Triazole-based ferrocenyl dendrimers as a medium for encapsulated palladium nanoparticles

Article abstract of DOI:10.1055/s-0032-1318236

Novel ferrocenyl dendrimers with 1,3,5-tris(aminothiophenol)benzeneamide core has been synthesized through click chemistry under microwave-assisted solid-support technique. The higher-generation ferrocenyl dendrimers can 'sense' and bind palladium nanopar

Full text of DOI:10.1055/s-0032-1318236

LETTER
▌575
letter
Triazole-Based Ferrocenyl Dendrimers as a Medium for Encapsulated
Palladium Nanoparticles
Triazole-Based Ferrocenyl Dendrimers
Perumal Rajakumar,*a Ramasamy Anandhan,a Sampath Malathi,b Sengottuvelan Balasubramanianb
a
Department of Organic Chemistry University of Madras, Guindy Campus Chennai – 600025, Tamil Nadu, India
Fax +91(44)22352492; E-mail: perumalrajakumar@gmail.com
b
Department of Inorganic Chemistry, University of Madras, Guindy Campus Chennai – 600025, Tamil Nadu, India
Received: 10.12.2012; Accepted after revision: 28.01.2013
try to their application in catalysis and nanosciences.9 The
1,2,3-triazole branching unit in dendrimer synthesis has
been achieved through click chemistry,10 followed by re-
duction of Pd(II) to Pd(0) which can agglomerate as PdNP
Abstract: Novel ferrocenyl dendrimers with 1,3,5-tris(aminothio-
phenol)benzeneamide core has been synthesized through click
chemistry under microwave-assisted solid-support technique. The
higher-generation ferrocenyl dendrimers can ‘sense’ and bind pal-
ladium nanoparticles (PdNP) by encapsulation whereas the lower- protected by the dendrimer frame.11
generation dendrimers stabilize the PdNP.
More recently, the synthesis of triazole ferrocenyl den-
Key words: ferrocenyl dendrimers, click chemistry, microwave,
drimers, which can recognize and ‘sense’ several transi-
tion-metal ions by using the variation of the potential of
the ferrocenyl wave, has been reported.12 Astruc and co-
workers13 reported an interesting family of ferrocenyl tri-
azolyl dendrimers by click reaction and applied them as
templates and hosting agents for PdNP and found that
1,2,3-triazole units formed by click reaction are capable of
binding Pd(OAc)2 in one-to-one stoichiometry. As evi-
denced by the change of redox wave of ferrocenyl units in
cyclic voltammetry, the complexation occurs in order,
from inner to outer, if the dendrimer contains more than
one layer of triazole units. Herein we report the synthesis
of ferrocenyl dendrimers 1–4 (Figure 1) through click
chemistry under microwave-assisted solid-support tech-
nique and their stabilization effect on palladium nano-
particles.
nanoparticles, palladium
Dendrimers which are peripherally functionalized with
the electrochemically active ferrocene group can be used
as potential multi-electron redox catalysts, electron reser-
voirs, electrode modifiers, ion sensors, mimics of biolog-
ical redox processes,1 and in nanosciences, such as
nanoreactors2 and nanomedicine.3 The properties of such
dendrimers are of great interest because the number of
electrochemically active functional groups can be precise-
ly controlled. The electrochemical properties of the ferro-
cenyl dendrimers are of particular interest in mimic-
related nanometer-sized biological processes and provide
useful energy-relevant devices. Microwave-assisted syn-
thesis has been utilized as a powerful and effective tech-
nique to promote a group of chemical reactions.4
Huisgen’s 1,3-dipolar cycloaddition of alkyne to azide
yielding triazole is, undoubtedly, the premier example of
‘click chemistry’ reactions.5 The mechanistic proposal of
the Cu(I)-catalyzed alkyne–azide 1,3-dipolar cycloaddi-
tion was reported and implicated a polar transition state,
