Synthesis and coordination chemistry of ferrocenyl-1,2,3-triazolyl ligands

Article abstract of DOI:10.1021/ic8002405

Click reactions between ethynylferrocene and mono-, bis-, and tris-azido aromatic derivatives yielded mono-, bis-, and tris-1,2,3- ferrocenyltriazoles (1, 2, and 3, respectively) as orange crystals. The X-ray crystal structure of the monoferrocenyltriazole compound 1 was solved with two nearly identical molecules within the asymmetric unit. In both molecules, the two Cp rings make a tilt angle of 2.1(3)° [0.7(3)°], and they are roughly eclipsed with a twist angle of 2.4(3)° [1.8(3)°]. Reaction of 1 with [PdCl₂(PhCN)₂] in dimethylsulfoxide (DMSO) yielded orange crystals of [PdCl₂L₂] (4; L = 1), for which the X-ray crystal structure shows trans coordination to the nitrogen atom close to the ferrocene substitution. The Pd atom is located on an inversion center and displays a nearly perfect square planar environment. In DMSO-d₆, 4 reversibly dissociates to regenerate 1, whose ¹H NMR spectrum is then observed. The ¹H NMR study also shows that progressive addition of PdCl₂ or [PdCl₂(NCR)₂] (R = Me or Ph) to DMSO-d₆ solutions of 1 reversibly leads to the formation of 4 and the addition of excess Pd^II is necessary to lead to the complete disappearance of the signals of 1. The cyclic voltammograms of 1, 2, and 3 show the reversible oxidation wave of the ferrocenyl group, and that of 4 shows that this wave appears with increased intensity tentatively attributable to redox-catalyzed oxidation.

Full text of DOI:10.1021/ic8002405

Inorg. Chem. 2008, 47, 4903-4908
Synthesis and Coordination Chemistry of Ferrocenyl-1,2,3-triazolyl
Ligands
Sihem Badèche,†,‡ Jean-Claude Daran,§ Jaime Ruiz,† and Didier Astruc*,†
Institut des Sciences Mole´culaires, UMR CNRS N°5255, UniVersite´ Bordeaux 1, 351 Cours de la
Libe´ration, 33405 Talence Cedex, France, Laboratoire de Chimie Mole´culaire, du Controˆle de
l’EnVironnement et de Mesures Physico-chimiques, De´partement de Chimie, UniVersite´ Fre`res
Mentouri, 25000 Constantine, Alge´rie, and Laboratoire de Chimie de Coordination, UPR CNRS
N°8241, 205 Route de Narbonne, 31077 Toulouse Cedex 04, France
Received February 6, 2008
“Click” reactions between ethynylferrocene and mono-, bis-, and tris-azido aromatic derivatives yielded mono-, bis-,
and tris-1,2,3-ferrocenyltriazoles (1, 2, and 3, respectively) as orange crystals. The X-ray crystal structure of the
monoferrocenyltriazole compound 1 was solved with two nearly identical molecules within the asymmetric unit. In
both molecules, the two Cp rings make a tilt angle of 2.1(3)° [0.7(3)°], and they are roughly eclipsed with a twist
angle of 2.4(3)° [1.8(3)°]. Reaction of 1 with [PdCl2(PhCN)2] in dimethylsulfoxide (DMSO) yielded orange crystals
of [PdCl2L2] (4; L ) 1), for which the X-ray crystal structure shows trans coordination to the nitrogen atom close
to the ferrocene substitution. The Pd atom is located on an inversion center and displays a nearly perfect square
planar environment. In DMSO-d6, 4 reversibly dissociates to regenerate 1, whose 1H NMR spectrum is then observed.
1
The H NMR study also shows that progressive addition of PdCl2 or [PdCl2(NCR)2] (R ) Me or Ph) to DMSO-d6
solutions of 1 reversibly leads to the formation of 4 and the addition of excess PdII is necessary to lead to the
complete disappearance of the signals of 1. The cyclic voltammograms of 1, 2, and 3 show the reversible oxidation
wave of the ferrocenyl group, and that of 4 shows that this wave appears with increased intensity tentatively
attributable to redox-catalyzed oxidation.
Introduction
has been made in inorganic chemistry, however, although
the disubstituted 1,2,3-triazole ligands formed in this click
reaction can also coordinate transition metals. Indeed, we
recently reported the synthesis of ferrocenyl triazolyl den-
drimers that can recognize and sense several transition metal
ions by using the variation of the potential of the ferrocenyl
wave.6a Titration of the ions could be carried out in order to
Triazole ligands have been known for a long time, and
their coordination has been investigated with a variety of
transition metals.1–3 Recently, the dipolar Huisgen-type
cycloaddition4 between alkynes and azido derivatives, made
selective, catalytic, and convenient and called “click”
chemistry, has been widely used in organic and bio-organic
chemistry.5 These highlighted advantages have considerably
renewed the interest in 1,2,3-triazolyl derivatives. Little use
(5) (a) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed.
