Synthesis and tunability of abnormal 1,2,3-triazolylidene palladium and rhodium complexes

Article abstract of DOI:10.1021/om101076u

Palladation of N3-alkylated 1,2,3-triazolium salts with Pd(OAc)₂ afforded a μ²-I₂ bridged bimetallic complex [Pd(trz)I₂]₂ and monometallic bis(carbene) complexes Pd(trz)₂I₂ as a mixture of trans and cis isomers (trz = 1,2,3-triazol-5-ylidene). Addition of excess halide or modification of the palladation procedure from direct functionalization to a transmetalation sequence involving a silver intermediate allowed for chemoselective formation of the bis(carbene) complex, while subsequent anion metathesis with NaI produced the monometallic bis(carbene) complexes exclusively. Modification of the wingtip group had little influence on the metalation to palladium or rhodium(I) via transmetalation. According to NMR analysis using δ_C and ¹J_Rh-C, subtle but noticeable tunability of the metal electronic properties was identified. In addition, phenyl wingtip groups as N-substituents in the triazolylidene ligands were susceptible to cyclopalladation in the presence of NaOAc and are thus not chemically inert.

Full text of DOI:10.1021/om101076u

Organometallics 2011, 30, 1021–1029 1021
DOI: 10.1021/om101076u
Synthesis and Tunability of Abnormal 1,2,3-Triazolylidene Palladium and
Rhodium Complexes
†
Aurelie Poulain, Daniel Canseco-Gonzalez, Rachel Hynes-Roche, Helge Muller-Bunz,
‡
‡
‡
ꢀ
€
Oliver Schuster,† Helen Stoeckli-Evans,§ Antonia Neels, and Martin Albrecht*,†,‡
†
ꢀ
Department of Chemistry, University of Fribourg, Chemin du Musee 9, CH-1700 Fribourg, Switzerland,
‡School of Chemistry & Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland,
§Institute of Physics, University of Neucha^tel, Rue Emile-Argand 11, CH-2000 Neucha^tel, Switzerland, and
^
XRD Application Lab, CSEM, Rue Jaquet-Droz 1, CH-2002 Neuchatel, Switzerland
Received November 15, 2010
Palladation of N3-alkylated 1,2,3-triazolium salts with Pd(OAc)2 afforded a μ2-I2 bridged
bimetallic complex [Pd(trz)I2]2 and monometallic bis(carbene) complexes Pd(trz)2I2 as a mixture
of trans and cis isomers (trz = 1,2,3-triazol-5-ylidene). Addition of excess halide or modification of
the palladation procedure from direct functionalization to a transmetalation sequence involving a
silver intermediate allowed for chemoselective formation of the bis(carbene) complex, while
subsequent anion metathesis with NaI produced the monometallic bis(carbene) complexes exclu-
sively. Modification of the wingtip group had little influence on the metalation to palladium or
1
rhodium(I) via transmetalation. According to NMR analysis using δC and JRh-C, subtle but
noticeable tunability of the metal electronic properties was identified. In addition, phenyl wingtip
groups as N-substituents in the triazolylidene ligands were susceptible to cyclopalladation in the
presence of NaOAc and are thus not chemically inert.
Introduction
Such modifications include, for example, expansion of the
heterocyclic ring from classic five-membered imidazol-
derived structures to six- and seven-membered heterocycles3
or the displacement of one or both carbene-stabilizing hetero-
atoms into more remote positions.4 Depending on the loca-
tion of the heteroatoms, a neutral resonance structure may
no longer be conceivable and mesoionic resonance structures
become largely dominant.5 A pronounced mesoionic char-
acter may be an attractive feature, for example in redox
catalysis,6 and has been exploited recently in a variety of
carbene-type scaffolds (abnormal carbenes).7
In this context, 1,3-disubstituted 1,2,3-triazolylidenes con-
stitute a particularly attractive class of ligands (Scheme 1).8,9
The heterocyclic ligand precursor is accessible via a syn-
thetically highly versatile “click reaction” involving a cop-
per-catalyzed [3þ2] cycloaddition of azides and alkynes
The enormous impact of N-heterocyclic carbenes as spec-
tator ligands in all areas of transition metal chemistry1;and
in catalysis in particular2;has stimulated significant re-
search interest in developing NHC-type scaffolds that allow
for substantial modification of steric and electronic properties.
*To whom correspondence should be addressed. E-mail: martin.
albrecht@ucd.ie. Fax: þ35-317162501.
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Synthesis; Wiley-VCH: Weinheim, Germany, 2006. (c) Hahn, F. E.; Jahnke,
M. C. Angew. Chem., Int. Ed. 2008, 47, 3122. (d) Hindi, K. M.; Panzner,
M. J.; Tessier, C. A.; Cannon, C. L.; Youngs, W. J. Chem. Rev. 2009, 109,
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(6) Lalrempuia, R.; McDaniel, N. D.; Muller-Bunz, H.; Bernhard, S.;
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om101145y).
r
2011 American Chemical Society
Published on Web 01/18/2011
pubs.acs.org/Organometallics

1022 Organometallics, Vol. 30, No. 5, 2011
Poulain et al.
Scheme 1. Retrosynthetic Approach toward Triazolylidene
Metal Complexes
The molecular structures of complexes 2a, trans-3a, and
cis-3a are depicted in Figure 1. The unit cell of the dimeric
complex 2a consists of two crystallographically independent
centrosymmetric binuclear molecules. In all three complexes
the palladium constitutes the center of a distorted square
plane with the triazole rings oriented essentially perpendi-
cular with respect to the metal coordination plane. The
C2-C1-Pd1-I1 torsion angles are 88.5(5)°, 98.7(5)°, and
77.9(3)° for 2a, trans-3a, and cis-3a, respectively. The
Pd-Ccarbene bond is slightly shorter in the dimeric structure
(Scheme 1).10 This click reaction tolerates a wide variety of
functional groups both in the azide and in the alkyne reactant,11
and hence allows for synthetic variation of wingtip groups that
may not be (easily) conceivable in NHC chemistry relying on
imidazole-derived heterocycles. Unlike their much more inves-
tigated 1,2,4-triazolylidene homologues,12 1,2,3-triazolylidenes
have a strong mesoionic character, as demonstrated in elegant
work by Bertrand and co-workers on the free carbene ligand.13
Following our initial studies,8 we report here on a detailed
investigation of the factors that influence the metalation of
triazolium salts with palladium and rhodium. Wingtip mod-
ification has been probed as a methodology for tuning the
stability and the donor ability of the ligand. Specifically,
N-bound phenyl groups were observed to undergo facile
cyclopalladation.
˚
2a (1.967(6), 1.979(6) A) than in monomeric species cis-3a
˚
(1.993(5), 1.997(5) A), and significantly shorter than in trans-
˚
3a (2.049(3) A), reflecting the expected increase of the trans
influence from μ2-I- to terminal I- to carbene (Table 1). The
same conclusions can be drawn when comparing the Pd-I
distances in the three complexes. No significant perturbation
of the bond lengths in the heterocycles were noted; the C-C
bond is in all complexes in the range of conjugated CdC
bonds.
The availability of crystalline samples and structural
evidence allowed for identifying the diagnostic ethyl group
resonances of complex 2a in solution, δH 4.71 and 1.63.
Attempts to collect sufficient crystalline material of 3a
always resulted in a mixture of trans and cis isomers, as
indicated by two sets of resonances at 4.65 and 1.56 ppm, and
at 4.85 and 1.71 ppm. Therefore, NMR spectroscopy did not
allow cis and trans configurations to be unequivocally dis-
tinguished. Steric considerations suggest that the former set,
which is the major one in the crude reaction mixture, is due to
trans-3a. The trans configuration is expected to alleviate steric
congestion around the metal coordination sphere and may
therefore be more easily accessible than cis-3a.
Results and Discussion
Synthesis of Palladium Complexes. Direct palladation of
the triazolium salt 1a was accomplished thermally by stirring
the ligand precursor and Pd(OAc)2 in DMSO at 120 °C.14
Analysis of the crude reaction mixture revealed three sepa-
rate sets of signals for the ethyl group in the 1H NMR
spectrum, while the aromatic region was more complex.
Sequential extraction with MeCN and CH2Cl2 and frac-
tional crystallization allowed for isolating the three major
compounds, i.e., dimeric complex 2a and the monomeric
complex 3a as a mixture of trans and cis isomers, i.e., trans-3a
and cis-3a (Scheme 2).15 Specifically, the bimetallic complex
2a is soluble in MeCN, while 3a is only sparingly, thus
allowing for separating the red complex 2a from the two
yellow bis(carbene) palladium complexes trans-3a and cis-3a
by straightforward consecutive extractions. The residual cis/
trans mixture of 3a was further purified by fractional crystal-
lization by slow diffusion of pentane into a CH2Cl2 solution
of 3a.
