Synthesis of ferrocenyl-bearing dendrimers with a resorcinarene core

Article abstract of DOI:10.1016/j.ica.2007.05.002

A series of ferrocenyl ended dendrons containing π-conjugated systems were obtained using Wittig and Heck reactions. The dendrons were attached to eight functionalized resorcinarenes via Williamson reaction obtaining high molecular weight dendrimers. No electronic communication between metal centers was observed by cyclic voltammetry. All the dendrimers were characterized by ¹H, ¹³C NMR, FTIR, UV-Vis, MALDI-TOF, elemental analyses, and electrochemical studies.

Full text of DOI:10.1016/j.ica.2007.05.002

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 1597–1605
www.elsevier.com/locate/ica
Synthesis of ferrocenyl-bearing dendrimers with a resorcinarene core
a
a
b
b
´
´
´
M.I. Reyes Valderrama , R.A. Vazquez Garcıa , T. Klimova , E. Klimova ,
c
d,
*
´
L. Ortiz-Frade , M. Martınez Garcıa
a
Centro de Inv. En Materiales y Metalurgia, Universidad Auto´noma del Estado de Hidalgo, Carr. Tulancingo Km. 4.5, C.P. 42184 Pachuca Hgo, Mexico
b
Facultad de Quı´mica, UNAM, Cd. Universitaria, Circuito Interior, C.P. 04510 Me´xico DF, Mexico
Facultad de Estudios Superiores Zaragoza, UNAM, Batalla 5 de mayo s/n Esq. Fuerte de Loreto, Col. Eje´rcito de Oriente Iztapalapa,
c
C.P. 09230 Me´xico DF, Mexico
Instituto de Quı´mica, UNAM, Cd. Universitaria, Circuito exterior, Coyoaca´n, C.P. 04510 Me´xico DF, Mexico
d
Received 21 December 2006; received in revised form 2 May 2007; accepted 2 May 2007
Available online 10 May 2007
Dedicated to Prof. Piero Zanello.
Abstract
A series of ferrocenyl ended dendrons containing p-conjugated systems were obtained using Wittig and Heck reactions. The dendrons
were attached to eight functionalized resorcinarenes via Williamson reaction obtaining high molecular weight dendrimers. No electronic
1
communication between metal centers was observed by cyclic voltammetry. All the dendrimers were characterized by H, 13C NMR,
FTIR, UV–Vis, MALDI-TOF, elemental analyses, and electrochemical studies.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Ferrocene; Oligophenylvinylene OPV; Resorcinarene; Dendrimers
1. Introduction
electrochemistry and catalysis [6], as molecular sensors [1],
molecular receptors [7], as ferromagnets [8,9] and in non-
linear optics [10,11]. It is now well established that molecu-
lar structures with differences between ground-state and
excited-state dipole moments and large transition moments
have large second-order non-linearities [12]. Molecules with
p-donor–acceptor interactions, such as ferrocene or deriva-
tives, are promising candidates to show these properties.
One of the characteristic structures of dendrimers is hav-
ing a precise central core unit. When the core is a high func-
tionalized molecule, high molecular weight dendrimers can
be prepared rapidly by the convergent method; another
important feature is that the core provides ample spacing
between the reactive groups at each chain end. We were
interested in resorcinarenes as eight functionalized core mol-
ecules because they can be easily synthesized with a ‘‘crown’’
conformation and they are less affected by steric constraints.
In this paper, we report on the synthesis of ferrocenyl
ended dendrimers with p-conjugated systems using resorcin-
arene as core molecule and their electrochemical behavior.
The chemistry of dendrimers has been enjoying rapid
development in recent years and many organometallic
species have been incorporated into their structures [1]. Fer-
rocene-containing dendrimers have attracted a lot of interest
since the first experiments to link ferrocene to the surface of
small silicon-containing dendrimers [2]. Lately a good deal
of this work has been reviewed [3]. Ferrocene may form
the center of the dendritic system [4] or be attached to the
peripheries. Recently, a rapid convergent route to form
structures with high molecular weight has been reported
[5]. Dendrimers with ferrocene occupying positions only at
the periphery were synthesized by successive condensations
of 4-hydroxybenzaldehyde sodium salt with dichloro(meth-
ylhydrazino) phosphine sulfide to afford giant materials [2].
Compounds containing ferrocene have already been used in
*
Corresponding author. Tel.: +52 55 56224451; fax: +52 55 56224416.
´
E-mail address: margar@servidor.unam.mx (M.M. Garcıa).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.05.002

1598
M.I. Reyes Valderrama et al. / Inorganica Chimica Acta 361 (2008) 1597–1605
2. Experimental
2.1. General procedure
Solvents and reagents were purchased as reagent grade
and used without further purification. Acetone was dis-
tilled over calcium chloride. Tetrahydrofuran was distilled
from sodium and benzophenone. Column chromatography
2.1.1. Vinylferrocene (2)
Orange powder, 1.8 g yield (90.9%). UV CHCl3 (nm):
442, 274, 245. IR (KBr)/(cmÀ1): 3081, 1628, 1408, 1239,
1
1102, 1047, 1024, 998, 895, 817, 726, 519, 482. H NMR
1
˚
was performed on Merck silica gel 60 A (70–230 mesh). H
(300 MHz, CDCl3): dH (ppm): 6.42 (q, 1H, @C–H), 5.31
(d, 1H, @CH2, J = 17.4 Hz), 5.00 (d, 1H, @CH2,
J = 10.8 Hz), 4.33 (s, 2H, C5H4), 4.18 (s, 2H, C5H4), 4.08
(s, 5H, C5H5). 13C NMR (75 MHz, CDCl3): dC (ppm):
134.5 (HC@), 110.9 (@CH2), 83.5 (Fcipso), 69.2 (C5H5),
68.6 (C5H4), 66.6 (C5H4). Ms (m/z): 212. Anal. Calc. for
C12H12Fe: C, 67.96; H, 5.70. Found: C, 67.96; H, 5.71%.
NMR and 13C were recorded on a Varian-Unity-300 MHz
with tetra-methylsilane (TMS) peaks as an internal refer-
ence. Infrared (IR) spectra were measured on a spectropho-
tometer Nicolet FT-SSX instrument, in solution (CHCl3).
