"click" synthesis and properties of carborane-appended large dendrimers

Article abstract of DOI:10.1021/ic101729s

Large dendrimers, noted G_n-3ⁿ⁺²cage, containing 3ⁿ⁺²o-carborane cluster cages MeC₂B₁₀H ₁₀at their peripheries (n = number of generation noted G_n) have been synthesized by Huisgen

Full text of DOI:10.1021/ic101729s

10702 Inorg. Chem. 2010, 49, 10702–10709
DOI: 10.1021/ic101729s
“Click” Synthesis and Properties of Carborane-Appended Large Dendrimers
Rodrigue Djeda,† Jaime Ruiz,† Didier Astruc,*,† Rashmirekha Satapathy,‡ Barada Prasanna Dash,‡ and
Narayan S. Hosmane*,‡
†
ꢀ
ꢀ
Institut des Sciences Moleculaires, UMR CNRS N°5255, Universite Bordeaux 1, 33405 Talence Cedex,
‡
France, and Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb,
Illinois 60115-2862, United States
Received August 25, 2010
Large dendrimers, noted Gn-3nþ2cage, containing 3nþ2 o-carborane cluster cages MeC2B10H10 at their peripheries
(n = number of generation noted Gn) have been synthesized by Huisgen-type azide alkyne CuI-catalyzed dipolar “click”
cycloaddition reactions (CuAAC) between an o-carborane monomeric cluster containing an ethynyl group and arene-
centered azido-terminated dendrimers Gn-3nþ2N3 of generations 0, 1, and 2. Attempts to synthesize higher-generation
dendrimers of this family yielded insoluble materials. The carborane dendrimers G0-9cage, G1-27cage, and G2-81cage
have been characterized by 1H, 13C, 11B NMR, elemental analysis, matrix-assisted laser desorption/ionization time of
flight (MALDI-TOF) mass spectroscopy, and size exclusion chromatography (SEC) showing low polydispersities,
dynamic light scattering (DLS) showing hydrodynamic diameters of 5.7 nm for the G1-27cage and the 12.9 nm for the
G2-81cage. These dendrimers are extremely robust thermally, with 10% mass loss temperatures of 411 °C for the
G0-9cage, 371 °C for the G1-27cage, and 392 °C for the G2-81cage. They all showed a strong absorption in the UV
region peaking at 258 nm, whereas emission spectra of low intensities were observed between 280 and 480 nm.
Introduction
dendrimers containing up to 12 o-carborane clusters.7 Grimes
also reported a remarkable dendrimer containing 128 boron
atoms.8 Large dendrimers encapsulating carboranes have
been recently reported for boron neutron capture therapy
(BNCT) application with a G5-PAMAM dendrimer.9 One of
our groups has recently reported star hexacarboranes and
small dendrimers containing 12 carboranes.6,10 The thermal
stability of small star-shaped hexacarboranyl dendrimers
and sandwiched hexametallacarboranyl dendrimers, pre-
pared by one of our groups,6,10 also contributed to rekindle
our interest in exploring new synthetic strategies for the
construction of large carborane-appended dendritic mole-
cules and to study their reactivity patterns.
Polymeric and dendritic carborane clusters are useful for a
number of applications in nanomedicine,1 materials science,2
and organometallic chemistry.3 The dendritic strategy that
consisted in loading a large number of boron atoms in a
dendritic molecule has been pioneered by Newkome et al.
who introduced 12 boron cluster termini at the periphery
of arborol tethers.4,5 This goal was further explored success-
fully by introducing six high boron-containing carboranes
in star molecules bearing peripheral carboranes6 or in small
*To whom correspondence should be addressed. E-mail: d.astruc@
ism.u-bordeaux1.fr (D.A.), hosmane@niu.edu (N.S.H.).
(1) Valliant, J. F.; Guenther, K. J.; Arienne, S. Coord. Chem. Rev. 2002,
232, 173–230. Yinghuai, Z.; Peng, A. T.; Carpenter, K.; Maguire, J. A.; Hosmane,
N. S.; Takagaki, M. J. Am. Chem. Soc. 2005, 127, 9875–9880. Parrott, M. C.;
Marchington, E. B.; Valliant, J. F.; Adronov, A. J. Am. Chem. Soc. 2005, 127,
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(2) Plesek, J. Chem. Rev. 1992, 92, 269–278. Grimes, R. N. J. Chem. Educ.
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(3) Zhu, Y.; Cheng, K. Y.; Maguire, J. A.; Hosmane, N. S. Curr. Chem.
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(4) Newkome, G. R.; Moorefield, C. N.; Keith, J. M.; Baker, G. R.;
Escamilla, G. S. Angew. Chem., Int. Ed. Engl. 1994, 33, 666–668.
