From simple monopyridine clusters [Mo6Br13(Py-R)][n- Bu4N] and hexapyridine clusters [Mo6X8(Py-R) 6][OSO2CF3]4 (X = Br or I) to cluster-cored organometallic stars, dendrons, and dendrimers

Article abstract of DOI:10.1021/ic051680f

Hexasubstitution of apical triflate ligands in the octahedral clusters [M]₂[Mo₆X₈(CF₃SO₃) ₆] (M = n-Bu₄N or Cs, X = Br or I) and monosubstitution in [n-Bu₄N]₂[Mo₆Br₁₃(CF ₃SO₃)] was carried out in tetrahydrofuran at 60°C with simple pyridines and then extended to organometallic pyridines, yielding cluster-cored stars, and to dendronic polyallyl-and polyferrocenylpyridines, yielding cluster-cored polyallyl and polyferrocenyl dendrimers and dendrons. The orange pyridine-substituted clusters, whose pyridine protons are deshielded in ¹H NMR (a practical tool for characterization), are air-stable and thermally stable with simple pyridines, light- and air-sensitive with organometallic pyridines, and air-fragile and thermally fragile with large dendronized pyridines.

Full text of DOI:10.1021/ic051680f

Inorg. Chem. 2006, 45, 1156−1167
From Simple Monopyridine Clusters [Mo6Br13(Py-R)][n-Bu4N] and
Hexapyridine Clusters [Mo6X8(Py-R)6][OSO2CF3]4 (X Br or I) to
)
Cluster-Cored Organometallic Stars, Dendrons, and Dendrimers
Denise Me´ry,† Lauriane Plault,† Ca´tia Ornelas,† Jaime Ruiz,† Sylvain Nlate,† Didier Astruc,*,†
Jean-Claude Blais,‡ Joa˜o Rodrigues,§ Ste´phane Cordier,| Kaplan Kirakci,| and Christiane Perrin*,|
Nanosciences and Catalysis Group, LCOO, UMR CNRS No. 5802, UniVersite´ Bordeaux 1,
351 cours de la Libe´ration, 33405 Talence Cedex, France, LCSOB, UMR CNRS No. 7613,
UniVersite´ Paris VI, 75252 Paris Cedex, France, Centro de Qu´ımica da Madeira, LQCMM,
Departamento de Qu´ımica, UniVersidade da Madeira, Campus da Penteada, 9000-390 Funchal,
Portugal, and Laboratoire de Chimie du Solide et Inorganique Mole´culaire, Institut de Chimie de
Rennes, UMR CNRS No. 6511, UniVersite´ de Rennes 1, AV. du Ge´ne´ral-Leclerc,
35042 Rennes Cedex, France
Received September 29, 2005
Hexasubstitution of apical triflate ligands in the octahedral clusters [M]2[Mo6X8(CF3SO3)6] (M
)
n-Bu4N or Cs, X
)
Br or I) and monosubstitution in [n-Bu4N]2[Mo6Br13(CF3SO3)] was carried out in tetrahydrofuran at 60
°C with simple
pyridines and then extended to organometallic pyridines, yielding cluster-cored stars, and to dendronic polyallyl-
and polyferrocenylpyridines, yielding cluster-cored polyallyl and polyferrocenyl dendrimers and dendrons. The orange
pyridine-substituted clusters, whose pyridine protons are deshielded in 1H NMR (a practical tool for characterization),
are air-stable and thermally stable with simple pyridines, light- and air-sensitive with organometallic pyridines, and
air-fragile and thermally fragile with large dendronized pyridines.
Introduction
potential of octahedral hexametallic clusters to be used as
starting points for the synthesis of molecular assemblies and
nanosized materials with catalytic and unusual physical
properties.5 Among these clusters based on early-transition
elements, the hexamolybdenum series built up from
[Mo6X14]2- units (X ) Cl, Br, I) constitute relevant starting
materials easily available from inorganic solids that have
been structurally characterized 60 years ago.6 The octahedral
molybdenum clusters became most popular when the super-
conducting properties of the related chalcogenides MxMo6Y8
(Y ) chalcogen), known as Chevrel phases, were discov-
ered.7 Photophysical and redox properties of [Mo6X14]2-
added further interest.8 Among the 14 halide ligands, the 8
Octahedral clusters have been shown by Zheng’s group1
with hexarhenium selenides to serve as versatile building
blocks for the synthesis of various architectures including
dendrimers,1b,2 and coordination networks with structures
constructed from hexatungsten sulfides have been disclosed
by the DiSalvo group.3 Other groups have utilized metal
clusters for the design of extended molecular arrays,4 but
the two above-mentioned successful examples illustrate the
* To whom correspondence should be addressed. E-mail: diastruc@
lcoo.u-bordeaux1.fr (D.A.).
† Universite´ Bordeaux 1.
‡ Universite´ Paris VI.
§ Universidade da Madeira.
| Universite´ de Rennes 1.
(4) (a) Rosi, N.; Eckert, J.; Eddaoudi, M.; Vodak, D. T.; Kim, J.; O’Keefe,
M.; Yaghi, O. M. Science 2003, 300, 1127. (b) Seo, J. S.; Whang, D.;
Lee, H.; Jun, S. I.; Oh, J.; Jeon, Y. J.; Kim, K. A. Nature 2000, 404,
982. (c) Bain, R. L.; Shriver, D. F.; Ellis, D. E. Inorg. Chim. Acta
2001, 325, 171.
(1) (a) Selby, H. D.; Roland, B. K.; Zheng, Z. Acc. Chem. Res. 2003, 36,
933. (b) Wang, R.; Zheng, Z. J. Am. Chem. Soc. 1999, 121, 3549. (c)
Roland, B. K.; Carter, C.; Zheng, Z. J. Am. Chem. Soc. 2002, 124,
6234.
(2) (a) Newkome, G. R.; Moorefield, C. N.; Vo¨gtle, F. Dendrimers and
Dendrons: Concepts, Syntheses and Applications; Wiley-VCH: New
York, 2001. (b) Dendrimers and Other Dendritic Polymers; Tomalia,
D., Fre´chet, J. M. J., Eds.; Wiley-VCH: New York, 2002. (c)
Dendrimers and Nanoscience; Astruc, D., Ed.; Elsevier: Paris, 2003;
Vols. 8-10, p 6.
(5) (a) Golden, J. H.; Deng, H.; DiSalvo, F. J.; Fre´chet, J. M. J.; Thompson,
P. M. Science 1995, 268, 1463. (b) Ziolo, R. F. Science 1992, 257,
219. (c) Real, J. A.; Andre´r, E.; Mun˜oz, M. C.; Julve, M.; Granier,
T.; Bousseksou, A.; Varret, F. Science 1995, 268, 265. (d) Dunbar,
K. R. Inorg. Chem. 1992, 13, 313. (e) Gabriel, J.-C. P.; Boubekeur,
K.; Uriel, S.; Batail, P. Chem. ReV. 2001, 101, 2037. (f) Gorman, C.;
Smith, J. C. Acc. Chem. Res. 2001, 34, 60.
(3) Jin, S.; DiSalvo, F. J. Chem. Mater. 2002, 7, 109.
1156 Inorganic Chemistry, Vol. 45, No. 3, 2006
10.1021/ic051680f CCC: $33.50
© 2006 American Chemical Society
Published on Web 01/10/2006