The UV–Vis absorption spectra were recorded on a spec-
trophotometer UV–Vis Varian Cary-100, in different sol-
vents (toluene, dichloromethane, and acetonitrile) at
room temperature. Elemental analysis was determined by
Galbraith Laboratories, INC Knoxville. FAB+-mass spec-
tra were taken on a JEOL JMS AX505 HA instrument.
Matrix-assisted laser desorption/ionization time-of-flight
(MALDITOF) mass spectra were obtained by means of
an (Micromass TofSpec) operated in the linear-positive
mode. The samples were dissolved in tetrahydrofuran
(THF) and mixed with 2,5-dihydroxybenzoic acid as the
matrix. All electrochemical measurements were performed
in CHCl3 solution containing 0.1 M tetra-N-butylammo-
nium tetrafluoroborate (TBABF4) as supporting electro-
lyte. All electrochemical experiments were obtained at
sample concentrations of ca. 1 · 10À3 M. A potentiostat/
galvanostat EG&G PAR model 263 controlled by a PC
software was used. A typical three-electrode array was
employed for all electrochemical measurements: platinum
disk as working electrode, platinum wire as counter-elec-
trode, and a pseudo reference electrode of silver wire
immersed in an CHCl3 solution with 0.1 M tetra-N-buty-
lammonium chloride (TBACl). All solutions were bubbled
with nitrogen prior each measurement.
2.1.2. (E)-1-Styryl-4-vinylferrocene (7)
Orange powder, 4.5 g yield (76.3%). UV CHCl3 (nm):
456, 328, 273, 244. IR (KBr)/(cmÀ1): 3055, 1437, 1187,
1
1118, 998, 794, 721, 696, 542, 505. H NMR (300 MHz,
CDCl3): dH (ppm): 7.69 (br, 2H, Ar), 7.48 (br, 2H, Ar),
6.87 (d, 1H, HC@, J = 16.2 Hz), 6.67 (d, 1H, HC@,
J = 14.4 Hz), 6.74–6.64 (q, 1H, HC@), 5.74 (d, 1H,
@CH2, J = 17.1 Hz), 5.22 (d, 1H, @CH2, J = 10.1 Hz),
4.67 (s, 2H, C5H4), 4.50 (s, 2H, C5H4), 4.26 (s, 5H,
C5H5). 13C NMR (300 MHz, CDCl3): dC (ppm): 137.0
(Cipso), 136.4 (C@CH2), 136.2 (Cipso), 131.8 (@CH), 128.5
(Ar), 126.9 (Ar), 131.7 (CH@), 125.5 (CH@), 69.0
(C5H4), 69.1 (C5H5), 66.8 (C5H4). Ms (m/z): 314 (M). Anal.
Calc. for C20H18Fe: C, 76.45; H, 5.77. Found: C, 76.46; H,
5.77%.
A mixture of 2, 7 (8.51 mmol) and 3 (3.87 mmol),
Pd(OAc)2 (0.193 mmol), and tri-o-tolylphosphine POT
(0.967 mmol) in Et3N/DMF 1:1 (30 mL) was stirred under
N2 at 120 ꢁC for 48 h. After cooling, the resulting mixture
was filtered and the solvents evaporated. The crude prod-
uct was purified by column chromatography (SiO2,
CH2Cl2/hexane 2:3).
Cyclic voltammetry were initiated from open circuit
potential (Eocp), the scan potential was obtained in both
positive and negative directions. One step chronoampero-
metric experiments were carried out from open circuit
potential Eocp to variable potential E1, using a pulse width
of 3 s. Double step chronoamperometric (CA) study was
performed from first potential E1 = 0.4 V/Fc À Fc+ to var-
iable second step E2 = (À0.1 to 0.36 V/Fc À Fc+). Each
step was held during 3.0 s.
2.1.3. (E)-4-Vinylferrocenylbenzaldehyde (4)
Orange powder, 6 g yield (67.4%). UV CH3Cl (nm): 483,
345, 245. IR (KBr)/(cmÀ1): 3091, 2824, 2733, 1693, 1594,
1
1305, 1214, 1165, 960, 810. H NMR (300 MHz, CDCl3):
dH (ppm): 9.96 (s, 1H, O@C–H), 7.82 (d, 2H, Ar,
J = 7.5 Hz), 7.50 (d, 2H, Ar, J = 7.5 Hz), 7.02 (d, 1H,
@CH, J = 15.3 Hz), 6.62 (d, 1H, @CH, J = 15.3 Hz),
4.67 (s, 2H, C5H4), 4.50 (s, 2H, C5H4), 4.26 (s, 5H,
C5H5). 13C NMR (75 MHz, CDCl3): dC (ppm): 191.4 (H–
C@O), 143.7 (Cipso), 134.7 (Cipso), 131.4 (@C), 130.1 (Ar),
126.2 (Ar), 125.1 (@C), 84.2 (Fcipso), 70.9 (C5H4), 70.5
(C5H5), 68.1 (C5H4). Ms (m/z): 316 (M). Anal. Calc. for
C12H16FeO: C, 72.18; H, 5.10. Found: C, 72.19; H, 5.11%.
All potentials were reported versus the couple Fc/Fc+
according to IUPAC [15]. Although positive feedback iR
compensation was applied during all the experiments, high
values of the peak-to-peak separation were observed (due to
the high resistance of CHCl3 solutions). The value of DEp
for couple Fc/Fc+ was 0.140 V (scan rate = 0.10 V sÀ1).
To a mixture of methyl triphenylphosphine (8.7 mmol)
in dry THF (100 mL) and n-butyl lithium 2.5 M in hexanes
(8.7 mmol) at 0 ꢁC in N2 atmosphere, was added 1, 3, or 4
(9.3 mmol) in dry THF (10 mL). The mixture was stirred
for 24 h and water was added (300 mL). The organic phase
was evaporated to dryness, and purified by column chro-
matography using hexane:ethyl acetate 4:1.