2001, 40, 2004–2021. (b) Tornoe, C.; Christensen, C.; Meldal, M. J.
Org. Chem. 2002, 67, 3057. (c) Rostovtsev, V. V.; Green, L. G.; Fokin,
V. V.; Sharpless, K. B. Angew. Chem., Int. Ed. 2002, 42, 2596. (d)
Bock, V. D.; Hiemstra, H.; van Maarseveen, J. H. Eur. J. Org. Chem.
2006, 51–68. (e) Moses, A. D.; Moorhouse, A. D. Chem. Soc. ReV.
2007, 36, 1249–1262.
* To whom correspondence should be addressed. E-mail: d.astruc@ism.u-
bordeaux1.fr. Fax: (33) 540 00 66 46.
†
Universite´ Bordeaux 1.
Universite´ Fre`res Mentouri.
Laboratoire de Chimie de Coordination.
‡
(6) (a) Ornelas, C.; Ruiz, J.; Cloutet, E.; Alves, S.; Astruc, D. Angew.
Chem., Int. Ed. 2007, 46, 872–877. (b) Diallo, A. K.; Ornelas, C.;
Salmon, L.; Ruiz, J.; Astruc, D. Angew. Chem., Int. Ed. 2007, 46,
8644–8648. (c) Ornelas, C.; Salmon, L.; Ruiz, J.; Astruc, D. Chem.
Commun. 2007, 4946–4948. (d) Ornelas, C.; Salmon, L.; Ruiz, J.;
Astruc, D. Chem.sEur. J. 2008, 14, 50–64. (e) Astruc, D.; Ruiz, J.;
Ornelas, C. J. Inorg. Organomet. Polym. Mater. 2008, 18, 4–17. (f)
Candelon, N.; Laste´coue`res, D.; Diallo, A. K.; Ruiz, J.; Astruc, D.;
Vincent, J.-M. Chem. Commun. 2008, 741–743. (g) Ornelas, C.;
Salmon, L.; Ruiz, J.; Astruc, D. AdV. Synth. Catal. 2008, 18, 4–17.
§
(1) Barz, M.; Herdtweck, E.; Thiel, W. R. Angew. Chem., Int. Ed 1998,
37, 2262–2265.
(2) PtII complexes: Komeda, S.; Lutz, M.; Spek, A. L.; Yamanaka, Y.;
Sato, T.; Chikuma, M.; Reedjik, J. J. Am. Chem. Soc. 2002, 124, 4738–
4746.
(3) CuI complexes: Chan, T. R.; Hilgraf, R.; Sharpless, K. B.; Fokin, V. V.
Org. Lett. 2004, 6, 2853–2855.
(4) Huisgen, R. Angew. Chem., Int. Ed. Engl. 1968, 7, 321–328.
10.1021/ic8002405 CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 11, 2008 4903
Published on Web 04/25/2008

Bade`che et al.
determine the number of PdII ions that bound triazole ligands
inside the dendrimer.6b The resulting ligand-PdII interaction
allowed the designing of Pd nanoparticles (NPs) of precise
sizes for mechanistic investigation of their catalytic effi-
ciency.6b–d
Therefore, we wished to investigate simple but precise
coordination modes of nondendritic disubstituted 1,2,3-
triazolylferrocene ligands resulting from click reactions
between ethynylferrocene and simple terminal alkynes. Here,
we report such studies involving mono-, di-, and triazides
1
as well as H NMR, electrochemical, and X-ray structural
cm–1) in the IR spectrum, by the characteristic position of
the triazolyl proton signal at 8.1 ppm versus TMS in DMSO-
d6 in H NMR, and by elemental analysis. In addition, the
ferrocene signals in 1H NMR are characteristic, with the free
Cp being found at 4.0 ppm, whereas the protons of the
substituted cyclopentadienyl are located downfield at 4.70
ppm for the R protons and 4.28 ppm for the ꢀ proton. Finally,
the X-ray crystal structure of 1 could be solved (Figure 1).
studies of the interaction of some mono-1,2,3-triazolylfer-
rocene derivatives with several transition metal compounds
in dimethylsulfoxide (DMSO). There are a few reports of
click reactions between azido derivatives and ethynylfer-
rocene, in polymer7 and surface8 chemistry.
