Electroactive metallomacromolecules via tetrabis(2,2′:6′,2″-terpyridine)ruthenium(II) complexes: Dendritic nanonetworks toward constitutional isomers and neutral species without external counterions

Article abstract of DOI:10.1021/ja001401h

The concept of dendritic networks via four bis(2,2′:6′,2″-terpyridine)ruthenium(II) connectivities was utilized to create "dendritic methane"-type metallomacromolecules. In addition, two structurally isomeric metallodendrimers (16 and 17) were designed, s

Full text of DOI:10.1021/ja001401h

J. Am. Chem. Soc. 2000, 122, 9993-10006
9993
Electroactive Metallomacromolecules via
Tetrabis(2,2′:6′,2′′-terpyridine)ruthenium(II) Complexes: Dendritic
Nanonetworks toward Constitutional Isomers and Neutral Species
without External Counterions
George R. Newkome,* Enfei He, Luis A. God´ınez,† and Gregory R. Baker
Contribution from the Center for Molecular Design and Recognition, Department of Chemistry,
UniVersity of South Florida, 4202 E. Fowler AVenue, Tampa, Florida 33620-5250
ReceiVed April 21, 2000
Abstract: The concept of dendritic networks via four bis(2,2′:6′,2′′-terpyridine)ruthenium(II) connectivities
was utilized to create “dendritic methane”-type metallomacromolecules. In addition, two structurally isomeric
metallodendrimers (16 and 17) were designed, synthesized, and characterized. These two isomers were spectrally
alike and displayed very similar physical and chemical properties; however, the internal density and void
regions of these molecules were differentiated by cyclic voltammetry. The effects of the bulkiness of internal
and external dendritic branches on the terpyridine-ruthenium complexes are described. A similar synthetic
strategy allowed the preparation of two generations of neutral metallomacromolecules (33 and 36) possessing
no external counterions. The benefits of these internally charge-balanced, neutral species are described, and
the effects of increasing dendritic branching on their electrochemical behavior are detailed.
Introduction
This type of modular chemistry, at the same time, provides the
possibility of discovering new materials possessing utilitarian
applications.
Various routes for the construction of metallo-macromolecules
have been widely investigated1-11 due to their purported or
envisioned magnetic, electronic, photooptical, or catalytic
properties. An important feature of many of the synthetic
strategies is the use of branched monomers12 for the construction
of dendritic architectures,13,14 which provide the inherent
synthetic control to afford predetermined structures, incorporat-
ing the desired utilitarian subunits into the superstructure. The
assembly of diverse dendritic subunits led to the creation of a
series of “dendritic networks”,15-20 which can, at least structur-
ally, mimic molecular assemblies but on the nanoscopic scale.
† Current address: Centro de Investigacio´n y Desarrollo Tecnolo´gico
en Electroqu´ımica, Parque Tecnolo´gico Quere´taro Sanfandila, Apdo. Postal
064, Pedro Escobedo, C. P. 76700, Quere´taro, Me´xico.
(1) Cuadrado, I.; Mora´n, M.; Casado, C. M.; Alonso, B.; Losada, J.
Coord. Chem. ReV. 1999, 193-195, 395-445.
(2) Hearshaw, M. A.; Moss, J. R. Chem. Commun. 1999, 1-8.
(3) Newkome, G. R.; He, E.; Moorefield, C. N. Chem. ReV. 1999, 99,
1689-1746.
(4) Stoddart, F. J.; Welton, T. Polyhedron 1999, 18, 3575-3591.
(5) Caruso, F.; Schu¨ler, C.; Kurth, D. G. Chem. Mater. 1999, 11, 3394-
3399.
Discrete constitutional (or structural) isomers are common
in small molecules, but are not seen in highly branched
macromolecules (nanoscopic regime) or polymers, although
recently, Stang’s metallacycles have been demonstrated21 to
possess diastereomeric properties. The first criterion for being
constitutional isomers is that the related molecules need to
possess a single molecular weight and composition. Dendrimers,
which are constructed via stepwise syntheses, should have a
single molecular weight, if no defects are present. In contrast,
hyperbranched macromolecules and regular polymers are gener-
ally synthesized via a one-pot reaction and are polydisperse,
thus displaying a molecular weight distribution. Even if
structural isomers may be present in the bulk materials, there
are yet no known methods to isolate two isomeric hyperbranched
macromolecules or polymers in pure, defect-free form from the
reaction mixtures. On the other hand, since dendrimers possess
precise molecular weights, access to their pure isomeric forms
should be possible.
(6) Venturi, M.; Serroni, S.; Juris, A.; Campagna, S.; Balzani, V. Top.
Curr. Chem. 1998, 197, 193-228.
(15) Newkome, G. R.; Gu¨ther, R.; Moorefield, C. N.; Cardullo, F.;
Echegoyen, L.; Pe´rez-Cordero, E.; Luftmann, H. Angew. Chem., Int. Ed.
Engl. 1995, 34, 2023-2026.
(7) Narayanan, V. V.; Newkome, G. R. Top. Curr. Chem. 1998, 197,
19-77.
(8) Gorman, C. AdV. Mater. 1998, 10, 295-309.
(9) Zeng, F.; Zimmerman, S. C. Chem. ReV. 1997, 97, 1681-1712.
(10) Boulas, P. L.; Go´mez-Kaifer, M.; Echegoyen, L. Angew. Chem.,
Int. Ed. 1998, 37, 216-247.
(16) Newkome, G. R.; He, E.; God´ınez, L. A.; Baker, G. R. Chem.
Commun. 1998, 27-28.
(17) Anthony, J.; Boldi, A. M.; Rubin, Y.; Hobi, M.; Gramlich, V.;
Knobler, C. B.; Seiler, P.; Diederich, F. HelV. Chim. Acta 1995, 78, 13-
45.
(18) Liu, F. Q.; Tilley, T. D. Inorg. Chem. 1997, 36, 5090-5096.
(19) St. Pourcain, C. B.; Griffin, A. C. Macromolecules 1995, 28, 4116-
4121.
(20) de Leuze-Jallouli, A. M.; Dvornic, P. R.; Perz, S. V.; Owen, M. J.
Polym. Prepr. 1998, 39, 475-476.
(21) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. ReV. 2000, 100, 853-
908.
(11) Chow, H.-F.; Mong, T. K. K.; Nongrum, M. F.; Wan, C.-W.
Tetrahedron 1998, 54, 8543-8660.
(12) Newkome, G. R.; Moorefield, C. N.; Baker, G. R. Aldrichimica
Acta 1992, 25, 31-38.
(13) Newkome, G. R.; He, E.; God´ınez, L. A. Macromolecules 1998,
31, 4382-4386.
(14) Newkome, G. R.; Weis, C. D.; Moorefield, C. N.; Baker, G. R.;
Childs, B. J.; Epperson, J. Angew. Chem., Int. Ed. 1998, 37, 307-310.
10.1021/ja001401h CCC: $19.00 © 2000 American Chemical Society
Published on Web 09/27/2000

9994 J. Am. Chem. Soc., Vol. 122, No. 41, 2000
He et al.
Figure 2. Neutral metallodendrimers vs metallodendrimers with
counterions.
Cl-, BF4-, and PF6-. Construction of metallodendrimers without
external counterions not only provides additional synthetic
challenges but also provides a better understanding of these
materials. Some interesting questions can be answered by the
construction of a series of related neutral metallodendrimers,
for example: whether they will have less ionic character because
of their zwiterionic behavior than those with typical external
counterions (Figure 2); whether the physical, chemical, and
electrochemical properties of these materials will be different
when compared to our previous metallodendrimers; whether
their solubility characteristics would change; whether the
counterions would be conveniently interchangeable; whether
they would be more volatile, thus aiding in mass spectrometric
characterization.
Our approach to the construction of such a neutral metallo-
dendrimer takes advantage of a supramolecular dendritic
network concept utilizing four [- Ru -] linkages, which
generate precise predetermined structures due to the discrete
assembly process associated with the complexation sequence.
On the basis of the structural analysis of its components, eight
internal carboxylate ions are designed to compensate the charges
of these four Ru(II) centers; the external counterions can be
removed during the final step of the synthesis.
Figure 1. Idealized representation of two isomeric metallodendrimers
illustrating the concept of a “dendritic network” based on a “methane”
architecture.
The strategy for the construction of isomeric macromolecules
is based on simple organic molecular models and supramolecular
dendritic networks. The emergence of supramolecular chemistrys
“chemistry beyond molecules,” as defined by Lehn22,23shas led
dendrimer chemistry into a new era. Many suprasupermolecular
assemblies,3 such as rosettes of metallodendrimers,24-26 double-
27 and triple-helical28 metal complexes, racks, ladders, and grids
of metal complex arrays,29-31 are in fact different types of
molecular networks formed by using either metal-ligand
coordination bonding or H-bonding. Common aspects of various
networks include self-assembly, geometric compatibility of
components, and the incorporation of redundant atomic motifs.
Combining these parameters with related terpyr-Ru-terpyr
(depicted as [- Ru -])-based chemistries developed in our
laboratories, “dendritic methane” topologies (a 1 f 4 nanoscopic
dendritic network via metal complexation) can be envisioned
(see Figure 1). Essentially, the central dendritic core can be
viewed (for descriptive purposes only) as a nanoscale “carbon”
atom, and the appendage dendrimers can be considered as
nanoscale “hydrogen” atoms. The use of [- Ru -] connectivity
capitalizes on the formation of four stable complexes connecting
the dendritic core with four identical monomeric dendrons,
which can be viewed as the bonding between the “C” and “H”.
The shape of “CH4” is created through a suprasupermolecular
network in nanoscopic scale. In the quest for new procedures
toward tailor-made supramolecular dendritic assemblies, the two
new isomeric metallomacromolecules 16 and 17 are created
(Figure 1).