(5) For a recent review of cluster-containing dendrimers, see: Hwang,
S.-H.; Shreiner, C. D.; Moorefield, C. N.; Newkome, C. N. New J. Chem.
2007, 31, 1192–1217.
(6) Dash, B. P.; Satapathy, R.; Maguire, J. A.; Hosmane, N. S. Org. Lett.
2008, 10, 2247–2250. Dash, B. P.; Satapathy, R.; Maguire, J. A.; Hosmane, N. S.
Chem. Commun. 2009, 3267–3269. Dash, B. P.; Satapathy, R.; Gaillard, E. R.;
Maguire, J. A.; Hosmane, N. S. J. Am. Chem. Soc. 2010, 132, 6578–6587.
Huisgen-type azide alkyne CuI-catalyzed dipolar “click”
cycloaddition reactions (CuAAC) have recently proved in-
valuable for connecting organic and bioorganic segments and
(7) Juarez-Perez, E. J.; Vinas, C.; Teixidor, F.; Nunez, R. Organometallics
2009, 28, 5550–5559.
(8) Yao, H.; Grimes, R. N.; Corsini, M.; Zanello, P. Organometallics
2003, 22, 4381–4383.
(9) Wu, G.; Barth, R. F.; Yang, W.; Chatterjee, M.; Jjarks, W.; Ciesielki,
M. J.; Fenstermaker, R. A. Bioconjug. Chem. 2004, 15, 185–194. Shukla, R.;
Thomas, T. P.; Peters, J. L.; Desai, A. M.; Kukowska-Latallo, J.; Patri, A. K.;
Kotlyar, A.; Baker, J. R., Jr. Bioconjugate Chem. 2006, 17, 1109–1115. Wu, G.;
Barth, R. F.; Swidall, M.; Bandyopadhyaya, A. K.; Jjarks, W.; Khorsandio, B.;
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(10) Dash, B. P.; Satapathy, R.; Maguire, J. A.; Hosmane, N. S. Orga-
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r
pubs.acs.org/IC
Published on Web 10/15/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 22, 2010 10703
Scheme 1. General Scheme for the Synthesis of the Dendrimers Gn-3nþ2-N3 (Generation Numbers n = 0-2) Used for the “Click” Reactionsa
a See also references12-18, and 20.
functions.11,12 We wish to report here the “click” synthesis,
spectroscopic and analytical characterization, and thermal
stability of large arene-centered dendrimers with up to 81
o-carborane cluster termini MeC2B10H10, that is, 810 B
atoms per dendrimer molecule.
Results and Discussion
1. Synthesis of the Organic Precursors. Arene-centered
dendrimers have been synthesized as previously reported
by η5-C5H5Feþ-induced nona-allylation of mesitylene,13
followed by photochemical decomplexation using visible
light,14 hydrosilylation of the terminal double bonds with
chloromethyldimethylsilane, and Williamson reaction with
the phenoltriallyl dendron p-HO-C6H4C(CH2CHdCH2)3
(11) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B.
Angew. Chem., Int. Ed. 2002, 41, 2596–2600. Tornøe, C. W.; Christensen, C.;
Meldal, M. J. Org. Chem. 2002, 67, 3057–3064. Meldal, M.; Tornøe, C. W.
Chem. Rev. 2008, 108, 2952–3015. Meldal, M. Macromol. Rapid Commun.
2008, 29, 1016–1051.
(12) For “click” metallodendrimers, see: Ornelas, C.; Ruiz, J.; Cloutet, E.;
Alves, S.; Astruc, D. Angew. Chem., Int. Ed. 2007, 46, 872–877; For a review of
“click” dendrimers, see:. Franc, G.; Kakkar, A. Chem. Commun. 2008, 5267–
5276.
(13) Moulines, F.; Astruc, D. Angew. Chem., Int. Ed. Engl. 1988, 27, 1347–
1349. Moulines, F.; Gloaguen, B.; Astruc, D. Angew. Chem., Int. Ed. Engl..
1992, 28, 458–460. Moulines, F.; Djakovitch, L.; Boese, R.; Gloaguen, B.; Thiel,
W.; Fillaut, J.-L.; Delville, M.-H.; Astruc, D. Angew. Chem., Int. Ed. Engl. 1993,
32, 1075–1077.

10704 Inorganic Chemistry, Vol. 49, No. 22, 2010
Djeda et al.
Scheme 2. Synthesis of the Functionalized Carborane Cluster 5 with a
Terminal Alkyne Group
in the formation of insoluble materials presumably result-
ing from steric saturation at the dendrimer periphery,19
and further analyses of these insoluble materials were not
performed.