favorable for microwave activation.6
Reaction of 3,5-bis(propargyloxy)benzyl chloride (6)
with two equivalents of azidomethyl ferrocene 5 under
microwave-catalyzed click-reaction conditions using
Na2SO4 as a solid support gave first-generation ferroce-
nyldendritic chloride 7 in 96% yield (AB2-type). The use
of NaN3 in a mixture of acetone and water (4:1) at 60 °C
allowed the transformation of the ferrocenyldendritic
chloride 7 to the corresponding ferrocenyldendritic azide
8 in 98% yield (Scheme 1). 3,5-Bis(propargyloxy)benzyl-
chloride (6)14 and 3,4,5-tris(propargyloxy)benzylchloride
(9)14 were prepared by the conventional propargylation of
methyl 3,5-dihydroxy benzoate and methyl 3,4,5-tri-
hydroxy benzoate, respectively, followed by treatment
with LAH and further with thionyl chloride and pyridine
in dichloromethane. Reaction of 2-aminothiophenol with
3,5-bis(propargyloxy)benzyl chloride (6) or rather 3,4,5-
tris(propargyloxy)benzyl chloride (9) in toluene and
aqueous KOH in the presence of a catalytic amount of
tetrabutylammonium bromide (TBAB) as phase-transfer
catalyst at reflux furnished 3,5-bis(propargyloxy)benzyl-
2-aminothiophenol (10) and 3,4,5-tris(propargyloxy)-
benzyl-2-aminothiophenol (11) in 86% and 79% yields,
respectively.15,16 Reaction of three equivalents of 3,5-
bis(propargyloxy)benzyl-2-aminothiophenol (10) or rath-
er 3,4,5-tris(propargyloxy)benzyl-2-aminothiophenol (11)
The dendrimer chemistry offers some significant advan-
tages for preparing nanoparticles in the size range of 1–2
nm. One of the most remarkable examples of dendritic en-
capsulation is that of transition-metal nanoparticles (NP)
that was disclosed more than a decade ago using polyam-
idoamine (PAMAM) dendrimer7 and polypropyleneimine
(PPI) dendrimer.8 In particular, NP encapsulation has
been applied to many transition metals including the use
of a redox reaction between a NP and other metal cations.
Most of the advantages arise by the presence of the den-
drimer, which can template and stabilize the encapsulated
nanoparticles. The synthesis and stabilization of transi-
tion-metal NP inside dendrimers has created a timely en-
SYNLETT 2013, 24, 0575–0580
Advanced online publication: 12.02.2013
DOI: 10.1055/s-0032-1318236; Art ID: ST-2012-B1057-L
© Georg Thieme Verlag Stuttgart · New York
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6

576
P. Rajakumar et al.
LETTER
with one equivalent of benzene-1,3,5-tricarboxylic acid dendrimers 1–419–23 in 96%, 84%, 87%, and 77% yields,
chloride in the presence of Et3N in dry dichloromethane at respectively (Scheme 2). The 1H NMR spectrum of den-
room temperature under N2 afforded the amide-core- drimer 4 displayed a sharp singlet at δ = 4.94 and 5.22
based propargylated dendritic wedges 12 and 1317,18 in ppm for the O-mehtylene and N-methylene protons, the
75% and 71% yields, respectively.
two different triazolyl protons and amide protons are rep-
resented as a singlet at δ = 7.57, 7.61, and 9.51 ppm, re-
spectively in addition to other aliphatic and aromatic
protons. The 13C NMR spectrum of 4 displayed ferrocenyl
methylene carbons at δ = 61.8 and 80.8 ppm, respectively,
and the carbons at δ = 68.8, 68.9, and 69.0 ppm, the O-
methylene and N-carbons at δ = 68.8, 68.9, and 69.0 ppm,
the O-methylene and N-methylene carbons at δ = 61.8 and
80.8 ppm, respectively. The triazole and amide carbons
appeared at δ = 143.2, 143.4, 143.8, and 163.1 ppm, re-
spectively, in addition to other aliphatic and aromatic car-
bons. The appearance of the molecular ion peak at m/z =
7821 [M+ + Na] also confirmed the structure of ferrocenyl
dendrimer 4. Similarly, the structure of the three other
dendrimers 1–3 is confirmed from the spectral and analyt-
ical data.