The most significant difference in the 13C NMR spectra
of the complexes comprises the palladium-bound carbene
resonance, which appears at δC 128.5 in complex 2a,16 yet at
substantially lower field (δC 154.6 and 154.0) for the cis/trans
mixture of 3a. This effect is much smaller for the phenyl-
bound heterocyclic carbon, which resonates at δC 142.5 in 2a
and at 144.1 in 3a. No difference between the cis and trans
isomers was detected for this nucleus. All other 13C NMR
signals differ by less than 1 ppm in the three sets and hence do
not allow for an unambiguous distinction between the three
structures.
Factors Affecting Product Selectivity. Upon repeating the
palladation reaction, the dimetallic complex 2a and mono-
meric 3a were obtained invariably in an approximate 1:1
ratio, with a 5:2 trans/cis isomeric distribution in the latter.
When the metalation was carried out with excess KI (4 molar
equiv) and under otherwise identical conditions, complex 2a
became the major product (ca. 8:1 ratio) as deduced from the
crude 1H NMR spectra. This preference is in agreement with
the asymmetric halide/carbene stoichiometry in the dimetal-
lic product. Replacing KI by KCl (2 molar equiv) similarly
favored the production of the dimetallic complex (5:1 ratio
obtained after stirring the product mixture with NaI in order
to convert the initial chloropalladium products into their iodide
analogues). Likewise, using NaOAc as an additive increased the
ratio of the dimetallic complex (ca. 4:1), thus demonstrating
that large and potentially μ2 or κ2 coordinating anions favor the
(10) (a) Sheehan, J. C.; Robinson, C. A. J. Am. Chem. Soc. 1951, 73,
1207. (b) Huisgen, R. Angew. Chem., Int. Ed. 1963, 2, 565. (c) Kolb, H.;
Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed. 2001, 40, 2004. (d)
Bock, V. D.; Hiemstra, H.; van Maarseveen, J. H. Eur. J. Org. Chem. 2006,
51.
(11) For reviews, see: (a) Moses, J. E.; Moorhouse, A. D. Chem. Soc.
Rev. 2007, 36, 1249. (b) Meldal, M.; Tornoe, C. W. Chem. Rev. 2008, 108,
2952. (c) Franc, G.; Kakkar, A. Chem. Commun. 2008, 5267. (d) Finn, M. G.;
Fokin, V. V. Chem. Soc. Rev. 2010, 39 (themed issue), 1231.
(12) (a) Guerret, O.; Sole, S.; Gornitzka, H.; Teichert, G.; Trinquier,
G.; Bertrand, G. J. Am. Chem. Soc. 1997, 119, 6668. (b) Enders, D.;
Niemeier, O.; Henseler, A. Chem. Rev. 2007, 107, 5606. (c) Kamber, N. E.;
Jeong, W.; Waymouth, R. M.; Pratt, R. C.; Lohmeijer, B. G. G.; Hedrick, J. L.
Chem. Rev. 2007, 107, 5813.
(13) (a) Guisado-Barrios, G.; Bouffard, J.; Donnadieu, B.; Bertrand,
G. Angew. Chem., Int. Ed. 2010, 49, 4759. (b) Keske, E.; Praetorius, J. M.;
Crudden, C. M. 93rd Canadian Chemistry Conference, Toronto 2010,
Abstract INP-126.
(14) (a) Herrmann, W. A.; Schwarz, J.; Gardiner, M. G. Organome-
tallics 1999, 18, 4082. (b) Heckenroth, M.; Kluser, E.; Neels, A.; Albrecht,
M. Dalton Trans. 2008, 6242.
(16) In 2a, the carbene resonance coincides with those due to the meta
carbons of the phenyl substituent, but was unambiguously identified by
long-range CH correlation spectroscopy: Fribolin, H. Basic One- and
Two-Dimensional NMR Spectroscopy; Wiley-VCH: Weinheim, Germany,
1998.
(15) Similar mixtures of dimetallic and monometallic complexes have
been reported in the palladation of imidazolium salts: Baker, M. V.;
Brown, D. H.; Simpson, P. V.; Skelton, B. W.; White, A. H. Eur. J. Inorg.
Chem. 2009, 1977.

Article
Organometallics, Vol. 30, No. 5, 2011 1023
Figure 1. ORTEP drawings of complex 2a (a; only one of the two crystallographically independent molecules is shown), trans-3a (b),
and cis-3a (c). All structures are at the 50% probability level; hydrogen atoms and cocrystallized solvents are omitted for clarity.
Scheme 2. Synthesis of Complexes 2, trans-3, and cis-3 by Direct Metalation
˚
Table 1. Selected Bond Lengths (A) and Angles (deg) for 2a,
trans-3a, and cis-3a
(R = Me, Ph) at room temperature and subsequent stirring of
the product in the presence of NaI, produced the bimetallic
complex 2a only.18 Most remarkably, slight modification in this
procedure, viz., omitting NaI for anion metathesis, inverted
the selectivity and afforded the monometallic bis(carbene)
complex 4a, containing chloride anions as the exclusive product
(Scheme 3). Again a mixture of cis and trans isomers was
formed (1:6 ratio). The room-temperature 1H NMR spectrum
in CD3CN featured broad signals, indicating a dynamic beha-
vior. The spectrum recorded at þ75 °C showed sharp signals
for a single species and is in agreement with fast cis-trans
isomerization at this temperature.19 At the slow exchange limit
(-20 °C), four sets of signals were well resolved and were
assigned to syn and anti conformations of the trans and cis
isomers of 4a (relative distribution of the sets was 52%, 32%,
11%, and 5%). Variable-temperature NMR spectroscopy
revealed a coalescence of the multiplets at around 20 °C for
the two major components (ΔG‡ = 58.7 ( 0.8 kJ mol-1), while
the other pair of signals was still sharp. Coalescence of this set
required warming to 60 °C (ΔG‡ ca. 67 kJ mol-1). This
coalescence was complicated by the fact that the two pairs of
sets coalesce at only slightly higher temperature (ca. 65 °C).
Tentatively, we have assigned the more hindered rotation about
the C-Pd bond (syn-anti isomerization) to the sterically
congested cis isomer, while the same type of rotation is expected
to be comparably facile in trans-4a. In line with this model, the
syn-anti isomerization process in the cis isomer should have a
similar activation barrier to the cis-trans interconversion, in
particular in coordinating solvents such as MeCN. Accord-
ingly, the activation barrier for cis-trans isomerization is
2aa
molecule 1
molecule 2
trans-3ab
cis-3ac
Pd1-C1
Pd1-I1
Pd1-X1
Pd1-X2
C1-C2
1.967(6)
1.979(6)
2.5916(6)
2.6733(6)
2.6195(6)
1.377(9)
2.049(3)
2.6181(3)
2.049(3)
2.6181(3)
1.394(4)
1.993(5)
2.6622(6)
2.6506(5)
1.997(5)
1.393(8)
2.5732(7)
2.6821(19)
2.6369(19)
1.402(9)
C1-Pd1-I1
C1-Pd1-X2
C1-Pd1-X1
I1-Pd1-X1
X1-Pd-X2
I1-Pd1-X2
C2-C1-N1
87.26(17)
86.98(15)
91.73(15)
177.55(16)
94.16(2)
87.20(2)
177.88(2)
103.8(5)
90.49(8)
89.51(8)
180
89.51(8)
90.49(8)
180
89.50(16)
88.4(2)
175.47(15)
94.54(2)
87.67(16)
177.24(15)
102.9(5)
90.02(18)
174.05(18)
93.70(4)
89.67(6)
173.01(4)
104.4(5)
103.3(3)
a X1 = I2, X2 = I2a; in molecule 1, the iodide was found to be
disordered over two positions (occupancies 0.7/0.3); only the major
component is considered here; labeling scheme adapted for molecule 2.
b X1 = C1a, X2 = I1a. c X1 = I2, X2 = C12.
formation of complex 2a comprising a 1:1 palladium to carbene
ratio.
Attempts to favor the formation of the bis(carbene) complex
3a initially focused on the modification of the ligand/palladium
stoichiometry in the reaction mixture. However, even in the
presence of a 4-fold excess of triazolium salt, the product
distribution remained at an approximate 1:1 ratio. This ob-
servation may suggest that species such as 2a are poor sub-
strates for the second Pd-carbene bond formation. Utilization
of a transmetalation protocol was more successful.17 Forma-
tion of the silver intermediate from Ag2O and the triazolium
precursor,8 followed by transmetalation with PdCl2(NCR)2
around 70 kJ mol-1
.