Experimental Section
Apparatus and Materials. Melting points are uncorrected and were
1
measured on a Mel-Temp melting point apparatus. H- and 13C NMR
spectra were recorded on a Bruker DPX 250 MHz spectrometer using
CDCl3 as solvent, unless otherwise indicated, with Me4Si as the internal
standard (0 ppm). Infrared spectra (IR) were recorded on a Mattson
Genesis Fourier transform infrared spectrophotometer. UV-vis spectra
were recorded on a HP8452A diode array spectrophotometer; molar
absorptivities were determined via single-point measurements. M-H-W
Laboratories, Phoenix, AZ, and Atlantic Microlab, Inc., Norcross, GA,
performed elemental analyses. Electrospray mass spectra were obtained
on a Bruker Esquire electrospray-ion trap mass spectrometer; constant
microspray of the sample was made by loading the solutions (1.0 ×
10-4 to 1.0 × 10-3 M in MeOH or MeCN) into a 250 µL syringe with
a delivery rate of 70 µL/h. MALDI-TOF mass spectra were performed
on a Bruker Reflex II mass spectrometer using a Nd:YAG laser (355
nm) in linear and reflectron modes. Samples were prepared by mixing
10 µL of a 70% MeOH/H2O solution of sample (1.0 × 10-4 to 1.0 ×
10-3 M) with 10 µL of a saturated solution of the indicated matrix; 1
µL of this solution was loaded onto the stainless steel sample plate
and allowed to evaporate to dryness.
Cyclic voltammetry (CV) experiments on 1.0 mM solutions of the
desired compound were conducted in dried and deoxygenated MeCN
or DMF. CV experiments utilized a Princeton Applied Research (PAR)
model 173 potentiostat coupled to a model 175 programmer, and a
Houston Instruments model 2000 X-Y recorder. Resistance compensa-
tion was performed using a PAR digital coulometer module (model
179) integrated to the potentiostat. The electrochemical experiments
were conducted using a three electrode standard setup (Cypress Systems,
Lawrence, Kansas), in which a glassy carbon disk electrode (1 mm
diameter), a platinum wire, and a silver wire were properly fitted as
the working, counter and pseudoreference electrodes, respectively. All
Additional considerations concerning metallomacromolecules3
include counterion associations, which traditionally have been
limited to the normal series of external counterions, such as
(22) Lehn, J.-M. Angew. Chem., Int. Ed. Engl. 1988, 27, 89-112.
(23) Lehn, J.-M. Angew. Chem., Int. Ed. Engl. 1990, 29, 1304-1319.
(24) Huck, W. T. S.; Hulst, R.; Timmerman, P.; van Veggel, F. C. J.
M.; Reinhoudt, D. N. Angew. Chem., Int. Ed. Engl. 1997, 36, 1006-1008.
(25) Huck, W. T. S.; Prins, L. J.; Fokkens, R. H.; Nibbering, N. M. M.;
van Veggel, F. C. J. M.; Reinhoudt, D. N. J. Am. Chem. Soc. 1998, 120,
6240-6246.
(26) Huisman, B.-H.; Scho¨nherr, H.; Huck, W. T. S.; Friggeri, A.; van
Manen, H.-J.; Menozzi, E.; Vancso, G. J.; van Veggel, F. C. J. M.;
Reinhoudt, D. N. Angew. Chem., Int. Ed. 1999, 38, 2248-2251.
(27) Hasenknopf, B.; Lehn, J.-M. HelV. Chim. Acta 1996, 79, 1643-
1650.
(28) Zelikovich, L.; Libman, J.; Shanzer, A. Nature 1995, 374, 790-
792.
(29) Hanan, G. S.; Schubert, U. S.; Volkmer, D.; Rivie`re, E.; Lehn, J.-
M.; Kyritsakas, N.; Fischer, J. Can. J. Chem. 1997, 75, 169-182.
(30) Schubert, D.; van den Broek, J. A.; Sell, B.; Durchschlag, H.;
Ma¨chtle, W.; Schubert, U. S.; Lehn, J.-M. Prog. Colloid Polym. Sci. 1997,
107, 166-171.
(31) Tziatzios, C.; Durchschlag, H.; Sell, B.; van den Broek, J. A.;
Ma¨chtle, W.; Haase, W.; Lehn, J.-M.; Weidl, C. H.; Eschbaumer, C.;
Schubert, D.; Schubert, U. S. Prog. Colloid Polym. Sci. 1835, 113, 114-
120.

Synthesis of Isomeric Metallodendrimers
J. Am. Chem. Soc., Vol. 122, No. 41, 2000 9995
the solutions [1.0 mM of the electroactive dendrimer in 0.1 M of Et4-
NBF4 in anhydrous MeCN or DMF] were carefully deoxygenated by
bubbling dry nitrogen for at least 10 min. Since the potential was
followed through a pseudoreference silver electrode, a second set of
voltammograms was obtained after adding a small amount of ferrocene
to the solution. The reversible electrochemical signal of the ferrocene/
ferrocenium couple did not interfere with the electrochemistry of any
of the compounds under study and therefore allowed its use as a
reference against which the potentials reported in this work were
measured.
All reagents where purchased from Aldrich Chemical Co. Column
chromatography was performed using activated basic aluminum oxide
(∼150 mesh, Brockmann I; Aldrich Chemical Co.). All reactions were
conducted under nitrogen atmosphere, unless obviously unnecessary
or otherwise specified.
General Procedures. Method 1 (DCC coupling).32 The reaction
mixture was stirred for 24-48 h, after which the white precipitate was
filtered. The filtrate was concentrated in vacuo affording a crude oil,
which was dissolved in Et2O (100 mL), washed sequentially with 10%
aqueous Na2CO3 (2 × 80 mL) and brine (2 × 80 mL), dried (MgSO4),
and concentrated in vacuo to afford the crude product.
Method 2 (Pd/C Reduction). The slurry was heated to 50 °C with
stirring, and then HCO2NH4 (2.0 g, excess) was added; after 30 min,
the mixture was cooled to 25 °C and then filtered through Celite. The
filtrate was concentrated in vacuo to give a solid, which was extracted
by Et2O or CH2Cl2 (2 × 100 mL). Solvent was evaporated in vacuo to
give the crude solid.
Method 3 (Acyl Chloride Coupling). The solution was stirred for
12-24 h, and then the white precipitate was filtered and washed well
with dry THF. The filtrate was collected, and the THF was removed
to give a light yellow solid that was dissolved in CHCl3 (200 mL).
The solution was washed with 10% aqueous Na2CO3 (2 × 100 mL)
and brine (3 × 100 mL). (It could take considerable time before the
two layers separated.) The organic layer was dried (MgSO4) and
concentrated in vacuo to give a crude product.
Method 4 (Metal Complexation). The mixture was refluxed for
4-6 h until turning into a clear red solution. After cooling to 25 °C,
excess saturated NH4PF6 in MeOH (10 mL) was added, and then the
MeOH was removed. The solid was dissolved in a small amount of
CHCl3 and precipitated with Et2O (120 mL). H2O (100 mL) was added
into the solid that was ground into powder form. The slurry was stirred
for 1 h; the solid was collected and then dried in vacuo to afford the
product.
Method 5 (Metal Complexation). The mixture was refluxed for 6
h during which the solution turned clear red. After cooling to 25 °C,
the solution was filtered to remove any insoluble materials, the EtOH
was removed from the filtrate to afford a red solid, which was dissolved
in MeOH (4 mL), and then H2O (50 mL) was added. The solution was
sealed into a membrane (cutoff mass ) 1000) to dialyze for 24 h. The
solution was concentrated and dried in vacuo to afford the product.
Method 6 (Deprotection). After the reaction, the formic acid was
removed in vacuo; a mixture of MeOH (5 mL) and H2O (50 mL) was
added to dissolve the resultant material. The solution was sealed into
a membrane (cutoff mass ) 3500) to dialyze for 24 h, and then the
solution was concentrated and dried in vacuo to afford the product.
N-{Tris[(2-tert-butoxycarbonyl)ethyl]methyl-1-nitroisophthala-
mide Monocarboxylic Acid (3). To a stirred solution of Behera’s
amine33-35 2 (2.72 g, 6.54 mmol) and Et3N (1.65 g, 2.5 equiv) in dry
THF (100 mL) at -5 °C, was added dropwise a solution of nitroisoph-
thalic monoacyl chloride36 (1, 1.50 g, 6.53 mmol) in THF (20 mL).
After 12 h of agitation, the white precipitate was filtered and washed
well with dry THF. The filtrate was collected, and the THF was
removed in vacuo to give a white solid, which was dissolved in CH2-
Cl2 (150 mL). The solution was washed sequentially with 10% cold
aqueous HCl (2 × 80 mL) and brine (2 × 80 mL), dried (MgSO4),
and concentrated in vacuo to give a crude product, which was dissolved
in CHCl3 (20 mL) and then slowly added into Et2O (200 mL) to yield
a white solid. When left overnight, half of the solvent evaporated; the
resulting solid was collected and then dried in vacuo to afford (54%)
3, as a white solid: 2.14 g; mp 168-170 °C (CHCl3); 1H NMR δ 1.43
(s, CH3, 27H), 2.18 (t, J ) 7.0 Hz, CH2CO2, 6H), 2.37 (t, J ) 7.1 Hz,
CH2CH2CO2, 6H), 8.30 (s, NH, 1H), 8.93-9.00 (m, ArH, 3H); 13C
NMR δ 28.2 (CH3), 30.3, 30.6 (CH2CH2), 58.7 (4°C), 81.6 (CMe3),
126.8, 127.3 (2, 6-ArC), 132.0 (ArCCO2H), 134.3 (ArCCONH), 137.5
(4-ArC), 148.7 (ArCNO2), 163.5 (CON), 167.6 (CO2H), 173.9 (CO2C);
IR (KBr) 3381, 3090, 2981, 2937, 1726, 1600, 1540, 1463, 1342, 1156,
849, 723 cm-1; ESI-MS m/z 631.7 (M + Na)+. Anal. Calcd for
C30H44N2O11: C, 59.20; H, 7.29; N, 4.60. Found: C, 59.17; H, 7.35;
N, 4.40.