The 1H NMR spectrum of propargylated dendritic wedge
13 displayed two different triplets for the two different
acetylene protons at δ = 2.34 and 2.45 ppm, and a singlet
for S-methylene protons at δ = 3.89 ppm and an NH pro-
ton as a broad singlet at δ = 9. 31 ppm. In the 13C NMR
spectrum, the propargylated dendritic wedge 13 displayed
the two different acetylene carbons at δ = 75.3 and 75.9
ppm, the S-methylene carbon at δ = 41.8 ppm, and the car-
bonyl carbon at δ = 168.7 ppm. The FTIR spectrum also
showed the carbonyl stretching frequency at 1639 cm–1
for the propargylated dendritic wedge 13. The click chem-
istry on the propargylated dendritic wedge 12 and 13 with
azidomethyl ferrocene 5 and dendritic azide 8 under
microwave-assisted click-reaction conditions with solid
support (Na2SO4) as mentioned earlier gave ferrocenyl
OR
OR
OR
OR
OR
OR
RO
RO
S
S
OR
NH
O
O
NH
RO
S
S
H
H
O
N
N
O
HN
S
O
O
HN
S
RO
RO
RO
OR
OR
OR
2
1
RO
OR
OR
OR
OR
RO
RO
N
N
OR
N
N
N
N
N
N
N
OR
N
N
N
O
OR
OR
N
N
N
O
OR
OR
O
N
N
N
RO
S
N
N
N
O
O
O
O
N
RO
RO
O
NH
O
O
S
N
N
O
N
NH
N
O
N
S
H
N
N
N
O
N
S
RO
H
N
HN
S
O
O
OR
O
HN
OR
S
O
O
N
N
O
O
N
N
O
N
N
N
N
N
OR
N
RO
N
N
N
N
OR
RO
N
RO
OR
OR
RO
RO
OR
3
R =
N
N
Fe
4
N
Figure 1 Structure of the ferrocenyl dendrimers 1–4
Synlett 2013, 24, 575–580
© Georg Thieme Verlag Stuttgart · New York

LETTER
Triazole-Based Ferrocenyl Dendrimers
577
The PdNP24 were synthesized by reaction between the fer-
rocenyl dendrimers containing triazolyl groups with a
stoichiometric amount of PdCl2 (1 equiv per triazole unit)
in a mixture of chloroform and methanol (2:1), followed
by addition of NaBH4 (10 equiv per Pd) as reducing agent.
Though methanol is able to reduce PdCl2 to Pd(0), which
could retain the Pd(0) atoms inside the dendrimer, in the
present investigation a combination of MeOH and NaBH4
is used. Addition of NaBH4 not only helps the reaction to
proceed faster but also generates PdNP of smaller size.
The formation of the NP was observed by the color
change of the solution from yellow to golden brown and
confirmed by UV-vis spectroscopy (Figure 2). The UV-
vis spectrum of the ferrocenyl dendrimer 1 (DEN-6 teth-
ers) and ferrocenyl dendrimer 4 (DEN-18 tethers) show a
new band at 326 and 360 nm that corresponds to the for-
mation of PdNP that are stabilized by adsorption of PdNP
on the triazole unit of the dendrimers (Table 1).
X
X
O
O
X
i
N
N
N
+
O
O
Fe
N
N
N
5 X = CH2N3
6 X = CH2Cl
Fe
ii
Fe
7 X = CH2Cl
8 X = CH2N3
Scheme 1 Reagents and conditions: (i) Na2SO4, CuSO4 (5 mol%),
sodium ascorbate (10 mol%), MW (80 W), 1 min; (ii) NaN3 (1.5
equiv), acetone–H2O, 60 °C, 3 h.
Table 1 Optical Properties of Ferrocenyl Dendrimers 1 and 4 before and after Addition of PdCl2 and NaBH4 (PdNP)a
Entry
Dendrimers at λmax (nm)
Dendrimers with PdCl2 at λmax (nm)
Dendrimers with PdNPs at λmax (nm)
Dendrimer 1
Dendrimer 4
239
243
241
245
360
326
a PdNP that are stabilized by adsorption of PdNP on the triazole unit of the dendrimers.