1
Results and Discussion
Synthesis of Mono-, Bis-, and Tris(1,2,3-ferrocenyl-
triazole) Derivatives. We started from 4-methoxybenzyl-
bromide, which was easily converted to 4-methoxybenzyl-
azide9 upon reaction with sodium azide in DMSO. Then,
reaction of the latter with ethynylferrocene in THF/water in
the presence of catalytic amounts of copper sulfate and
sodium ascorbate under ambient conditions led to the
formation of the 1,2,3-ferrocenyltriazole (1) in a 67.7% yield
of orange microcrystals (eq 1). Similarly, p-dibromomethyl-
Reaction of p-Methoxybenzyl-1,2,3-triazolylferrocene
(1) with PdCl2(C6H5CN)2 and Compared X-ray Crystal
Structures of 1 and Its PdIICl2 Complex 4. The reaction
of [PdCl2(C6H5CN)2] with 1 (eq 1) was carried out under
benzene was converted to p-diazidomethylbenzene,9a,b and
the click reaction under the same conditions yielded bis(fer-
rocenyl-1,2,3-triazolylmethyl)benzene (2) in a 45% yield of
yellow-orange microcrystals (eq 2). Finally, tris(1,3,5-
bromomethyl)benzene was similarly converted to tris-1,3,5-
tris(azidomethyl)benzene,9c and the reaction of the latter with
ethynylferrocene yielded tris-1,3,5-tri(ferrocenyl-1,2,3-tri-
azolymethyl)benzene (3) in a 27% yield of orange-brown
microcrystals (eq 3). These 1,2,3-ferrocenyltriazole deriva-
tives were characterized by the lack of an azide band (2095
1
ambient conditions in toluene. The H NMR spectrum of
the crude reaction product in DMSO-d6 showed both series
of signals of the Pd-coordinated and the noncoordinated
triazole compounds. Crystallization of the crude reaction
product in DMSO-d6 yielded light brown crystals of the Pd
complex 4 that were subjected to X-ray crystal structure
analysis. The X-ray crystal structures of 1 and 4 are compared
(Table 1).
The structure of compound 1 obtained by X-ray diffraction
is presented in Figure 1 and shows the occurrence of two
nearly identical molecules (A and B) within the asymmetric
unit. In both molecules, the two Cp rings make a tilt angle
of 2.1(3)° [0.7(3)°], and they are roughly eclipsed with a
twist angle of 2.4(3)° [1.8(3)°]. The other geometrical
parameters within the ferrocene framework are as usually
observed. As expected, the triazole ring is planar, and it is
slightly twisted with respect to the Cp ring to which it is
(7) Jim, C. K. W.; Qin, A.; Lam, J. W. Y.; Haussler, M.; Tang, B. Z.
J. Inorg. Organomet. Polym. Mater. 2007, 17, 289–293.
(8) (a) Devadoss, A.; Chidsey, C. E. D. J. Am. Chem. Soc. 2007, 129,
5370–5371. (b) Collman, J. P.; Devaraj, N. K.; Eberspacher, T. P. A.;
Todd, P. A.; Chidsey, C. E. D. Langmuir 2006, 22, 2457–2464. (c)
Collman, J. P.; Devaraj, N. K.; Chidsey, C. E. D. Langmuir 2004, 20,
1051–1053.
(9) (a) Sommers, A. H.; Barnes, J. D. J. Am. Chem. Soc. 1957, 79, 3491–
3492. (b) Richards, J. P.; Amyes, T. L.; Stevens, I. W. Tetrahedron
Lett. 1991, 32, 4255–4258. (c) Heyer, D.; Lehn, J.-M. Tetrahedron
Lett. 1986, 27, 5869–5872.
4904 Inorganic Chemistry, Vol. 47, No. 11, 2008

Chemistry of Ferrocenyl-1,2,3-triazolyl Ligands
Figure 2. Molecular view of compound 4 with the atom-labeling scheme.
Displacement ellipsoids are drawn at the 30% probability level. H atoms
have been omitted for clarity.
Figure 1. Molecular view of compound 1 with the atom-labeling scheme.
Displacement ellipsoids are drawn at the 30% probability level. H atoms
have been omitted for clarity.
