the amine functionalized isocyanide, which was
supposed to cyclize to the NH,NH-stabilized NHC ligand.
Following published procedures,14,18 we treated complex [3]
with H2O/HBr in methanol. The NMR spectra indicated the
formation of a product mixture and were inconsistent with the
formation of a carbene complex. Treatment of [3] with an
equimolar amount of HCl · Et2O yielded a uniform reaction
product. Again no carbene complex was detected by NMR
spectroscopy. The 13C{1H} NMR spectrum exhibits the reso-
nance for an isocyanide carbon atom at δ ) 142.6 ppm
essentially unchanged from the isocyanide carbon resonance in
[2a] and [3]. Surprisingly, the 31P{1H} NMR spectrum exhibited
a signal at δ ) 38.8 ppm. This value is typical for quasi-
phosphonium compounds (-NH+-PPh3) with a phosphorus-
nitrogen bond.23 From the spectroscopic data, it was concluded
that the PdN bond in [3] was not cleaved but instead [4]Cl
(Scheme 3) containing a protonated phosphinimine group had
been obtained.
1
the free ligand 1a, the H NMR spectrum of [2a] exhibits two
well-resolved triplets for the isocyanide methylene groups at δ
) 4.04 and 3.69 ppm (1a, broad singlet at δ ) 3.60 ppm).18
Notably, the IR spectrum of [2a] exhibits two vibrations at ν˜
) 2138 and 2106 cm-1 for the azido functionality. The existence
of two vibrational modes for an azido substituent has been
reported for only a few other compounds.21 The isocyanide
stretching vibration was observed at ν˜ ) 2199 cm-1 and thus
shifted by 53 cm-1 to higher wavenumbers compared with the
free ligand 1a (ν˜ ) 2152 cm-1) implying a desirable activation
of the isocyanide carbon toward nucleophilic attack.12d
Single crystals of [2a] suitable for an X-ray diffraction
analysis were grown by cooling of a saturated ethanol solution
of the complex. The structure analysis reveals essentially linear
isocyanide and azido functionalities (Figure 1). Bond parameters
within the isocyanide ligand of [2a] do not differ significantly
from equivalent parameters reported for complex [W(CO)5-
(1b)].14a
This assumption was confirmed by an X-ray diffraction study
with crystals of [4]Cl · 0.5EtOH (Figure 2) obtained by slow
evaporation of the solvents from an ethanol/acetone solution
of [4]Cl. The cation [4]+ contains an isocyanide ligand
substituted with a protonated phosphinimine. The geometric
parameters of the isocyanide group are identical within experi-
mental error to those found for [2a]. Protonation of the
phosphinimine is detectable by the expansion of the P-N2 bond
length to 1.633(5) Å relative to the values reported for related
phosphinimines (1.564(4) Å), which therefore are reasonably
described with a PdN double bond as depicted for [3] in
Scheme 3.14a The P-N2 bond length in [4]+ compares well to
We have demonstrated that coordinated azido functionalized
isocyanides react in a Staudinger-type reaction22 with tertiary
phosphines to yield phosphinimines,14,18 which upon hydrolysis
liberate an amine function (Scheme 2). This reaction was carried
out with ruthenium complex [2a], which reacts with triph-
enylphosphine under liberation of dinitrogen and formation of
complex [3] with a phosphinimine-substituted isocyanide (Scheme
3). The reaction can be monitored by IR spectroscopy. In the
course of the reaction, the intensity of the absorptions for the
azido function diminish. The isocyanide absorption is only
marginally shifted to higher wavenumbers (from ν˜ ) 2199 cm-1
for [2a] to ν˜ ) 2204 cm-1 for [3]). The 31P{1H} NMR spectrum
(21) Weidlein, J.; Mu¨ller, U.; Dehnicke, K. Schwingungsfrequenzen I;
Georg Thieme Verlag Stuttgart: New York, 1981.
(22) Staudinger, H.; Meyer, J. HelV. Chim. Acta 1919, 2, 635–646.