2.1.4. ((4-(E)-Vinylferrocen)-4-(E)-stiryl)benzaldehyde
(8)
Orange powder, 2.5 g yield (47.2%). UV CH3Cl (nm):
373, 245. IR (KBr)/cmÀ1: 3080, 3027, 2923, 2725, 1693,
1589, 1166, 966, 823, 541, 479. 1H NMR (300 MHz,
CDCl3): dH (ppm): 9.98 (s, 1H, O@C–H), 7.87 (d, 2H,

M.I. Reyes Valderrama et al. / Inorganica Chimica Acta 361 (2008) 1597–1605
1599
Ar, J = 8.1 Hz), 7.60 (d, 2H, Ar, J = 7.8 Hz), 7.54–7.50 (br,
4H, Ar), 7.30 (d, 1H, @CH, J = 16.2 Hz), 7.12 (br, 1H,
CH@), 6.97 (d, 1H, @CH, J = 15.9 Hz), 6.68 (br, 1H,
@CH), 5.41 (br, 2H, C5H4), 5.19 (br, 2H, C5H4), 4.77
(br, 5H, C5H5). 13C NMR (75 MHz, CDCl3): dC (ppm):
191.4 (O@C–H), 154.3 (Cipso), 143.0 (Cipso), 140.9 (Cipso),
135.3 (Cipso), 130.8 (C@), 130.0 (Ar), 127.6 (C@), 127.0
(Ar), 126.1 (C@), 80.9 (Cipso), 70.1 (C5H4), 69.1 (C5H5),
65.5 (C5H4). Ms (m/z): 418 (M). Anal. Calc. for
C27H22FeO: C, 77.52; H, 5.30. Found: C, 77.53; H, 5.31%.
To a suspension of LiAlH4 (4.3 mmol) in 50 mL of THF
under nitrogen were added 4, 8 (25 mmol) in 50 mL of
THF. The reaction mixture was continued for 24 h at room
temperature. Water (2 mL) were added dropwise. The mix-
ture was filtered and the residue washed with CH2Cl2. The
solvent was evaporated in vacuo and the residue was chro-
matographed (SiO2; hexane:ethyl acetate 80:20).
2.1.7. (E)-1-(Chloromethyl)-4-vinylferrocenylbenzene (6)
Orange powder 1.8 g yield (65.5%). UV CHCl3 (nm):
453, 315, 269, 243. IR (KBr)/(cmÀ1): 3303, 2923, 1632,
1511, 1414, 1178, 1002, 816, 711, 583. 1H NMR
(300 MHz, CDCl3): dH (ppm): 7.44 (d, 2H, Ar,
J = 8.4 Hz), 7.34 (d, 2H, Ar, J = 8.1 Hz), 6.90 (d, 1H,
@CH, J = 16.5 Hz), 6,7 (d, 1H, @CH, J = 16.2 Hz), 4.59
(s, 2H, H2C–OH), 4.46 (t, 2H, C5H4), 4.29 (t, 2H, C5H4),
4.13 (s, 10H, C5H5). 13C NMR (300 MHz, CDCl3): dC
(ppm): 139.3 (Cipso), 137.4 (Cipso), 127.4 (@CH), 127.0
(Ar), 125.9 (@CH), 125.5 (Ar), 69.1 (C5H4), 66.8 (C5H4),
70.1 (CH2–Cl), 65.2 (C5H5). Ms (m/z): 336 (M). Anal. Calc.
for C19H17ClFe: C, 67.79; H, 5.09. Found: C, 67.78; H,
5.06%.
2.1.8. 1-(Chloromethyl)-4-((E)-4-(E)-
vinylferrocenylstyryl)benzene (10)
Orange powder, 0.8 g yield (42%). UV CHCl3 (nm): 323,
243. IR (KBr)/(cmÀ1): 3383, 3055, 3018, 2958, 2925, 2855,
1721, 1597, 1513, 1453, 1281, 1139, 1077, 962, 808, 755,
696. 1H NMR (300 MHz, CDCl3): dH (ppm): 7.89 (br,
4H, Ar), 7.41 (d, 2H, Ar), 7.15 (br, 2H, Ar, J = 8.4 Hz),
7.00 (br, 2H, @CH), 6.90 (br, 1H, @CH), 6.70 (br, 1H,
@CH), 4.60 (s, 2H, H2C–Cl), 4.48 (s, 2H, C5H4), 4.31 (s,
2H, C5H4), 4.14 (s, 5H, C5H5). 13C NMR (300 MHz,
CDCl3): dC (ppm): 143.5 (Cipso), 141.4 (Cipso), 133.1 (Cipso),
132.9 (Ar), 132.6 (Cipso), 132.0 (Ar), 128.7 (C@), 127.3 (Ar),
126.6 (C@), 125.3(C@), 81.3 (Fcipso), 70.1 (CH2–Cl), 69.2
(C5H5), 68.0 (C5H4), 66.2 (C5H4). Ms (m/z): 438 (M). Anal.
Calc. for C27H23ClFe: C, 73.91; H, 5.28. Found: C, 73.90;
H, 5.29%.
2.1.5. ((E)-(4-Vinylferrocenyl)phenyl)methanol (5)
Orange powder, 3 g yield (99%). UV CHCl3 (nm): 452,
312, 267 IR (KBr)/(cmÀ1): 3303, 2923, 1632, 1511, 1414,
1
1178, 1002, 816, 711, 583. H NMR (CDCl3) dH (ppm):
7.44 (d, 2H, Ar, J = 8.4 Hz), 7.38 (d, 2H, Ar,
J = 8.1 Hz), 6.98 (d, 1H, @CH, J = 16.2 Hz), 6.69 (d, 1H,
@CH, J = 16.4 Hz), 4.67 (s, 2H, H2C–OH), 4.46 (t, 2H,
C5H4), 4.29 (t, 2H, C5H4), 4.13 (s, 10H, C5H5). 13C
NMR (CDCl3) dC (ppm): 139.3 (Cipso), 137.4 (Cipso),
127.4 (Ar), 127.0 (@CH), 125.9 (Ar), 125.5 (@CH), 83.2
(Cipso), 69.1 (C5H4), 69.0 (C5H4), 66.8 (C5H4), 65.2 (CH2–
O). Ms (m/z): 318 (M). Anal. Calc. for C19H18FeO: C,
71.72; H, 5.70. Found: C, 71.71; H, 5.71%.
The resorcinarenes were obtained following the method-
ology reported in 14.
2.1.6. (((4-(E)-Vinylferrocenyl)-4-(E)-
styryl)phenyl)methanol (9)
A mixture of 1 mmol of the respective monochloride
generation of dendron 6 or 10, potassium carbonate
(21.2 mmol) and 18-crown-6 (0.56 g, 2.12 mmol) in dry ace-
tone (80 mL) was heated to reflux and stirred vigorously
under nitrogen for 20 min. The resorcinarene 11–13
(0.110 mmol) dissolved in dry acetone (40 mL) was added
dropwise and the reaction was continued for 48 h. The mix-
ture was allowed to cool and the precipitate was filtered.