Table 2. Comparison of Selected Parameters within the Free Ligand 1
and the Complex 4 (Å, deg)
Table 1. Crystal Data and Structure Refinement
1A
1B
4
1
4
Fe(1)-Cg(1)
1.6438(16)
1.6453(18)
1.6444(16)
1.6452(17)
1.642(2)
1.649(3)
empirical formula
C40H38Fe2N6O2
C20H19ClFeN3OPd0.50
0.33(H2O)
467.89
·
Fe(1)-Cg(2)
C(1)-N(1)
fw
T, K
746.46
180(2)
N(1)-N(2)
1.322(3)
1.345(4)
1.362(4)
1.348(4)
1.453(4)
1.323(4)
1.333(4)
1.360(4)
1.343(4)
1.468(4)
1.328(4)
1.333(4)
1.344(4)
1.328(5)
1.475(5)
1.993(3)
2.2866(10)
177.46(4)
111.5(3)
112.0(3)
104.9(3)
120.3(3)
127.7(3)
106.0(3)
105.7(3)
127.0(3)
127.4(3)
89.88(9)
90.12(9)
180(2)
N(2)-N(3)
cryst syst
space group
a, Å
b, Å
c, Å
monoclinic
P21/n
9.6335(7)
33.4307(18)
11.3666(8)
90.0
114.273(9)
90.0
3337.1(4)
4
trigonal
R3
27.4194(7)
27.4194(7)
13.5881(4)
90.0
90.0
120.0
8847.2(4)
18
1.581
N(1)-C(11)
j
N(3)-C(12)
N(3)-C(13)
Pd(1)-N(1)
Pd(1)-Cl(1)
R, deg
Cg(1)-Fe(1)-Cg(2)
N(2)-N(1)-C(11)
C(12)-N(3)-N(2)
N(1)-N(2)-N(3)
N(2)-N(3)-C(13)
C(12)-N(3)-C(13)
N(3)-C(12)-C(11)
N(1)-C(11)-C(12)
N(1)-C(11)-C(1)
C(12)-C(11)-C(1)
N(1)a-Pd(1)-Cl(1)
N(1)-Pd(1)-Cl(1)
178.62(10)
179.47(9)
ꢀ, deg
γ, deg
V, Å3
Z
Dcalcd, Mg/m3
µ, mm-1
F(000)
1.486
0.917
1552
1.362
4272
cryst size, mm3
θ range, deg
reflns collected
unique reflns [Rint
0.383 × 0.115 × 0.077 0.281 × 0.222 × 0.162
2.64-26.37
25 882
2.97-26.37
23 181
4029 [0.0282]
3133
]
6810 [0.0687]
a The symmetry code used to generate equivalent atoms: -x + 1, -y,
-z + 2.
obsd reflns [I > 2σ(I)] 2865
completeness
abs correction
Tmin/Tmax
99.9
99.8
multiscan
1.0/0.85835
453
multiscan
1.0/0.69297
251
The asymmetric unit is built up from half of the complex
and contains 0.33 solvate water molecules. As observed in
Table 2, the coordination to the Pd atom through the N1
atom does not affect significantly the geometry of the ligand.
The largest differences appear in the dihedral angle between
the triazolyl ring and the Cp ring to which it is attached,
14.2(3)° compared to 17° (mean value), and the tilt angle
between the two Cp rings, 3.7(4)° in place of 1.5° (mean
value). A ConQuest search of the Cambridge Structural
params
GOF on F2
0.876
1.043
R1, wR2 [I > 2σ(I)]
0.0356, 0.0644
0.1116, 0.0845
-0.440, 0.351
0.0373, 0.0936
0.0542, 0.1080
-0.868, 1.206
R1, wR2 (all data)
∆Fmin, ∆Fmax (e·Å-3
)
attached, making a dihedral angle of 17.3(2)° [16.9(2)°]. The
largest difference between the two molecules building the
asymmetric unit is reflected in the dihedral angle between
the methoxy substituted phenyl ring and the triazole, which
is 87.0(1)° for molecule A, as compared to 69.3(1)° for
molecule B.
The structure of the Pd complex 4 is presented in Figure
2. The Pd atom is located on an inversion center and displays
a nearly perfect square planar environment with two N atoms
from a symmetry-related ligand and two Cl atoms trans to
each other. The triazolyl ring is nearly perpendicular to the
Pd square plane with a dihedral angle of 84.1(1)°. The two
p-methoxybenzyltriazolylferrocene ligands are coordinated
to PdCl2 in the trans position via a Pd-N bond in the ꢀ
position with respect to the ferrocenyl ring.
(10) Bruno, I. J.; Cole, J. C.; Edgington, P. R.; Kessler, M.; Macrae, C. F.;
McCabe, P.; Pearson, J.; Taylor, R. Acta Crystallogr., Sect. B: Struct.
Sci. 2002, 58, 389–397.
(11) Cotton, F. A.; Francis, R. J. Am. Chem. Soc. 1960, 82, 2986–2991.
(12) Meek, D. W.; Straub, D. K.; Drago, D. S. J. Am. Chem. Soc. 1960,
82, 6013–6016.
(13) Gopalakrisnan, J.; Patel, C. C. J. Sci. Ind. Res. 1968, 27, 475.
(14) (a) Bennett, M. J.; Cotton, F. A.; Weaver, D. L. J. Acta Crystallogr.
1967, 23, 581–586. (b) Bennett, M. J.; Cotton, F. A.; Weaver, D. L.;
Williams, R. J.; Watson, W. H. Acta Crystallogr. 1967, 23, 788–796.
(15) Kitching, W.; Moore, C. J.; Doddrell, D. Inorg. Chem. 1970, 9, 541–
549.