Organometallic Stars, Dendrons, and Dendrimers
Scheme 1
face-capping ones are relatively unreactive, which makes
resistant cluster cores [Mo6X8]4+. In the case of [Mo6Cl14]2-
units, the inner chloride ligands can be replaced by chalcogen
ligands, a soft route to Chevrel phases. The substitution of
the six semilabile apical ligands in [Mo6X14]2- can be
achieved easily and leads to various [Mo6Y8L6] clusters,9
which have been examined for a long time.10 In par-
ticular, the hexamethoxy clusters [Mo6Br8(OMe)6]2-, reported
by Nannelli and Block,11 and the hexatriflate clusters
[Mo6Br8(OSO2CF3)6]2-, reported by Shriver et al.,4c,12 are
the most useful starting materials for further substitution.
We have investigated mono- and hexapyridine com-
plexes of the [Mo6Br8]4+ and [Mo6I8]4+ cores by simple
substitution of the triflate ligands in Shriver’s complex
[Mo6Br8(OSO2CF3)6]2- and its homologue [Mo6I8(OSO2-
CF3)6]2-, to further assemble functional mono- and hexa-
pyridine Mo6 complexes into dendritic and nanoscopic
structures. The synthetic findings are reported here. Although
hexapyridine hexametallic clusters are known with the
9b
[Re6Se8]2+,1,13 W6S8,14 and Mo6S8 cluster series, there is
no report with the [Mo6X8]4+ core. Some 4,4′-bipyridine
complexes have been reported by Shriver’s group, however,
in the chloro series.15a Our investigation is extended to
pyridines substituted by transition-metal groups and to
dendronic pyridines including ferrocenyl dendronic pyridines.
Metal-cluster-cored dendrimers have already been reported
by Gorman5f,16a with the biomimetic Fe4S4 core and by
2+
Zheng1,13 with the Re6L8 cores (L ) S, Se).
Results and Discussion
A. Cluster Hexasubstitution. Hexatriflate Clusters.
Shriver-type hexatriflate clusters [M]2[Mo6X8(CF3SO3)6] 1-4
serve as starting points. They are prepared by reactions of
the clusters Mo6X14M2 and silver triflate, a reaction that is
carried out in tetrahydrofuran (THF) at 45 °C for 24 h in
the case of [M]2[Mo6X8(CF3SO3)6] (M ) n-Bu4N or Cs).
Starting from the clusters Cs2Mo6X14 (X ) Br or I) that are
insoluble in THF, the clusters [Cs]2[Mo6X8(CF3SO3)6], 3
(X ) Br) and 4 (X ) I), are synthesized according to the
substitution reaction that is carried out in acetone at 45 °C
for 24 h (and the resulting clusters 3 and 4 are THF-soluble).
The clusters 1-4 are purified by simple filtration of the
reaction mixture on Celite under an inert atmosphere in order
to remove AgX, and the yields are virtually quantitative
(Scheme 1).
(6) (a) Brosset, C.; Kemi, A. Mineral. Geol. 1945, 20A (No. 7), 1; 1946,
22A (No. 11), 1. (b) For a review, see: Perrin, C. J. Alloys Compds.
1997, 10, 262. (c) For recent inorganic substitution chemistry, see:
Cordier, S.; Naumov, N.; Salloum, D.; Paul, F.; Perrin, C. Inorg. Chem.
2004, 43, 219. (d) Pilet, G.; Cordier, S.; Gohlen, S.; Perrin, C.; Ouahab,
L.; Perrin, A. Solid State Sci. 2003, 5, 1359. For X-ray crystal structures
of Mo6 halide clusters, see: (e) Kirakci, K.; Cordier, S.; Perrin, C. Z.
Anorg. Allg. Chem. 2005, 631, 411. (f) Pilet, G.; Kirakci, K.; de
Montigny, F.; Cordier, S.; Lapinte, C.; Perrin, C.; Perrin, A. Eur. J.
Inorg. Chem. 2005, 5, 919. (g) Kirakci, K.; Cordier, S.; Roisnel, T.;
Golhen, S.; Perrin, C. Z. Kristallogr.sNew Cryst. Struct. 2005, 220,
116.
(7) (a) Chevrel, R.; Sergent, M.; Prigent, J. J. Solid State Chem. 1971, 3,
515. (b) Chevrel, R.; Hirrien, M.; Sergent, M. Polyhedron 1986, 5,
87.
(8) (a) Maverick, A. W.; Gray, H. B. J. Am. Chem. Soc. 1981, 103, 1298.
(b) Jackson, J. A.; Turro, C.; Newsham, M. D.; Nocera, D. G. J. Phys.
Chem. 1990, 94, 4500.
Clusters 5-10 Hexasubstituted with Simple Pyridines.
The substitution reaction of the six triflate ligands with six
pyridine ligands in the complexes 1-4 is completed in 2
days at 60 °C in pyridine/THF (Scheme 2). The reaction is
(9) (a) McCarley, R. E.; Hilsenbeck, S. J.; Xie, X. J. Solid State Chem.
1995, 117, 269. (b) Saito, T.; Yoshikawa, A.; Yamagata, T. Inorg.
Chem. 1989, 28, 3588. (c) For a recent report, see: Popp, F.; Boettcher,
S. W.; Yuan, M.; Oertel, C. M.; DiSalvo, F. J. J. Chem. Soc., Dalton
Trans. 2002, 3096.
1
followed by H NMR by comparison of the intensities of
(13) Roland, B.; Shelby, H. D.; Carducci, M. D.; Zheng, Z. J. Am. Chem.
Soc. 2002, 124, 3222.
(10) (a) Sheldon, J. C. Nature 1959, 184, 1210. (b) Nannelli, P.; Block, B.
P. Inorg. Chem. 1968, 7, 2423; 1969, 8, 1767. (c) Chisholm, M. H.;
Heppert, J. A.; Huffman, J. C. Polyhedron 1984, 3, 475. (d) Perchenek,
N.; Simon, A. Z. Anorg. Allg. Chem. 1993, 619, 98 and 103.
(11) Nannelli, P.; Block, B. P. Inorg. Synth. 1971, 13, 99.
(12) Johnston, D. H.; Gaswick, D. C.; Lonergan, M. C.; Stern, C. L.;
Shriver, D. F. Inorg. Chem. 1992, 31, 1869.
(14) Jin, S.; Adamchuk, J.; Xiang, B.; DiSalvo, F. J. J. Am. Chem. Soc.
2002, 124, 9229.
(15) Robinson, L. M.; Brain, R. L.; Shriver, D. F.; Ellis, D. E. Inorg. Chem.
1995, 34, 5588.
(16) For previous metal-cluster-cored dendrimers, see refs 1 and 9 and the
following: Gorman, C. B.; Parkhurst, B. L.; Su, W. Y.; Chen, K.-Y.
J. Am. Chem. Soc. 1997, 119, 1141.
Inorganic Chemistry, Vol. 45, No. 3, 2006 1157

Me´ry et al.
Scheme 2
Scheme 3
the pyridine protons with those of the tetrabutylammonium
countercation. In the pyridine-substituted clusters, the pyri-
dine protons are all deshielded compared to free pyridine.
For example, this deshielding effect is most marked for the
ortho-substituted pyridine protons moving from 8.41 ppm
vs tetramethylsilane (TMS) in CDCl3 in free pyridine to 8.76
ppm in 5. From the yellow starting cluster 1, the new orange
complex 5 precipitates from the reaction medium. The triflate
salt [n-Bu4N][CF3SO3] is thus readily separated because it
is soluble in THF, and the orange solid product 5 is washed
with THF. It is sparingly soluble in dichloromethane and
chloroform. It is insoluble in pyridine, ether, THF, and
1158 Inorganic Chemistry, Vol. 45, No. 3, 2006