The filtrate was evaporated to dryness under reduced pres-
sure. The residue was dissolved in diethyl ether and washed
with an aqueous solution of 5% Na2CO3 (three times). The
organic layer was dried and evaporated to dryness, the
product was obtained from a reprecipitation with dichloro-
methane–methanol.
Orange powder 1.8 g yield (99.5%). UV CHCl3 (nm):
452, 312, 267, IR (KBr)/(cmÀ1): 3303, 2923, 1632, 1511,
1414, 1178, 1002, 816, 711, 583. 1H NMR (300 MHz,
CDCl3): dH (ppm): 7.87 (d, 2H, Ar, J = 8.2 Hz), 7.66 (d,
2H, Ar, J = 8.2 Hz), 7.51 (d, 2H, Ar, J = 8.4 Hz), 7.45
(d, 2H, Ar, J = 8.3 Hz), 7.26 (d, 1H, @CH, J = 16.2 Hz),
7.15 (d, 1H, @CH, J = 16.4 Hz), 6.95 (d, 1H, @CH,
J = 15.8 Hz), 6.72 (d, 1H, @CH, J = 16.4 Hz), 6.72 (s,
2H, H2C–OH), 4.48 (t, 2H, C5H4), 4.31 (t, 2H, C5H4),
4.14 (s, 5H, C5H5). 13C NMR (300 MHz, CDCl3): dC
(ppm): 143.64 (Cipso), 138.3 (Cipso), 135.3 (Cipso), 132.0
(Ar), 128.5 (Cipso), 127.8 (C@), 127.3 (Ar), 126.2 (C@),
83.1 (Fcipso), 69.2 (C5H5), 67.02 (C5H4), 65.3 (C5H4), 65.2
(CH2–O). Ms (m/z): 420 (M). Anal. Calc. for C27H24FeO:
C, 77.15; H, 5.76. Found: C, 71.18; H, 5.78%.
2.1.9. Dendrimer G1 14
To a mixture of pyridine (1.5 mL) and CH2Cl2 (150 mL)
was added 6 or 10 and cooled at 0 ꢁC under nitrogen and
vigorously stirred for 20 min. Thionyl chloride (20.29
mmol) was added dropwise, the reaction was continued
for 4 h at room temperature and the solvent was evapo-
rated in vacuo. The product was washed with a mixture
hexane:ethyl acetate, the solvent was evaporated to give
the following.
Brown powder, 0.6 g yield (78%), UV CHCl3 (nm): 301,
244. IR (KBr)/(cmÀ1): 3375, 3085, 3059, 3020, 2914, 2827,
1606, 1495, 1455, 1410, 1378, 1352, 1287, 1247, 1217, 1180,
1108, 1028, 961, 908, 836, 754, 700, 664. 1H NMR
(300 MHz, CDCl3): dH (ppm): 7.26–7.09 (br, 88H, Ar)
6.85 (br, 16H, @CH), 4.44 (s, 16H, C5H4), 4.27 (s, 16H,
C5H4), 4.11 (s, 40H, C5H5), 3.58 (br, 20H, –O–CH2, CH),
2.56 (br, 8H, CH2), 2.35 (br, 8H, CH2). 13C NMR

1600
M.I. Reyes Valderrama et al. / Inorganica Chimica Acta 361 (2008) 1597–1605
(300 MHz, CDCl3): dC (ppm): 160.21 (CAr–O), 154.19
(Aripso), 142.2 (Cipso), 137.0 (Cipso), 136.1 (Ar), 128.1 (Ar),
127.5 (CH@), 125.7 (Ar), 101.3 (Ar), 83.2 (Fcipso), 69.9
(C5H5), 69.1 (–O–CH2), 66.8 (C5H4), 34.8 (CH), 34.61
65.3 (C5H4), 34.2 (–CH2), 31.5 (–CH). Anal. Calc. for
C276H232Fe8O8: C, 80.32; H, 5.67. Found: C, 80.34; H,
5.67%.
(–CH2). MALDI-TOF: 3304.
Anal. Calc. for
2.1.13. Dendrimer G2 18
C
5.59%.
212H184Fe8O8: C, 77.01; H, 5.61. Found: C, 77.03; H,
Brown powder, 0.15 g yield (82%). UV CHCl3 (nm):
322, 245. IR (KBr)/(cmÀ1): 3610, 3522, 3460, 2893, 2828,
2748, 715, 1975, 1920, 1629, 1471, 1455, 1287, 1250,
1105, 1013, 964, 838, 759, 700, 662, 582, 533, 492. 1H
NMR (300 MHz, CDCl3): dH (ppm): 7.90 (br, 32H, Ar),
7.40–7.15 (br, 40H, Ar), 7.0 (br, 32H, @CH), 4.09 (br,
4H, –CH), 4.04 (br, 32H, C5H4), 3.66 (br, 56H, C5H5,
–O–CH2), 3.43 (br, 4H, CH), 1.24 (br, 32H, CH2), 0.87
(br, 12H, CH3). 13C NMR (300 MHz, CDCl3): dC (ppm):
160.6 (O–Ar), 140.5 (Cipso), 139.8 (Cipso), 133.0 (Cipso),
129.9 (C@), 129.2 (Ar), 128.7 (C@), 126.2 (Ar), 124.2
(Ar), 72.3 (Fcipso), 69.9 (C5H5), 67.2 (–O–CH2) 69.0
(C5H4), 29.4 (–CH), 22.4 (CH2), 13.8 (CH3). Anal. Calc.
for C264H240Fe8O8: C, 80.32; H, 6.07. Found: C, 80.30;
H, 6.09%.