(16) Clark, H. C.; Ferguson, G.; Jain, V. K.; Parvez, M. Inorg. Chem. 1985,
24, 1477–1482.
Inorganic Chemistry, Vol. 47, No. 11, 2008 4905

Bade`che et al.
Scheme 1
[PdCl2(MeCN)2] or [PdCl2(PhCN)2] is added to 1 in DMSO-
d6, this same new set of signals is observed, and their
intensity increases as more Pd-nitrile complex is added until
complete disappearance with 2 equiv of Pd-nitrile complex
(Figure 3). The fact that the same new spectrum appears in
these different conditions is consistent with the formula of
4 that does not contain solvent ligand but only the two
triazoles in the trans positions shown in the X-ray crystal
structure of 4. In DMSO- d6 only, minor signals are also
observed. The relative intensity of these minor signals
remains constant compared to those of the major signals as
more PdCl2 is added, which discards the presence of a
monotriazole complex. Their attribution is uncertain, but they
might be due to a chloro-bridged dinuclear Pd complex
formed in small amounts.
The fact that a monosubstituted complex [PdCl2(S)L] (S
) DMSO-d6 or PhCN; L ) 1) is not observed by 1H NMR,
indicating that its formation may only occur in a small
amount, is presumably due to the trans effect of the triazole
ligand that favors substitution of the ligand in the trans
position.17,18
With [Pd(OAc)2], a similar behavior is observed. A yellow-
orange color appears as well as a single set of new 1H NMR
signals shifted downfield, and full coordination of 1 is
observed after adding 4 equiv of [Pd(OAc)2] to 1. For
instance, the triazole proton is shifted downfield by 0.45 ppm.
With [Pd(OAc)2], this downfield shift is 0.4 ppm. This
downfield shift is only 0.23 ppm with [PdCl2(MeCN)2] in
CD3CN.
With [Cu(MeCN)4][BF4], a yellow color develops, and the
addition of 1 equiv to 1 in DMSO-d6 provokes a downfield
shift of all the signals of 1; the triazole proton is shifted by
0.2 ppm.
Database (CSD) reveals that such an eclipsed conformation
for a substituted ferrocene is quite common.
1H NMR Study of the Interaction of Transition
Metal Complexes with 1 in DMSO. The complexes
[MCl2(DMSO)2] (M ) Pd or Pt) are well-known11–16 and
have been largely studied. DMSO is a solvent that solubilizes
both 1 and transition metal mono- or dichlorides or acetates.
PdCl2 is a chloro-bridged polymer that depolymerizes in
DMSO solution. It forms the square-planar 16-electron d8
complex [PdCl2(DMSO)2] in which cis/trans isomerization
rapidly proceeds by pseudorotation of five-coordinate inter-
mediates in the presence of excess DMSO.15 The complex
[PdCl2(DMSO)2] is preferably trans with S coordination,
whereas the complex [PtCl2(DMSO)2] is preferably cis with
S coordination.15 Although dinuclear chloro-bridged Pd
complexes are known to form in solution, they lead to the
mononuclear complexes in the presence of a neutral do-
nor.15,16 Thus, in the present situation, where DMSO is in
large excess, essentially the mononuclear trans PdII (and cis
PtII) complexes are present. The situation is summarized in
Scheme 1 for PdII, with only the framed PdII complexes being
observed.
With [PtCl2(DMSO)2], a yellow solution forms, but full
complexation of 1 is never completely reached even after
addition of 8 equiv of metal complex to 1 in DMSO-d6 (only
1
84% complexation), although all the H NMR signals are
shifted downfield as well upon complexation of 1 with PtII.
With Cu(BF4)2, Cu(NO3)2, CuSO4 · 5H2O, NiCl2, HgCl2,
FeCl2, AgNO3, CdCl2, and SnCl2, which are soluble in
DMSO, the interaction of these salts with 1 or 2 in
homogeneous DMSO-d6 solutions does not result in any 1H
NMR signal shift when up to a 4-fold excess of 1 is added.
Thus, it appears that the DMSO-d6 ligands are not substituted
by 1 in the presence of excess DMSO-d6 with these metal
salts.
Electrochemical Study of Complexes 1-4 in DMSO.
Complexes 1-4 were studied by cyclic voltammetry in
DMSO solution on a Pt anode with 0.1 M tetrabutylammo-
nium hexafluorophosphate as the supporting electrolyte, and
the classic reversible ferrocenyl wave19a,b,20 of the FeIII/FeII
Upon addition of PdCl2 to 1 in DMSO-d6, a major set of
new signals (deshielded when compared to the signals of 1)
is observed in addition to the signals of 1. The triazole proton
at 8.6 ppm (deshielded by 0.35 ppm relative to 1) and the
two protons of the cyclopentadienyl in the R position at 5.6
ppm (deshielded by 0.9 ppm) are especially characteristic.