(23) Imrie, C.; Modro, T. A.; van Rooyen, P. H.; Wagener, C. C. P.;
Wallace, K.; Hudson, H. R.; McPartlin, M.; Nasirun, J. B.; Powroznyk, L.
J. Phys. Org. Chem. 1995, 8, 41–46.

Template Synthesis of Ruthenium Complexes
Organometallics, Vol. 28, No. 3, 2009 899
Figure 2. Molecular structure of [4]+ in [4]Cl · 0.5EtOH (50%
displacement ellipsoids;, hydrogen atoms are omitted with the
exception of the hydrogen atom bound to N2). Selected bond lengths
(Å) and angles (deg): Ru-C1 1.980(6), Ru-Cl1 2.419(2), Ru-Cl2
2.417(2), P-N2 1.633(5), N1-C1 1.145(7), N2-C3 1.479(7);
Ru-C1-N1 176.2(5), P-N2-C3 120.4(4).
Figure 3. Molecular structure of [5a] (50% displacement ellipsoids;
hydrogen atoms have been omitted with the exception of the N-H
hydrogen atoms). Selected bond lengths (Å) and angles (deg):
Ru-I1 2.7255(5), Ru-I2 2.7161(5), Ru-C1 2.031(4), Ru-C4
2.177(4), Ru-C5 2.176(4), Ru-C6 2.279(4), Ru-C7 2.219(4),
Ru-C8 2.172(4), Ru-C9 2.198(4); N1-C1-N2 107.0(3).
the P-N bond lengths reported for some quasi-phosphonium
salts (1.621(3)-1.646(3) Å).23 Nitrogen atom N2 is sp2-
hybridized (angle P-N2-C3 120.4(4)°), while the phosphorus
atom is surrounded in a tetrahedral fashion. Significant (pfd)π
backbonding has been proposed for nitrogen-substituted quasi-
phosphonium salts.23
The Ru-C1 bond length (2.031(4) Å, Figure 3) compares
well to previously reported values for Ru-CNHC bond lengths
in [RuII(arene)(NHC)X2]28 and other RuIINHC complexes.29 The
trans effect of the carbene ligand manifests itself in different
Ru-Ccymene bond lengths. The Ru-Ccymene bond lengths trans
to the NHC ligand are significantly longer (Ru-C6 2.279(4)
Å, Ru-C7 2.219(4) Å) than those trans to the iodo ligands
(range 2.172(4)-2.198(4) Å).
Once a suitable protocol for the reduction of the azido group
in [RuCl2(p-cymene)(1a)] with FeCl3/NaI had been developed,
we extended this method to the analogous complex [RuCl2(p-
cymene)(1b)] [2b], bearing the aromatic azido-substituted
isocyanide ligand 1b (Scheme 3). The reduction of the azido
group in [2b] with FeCl3/NaI requires a slightly prolonged
reaction time compared with that for [2a] but gives the complex
with the benzannulated NH,NH-stabilized carbene ligand in high
yield (81%).
Complex [2b] exhibits the spectroscopic features expected
for the presence of an aromatic isocyanide. The isocyanide CtN
stretching mode was observed at ν˜ ) 2147 cm-1 in the IR
spectrum. The 13C{1H} NMR resonance for the isocyanide
carbon atom in [2b] (δ ) 154.4 ppm) vanishes upon reduction
of the azido group and the resonance for the newly formed
carbene carbon atom of [5b] was observed at δ ) 180.6 ppm.
Hydrolysis of the phosphinimine group in [3] at ambient
temperature appears impossible. A prolonged reaction time or
a higher reaction temperature led to decomposition of the
complex. We therefore searched for an alternative method to
convert the azido group in complexes of type [2] into a primary
amine group. A literature search revealed that BH3 · THF,
BHCl2 · Me2S,24 and Me3SiI25 have been used for the reduction
of organic azides to yield amines, but these methods proved
ineffective for our purposes. The reduction of organic azides to
amines with FeCl3/NaI mixtures followed by an aqueous workup
has been reported recently.26 We have adopted this method for
the reduction of the azido groups in organometallic compounds
of type [2] (Scheme 3). Both [2a] and [2b] react with a mixture
of FeCl3/NaI under reduction of the azido group to yield a
primary amine, which then intramolecularly attacks the isocya-
nide carbon atom with formation of the NH,NH-stabilized
carbene ligand. The required large excess of NaI leads to an
exchange of the halogenato ligands at the ruthenium atom
resulting in the diiodo complexes of type [5] (Scheme 3).