With G0-G2, the reaction mixture changed color from
brown at 0 °C to yellow at room temperature. The reac-
tion was not complete with catalytic amounts of CuI, that
were not sufficient, as in previous “click” reactions involving
dendrimers, presumably because of encapsulation of CuI
by coordinating to the resulting 1,2,3-triazolyl ligand.12,18
The copper salt was finally removed after stirring with an
aqueous NH3 solution as [Cu(NH3)2(H2O)2] [SO4]. The
resulting carborane-terminated dendrimers were purified,
after workup, by precipitation using methanol from dichloro-
methane (DCM) solutions. They were characterized by
1H, 13C, and 11B NMR, IR, UV-vis, matrix-assisted laser
desorption/ionization time of flight (MALDI-TOF) mass
spectroscopies, and elemental analysis. The IR spectra of
dendrimers containing o-carborane clusters showed strong
bands between 2574 and 2584 cm-1 corresponding to ν
(B-H). The 11B NMR spectra of carborane-appended den-
drimers showed peaks between -5.78 and -10.63 ppm
indicating the presence of o-carborane clusters.6,10 Size
exclusion chromatography (SEC, Figure 1) showed very
low polydispersity indices (PDI = 1.01 for G0 and G1, and
1.05 for G2). These low polydispersity values were measured
for the signal of each dendrimer only and do not take into
account the side signals of low intensities because of agglo-
merated dendrimers that are visible in Figure 1. Dynamic
light scattering (DLS) measurements for G1 and G2 indi-
cated hydrodynamic diameters of 5.7 nm for G1-27cage and
12.9 nm G2-81cage, and Table 1 shows the DLS data toge-
ther with the calculated diffusion coefficients, volumes and
densities of the carborane dendrimers. Finally, the MALDI-
TOF mass spectral data of G0-9cage, G1-27cage, and G2-
81cage dendrimers confirmed their formation. The MAL-
DI-TOF mass spectral data for the G0-9cage dendrimer
showed a sharp peak at m/z 3960.7 against the exact mole-
cular weight m/z 3963.2, whereas for the dendrimers con-
taining larger number of cages broad bands were observed
around the exact molecular weight. For the G1-27cage
dendrimer a broad band was observed between m/z 8268-
13849 peaking at m/z 11385 against the exact molecular
weight m/z 13650.7. Similarly for the G2-81cage dendri-
mer a broad band was observed between m/z 21311-
104535 peaking at m/z 48000 against the exact molecular
weight m/z 42695.2 (see the Supporting Information).
The relatively broad distribution observed for G1-27 and
G2-81 is due to the isotope distribution of boron atoms
and the presence of high numbers of boron atoms in these
molecules.
yielding a 27-allyl dendrimer.15 Reiteration of the hydro-
silylation with chloromethyldimethylsilane and subsequent
Williamson reaction with this dendron yielded the known
dendrimers containing 3nþ2 allyl termini, n being the gen-
eration number.16 Terminal functionalization with azido
groups could be achieved by nucleophilic substitution of
the terminal chloro group of the chloromethylsilyl-termi-
nated dendrimers of generations 0-2 (G0-G2) with sodium
azide (Scheme 1), which allowed to carry out “click”
reactions at the periphery of dendrimers with terminal
alkynes.17 This strategy has recently led to 1,2,3-triazoly-
ferrocenyl dendrimers up to G2 with 34 = 81 termini.12,18
Here, we are using these azido-terminated dendrimers for
“click” reactions with a carborane that is functionalized
with an alkyne group.
This alkyne precursor 5 used for the “click” reactions
and containing the o-carborane cluster MeC2B10H10 was
synthesized by deprotonation of 1-methyl-o-carborane,
2, with n-BuLi, followed by benzylation of the resulting
carborane anion using p-I-C6H4CH2Br, giving 3, which
was subsequently coupled with trimethylsilylacetylene
using the Sonogashira coupling catalyzed by PdCl2-
(PPh3)2 and CuI in the presence of triethylamine, and
finally deprotection of this alkyne 4 using K2CO3 in
methanol (Scheme 2).
2. “Click” Synthesis of the Carborane-Terminated Den-
drimers. The CuI-catalyzed alkyne azide 1,3-dipolar cy-
cloaddition (CuAAC) was carried out between the alkyne
5 and the three dendrimers G0-9N3, G1-27 N3, and G2-
81N3 using a stoichiometric amount of CuI generated from
CuSO4 and sodium ascorbate in water-tetrahydrofuran
(THF, 1:1) mixture (Schemes 3 and 4, Charts 1 and 2).
Attempts to carry out such reactions with higher azido-
terminated dendrimers (G3-243N3 and G4-729N3) resulted
(14) Catheline, D.; Astruc, D. J. Organomet. Chem. 1983, 248, C9–C12.
Catheline, D.; Astruc, D. J. Organomet. Chem. 1984, 272, 417–426. Sandler,
A. C.; Ruiz, J.; Astruc, D. Organometallics, 2010, 29, DOI: 10.1021/om100168x.
(15) 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, 2929–2930. Nlate, S.; Ruiz, J.; Blais, J.-C.; Astruc, D. Chem. Commun.