2.1.10. Dendrimer G1 15
Brown powder, 0.74 g yield (92%), UV CHCl3 (nm):
311, 266, 244. IR (KBr)/(cmÀ1): 3385, 3093, 3010, 2924,
2853, 1703, 1609, 1499, 1462, 1410, 1376, 1352, 1292,
1247, 1217, 1180, 1108, 1042, 1025, 1003, 959, 818, 756,
1
665. H NMR (300 MHz, CDCl3): dH (ppm): 7.4–7.0 (br,
40H, Ar), 6.89 (d, 8H, CH@, J = 15.0 Hz), 6.70 (d, 8H,
CH@, J = 16.2 Hz). 4.45 (s, 14H, C5H4), 4.29 (s, 16H,
C5H4), 4.13 (2, 40H, C5H5), 3.63 (br, 20H, –O–CH2,
CH), 2.04 (br, 8H, CH2), 1.68 (br, 8H, CH2), 1.26 (br,
16H, CH2), 0.86 (t, 12H, CH3). 13C NMR (300 MHz,
CDCl3): dC (ppm): 160.9 (O–Ar), 140.5 (Cipso), 135.8
(Cipso), 130.0 (Cipso), 1292 (Ar), 127.2 (CH@), 125.7 (Ar),
125.0 (Ar), 101.5 (Ar), 83.2 (Fcipso), 70.0 (–O–CH2), 69.1
(C5H5), 66.8 (C5H4), 40.5 (CH), 31.9 (CH2), 29.6 (CH2),
29.4 (CH2), 22.6 (CH2), 14.1 (CH3). MALDI-TOF: 3168.
Anal. Calc. for C200H192Fe8O8: C, 75.77; H, 6.10. Found:
C, 75.78; H, 6.59%.
2.1.14. Dendrimer G2 19
Brown powder, 0.15 g yield (76%). UV CHCl3 (nm):
322, 245. IR (KBr)/(cmÀ1): 3611, 3530, 3464, 3066, 2895,
2830, 2748, 2717, 2626, 1978, 1861, 1651, 1631, 1404,
1373, 1355, 1289, 1253, 1138, 1107, 1009, 966, 836, 761,
1
704, 664, 584, 535, 492. H NMR (300 MHz, CDCl3): dH
2.1.11. Dendrimer G1 16
(ppm): 7.87 (br, 32H, Ar), 7.43–7.11 (br, 40H, Ar), 7.11
(br, 32H, @CH), 4.02 (br, 4H, –CH), 4.03 (br, 32H,
C5H4), 3.56 (br, 56H, C5H5,–O–CH2), 3.41 (br, 4H, CH),
1.25 (br, 80H, CH2), 0.87 (br, 12H, CH3). 13C NMR
(300 MHz, CDCl3): dC (ppm): 159.6 (O–Ar), 143.5 (Cipso),
140.8 (Cipso), 132.7 (Cipso), 129.6 (C@), 129.2 (Ar), 128.3
(C@), 126.2 (Ar), 124.2 (Ar), 72.3 (Fcipso), 69.9 (C5H5),
67.2 (–O–CH2) 69.0 (C5H4), 29.4 (–CH), 22.4 (CH2), 13.8
(CH3). Anal. Calc. for C288H288Fe8O8: C, 79.99 H 6.71.
Found: C, 80.01; H, 6.69%.
Brown powder, 0.7 g yield (83%). UV CHCl3 (nm): 445,
311, 245. IR (KBr)/(cmÀ1): 3438, 3094, 2911, 2746, 1609,
1502, 1456, 1434, 1409, 1379, 1351, 1286, 1247, 1182,
1107, 1025, 959, 836, 752, 661. 1H NMR (300 MHz,
CDCl3): dH (ppm): 7.78–7.09 (br, 40H, Ar) 6.93 (br, 16H,
@CH), 4.45 (br, 16H, C5H4), 4.28 (br, 16H, C5H4), 4.13
(br, 40H, C5H5), 3.53 (br, 20H, CH2, –CH), 2.59 (br, 8H,
CH2), 2.03 (br, 8H, CH2), 1.53 (br, 8H, CH2) 1.32 (br,
64H, CH2), 0.88 (br, 12H, CH3). 13C NMR (300 MHz,
CDCl3): dC (ppm): 160.7 (O–Ar), 140.4 (Cipso), 137.2
(Cipso), 132.7 (Cipso), 132.0 (Ar), 130.8 (Cipso), 128.2 (C@),
125.7 (Ar), 83.2 (Fcipso), 69.1 (C5H5), 67.1 (–O–CH2),
66.83 (C5H4), 31.9 (CH2), 29.6 (–CH2), 22.5 (CH2), 14.0
3. Results and discussion
Dendrons containing ferrocenyl groups were prepared
´
(CH3).
MALDI-TOF:
3504.
Anal.
Calc.
for
according to the convergent Frechet approach [13]. Vinyl
C
6.93%.
224H240Fe8O8: C, 76.71; H, 6.90. Found: C, 76.69; H,
ferrocene was synthesized from the ferrocene carboxalde-
hyde by the Wittig reaction (Scheme 1). Following Heck
reaction coupling of the vinyl ferrocene
2
and
2.1.12. Dendrimer G2 17
4-bromo-benzaldehyde 3 in dimethyl formamide and tri-
ethylamine using Palladium acetate as catalyst afforded
4. This was reduced with LiAlH4 in THF at 0 ꢁC to give
alcohol 5, which was converted into the chloride 6 upon
treatment with thionyl chloride in dichloromethane at
0 ꢁC. This chloride was used as the reagent for the syn-
thesis of the first generation of ferrocenyl-containing
dendrimers.
Brown powder, 0.1 g yield (53%). UV CHCl3 (nm): 323,
244. IR (KBr)/(cmÀ1): 3422, 3084, 3058, 3025, 2914, 2743,
1693, 1646, 1629, 1515, 1497, 1451, 1405, 1373, 1353, 1284,
1250, 1107,1007, 961, 833, 754, 701, 663, 618, 578, 534, 500.
1H NMR (300 MHz, CDCl3): dH (ppm): 7.96–7.09 (br,
88H, Ar), 6.9 (br, 32H, @CH), 4.08 (br, 16H, C5H4), 3.86
(br, 16H, C5H4), 3.62 (br, 56H, C5H5, –O–CH2). 3.38 (br,
4H, CH). 13C NMR (300 MHz, CDCl3): dC (ppm): 160.7
(O–Ar), 140.5 (Cipso), 139.8 (Cipso), 133.0 (Cipso), 132.0
(Ar), 130.0 (Cipso), 129.6 (C@), 128.0 (C@), 124.2 (Ar),
72.3 (Fcipso), 69.8 (C5H5), 69.3 (–O–CH2), 69.0 (C5H4),
Chloride 10, a second generation dendron, was obtained
following the same methodology. Dendrons 6 and 10 were
1
characterized by H and 13C NMR, IR, FAB+ mass spec-
trometry. The presence of two sets of signals of the vinylic

M.I. Reyes Valderrama et al. / Inorganica Chimica Acta 361 (2008) 1597–1605
1601
1
protons in their H NMR spectra with a calculated cou-
The obtained dendrimers 14–19 are readily soluble in
common organic solvents. The H NMR spectrum of den-
1
pling constant of ca. 17 Hz is characteristic of an AB sys-
tem confirming the E stereochemistry of the double
bonds in the dendrons.