(18) An earlier report suggested the formation of a monometallic
complex under these conditions; see: Karthikeyan, T.; Sankararaman,
S. Tetrahedron Lett. 2009, 50, 5834.
(19) Cetinkaya, B.; Cetinkaya, E.; Lappert, M. F. J. Chem. Soc.,
Dalton Trans. 1973, 906.
(17) (a) Garrison, J. C.; Youngs, W. J. Chem. Rev. 2005, 105, 3978. (b)
Lin, J. C. Y.; Huang, R. T. W.; Lee, C. S.; Bhattacharyya, A.; Hwang, W. S.;
Lin, I. J. B. Chem. Rev. 2009, 109, 3561.

1024 Organometallics, Vol. 30, No. 5, 2011
Scheme 3. Selective Synthesis of Either Dimetallic Complex 2 or Monometallic Bis(carbene) Complex 4
Poulain et al.
Variation of the Wingtip Groups. In an effort to evaluate
the influence of the ortho substituents (wingtip groups), a
series of triazolium salts 1b-f were synthesized in good to
excellent yields by established [3þ2] cycloaddition protocols
using the corresponding azides and alkynes20 and subse-
quent alkylation with MeI. Selective N3-methylation was
unambiguously confirmed by NOE and long-range CH
cross-correlation experiments. Direct palladation using Pd-
(OAc)2 as described above again provided a mixture of
complexes 2, cis-3, and trans-3 (cf. Scheme 2). The 2:3 ratio
showed a moderate dependence on the wingtip group pat-
tern. While for the dialkylated systems 2b and 2c, about
equimolar quantities of monomeric species (3b and 3c,
respectively) were formed, the dimetallic complex 2d was
slightly more preferred over the corresponding monometal-
lic complex (1.25:1). Swapping the phenyl and butyl substit-
uents resulted in an inversion of the selectivity, with the
monometallic species favored (ratio 2e/3e approximately
0.5:1). With two phenyl wingtip groups, the ratio could not
be determined unambiguously due to considerable signal
overlap in both the 1H and 13C NMR spectra.
Purification of the mixtures by MeCN extraction and
crystallization provided pure fractions of the dimetallic
complexes 2b-f.21 Analysis of their 13C NMR spectra
reveals a moderate correlation between δC and the electronic
properties of the wingtip groups. The most shielded carbenes
were observed for triazolylidenes possessing two alkyl wing-
tip groups (cf. δC 126.0 and 126.4 for 2b and 2c, respectively),
whereas introduction of a phenyl group shifts the resonance
to lower field (cf. δC 128.5, 128.4, and 129.1 for 2a, 2d, and 2e,
respectively). The carbene signal for the supposedly most
deshielded carbene in 2f was not resolved.
Figure 2. ORTEP representation of complex trans-4a (50%
probability level, hydrogen atoms omitted for clarity). Selected
bond lengths (A) and angles (deg): Pd1-C1 2.037(3); Pd1-Cl1
2.3534(8); C1-Pd1-C1a 180; C1-Pd1-Cl1 88.8(1).
˚
similar to those of 2a (Table 2). Again, the triazolylidene ring
is oriented almost perpendicular to the palladium square
plane, with dihedral angles between 71° (2e) and 88° (2b).
The Pd1-I2 bond trans to the carbene ligand is slightly
shorter in the phenyl-substituted triazolylidene complexes
than in the complexes comprising exclusively alkyl wingtip
groups. These observations may point to a moderate tun-
ability of the trans influence of the triazolylidene ligand via
wingtip group modification.
Upon crystallization of complex 2e, a smooth color
change from orange to yellow was noted in some cases.
Analysis of this yellow fraction gave broad NMR resonances
in the aromatic region. Measurements at 60 °C revealed four
distinct resonances between 7 and 8 ppm. Desymmetrization
of the phenyl ring and loss of one proton resonance are
indicative for orthopalladation and the formation of the
palladacycle 5e (Scheme 4). The presence of a Pd-Caryl bond
was also supported by a low-field 13C NMR signal at δC
144.6. Related cyclopalladation was also observed in imida-
zolium-derived N-heterocyclic carbenes.23 Unambiguous
evidence for the formation of a cyclopalladated product
was provided by X-ray diffraction analysis (Figure 4). Crys-
tals of 5e contained two crystallographically independent
molecules, which differed considerably in their global struc-
ture. One molecule is located on a crystallographic inversion
center and features a planar Pd2I2 core, thus resulting in a
coplanar arrangement of the two metalacycles. In contrast
the second molecule is characterized by an open book-type
Complexes 2b-e were investigated in the solid state by
X-ray diffraction analysis (Figure 3). The global structure of
all dimeric compounds is identical to that of 2a (cf. Figure 1a)
and comprises two palladium centers, two bridging iodides,
and at each metal center one triazolylidene and one iodide
ligand. In all complexes the center of the Pd2I2 square is a
crystallographic inversion center. As a consequence, the
wingtip groups in complexes 2d and 2e adopt a mutual anti
conformation. The Pd-C bond lengths in all complexes are
˚
identical within esd’s and average 1.97(1) A. This distance is
in the range generally observed for abnormal palladium
carbene complexes.22 Further bond lengths and angles are
(20) (a) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless,
K. B. Angew. Chem., Int. Ed. 2002, 41, 2596. (b) Appukkuttan, P.; Dehaen,
W.; Fokin, V. V.; van der Eycken, E. Org. Lett. 2004, 6, 4223.
(21) Transmetalation using PdCl2(MeCN)2 and subsequent halide
metathesis with NaI provides an alternative access to pure dimetallic
complexes, thus suppressing the formation of bis(carbene) palladium
complexes 3. See Experimental Section for further details.
(22) Poulain, A.; Iglesias, M.; Albrecht, M. Curr. Org. Chem. 2011,
in press.
(23) (a) Hiraki, K.; Onishi, M.; Sugino, K. J. Organomet. Chem. 1979,
171, C50. (b) Hiraki, K.; Sugino, K. J. Organomet. Chem. 1980, 201, 469.
(c) Stylianides, N.; Danopoulos, A. A.; Pugh, D.; Hancock, F.; Zanotti-
Gerosa, A. Organometallics 2007, 26, 5627. (d) Frey, G. D.; Sch€utz, J.;
Herdtweck, E.; Herrmann, W. A. Organometallics 2005, 24, 4416. (e) Liu,
Z.; Zhang, T.; Shi, M. Organometallics 2008, 27, 2668. For a related
cycloplatination, see: (f) Petretto, G. L.; Wang, M.; Zucca, A.; Rourke, J. P.
Dalton Trans. 2010, 39, 7822.

Article
Organometallics, Vol. 30, No. 5, 2011 1025
Figure 3. ORTEP drawings of complex 2b (a; only one of the two crystallographically independent molecules shown), 2c (b), 2d (c),
and 2e (d). All structures are at the 50% probability level except 2b, which is at 30% probability; hydrogen atoms and cocrystallized
solvents in 2d and 2e are omitted for clarity.
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) for
Complexes 2b-e
Scheme 4. Reversible Cyclopalladation of Triazolylidenes
Comprising N-Phenyl Wingtip Groups
2b
2c
2d
2e
Pd1-C1
Pd1-I1
Pd1-I2
Pd1-I2a
C1-C2
1.96(3)
1.969(5)
2.5876(5)
2.6814(6)
2.6050(5)
1.377(7)
1.977(13)
2.5918(15)
2.6574(13)
2.6070(15)
1.366(18)
1.972(6)
2.6039(6)
2.6652(5)
2.6065(6)
1.383(8)
2.587(2)
2.667(3)
2.605(2)
1.38(4)
C1-Pd1-I1
C1-Pd1-I2
C1-Pd1-I2a
I1-Pd1-I2
I1-Pd1-I2a
I2-Pd1-I2a
C2-C1-N1
87.6(8)
178.6(8)
90.7(8)
93.68(8)
177.34(11)
88.04(8)
100(3)
88.98(16)
89.0(5)
178.2(5)
90.3(5)
92.52(5)
178.15(5)
88.17(4)
103.2(11)
88.84(18)
177.02(17)
90.66(18)
93.770(18)
178.33(2)
86.766(17)
103.0(5)
175.24(15)
89.52(16)
94.67(2)
178.49(2)
86.84(2)
102.8(4)
quantitative, however, when 2e and an excess of NaOAc were
kept at 120 °C for 2 h. Longer reaction times led to significant
decomposition, as indicated by the formation of a black
precipitate. Acetate seems to be a privileged base in this
cyclometalation process.25 Attempts to substitute acetate by
NEt3 were unsuccessful and gave either no reaction at all
(room temperature) or decomposition products only (3 h at
80 °C). Moreover, only N-bound phenyl wingtip groups were
observed to undergo cyclopalladation. For example, complex
2funderwentC-H activationinthe presence of acetateto give
the cyclopalladated complex 5f.24 In this complex, the N-bound
phenyl was palladated exclusively, and neither activation of
the C-bound phenyl group in 2f nor isomerization of the
palladacycle in 5f was observed. Along the same lines,
complexes 2a and 2d, both featuring only a C-bound phenyl
wingtip group, were inert under the conditions used for
cyclopalladation of complex 2e. Apparently, the electron-releas-
ing character of nitrogen is beneficial to aryl functionalization,
arrangement, with the metallacycles mutually tilted.24 De-
spite this different arrangement, bond lengths and angles in
both molecules are highly similar. The Pd-Ccarbene bonds
are longer than in the monodentate complexes 2 and only
slightly shorter than the Pd-Caryl bonds (Table 3).