The 13C{1H} NMR spectrum of [5a] shows the characteristic
resonance for the carbene carbon atom at δ ) 205.6 ppm. The
Conclusion
1
NH protons were observed in the H NMR spectrum at δ )
Despite the dominance of azolium salts as precursors for
N-heterocyclic carbenes and their metal complexes,1 alternative
synthetic strategies for the generation of NHC complexes are
still needed. This is particularly true when the NHC ligand itself
is not stable or when complexes with reactive NHCs that can
be modified at the ring nitrogen atoms are required. The
template-controlled cyclization of 2-azido-substituted isocya-
nides provides access to NH,NH-stabilized cyclic diaminocar-
bene ligands, which subsequently can be substituted with alkyl
groups at the ring nitrogen atoms. The standard procedure for
the cyclization of 2-azido-functionalized isocyanides (Staudinger
reaction followed by hydrolysis) does not work for 2-azidoethyl
isocyanide coordinated to the {Ru(p-cymene)X2} complex
fragment, which yields upon hydrolysis a RuII complex with a
6.80 ppm. Interestingly, the IR spectrum (in KBr) showed two
NH vibrations at ν˜ ) 3432 cm-1 and ν˜ ) 3348 cm-1. In the
solid state, this behavior is due to an intermolecular hydrogen
bond between an NH proton and a iodo ligand from an adjacent
molecule.
Crystals of [5a] suitable for an X-ray diffraction study were
obtained by slow evaporation of the solvent from a dichlo-
romethane solution of [5a]. The structure analysis confirms both
the formation of a diiodo NHC RuII complex and the existence
of an intermolecular NH · · · I hydrogen bond (NH · · · I distance
3.016 Å). Similar NHC-NH · · · X interactions have previously
been described.19,27
(24) Salunkhe, A. M.; Ramachandran, P. V.; Brown, H. C. Tetrahedron
2002, 58, 10059–10064.
(25) Kamal, A.; Rao, N. V.; Laxman, E. Tetrahedron Lett. 1997, 38,
6945–6948.
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Lett. 2002, 43, 6861–6863.
(27) Hahn, F. E.; Klusmann, D.; Pape, T. Eur. J. Inorg. Chem. 2008,
4420–4424.
¨
(28) (a) Ozdemir, I.; Demir, S.; C¸ etinkaya, B.; Toupet, L.; Castarlenas,
R.; Fischmeister, C.; Dixneuf, P. H. Eur. J. Inorg. Chem. 2007, 2862–
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2869. (b) C¸ etinkaya, B.; Demir, S.; Ozdemir, I.; Toupet, L.; Se´meril, D.;
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900 Organometallics, Vol. 28, No. 3, 2009
Kaufhold et al.
3
(sept, 1H, J ) 6.9 Hz, CH(CH3)2), 2.28 (s, 3H, Ar-CH3), 1.30
(d, 6H, 3J ) 6.9 Hz, CH(CH3)2). 13C{1H} NMR (100.6 MHz,
CDCl3): δ 142.4 (CN), 107.9 (Ar-C-iPr), 107.4 (Ar-C-Me),
88.1, 87.9 (Ar-CH), 49.9 (CH2N3), 44.9 (CH2NC), 31.2
(CH(CH3)2), 22.4 (CH(CH3)2), 18.8 (Ar-CH3). IR (KBr, cm-1): ν˜
2199 (vs, CN), 2138 (s, N3), 2106 (s, N3). MS (MALDI) m/z: 402
[M]+, 367 [M - Cl]+.