2000, 417–418. Nlate, S.; Ruiz, J.; Sartor, V.; Navarro, R.; Blais, J.-C.; Astruc, D.
Chem.;Eur. J. 2000, 6, 2544–2553.
(16) Ruiz, J.; Lafuente, G.; Marcen, S.; Ornelas, C.; Lazare, S.; Cloutet,
E.; Blais, J.-C.; Astruc, D. J. Am. Chem. Soc. 2003, 125, 7250–7257.
(17) Ornelas, C.; Boisselier, E.; Martinez, V.; Pianet, I.; Ruiz, J..; Astruc,
D. Chem. Commun. 2007, 5093–5095. Boisselier, E.; Diallo, A. K.; Salmon, L.;
Ruiz, J.; Astruc, D. Chem. Commun. 2008, 4819–4821. Boisselier, E.; Ornelas,
C.; Pianet, I.; Ruiz, J.; Astruc, D. Chem.;Eur. J. 2008, 14, 5577–5587.
(18) Ornelas, C.; Salmon, L.; Ruiz, J.; Astruc, D. Chem.;Eur. J. 2008, 14,
50–64. Ornelas, C.; Ruiz, J.; Salmon, L.; Astruc, D. Adv. Synth. Catal. 2008,
350, 837–845.
3. Thermal Properties. Recent investigations on the
thermal properties of carborane-appended compounds
have led to a conclusion that incorporation of multiple
carborane clusters make the compound highly thermally
stable.6,10 A systematic thermal analysis of polycarborane
dendrimers also gave similar results, and these compounds
(19) For steric saturation of the dendrimer peripheries, see: de Gennes,
P. G.; Hervet, H. J. Phys., Lett. 1983, 44, L351–L360. Naidoo, K. J.; Hugues,
€
S. J.; Moss, J. R. Macromolecules 1999, 32, 331–341. Potschke, D.; Ballauf, M.;
€
Lindner, P.; Fischer, M.; Vogtle, F. Macromolecules 1999, 32, 4079–4087.
(20) Astruc, D.; Ruiz, J. Tetrahedron 2010, 66, 1769–1785; Tetrahedron
Report No. 903.

Article
Inorganic Chemistry, Vol. 49, No. 22, 2010 10705
Scheme 3
Scheme 4
are found to be thermally very robust (Figure 2). The
temperatures at which 10% mass loss of all the dendrimers
occurred are summarized in Table 2. For the G0-9cage
dendrimer that contains nine o-carborane clusters, the
point at which 10% mass loss occurred is found to be
411 °C, and finally about 32-weight % of the residue is
maintained at 600 °C. For the G1-27cage dendrimer, that
contains 27 o-carboranes, the 10% mass loss occurs at
371°C, and about 18-weight% oftheresidueismaintained
at 600 °C. The G2-81cage dendrimer that contains eighty-
one Ccage-appended o-carboranes, the 10% mass loss occ-
urred at 392 °C, and about 24-weight % of the residue is
maintained at 600 °C. The G0-9cage dendrimer is found to
be the most stable compound in the series. The result is
consistent with the boron content of the dendrimers. The
G0-9cage dendrimer has the highest boron content that
is about 24.5%, whereas the dendrimers G1-27cage and
G2-81cage possess about 21 and 20.5% boron by weight
respectively. In addition, G0-9cage does not contain the
phenolate linkage that is relatively fragile, whereas the
larger dendrimers do, which favors G0-9cage in terms of
thermal stability. Finally, a dendrimer effect seems to better
stabilize G2-81cage compared to G1-27cage. Further, it
should be noted that these carborane-appended dendrimers
are still less thermally stable than recently reported co-
baltabisdicarbollides for which only a 10-30% mass loss
occurs at 700 °C.10
be fluorescent compounds. Although these dendrimers
contain multiple phenyl rings, they are not conjugated.
Thus, a strong absorption band was observed for all den-
drimers peaking at 258 nm, and emission spectra of lower
intensity were observed between 280 and 480 nm for all
three dendrimers (Figure 3).
Concluding Remarks
Huisgen-type azide alkyne CuI-catalyzed dipolar “click”
cycloaddition reactions (CuAAC) between a o-carborane
monomeric cluster containing an ethynyl group and arene-
centered azido-terminated dendrimers Gn-3nþ2N3 of genera-
tions 0, 1, and 2 have proved to be very facile, leading to
well-characterized, thermally robust o-carborane-containing
dendrimers. Higher-generation analogues were prepared, but
their insolubility in all solvents, presumably because of steric
saturation at the dendrimer peripheries, precluded their char-
acterization. It is likely that the tether-lengthening strategy
recently used for the synthesis of dendritic molecular batteries
and that led to metallodendrimers containing up to 14,000
metallocenyl termini (Fe, Co)21 might also push the limit of
carborane dendrimer syntheses far beyond the current limit.