Investigation of the cyclopalladation revealed that heating
of complex 2e in DMSO to 120 °C for 3.5 h, i.e., conditions
used for the preparation of 2, did not induce any significant
palladacycle formation. In the presence of a weak base such
as acetate, several products yet no 5e were formed at room
temperature, perhaps originating from anion metathesis due
to the coordination ability of acetate. A similar outcome was
noted when the reaction mixture was heated to 50 °C. Further
elevation of the temperature to 80 °C induced formation of 5e,
albeit incomplete after 3 h. Cyclopalladation was essentially
(25) (a) Davies, D. L.; Donald, S. M. A.; Macgregor, S. A. J. Am.
Chem. Soc. 2005, 127, 13754. (b) Dupont, J.; Pfeffer, M., Eds. Pallada-
cycles; Wiley-VCH: Weinheim, Germany, 2008.
(24) See the Supporting Information for representations and crystal-
lographic details.

1026 Organometallics, Vol. 30, No. 5, 2011
Poulain et al.
Figure 4. ORTEP drawings of the two crystallographically independent molecules of 5e (50% probability, cocrystallized solvent
molecules and hydrogen atoms omitted for clarity).
a
˚
Table 3. Selected Bond Lengths (A) and Angles (deg) for 5e
Scheme 5. Synthesis of the Rhodium Complexes 6 and 7
molecule 1
molecule 2 (Pd2)
molecule 2 (Pd3)
Pd1-C1
Pd1-C4
Pd1-I1
Pd1-I1a
1.983(8)
2.034(8)
2.6539(9)
2.6842(8)
2.010(9)
2.047(8)
2.6482(10)
2.7045 (9)
1.979(8)
2.031(8)
2.6683(9)
2.6901(9)
C1-Pd1-C4
C1-Pd1-I1
C1-Pd1-I1a
C4-Pd1-I1
C4-Pd1-I1a
I1-Pd1-I1a
80.6(3)
80.7(3)
175.1(2)
97.8(2)
94.9(3)
176.1(2)
86.72(3)
81.1(3)
176.3(2)
96.8(2)
95.3(3)
172.3(2)
86.61(3)
174.5(2)
97.6(2)
95.7(2)
174.1(2)
86.50(3)
a Numbering scheme for molecule 2 adapted.
which is in line with an electrophilic mechanism for this
cyclopalladation.26
Exposure of complexes 6 to a CO-saturated environment
afforded the corresponding carbonyl analogues 7 in essen-
tially quantitative yield.30
Metallacycle formation is fully reversible. When exposing
complex 5a to excess HI, complex 2e is recovered in high
yields. Cleavage of the metallacycle was indicated macroscopi-
cally by the instantaneous color change from yellow to orange
The 13C NMR chemical shift of the rhodium-bound
triazolylidene carbon shows an apparent correlation with
the nature of the wingtip group. With alkyl wingtip groups,
the doublet (1JRhC = 46.5 ( 3 Hz for all complexes)
appeared at highest field (δC 168.5 and 168.6 for 6b and 6c,
respectively), while the presence of one phenyl group as in 6d
and 6e induces a downfield shift (δC 170.4 for both complex-
es). When incorporating a second phenyl group (6f), the
resonance is shifted by another 2 ppm to lower field (δC
172.2). A similar trend was observed when comparing the
carbene resonance of the carbonyl complexes 7, although the
effect is more gradual and not additive as in complexes 6
(Table 4). In agreement with the stronger trans influence of
CO as opposed to olefins, the Rh-Ccarbene coupling constant
1
and microscopically by the pertinent H NMR data, which
were identical to those of the parent complex 2e. Exposure of 2e
to HI for several days did not induce any complex degradation
and hence demonstrates a remarkable resistance of the palla-
dium-carbene bond toward acidolysis.14,27 Both the stability
of the Pd-Ccarbene bond toward acids and bases and the
sensitivity of N-bound phenyl groups toward cyclopalladation
under basic conditions;typical conditions for example in
cross-coupling reactions28;have obvious implications when
using this type of complexes in catalysis.9a
Synthesis of Rhodium Complexes. Ligand complexation to
rhodium provides a useful probe for evaluating ligand
effects, first by measuring the CO stretch vibration in the
corresponding rhodium carbonyl complexes (translating
into Tolman electronic parameters, TEPs),29 and second by
NMR spectroscopy due to the I = 1/2 spin of 103Rh. There-
fore, the rhodium complexes 6 were prepared using classical
transmetalation procedures involving Ag2O as a basic silver
salt and [Rh(cod)Cl]2 as transmetalating agent (Scheme 5).
1
is smaller in complexes 7, with JRhC = 39.1 ( 4. When
considering the NMR characteristics of the CO ligand trans
to the carbene,31 an increase of the coupling constant was
observed upon reducing the wingtip donation. Thus, the
lowest coupling constant was noted for the alkyl-substituted
carbene complexes 7b and 7c (1JRhC = 53.4), and this value
increases upon replacing electron-releasing alkyl groups with
(30) (a) Cetinkaya, B.; Dixneuf, P.; Lappert, M. F. J. Chem. Soc.,
Dalton Trans. 1974, 1827. (b) Herrmann, W. A.; Elison, M.; Fischer, J.;
€
(26) Albrecht, M. Chem. Rev. 2010, 110, 576.
(27) Heckenroth, M.; Neels, A.; Garnier, M. G.; Aebi, P.; Ehlers,
A. W.; Albrecht, M. Chem.;Eur. J. 2009, 15, 9375.
(28) De Meijere, A.; Diederich, F., Eds. Metal-Catalyzed Cross-
Coupling Reactions; Wiley-VCH: Weinheim, Germany, 2004.
Kocher, C.; Artus, G. R. J. Chem.;Eur. J. 1996, 2, 772.
(31) According to these coupling constants, the triazolylidene ligands
in 6 have similar donor strength to normal imidazol-2-ylidenes. See for
example: (a) Burling, S.; Field, L. D.; Li, H. L.; Messerle, B. A.; Turner,
P. Eur. J. Inorg. Chem. 2003, 3179. (b) Mata, J. A.; Chianese, A. R.;
Miecznikowski, J. R.; Poyatos, M.; Peris, E.; Faller, J. W.; Crabtree, R. H.
Organometallics 2004, 23, 1253.
€
(29) (a) Strohmeier, W.; Muller, F.-J. Chem. Ber. 1967, 100, 2812.
(b) Tolman, C. A. Chem. Rev. 1977, 77, 313.

Article
Organometallics, Vol. 30, No. 5, 2011 1027
Table 4. Selected Spectroscopic Data for Complexes 7a-fa
7a
7b
7c
7d
7e
7f
δ
δ
δ
C (1JRhC) Ccarbene
C (1JRhC) COtrans
C (1JRhC) COcis
161.2 (39.4)
186.1 (54.1)
183.5 (75.4)
159.8 (39.4)
186.8 (53.4)
184.3 (74.6)
160.4 (39.4)
187.0 (53.4)
184.4 (74.8)
161.3 (39.4)
186.8 (54.2)
183.9 (75.4)
161.8 (39.4)
186.7 (54.9)
183.8 (75.4)
162.6 (39.4)
186.7 (54.8)
183.7 (74.6)
a In CD2Cl2, δC in ppm, 1JRhC in Hz, trans refers to the carbene position; data for 7a from ref 8.
electron-withdrawing phenyl wingtips. The trend is not rigid
(cf. 7e and 7f). Since larger coupling constants may be
attributed to weaker ligand donor properties in trans
passage through solvent purification column. The preparation
of the triazolium salts is detailed in the Supporting Information.