The signals of 1 progressively decrease as more PdCl2 is
added, and it is necessary to add up to 4 equiv of PdCl2 to
see the signals of 1 disappearing. This is the sign of an
equilibrium, as indicated in Scheme 1. Consistently, the
spectrum of 4 in DMSO-d6 shows a high proportion of
dissociated 1 in addition to the same new spectrum. If
(17) Kauffmann, G. B. J. Chem. Educ. 1977, 54, 86–89.
(18) Astruc, D. Organometallic Chemistry and Catalysis; Springer: Berlin,
Germany, 2007; p 123.
(19) (a) Astruc, D. Electron Transfer and Radical Processes in Transition
Metal Chemistry; VCH: New York, 1995. (b) Reference 19a, p 142.
(c) Reference 19a, p 482.
(20) Geiger, W. E. Organometallics 2007, 26, 5738–5765.
(21) (a) Ruiz, J.; Astruc, D. C. R. Acad. Sci., Ser. IIc 1998, 21–27. (b)
Ruiz, J.; Daniel, M.-C.; Astruc, D. Can. J. Chem. 2006, 84, 288–299.
4906 Inorganic Chemistry, Vol. 47, No. 11, 2008

Chemistry of Ferrocenyl-1,2,3-triazolyl Ligands
Figure 3. 1H NMR spectrum of 1 in DMSO-d6 upon addition of [PdCl2(C6H5CN)2]: (A) 1 alone; (B) 1 equiv of 1 and 0.5 equiv of [PdCl2(C6H5CN)2]; (C)
1 equiv of 1 and 1 equiv of [PdCl2(C6H5CN)2]; (D) 1 equiv of 1 and 1.5 equiv of [PdCl2(C6H5CN)2]; (E) 1 equiv of 1 and 2 equiv of [PdCl2(C6H5CN)2].
linkers in bio-organic chemistry. Given the potential of these
ligands to bind, recognize, and sense transition metals, it was
informative to investigate the synthetic and structural aspects
of PdII complexes, probably the most studied metal with this
series of ligands. The compared crystal structures of 1 and
4 show the weak structural changes within the triazole ring
occurring upon coordination, the coordination site of the
triazole nitrogen atom in the R position, and finally the
remarkable shielding of the imidazole and the ferrocenyl
protons in 1H NMR. From the 1H NMR study, we also learn
the fragility of the ligand binding probably related to the
steric effect of the disubstituted PdII complex, for which
Figure 4. Cyclic voltammetry of 1 and 4 (that partly dissociates in DMSO
solution to 1 and [PdCl2(DMSO)2], as shown by 1H NMR (see text and
Scheme 1). Solvent, DMSO; temperature, 20 °C; supporting electrolyte,
0.1 M [n-Bu4N][PF6]; working and counter electrodes, Pt; reference
electrode, Ag; scan rate, 0.200 V ·s-1; internal reference, decamethylfer-
rocene.
equilibriums are observed between the DMSO, nitriles, and
triazole ligands. In electrochemistry, the behavior in DMSO
is strongly induced by this special solvent and is very
different from the trends observed in methylene chloride,
which allowed sensing the oxo-anions and metal cations.
redox system was recorded at 0.5 V versus decamethylfer-
rocene used as an internal reference.21 Only one reversible
ferrocenyl wave is observed for each of the four compounds,
indicating that the ferrocenyl redox systems are independent
in 2 and 3 (the electrostatic factor is extremely small). In
the case of 4, the anodic part of the ferrocenyl wave is
broader, which may be attributed to an electrocatalytic
process corresponding to the oxidation of chloride to
chlorine.19a,c This process should be facilitated by the fact
that the ferrocenyl and the chloride are connected (inner-
sphere process) via the PdII. This same electrocatalytic wave
also appears when PdCl2 is added to the electrochemical cell
containing the DMSO solution of 1 (Figure 4).
Experimental Section
General Data. p-Methoxybenzylazide and p-diazidomethylben-
zene were synthesized from p-methoxybenzylbromide and p-
dibromomethylbenzene, respectively, according to Sommers and
Barnes (i.e., by reaction with NaN3 in DMF under ambient
conditions).9a,b The same procedure was used with 1,3,5-tris(bro-
momethyl)benzene for the synthesis of 1,3,5-tris(azido-
methyl)benzene.9c [PdCl2(CH3CN)2] was synthesized according to
Komiya.22 The complex [Cu(CH3CN)4BF4] was synthesized ac-
cording to Kubas.23 Ethynylferrocene, phenylacetylene, and
[Cu(BF4)2] were purchased from Sigma-Aldrich. [PdCl2(C6H5CN)2],
(22) Komiya, S. Synthesis of Organometallic Compounds, A Practical
Guide; Wiley: New York, 1996.