O
R
O
H2N
S
R
O
S
O
Cl
O
NH
i
S
ii
H
N
O
O
O
R
O
O
O
HN
R
S
6 R = H
10 R = H
O
O
9 R =
11 R =
O
O
R
12 R = H
O
13 R =
iii
ferrocenyl dendrimers 1–4
Scheme 2 Reagents and conditions: (i) 2-aminothiophenol, TBAB, toluene–H2O, reflux, 12 h; (ii) benzene-1,3,5-tricarboxylic acid chloride,
Et3N, CH2Cl2 (dry), 24 h; (iii) azidomethyl ferrocene 5 (6 and 9 equiv) and dendritic azide 8 (6 and 9 equiv), CuSO4 (5 mol %), sodium ascorbate
(10 mol%), MW (80 W), 1 min.
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 575–580

578
P. Rajakumar et al.
LETTER
Figure 2 (a) UV-vis spectra of PdNP stabilized by ferrocenyl
dendrimer 1; (b) UV-vis spectra of PdNP stabilized by ferrocenyl
dendrimer 4.
The size of the PdNP generated using the ferrocenyl den-
drimers is controlled due to the complexation of the ferro-
cenyltriazolyl unit to Pd(II) and thus the ferrocenyl group
plays an important role. It blocks the periphery, which re-
tains the Pd(0) atoms inside the dendrimer, and conse-
quently leads to the formation of very small PdNP. Thus,
the size of the generated PdNP is controlled by the den-
drimer generations. Transmission electron microscopy
(TEM) images show that lower-generation ferrocenyl
dendrimers 1 and 2 (DEN-6 and DEN-9 tethers) are capa-
ble of stabilizing the PdNP of large size (5.3 ± 0.05 and
3.3 ± 0.05 nm). On the other hand, the higher-generation
ferrocenyl dendrimers 3 and 4 (DEN-12 and DEN-18 teth-
ers) are able to encapsulate PdNP of small size (1.64 ±
0.05 and 1.32 ± 0.05 nm, Figure 3).
Figure 3 (a) Ferrocenyl dendrimer 1 DEN-6-G0/PdNP: TEM image
and size distribution; (b) ferrocenyl dendrimer 2 DEN-9-G0/PdNP:
TEM image and size distribution; (c) ferrocenyl dendrimer 3 DEN-
12-G1/PdNP: TEM image and size distribution; (d) ferrocenyl den-
drimer 4 DEN-18-G1/PdNP: TEM image and size distribution.
Acknowledgment
The authors thank CSIR, New Delhi, India, for financial assistance
and DST-FIST for providing NMR facility to the department. RA
thanks CSIR, New Delhi, for fellowship, SAIF-IITM for MALDI-
TOF mass spectra and the National Center for Nanoscience and
Nanotechnology (NCNST), University of Madras, for HRTEM
studies.
Hence higher-generation ferrocenyl dendrimers 3 and 4
can sense the binding metal to the triazole and block the
periphery by encapsulation of the nanoparticles inside the
dendrimers better than the lower-generation dendrimers 1
and 2.
References and Notes
In conclusion various ferrocenyl dendrimers 1–4 with an
aminothiophenol core has been obtained through click
chemistry under microwave-assisted solid-support syn-
thesis. The size of the generated PdNP is controlled by the
dendrimer generations. Ferrocenyl dendrimers 1 and 2
stabilizes the PdNP of larger size and ferrocenyl den-
drimers 3 and 4 stabilizes the PdNP of smaller size by en-
capsulation.
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Synlett 2013, 24, 575–580
© Georg Thieme Verlag Stuttgart · New York

LETTER
Tekade, R.; Kumar, P. V.; Jain, N. K. Chem. Rev. 2009, 109,
Triazole-Based Ferrocenyl Dendrimers
579
H) ppm. 13C NMR (75 MHz, CDCl3): δ = 39.7, 55.9, 75.6,
78.4, 101.5, 108.4, 114.9, 117.2, 118.5, 130.1, 136.6, 140.8,
148.7, 158.5 ppm. MS–FAB: m/z = 323 [M+]. Anal. Calcd
(%) for C19H17NO2S: C, 70.56; H, 5.30; N, 4.33. Found: C,
70.49; H, 5.25; N, 4.31.