All other chemicals were commercially available and were used
1
as received. H and 13C{1H} NMR spectra were recorded on
1
position,32 this trend in JRhC and chemical shift analyses
Bruker spectrometers at room temperature, unless stated other-
wise, and were referenced to the protio signal of the solvent and
are reported downfield from SiMe4. Chemical shifts (δ) are
given in ppm; coupling constants J are given in Hz. NMR
assignments are based on distortionless enhancement of polar-
ization transfer (DEPT) experiments or on homo- and hetero-
nuclear shift correlation spectroscopy. Elemental analyses were
performed by the Microanalytical Laboratory of the ETH
are both in line with a soft yet noticeable tunability of
electronic properties via wingtip group modifications.
The CO stretch vibrations occur in the IR spectrum at
1983 and 2065 cm-1 for all complexes except for 7f (νCO
=
1988 and 2068 cm-1). Depending on the applied linear
regression,33 these values translate into a TEP in the range
2035 to 2042 cm-1. Because of the identical CO absorption
energies, the calculated TEPs for the triazolylidene ligands in
complexes 7b-e are obviously the same, which may indicate
some limitation of this method for evaluating ligand donor
properties.34 Perhaps, steric effects may affect the Rh-COcis
bond and may thus interfere with the electronic component
exerted by the ligand. Such stereoelectronic perturbation has
been noted before5c,35 and may, in the complexes investi-
gated here, compensate the moderate donor differences due
to wingtip modifications.
€
Zurich (Switzerland). Mass spectra were measured by electro-
spray ionization (ESI-MS) in MeCN on a Bruker 4.7 BioAPEX
II instrument, and infrared spectra on a Bruker Tensor 27 using
a Golden Gate ATR. Details on crystallographic structure
determination and refinement of the complexes are compiled
in the Supporting Information. CCDC 800720-800720 contain
the supplementary crystallographic data for this paper. These
data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/da-
ta_request/cif.
Palladation Reactions. Method A. A solution of triazolium
salt and Pd(OAc)2 (1 equiv) in DMSO was stirred at 120 °C for
3.5 h. After addition of CH2Cl2, the solution was filtered
through Celite, H2O was added, and the solution was extracted
with CH2Cl2. The organic phases were combined, washed with
H2O, and dried over Na2SO4. Then all volatiles were evapo-
rated, yielding a mixture of 2 and 3. Repeated extraction of this
mixture with small portions of MeCN gave complex 2 in almost
pure form, while subsequent extraction of the residue with
CH2Cl2 yielded the mono(carbene) species 3. Further purifica-
tion of the fractions was achieved by crystallization.
Method B. The triazolium salt (1 equiv) and Ag2O (1 equiv) in
CH2Cl2 were stirred at rt for 24 h. After filtration through Celite,
PdCl2(NCMe)2 (1 equiv) was added and the solution was stirred
at rt during 4 h. The solution was filtered through Celite, and a
solution of NaI (6 equiv) in acetone was added and stirred at rt
for another hour. After evaporation of volatiles and addition of
H2O, the residue was extracted with CH2Cl2. The combined
organic phases were washed with H2O, then with a saturated
aqueous solution of sodium pyrosulfite (Na2S2O5), dried over
Na2SO4, and evaporated to dryness.
Conclusions
Palladation of triazolium salts afforded different types of
complexes, including monometallic bis(carbene) species and
bimetallic complexes with 1:1 metal carbene stoichiometry.
Careful choice of reaction conditions and workup procedures
provides access to pure materials. Variation of the wingtip
groups has distinct implications on the properties of the
triazolylidene ligand. Accordingly, swapping from an alkyl to
an aryl substituent reduces the electron density at the metal
center. The arrangement of the substituents (e.g., C-bound vs
N-bound phenyl as in 6d and 6e) appears to play no significant
role for tuning the electronic properties of the metal center. This
wingtip arrangement strongly affects, however, the stability of
the corresponding palladium complexes, since N-bound phenyl
groups tend to cyclopalladate, while the C-bound analogue
resists such processes. Ligand tunability and stability will have
profound implications for applying this class of complexes in
catalysis. Investigations along these lines are currently in pro-
gress and will be the subject of a forthcoming report.
Synthesis of 2a. According to method B, 1a (0.237 g, 0.75
mmol) in CH2Cl2 (15 mL) was stirred at rt with Ag2O (0.173 g,
0.75 mmol) for 24 h, and PdCl2(MeCN)2 (0.196 g, 0.75 mmol)
was then added. After filtration through Celite, NaI (0.668 g,
4.46 mmol) dissolved in acetone (25 mL) was added, and the
mixture was stirred for 1.5 h. All volatiles were evaporated, and
the residue was extracted to yield a red powder (0.313 g, 76%).
Analytically pure 2a was obtained after recrystallization by slow
diffusion of pentane into a saturated CH2Cl2 solution.
Experimental Section
General Comments. Air-sensitive reactions were carried out
under Ar using Schlenk techniques. CH2Cl2 was dried by
(32) Appleton, T. G.; Bennett, M. A. Inorg. Chem. 1978, 17, 738.
(33) (a) Chianese, A. R.; Li, X.; Janzen, M. C.; Faller, J. W.; Crabtree,
R. H. Organometallics 2003, 22, 1663. (b) Kelly, R. A.; Clavier, H.; Guidice,
S.; Scott, N. M.; Stevens, E. D.; Bordner, J.; Samardjiev, I.; Hoff, C. D.;
Cavallo, L.; Nolan, S. P. Organometallics 2008, 27, 202. (c) Wolf, S.; Plenio,
H. J. Organomet. Chem. 2009, 694, 1487. (d) Tonner, R.; Frenking, G.
Organometallics 2009, 28, 3901.
1H NMR (400 MHz, DMSO-D6): δ 7.98-7.92 (m, 4H,
3
Horthoph), 7.63-7.52 (m, 6H, Hmetaph, Hparaph), 4.71 (q, JHH
=
7.2 Hz, 4H, NCH2CH3), 4.06 (s, 6H, NCH3), 1.63 (t, 3JHH = 7.2
Hz, 6H, NCH2CH3). 13C{1H} NMR (100 MHz, DMSO-D6): δ
142.5 (Ctrz), 130.0 (Corthoph), 129.8 (Cparaph), 128.5 (Cmeta
þ
ph
Ctrz-Pd), 126.9 (Cipsoph), 50.8 (NCH2CH3), 38.1 (NCH3), 14.2
(NCH2CH3); Anal. Found (calcd) for C22H26I4N6Pd2 (1094.93) ꢀ
1/2 C5H12: C 26.17 (26.02), H 2.60 (2.85), N 7.85 (7.43).
€
(34) (a) Furstner, A.; Alcarazo, M.; Krause, H.; Lehmann, C. W. J.
Am. Chem. Soc. 2007, 129, 12676. (b) Song, G.; Zhang, Y.; Li, X.
Organometallics 2008, 27, 1936. (c) Kuchenbeiser, G.; Soleilhavoup, M.;
Donnadieu, B.; Bertrand, G. Chem. Asian J. 2009, 4, 1745.
(35) For alternative methods, see ref 4h and: Huynh, H. V.; Han, Y.;
Jothibasu, R.; Yang, J. A. Organometallics 2009, 28, 5395.
Synthesis of 2b. According to method B, 2b was obtained
starting from 1b (0.104 g, 0.39 mmol) in CH2Cl2 (10 mL), Ag2O

1028 Organometallics, Vol. 30, No. 5, 2011
Poulain et al.
(0.090 g, 0.39 mmol), and PdCl2(MeCN)2 (0.101 g, 0.39 mmol).
After stirring for 20 h, Celite filtration, addition of NaI (0.359 g,
2.39 mmol) dissolved in acetone (20 mL), and purification gave
2b as a red solid (0.084 g, 43%).
Synthesis of 2f. According to method B, 2f was obtained
starting from 1f (0.105 g, 0.29 mmol) in CH2Cl2 (20 mL), Ag2O
(0.065 g, 0.28 mmol), and PdCl2(MeCN)2 (0.074 g, 0.29 mmol).
Stirring for 6 h, Celite filtration, and addition of NaI (0.260 g,
1.73 mmol) dissolved in acetone (25 mL) were followed by
evaporation of volatiles and extraction (0.091 g, 53% yield).