N-{Tris[(2-tert-butoxycarbonyl)ethyl]methyl}-N′-[4′-oxa-(2,2′:
6′,2′′-terpyridinyl)]nitroisophthalamide (5). To a solution of acid 3
(307 mg, 504 µmol) in dry DMF (10 mL) were added dicyclohexyl-
carbodiimide (DCC; 104 mg, 504 µmol) and 1-hydroxybenzotriazole
(1-HOBT; 68 mg, 504 µmol) at 25 °C. The mixture was stirred for 1
h, then 5-aminopentyl 4′-(2,2′: 6′,2′′-terpyridinyl) ether37 (4, 169 mg,
504 µmol) was added. Following Method 1, the crude product was
column chromatographed eluting with 20% of EtOAc in CH2Cl2 to
afford (84%) 5, as a white solid: 392 mg [In larger-scale reactions,
when the crude product was greater than 1.0 g, it was dissolved in
Et2O (20 mL), and pure 5 generally precipitated within 1 h.]; mp 133-
136 °C (Et2O); 1H NMR δ 1.33 (s, CH3, 27H), 1.38-1.84 (br m,
CH2CH2CH2, 6H), 2.05 (t, J ) 7.1 Hz, CH2CO2, 6H), 2.23 (t, J ) 7.2
Hz, CH2CH2CO2, 6H), 3.42 (t, J ) 6.0 Hz, CH2NH, 2H), 4.12 (t, J )
6.1 Hz, OCH2, 2H), 7.21 (m, 5,5′′-tpyH, 2H), 7.75 (td, J ) 7.2, 1.6
Hz, 4,4′′-tpyH, 2H), 7.85 (s, 3′,5′-tpyH, 2H), 7.89 (s, NH, 1H), 7.92
(s, NH, 1H), 8.48 (d, J ) 8.0 Hz, 3,3′′-tpyH, 2H), 8.55 (d, J ) 4.9 Hz,
6,6′′-tpyH, 2H), 8.71 (m, ArH, 3H); 13C NMR δ 23.6 (CH2CH2CH2-
NH), 28.2 (CH3), 28.7, 29.3 (CH2CH2CH2CH2NH), 30.1 (CH2CO2),
30.5 (CH2CH2CO2), 40.5 (CH2NH), 58.5 (4°C), 67.9 (OCH2), 81.2
(CMe3), 107.5 (5,5′′-tpyC), 121.5 (4,4′′-tpyC), 123.9 (3,′′-tpyC), 124.3,
125.0, 131.1, 136.8, 136.9 (2,6,4,3,5-ArC), 137.1 (3′,5′-tpyC), 148.6
(ArCNO2), 149.1 (6,6′′-tpyC), 156.2 (2,2′′-tpyC), 157.2 (2′,6′-tpyC),
163.5 (CONHC), 164.6 (CH2NHCO), 167.2 (4′-tpyC), 173.4 (CO2);
IR (KBr) 3339, 3081, 2982, 2938, 1727, 1672, 1655, 1600, 1583, 1556,
1462, 1363, 1154, 851, 791, 741 cm-1; ESI-MS m/z 947.8 (M + Na)+.
Anal. Calcd for C50H64N6O11: C, 64.92; H, 6.97; N, 9.08. Found: C,
64.88; H, 6.87; N, 8.86.
First Tier Key Building Block (6). To a solution of 5 (1.50 g. 1.62
mmol) in MeOH (80 mL), was added 10% Pd/C (1.0 g). Following
Method 2, the crude material was column chromatographed eluting
with 20% CH2Cl2 in EtOAc to give (87%) 6, as a white solid: 1.26 g;
1H NMR δ 1.31 (s, CH3, 27H), 1.38-1.74 (br m, CH2CH2CH2, 6H),
1.99 (t, J ) 7.4 Hz, CH2CO2, 6H), 2.17 (t, J ) 7.4 Hz, CH2CH2CO2,
6H), 3.31 (t, J ) 5.9 Hz, CH2NH, 2H), 4.06 (t, J ) 6.1 Hz, OCH2,
2H), 6.75 (s, NH, 1H), 6.97 (s, NH, 1H), 7.08-7.37 (m, 5,5′′-tpyH,
ArH, 5H), 7.72 (td, J ) 7.9, 1.6 Hz, 4,4′′-tpyH, 2H), 7.87 (s, 3′,5′-
tpyH, 2H), 8.48 (d, J ) 8.0 Hz, 3,3′′-tpyH, 2H), 8.56 (d, J ) 4.9 Hz,
6,6′′-tpyH, 2H); 13C NMR δ 23.4 (CH2CH2CH2NH), 28.0 (CH3), 28.6,
29.3 (CH2CH2CH2CH2NH), 29.8, 30.0 (CH2CH2COO), 39.9 (CH2NH),
57.9 (4°C), 67.9 (OCH2), 80.7 (CMe3), 107.3 (5,5′′-tpyC), 114.0, 116.1,
116.4 (4,3,5-ArC), 121.3 (4,4′′-tpyC), 123.8 (3,3′′-tpyC), 136.0, 136.2
(2,6-ArC), 136.8 (3′,5′-tpyC), 147.5 (ArCNH2), 148.9 (6,6′′-tpyC), 156.0
(2,2′′-tpyC), 157.0 (2′,6′-tpyC), 166.5, 167.1, 167.3 (CONHC, CH2-
NHCO, 4′-tpyC), 172.9 (CO2); IR (KBr) 3443, 3361, 3251, 3060, 2976,
2938, 1727, 1644, 1594, 1567, 1528, 1363, 1149, 846, 791, 741 cm-1
;
ESI-MS m/z 918.5 (M + Na)+. Anal. Calcd for C50H66N6O9: C, 67.09;
(32) Klausner, Y. S.; Bodansky, M. Synthesis 1972, 453-463.
(33) Newkome, G. R.; Behera, R. K.; Moorefield, C. N.; Baker, G. R.
J. Org. Chem. 1991, 56, 7162-7167.
H, 7.42; N, 9.39. Found: C, 67.08; H, 7.62; N, 9.27.
Triacid (7). A solution of 5 (1.60 g, 1.73 mmol) in formic acid (50
mL) was stirred for 12 h at 25 °C, then most of the formic acid was
removed in vacuo; H2O (20 mL) and acetone (100 mL) were
subsequently added to dissolve the residual oil. All the solvents were
(34) Newkome, G. R.; Nayak, A.; Behera, R. K.; Moorefield, C. N.;
Baker, G. R. J. Org. Chem. 1992, 57, 358-362.
(35) Newkome, G. R.; Weis, C. D. Org. Prep. Proced. Int. 1996, 28,
485-488.
(36) Landsteiner, K.; van der Scheer, J. J. Exp. Med. 1938, 67, 709-
723.
(37) Newkome, G. R.; He, E. J. Mater. Chem. 1997, 7, 1237-1244.

9996 J. Am. Chem. Soc., Vol. 122, No. 41, 2000
He et al.
again removed in vacuo to ensure the removal of excess formic acid;
this was repeated twice. The residue was dissolved in hot acetone (3
mL), and then the solution was carefully added into Et2O (200 mL)
with stirring to afford a white precipitate, which was filtered and dried
in vacuo to give (95%) 7, as a white solid: 1.25 g; mp 166-168 °C;
1H NMR (DMSO-d6) δ 1.40-1.60 [br m, (CH2)3, 6H], 2.05-2.20 (br
m, CH2CH2CO2H, 12H), 3.34 (t, J ) 6.4 Hz, CH2NH, 2H), 4.17 (t, J
) 6.1 Hz, OCH2, 2H), 7.44 (m, 5,5′′-tpyH, 2H), 7.89-8.06 (br m, NH,
4,4′′,3′,5′-tpyH, 6H), 8.54 (d, J ) 7.8 Hz, 3,3′′-tpyH, 2H), 8.65 (d, J
) 5.0 Hz, 6,6′′-tpyH, 2H), 8.76-8.98 (m, ArH, 3H); 13C NMR (DMSO-
d6) δ 23.1 (CH2CH2CH2NH), 28.3, 28.4, (CH2CH2COOH), 28.8, 29.1
(CH2CH2CH2CH2NH), 40.5 (CH2NH), 58.1 (4°C), 67.9 (OCH2), 106.8
(5,5′′-tpyC), 121.0 (4,4′′-tpyC), 124.2 (d, 2,6-ArC), 124.5 (3,3′′-tpyC),
132.6, 136.1, 137.1 (4,3,5-ArC), 137.3 (3′,5′-tpyC), 147.7 (ArCNO2),
149.2 (6,6′′-tpyC), 155.0 (2,2′′-tpyC), 156.7 (2′,6′-tpyC), 163.8 (CON-
HC), 164.1 (CH2NHCO), 166.8 (4′-tpyC), 174.6 (CO2); IR (KBr) 3355,
3085, 2942, 1734, 1718, 1652, 1552, 1462, 1205, 792 cm-1; ESI-MS
m/z 757.8 (M + H)+. Anal. Calcd for C38H40N6O11: C, 60.31; H, 5.33;
N, 11.11. Found: C, 60.47; H, 5.37; N, 11.25.