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(17) General Procedure for the Amide-Core-Based
Propargylated Dendritic Wedge
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Chem. Soc. 2004, 126, 1604.
A solution of the benzene-1,3,5-tricarboxylic acid chloride
(1.0 mmol) in dry CH2Cl2 (100 mL) and a solution of the
propargyloxy benzyl-2-aminothiophenol derivative 10 or 11
(3.0 mmol) and Et3N (3.1 mmol) in dry CH2Cl2 (100 mL)
were simultaneously added dropwise to a well-stirred
solution of dry CH2Cl2 (500 mL) during 6 h. After the
addition was complete, the reaction mixture was stirred for
another 6 h. The solvent was removed under reduced
pressure, and the residue obtained was then dissolved in
CH2Cl2 (300 mL), washed with H2O (2 × 100 mL) to remove
Et3N·HCl and then dried over Na2SO4. CH2Cl2 was
evaporated under vacuum, and the residue obtained was
purified by column chromatography with CHCl3–MeOH as
eluent to give the corresponding amide-core-based
propargylated dendritic wedge.
(18) Dendritic Wedge 13
(9) (a) Esumi, K.; Suzuki, A.; Aihara, N.; Usui Torigoe, K. K.
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2011, 4687. (c) Hawker, C. J.; Wooley, K. L. Science 2005,
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J. 2008, 14, 50. (b) Boisselier, E.; Diallo, A. K.; Salmon, L.;
Ornelas, C.; Ruiz, J.; Astruc, D. J. Am. Chem. Soc. 2010,
132, 2729. (c) Astruc, D.; Liang, L.; Rapakousiou, A.; Ruiz,
J. Acc. Chem. Res. 2012, 45, 630.
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Chem Commun. 2007, 46, 4946.
Pale yellow solid; yield 71%; Rf = 0.54 (CHCl3–MeOH =
99:1); mp 79 °C. 1H NMR (300 MHz, CDCl3): δ = 2.34 (t,
J = 2.4 Hz, 3 H), 2.45 (t, J = 2.4 Hz, 6 H), 3.90 (s, 6 H), 4.49
(d, J = 2.4 Hz, 12 H), 4.55 (d, J = 2.4 Hz, 6 H), 6.36 (s, 6 H),
7.13 (dt, J = 7.5, 0.9 Hz, 3 H), 7.44 (dt, J = 7.8 Hz, 1.2 Hz, 3
H), 7.52 (dd, J = 7.5 Hz, 1.2 Hz, 3 H), 8.47 (d, J = 7.8 Hz, 3
H), 8.70 (d, J = 1.5 Hz, 3 H), 9.31 (s, 3 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 41.8, 56.9, 60.2, 75.3, 75.9, 78.3,
79.0, 108.8, 120.8, 123.5, 125.0, 130.3, 130.6, 131.1, 131.4,
133.8, 135.8, 136.3, 139.9, 151.5, 163.1, 168.7 ppm. MS–
FAB: m/z = 1287 [M+]. Anal.Calcd (%) for C75H57N3O12S3:
C, 69.91; H, 4.46; N, 3.26. Found: C, 69.85; H, 4.40; N, 3.21.
(19) General Procedure for the Microwave-Assisted Solid-
Support Click Chemistry
A mixture of azide 5 (2 equiv, 2.0 mmol)/ 5 (6 equiv, 6.0
mmol/ 5 (9 equiv, 9.0 mmol)/ 8 (6 equiv, 6.0 mmol)/ 8 (9
equiv, 9.0 mmol) and alkyne dendron 6/12/13/12/13 (1
equiv, 1.0 mmol) each in Na2SO4 (0.5 g) in the presence of
CuSO4·5H2O (5 mol%) and NaAsc (10 mol%) was kept
under microwave irradiation (80 W) for 1 min. The crude
residue was treated with H2O (150 mL) for 10 min in order
to resume all the Cu(I) trapped in the dendrimer as
Cu(NH3)6+ and then extracted with CHCl3 (2 × 150 mL). The
organic layer was separated, washed with brine (1 × 150
mL), dried over Na2SO4, and evaporated to give the crude
triazole, which was purified by column chromatography
(SiO2), using the eluent as mentioned under each compound.