1H NMR (500 MHz, DMSO-D6): δ 8.34-8.31 (m, 4H,
HorthoNPh), 8.04-8.02 (m, 4H, HorthoCPh), 7.72-7.68 (m, 4H,
HmetaNPh), 7.66-7.57 (m, 8H, HmetaCPh, HparaCPh, HparaNPh),
4.17 (s, 6H, NCH3). 13C{1H} NMR (125 MHz, DMSO-D6): δ
143.3 (Ctrz), 139.0 (CipsoNPh), 130.3 (CparaNPh), 130.2 (CorthoCPh),
130.0 (CparaCPh), 129.2 (CmetaNPh), 128.5 (CmetaCPh), 126.9
(CipsoCPh), 124.7 (CorthoNPh), 38.4 (NCH3), Ctrz-Pd not ob-
served. Anal. Found (calcd) for C30H26I4N6Pd2 (1191.02) ꢀ 1/
2 CH2Cl2: C 28.73 (29.18), H 2.15 (2.21), N 6.65 (6.59).
1H NMR (500 MHz, DMSO-D6): δ 4.56 (q, 3JHH = 7.3 Hz,
3
4H, NCH2CH3), 4.06 (s, 6H, NCH3), 2.85 (q, JHH = 7.6 Hz,
4H, CCH2CH3), 1.54 (t, 3JHH = 7.3 Hz, 6H, NCH2CH3), 1.34
(t, 3JHH = 7.6 Hz, 6H, CCH2CH3). 13C{1H} NMR (125 MHz,
DMSO-D6): δ 144.1 (Ctrz), 126.0 (Ctrz-Pd), 50.3 (NCH2CH3),
36.6 (NCH3), 18.1 (CCH2CH3), 14.2 (NCH2CH3), 12.0
(CCH2CH3). Anal. Found (calcd) for C14H26I4N6Pd2 (998.86):
C 16.76 (16.83), H 2.55 (2.62), N 8.09 (8.41).
Synthesis of 2c. According to method B, 2c was obtained
starting from 1c (0.113 g, 0.35 mmol) in CH2Cl2 (15 mL), Ag2O
(0.082 g, 0.35 mmol), and PdCl2(MeCN)2 (0.092 g, 0.35 mmol).
Stirring for 5 h, Celite filtration, and addition of NaI (0.202 g,
1.35 mmol) in acetone (15 mL) were followed by an extraction
and recrystalliztion by slow diffusion of pentane into CH2Cl2.
This procedure gave an analytically pure fraction of 2c (0.137 g,
71%).
Synthesis of 3a. According to method A, 1a (0.301 g, 0.95
mmol) in DMSO (25 mL) was heated with Pd(OAc)2 (0.214 g,
0.95 mmol). After extraction 0.315 g of a mixture of 2a and 3a
was obtained. This mixture was washed with MeCN, and the
residue was dried in vacuo, thus giving 3a (0.091 g, 26%) as an
analytically pure cis/trans mixture (1:2.5 ratio).
1H NMR (500 MHz, DMSO-D6): δ 4.52 (t, 3JHH = 7.2 Hz,
3
1
4H, NCH2CH2CH2CH3), 4.04 (s, 6H, NCH3), 2.84 (t, JHH
=
Major isomer: H NMR (400 MHz, DMSO-D6): δ 8.13 (d,
3JHH = 7.3 Hz, 4H, Horthoph), 7.58-7.49 (m, 6H, Hmeta
,
7.9 Hz, 4H, CCH2CH2CH2CH3), 2.08 (quint, 3JHH = 7.2 Hz, 4H,
NCH2CH2CH2CH3), 1.85 (quint, 3JHH = 7.9 Hz, 4H, CCH2CH2-
CH2CH3), 1.37 (sext, 3JHH = 7.5 Hz, 4H, CCH2CH2CH2CH3),
ph
Hparaph), 4.65 (q, JHH = 7.3 Hz, 4H, NCH2), 4.09 (s, 6H,
NCH3), 1.56 (t, 3JHH = 7.3 Hz, 6H, NCH2CH3). 13C{1H} NMR
(100 MHz, DMSO-D6): δ 154.6 (Ctrz-Pd), 144.1 (Ctrz), 129.8
(Corthoph), 128.3 (Cipsoph), 128.1 (Cmetaph), Cparaph not observed,
49.6 (NCH2), 37.5 (NCH3), 14.9 (NCH2CH3).
3
3
1.30 (sext, JHH = 7.5 Hz, 4H, NCH2CH2CH2CH3), 0.93 (q,
3JHH = 7.5 Hz, 12H, CCH2CH2CH2CH3, NCH2CH2CH2CH3).
13C{1H} NMR (125 MHz, DMSO-D6): δ 143.5 (Ctrz), 126.4
(Ctrz-Pd), 54.6 (NCH2CH2CH2CH3), 36.6 (NCH3), 29.9 (NC-
H2CH2CH2CH3), 29.2 (CCH2CH2CH2CH3), 24.5 (CCH2CH2-
CH2CH3), 21.9 (CCH2CH2CH2CH3), 19.0 (NCH2CH2CH2-
CH3), 13.7 (CCH2CH2CH2CH3), 13.3 (NCH2CH2CH2CH3).
Anal. Found (calcd) for C22H42I4N6Pd2 (1111.07): C 23.70
(23.78), H 3.82 (3.81), N 7.42 (7.56).
1
Minor isomer: H NMR (400 MHz, DMSO-D6): δ 7.93 (d,
3JHH = 7.1 Hz, 4H, Horthoph), 7.58-7.41 (m, 6H, Hmeta
,
ph
3
Hparaph), 4.85 (q, JHH = 7.2 Hz, 4H, NCH2), 4.05 (s, 6H,
NCH3), 1.71 (t, 3JHH = 7.2 Hz, 6H, NCH2CH3). 13C{1H} NMR
(100 MHz, DMSO-D6): δ 154.0 (Ctrz-Pd), 144.1 (Ctrz), 129.6
(Corthoph), 129.1 (Cmetaph), 128.8 (Cparaph), 127.9 (Cipsoph), 50.0
(NCH2), 37.6 (NCH3), 14.6 (NCH2CH3). Anal. Found (calcd)
for C22H26I2N6Pd (734.72): C 35.54 (35.96), H 3.49 (3.57), N
11.13 (11.44).
Synthesis of 2d. According to method B, 2d was obtained
starting from 1d (0.150 g, 0.44 mmol) in CH2Cl2 (15 mL), Ag2O
(0.100 g, 0.43 mmol), and PdCl2(MeCN)2 (0.115 g, 0.44 mmol).
After stirring for 4 h, filtration through Celite, addition of NaI
(0.399 g, 2.66 mmol) dissolved in acetone (20 mL), followed by
evaporation of volatiles and extraction, recrystallization re-
sulted in an analytically pure fraction of 2d (0.189 g, 75% yield).
Synthesis of 4a. According to method B 4a was obtained
starting from 1a (400 mg, 1.27 mmol), Ag2O (490 mg, 2.1 mmol),
and PdCl2(NCMe)2 (315 mg, 1.2 mmol) in CH2Cl2 (20 mL) at rt
during 2 h. After filtration through Celite, the mixture was
eluted from a short pad of SiO2 by using CH2Cl2. After
evaporation of all volatiles, the residue was washed with pentane
(3 ꢀ 20 mL) to afford 4a as a yellow solid (334 mg, 96%).
1H NMR (500 MHz, CD3CN, 348 K): δ 8.10 (br s, 4H, Har),
7.55 (br s, 6H, Har), 4.92 (q, 3JHH = 7.1 Hz, 4H, NCH2), 4.02 (s,
6H, NCH3), 1.76 (t, 3JHH = 7.1 Hz, 6H, NCH2CH3). 13C{1H}
NMR (125 MHz CDCl3) major isomer: δ 159.0 (Ctrz-Pd), 144.5
(Ctrz), 132.3 (Cipsoph), 130.3 (Cmetaph), 129.0 (Cparaph), 128.4
(Corthoph), 49.7 (NCH2), 36.9 (NCH3), 15.5 (NCH2CH3). 13C-
{1H} NMR (125 MHz CDCl3) minor isomer: δ 158.1 (Ctrz-Pd),
144.8 (Ctrz), 132.7 (Cipsoph), 130.4 (Cmetaph), 129.2 (Cparaph),
128.3 (Corthoph), 50.0 (NCH2), 36.8 (NCH3), 15.2 (NCH2CH3).
Anal. Found (calcd) for C22H26Cl2N6Pd (550.06) ꢀ 1/4 CH2Cl2:
C 46.51 (46.64); H, 4.50 (4.66); N, 14.54 (14.67).