Organometallic Stars, Dendrons, and Dendrimers
Scheme 4
alkanes, and it decomposes in methanol and water. The
cluster 5 is air-stable even in acetone and in the presence of
light. The same remarks apply to the synthesis of the cluster
[n-Bu4N][CF3SO3] from the new clusters 7 and 9 is tedious
because these clusters are now much more soluble in a
variety of solvents such as pyridine and THF. It proceeds
by successive precipitations from acetone by controlled
addition of pentane and is checked by 1H NMR. Several such
reprecipitations are required in order to remove the salt. Thus,
finally, removal of this salt is only complete with the
approximation of the 1H NMR accuracy of ca. 98%.
Elemental analyses show carbon contents that are often low,
presumably because of the presence of this and/or other extra
salts in analyzed samples. Again, the orange cluster com-
pounds obtained are air- and light-stable even in solution
for at least several hours. They are unstable in water. For 8
and 10, a precipitate forms in the course of the reaction.
Simple washing with pentane and THF then purifies the
clusters. The yields are analogous whatever the halide ligands
in the cluster, the nature of the countercation seemingly does
not influence the reactions, and the color slightly varies from
orange for the bromo clusters to dark orange for the iodo
clusters.
1
6. The ortho-substituted pyridine protons are shifted in H
NMR from 8.41 ppm vs TMS in CDCl3 for free pyridine to
8.70 ppm for 6, and the solubility properties are the same
for 5 and 6. The isolated reaction yields are 79% for 5 and
76% for 6 (Scheme 2). The reactivity and yields are
seemingly not influenced by the nature of the countercation,
Cs+ or n-Bu4N+, but the reaction cannot be followed by 1H
NMR with the cesium salt (the relative intensities of the
coordinated and free pyridine signals can be compared,
however).
Ligand substitution of 1-4 with para-substituted pyridines
was conducted in THF at 60 °C using about a 100-fold excess
of para-substituted pyridine, i.e., in pyridine/THF solvents,
and the reactions lasted 2 days (Scheme 2). Reactions were
monitored analogously by comparing the intensity of the
tetrabutylammonium 1H NMR peaks with those of the ortho
protons of the pyridine ligands. No precipitate formed, with
the orange solution remaining homogeneous at the end of
the reaction with 4-tert-butylpyridine. The separation of
Clusters 13 and 14 Hexasubstituted by Organometallic
Pyridines. We synthesized the known rigid organoruthenium
Inorganic Chemistry, Vol. 45, No. 3, 2006 1159

Me´ry et al.
Scheme 5
pyridine ligand 1117 by a new route involving the reaction
of commercial 4-ethynylpyridine hydrochloride with [RuCp-
(PPh3)2Cl] in the presence of triethylamine and [NH4][PF6]
in methanol. This general procedure was reported for the
synthesis of the complexes [RuCp(PPh3)2(η1-alkynyl)] with
(Cp ) η5-C5H5).18,19 The yellow complex 11 was character-
ized by standard spectroscopic techniques including 31P
NMR, infrared spectroscopy (νCC ) 2070 cm-1), and the
MALDI TOF mass spectrum with the dominant molecular
peak at 794 Da. The reaction of 11 with the cluster
[Mo6Br8(CF3SO3)6][n-Bu4N]2, 1, was carried out in refluxing
THF for 1 week (Scheme 3).
pound 14 was isolated by precipitation from a THF solution
by slow addition of pentane and characterized inter alia by
an infrared alkynyl absorption at 2181 cm-1, with ferrocene
signals including a single Cp signal for the free Cp rings in
the 1H and 13C NMR spectra. This complex 14 is very light-
and air-sensitive. Its cyclic voltammogram (CV) in CH2Cl2
shows two close reversible ferrocenyl waves at E1/2 ) 0.800
V vs [FeCp*2] with a less intense shoulder at E1/2 ) 0.710
V vs [FeCp*2]; these values compare with the value obtained
for the starting monomeric complex 12, E1/2 ) 0.720 V vs
[FeCp*2]. Thus, it is probable that this shoulder does
correspond to some decoordinated monoferrocenyl ligand
formed in the electrochemical cell.
The new hexaruthenium hexamolybdenum cluster 13 was
recovered by slow precipitation using pentane. A single peak
was found in the 31P NMR spectrum, a single Cp peak was
Cluster-Cored Dendrimers 17 and 18: Hexasubstitu-
tion by Dendronic Pyridines. The dendronic pyridine 3,3′-
py{CH2O-p-C6H4C(CH2CHdCH2)3}2, 15, is synthesized by
1
observed in the H NMR spectrum at δ ) 4.42 ppm, and a
single infrared absorption was obtained at νCC ) 2018 cm-1.
This behavior is in accord with the coordination of the cluster
by the six organoruthenium pyridine ligands and the absence
of a free pyridine ligand in the sample.
22
the reaction of 3,3′-py(CH2Br)2 with the phenol dendron
HO-p-C6H4C(CH2CHdCH2)3.23 The reaction of 15 with 1
was carried out for 6 days in refluxing THF using 6.2 equiv
of dendron 15 to give the orange cluster 17 (Scheme 5). The
1H NMR spectra show that the reaction is complete from
the relative intensity ratio between the ammonium protons
and the coordinated pyridine protons. Indeed, the para-
substituted pyridine proton is deshielded from 7.95 ppm in
free pyridine to 8.66 ppm in the coordinated pyridine
dendron. The solution is orange at the end of the reaction,
and the reaction time is seemingly not longer than that with
In a similar approach, the red complex 1-ferrocenyl-2-(4-
pyridinyl)acetylene 12 was synthesized using the reaction
of Vargas’ group.20 The reaction of the ferrocenyl-containing
pyridinyl ligand 12 with the cluster 1 was carried out in
refluxing THF for 1 week to give the new hexasubstituted
hexaferrocenyl Mo6 cluster 14 (Scheme 4). The red com-
(17) Wu, I.-Y.; Lin, J. T.; Luo, J.; Sun, S.-S.; Li, C.-S.; Lin, K. J.; Tsai,
C.; Hsu, C.-C.; Lin, J.-L. Organometallics 1997, 16, 2038.
(18) Bruce, M. I.; Ke, M.; Kelly, B. D.; Low, P. J.; Smith, M. E.; Skelton,
B. W.; White, A. H. J. Organomet. Chem. 1999, 590, 184.
(19) Me´ry, D.; Ornelas, C.; Daniel, M.-C.; Ruiz, J.; Rodrigues, J.; Astruc,
D.; Cordier, S.; Kirakci, K.; Perrin, C. C. R. Chim. 2005, 8, 1789.
Me´ry, D.; Plault, L.; Nlate, S.; Astruc, D.; Cordier, S.; Kirakci, K.;
Perrin, C. Z. Anorg. Allg. Chem. 2005, 631, 2746.
(21) Holm, R. H.; Zheng, Z. Inorg. Chem. 1997, 36, 5173. Willer, M. W.;
Long, J. R.; McLauchlan, C. C.; Hom, R. H. Inorg. Chem. 1988, 27,
328.
(22) Momenteau, M.; Mispelter, J.; Loock, B.; Lhoste, J. M. J. Chem. Soc.,
Perkin Trans. 1985, 61.
(23) Sartor, V.; Djakovitch, L.; Fillaut, J.-L.; Moulines, F.; Neveu, F.;
Marvaud, V.; Guittard, J.; Blais, J.-C.; Astruc, D. J. Am. Chem. Soc.
1999, 121, 2929.
(20) Torres, J. C.; Pilli, R. A.; Vargas, M. D.; Violante, F. A.; Garden, S.
J.; Pinto, A. C. Tetrahedron 2002, 58, 4487.
1160 Inorganic Chemistry, Vol. 45, No. 3, 2006