protonated phosphinimine ligand. We have introduced the
reduction of coordinated 2-azido-substituted isocyanides with
FeCl3/NaI, which works for both aliphatic and aromatic iso-
cyanides yielding NH,NH-stabilized saturated imidazolidin-2-
ylidenes and unsaturated benzimidazolin-2-ylidenes. Further
work is directed toward the functionalization of the NH,NH-
stabilized NHC ligands at the RuII center with alkyl groups and
the linkage of the NH,NH-stabilized carbene ligands to other
donors coordinated to the metal center.14b,19
Complex [2b]. The complex was prepared as described for [2a]
from 200 mg (0.33 mmol) of [RuCl2(p-cymene)]2 and 99 mg (0.68
mmol) of 1b by using a reaction time of 14 h. Yield: 270 mg (0.60
mmol, 91%) of a red crystalline solid. 1H NMR (400.1 MHz,
CDCl3): δ 7.42 (m, 2H, Arbenzyl-H), 7.24 (m, 1H, Arbenzyl-H), 7.14
Experimental Procedures
3
(m, 1H, Arbenzyl-H), 5.75 (d, 2H, J ) 6.0 Hz, Arcymene-H), 5.56
General Comments. Caution! Aliphatic azides are high energy
density materials. Vigorous heating of 2-azidoethylamine did cause
an explosiVe decomposition. Organic azides should not be heated
to temperatures higher than 100 °C. All preparations were carried
out under an argon atmosphere using conventional Schlenk
techniques. Solvents were dried and degassed by standard methods
prior to use. The preparation of 2-azidoethyl isocyanide 1a18 and
of 2-azidophenyl isocyanide 1b14a by formylation of the corre-
sponding primary amines followed by dehydration has been
reported. Here we used a new synthetic approach to these
isocyanides leading to materials with spectroscopic properties
identical to those previously reported. [RuCl2(p-cymene)]2 was
prepared according to a literature procedure.30 Triphenylphosphine
was recrystallized from hot hexane prior to use. All other chemicals
were used as received. 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.
2-Azidoethyl Isocyanide, 1a. A mixture of 2-azidoethylamine
(27.0 g, 0.31 mol), chloroform (31 mL, 0.39 mmol), dichlo-
romethane (100 mL), aqueous sodium hydroxide (90 g of a 50%
solution, 1.13 mol), and tetrabutylammonium bromide (1.4 g, 4.34
mmol) was stirred vigorously at ambient temperature for 4 days.
Ice cold water was then added to dissolve the formed colorless
solid. The organic phase was separated and dried over sodium
carbonate. At ambient temperature, the organic solvents and
unreacted starting material were removed under high vacuum. The
resulting brown oil was heated to 60 °C and condensed into a flask
cooled with liquid nitrogen under high vacuum. Yield: 14.0 g (0.15
mol, 47%) of a colorless liquid. The analytical data for 1a obtained
this way are identical to those previously reported.18
3
3
(d, 2H, J ) 6.0 Hz, Arcymene-H), 2.97 (sept, 1H, J ) 6.9 Hz,
CH(CH3)2), 2.34 (s, 3H, Ar-CH3), 1.33 (d, 6H, 3J ) 6.9 Hz,
CH(CH3)2). 13C{1H} NMR (100.6 MHz, CDCl3): δ 154.4 (CN),
137.1, 130.7, 128.5, 125.4, 118.9 (Arbenzyl-C), 108.9
(Arcymene-C-iPr), 108.8 (Arcymene-C-Me), 89.2, 88.9
(Arcymene-CH), 31.2 (CH(CH3)2), 22.4 (CH(CH3)2), 18.9 (Ar-CH3).
IR (KBr, cm-1): ν˜ 2147 (vs, CN), 2120 (s, N3). Elemental analyses
of complexes [2a] and [2b] with azido-functionalized isocyanide
ligands could not be obtained due to their propensity for explosive
decomposition.