1H NMR (500 MHz, DMSO-D6): δ 7.97-7.94 (m, 4H,
3
Horthoph), 7.60-7.53 (m, 6H, Hmetaph, Hparaph), 4.66 (t, JHH
=
7.4 Hz, 4H, NCH2CH2CH2CH3), 4.06 (s, 6H, NCH3), 2.16 (quint,
3JHH = 7.4 Hz, 4H, NCH2CH2CH2CH3), 1.40 (sext, 3JHH = 7.4
3
Hz, 4H, NCH2CH2CH2CH3), 0.96 (t, JHH = 7.4 Hz, 6H,
NCH2CH2CH2CH3). 13C{1H} NMR (125 MHz, DMSO-D6):
δ 142.6 (Ctrz), 129.9 (Corthoph), 129.7 (Cparaph), 128.4 (Cmetaphþ
Ctrz-Pd), 127.0 (Cipsoph), 54.9 (NCH2CH2CH2CH3), 38.0
(NCH3), 29.9 (NCH2CH2CH2CH3), 19.0 (NCH2CH2CH2CH3),
13.4 (NCH2CH2CH2CH3). Anal. Found (calcd) for C26H34I4N6Pd2
(1151.05): C 27.07 (27.13), H 2.98 (2.98), N 7.21 (7.30).
Synthesis of 2e. According to method B, 2e was obtained
starting from 1e (0.073 g, 0.21 mmol) in CH2Cl2 (10 mL), Ag2O
(0.050 g, 0.21 mmol), and PdCl2(MeCN)2 (0.056 g, 0.21 mmol).
After stirring for 20 h, filtration through Celite, addition of NaI
(0.194 g, 1.29 mmol) dissolved in acetone (20 mL), evaporation
of volatiles, and extraction, an analytically pure fraction of 2e
was obtained (0.106 g, 87% yield).
Synthesis of Complex 5e. The title complex was obtained upon
recrystallization of a solution of 2e by slow evaporation of a
warm MeCN solution.
1H NMR (500 MHz, DMSO-D6, 333 K): δ 7.89 (br s, 2H,
H
ph), 7.38 (d, 3JHH = 7.5 Hz, 2H, Hph), 7.15 (d, 3JHH = 7.5 Hz,
1H NMR (500 MHz, DMSO-D6): δ 8.23 (d, 3JHH = 7.8 Hz,
2H, Hparaph), 7.08-7.05 (m, 2H, Hph), 4.14 (s, 6H, NCH3),
3.12-3.11 (m, 4H, CH2CH2CH2CH3), 1.60-1.57 (m, 4H,
CH2CH2CH2CH3), 1.47-1.40 (m, 4H, CH2CH2CH2CH3),
4H, Horthoph), 7.68-7.58 (m, 6H, Hmetaph, Hparaph), 4.18 (s, 3H,
NCH3), 2.98 (t, JHH = 7.8 Hz, 4H, CH2CH2CH2CH3), 1.93
3
(quint, 3JHH = 7.8 Hz, 4H, CH2CH2CH2CH3), 1.44 (sext, 3JHH
=
0.95 (t, JHH = 7.3 Hz, 6H, CH2CH2CH2CH3). 13C{1H}
3
3
7.4 Hz, 4H, CH2CH2CH2CH3), 0.97 (t, JHH = 7.4 Hz, 6H,
CH2CH2CH2CH3). 13C{1H} NMR (75 MHz, DMSO-D6): δ
NMR (125 MHz, DMSO-D6, 333 K): δ 146.3 (Ctrz), 144.6
(Cph), 127.2 (CHph), 124.5 (CHph), 112.7 (CHph), 36.1
(NCH3), 30.6 (CH2CH2CH2CH3), 23.6 (CH2CH2CH2CH3),
21.5 (CH2CH2CH2CH3), 13.3 (CCH2CH2CH2CH3), 2 Cph and
Ctrz-Pd not observed. Anal. Found (calcd) for C26H32I2N6Pd2
(895.22): C 35.19 (34.88), H 3.77 (3.60), N 9.46 (9.39).
144.2 (Ctrz), 139.1 (Cipsoph), 130.0 (Cparaph), 129.1 (Cmeta
þ
ph
Ctrz-Pd), 124.4 (Corthoph), 37.0 (NCH3), 29.0 (CH2CH2-
CH2CH3), 24.8 (CH2CH2CH2CH3), 21.9 (CH2CH2CH2CH3),
13.6 (CCH2CH2CH2CH3). Anal. Found (calcd) for C26H34-
I4N6Pd2 (1151.05): C 27.35 (27.13), H 3.10 (2.98), N 7.25 (7.30).

Article
General Procedure for the Synthesis of Rhodium Complexes 6.
General method: A flask, protected against light, containing 1
(1 equiv) in CH2Cl2 and Ag2O (1 equiv) was stirred at rt during
24 h. After filtration through Celite, [Rh(COD)Cl]2 (0.5 equiv)
was added, and the solution was stirred for the time indicated
and then filtered through Celite to give complex 6. Analytically
pure samples were typically obtained by precipitation from
CH2Cl2 and pentane.
Organometallics, Vol. 30, No. 5, 2011 1029
Ctrz), 130.6 (Corthoph), 129.7 (Cparaph), 129.0 (Cipsoph), 128.8
1
(Cmetaph), 96.3 (CHCOD), 96.2 (CHCOD), 70.2 (d, JCRh = 13.9
Hz, CHCOD), 67.7 (d, JCRh = 14.7 Hz, CHCOD), 55.3 (NCH2-
1
CH2CH2CH3), 37.8 (NCH3),33.6(CH2 COD), 32.7 (CH2 COD),32.5,
(NCH2CH2CH2CH3), 29.5 (CH2 COD), 29.4 (CH2 COD), 20.5
(NCH2CH2CH2CH3), 14.1 (NCH2CH2CH2CH3). Anal. Found
(calcd) for C21H29ClN3Rh (461.83) ꢀ 1/8 CH2Cl2: C 53.64
(53.70), H 6.13 (6.24), N 8.66 (8.89).
Synthesis of 6b. According to the general method, 1b (0.110 g,
0.41 mmol) in CH2Cl2 (10 mL) was stirred with Ag2O (0.095 g,
0.41 mmol). After filtration through Celite, [Rh(COD)Cl]2 (0.091 g,
0.18 mmol) was added, and the solution was stirred and, after 3 h,
filtrated through Celite to give complex 6b (0.14 g, 88%).
1H NMR (300 MHz, CD2Cl2): δ 4.84-4.77 (m, 4H, NCH2CH3,
CHCOD), 3.88 (s, 3H, NCH3), 3.24 (br s, 2H, CHCOD), 2.95 (q,
3JHH = 7.6 Hz, 2H, CCH2CH3), 2.46-2.25 (br m, 4H, CH2 COD),
Synthesis of 6e. According to the general method, 1e (0.061 g,
0.17 mmol) in CH2Cl2 (10 mL) was stirred with Ag2O (0.042 g,
0.18 mmol) for 20 h. After filtration through Celite,
[Rh(COD)Cl]2 (0.044 g, 0.09 mmol) was added and the solution
was stirred and, after 5 h, filtrated through Celite to give
complex 6e (0.078 g, quantitative).
1H NMR (400 MHz, CD2Cl2): δ 8.64-8.61(m, 2H, Horthoph),
7.62-7.52 (m, 3H, Hmetaph, Hparaph), 4.94-4.80 (m, 2H, CHCOD),
4.02 (s, 3H, NCH3), 3.27-3.19 (1H), 3.16-3.10 (1H), 3.00-3.92
(1H), 2.63-2.58 (1H), 2.41-2.26 (2H), 2.20-1.93 (3H), 1.91-1.82
3
1.97-1.81 (br m, 4H, CH2 COD), 1.64 (t, JHH = 7.3 Hz, 3H,
3
NCH2CH3), 1.47 (t, JHH = 7.6 Hz, 3H, CCH2CH3). 13C{1H}
NMR (75 MHz, CD2Cl2): δ 168.5 (d, 1JCRh = 46.2 Hz, Ctrz-Rh),
(1H), 1.80-1.69 (3H), 1.62-1.51 (3H) (2H, CHCOD, 8H, CH2 COD,
145.5 (d, 2JCRh = 2.8 Hz, Ctrz), 96.6 (d, 1JCRh = 7.2 Hz, CHCOD),
96.2 (d, JCRh = 7.2 Hz, CHCOD), 68.3 (d, JCRh = 14.9 Hz,
2H, CH2CH2CH2CH3, 2H, CH2CH2CH2CH3, 2H, CH2CH2-
CH2CH3), 1.08 (t, 3JHH = 7.3 Hz, 3H, CH2CH2CH2CH3). 13C{1H}
NMR (100 MHz, CD2Cl2): δ 170.4 (d, 1JCRh = 46.8 Hz, Ctrz-Rh),
146.1 (d, 2JCRh = 1.5 Hz, Ctrz), 140.6 (Cipsoph), 129.8 (Cparaph), 129.2
(Cmetaph), 124.6 (Corthoph),96.1(d, 1JCRh =7.3Hz, CHCOD),95.8(d,
1JCRh = 7.3 Hz, CHCOD), 69.0 (d, 1JCRh = 14.6 Hz, CHCOD), 68.6
(d, 1JCRh = 14.6 Hz, CHCOD), 36.6 (NCH3), 33.1, 33.0, 31.9, 29.7,
29.2, 26.3, 23.5 (4 ꢀ CH2 COD, CH2CH2CH2CH3, CH2CH2-
CH2CH3, CH2CH2CH2CH3), 14.3 (CCH2CH2CH2CH3). Anal.