631 mg; 1H NMR δ 1.30 (br s, CH3, 108H), 1.38-1.72 (br m,
CH2CH2CH2, 24H), 2.00-2.20 (br m, CH2CH2CO2, 48H), 2.43 (br s,
CH2CONH, 8H), 3.32 (br m, CH2CHCONH, CONHCH2, 16H), 3.55-
4.10 (br m, OCH2, 16H), 6.84 (s, NH, 4H), 7.21 (m, 5,5′′pyH, 8H),
7.30 (s, NH, 4H) 7.68-8.06 (br m, ArH, 4,4′′,3′,5′-tpyH, 28H), 8.45
(d, J ) 8.0 Hz, 3,3′′-tpyH, 8H), 8.55 (d, J ) 4.5 Hz, 6,6′′-tpyH, 8H),
9.16 (s, NH, 4H); 13C NMR δ 23.5 (CH2CH2CH2NH), 28.0 (CH3), 28.6,
29.2 (CH2CH2CH2CH2NH), 29.7,29.8 (CH2CH2CO2), 37.9 (CH2-
CONH), 40.1 (CONHCH2), 45.3 (4°C), 58.1 (4°C), 67.5, 67.9, 70.3 (all
OCH2), 80.6 (CMe3), 107.4 (5,5′′-tpyC), 120.4 (4-ArC), 121.3 (4,4′′-
tpyC), 123.8 (3,3′′-tpyC), 135.7, 136.1, (2,3,5,6-ArC), 136.8 (3′,5′-
tpyC), 139.2 (ArCNHCO), 148.9 (6,6′′-tpyC), 156.0 (2,2′′-tpyC), 157.0
(2′,6′-tpyC), 166.1, 166.8 (CONH, CH2NHCO), 167.1 (4′-tpyC), 170.8
(OCH2CH2CONH), 172.8 (CO2); IR (KBr) 3328, 3064, 2976, 2938,
2872, 1727, 1661, 1561, 1440, 1367, 1154, 840, 791, 741 cm-1; ESI-
MS m/z 1988.7 (M + 2Na)2+. Anal. Calcd for C217H284N24O44: C, 66.27;
H, 7.28; N, 8.54. Found: C, 65.93; H, 7.40; N, 8.40.
Second Tier Dendritic Core (12). To a stirred solution of the second
tier building block 9 (1.80 g, 938 µmol) and Et3N (142 mg, 1.41 mmol,
6 equiv.) in dry THF (40 mL) at -5 °C, was added dropwise a solution
of tetraacid chloride 10 (117 mg, 234 µmol) in THF (10 mL). Following
Method 3, the crude material was column chromatographed eluting
with a solution of hexane (25%) in EtOAc, followed by a solution of
MeOH (5%) in EtOAc to afford (24%) the pure 12, as a light yellow
Nitro Nonaester (8). To a solution of triacid 7 (800 mg, 1.06 mmol)
in dry DMF (10 mL) were added DCC (654 mg, 3.17 mmol) and
1-HOBT (428 mg, 3.17 mmol) at 25 °C. The mixture was stirred for
1 h, and then amine 2 (1.318 g, 3.17 mmol) was added. Following
Method 1, the crude product was column chromatographed eluting with
a solution of EtOAc (70%) in hexane to afford (90%) 8, as a white
1
solid: 452 mg; H NMR δ 1.30 (br s, CH3, 324H), 1.38-2.50 (br m,
1
CH2, 224H), 3.32 (br m, CH2O, CONHCH2, 16H), 3.55-4.10 (br m,
OCH2, 16H), 6.94 (s, NH, 4H), 7.20 (m, 5,5′′-tpyH, 8H), 7.30 (s, NH,
4H) 7.68-8.06 (br m, ArH, 4,4′′,3′,5′-tpyH, 28H), 8.45 (d, J ) 8.0
Hz, 3,3′′-tpyH, 8H), 8.60 (d, J ) 4.2 Hz, 6,6′′-tpyH, 8H), 9.16 (s, NH,
4H); 13C NMR δ 23.5 (CH2CH2CH2NH), 28.0 (CH3), 28.3, 28.8 (CH2-
CH2CH2CH2NH), 29.8,29.9 (CH2CH2CO2), 33.2, 33.2 (CH2CH2CONH),
38.6 (CH2CONH), 40.2 (CONHCH2), 45.6 (4°C), 57.3 (12 4°C), 58.6
(4 4°C), 68.0, 68.1, 69.7 (all OCH2), 80.3 (CMe3), 107.4 (5,5′′-tpyC),
120.4 (4-ArC), 121.2 (4,4′′-tpyC), 123.7 (3,3′′-tpyC), 135.8, 135.9,
(2,3,5,6-ArC), 136.6 (3′,5′-tpyC), 138.7 (ArCNHCO), 148.9 (6,6′′-
tpyC), 156.1 (2,2′′-tpyC), 156.9 (2′,6′-tpyC), 166.1, 166.5 (CONH, CH2-
NHCO), 167.2 (4′-tpyC), 170.7 (OCH2CH2CONH), 172.7 (CO2), 173.0
(CH2CONH); IR (KBr) 3361, 3063, 2976, 2936, 1729, 1652, 1558,
1453, 1370, 1150, 847 cm-1; MALDI-TOF-MS m/z 8075 (M + 2Na
-H)+, 2,5-dihyroxybenzoic acid (DHB) matrix. Anal. Calcd for
solid: 1.86 g; H NMR δ 1.33 (br s, CH3, 81H), 1.38-2.15 (br m,
CH2CH2CONH, CH2CH2CO2, CH2CH2CH2, 54H), 3.46 (br s, CH2NH,
2H), 4.16 (t, J ) 6.0 Hz, OCH2, 2H), 7.21 (m, 5,5′′-tpyH, 2H), 7.75
(td, J ) 7.2, 1.6 Hz, 4,4′′-tpyH, 2H), 7.91 (br m, NH, 3′,5′-tpyH, 4H),
8.51 (d, J ) 8.2 Hz, 3,3′′-tpyH, 2H), 8.58 (d, J ) 4.7 Hz, 6,6′′-tpyH,
2H), 8.83-8.98 (m, ArH, 3H); 13C NMR δ 23.4 (CH2CH2CH2NH),
28.0 (CH3), 28.3, 28.7 (CH2CH2CH2CH2NH), 29.5,29.8 (CH2CH2CO2),
31.8, 32.0 (CH2CH2CONH), 40.3 (CH2NH), 57.5 (3 4°C), 58.6 (4°C),
67.9 (OCH2), 80.5 (CMe3), 107.3 (5,5′′-tpyC), 121.2 (4,4′′-tpyC), 123.7
(3,3′′-tpyC), 124.4, 125.7, 130.3, 136.5, 136.6 (2,6,4,3,5-ArC), 136.7
(3′,5′-tpyC), 148.7 (ArCNO2), 148.9 (6,6′′-tpyC), 156.0 (2,2′′-tpyC),
157.0 (2′,6′-tpyC), 163.6 (CONHC), 164.5 (CH2NHCO), 167.1 (4′-
tpyC), 172.7 (CO2), 173.0 (CH2CONH); IR (KBr) 3365, 3058, 2976,
2937, 1726, 1655, 1556, 1452, 1370, 1151, 850 cm-1; ESI-MS m/z
1973.6 (M + Na)+. Anal. Calcd for C104H157N9O26: C, 64.07; H, 8.12;
N, 6.47. Found: C, 63.88; H, 8.10; N, 6.28.
C
433H656N36O104: C, 64.77; H, 8.23; N, 6.28. Found: C, 64.93; H, 8.43;
N, 6.40.
Dendritic Assembly (15). To a suspension of complex 13 (143 mg,
Second Tier Key Building Block (9). To a solution of 8 (2.45 g.