Complex [3]. A solution of [2a] (330 mg, 0.82 mmol) and
triphenylphosphine (250 mg, 0.95 mmol) in dichloromethane (10
mL) was stirred for 3 h at ambient temperature. The solvent was
removed in vacuo, and the residue was washed with diethyl ether
1
(3 × 10 mL). Yield: 509 mg (0.80 mmol, 98%) of a red solid. H
NMR (400.1 MHz, CDCl3): δ 7.58 (m, 6H, Arphosphine-H), 7.46
(m, 9H, Arphosphine-H), 5.46 (d, 2H, 3J ) 6.0 Hz; Arcymene-H), 5.27
(d, 2H, 3J ) 6.0 Hz, Arcymene-H), 3.86 (t, 2H, 3J ) 6.6 Hz, CH2NC),
3
3
3.43 (dt, 2H, J ) 6.6 Hz, JH,P ) 15.2 Hz, CH2NdPPh3), 2.78
3
(sept, 1H, J ) 6.9 Hz, CH(CH3)2), 2.15 (s, 3H, Ar-CH3), 1.15
(d, 6H, 3J ) 6.9 Hz, CH(CH3)2). 13C{1H} NMR (100.6 MHz,
CDCl3): δ 137.9 (CN), 132.3 (d, JC,P ) 9.2 Hz, o-Cphosphine), 131.9
(d, JC,P ) 2.3 Hz, p-Cphosphine), 128.8 (d, JC,P ) 11.6 Hz; m-Cphosphine),
107.0, 106.6 (Arcymene-C-iPr and Arcymene-C-Me), 87.4, 87.2
2
(Arcymene-CH), 49.0 (d, JC,P ) 23.0 Hz, CH2NdPPh3), 45.1 (d,
3JC,P ) 2.3 Hz, CH2CH2NdPPh3), 31.0 (CH(CH3)2), 22.4
(CH(CH3)2), 18.7 (Ar-CH3). 31P{1H} NMR (162.0 MHz, CDCl3):
δ 15.1 (br). IR (KBr, cm-1): ν˜ 2204 (s, CN). MS (MALDI) m/z:
637 [M + H]+.
Complex [4]Cl. A solution of [3] (75 mg, 0.118 mmol) in
dichloromethane (5 mL) was treated with HCl · Et2O (2 M solution,
0.06 mL, 0.12 mmol) at ambient temperature. After the addition,
the solution was stirred for 2 h. The solvents were removed, and
the remaining solid residue was washed with diethyl ether (2 × 10
mL). Yield: 78 mg (116 mmol, 99%) of a red solid. 13C{1H} NMR
(100.6 MHz, CDCl3): δ 142.6 (CN), 135.1 (s, p-Cphosphine), 134.2
(d, JC,P ) 7.9 Hz, Cphosphine), 130.6 (d, JC,P ) 11.3 Hz, Cphosphine),
120.3 (d, 1JC,P ) 102.3 Hz, ipso-Cphosphine), 107.9 (Arcymene-C-iPr),
105.3 (Arcymene-C-Me), 89.1, 88.8 (Arcymene-CH), 48.6 (m, CH2),
43.8 (m, CH2), 31.0 (CH(CH3)2), 22.7 (CH(CH3)2), 19.3 (Ar-CH3).
31P{1H} NMR (162.0 MHz, CDCl3): δ 38.8. IR (KBr, cm-1): ν˜
1993 (s, CN). MS (MALDI) m/z: 637 [M - Cl]+.
2-Azidophenyl Isocyanide, 1b. A suspension made up from
2-azidoaniline (9.3 g, 69.3 mmol), chloroform (7.2 mL, 90.2 mmol),
dichloromethane (200 mL), aqueous sodium hydroxide (20 g of a
50% solution, 250 mmol), and benzyltriethylammonium chloride
(220 mg, 0.1 mmol) was heated under reflux in the dark for 16 h.
After the mixture cooled to room temperature, ice cold water (20
mL) was added. The organic phase was separated and dried over
magnesium sulfate. The crude reaction product was purified by
column chromatography (SiO2, diethyl ether/petrol ether 1:15, v/v).