Organometallic Stars, Dendrons, and Dendrimers
Scheme 6
Scheme 7
the other pyridines, as monitored by 1H NMR. After
numerous reprecipitations in order to remove the salts, the
1H NMR spectrum shows that the ammonium salt is no
longer present and the carbon content in the elemental
analysis of the cluster-cored dendrimer 17 is acceptable. The
orange compound 17 is soluble in dichloromethane and air-
and light-stable in this solvent; however, it is insoluble in
pentane. After 1 day in a chloroform solution under an inert
atmosphere, the solution is still orange, but some decomposi-
tion to an insoluble film is observed. Although the conversion
is complete as monitored by 1H NMR, the yield is eventually
mediocre because of the repeated precipitations (Scheme 5).
Olefin metathesis reactions were attempted at 45 °C in
dichloromethane with Grubbs’ second-generation commercial
catalyst [RuCl2(dCHPh)(NHC)] (NHC ) bis-mesityl N-
heterocyclic carbene) with 17, but all attempts failed presum-
ably because of partial pyridine decoordination and subse-
quent coordination to the ruthenium of the catalyst, which
inhibits metathesis activity.
The dendronic pyridine 3,3′-{CH2O-p-C6H4C(CH2CH2-
CH2SiMe2C5H5FeCp)3}2Py, 16, is synthesized by the reaction
of the phenol dendron HO-p-C6H4C(CH2CH2CH2SiMe2C5H5-
FeCp)3 with 3,3′-py(CH2Br)2 (Scheme 6).
Reaction of 16 with 1 was carried out for 6 days in
refluxing THF using 6.2 equiv of dendron 16 to give the
1
orange cluster 18 (Scheme 7). H NMR shows that the
reaction is completed from the relative intensity ratio between
the ammonium protons and the coordinated pyridine protons.
Indeed, the para-substituted pyridine proton is deshielded
from 7.91 ppm in free pyridine to 8.50 ppm in the
coordinated pyridine dendron. The final solution is orange.
After numerous reprecipitations in order to remove the salts,
1H NMR shows that the ammonium salt is no longer present
and the carbon content in the elemental analysis of the
cluster-cored dendrimer 18 is acceptable. The orange cluster
compound 18, insoluble in pentane, is soluble in dichloro-
methane, but it is neither air- nor light-stable. Although the
conversion is complete as monitored by 1H NMR, the yield
Inorganic Chemistry, Vol. 45, No. 3, 2006 1161

Me´ry et al.
Scheme 8
Scheme 9
1162 Inorganic Chemistry, Vol. 45, No. 3, 2006

Organometallic Stars, Dendrons, and Dendrimers
Scheme 10
is eventually mediocre because of the repeated precipitations
required to purify this cluster-cored dendrimer 18. The
thermal stability of 18 is weak because it decomposes over
periods of several days at room temperature under an inert
atmosphere.
be envisaged. The monosubstitution reaction of a bromide
by a triflate is best performed for 24 h at 45 °C (Scheme 8).
Silver triflate is slowly introduced into the reaction medium
in order to favor monosubstitution whose yield is virtually
quantitative. The monosubstituted triflate cluster 19 is a THF-
soluble yellow solid serving as an intermediate for further
introduction of a pyridine-type ligand. We have not inves-
tigated the compared rates of mono- and disubstitutions,
although the yields of monopyridine-substituted products
indicate that the second substitution does not occur more
rapidly than the first one.
The CV of a freshly prepared sample of 18 in dichloro-
methane shows a single reversible wave, indicating that the
36 ferrocenyl centers are seemingly identical and sufficiently
remote from one another to render the electrostatic factor
negligible. No adsorption was noted under these conditions,
allowing the determination of the number of redox-active
units by comparison of the current intensity of the cluster
wave with that of an internal reference such as deca-
methylferrocene. The Bard-Anson equation, involving these
intensities and the respective molecular weights of the
compound and reference,24 provides a number of ferrocenyl
redox centers equal to 37 ( 3, showing a good agreement
with the theoretical number of 36.25
B. Cluster Monosubstitution. Clusters Monosubstituted
by Simple Pyridines. Given the progressive substitution of
the apical halide ligands in the hexamolybdenum clusters,
we investigated the possibility of also synthesizing mono-
substituted pyridine clusters in order to eventually introduce
a single functional group to derivatize the cluster. In a
systematic study of the hexarhenium sulfide clusters, Holm’s
group could optimize the synthesis of all of the possible
substituted clusters.21 The present hexamolydenum clusters
are far from being as air-stable as hexarhenium clusters;
therefore, this strategy is much more limited here. In
particular, for this reason, chromatographic separation cannot
The substitution of the triflate ligand by a pyridine
derivative is complete in 2 days at 60 °C in THF (Schemes
1
8 and 10). This type of reaction is monitored by H NMR
by comparing the intensities of the signals of the coordinated
pyridine with those of the countercation n-Bu4N+. Here
again, the signals of the pyridine protons are shifted upon
coordination to the cluster. The monosubstituted clusters 20
and 21 are orange, and they are much less soluble in common
solvents than the hexasubstituted analogues. They precipitate
during the reaction; thus, purification is simple by washing
the precipitate with pentane and then with THF, followed
1
by filtration on Celite, and H NMR analysis is carried out
in acetone-d6. The yields are modest (48% for 20 and 37%
for 21), which indicates that disubstitution also simulta-
neously occurs because of near-statistical substitution. The
disubstituted products are neutral, and thus probably well
THF-soluble, but were not investigated. With the unsubsti-
tuted triflate cluster complex being also THF-soluble, the
monopyridine clusters are the only THF-insoluble products
among these three compounds (non-, mono-, and disubsti-
tuted). Olefin metathesis experiments were carried out with
21 as with 17, but they were not successful, presumably for
the same reason involving some partial decoordination of
(24) Nlate, S.; Ruiz, J.; Sartor, V.; Navarro, R.; Blais, J.-C.; Astruc, D.
Chem.sEur. J. 2000, 6, 2544.
(25) Flanagan, J. B.; Margel, S.; Bard, A. J.; Anson, F. C. J. Am. Chem.
Soc. 1978, 100, 4248.
(26) For earlier detailed related work, see: Daniel, M.-C.; Ruiz, J.; Blais,
J.-C.; Daro, N.; Astruc, D. Chem.sEur. J. 2003, 9, 4371.
Inorganic Chemistry, Vol. 45, No. 3, 2006 1163