(23) Kubas, G. J. Inorg. Synth. 1979, 19, 90.
Concluding Remarks. Click chemistry now very easily
provides access to disubstituted 1,2,3-triazoles that serve as
Inorganic Chemistry, Vol. 47, No. 11, 2008 4907

Bade`che et al.
FeCl2, CuSO4 ·5H2O, NiCl2, AgNO3, and CdCl2 were purchased
from Strem and used as received. The 1H NMR spectra were
recorded at 25 °C with a Brucker AC (300 MHz) spectrometer.
The 13C NMR spectra were obtained in the pulsed FT mode at
75.0 MHz with a Brucker AC 300 spectrometer. All chemical shifts
are reported in parts per million (δ, ppm) with reference to Me4Si
(TMS). All the electrochemical measurements were recorded on a
PAR 273 apparatus under a nitrogen atmosphere. The conditions
are as follows: solvent, DMSO; temperature, 20 °C; supporting
electrolyte, 0.1 M [n-Bu4N][PF6]; working and counter electrodes,
Pt; reference electrode, Ag; internal reference, FeCp*2 (Cp* ) η5-
145.51 (Cq, triazole), 129.27 (CH, arom), 120.39 (CH, triazole),
(CH, arom), 75.94, (Cq, Cp), 69.16 (CH, Cp), 68.17 (CH, Cp),
66.26 (CH, Cp), 52.29 (CH2). Anal. Calcd for C45H39Fe3N9: C,
61.88; H, 4.5. Found: C, 61.09; H, 4.54. E1/2 ) 0.53 V versus
decamethylferrocene, reversible.
Synthesis of 4. [PdCl2(C6H5CN)2] (0.05 g), ferrocenyltriazole
(1, 0.12 g), and 50 mL of toluene were introduced under an inert
atmosphere into a Schlenk flask. The solution was stirred at room
temperature for 2.5 h. After the solvent was removed under vacuum,
1
the product was washed twice using diethylether. The H NMR
spectrum of the crude reaction product in DMSO-d6 showed both
series of signals of the Pd-coordinated and the noncoordinated
triazole compounds. Crystallization of the crude reaction product
in DMSO-d6 yielded light brown crystals of the Pd complex 4. 1H
NMR (DMSO-d6, 300 MHz): 8.59 (s, 1H of 4), 8.16 (s, 1H of 1),
C5Me5); scan rate, 0.200 V ·s1-
.
General Procedure for the Click Reactions. The benzylazido
derivative (1 equiv) and ethynylferrocene (1.5 equiv per branch)
were dissolved in THF, and water was added (THF/water ) 1:1).
At 208 °C, CuSO4 (1 M aqueous solution, 1 equiv per azido group)
was added, and then, a freshly prepared solution of sodium ascorbate
(1 M aqueous solution, 2 equiv per azido group) was added
dropwise. The solution was then stirred for 2 h at room temperature.
After removing the THF under vacuum, dichloromethane and an
aqueous solution of ammonia were added. The mixture was stirred
for 10 min to remove all the CuI derivative trapped inside the
product as [Cu(NH3)6]+. The organic phase was washed twice with
water and filtered through Celite, and the solvent was removed
under vacuum. The product was washed with pentane to remove
the excess of ethynylferrocene and precipitated by addition of
dichloromethane/pentane. The ferrocenyl triazoles were obtained
as orange-brown microcrystals. The elemental analyses were
performed by the Center of Microanalyses of the CNRS at Lyon
Villeurbanne, France.
3
3
7.22 (d, 2H, J ) 9, of 1 and 4), 6.94 (d, 2H, J ) 9, of 1 and 4),
5.61 (s, 2H of 4), 5.50 (s, 2H of 1 and 4), 4.69 (s, 2H of 1), 4.46
(s, 2H of 4), 4.28 (s, 2H of 1), 4.15 (s, 5H of 4), 409 (s, 5H of 1),
3.73 (s, 3H of 1 and 4). Anal. Calcd for C40H38Cl2Fe2N6O2Pd: C,
52.00; H, 4.14. Found: C, 53.36; H, 4.12. E1/2 ) 0.53 V versus
decamethylferrocene, reversible; ipc/ipa ) 0.45.
X-ray Crystallography. A single crystal of each compound was
mounted under inert perfluoropolyether at the tip of a glass fiber
and cooled in the cryostream of an Oxford-Diffraction XCALIBUR
CCD diffractometer. Data were collected using monochromatic Mo
KR radiation (λ ) 0.71073).