Such a goal is important in view of the requirement of high
content of boron atoms in a small nanospace for boron
neutron capture therapy.1,2 Nevertheless, this useful “click”
strategy has produced here among the largest characterized
4. Photophysical Properties. Recently, the incorpora-
tion of o-carborane clusters into π-conjugated compounds
was reported to result in enhanced emission intensity.6,10
However, the dendrimers described here are not found to
(21) Ornelas, C.; Ruiz, J.; Belin, C.; Astruc, D. J. Am. Chem. Soc. 2009,
131, 590–601. Ornelas, C.; Ruiz, J.; Astruc, D. Organometallics 2009, 28, 2716–
2723. Astruc, D.; Ornelas, C.; Ruiz, J. Chem., Eur. J. 2009, 15, 8936–8944.
Djeda, R.; Ornelas, C.; Ruiz, J.; Astruc, D. Inorg. Chem. 2010, 49, 6085–6101.

10706 Inorganic Chemistry, Vol. 49, No. 22, 2010
Djeda et al.
Chart 1
carborane dendrimers known to-date with up to 810 boron
atoms in a single molecule.
Zetasizer 3000 HSA instrument at 25 °C at an angle of 90°.
Infrared spectra were recorded on an ATI Mattson Genesis
series FT-IR spectrophotometer. UV absorption and emission
spectra were measured with Perkin-Elmer Lambda 19 UV-vis
spectrometer and Hitachi F-2500 Fluorescence spectrophotom-
eter, respectively. Thermal gravimetric analysis (TGA) was
performed on a Perkin-Elmer Pyris 1 analyzer at a heating rate of
5 °C/min under argon. The elemental analyses were performed by
the Center of Microanalyses of the CNRS at Lyon Villeurbanne,
France. The dendrimers G0-9N3, G1-27N3, and G2-81N3 were
synthesized according to references 12 and 18. The dendron 1 was
synthesized according to references 15 and 20. 1-Me-o-carborane
2 was prepared using a previously reported procedure.6
Experimental Section
General Data. Reagent-grade diethyl ether, dimethoxyethane
(DME) and tetrahydrofuran (THF) were predried over Na foil
and distilled from sodium-benzophenone anion under argon
immediately prior to use. Dichloromethane (DCM) was distilled
from calcium hydride just before use. All other solvents (hexane,
methanol) and chemicals were used as received. The Kartsted
catalyst and anhydrous DMF were purchased from Aldrich. 1H
NMR spectra were recorded at 25 °C with a Bruker AC 200,
300, or 500 (200, 300, or 500 MHz) spectrometer. The 13C NMR
spectra were obtained in the pulsed FT mode at 50, 75, or 125
MHz with a Bruker AC 200, 300, or 500 spectrometer, and the
11B NMR spectra were recorded at 160.5 MHz with a Bruker
Carborane Derivative 3. 1-Methyl-o-carborane, 2, (1.4 g, 8.86
mmol) was solubilized in 60 mL of dry DME), then n-BuLi
(1.6 M in hexanes, 6.64 mL, 10.63 mmol) was added to it at 0 °C.
This reaction mixture was stirred at 0 °C for 1 h, and a solution
of 4-iodo benzyl bromide (2.10 g, 7.08 mmol) in 5 mL of DME
was added at 0 °C. The reaction mixture was refluxed at 100 °C
for 24 h, then cooled to room temperature, and filtered over
a short silica gel column. Recrystallization in hexane/dichloro-
methane yielded 2.1 g (65%) of the pure compound 3. M.P:
123 °C. 1H NMR (CDCl3, 500 MHz): δ 7.71 (d, 2H, J = 8.0 Hz),
AC 500 relative to BF3 Et2O. All chemical shifts are reported in
3
parts per million (δ, ppm) with reference to Me4Si (TMS) for the
1H and 13C NMR spectra and with reference to BF3 Et2O for
3
the 11B NMR spectra. The mass spectra were recorded using an
Applied Biosystems Voyager-DE STR-MALDI-TOF spectrom-
eter. The DLS measurements were made using a Malvern

Article
Inorganic Chemistry, Vol. 49, No. 22, 2010 10707
Chart 2
74.8 (Ccage), 40.7, 23.7. 11B NMR (CDCl3, proton decoupled, 64.2
MHz): δ -3.98 (1 B), -5.50 (1 B), -10.1 (8 B). B10C10H17I: calcd.
C 32.26, H 4.60; found C 32.28, H 4.59.