Resorcinarenes 11–13 were obtained from resorcinol
and aldehydes. The products were obtained as precipi-
tates. The structure of these resorcinarenes was con-
firmed by NMR and FAB+ mass spectrometry. Cyclic
tetramers gave a well resolved triplet at 4.36 ppm, which
is attributed to methine protons with an rccc conforma-
tion [14].
drimer 14 showed one broad signal at d 7.3–7.09 assigned
to the aromatic protons, one broad signal at d 6.85 due to
the vinylic protons, three singlets characteristic for the fer-
rocene groups at d 4.45, 4.27, and 4.15 for the C5H4 and
1
C5H5. Also the H NMR spectra showed in all examples
one signal (vicinal coupling) for the methine groups
together with the CH2–O groups, which confirmed the
rccc conformation of the obtained resorcinarene-
dendrimers.
4. Electrochemical properties
HO
OH
R1
H
C
HO
OH
Typical CV of compound 14 is presented in Fig. 2, when
the scan potential was initiated in positive direction one
oxidation signal Ia is observed. After the reversal scan,
one reduction signal Ic is detected. A controlled potential
MeOH
HCl
O
R1
+
R1= -(CH2)2-C6H5 (11)
-(CH2)4-CH3 (12)
-(CH2)10-CH3 (13)
4
11-13
coulommetry at potential more positive than Epa
I
(0.36 V/Fc–Fc+) established an oxidation of eight electrons
per molecule, attributed to each ferrocene moiety. A single
oxidation process suggests no electronic communication
between the metal sites in the structure of 14.
The dendrimers 14–19 were obtained from the den-
drons 6, 10, and resorcinarenes 11–13 in acetone and
K2CO3 at reflux for 3 days. The structures of first and
second generation dendrimers, 14–16 and 17–19 respec-
tively, were confirmed by 1H and 13C NMR, IR, UV–
Vis, and elemental analysis. In addition, molecular masses
of the first generation dendrimers 14–16 was determined
by MALDI-TOF mass spectrometry (Fig. 1). The molec-
ular masses of the second generation dendrimers 17–19
could not be determined by MALDI-TOF mass spectros-
copy due to their poor volatility properties. However,
GPC profiles of these dendrimers showed a sharp unimo-
dal peak.
Fig. 3 shows CV experiments at scan rates from 0.025 to
0.125 V sÀ1, a linear relationship of anodic peak current
with v1/2 indicated that the process Ia is diffusion controlled
at this range [16]. The ratio of cathodic to anodic peak cur-
rents in the scan rates employed was larger than the unity
(Fig. 3), this indicates no simple electron transfer process
[17,18].
In order to obtain a value of half wave potential (E1/2
)
and to understand the process, one step and double poten-
tial step chronoamperometry experiments were performed.
Acetone
6
14 - 16
17 - 19
+
11-13
Reflux, K2CO3
10
Fe
Fe
Fe
Fe
Fe
Fe
O
O
O
O
O
Fe
Fe
Fe
Fe
O
O
O
O
O
O
Fe
O
O
O
O
Fe
O
Fe
Fe
14
Fe
17
Fe

1602
M.I. Reyes Valderrama et al. / Inorganica Chimica Acta 361 (2008) 1597–1605
H
O
OH
Cl
H
O
O
CH2
H
b
c
a
d
Fe
Fe
+
Br
3
2
1
Fe
Fe
Fe
5
4
6
OH
Cl
H
O
H
CH2
H
O
H
O
b
cd
a
+
Br
Fe
Fe
3
7
4
Fe
Fe
Fe
10
9
8
Scheme 1. Synthesis of lineal dendrons of first and second generation: (a) CH3(Ph)3PBr, n-BuLi, THF, 0 ꢁC; (b) Pd(OAc)2/TOP DMF/ET3N, 120 ꢁC;
(c) THF, LiAlH4, 0 ꢁC; (d) Py, CH2Cl2, SOCl2, 0 ꢁC.
Fig. 1. MALDI-TOF mass spectra of 16 first generation dendrimers.
Fig. 4 shows a typical current-sampled versus potential plot
I(t)–E, constructed from chronoamperograms at different
potential step E1, with pulse width of 3 s. At current sam-
pling time of 0.3 s two plateaus were observed (A and B),
the first of them corresponds to process I. When the current
sampling time was increased, the current of second plateau
B was decreased, this process can be attributed to an adsorp-
tion. The half wave potential (E1/2) of process I was evalu-

M.I. Reyes Valderrama et al. / Inorganica Chimica Acta 361 (2008) 1597–1605
1603
7
4
3
Ιa
Β
Β
6
E+λ
Α
2
5
4
3
2
1
1
0
-1
-2
-3
-4
-5
-6
Α
E-λ
Ιc
0
-1.4
-1.2
-1.0
-0.8
-0.6
E(V/Fc-Fc+)
-0.4
-0.2
0.0
0.2
0.4
-0.6
-0.4
-0.2
0.0
0.2
0.4
E(V/Fc-Fc+)
Fig. 2. Cyclic voltammogram obtained for 1 mM 14 in CHCl3 in presence
of 0.1 M TBABF4. The scan potential was initiated from Eocp to positive
direction. Scan rate 0.1 V sÀ1. Platinum electrode was used.
Fig. 4. Current–potential curves I–E, constructed from the chronoam-
perograms at different potentials, E1, corresponding to the oxidation of
compound 14. The current I–E plot was constructed for current sampling
times 1.1 s (s) and 0.3 s (d).