(20) Ferrocenyl Dendrimer 1
(14) (a) Wu, P.; Feldman, A. K.; Nugent, A. K.; Hawker, C. J.;
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Reiser, O. Org. Lett. 2008, 10, 4171.
(15) General Procedure for the S-Alkylation
A mixture of propargyloxybenzyl chloride derivatives 6 and
9 (1.0 mmol, 1 equiv), 2-aminothiophenol (1.2 mmol, 1.2
equiv), and TBAB (5 mg), KOH (1.5 mmol, 1.5 equiv), in a
mixture of toluene–H2O (1:1, 40 mL), was refluxed for 4 h.
The toluene layer was separated, washed with 5% KOH
solution (2 × 10 mL), H2O (20 mL), and then dried over
Na2SO4. Toluene was evaporated under vacuum, and the
residue obtained was purified by column chromatography
with hexane–CHCl3 as eluent to give the corresponding
propargyloxybenzyl-2-aminothiophenol.
Pale yellow solid; yield 96%; Rf = 0.52 (CHCl3–MeOH,
25:3); mp 111–113 °C. 1H NMR (300 MHz, CDCl3): δ =
3.78 (s, 6 H), 4.14, 4.16, 4.18 (s, 54 H, Cp), 4.73 (s, 12 H),
5.18 (s, 12 H), 6.17 (s, 6 H), 7.13 (t, J = 7.5 Hz, 3 H), 7.37 (t,
J = 7.2 Hz, 3 H), 7.47 (s, 6 H), 7.54 (t, J = 8.1 Hz, 3 H), 8.38
(s, 3 H), 8.41–8.47 (m, 6 H), 9.41 (s, 3 H) ppm. 13C NMR (75
MHz, CDCl3): δ = 50.0, 61.8 [68.9, 69.0 (2 C), Cp], 80.9,
107.4, 121.0, 122.3, 122.5, 124.3, 125.1, 128.8, 130.2,
135.4, 135.9, 139.9, 140.0, 143.4, 159.3, 163.0 ppm. MS
(MALDI-TOF): m/z = 2595 [M+ + Na]. Anal. Calcd (%) for
C132H117Fe6N21O9S3: C, 61.62; H, 4.58; N, 11.43. Found: C,
61.53; H, 4.54; N, 11.52.
(16) 3,5-Bis(propargyloxy)benzyl-2-aminothiophenol (10)
Colorless liquid; yield 86%; Rf = 0.45 (hexane–CHCl3 =
3:7). 1H NMR (300 MHz, CDCl3): δ = 2.52 (t, J = 2.4 Hz, 2
H), 3.82 (s, 2 H), 4.25 (br s, 2 H), 4.57 (d, J = 2.4 Hz, 4 H),
6.37 (d, J = 2.4 Hz, 2 H), 6.47 (t, J = 2.4 Hz, 1 H), 6.63 (dt,
J = 7.5, 1.5 Hz, 1 H), 6.70 (dd, J = 9.0 Hz, 1.2 Hz, 1 H), 7.11
(dt, J = 9.0 Hz, 1.8 Hz, 1 H), 7.23 (dd, J = 7.8 Hz, 1.5 Hz, 1
(21) Ferrocenyl Dendrimer 2
Pale yellow solid; yield 84%; Rf = 0.65 (CHCl3–MeOH,
25:1); mp 116–118 °C. 1H NMR (300 MHz, CDCl3): δ =
3.75 (s, 6 H), 4.12, 4.17, 4.18 (s, 81 H, Cp), 4.78 (s, 12 H),
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 575–580

580
P. Rajakumar et al.
LETTER
4.87 (s, 6 H), 5.10 (s, 6 H), 5.17 (s, 12 H), 6.24 (s, 6 H), 7.11
(t, J = 7.5 Hz, 3 H), 7.36 (t, J = 7.8 Hz, 3 H), 7.43 (d, J = 7.8
Hz, 3 H), 7.53 (s, 6 H), 7.61 (s, 3 H), 8.32 (d, J = 8.4 Hz, 3
H), 8.43 (s, 3 H), 9.43 (s, 3 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 49.8, 50.0, 62.9 [68.9, 69.0 (2 C), Cp], 81.2,
81.6, 108.1, 122.9, 123.3, 124.3, 125.1, 128.9, 130.1, 130.2,
133.6, 135.6, 136.1, 136.6, 139.9, 143.4, 143.6, 152.0, 163.1
ppm. MS (MALDI-TOF): m/z = 3481 [M+ + Na]. Anal.