Carborane Derivative 4. To a mixture of compound 3 (3.0 g,
8.01 mmol) in 40 mL of dry THF and 40 mL of Et3N,
[PdCl2(PPh3)2] (224 mg, 0.32 mmol), CuI (76.2 mg, 0.4 mmol),
ethynyltrimethylsilane (1.67 mL, 12.02 mmol) were added at
room temperature (rt). The reaction mixture was then stirred
at rt overnight, then filtered over a silicagel pad. After evapora-
tion of the solvent, the crude reaction product was purified by
silica gel column chromatography with hexane as eluent, which
gave 2.48 g of pure compound 4 as a colorless solid. Yield: 90%.
M.P: 98 °C. 1H NMR (CDCl3, 500 MHz): δ 7.47(d, 2H, J = 8.0
Hz), 7.14(d, 2H, J = 8.0 Hz), 3.45(s, 2H), 2.16 (s, 3H, cluster-
CH3), 0.28(s, 9H, SiMe3).13C NMR (CDCl3, 125 MHz): δ 135.2,
132.1, 130.2, 123.0, 104.3, 95.3, 77.1(Ccage), 74.8(Ccage), 41.0,
23.6, -0.0., 11B NMR (CDCl3, proton decoupled, 64.2 MHz): δ
-4.03 (1 B), -5.52 (1 B), -10.11 (8 B). IR (KBr): 2959, 2594,
2898, 2162, 1505, 1462, 1250, 1020 cm-1. B10C15H28Si: calcd. C
52.28, H 8.19; found C 52.11, H 7.93.
Figure 1. Size exclusion chromatograms of the carborane dendrimers.
Red line, G0-9cage; black line, G1-27cage; blue line, G2-81cage. The poly-
dispersities indices (PDI) are 1.01 (G0-9cage), 1.01 (G1-27-cage), and 1.05
(G2-81-cage).
Carborane Derivative 5. Compound 4 (2.2.g, 6.37 mmol) was
dissolved in 20 mL of THF and 20 mL of MeOH, then K2CO3
(968 mg, 7.01 mmol) was added, and the mixture was stirred at rt
6.96 (d, 2H, J = 8.0 Hz), 3.42 (s, 2H), 2.17(s, 3H cluster-CH3).13C
NMR (CDCl3, 125 MHz): δ 137.7, 134.5, 132.1, 93.9, 76.8 (Ccage),

10708 Inorganic Chemistry, Vol. 49, No. 22, 2010
Djeda et al.
Table 1. Hydrodynamic Diameters (2ꢀRh) Determined by DLS, and Calculated Volumes, Diffusion Coefficients, and Densities for G1-27cage and G2-81cage
producta
MMb
2 ꢀ Rh
D (m2.s-1 d
)
volumee(m3)
df
c
9-cage
27-cage
81-cage
3963
13693
42821
5.7 ( 0.8
12.9 ( 2.0
17 ꢀ 10-14
7.4 ꢀ 10-14
(0.97 ( 0.44) ꢀ 10-25
(11.2 ( 5.0) ꢀ 10-25
230 ( 100
63 ( 28
a The hydrodynamic diameter of G1-9cage could not be obtained by DLS because it is below the lower limit of the technique. b MM: molecular mass
(g mol-1.). c 2ꢀRh: hydrodynamic diameter (nm) measured in THF at 25 °C. d D: diffusion coefficient (m2 s-1). e considering the globular shape of
the dendrimer as a perfect sphere (V = (4/3)πRh3) f d: density (kg/m3).
General Procedure for the “Click” Synthesis of the Polycar-
borane Dendrimers Gn-3nþ2cage, (n = 0, 1, 2). The compound 5
(1.5 equiv per branch) and the azido-terminated dendrimer were
dissolved in 50 mL of degassed THF, then 50 mL of degassed
water was added; then the reaction mixture was cooled to 0 °C,
and an aqueous solution of CuSO4 1 M (1 equiv per branch,
THF-H2O, 1:1) was added at 0 °C, followed by the dropwise
addition of a freshly prepared solution of sodium ascorbate 1 M
(2 equiv per branch). The color of the solution, that was brown at
0 °C, changed to yellow at rt. The reaction mixture was allowed to
stir for 24 h under nitrogen atmosphere at rt. Then, 100 mL of
DCMwasadded, followedbythe additionofanaqueoussolution
of ammonia. The mixture was allowed to stir for10 min to remove
all the copper salt [Cu(H2O)2(NH3)2][SO4] trapped inside the
dendrimer. The organic phase was washed twice with water, dried
Figure 2. Thermogravimetric analysis (TGA) curves of carborane den-
over sodium sulfate, filtered, and the solvent was removed under
drimers under argon. Blue line, G0-9cage; red line, G1-27cage; green line,
vacuum. The product was then washed with methanol to remove
G2-81cage.
the excess alkyne and precipitated from a DCM solution with
methanol.