1.26 mmol) in MeOH (80 mL), was added 10% Pd/C (1.0 g). Following
Method 2, the crude material was column chromatographed eluting
with a solution of MeOH (5%) and hexane (20%) in EtOAc to give
153 µmol) in MeOH (20 mL), were added the first tier dendritic core
11 (150 mg, 38.1 µmol) and 4-ethylmorpholine (4 drops). Following
Method 4, complex 15 was isolated (97%) as a red solid: 311 mg; mp
1
(83%) 9, as a white solid: 2.01 g; H NMR δ 1.33-1.40 (br s, CH3,
1
> 152 °C (dec); H NMR (CD3CN) δ 1.20-1.40 (br d, CH3, 216H),
81H), 1.40-2.15 (br m, CH2CH2CONH, CH2CH2CO2, CH2CH2CH2,
54H), 3.42 (br s, CH2NH, 2H), 4.16 (t, J ) 6.0 Hz, OCH2, 2H), 6.25
(s, NH2, 2H), 7.21-7.52 (m, NH, ArH, 5,5′′-tpyH, 7H), 7.74 (td, J )
7.9, 1.4 Hz, 4,4′′-tpyH, 2H), 7.91 (s, 3′,5′-tpyH, 2H), 8.51 (d, J ) 7.9
Hz, 3,3′′-tpyH, 2H), 8.58 (d, J ) 4.0 Hz, 6,6′′-tpyH, 2H); 13C NMR δ
23.4 (CH2CH2CH2NH), 28.0 (CH3), 28.6, 29.0 (CH2CH2CH2CH2NH),
29.5,29.7 (CH2CH2CO2), 31.8, 32.3 (CH2CH2CONH), 39.9 (CH2NH),
57.3 (3 4°C), 58.2 (4°C), 67.9 (OCH2), 80.5 (CMe3), 107.3 (5,5′′-tpyC),
113.8, 116.1, 117.0 (4,3,5-ArC), 121.2 (4,4′′-tpyC), 123.7 (3,3′′-tpyC),
135.5, 135.8 (2,6-ArC), 136.6 (3′,5′-tpyC), 147.6 (ArCNH2), 148.9
(6,6′′-tpyC), 156.0 (2,2′′-tpyC), 156.9 (2′,6′-tpyC), 166.7, 167.1, 167.3
(CONHC, CH2NHCO, 4′-tpyC), 172.6 (COO), 173.0 (CH2CONH); IR
(KBr) 3359, 3063, 2976, 2947, 1732, 1655, 1567, 1452, 1370, 1151,
848, 790 cm-1; ESI-MS m/z 1942.8 (M + Na)+. Anal. Calcd for
1.50-2.50 (br m, CH2, 128H), 3.00-3.40 (br m, CH2, 24H), 4.40-
4.50 (br m, OCH2, 32H), 6.39 (br s, NH, 4H), 7.00-8.70 (br m, NH,
ArH, tpyH, 104H); 13C NMR (CD3CN) δ 24.4 (CH2CH2CH2NH), 25.3
(OCH2CH2CH2CONH), 28.4 (CH3), 28.6, 29.0 (CH2CH2CH2CH2NH),
30.8 (d, CH2CH2CO2), 33.0 (OCH2CH2CH2CONH), 37.9 (OCH2CH2-
CONH), 40.2 (CONHCH2), 45.2 (4°C), 58.8 (12 4°C), 59.6 (4 4°C), 66.0,
68.5, 70.7, 71.7 (all OCH2), 81.2, 81.3 (all CMe3), 112.6 (d, 5,5′′-
tpyC), 122.8 (4-ArC), 125.8 (d, 4,4′′-tpyC), 128.8 (d, 3,3′′-tpyC), 136.7,
137.2 (2,3,5,6-ArC), 139.1 (d, 3′,5′-tpyC), 140.9 (ArCNHCO), 153.7
(d, 6,6′′-tpyC), 157.7 (d, 2,2′′-tpyC), 159.7 (d, 2′,6′-tpyC), 167.2 (d,
4′-tpyC), 67.2, 167.6 (CONH, CH2NHCO), 171.8 (OCH2CH2CONH),
173.3 (OCH2CH2CH2CONH), 174.0 (d, CO2); IR (KBr) 3428, 3081,
2976, 2938, 1721, 1650, 1617, 1540, 1457, 1369, 1154, 846, 791, 758;
UV-vis λmax 242 (ꢀ ) 2.74 × 105), 268 (2.37 × 105), 306 (2.32 ×
105), 488 nm (6.67 × 104 dm3 mol-1 cm-1); MALDI-TOF-MS m/z
8283 (M - PF6)+, DHB matrix. Anal. Calcd for C381H508F48N40O76P8-
Ru4: C, 54.29; H, 6.08; N, 6.65. Found: C, 54.34; H, 6.13; N, 6.79.
Isomeric Metallodendrimer (16). To a solution of complex 14 (200
mg, 102 µmol) in MeOH (30 mL), were added the first tier dendritic
core 11 (100 mg, 25.4 µmol) and 4-ethylmorpholine (4 drops).
Following Method 4, complex 16 was generated (93%) as a red solid:
296 mg; mp > 152 °C (dec); 1H NMR (CD3CN) due to peaks
overlapping and broadening, the spectrum did not afford discernible
data; 13C NMR (CD3CN) δ 23.2 (CH2CH2CH2NH), 24.8 (OCH2CH2-
C
104H159N9O24; C, 65.08; H, 8.35; N, 6.57. Found: C, 64.93; H, 8.43;
N, 6.40.
First Tier Dendritic Core (11). To a stirred solution of first tier
building block 6 (800 mg, 894 µmol) and Et3N (135 mg, 1.34 mmol)
in dry THF (40 mL) at -5 °C, was added dropwise a solution of
tetraacid chloride38 10 (111 mg, 223 µmol) in THF (10 mL). Following
Method 3, crude material was column chromatographed eluting with a
solution of CHCl3 (30%) in EtOAc, followed by a mixture of MeOH
(5%) in EtOAc to afford (72%) the pure 11, as a light yellow solid:
(38) Newkome, G. R.; Lin, X. Macromolecules 1991, 24, 1443-1444.

Synthesis of Isomeric Metallodendrimers
J. Am. Chem. Soc., Vol. 122, No. 41, 2000 9997
CH2CONH), 28.1 (d, CH3), 28.6, 29.0 (CH2CH2CH2CH2NH), 29.8 (d,
36CH2CH2CO2), 31.5 (d, 12CH2CH2CO2), 33.0 (OCH2CH2CH2CONH),
34.7 (d, CH2CH2CONH), 37.8 (OCH2CH2CONH), 40.2 (CONHCH2),
45.0 (4°C), 57.7 (36 4°C), 58.3, 58.4 (4 4°C and 12 4°C), 66.0, 68.5,
69.3, 71.1 (all OCH2), 80.6, 81.4 (all CMe3), 111.2 (d, 5,5′′-tpyC), 121.5
(4-ArC), 124.6 (d, 4,4′′-tpyC), 127.7 (d, 3,3′′-tpyC), 136.1, 136.4,
(2,3,5,6-ArC), 137.9 (d, 3′,5′-tpyC), 138.8 (ArCNHCO), 152.0 (d, 6,6′′-
tpyC), 156.0 (d, 2,2′′-tpyC), 158.2 (d, 2′,6′-tpyC), 166.3 (d, 4′-tpyC),
166.4, 166.5 (CONH, CH2NHCO), 171.8 (OCH2CH2CONH), 172.4
(12CH2CH2CONH), 172.8 (36 CO2), 173.5 (12 CO2); IR (KBr) 3411,-
CHCl3 (15 mL), then added into Et2O (200 mL); the solution was
allowed to stand for 36 h during which time half of the solvent
evaporated. The precipitated solid was collected and then dried in vacuo
to give (58%) 20, as a white solid: 2.50 g; mp 164-166 °C; 1H NMR
δ 1.43 (br s, CH3, 21H), 2.16 (t, J ) 7.0 Hz, CH2CO2, 4H), 2.38 (t, J
) 7.1 Hz, CH2CH2CO2, 4H), 7.95 (s, NH, 1H), 8.80-8.99 (m, ArH,
3H); 13C NMR δ 23.5 (CH3), 28.0 [C(CH3)3], 30.4 (CH2CH2CO2), 33.4
(CH2CH2CO2), 56.4 (4°C), 81.4 (CMe3), 126.1, 126.9, 132.8, 133.9,
137.3 (2,3,4,5,6-ArC), 148.4 (ArCNO2), 164.0 (CONH), 165.9 (CO2H),
174.1 (CO2); IR (KBr) 3405, 3090, 2980, 2940, 1734, 1710, 1671, 1545,
1467, 1167, 851, 734 cm-1; ESI-MS m/z 517.7 (M + Na)+. Anal. Calcd
for C24H34N2O9: C, 58.29; H, 6.93; N, 5.66. Found C, 58.18; H, 6.95;
N, 5.68.
Nitro Precursor (21). To a solution of acid 20 (500 mg, 1.01 mmol)
in dry DMF (12 mL) were added DCC (209 mg, 1.01 mmol) and
1-HOBT (137 mg, 1.01 mmol) at 25 °C. The mixture was stirred for
1 h, then 5-aminopentyl 4′-(2,2′: 6′,2′′-terpyridinyl) ether (4, 338 mg,
1.01 mmol) was added. Following Method 1, the crude product was
dissolved in ether (20 cm3), from which an insoluble white solid (urea)
was filtered. The filtrate was allowed to stand for 2 days affording a
solid, which was flash column chromatographed eluting with a solution
of EtOAc (30%) in CH2Cl2 to yield (92%) 21, as a white solid: 753
mg; the recrystallized mother solution was also collected, dried, and
column chromatographed eluting with 20% of EtOAc in CH2Cl2: 1H
NMR δ 1.31 (br m, 35H), 3.34 (br s, CH2NHCO, 2H), 4.16 (br s, OCH2,
2H), 7.20 (m, 5,5′′-tpyH, 2H), 7.60-7.90 (br m, NH, NH, 3′,5′,4,4′′-
tpyH, 6H), 8.30-8.95 (br m, ArH, 3,3′′,6,6′′-tpyH, 7H); 13C NMR δ
23.5 (d, CH2CH2CH2NHCO, CH3), 28.0 (CH3), 28.6, 29.1 (CH2-
CH2CH2CH2NHCO), 30.3 (CH2CO2), 33.3 (CH2CH2CO2), 40.4 (CH2-
NHCO), 56.2 (4°C), 67.9 (OCH2), 81.0 (CMe3), 107.3 (5,5′′-tpyC), 121.4
(4,4′′-tpyC), 123.9 (3,3′′-tpyC), 124.2, 124.7, 131.2, 136.6, 136.7
(2,3,4,5,6-arC), 136.9 (3′,5′-tpyC), 148.2 (ArCNO2), 148.9 (6,6′′-tpyC),
155.9 (2,2′′-tpyC), 156.9 (2′,6′-tpyC), 163.8, 164.8 (CONHC, CH2-
NHCO), 167.0 (4′-tpyC), 173.7 (CO2); IR (KBr) 3342, 3082, 2980,
2940, 1734, 1671, 1537, 1371, 1151, 796, 734 cm-1; ESI-MS m/z 812.0
(M + H)+. Anal. Calcd for C44H54N6O9: C, 65.17; H, 6.71; N, 10.36.
Found C, 64.92; H, 6.58; N, 10.25.
3075, 2982, 2938, 1732, 1655, 1611,1534, 1457,1363, 1154, 842 cm-1
;
UV-vis λmax 242 (ꢀ ) 2.54 × 105), 268 (2.15 × 105), 306 (2.15 ×
105), 488 nm (6.54 × 104 dm3 mol-1 cm-1); MALDI-TOF-MS m/z
12 369 (M - PF6)+, DHB matrix. Anal. Calcd for C597H880F48N52O136P8-
Ru4: C, 57.25; H, 7.08; N, 5.81. Found: C, 56.86; H, 6.93; N, 5.42.