Found (calcd) for C21H29ClN3Rh (461.84): C 54.86 (54.61), H
6.13 (6.33), N 9.05 (9.10).
1
1
1
CHCOD), 67.9 (d, JCRh = 14.9 Hz, CHCOD), 50.6 (NCH2CH3),
36.2 (NCH3), 33.8 (CH2 COD), 33.1 (CH2 COD), 29.6 (CH2 COD),
29.3 (CH2 COD), 19.3 (CCH2CH3), 16.0 (NCH2CH3), 14.5
(CCH2CH3). Anal. Found (calcd) for C15H25ClN3Rh (385.74) ꢀ
2/3 CH2Cl2: C 42.83 (42.54), H 5.93 (6.00), N 9.18 (9.50).
Synthesis of 6c. According to the general method, 1c (0.103 g,
0.32 mmol) in CH2Cl2 (15 mL) was stirred with Ag2O (0.074 g,
0.32 mmol). After filtration through Celite, [Rh(COD)Cl]2
(0.077 g, 0.16 mmol) was added and the solution was stirred
and, after 8 h, filtrated through Celite to give complex 6c as a
dark yellow oil (0.140 g, 99%).
Synthesis of 6f. According to the general method, 1f (0.052 g,
0.14 mmol) in CH2Cl2 (20 mL) was stirred with Ag2O (0.033 g,
0.14 mmol). After filtration through Celite, [Rh(COD)Cl]2
(0.035 g, 0.07 mmol) was added and the solution was stirred
and, after 6 h, filtrated through Celite to give 1f as a yellow
powder (0.037 g, 55%).
1H NMR (300 MHz, CD2Cl2): δ 4.88-4.79 (m, 3H, NCH2-
CH2CH2CH3, CHCOD), 4.67-4.57 (m, 1H, CHCOD), 3.87 (s, 1H,
NCH3), 3.33-3.17 (m, 2H, CHCOD), 2.88 (t, 3JHH = 8.1 Hz, 2H,
CCH2CH2CH2CH3), 2.46-2.24 (m, 4H, CH2 COD), 2.22-1.97 (m,
4H, CCH2CH2CH2CH3, NCH2CH2CH2CH3), 1.95-1.73 (m, 4H,
CH2 COD), 1.36 (m, 4H, CCH2CH2CH2CH3, NCH2CH2CH2CH3),
1.07-1.00 (m, 6H, CCH2CH2CH2CH3, NCH2CH2CH2CH3). 13C-
1H NMR (400 MHz, CD2Cl2): δ 8.84-8.80 (m, 2H,
HorthoNph), 8.22-8.19 (m, 2H, HorthoCph), 7.66-7.54 (m, 6H,
Nph
HmetaCph, HparaCph, Hmeta
HparaNph), 4.87-4.83 (m, 2H,
1
{1H} NMR (75 MHz, CD2Cl2): δ 168.6 (d, JCRh = 46.7 Hz,
CHCOD), 4.13 (s, 1H, NCH3), 2.79-2.70 (m, 2H, CHCOD),
2.19-2.02 (m, 2H, CH2 COD), 1.91-1.82 (m, 1H, CH2 COD),
1.76-1.66 (m, 3H, CH2 COD), 1.64-1.50 (m, 2H, CH2 COD).
Ctrz-Rh), 144.5 (d, 2JCRh = 2.8 Hz, Ctrz), 96.4 (d, 1JCRh = 7.2 Hz,
CHCOD), 96.1 (d, 1JCRh = 7.2 Hz, CHCOD), 68.1 (d, 1JCRh = 14.9
Hz, CHCOD), 67.8 (d, JCRh = 14.9 Hz, CHCOD), 55.1 (NCH2-
1
1
13C{1H} NMR (100 MHz, CD2Cl2): δ 172.2 (d, JCRh = 46.8
CH2CH2CH3), 36.3 (NCH3), 33.9 (CH2 COD), 33.1 (CH2 COD),
32.5, 32.2 (NCH2CH2CH2CH3 þ CCH2CH2CH2CH3), 29.7
(CH2 COD), 29.3 (CH2 COD), 25.6 (CCH2CH2CH2CH3), 23.3, 20.5
(NCH2CH2CH2CH3 þ CCH2CH2CH2CH3)], 14.1, 14.0 (CCH2-
CH2CH2CH3 þ NCH2CH2CH2CH3). Anal. Found (calcd) for
C19H33ClN3Rh (441.84) ꢀ 1/4 CH2Cl2: C 49.97 (49.93), H 7.25
(7.29), N 9.04 (9.07).
Synthesis of 6d. According to the general method, 1d (0.114 g,
0.33 mmol) in CH2Cl2 (15 mL) was stirred with Ag2O (0.077 g,
0.33 mmol). After filtration through Celite, [Rh(COD)Cl]2
(0.074 g, 0.15 mmol) was added, and, after stirring 6 h, the
solution was filtrated through Celite to afford 6d as a dark
yellow solid (0.12 g, 77%).
Hz, Ctrz-Rh), 145.1 (d, 2JCRh = 1.5 Hz, Ctrz), 140.5 (CipsoNph),
131.0 (CorthoCph), 129.9 (Cparaph), 129.3 (Cmetaph), 129.1
=
1
(Cipsoph), 128.9 (Cmetaph), 124.5 (CorthoNph), 96.2 (d, JCRh
1
8.1 Hz, CHCOD), 95.8 (d, JCRh = 7.3 Hz, CHCOD), 69.9 (d,
1JCRh = 14.6 Hz, CHCOD), 68.0 (d, 1JCRh = 14.6 Hz, CHCOD),
38.1 (NCH3), 33.1 (CH2 COD), 32.7 (CH2 COD), 29.4 (CH2 COD).
Anal. Found (calcd) for C23H26ClN3Rh (482.84): C 57.21
(57.12), H 5.55 (5.43), N 8.61 (8.70).
Acknowledgment. We thank S. Dobarco and P. Mathew
for synthetic assistance. This work was fiancially
supported by the Swiss National Science Foundation, a
UCD start-up grant, the European Union through a
Marie-Curie IEF, and the Alfred Werner Foundation
through an Assistant Professorship (M.A.).
1H NMR (400 MHz, CD2Cl2): δ 8.09-8.07 (m, 2H, Horthoph),
7.60-7.50 (m, 3H, Hmetaph, Hparaph), 5.09-5.02 (m, 1H, NCH2-
CH2CH2CH3), 4.92-4.75 (m, 2H, CHCOD), 4.67-4.60 (m, 1H,
NCH2CH2CH2CH3), 4.01 (s, 3H, NCH3), 3.14 (br s, 1H, CHCOD),
2.59 (br s, 1H, CHCOD), 2.35-2.13 (m, 5H, NCH2CH2CH2CH3 þ
CH2 COD), 1.82-1.64 (m, 5H, NCH2CH2CH2CH3 þ CH2 COD),
1.55-1.48 (m, 2H, NCH2CH2CH2CH3), 1.07 (t, 3JHH = 7.5 Hz,
3H, NCH2CH2CH2CH3). 13C{1H} NMR (100 MHz, CD2Cl2): δ
Supporting Information Available: Synthetic details for the
triazolium salts 1 and for the rhodium complexes 7, crystal-
lographic analysis of a pseudopolymorph of cis-3a and complex
5f, and crystallographic details for complexes 2a-e, trans-3a,
cis-3a, trans-4a, 5e, and 5f in CIF format. This material is
available free of charge via the Internet at http://pubs.acs.org.
1
2
170.4 (d, JCRh = 46.8 Hz, Ctrz-Rh), 144.3 (d, JCRh = 2.2 Hz,