Yield: 5.7 g (39.5 mmol, 57%) of a pale brown solid. The analytical
data for 1b obtained this way are identical to those previously
reported.14a
Complex [2a]. A solution of [RuCl2(p-cymene)]2 (305 mg, 0.50
mmol) and 2-azidoethyl isocyanide 1a (110 mg, 1.15 mmol) in
dichloromethane (15 mL) was stirred for 90 min at ambient
temperature. The solvent was removed in vacuo, and the remaining
solid residue was washed with diethyl ether (3 × 10 mL) and dried
in vacuo. Yield: 380 mg (0.95 mmol, 95%) of a red crystalline
Complex [5a]. To a solution of FeCl3 (200 mg, 1.24 mmol) and
NaI (1.50 g, 10.0 mmol) in acetonitrile (10 mL) was added solid
[2a] (332 mg, 0.83 mmol). After the solution was stirred for 90
min at ambient temperature, the solvent was removed in vacuo.
The residue was dissolved in dichloromethane (30 mL) and treated
with aqueous Na2S2O3 (5 mL of a 20% solution) and aqueous
Na2CO3 (5 mL of a 20% solution). The organic phase was separated
and dried over Na2CO3. The solvent was then removed in vacuo.
1
3
solid. H NMR (400.1 MHz, CDCl3): δ 5.65 (d, 2H, J ) 6.1 Hz,
3
Arcymene-H), 5.46 (d, 2H, J ) 6.1 Hz, Arcymene-H), 4.04 (t, 2H,
3
3J ) 5.5 Hz, CH2NC), 3.69 (t, 2H, J ) 5.4 Hz, CH2N3), 2.87
1
Yield: 395 mg (0.71 mmol, 86%) of a dark red solid. H NMR
(400.1 MHz, CDCl3): δ 6.80 (s, br, 2H, NH), 5.45 (d, 2H, 3J ) 6.0
3
Hz, Arcymene-H), 5.24 (d, 2H, J ) 6.0 Hz, Arcymene-H), 3.75 (s,
(30) Bennett, M. A.; Huang, T. N.; Metheson, T. W.; Smith, A. K. Inorg.
Synth. 1982, 21, 74–79.
3
4H, NCH2CH2N), 3.00 (sept, 1H, J ) 6.9 Hz, CH(CH3)2), 2.34

Template Synthesis of Ruthenium Complexes
Organometallics, Vol. 28, No. 3, 2009 901
3
(s, 3H, Ar-CH3), 1.27 (d, 6H, J ) 6.9 Hz, CH(CH3)2). 13C{1H}
Table 1. Crystallographic Data for the Complexes [2a],
[4]Cl · 0.5EtOH, and [5b]
NMR (100.6 MHz, CDCl3):
δ
205.6 (NCN), 108.6
(Arcymene-C-iPr), 101.2 (Arcymene-C-Me), 86.4, 85.0
(Arcymene-CH), 46.3 (NCH2CH2N), 31.5 (CH(CH3)2), 22.9
(CH(CH3)2), 19.8 (Ar-CH3). IR (KBr, cm-1): ν˜ 3432 (s, NH), 3348
(s, NH). MS (MALDI) m/z: 433 [M - I]+. Anal. Calcd: C, 27.92;
H, 3.61; N, 5.01. Found: C, 28.15; H, 3.66; N, 5.33.