Me´ry et al.
recognize the n-Bu4N+ salt of ATP2-, and when this salt is
added to the electrochemical cell containing the modified
electrode, a new reversible wave appears at 90 mV less
positive potential.22
Concluding Remarks
(i) An easy route to a family of new mono- and hexa-
pyridine octahedral hexamolybdenum hexapyridine clusters
[Mo6X8(4-Py-R)6][CF3SO3]4 has been disclosed starting from
the precursor complex [M]2[Mo6X14] via the triflate inter-
mediates. The homogeneity of the reaction mixture allows
1
monitoring of their formation by H NMR by comparison
of the relative intensities of the tetrabutylammonium signals
and those of the pyridine protons that become deshielded
upon pyridine coordination. The use of substituted pyridine
largely increases the solubility of the new clusters, which
renders the separation of the Mo6 cluster from the salt
[n-Bu4N][OSO2CF3] difficult with the tetrabutylammonium
salt used at the beginning of the synthesis. This separation
can be achieved by successive reprecipitations, however.
(ii) Organometallic pyridines could be grafted onto the
six apical positions of the cluster, yielding light- and air-
sensitive clusters surrounded by organometallic fragments.
(iii) Cluster-cored dendrimers could be prepared including
ferrocenyl dendrimers, and the number of redox-active units
has been successfully determined therein using the Bard-
Anson equation in cyclic voltammetry. The pyridine-
substituted clusters with small pyridine substituents are
thermally stable, but the cluster-cored polyferrocenyl den-
drimers have a limited thermal stability, probably because
the large sizes of the dendrons destabilize the cluster-
pyridine bond.
Figure 1. CVs of the cluster-cored dendron 26: solvent, CH2Cl2; reference
electrode, Ag/Ag+; working electrode, none; counter electrode, Pt; sup-
porting electrolyte, 0.1 M n-Bu4NPF6; internal reference, FeCp2*; (a) 26 in
solution; (b) 26 coated over a Pt electrode at various scan rates (E1/2
)
0.53 V vs FeCp2*); (c) inset by 26. The intensity was as a function of the
scan rate. The linearity shows the expected behavior of the modified
electrode with full adsorption of 26. The surface coverage by 26 was
determined from the integrated charge of the CV wave. Thus, the surface
coverage for the electrode modified with 26 was Γ ) 1.3 × 10-10 mol
cm-2 (iron sites), corresponding to 1.08 × 10-11 mol cm-2 of 26. The
difference between the anodic and cathodic potentials is ∆E ) Ec - Ea )
0.0 V, and the full width at half-maximum (∆Efwhm) is 0.90 V.
the substituted pyridine from the cluster and inhibition of
the ruthenium catalyst.
Ferrocenyl-Dendronized Cluster 26 Monosubstituted
by a 12-Ferrocenylpyridine Dendron 25. The reaction of
1 equiv of 19 with 1 equiv of monopyridine dendron 25
bearing 12 ferrocenyl groups at the periphery (Scheme 9) is
also carried out in THF at 60 °C for 2 days and yields the
thermally sensitive pentane-soluble orange compound 26
(Scheme 10).
Experimental Section
The para-substituted pyridine protons of 26 are found at
8.22 ppm vs TMS in CDCl3 (compared to free pyridine at
7.90 ppm). The solubility of 26 in pentane precludes
purification from other pentane-soluble impurities such as
the free ligand and, in addition, 26 is not thermally stable at
room temperature over a few hours. Thus, its synthesis must
be carried out in the presence of only 1 equiv of the
dendronic pyridine ligand, whose coordination can be
General Data. Reagent-grade THF and pentane were predried
over Na foil and distilled from a sodium benzophenone anion under
argon immediately prior to use. Other commercial chemicals were
purchased from Aldrich and used as received. All manipulations
were carried out using Schlenk flasks, and samples were transferred
1
in a nitrogen-filled, vacuum atmosphere drylab. H NMR spectra
were recorded at 25 °C with a Bruker AC 300 (300 MHz)
spectrometer. 13C NMR spectra were obtained in the pulsed Fourier
transform mode at 75 MHz with a Bruker AC 300 spectrometer.
All chemical shifts are reported in parts per million (δ, ppm) with
reference to TMS. Elemental analyses were carried out at the
Vernaison CNRS center. The infrared spectra were recorded in KBr
pellets on a FT-IR Paragon 1000 Perkin-Elmer spectrometer.
(i) MALDI-TOF Mass Spectrometry. The MALDI mass
spectra were recorded with a PerSeptive Biosystems Voyager Elite
(Framingham, MA) time-of-flight mass spectrometer. This instru-
ment is equipped with a nitrogen laser (337 nm), a delayed
extraction, and a reflector. It was operated at an accelerating
potential of 20 kV in both linear and reflection modes. The mass
spectra shown represent an average of over 256 consecutive laser
shots (3-Hz repetition rate). Peptides were used to calibrate the
mass scale using the two-point calibration software 3.07.1 from
PerSeptive Biosystems. Mentioned m/z values correspond to
monoisotopic masses. The solutions (10-3 M) were prepared in
THF. Matrix compounds were from Sigma (France) and used
1
monitored by H NMR using the signals of the pyridine
protons, and indeed coordination is completed. It is possible,
however, that some disubstituted compound is present in the
reaction mixture.
The CV of a freshly prepared sample of 26 shows a single
ferrocenyl wave for the 12 ferrocenyl groups, and application
of the Bard-Anson equation21 leads to a number of redox
centers equal to 14 ( 2. The error on this measurement is
somewhat larger than that in the case of the cluster-cored
ferrocenyl dendrimer 18 presumably because of the purity
of the sample, which is lower for 26 than for 18. A modified
Pt electrode is prepared with 18 by scanning about 100 times
around the ferrocenyl redox potential region, which produced
an electrode, giving the CV shown in Figure 1 in which the
0 V difference between Epa and Epc values confirms correct
electrode modification. The modified electrode can also
1164 Inorganic Chemistry, Vol. 45, No. 3, 2006