The structures were solved by direct methods (SIR97)22 and
refined by least-squares procedures on F2 using SHELXL-97.23 All
H atoms attached to carbon were introduced in idealized positions
and treated as riding on their parent atoms in the calculations. In
molecule 4, there is a water molecule statistically distributed over
three positions occupying a void in the structure located around
the threefold axis, leading to a total amount of six water molecules
within the unit cell. The drawing of the molecules was realized
with the help of ORTEP-3 for Windows.24 Crystal data and
refinement parameters are shown in Table 1. Bond distances and
angles are given in Table 2.
Synthesis of 1. The reaction between p-methoxybenzylazide
(0.32 g, 1.96 mmol) and ethynylferrocene (0.62 g, 2.94 mmol) was
carried out using the above general procedure for click reactions.
Ferrocenyltriazole (1) was obtained as orange microcrystals (0.5g,
67.7% yield). 1H NMR (DMSO-d6, 300 MHz): 8.17 (s, 1H,
3
3
triazole), 7.28 (d, 2H, J ) 9, arom), 6.94 (d, 2H, J ) 9, arom),
5.55 (s, 2H), 4.7 (s, 2H, HR of Cp), 4.28 (s, 2H, Hꢀ of Cp), 4.02 (s,
5H, Cp), 3.73 (s, 3H). 13C NMR (DMSO-d6, 75.5 MHz): 159.04
(Cq, arom), 145.51 (Cq, triazole), 129.27 (CH, arom), 120.39 (CH,
triazole), 114.08 (CH, arom), 75.94 (Cq, Cp), 69.16 (CH, Cp), 68.17
(CH, Cp), 66.26 (CH, Cp), 55.09 (CH3), 52.29 (CH2). Anal. Calcd
for C20H19FeN3O: C, 64.36; H, 5.13. Found: C, 64.12; H, 5.19.
E1/2 ) 0.53 V versus decamethylferrocene, reversible.
Crystallographic data (excluding structure factors) have been
deposited with the Cambridge Crystallographic Data Center as
supplementary publication no. CCDC 685263 and 685264. Copies
of the data can be obtained free of charge on application to the
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax:
(+44) 1223-336-033. e-mail: deposit@ccdc.cam.ac.uk).
Synthesis of 2. The reaction between p-diazidomethylbenzene
(0.2 g, 1.06 mmol) and ethynylferrocene (0.67 g, 3.18 mmol) was
carried out using the general procedure for click reactions and
yielded yellow-orange microcrystals of bis(ferrocenyl-1,2,3-triaz-
olylmethyl)benzene (2) (0.29 g, 45% yield). 1H NMR (DMSO-d6,
300 MHz): 8.20 (s, 2H, triazole), 7.31 (s, 4H, arom), 5.59 (s, 4H),
4.69 (s, 4H, HR of Cp), 4.28 (s, 4H, Hꢀ of Cp), 4.00 (s, 10H, Cp).
13C NMR (DMSO-d6, 75.5 MHz): 129.27 (CH, arom), 120.39 (CH,
triazole), 75.94 (Cq, Cp), 69.16 (CH, Cp), 68.17 (CH, Cp), 66.26
(CH, Cp), 52.29 (CH2). Anal. Calcd for C32H28Fe2N6: C, 63.18; H,
4.64. Found: C, 63.40; H, 4.93. E1/2 ) 0.53 V versus decameth-
ylferrocene, reversible.
Acknowledgment. Financial support from the CNRS, the
Institut Universitaire de France (DA), the Agence Nationale
de la Recherche (ANR-06-NANO-026-01, project 0169), and
the Universite´ Bordeaux 1 is gratefully acknowledged.
Supporting Information Available: 1H NMR spectra of 1 and
1
4 in DMSO-d6 and H NMR spectra of 1 + [Pd(CH3CN)2Cl2], 1
+ [Cu(CH3CN)4Cl2], and 1 + PtCl2 in DMSO-d6. This material is
available free of charge via the Internet at http://pubs.acs.org.
IC8002405
Synthesis of 3. The reaction between 0.135 g (0.55 mmol) of
tris(azidomethyl)benzene and 0.52 g (2.48 mmol) using the general
procedure for click reactions gave tri(ferrocenyl-1,2,3-triazolyl-
methyl)benzene (3) as orange-brown microcrystals. The yield was
0.13 g, 27%. 1H NMR (DMSO-d6, 300 MHz): 8.16 (s, 3H, triazole),
7.22 (s, 4H, arom), 5.95 (s, 6H), 4.68 (s, 6H, HR of Cp), 4.28 (s,
6H, Hꢀ of Cp), 4.02 (s, 15H, Cp). 13C NMR (DMSO-d6, 75.5 MHz):
(24) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115–119, SIR97sa program for
automatic solution of crystal structures by direct methods.
(25) Sheldrick, G. M. SHELXL97, Program for Crystal Structure Refine-
ment; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(26) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565, ORTEP-3 for
Windows.
4908 Inorganic Chemistry, Vol. 47, No. 11, 2008