5
Ιa
4
2
1
3
E+λ
2
1
0
0
-1
-1
-2
D
-2
-3
-4
E-λ
-3
-4
D
-5
-5
Ιc
-6
-6
C
-1.4
-1.2
-1.0
-0.8
-0.6
E(V/Fc-Fc+)
-0.4
-0.2
0.0
0.2
0.4
-7
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
E(V/Fc-Fc+)
Fig. 3. Cyclic voltammograms obtained for 1 mM of 14 in CHCl3 in
presence of 0.1 M TBABF4. Scan rate 0.025, 0.050, 0.075, 0.1, and
0.125 V sÀ.
Fig. 5. Current–potential curves I–E, constructed from the chronoam-
perograms at different reverse potentials E2 for compound 14. The
potential E1 was held 3.0 s with a value of 0.40 V/Fc–Fc+. The current I–E
plot was constructed for current sampling reverse times 1.1 s (s) and 0.3 s
(d).
ated from the intercept of a plot E versus log[Id(t) À I(t)/
I(t)]. The obtained value was À0.063 V/Fc–Fc+.
Information of coupled processes with electron transfer
can be obtained from the construction of current-sampled
versus potential plots in the reversal step [19]. Fig. 5 shows
a typical I(t)–E plot for the reverse pulse. For sampling
time of 0.3 s one plateau (D) and a signal (C) with a max-
imum of current at À0.240 V/Fc–Fc+ were observed. When
the sampling time was increased at 1.1 s, the plateau D is
detected and the signal C was not observed. The shape of
signal C and the ratio of cathodic to anodic peak currents
in the employed scan rates suggest a weak adsorption of
the oxidized product in the electrode at short sampling
times [6].
Fig. 6 shows typical voltammogram of 16 obtained in a
platinum electrode, when the potential scan was initiated in
the positive direction, two oxidation signals (Ia and IIa)
were observed in the voltammogram, and when the poten-
tial scan was reversed three reduction signals were detected
(Ic, IIc, and I*). The anodic and cathodic peak potential
values for signals Ia, IIa, Ic, IIc, and I* are 0.003, 0.201,
0.057, À0.078, and À0.461 V/Fc–Fc+ respectively. The
dependence of signal Ia with IIa and signal Ic with IIc was
established by modifying the switching potentials E+k

1604
M.I. Reyes Valderrama et al. / Inorganica Chimica Acta 361 (2008) 1597–1605
A typical current-sampled versus potential plot, for 16,
ΙΙa
Ιa
constructed from one step chronoamperometric experi-
ments at current sampling time of 1.1 s is shown in
Fig. 8. A pre-wave, a diffusion controlled region, and a
plateau (zones I, II and a respectively) are observed. This
behavior is characteristic of adsorption with simultaneous
oxidation process followed by diffusion controlled
oxidation process in dc polarography [16]. Oxidation of
ferrocene moieties in adsorbed I and non-adsorbed II
(controlled by linear diffusion) molecules is proposed.
The half wave potential (E1/2) for processes I and II were
evaluated from current-sampled versus potential plot,
E1/2(I) = À0.150 V/Fc–Fc+ and E1/2(II) = 0.149 V/Fc–Fc+
(Fig. 8).
The electrochemical behavior of the compounds 17–19 is
very similar to that observed for 16. The half wave poten-
tial (E1/2) was evaluated for electrochemical processes I and
II in all the compounds (Table 1). The values in table I
indicate that the adsorption process (I), accompanied with
electron transfer exchange, occurs at very similar potential
6
4
E+λ
2
ΙΙc
0
E-λ
-2
-4
Ιc
Ι*
-1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0
0.2
0.4
0.6
E(V/Fc-Fc+)
Fig. 6. Cyclic voltammogram obtained for 1 mM 16 in CHCl3 in presence
of 0.1 M TBABF4. The scan potential was initiated from Eocp to positive
direction. Scan rate 0.1 V sÀ1. Platinum electrode was used.
(Fig. 7). The value of DEp for process I at a scan rate of
0.10 V sÀ1 was 0.07 V, which is lower than the obtained
for the couple Fc/Fc+ (0.140 V) at the same scan rate. This
fact suggests that process I can be attributed to a possible
adsorption with the simultaneous oxidation of ferrocene
moieties [16,20].
A
8
ΙΙ
6
The electronic communication between the neighboring
metal centers must be neglected. An increase in the number
of saturated carbon atoms, in non-bridged moiety (16 ver-
sus 14) is not an important factor in electronic communica-
tion [21]. The adsorption of several ferrocenyl dendrimers
in electrochemical experiments has been reported in the lit-
erature [22–25].
Ι
4
2
0
-0.6
-0.4
-0.2
0.0
0.2
0.4
ΙΙa
Ιa
E(V/Fc-Fc+)
6
4
Fig. 8. Current–potential curves I–E, constructed from the chronoam-
perograms at different potentials E1 corresponding to the oxidation of
compound 16. The current I–E plot was constructed for current sampling
time 1.1 s.
E+λ
2
Table 1
ΙΙc
0
Electrochemical potentials E1/2(I), E1/2(II), for compounds 14–16 and 17–
19
Compound
E1/2(I)a
E1/2(II)b
E-λ
-2
-4
Ιc
14
15
16
17
18
19
No
No
À0.150
À0.121
À0.119
À0.075
À0.063
À0.04
0.149
0.178
0.153
0.144
Ι*
-1.2 -1.0 -0.8 -0.6 -0.4 -0.2
E(V/Fc-Fc+)
0.0
0.2
0.4
0.6
Fig. 7. Cyclic voltammograms obtained for 1 mM 16 solution in CHCl3 in
the presence of 0.1 M TBABF4. The scan potential was initiated from Eocp
Reported vs ferrocene in 0.1 M TBABF4–CHCl3. No: not observed.
a
Adsorption with simultaneous redox process.
b
to different inversion potentials (E+k). Scan rate 0.1 V sÀ1
.
Redox diffusion controlled process.

M.I. Reyes Valderrama et al. / Inorganica Chimica Acta 361 (2008) 1597–1605
1605
(c) G. Wagner, R. Herrmann, in: A. Togni, T. Hayashi (Eds.),
Ferrocenes, VCH, Weinheim, 1995, p. 433.
[4] (a) C.M. Cardona, T.D. McCarley, A.E. Kaifer, J. Org. Chem. 65
(2000) 1857;
(b) C.M. Cardona, A.E. Kaifer, J. Am. Chem. Soc. 120 (1998) 4023.