Organometallic Stars, Dendrons, and Dendrimers
without further purification. The matrixes, 2,5-dihydroxybenzoic
acid (2,5-DHB), 1,8-dihydroxy-9(10H)-anthracenone (dithranol),
6-azathiothymine, 2,4,6-trihydroxyacetophenone, 7-hydroxycou-
marin, or 2-anthramine, were also dissolved in THF (10 g L-1). A
total of 1 µL of solution was mixed with 50 µL of the matrix
solution. A total of 10 µL of an alkali iodide (LiI, NaI) solution (5
g L-1 in THF) was added in some experiments to induce
cationization. A total of 1 µL of the final solution was deposited
onto the sample stage and allowed to dry in air.
Cyclic voltammetry data were recorded with a PAR 273
potentiostat galvanostat. The reference electrode was an Ag quasi-
reference electrode (QRE). The QRE potential was calibrated by
adding the reference couple [FeCp2*]+/[FeCp2*] (Cp* ) penta-
methylcyclopentadienyl). The working electrode (platinum) was
treated by immersion in 0.1 M HNO3 and then polished before
use and between each recording when necessary. The cluster
[n-Bu4N]2[Mo6Br8(CF3SO3)6] is irreversibly oxidized at +1.5 V vs
Cp*2Fe+/0 in CH3CN, whereas the hexa-tert-butylpyridine cluster
7 is irreversibly reduced at -0.7 V vs Cp*2Fe+/0 in dimethyl-
formamide (DMF; both measurements were carried out at 25 °C,
0.2 V s-1 with 0.1 M n-Bu4NPF6).
(d, 12H), 6.65 (q, 6H), 6.00 (d, 6H), 5.51 (d, 6H). 13C NMR (CDCl3,
75.47 MHz) δppm: 150.5 (Co), 135.1 (CHdCH2), 121.1 (Cm), 119.0
(CHdCH2). Elem anal. Calcd for C46H48Br8F12Mo6N6O12S4: C,
22.57; H, 1.98. Found: C, 22.09; H, 1.61. M ) 2448.04 g mol-1
.
Cluster Mo6I8(4-tert-butylpyridine)6Tf4, 9. A yellow THF
solution of 2 (0.686 g, 0.231 mmol) and 4-tert-butylpyridine (1.8
mL) was stirred at 60 °C for 2 days. The solvent was removed
under vacuum, and the product was precipitated with THF/pentane
and dried under vacuum to yield complex 9 as an orange solid.
Yield: 0.512 g of 9 (74%). 1H NMR (CDCl3, 300 MHz) δppm: 8.52
(d, 12H), 7.33 (m, 12H), 1.32 (m, 54H). 13C NMR (CDCl3, 75.47
MHz) δppm: 147.4 (Co), 122.1 (Cm), 34.5 (CMe3), 30.7 (CH3). Elem
anal. Calcd for C58H78F12I8Mo6N6O12S4: C, 23.23; H, 2.62.
Found: C, 22.52; H, 2.01. M ) 2998.41 g mol-1
.
Cluster Mo6I8(4-vinylpyridine)6Tf4, 10. A yellow THF solution
of 2 (0.686 g, 0.231 mmol) and 4-vinylpyridine (1.8 mL) was stirred
at 60 °C for 2 days. The reaction product progressively precipitated
from the reaction mixture as a very fine powder. The solvent was
removed under vacuum to give an orange solid, which was washed
with pentane and THF and dried under vacuum to yield complex
10 as an orange solid. Yield: 0.528 g of 10 (81%). 1H NMR
(CDCl3, 300 MHz) δppm: 8.46 (d, 12H), 7.17 (m, 12H), 6.52 (q,
6H), 5.85 (d, 6H), 5.38 (d, 6H). 13C NMR (CDCl3, 75.47 MHz)
The syntheses and characterizations of the starting halogen cluster
compounds M2Mo6X14 have been performed according to the
procedure described in ref 6e, and the synthesis of the triflate cluster
compounds is reported in Shriver’s publication.12
δ
ppm: 151.6 (Co), 134.9 (CHCH2), 122.3 (Cm), 120.0 (CH2). Elem
anal. Calcd for C46H48F12I8Mo6N6O12S4: C, 19.56; H, 1.71.
Found: C, 19.37; H, 1.52. M ) 2824.04 g mol-1
Cluster Mo6Br8Py6Tf4, 5. A yellow THF solution of 1 (0.585
g, 0.231 mmol) and pyridine (1.8 mL, 0.023 mol) was stirred at 60
°C for 2 days. The reaction product progressively precipitated from
the reaction mixture as a very fine powder. The solvent was
removed under vacuum to give an orange solid, which was washed
with pentane and THF and dried under vacuum to yield complex
5 as an orange solid. Yield: 0.416 g of 5 (79%). 1H NMR (CDCl3,
300 MHz) δppm: 8.76 (d, 12H), 8.03 (m, 6H), 7.60 (m, 12H). 13C
NMR (CDCl3, 75.47 MHz) δppm: 147.7 (Co), 141.5 (Cp), 126.3
(Cm). Elem anal. Calcd for C34H30Br8F12Mo6N6O12S4: C, 17.87;
.
[RuCp(PPh3)2(CC-C5H4N)], 11. A methanol solution of 4-eth-
ynylpyridine (0.296 g, 2.07 mmol) and triethylamine (5 mL) was
added to a suspension of [RuCp(PPh3)2Cl] (1 g, 1.38 mmol) and
NH4PF6 (0.449 g, 2.76 mmol) in methanol. The solution was stirred
at room temperature for 3 days. The solvent was removed under
vacuum, and the product was extracted with toluene. The product
was precipitated with toluene/pentane. The yellow powder was dried
under vacuum. Yield: 0.350 g of 11 (32%). 1H NMR (MeOD, 300
MHz) δppm: 8.06 (d, NCH), 7.30-7.04 (m, PPh3), 6.80 (d, NCCH),
4.29 (s, Cp). 31P NMR (MeOD, 100 MHz) δppm: 49.60 (PPh3). IR:
H, 1.32. Found: C, 17.21; H, 1.09. M ) 2285.76 g mol-1
.
Cluster Mo6I8Py6Tf4, 6. A yellow THF solution of 2 (0.686 g,
0.231 mmol) and pyridine (1.8 mL, 0.023 mol) was stirred at 60
°C for 2 days. The reaction product progressively precipitated from
the reaction mixture as a very fine powder. The solvent was
removed under vacuum to give an orange solid, which was washed
with pentane and THF and dried under vacuum to yield complex
6 as an orange solid. Yield: 0.467 g of 6 (76%). 1H NMR (CDCl3,
300 MHz) δppm: 8.70 (d, 12H), 7.81 (m, 6H), 7.42 (m, 12H). 13C
NMR (CD3COCD3, 75.47 MHz) δppm: 147.9 (Co), 143.2 (Cp), 128.6
(Cm). Elem anal. Calcd for C34H30F12I8Mo6N6O12S4: C, 15.34; H,
ν
CC 2070 cm-1. MS (MALDI-TOF; m/z). Calcd for C48H39NP2Ru:
792.85. Found: 794.24. CV in CH2Cl2: E1/2 ) 0.700 V vs Fc* at
20 °C (partially chemically reversible: ic/ia ) 0.5).
Hexasubstituted Mo6Ru6 Cluster, 13. A THF solution of 11
(0.131 g, 0.165 mmol) and 1 (0.069 g, 0.0265 mmol) was stirred
at 60 °C for 7 days. The solvent was removed under vacuum, and
the product was precipitated with THF/pentane. The red powder
was dried under vacuum. Yield: 0.115 g of 13 (65%). Elem anal.
Calcd for Mo6Br8C292H234F12S4O12N6P12Ru6: C, 53.39; H, 3.39.
Found: C, 52.59; H, 2.97.
1H NMR (MeOD, 300 MHz) δppm: 8.12 (d, NCH), 7.23-7.08
(m, PPh3), 7.04 (d, NCCH), 4.42 (s, Cp). 31P NMR (MeOD, 100
MHz) δppm: 49.51 (PPh3). IR: νCC 2018 cm-1. CV in CH2Cl2: E1/2
) 0.650 V vs Fc* at 20 °C in CH2Cl2 (partially chemically
reversible: ic/ia ) 0.1).
Hexaferrocenyl Mo6Fc6 Cluster, 14. A THF solution of 12
(0.054 g, 0.187 mmol) and 1 (0.063 g, 0.029 mmol) was stirred at
60 °C for 7 days. The solvent was removed under vacuum, and the
product was precipitated with THF/pentane. The red powder was
dried under vacuum. Yield: 0.073 g of 14 (63%). 1H NMR (CDCl3,
300 MHz) δppm: 8.64 (d, NCH), 7.51 (d, NCCH), 4.62 and 4.41
(t, FeCH), 4.32 (s, Cp). 13C NMR (CDCl3, 63 MHz) δppm: 69.9
(FeC), 70.2 (Cp), 72.0 (FeC), 76.95 (C), 125.9 (NCC), 147.5 (NC).
IR: νCC 2 181 cm-1. Elem anal. Calcd: C, 36.03; H, 2.22. Found:
C, 35.29; H, 1.59. CV in CH2Cl2 at 20 °C: E1/2 ) 0.800 V vs
[FeCp*2] in CH2Cl2.
1.14. Found: C, 14.69; H, 0.86. M ) 2661.77 g mol-1
.
Cluster Mo6Br8(4-tert-butylpyridine)6Tf4, 7. A THF solution
of 1 (1 g, 0.394 mmol) and 4-tert-butylpyridine (2 mL) was stirred
at 60 °C for 2 days. The solvent was removed under vacuum, and
the product was precipitated with THF/pentane and dried under
vacuum to yield complex 7 as an orange solid. Yield: 0.826 g
(80%). 1H NMR (CDCl3, 300 MHz) δppm: 8.59 (d, 12H), 7.49 (d,
12H), 1.35 (s, 54H). 13C NMR (CDCl3, 75.47 MHz) δppm: 147.4
(Co), 122.1 (Cm), 34.5 (CMe3), 30.7 (CH3). Elem anal. Calcd for
C58H78Br8F12Mo6N6O12S4: C, 26.56; H, 3.00. Found: C, 26.15;
H, 2.69. M ) 2622.40 g mol-1
.
Cluster Mo6Br8(4-vinylpyridine)6Tf4, 8. A THF solution of 1
(0.300 g, 0.141 mmol) and 4-vinylpyridine (1 mL) was stirred at
60 °C for 2 days. The solvent was removed under vacuum to give
a solid residue, which was washed with pentane and THF and dried
under vacuum to yield complex 8 as an orange solid. Yield: 0.293
1
g (85%). H NMR (CDCl3, 300 MHz) δppm: 8.57 (d, 12H), 7.27
Inorganic Chemistry, Vol. 45, No. 3, 2006 1165