Dendrimer G0-9cage. The synthesis was carried out from
Table 2. 10% Mass Loss Temperatures from TGA
ethynylcarborane (0.121 g, 0.445 mmol) and G0-9N3 (0.050 g,
dendrimers
temperature (°C)
0.033 mmol) using the general procedure for the “click” synthesis
of the polycarboranes Gn-3nþ2cage, (n =0-2). The nonacarbor-
ane G0-9cage was obtained as a colorless dusty powder (0.110 g,
G0-9cage
G1-27cage
G2-81cage
411
371
392
1
yield 85%). H NMR (CDCl3, 200 MHz), δppm: 7.77 (d, 18H,
arom-cluster), 7.75(s,9Hoftriazole), 7.18(d, 18H, arom.), 6.97 (s,
3H, CH core), 3.89 (s, 18H, SiCH2-triazole), 3.44 (s, 18H, cluster-
CH2-), 2.16 (s, 27H, cluster-CH3), 1.62 (s, 18H, CH2CH2CH2Si),
1.09 (s, 18H, CH2CH2CH2Si), 0.62 (s, 18H, CH2CH2CH2Si), 0.09
(s, 54H, Si(CH3)2). 13C NMR (CDCl3, 50 MHz), δppm: 146.5 (Cq-
triazole), 145.7 (Cq-core), 134.5 (Cq of Ar-cluster), 130.7 and
125.5 (CH of Ar-cluster), 121.6 (CH of arom. core), 121.0 (CH-
triazole), 77.4 and 75.0 (C of cluster) 43.9 (CqCH2CH2CH2Si),
41.7 (CqCH2CH2CH2Si), 41.3 (triazole-CH2Si), 40.8 (cluster-
CH2-Ar), 23.5 (cluster-CH3), 17.5 (CqCH2CH2CH2Si), 14.9
(CqCH2CH2CH2Si), -3.8 (Si(CH3)2). 11B NMR (CDCl3, proton
decoupled, 160.5 MHz): δ -5.78 (18 B), -10.42 (72 B). IR (KBr):
2926, 2584 (B-H), 1494, 1372, 1256, 814 cm-1. MALDI-TOF-
MS (m/z): calcd 3963.2; found 3960.7 (Mþ-2, 100%). Anal. Calcd
for C171H309B90Si9N27: C 51.54, H 7.76 ; found: C 50.83, H 7.91.
Dendrimer G1-27cage. The dendrimer G1-27cage was synthe-
sized from ethynylcarborane (0.088 g, 0.322 mmol) and G1-27N3
(0.050 g, 0.008 mmol) using the general procedure for the “click”
synthesis of the polycarboranes Gn-3nþ2carborane, (n = 0-2).
The dendrimer G1-27cage was obtained as a colorless dusty
powder (0.088 g, yield 81%). 1H NMR (CDCl3, 200 MHz),
Figure 3. Absorption and emission spectra of the carborane dendrimers
in DCM. Bluelines, G0-9cage; red lines, G127cage; green lines, G2-81cage.
for 5 h. The crude reaction mixture was filtered over a cotton
plug. After evaporation of the solvent under vacuum, the crude
reaction product was purified by silica gel column chromatog-
raphy with 20% ethyl acetate in hexane as eluent, giving 1.66 g of
pure compound 5 as a colorless solid. Yield: 95%. M.P: 120 °C.
1H NMR (CDCl3, 500 MHz): δ 7.50 (d, 2H, J = 8.0 Hz), 7.17(d,
2H, J = 8.0 Hz), 3.47(s, 2H), 3.14 (s, 1H), 2.17(s, 3H cluster-
CH3). 13C NMR (CDCl3, 125 MHz): δ 135.6, 132.3, 130.3,
122.0, 83.0, 78.1(Ccage), 77.0(Ccage), 74.9, 41.0, 23.6. 11B NMR
(CDCl3, proton decoupled, 64.2 MHz): δ -3.95 (1 B), -5.53
(1 B), -10.0 (8 B). IR (KBr): 3049, 2933, 2563, 2107, 1507, 1237,
1153, 1028 cm-1. B10C12H20: calcd. C 52.91, H 7.40; Found C
52.93, H 7.31. HRMS (ES) (m/z): calcd for B10C12H20: 274.2495;
Found 274.2496.