Isomeric Metallodendrimer (17). To a solution of complex 13 (84.3
mg, 89.7 µmol) in MeOH (30 mL), were added the second tier dendritic
core 12 (180 mg, 22.4 µmol) and 4-ethylmorpholine (4 drops).
Following Method 4, complex 17 was isolated (80%) as a red solid:
223 mg; mp > 152 °C (dec); 1H NMR (CD3CN) due to peaks
overlapping and broadening, the spectrum did not afford discernible
data; 13C NMR (CD3CN) δ 24.6 (CH2CH2CH2NH), 25.2 (OCH2CH2-
CH2CONH), 28.7 (d, CH3), 28.8, 29.0 (CH2CH2CH2CH2NH), 30.8 (d,
all CH2CH2CO2), 32.5 (d, CH2CH2CONH), 32.9 (OCH2CH2CH2-
CONH), 38.8 (OCH2CH2CONH), 41.2 (CONHCH2), 45.2 (4°C), 58.6
(36 4°C), 58.9, 59.8 (4 4°C and 12 4°C), 66.1, 68.7, 70.7, 71.4 (all OCH2),
81.2, 81.3 (all CMe3), 112.5 (d, 5,5′′-tpyC), 122.3 (4-ArC), 125.8 (d,
4,4′′-tpyC), 128.8 (d, 3,3′′-tpyC), 136.8, 137.6, (2,3,5,6-ArC), 139.1
(d, 3′,5′-tpyC), 140.2 (ArCNHCO), 153.8 (d, 6,6′′-tpyC), 157.8 (d, 2,2′′-
tpyC), 159.7 (d, 2′,6′-tpyC), 167.2 (d, 4′-tpyC), 167.7, 168.3 (CONH,
CH2NHCO), 172.1 (OCH2CH2CONH), 173.3 (OCH2CH2CH2CONH),
173.9 (36 CO2), 174.4 (12CO2); IR (KBr) 3405,3074, 2980, 2936, 1734,
1652, 1558, 1156, 841 cm-1; UV-vis λmax 242 (ꢀ ) 2.82 × 105), 268
(2.54 × 105), 306 (2.58 × 105), 488 nm (6.73 × 104 dm3 mol-1 cm-1);
MALDI-TOF-MS m/z 12 372 (M - PF6)+, DHB matrix. Anal. Calcd
for C597H880F48N52O136P8Ru4: C, 57.25; H, 7.08; N, 5.81. Found: C,
57.02; H, 6.99; N, 5.75.
Di-tert-butyl 4-Nitro-4-methylheptanedicarboxylate (18). To a
solution of tert-butyl acrylate (128.2 g, 1.00 mol) in liquid NH3 (300
mL), was added EtNO2 (75.07 g, 1.00 mol) at -78 °C slowly. The
mixture was stirred overnight and allowed to warm to 25 °C. The
resulting solid was further dried in vacuo to afford (95%) 18, as a white
solid: 314.8 g; mp 46-47 °C; 1H NMR δ 1.36 (s, 18H), 1.51 (s, 3H),
2.00-2.45 (m, 8H); 13C NMR δ 21.8 (CH3), 28.1 (CMe3), 30.2
(CH2CH2CO2), 34.4 (CH2CH2CO2), 81.1 (CMe3), 89.9 (O2NC), 171.3
(CO2); IR (KBr) 3003, 2979, 2940, 1726, 1537, 1159 cm-1; ESI-MS
m/z 332.6 (M + H)+. Anal. Calcd for C16H29NO6: C, 57.99; H, 8.82;
N, 4.23. Found C, 58.16; H, 8.59; N, 4.31.
Amino Terpyridine Monomer (22). To a solution of 21 (4.40 g.
5.43 mmol) in MeOH (80 mL), was added 10% Pd/C (1.5 g). Following
Method 2, the crude material was column chromatographed eluting a
solution of CH2Cl2 (10%) in EtOAc, then with 5% MeOH in CH2Cl2
to give (90%) 22, as a white solid: 3.81 g; 1H NMR δ 1.20-1.80 (br
m, 27H), 2.10-2.35 (br m, 8H), 3.32 (br s, CH2NHCO, 2H), 4.28 (br
s, OCH2, 2H), 6.45 (s, 2H), 6.75-7.35 (br m, NH, 5,5′′-tpyH, ArH,
7H), 7.68 (br s, 4,4′′-tpyH, 2H), 7.88 (s, 3′,5′-tpyH, 2H), 8.36-8.60
(br m, 3,3′′,6,6′′-tpyH, 4H); 13C NMR δ 23.1, 23.5 (CH2CH2CH2NHCO,
CH3), 27.8 (CH3), 28.3, 29.0 (CH2CH2CH2CH2NHCO), 30.1 (CH2CO2),
33.1 (CH2CH2CO2), 39.7 (CH2NHCO), 55.4 (4°C), 67.6 (OCH2), 80.2
(CMe3), 107.0 (5,5′′-tpyC), 113.7 (4-ArC), 115.8 (d, 2,6-ArC), 121.1
(4,4′′-tpyC), 123.6 (3,3′′-tpyC), 135.7, 136.2 (3,5-ArC), 136.6 (3′,5′-
tpyC), 147.5 (ArCNH2), 148.6 (6,6′′-tpyC), 155.6 (2,2′′-tpyC), 156.6
(2′,6′-tpyC), 166.7, 166.8,167.3 (CONHC, CH2NHCO, 4′-tpyC), 172.9
(CO2); IR (KBr) 3445, 3357, 3066, 2980, 2940, 1734, 1655, 1584, 1561,
1537, 1372, 1151, 797, 750 cm-1; ESI-MS m/z 782.2 (M + H)+. Anal.
Calcd for C44H56N6O7: C, 67.67; H, 7.23; N, 10.76. Found C, 67.52;
H, 6.98; N, 10.57.
Tetrakisterpyridine Core (23). To a stirred solution of amine 22
(1.00 g, 1.28 mmol) and Et3N (194 mg, 7.68 mmol) in dry THF (30
mL) at -5 °C, was added a solution of tetraacyl chloride 10 (159.5
mg, 320 µmol) in THF (2 mL). Following Method 3, the crude material
was column chromatographed eluting with a solution of MeOH (3%)
and hexane (25%) in EtOAc to give (67%) pure 23, as a light yellow
solid: 745 mg; 1H NMR δ 1.15-1.75 (br m, 108H), 2.10-2.40 (br m,
40H), 3.32-3.53 (br m, 24H), 4.05 (br s, OCH2, 8H), 6.87 (s, NH,
4H), 7.20 (br s, 5,5′′-tpyH, 8H), 7.51 (s, NH, 4H), 7.75 (br m, 4,4′′-
tpyH, ArH, 12H), 7.83 (s, 3′,5′-tpyH, 8H), 8.05 (s, ArH, 8H), 8.46-
8.60 (br m, 3,3′′,6,6′′-tpyH, 16H); 9.40 (s, NH, 4H); 13C NMR δ 23.4,
23.7 (CH2CH2CH2NHCO, CH3), 28.0 (CH3), 28.6, 29.1 (CH2CH2CH2-
CH2NHCO), 30.3 (CH2CO2), 33.1 (CH2CH2CO2), 37.8 (CH2CH2-
CONH), 40.1 (CONHCH2), 45.1 (C - core) 55.9 (4°C), 67.4 (OCH2-
CH2CONH), 68.6 (CH2Otpy), 70.1 (CH2OCH2), 80.5 (CMe3), 107.3
Di-tert-butyl 4-Amino-4-methylheptanedicarboxylate (19). To a
solution of 18 (30.0 g, 93.5 mmol) in absolute EtOH (250 mL) was
added prepared Raney Nickel (20 g) catalyst. The reaction slurry was
shaken in a sealed bottle under H2 (60 psi) for 12 h at 25 °C, and then
the black (pyrophoric) catalyst was filtered with great caution. The
filtrate was collected, concentrated, and dried in vacuo to afford (96%)
19, as a white oil: 26.2 g; 1H NMR δ 1.10 (s, NH2, 2H), 1.38 (s, CH3,
3H), 1.52 (s, CH3, 18H), 1.75 (t, J ) 7.1 Hz, CH2CO2, 4H), 2.20 (t, J
) 7.1 Hz, CH2CH2CO2, 4H); 13C NMR δ 27.3 (CH3), 28.1 [C(CH3)3],
30.6 (CH2CH2CO2), 37.5 (CH2CH2CO2), 50.9 (H2NC), 80.3 (CMe3),
173.4 (CO2); IR (CHCl3) 3019, 2979, 2932, 1727, 1214, 1159 cm-1
;
ESI-MS m/z 324.7 (M + Na)+. Anal. Calcd for C16H31NO4: C, 63.75;
H, 10.37; N, 4.65. Found C, 63.84; H, 10.17; N, 4.77.
Monocarboxylic Acid (20). To a stirred solution of amine 19 (2.63
g, 8.71 mmol) and Et3N (2.20 g, 21.8 mmol, 2.5 equiv) in dry THF
(100 mL) at -5 °C, was added dropwise a solution of nitroisophthalic
acid monoacyl chloride 1 (2.00 g, 8.71 mmol) in THF (50 mL). After
the solution was stirred for 12 h, the white precipitate was filtered and
washed well with dry THF. The filtrate was collected and the THF
was removed in vacuo to give a white solid, which was dissolved in
CH2Cl2 (200 mL). The solution was washed sequentially with 5% cold
aq. HCl (2 × 100 mL), brine (2 × 150 mL), dried (MgSO4), and
concentrated in vacuo to give a crude product, which was dissolved in

9998 J. Am. Chem. Soc., Vol. 122, No. 41, 2000
He et al.