Me´ry et al.
Dendronic Pyridine Derivative, 15. In a Schlenk tube, 3,5-bis-
(bromomethyl)pyridine (0,17 mmol),23 p-(triallylmethyl)phenol
(1.13 mmol), and K2CO3 (2.26 mmol) were stirred for 2 days in
acetonitrile. Then, the solvent was removed under vacuum, and
the reaction product was extracted using diethyl ether and filtered
on Celite. The solvent was evaporated to dryness, and the product
15 was chromatographed on silica gel (eluent: diethyl ether/
and 4-tert-butylpyridine (0.028 mL, 0.19 mmol) was stirred at 60
°C for 2 days. The solvent was removed under vacuum to give an
orange solid, which was washed with pentane and THF and dried
under vacuum to yield complex 20 as an orange solid. Yield: 0.181
g (48%). 1H NMR (CDCl3, 300 MHz) δppm: 8.57 (d, 2H), 7.36 (d,
2H), 1.34 (s, 9H). 13C NMR (CDCl3, 75.47 MHz) δppm: 146.8 (Co),
122.2 (Cm), 33.9 (CMe3), 30.1 (CH3). Elem anal. Calcd for C25H49-
Br13Mo6N2: C, 15.07; H, 2.48. Found: C, 14.68; H, 2.27. M )
1
petroleum ether, 1:1). Yield: 70%. H NMR (250 MHz, CDCl3)
δppm: 8.66 (s, 2H, o-H pyridine), 7.90 (s, 1H, p-H pyridine), 7.23
1992.07 g mol-1
.
and 6.96 (d, 4H, H aromatic), 5.55 (m, 6H, CH allyl), 5.02 (m,
12H, CH2 allyl), 4.98 (s, 4H, CH2O), 2.42 (d,12H, Cq-CH2-CH).
13C NMR (63 MHz, CDCl3) δppm: 156.2 (Cq Ar-O), 148.5-138.5
(CH pyridine), 134.53 (CH allyl), 132.6 (Cq pyridine), 128.6-114.1
(CH Ar), 117.5 (CH2 allyl), 67.3 (CH2O), 44.7 (Cq Ar-Cq-CH2),
41.8 (Cq-CH2-CH). Elem anal. Calcd for C39H45NO2: C, 83.68;
Cluster [Mo6Br13(4-vinylpyridine)][n-Bu4N], 21. A THF solu-
tion of 19 (0.426 g, 0.19 mmol) and 4-vinylpyridine (0.021 mL,
0.19 mmol) was stirred at 60 °C for 2 days. The solvent was
removed under vacuum to give an orange solid, which was washed
with pentane and THF and dried under vacuum to yield complex
1
20 as an orange solid. Yield: 0.138 g (37%). H NMR (CDCl3,
H, 8.10. Found: C, 83.23; H, 8.12. M ) 559.79 g mol-1
.
300 MHz) δppm: 8.54 (d, 2H), 7.26 (d, 2H), 6.61 (q, 1H), 5.93 (d,
1H), 5.46 (d, 1H). 13C NMR (CDCl3, 75.47 MHz) δppm: 150.5 (Co),
135.1 (CHCH2), 121.1 (Cm), 119.0 (CH2). Elem anal. Calcd for
C23H43Br13Mo6N2: C, 14.08; H, 2.21. Found: C, 13.73; H, 2.02.
Dendronic Pyridine Derivative, 16. In a Schlenk tube, 3,5-bis-
(bromomethyl)pyridine (0.138 mmol), p-triferrocenylphenol20 (0.415
mmol), and K2CO3 (0.83 mmol) were stirred for 2 days in
acetonitrile at 40 °C. Then, the solvent was removed under vacuum,
and the reaction product was extracted using diethyl ether and
filtered on Celite. The solvent was evaporated to dryness, and the
product was chromatographed on silica gel (eluent: diethyl ether/
M ) 1962.00 g mol-1
.
Pyridine Dendron 22. In a Schlenk tube, 3,5-bromomethyl-
pyridine (1.5 mmol), dimethyl 5-hydroxyisophthalate (6 mmol), and
K2CO3 (12 mmol) were stirred for 1 day in acetonitrile at 60 °C.
Then, the solvent was removed under vacuum, and the reaction
product was extracted using diethyl ether and filtered on Celite.
The solvent was evaporated to dryness, and the product was
chromatographed on silica gel (eluent: diethyl ether/petroleum
1
petroleum ether, 1:1). Yield: 44%. H NMR (250 MHz, CDCl3)
δppm: 8.67 (s, 2H, o-H pyridine), 7.91 (s, 1H, p-H pyridine), 7.22
and 6.93 (d, 4H, H aromatic), 5.06 (s, 4H, CH2O), 4.30-4.08-
4.01 (CH ferrocenyl), 1.59-1.17 (m, 12H, Cq-CH2-CH2-CH),
0.64 (m, 6H, CH2-Si), 0.16 (CH3). 13C NMR (63 MHz, CDCl3)
1
ether, 1:1). Yield: 60%. H NMR (250 MHz, CDCl3) δ: 8.70 (s,
δ
ppm: 155.8 (Cq Ar-O), 148.5-132.7 (CH pyridine), 140.8 (Cqar-
2H), 7.94 (s, 1H), 8.34 (s, 2H), 7.85 (s, 4H), 5.21 (s, 4H), 3.95 (s,
12H). 13C NMR (63 MHz, CDCl3) δppm: 165.8 (Cq), 158.3 (Cq-
O), 148.6-134.5 (CH), 132.7 (Cq-CqOO), 123.7 (p-CHar), 120.0
(o-CHar), 67.7 (CH2-O), 52.4 (CH3). Elem anal. Calcd: C, 61.95;
H, 4.81. Found: C, 61.75; H, 4.96.
Pyridine Dendron 23. To a suspension of LiAlH4 (19.8 mmol)
in dry THF was added the pyridine dendron 22 (1.98 mmol)
dissolved in the same solvent. After 6 h of reflux, 4 mL of water
was slowly added in an ice bath. Then, the product was filtered
and extracted with hot methanol. A yellow solid was obtained after
precipitation with diethyl ether. Yield: 71%. 1H NMR (250 MHz,
methanol-d4) δ: 8.59 (s, 2H), 8.03 (s, 1H), 6.95 (s, 6H), 5.19 (s,
4H), 4.57 (s, 8H). 13C NMR (63 MHz, CD3OD) δppm: 158.7 (Cq-
O), 147.2-135.1 (CH), 133.8 (Cq), 143.2 (Cqar), 117.7 (p-CHar),
111.6 (o-CHar), 66.7 (CH2-O), 63.5 (CH2OH).
Cq), 134.6 (Cq pyridine), 127.6-114.0 (CHar), 72.9-70.5-68.0 (CH
ferrocenyl), 71.3 (Cq ferrocenyl), 67.3 (CH2O), 43.2 (Cqar-Cq-
CH2), 42.0 (Cq-CH2-CH2), 18.0 (CH2-CH2-CH2), 17.5 (Si-
CH2), -1.9 (CH3). Elem. anal. Calcd: C, 65.84; H, 7.02. Found:
C, 66.71; H, 6.80.
Hexasubstituted Cluster [Mo6Br8(dendron)6][CF3SO3]4, 17.
A yellow THF solution of 1 (0.100 g, 0.038 mmol) and the pyridine
dendron 15 (0.143 g, 0.255 mmol) was stirred at 60 °C for 7 days.
The solvent was removed under vacuum, and the product was
precipitated with THF/pentane. The orange powder was dried under
vacuum. Yield: 0.097 g of 17 (49%). 1H NMR (CDCl3, 300 MHz)
δppm: 8.90 (s, 12H, Ho), 8.66 (s, 6H, Hp), 7.27 (d, 24H), 6.96 (d,
24H), 5.53 (m, 36H, dCHa), 5.02 (m, 96H, dCH2a + OCH2), 2.45
(d, 72H, CH2). 13C NMR (CDCl3, 75.47 MHz) δppm: 155.46 (Co),
139.19 (Cm), 136.91 (Cp), 134.26 (CHdCH2), 127.96 (Car), 117.41
(CHdCH2), 114.20 (Car), 65.95 (OCH2), 42.84 (Cq), 41.85 (Cq-
CH2). Elem anal. Calcd for C238H270Br8F12Mo6N6O24S4: C, 55.29;
Pyridine Dendron 24. In a Schlenk tube, the pyridine dendron
23 (0.79 mmol) was stirred at 0 °C during the addition of
tribromophosphine (1.05 mmol). After 4 h in DMF at room
temperature, the product was extracted with dichloromethane; this
solution was washed several times with water and dried over
Na2SO4, and the solent was removed under vacuum, yielding a
H, 5.26. Found: C, 54.85; H, 4.98. M ) 5169.83 g mol-1
.
Hexasubstituted Cluster [Mo6Br8(dendron)6][CF3SO3]4, 18.
A yellow THF solution of 1 (0.012 g, 0.0046 mmol) and ′12 (0.058
g, 0.0285 mmol) was stirred at 60 °C for 6 days. The solvent was
removed under vacuum, and the product was precipitated with
CH2Cl2/pentane to give an orange solid 18. Yield: 0.039 g of 18
(59%). H NMR (CDCl3, 300 MHz) δppm: 8.82 (m, 12H), 8.50
(m, 6H), 7.22 (d, 24H), 6.92 (d, 24H), 5.20 (s, 24H), 4.31 (s, 72H),
4.08 (s, 180H), 4.02 (s, 72H), 1.63 (m, 72H), 1.12 (m, 72H), 0.64
(m, 72H), 0.16 (s, 216H). 13C NMR (CDCl3, 75.47 MHz) δppm
1
white solid. Yield: 44%. H NMR (250 MHz, CDCl3) δ: 8.67 (s,
2H), 7.90 (s, 1H), 7.05 (s, 2H), 6.95 (s, 4H), 5.13 (s, 4H), 4.44 (s,
8H). 13C NMR (63 MHz, CDCl3) δppm: 158.6 (Cq-O), 148.0-
134.9 (CH), 132.3 (Cq), 139.8 (Cqar-CH2Br), 122.5 (p-CHar), 115.4
(o-CHar), 67.3 (CH2-O), 32.6 (CH2Br). Elem anal. Calcd: C, 41.66;
H, 3.19. Found: C, 41.57; H, 3.34.
1
:
12-Ferrocenylpyridine Dendron, 25. In a Schlenk tube, pyridine
24 (0,0052 mmol), p-triferrocenylphenol20 (0.029 mmol), and
K2CO3 (0.063 mmol) were stirred for 2 days in acetonitrile at room
temperature. Then, the solvent was removed under vacuum,
and the reaction product was extracted using diethyl ether and
filtered on Celite. The solvent was evaporated to dryness, and the
product was chromatographed on silica gel (eluent: diethyl ether/
141.7 (Car), 127.7 (Car), 113.9 (Car), 72.9 (Car), 71.0 (OCH2), 70.6
(Car), 68.1 (Cp), 43.3 (Cq-CH2), 18.0 (CH2), 17.4 (SiCH2), -2.0
(SiCH3). Elem anal. Calcd for C670H846Br8F12Fe36Mo6N6O24S4-
Si36: C, 57.64; H, 6.11. Found: C, 55.97; H, 5.22. M ) 13 960.80
g mol-1
.
Cluster [Mo6Br13(4-tert-butylpyridine)][n-Bu4N], 20. A THF
solution of [n-Bu4N]2[Mo6Br13(CF3SO3)], 19 (0.426 g, 0.19 mmol),
1
petroleum ether, 7:3). Yield: 22%. H NMR (250 MHz, CDCl3)
1166 Inorganic Chemistry, Vol. 45, No. 3, 2006