[5] S. Nlate, J. Ruiz, J.C. Blais, D. Astruc, Chem. Commun. (2000)
417.
[6] (a) A. Togni, T. Hayashi, Ferrocenes, Homogeneous Catalysis,
Organic Synthesis, Materials Science, Verlag Chemie, New York,
1994;
E1/2(I). The values of potentials E1/2(II) associated with lin-
ear diffusion oxidation process II are very similar for com-
pounds 16 and 17–19. This fact suggests that there is no
influence of the subsistent on the energy to remove elec-
trons from ferrocene moieties. The E1/2(II) of compounds
14 and 15 are very similar, and they cannot be compared
with the values of E1/2(II) of 16 and 17, 18, due to the
adsorption in process I.
(b) D. Astruc, Electron Transfer and Radical Processes in Transition-
Metal Chemistry, Verlag Chemie, New York, 1995.
[7] E.C. Constable, Angew. Chem., Int. Ed. Engl. 30 (1991) 407.
[8] (a) C. Kollmar, M. Couty, O. Kahn, J. Am. Chem. Soc. 113 (1991)
7994;
(b) S.R. Marder, D.W. Bruce, D. O’Hare (Eds.), Inorganic Materials,
Wiley, Chichester, 1992, p. 115, and references cited therein.
[9] (a) Z. Yuan, G. Stringer, I.R. Jobe, D. Kreller, K. Scott, L. Koch,
N.J. Taylor, T.B. Marder, J. Organomet. Chem. 452 (1993)
115;
5. Conclusions
Ferrocenyl ended dendrons containing p-conjugated
systems were obtained using Wittig and Heck reactions.
NMR studies showed that the dendrons have trans confor-
mation. The synthesized dendrons were attached to eight
functionalized resorcinarenes via Williamson reaction
obtaining high molecular weight dendrimers. Cyclic vol-
tammetry, one step and double potential step chronoampe-
rometry experiments suggested adsorption of compounds
with simultaneous electron transfer (I), and diffusion con-
trolled oxidation process of ferrocene moieties (II). No
electronic communication between metal centers was
observed.
(b) K.L. Kott, D.A. Higgins, R.J. McMahon, R.C. Corn, J. Am.
Chem. Soc. 115 (1993) 5342;
(c) N.J. Long, Angew. Chem., Int. Ed. Engl. 34 (1995) 21.
[10] B.F. Levine, C.C. Betea, J. Chem. Phys. 66 (1977) 1070.
[11] J.L. Oudar, D.S. Chemla, J. Chem. Phys. 66 (1977) 2664.
[12] (a) M.L.H. Green, S.R. Marder, M.E. Thompson, J.A. Bandy, D.
Bloor, P.V. Kolinsky, R.J. Jones, Nature 330 (1987) 360;
(b) J.C. Calabrese, L.T. Cheng, J.C. Green, S.R. Marder, W. Tam, J.
Am. Chem. Soc. 113 (1991) 7227.
´
[13] C.J. Hawker, J.M. Frechet, J. Am. Chem. Soc. 112 (1990) 7638.
Acknowledgements
´
[14] M.A. Garcıa, E. Klimova, T. Klimova, P.B. Flores, A.M. Romero,
´
O.S. Hernandez, G.M. Martınez, Fullerene, Nanotubes Carbon
Nanostruct. 13 (2005) 171.
This work was supported by the DGAPA-UNAM (IN-
209106). We would also like to thank Z.S.M. Nieves, O.H.
[15] G. Gritzner, J. Kuta, Pure Appl. Chem. 4 (1984) 461.
¨
´
[16] A.J. Bard, L.R. Faulkner, Electrochemical Methods, Fundamentals
and Applications, John Wiley and Sons, NY, 1980.
[17] G. A Mabbott, J. Chem. Ed. 60 (1983) 697.
Rios, L. Velasco, P.J. Perez, M.M.R. Patino, and S.E.
˜
Huerta, for technical assistance.
[18] R.S. Nicholson, I. Shain, Anal. Chem. 36 (1964) 706.
References
´
´
[19] A.M. Sosa, V.M. Ugalde-Saldıvar, I. Gonzalez, L. Gasque, J.
Electroanal. Chem. 579 (2005) 103.
[1] (a) G.R. Newkome, E. He, C.N. Moorefield, Chem. Rev. 99 (1999)
1689;
[20] P. Zanello, Inorganic Electrochemistry, Theory, Practice and Appli-
cation, The Royal Society of Chemistry, Cambridge, UK, 2003.
[21] D. Astruc, Acc. Chem. Res. 30 (1997) 383.
(b) M. Venturi, A. Credi, V. Balzani, Coord. Chem. Rev. 23 (1999)
185.
[22] K. Takada, D.J. D´ıaz, H.D. Abruna, I. Cuadrado, C. Casado, B.
˜
[2] (a) B. Alonso, I. Cuadrado, M. Moran, J. Losada, J. Chem. Soc.,
Chem. Commun. (1994) 2575;
Alonso, M. Mora´n, J. Losada, J. Am. Chem. Soc. 119 (1997) 10763.
[23] C.O. Turrin, J. Chiffre, J.-C. Daran, D. de Montauzon, A.M.
Caminade, E. Manoury, G. Balavoine, J.-P. Majoral, Tetrahedron 57
(2001) 2521.
[24] C.M. Casado, I. Cuadrado, M. Mora´n, B. Alonso, B. Garc´ıa, B.
Gonza´lez, J. Losada, Coord. Chem. Rev. 85 (1999) 53.
(b) C.O. Turrin, J. Chiffre, D. Montauzon, J.C. Daran, A.M.
Caminade, E. Manoury, G. Balavoine, J.-P. Majoral, Macromole-
cules 33 (2000) 7328.
[3] (a) C. Muller, D. Vos, P. Jutzi, J. Organomet. Chem. 600 (2000) 127;
´
´
(b) C.M. Casado, I. Cuadrado, M. Moran, B. Alonso, B. Garcia, B.
[25] I. Cuadrado, C.M. Moran, C.M. Casado, B. Alonso, F. Lobete, B.
Gonzalez, J. Losada, Coord. Chem. Rev. 186 (1999) 53;
Garc´ıa, M. Ibisate, J. Losada, Organometallics 15 (1996) 5278.