(5,5′′-tpyC), 120.5 (4-ArC), 121.1 (4,4′′-tpyC), 123.8 (3,3′′-tpyC), 135.6,
136.2 (2,3,5,6-ArC), 136.8 (3′,5′-tpyC), 139.1 (ArCNHCO), 148.9 (6,6′′-
tpyC), 156.0 (2,2′′-tpyC), 156.9 (2′,6′-tpyC), 166.4, 167.0, 167.1
(CONHC, CH2NHCO, 4′-tpyC), 170.9 (OCH2CH2CONH), 173.1 (CO2);
UV-vis λmax 208 (ꢀ ) 3.05 × 104), 226 (2.91 × 104), 276 (2.63 ×
104), 302 (1.34 × 104), 394 (5.15 × 103), 462 nm (1.25 × 103 dm3
mol-1 cm-1). Anal. Calcd for C38H50Cl3N4O11Ru: C, 48.23; H, 5.33;
N, 5.92; Cl, 11.24. Found C, 48.06; H, 5.40; N, 6.20; Cl, 11.49.
The First Generation of Tert-butyl Ester Metallodendrimer (31).
To a suspension of the first generation of metalloappendage 26 (229
mg, 459 µmol) in EtOH (30 mL) were added tetrakisterpyridine core
23 (400 mg, 115 µmol) and 4-ethylmorpholine (6 drops). Following
Method 5, complex 31 was isolated (93%) as a red solid: 569 mg; mp
IR (KBr) 3326, 3066, 2980, 2940, 1734, 1663, 1569, 1160, 796 cm-1
;
ESI-MS m/z 1,740.7 (M + 2H)2+. Anal. Calcd for C193H244N24O36: C,
66.69; H, 7.08; N, 9.69. Found C, 66.56; H, 7.15; N, 9.23.
Propyl 4′-(2,2′:6′,2′′-Terpyridinyl) Ether (25). To a suspension of
powdered KOH (2.0 g) in dry DMSO (25 mL), was added propanol
(561 mg, excess). The suspension was heated to 60 °C for 30 min,
then 4′-chloro-2,2′:6′,2′′-terpyridine39 (4′-Cl-tpy, 24; 500 mg, 1.87
mmol) was added. After 24 h at 60 °C, the mixture was cooled and
poured into cold water (300 mL). The resultant solid was filtered,
washed with water, and dried in vacuo to give an off-colored white
material, which was flash column chromatographed eluting with a
solution of hexanes (50%) in CH2Cl2 to afford (93%) 25, as a white
solid: 506 mg; mp 112-114 °C; 1H NMR δ 0.94 (t, J ) 7.4 Hz, CH3,
3H), 1.76 (m, CH2CH2CH3, 2H), 4.04 (t, J ) 6.3 Hz, OCH2, 2H), 7.16
(br s, 5,5′′-tpyH, 2H), 7.68 (td, J ) 7.2, 1.6 Hz, 4,4′′-tpyH, 2H), 7.89
(s, 3′,5′-tpyH, 2H), 8.47 (d, J ) 7.9 Hz, 3′,3′′-tpyH, 2H), 8.55 (s, 6,6′′-
tpyH, 2H); 13C NMR δ 10.6 (CH2CH2CH3), 22.5 (CH2CH2CH3), 69.7
(OCH2), 107.4 (5,5′′-tpyC), 121.4 (4,4′′-tpyC), 123.8 (3,3′′-tpyC), 136.8
(3′,5′-tpyC), 149.0 (6,6′′-tpyC), 156.2 (2,2′′-tpyC), 157.0 (2′,6′-tpyC),
167.4 (4′-tpyC); IR (KBr) 3060, 2972, 2941, 2878, 1570, 1469, 1210,
1034, 801 cm-1; ESI-MS m/z 292.4 (M + H)+. Anal. Calcd for
C18H17N3O: C, 74.21; H, 5.88; N, 14.42. Found C, 74.26; H, 6.09; N,
14.45.
1
> 210 °C (dec); H NMR (MeOD) δ 1.25-1.49 (CH3, 96H), 1.60-
2.60 (br m, CH2, 80H), 3.20-3.55 (br m, overlap H2O, OCH2, NHCH2,
24H), 4.25 (br s, OCH2, 8H), 7.20 (br s, 5,5′′-tpyH, 16H), 7.42 (br s,
6,6′′-tpyH, 16H), 7.80-8.25 (br m, ArH, 4,4′′-tpyH, 28H), 8.60 (s, 3′,5′-
tpyH, 16H), 8.87 (br m, 3,3′′-tpyH, 16H); 13C NMR (MeOD) δ 10.6
(CH2CH2CH3), 23.1 (CH2CH2CH3), 23.8, 24.1 (CH3, CH2CH2CH2Opy),
28.0 (CH3), 29.2, 29.7 (CH2CH2CH2CH2Opy), 31.0 (CH2CH2CO2), 34.0
(CH2CH2CO2), 38.2 (OCH2CH2CONH), 40.5 (CONHCH2), 44.9 (4°C),
56.7 (4°C), 68.0, 70.2, 70.9, 72.6 (CH2OCH2CH2CONH, CH2Otpy,
tpyOCH2CH2CH3), 81.2 (CMe3), 111.9 (5,5′′-tpyC), 122.3 (4-ArC),
125.4 (4,4′′-tpyC), 128.4 (3,3′′-tpyC), 136.4, 137.4 (2,3,5,6-ArC), 138.6
(3′,5′-tpyC), 140.0 (ArCNHCO), 152.9 (6,6′′-tpyC), 157.3 (2,2′′-tpyC),
159.4 (2′,6′-tpyC), 167.3 (d, CONH, CONH), 168.5 (4′-tpyC), 172.3
(OCH2CH2CONH), 174.4 (CO2); IR (KBr) 3397, 3255, 3060, 2980,
2940, 1726, 1655, 1616, 1545, 1222, 1159, 796 cm-1; UV-vis λmax
214 (ꢀ ) 2.50 × 105), 240 (2.57 × 105), 266 (2.18 × 105), 304 (2.20
× 105), 484 nm (6.03 × 104 dm3 mol-1 cm-1); MALDI-TOF-MS a
broad signal at correct formula mass, IAA matrix. Anal. Calcd for
C
265H312Cl8N36O40Ru4: C, 59.72; H, 5.90; N, 9.46; Cl, 5.32. Found C,
Propyl 4′-(2,2′:6′,2′′-Terpyridine) Ether RuCl3 Complex (26). A
solution of RuCl3‚3H2O (179.5 mg, 686 µmol) and 25 (200 mg, 686
µmol) in EtOH (30 mL) was refluxed for 6 h. After cooling, the
precipitate was filtered, washed sequentially with EtOH (10 mL), water
(2 × 20 mL), and Et2O (2 × 10 mL), then dried in vacuo to afford
(89%) 26, as a golden solid: 304 mg; mp > 300 °C; IR (KBr) 3428,
3066, 2966, 2928, 1607, 1556, 1468, 1217, 795 cm-1; UV-vis λmax
206 (ꢀ ) 1.97 × 104), 238 (1.73 × 104), 274 (1.92 × 104), 312 (1.60
× 104), 370 (4.18 × 103), 530 nm (3.40 × 103 dm3 mol-1 cm-1). Anal.
Calcd for C18H17Cl3N3ORu: C, 43.35; H, 3.44; N, 8.42; Cl, 21.32.
Found C, 43.30; H, 3.69; N, 8.32; Cl, 21.22.
Terpyridine Triethyl Ester Monomer (29). To a solution of acid
28 (500 mg, 1.49 mmol) in dry DMF (30 mL), were added DCC (308
mg, 1.49 mmol) and 1-HOBT (202 mg, 1.49 mmol) at 25 °C. This
mixture was stirred for 1 h, and then Lin’s amine 27 (629 mg, 1.49
mmol) was added. Following Method 1, the crude material was column
chromatographed eluting with a solution of CH2Cl2 (40%) in EtOAc
to give (86%) pure 29, as a colorless oil: 947 mg; 1H NMR δ 1.16 (t,
J ) 7.1 Hz, CH3, 9H), 2.09 (m, J ) 6.6 Hz, CH2CH2CH2CONH, 2H),
2.35 (t, J ) 7.2 Hz, CH2CH2CONH, 2H), 2.44 (t, J ) 6.2 Hz,
OCH2CH2CO2Et, 6H), 3.60 (t, J ) 6.2 Hz, OCH2CH2CO2Et, 6H), 3.63
(s, CH2OCH2, 6H), 4.04 (q, J ) 7.2 Hz, OCH2CH3, 6H), 4.21 (t, J )
5.9 Hz, tpyOCH2, 2H), 6.09 (s, NH, 1H), 7.24 (td, J ) 5.3, 2.1 Hz,
5,5′′-tpyH, 2H), 7.76 (td, J ) 7.9, 1.2 Hz, 4,4′′-tpyH, 2H), 7.94 (s,
3′,5′-tpyH, 2H), 8.53 (d, J ) 8.0 Hz, 3′,3′′-tpyH, 2H), 8.60 (d, J ) 4.3
Hz, 6,6′′-tpyH, 2H); 13C NMR δ 14.3 (CH2CH3), 25.1 (CH2CH2CONH),
33.3 (CH2CH2CONH), 35.0 (CH2CO2Et), 59.8 (4°C), 60.5 (OCH2CH3),
66.8 (OCH2CH2CO2Et), 67.3 (tpyOCH2), 69.2 (CH2OCH2CH2CO2),
107.4 (5,5′′-tpyC), 121.3 (4,4′′-tpyC), 123.9 (3,3′′-tpyC), 136.8 (3′,5′-
tpyC), 149.1 (6,6′′-tpyC), 156.1 (2,2′′-tpyC), 157.1 (2′,6′-tpyC), 167.2
(4′-tpyC), 171.7 (CO2Et); IR (CHCl3) 3018, 2987, 1733, 1676, 1581,
1563, 1217 cm-1; ESI-MS m/z 739.8 (M + H)+. Anal. Calcd for
C38H50N4O11: C, 61.77; H, 6.82; N, 7.58. Found C, 61.53; H, 6.59; N,
7.58.