Organometallic Stars, Dendrons, and Dendrimers
ppm: 8.68 (s, 2H, o-H pyridine), 7.90 (s, 1H, p-H pyridine), 7.26
and 6.90 (d, 16H, H aromatic), 6.97 (s, 4H, o-CHar), 6.93 (s 2H,
p-CHar), 5,12 (s, 4H, CH2O), 5,02 (s, 8H, CH2O), 4.30-4.08-
4.01 (CH ferrocene), 1.59-1.17 (m, 12H, Cq-CH2-CH2-CH),
0.64 (m, 6H, CH2-Si), 0.16 (CH3). 13C NMR (63 MHz, CDCl3)
δ
73.3-70.0 (CH ferrocenyl), 72.6 (Cq ferrocenyl), 45.2 (Cqar-Cq-
CH2), 44.0 (Cq-CH2-CH2), 20.0 (CH2), 19.46 (Si-CH2), 2.9
(CH3).
Acknowledgment. Financial support from the Ministe`re
de la Recherche (ACI Nanostructures 2001 No. N18-01 and
grants to D.M., L.P., and K.K.), the Fundac¸a˜o para a Cieˆncia
e a Tecnologia (FCT), Portugal (Ph.D. grant to C.O.), the
Institut Universitaire de France (IUF; D.A.), the Centre
National de la Recherche Scientifique (CNRS), the Universi-
ties of Bordeaux I, Rennes 1, Paris VI, and Madeira, the
GRICES-EGIDE PESSOA exchange program (C.O., J.R.,
J.R.A., and D.A.), and the Fondation Langlois is gratefully
acknowledged.
δppm
: 127.6-114.0 (CHar), 72.9-70.5-68.0 (CH ferrocenyl),
71.3 (Cq ferrocenyl), 67.3 (CH2O), 43.6 (Cqar-Cq-CH2), 42.4
(Cq-CH2-CH2), 18.4 (CH2-CH2-CH2), 17.9 (Si-CH2), -1.53
(CH3). Elem anal. Calcd: C, 66.13; H, 7.23. Found: C, 65.80; H,
6.66.
Ferrocenyl-Dendronized Cluster, 26. A yellow THF solution
of 19 (0.016 g, 0.007 mmol) and ′25 (0.032 g, 0.007 mol) was
stirred at 60 °C for 2 days. The solvent was removed under vacuum
1
to give an orange solid. Yield: 0.042 g of 26 (35%). H NMR
(CDCl3, 300 MHz) δppm: 8.79 (m, 2H), 8.22 (m, 1H), 7.21 (d, 12H),
7.19 (m, 2H), 6.95 (d, 8H), 5.19 (s, 4H), 5.04 (s, 8H), 4.32 (s,
24H), 4.10 (s, 60H), 4.04 (s, 24H), 3.75 (t, 8H), 1.87 (m, 8H),
1.62 (m, 32H), 1.11 (m, 24H), 0.6 (m, 24H), 0.15 (s, 72H).
13C NMR (CDCl3, 75.47 MHz) δppm: 129.5-116.0 (CHar), 74.9-
1
Supporting Information Available: Structures and H NMR
spectra for complexes 5-11, 13-18, 25, and 26. This material is
available free of charge via the Internet at http://pubs.acs.org.
IC051680F
Inorganic Chemistry, Vol. 45, No. 3, 2006 1167