Calcd (%) for C174H156Fe9N30O12S3: C, 60.43; H, 4.53; N,
12.15. Found: C, 60.47; H, 4.50; N, 12.01.
5:1); mp 163–164 °C. 1H NMR (300 MHz, CDCl3): δ = 3.65
(s, 6 H), 4.13, 4.23 (s, 162 H, Cp), 4.94 (s, 54 H), 5.22 (s, 54
H), 6.43 (s, 33 H), 7.02–7.14 (m, 6 H), 7.28–7.30 (m, 3 H),
7.57 (s, 18 H), 7.61 (s, 9 H), 8.46–8.51 (m, 6 H), 9.51 (s, 3
H) ppm. 13C NMR (75 MHz, CDCl3): δ = 50.1, 53.8, 54.6,
58.5, 61.7, 61.9 [68.8, 68.9, 69.0, 69.1, Cp], 80.8, 80.9,
100.9, 101.8, 107.4, 107.7, 122.6, 123.3, 123.5, 124.7,
125.2, 128.9, 130.3, 131.3, 133.6, 134.3, 135.3, 135.4,
136.1, 137.0, 137.4, 139.6, 140.0, 134.2, 143.4, 143.8,
159.3, 159.7, 159.8, 163.1 ppm. MS (MALDI-TOF):
m/z = 7821 [M+ + Na]. Anal. Calcd (%) for
(22) Ferrocenyl Dendrimer 3
Pale yellow solid; yield 87%; Rf = 0.50 (CHCl3–MeOH,
20:3); mp 135–137 °C. 1H NMR (300 MHz, CDCl3): δ =
3.71 (s, 6 H), 4.13, 4.24, (s, 108 H, Cp), 4.67 (s, 12 H), 4.88–
4.95 (m, 24 H), 5.22–5.32 (m, 36 H), 6.13 (s, 6 H), 6.39–6.46
(m, 21 H), 7.04 (s, 6 H), 7.24 (s, 3 H), 7.51 (s, 18 H), 8.28 (s,
3 H), 8.37 (s, 3 H), 9.39 (s, 3 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 50.1, 61.9, 61.88 [68.9, 69.0 (2 C), Cp], 80.9,
107.4, 107.8, 109.7, 115.5, 120.4, 122.7, 123.1, 122.8,
129.0, 131.0, 135.4, 137.8, 139.3, 144.1, 143.2, 143.5,
159.5, 159.7 ppm. MS (MALDI-TOF): m/z = 5490 [M+ +
Na]. Anal. Calcd (%) for C276H249Fe12N57O21S3: C, 60.64; H,
4.59; N, 14.60. Found: C, 60.51; H, 4.50; N, 14.48.
(23) Ferrocenyl Dendrimer 4
C390H354Fe18N84O30S3: C, 60.06; H, 4.58; N, 15.09. Found:
C, 60.07; H, 4.44; N, 15.00.
(24) General Procedure for the Preparation of the PdNP
A solution of ferrocenyl dendrimers (1 mmol, 1 equiv) in
CHCl3 (3 mL) was placed in a round-bottom flask under an
inert atmosphere. A solution of PdCl2 (6 mmol, 9 mmol, 12
mmol, 18 mmol, 1 equiv per triazole) in a mixture of CHCl3–
MeOH (1:10, 0.5:5 mL) was added to this solution and
stirred continuously r.t. for 3 h. The solution was stirred for
5 min and NaBH4 (10 mmol, 10 equiv per Pd) was added
dropwise, and the yellow solution turned to golden brown
indicating the formation of PdNP.
Pale yellow solid; yield 77%; Rf = 0.72 (CHCl3–MeOH,
Synlett 2013, 24, 575–580
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