parameter
formula
[2a]
13H18N4Cl2Ru
0.15 × 0.02 × 0.02 0.08 × 0.06 × 0.02 0.20 × 0.10 × 0.03
[4]Cl · 0.5EtOH
[5a]
C
C32H37N2Cl3O0.5PRu C13H20N2I2Ru
cryst size
[mm3]
Mr
a [Å]
b [Å]
c [Å]
R [deg]
ꢀ [deg]
γ [deg]
V [Å3]
Z
402.28
5.8684(12)
15.528(3)
17.330(4)
90
94.179(4)
90
1575.0(6)
4
696.03
559.18
12.202(3)
12.792(3)
12.965(3)
68.867(4)
62.535(3)
72.561(4)
1652.9(6)
2
8.0779(12)
25.339(4)
8.4881(12)
90.0
110.130(3)
90.0
1631.3(4)
4
P21/n
Complex [5b]. Complex [5b] was prepard as described for [5a]
from [2b] (300 mg, 0.67 mmol) applying a 4 h reaction time. Yield:
1
328 mg (0.54 mmol, 81%) of a dark red solid. H NMR (400.1
MHz, CDCl3): δ 10.77 (s, br, 2H, NH), 7.09 (m, 2H, Arbenzyl-H),
3
6.85 (m, 2H, Arbenzyl-H), 5.67 (d, 2H, J ) 6.0 Hz, Arcymene-H),
3
3
5.54 (d, 2H, J ) 6.0 Hz, Arcymene-H), 2.89 (sept, 1H, J ) 6.7
j
P1
space group
P21/c
3
Hz, CH(CH3)2), 2.30 (s, 3H, Ar-CH3), 1.21 (d, 6H, J ) 7.0 Hz,
Fcalcd [g cm-3
]
1.697
1.399
2.277
CH(CH3)2). 13C{1H} NMR (100.6 MHz, CDCl3): δ 180.6 (NCN),
133.3(Arbenzyl-ipso-C),122.9(Arbenzyl-ortho-C),110.2(Arbenzyl-meta-
C), 108.8 (Arcymene-C-iPr), 102.4 (Arcymene-C-Me), 86.5, 85.4
(Arcymene-CH), 31.6 (CH(CH3)2), 22.9 (CH(CH3)2), 20.0 (Ar-CH3).
IR (KBr, cm-1): ν˜ 3312 (m, br, NH). MS (MALDI) m/z: 522 [M
- I + MeCN]+, 481 ([M - I]+). Anal. Calcd: C, 33.62; H, 3.32;
N, 4.61. Found: C, 33.86; H, 3.38; N, 4.87.
µ [mm-1
]
1.330
0.790
4.733
2θ range [deg] 3.5-50.0
data collected 12377
no. unique data, 2761, 0.0742
Rint
3.5-55.2
16025
3.2-60.1
18491
7602, 0.0788
4749, 0.0446
no. obsd data
2091
4492
4180
[I g 2σ(I)]
R
0.0397
0.702
0.0705
0.1326
357
0.0357
0.0717
166
wR
X-ray Diffraction Studies. X-ray diffraction data for [2a],
[4]Cl · 0.5EtOH, and [5a] were collected with a Bruker AXS APEX
CCD diffractometer equipped with a rotation anode at 153(2) K
([2a] and [5a]) or 298(2) K ([4]Cl · 0.5EtOH) using graphite-
monochromated Mo KR radiation (λ ) 0.71073 Å). Diffraction
data were collected over the full sphere and were corrected for
absorption. The data reduction was performed with the Bruker
SMART31 program package. For further crystal and data collection
details, see Table 1. Structure solutions were found with the
SHELXS-9732 package using the heavy-atom method and were
refined with SHELXL-9733 against F2 using first isotropic and later
anisotropic thermal parameters for all non-hydrogen atoms. Hy-
drogen atoms were added to the structure models on calculated
no. of variables 184
positions. Complex [4]Cl · 0.5EtOH crystallizes together with one
disordered molecule of ethanol in the unit cell.
Acknowledgment. The authors thank the Deutsche For-
schungsgemeinschaft and the Fonds der Chemischen Indus-
trie 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
Mu¨nster and the DGRI-SEP, Mexico, for predoctoral grants.
Supporting Information Available: X-ray crystallographic files
for complexes [2a], [4]Cl · 0.5EtOH, and [5a] in CIF format. This
material is available free of charge via the Internet at http://pubs.
acs.org.
(31) SMART; Bruker AXS: Madison, WI, 2000.
(32) Sheldrick, G. M. SHELXS-97. Acta Crystallogr. 1990, A46, 467–
473.
(33) Sheldrick, G. M. SHELXL-97; Universita¨t Go¨ttingen: Germany,
1997.
OM800964N