δppm: 7.77 (d, 54H, arom.), 7.67 (s, 27H of triazole), 7.19 (m,
72H, arom. and Ar-cluster), 6.89 (d, 18H, CH core), 3.88 (s, 54H,
SiCH2-triazole), 3.53 (s, 18H, OCH2Si), 3.44 (s, 54H, cluster-
CH2-), 2.15 (s, 81H, cluster-CH3), 1.58 (s, 72H, CH2CH2CH2Si),
1.09(s, 72H, CH2CH2CH2Si), 0.60 (s, 72H, CH2CH2CH2Si), 0.06
(s, 216H, Si(CH3)2). 13C NMR (CDCl3, 50 MHz), δppm: 159.0
(arom. OCq), 146.5 (Cq-triazole), 138.7 (arom. Cq), 134.5 (Cq of
Ar-cluster), 130.7 and 125.5 (CH of Ar-cluster), 127.0 and 113.4
(arom. CH of dendron), 120.6 (CH-triazole), 77.4 and 74.8 (C of
cluster), 60.3 (CH2OAr), 42.8 (CqCH2CH2CH2Si), 41.6(CqCH2-
CH2CH2Si), 40.9 (triazole-CH2Si), 40.8 (cluster-CH2-Ar), 23.5
(cluster-CH3), 17.3 (CqCH2CH2CH2Si), 14.7 (CqCH2CH2CH2Si),
-3.9 (Si(CH3)2). 11B NMR (CDCl3, proton decoupled, 160.5

Article
Inorganic Chemistry, Vol. 49, No. 22, 2010 10709
MHz): δ -5.84 (54 B), -10.42 (216 B). IR (KBr): 2931, 2581
(B-H), 1506, 1403, 1250, 814 cm-1. MALDI-TOF-MS (m/z):
calcd 13650.7; found a broad band between 8268 and 13849
peaking at 11385. Anal. Calcd for C612H1083B270Si36N81O9: C
53.67, H 7.91; found: C 53.68, H 8.15.
(CqCH2CH2CH2Si), -3.9 (Si(CH3)2). 11B NMR (CDCl3, proton
decoupled, 160.5 MHz): δ -5.86 (162 B), -10.63 (648 B). IR
(KBr): 2929, 2574 (B-H), 1503, 1381, 1254, 823 cm-1. MALDI-
TOF-MS (m/z): calcd 42695.2; found a broad band between 21311
and 104535 peaking at 47997. Anal. Calcd for C1935H3405B810Si117
-
N
243O36: C 54.26, H 7.95; found: C 54.59, H 8.35.
Dendrimer G2-81cage. The dendrimer G2-81cage was synthe-
sized from ethynylcarborane (0.081 g, 0.298 mmol) and G2-81N3
(0.050 g, 0.0025 mmol) using the general procedure for the “click”
synthesis of the polycarboranes Gn-3nþ2carborane, (n = 0-2).
The dendrimer G2-81cage was obtained as a colorless dusty
powder (0.083 g, yield 80%). 1H NMR (CDCl3, 200 MHz),
ꢁ
Acknowledgment. The Ministere de l’Enseignement
ꢀ
Superieur et de la Recherche Scientifique de Cote d’Ivoire (Ph.
D. grant to R.D.), the Universite Bordeaux 1, the Centre
^
ꢀ
National de la Recherche Scientifique (CNRS), the Institut
Universitaire de France (IUF, D.A.), the Agence Nationale
de la Recherche (ANR), and the National Science Foundation
(CHE-0840504 and CHE-0906179) are gratefully acknowledged
for financial support. The additional supports (to N.S.H.) from
the Alexander von Humboldt Foundation and the award from
NIU Inaugural Board of Trustees Professorship (N.S.H.) are
hereby acknowledged.
δppm: 7.76 (d, 162H, arom.), 7.65 (s, 81H of triazole), 7.19 (m,
234H, arom. and Ar-cluster), 6.87 (d, 72H, CH core), 3.87 (s,
162H, SiCH2-triazole), 3.50 (s, 72H, OCH2Si), 3.43 (s, 162H,
cluster-CH2-), 2.13 (s, 243H, cluster-CH3), 1.58 (s, 234H,
CH2CH2CH2Si), 1.07 (s, 234H, CH2CH2CH2Si), 0.58 (s, 234H,
CH2CH2CH2Si), 0.09 (s, 702H, Si(CH3)2). 13C NMR (CDCl3, 50
MHz), δppm: 159.0 (arom. OCq), 146.5 (Cq-triazole), 138.8 (arom.
Cq), 134.5 (Cq of Ar-cluster), 130.7 and 125.6 (CH of Ar-cluster),
127.0 and 113.5 (arom. CH of dendron), 120.7 (CH-triazole), 77.6
and 74.9 (C of cluster), 60.1 (CH2OAr), 42.9 (CqCH2CH2CH2Si),
41.7 (CqCH2CH2CH2Si), 41.0 (triazole-CH2Si), 40.8 (cluster-
CH2-Ar), 23.6 (cluster-CH3), 17.5 (CqCH2CH2CH2Si), 14.7
Supporting Information Available: 1H and 13C NMR, 11B, IR
and MALDI-TOF mass spectra of new products (PDF). This
material is available free of charge via the Internet at http://
pubs.acs.org.