59.25; H, 6.00; N, 9.08; Cl, 5.48.
The First Generation of Acid Metallodendrimer (32). A solution
of 31 (120 mg, 22.5 µmol) in formic acid (20 mL) was stirred for 6 h
at 25 °C. Following Method 6, complex 32 was formed (98%) as a red
1
solid: 107 mg; mp > 220 °C (dec); H NMR (MeOD) δ 1.26 (br m,
CH3, 12H), 1.50 (br s, CH3, 12H), 1.70-2.65 (br m, CH2, 80H), 3.20-
3.55 (br m, overlap H2O, OCH2, NHCH2, 24H), 4.50 (br s, OCH2, 8H),
7.20-8.90 (br m, ArH, tpyH, 92H); 13C NMR (MeOD) δ 11.5 (CH2-
CH2CH3), 23.9 (CH2CH2CH3), 24.6, 24.9 (CH3, CH2CH2CH2Opy), 30.1,
30.2 (CH2CH2CH2CH2Opy), 31.7 (CH2CH2CO2), 35.0 (CH2CH2CO2),
38.3 (OCH2CH2CONH), 41.9 (CONHCH2), 46.8 (4°C), 57.4 (4°C), 68.6,
69.0, 71.9, 73.4 (CH2OCH2CH2CONH, CH2Opy, pyOCH2CH2CH3),
112.7 (5,5′′-tpyC), 123.2 (4-ArC), 126.2 (4,4′′-tpyC), 129.2 (3,3′′-tpyC),
137.3, 138.3 (2,3,5,6-ArC), 139.4 (3′,5′-tpyC), 140.9 (ArCNHCO),
153.8 (6,6′′-tpyC), 158.1 (2,2′′-tpyC), 160.3 (2′,6′-tpyC), 166.8, 168.0,
168.1 (CONH, CONH, 4′-tpyC), 173.1 (OCH2CH2CONH), 177.9
(CO2H); IR (KBr) 3405, 3263, 3066, 2971, 2932, 1726, 1655, 1616,
1545, 1222, 796 cm-1; UV-vis λmax 214 (ꢀ ) 2.58 × 105), 240 (2.59
× 105), 266 (2.18 × 105), 304 (2.23 × 105), 484 nm (5.63 × 104 dm3
mol-1 cm-1); MALDI-TOF-MS m/z 4902 (M + Na)+, DHB matrix;
m/z 4740 (M - 4Cl)+, 4603 (M - 8Cl)+, 4600 (M - 8Cl)+, IAA
matrix. Anal. Calcd for C233H248Cl8N36O40Ru4: C, 57.34; H, 5.12; N,
10.33; Cl, 5.81. Found C, 57.89; H, 5.43; N, 10.68; Cl, 5.76.
The First Generation of Neutral Metallodendrimer (33). To a
stirred solution of acid 32 (150 mg, 30.7 µmol) in MeOH (5 mL) and
H2O (50 mL), was added KOH (1.721 mg, 30.7 µmol) in H2O (30
mL). The solution was sealed into a membrane (cutoff mass ) 3500)
to dialyze for 24 h, and then the solution was concentrated and dried
in vacuo to give (92%) the desired neutral metallodendrimer 33, as a
1
red solid: 130 mg; mp > 230 °C (dec); H NMR (MeOD) δ 1.35-
4.00 (br m, overlap H2O, CH2, CH3, 128H), 4.70 (br s, OCH2, 8H),
7.20-8.90 (br m, ArH, tpyH, 92H); 13C NMR (MeOD) δ 10.6 (CH2-
CH2CH3), 23.1 (CH2CH2CH3), 23.6, 24.1 (CH3, CH2CH2CH2Opy), 29.2,
29.6 (CH2CH2CH2CH2Opy), 32.9 (CH2CO2), 35.6 (CH2CH2CO2), 37.9
(OCH2CH2CONH), 41.5 (CONHCH2), 45.8 (4°C), 57.1 (4°C), 68.8, 69.0,
71.0, 72.4 (CH2OCH2CH2CONH, CH2Otpy, tpyOCH2CH2CH3), 111.8
(5,5′′-tpyC), 122.1 (4-ArC), 125.4 (4,4′′-tpyC), 128.5 (3,3′′-tpyC), 136.5,
137.8 (2,3,5,6-ArC), 138.7 (3′,5′-tpyC), 140.1 (ArCNHCO), 153.1 (6,6′′-
tpyC), 157.3 (2,2′′-tpyC), 159.4 (2′,6′-tpyC), 167.2, 167.7, 168.7
(CONH, CONH, 4′-tpyC), 172.0 (OCH2CH2CONH), 181.3 (CO2-); IR
(KBr) 3405, 3263, 3066, 2971, 2932, 1726, 1655, 1616, 1545, 1222,
796 cm-1; UV-vis λmax 212 (ꢀ ) 2.54 × 105), 242 (2.50 × 105), 266
(2.07 × 105), 306 (2.11 × 105), 486 nm (5.84 × 104 dm3 mol-1 cm-1);
Second Tier Ru(III)-Metalloappendage (30). A solution of RuCl3‚
3H2O (361 mg, 1.38 mmol) and 29 (1.02 g, 1.38 mmol) in EtOH (50
mL) was refluxed for 6 h. After cooling, the precipitate was filtered,
washed sequentially with EtOH (5 mL), water (2 × 20 mL), and Et2O
(2 × 10 mL), then dried in vacuo yielding (84%) 30, as a yellow-
brown solid: 1.10 g; mp > 250 °C (dec); IR (KBr) 3457, 3350, 3073,
2979, 2878, 1733, 1676, 1607, 1550, 1469, 1216, 1103, 856, 794 cm-1
;
(39) Constable, E. C.; Ward, M. D. J. Chem. Soc., Dalton Trans. 1990,
1405-1409.

Synthesis of Isomeric Metallodendrimers
J. Am. Chem. Soc., Vol. 122, No. 41, 2000 9999
MALDI-TOF-MS m/z 4590 (M + H)+, IAA matrix. Anal. Calcd for
Scheme 1. Construction of the First Tier Building Block for
the Dendritic Corea
C
233H240N36O40Ru4: C, 60.98; H, 5.27; N, 10.99; Cl, 0.00. Found C,
60.61; H, 5.45; N, 10.23; Cl, 0.00.
The Second Generation of Tert-butyl Ester Metallodendrimer
(34). To a stirred suspension of the second generation of metalloap-
pendage 30 (109 mg, 115 µmol) in EtOH (20 mL), were added
tetrakisterpyridine core 23 (100 mg, 28.8 µmol) and 4-ethylmorpholine
(6 drops). Following Method 5, complex 34 was isolated (96%) as a
1
red solid: 196 mg; mp > 176 °C (dec); H NMR (MeOD) δ 1.31-
1.47 (m, CH3, 120H), 1.60-2.40 (br m, 40H), 2.2-2.85 (br m, 64H),
3.40-3.90 (br m, overlap H2O, 72H), 4.20 (br s, 24H), 4.69 (br s, 16H),
7.36 (br s, 5,5′′-tpyH, 16H), 7.64 (br s, 6,′′-tpyH, 16H), 8.01-8.44 (br
m, ArH, 4,4′′-tpyH, 28H), 8.60-8.87 (br m, 3,3′′,3′,5′-tpyH, 32H); 13
C
NMR (MeOD) δ 14.6 (CH2CH3), 24.1, 24.5, 25.9 (CH2CH2CH2CONH,
CH2CH2CH2Otpy, CH3), 28.4 (CH3), 29.6, 30.1 (CH2CH2CH2CH2Otpy),
31.4 (CH2CH2CO2), 33.4 (CH2CH2CO2), 34.3 (CH2CH2CH2CONH),
35.9 (OCH2CH2CO2), 37.9 (OCH2CH2CONH), 41.4 (CONHCH2), 45.9
(4°C), 57.1 (4°C), 61.4 (4°C), 61.5 (OCH2CH3), 68.0 (OCH2CH2CO2),
69.8 (CH2OCH2CH2CO2), 70.0, 70.2, 70.4, 70.5 (CH2Otpy, tpyOCH2-
CH2CH2CONH, CH2OCH2CH2CONH), 81.4 (CMe3), 112.3 (5,5′′-
tpyC), 122.5 (4-ArC), 125.8 (4,4′′-tpyC), 128.8 (3, 3′′-tpyC), 136.8,
137.9 (2,3,5,6-ArC), 139.0 (3′,5′-tpyC), 140.4 (ArCNHCO), 153.4 (6,6′′-
tpyC), 157.7 (2,2′′-tpyC), 159.8 (2′,6′-tpyC), 167.3,167.6, 168.9
(CONH, CONH, 4′-tpyC), 172.6 (CONHAr), 173.3 (CO2Et), 174.6
(CO2t-Bu), 175.0 (OCH2CH2CH2CONH); IR (KBr) 3428, 3065, 2979,
2940, 1726, 1651, 1619, 1544, 1468, 1217, 1109 cm-1; UV-vis λmax
214 (ꢀ ) 2.48 × 105), 242 (2.57 × 105), 266 (2.25 × 105), 304 (2.22
× 105), 484 nm (6.13 × 104 dm3 mol-1 cm-1); MALDI-TOF-MS a
broad signal at correct formula mass, IAA matrix. Anal. Calcd for
C345H444Cl8N40O80Ru4: C, 58.20; H, 6.29; N, 7.87; Cl, 3.98. Found C,
58.32; H, 6.29; N, 8.02; Cl, 3.62.
The Second Generation of Acid Metallodendrimer (35). A
solution of 34 (620 mg, 87.1 µmol) in formic acid (40 mL) was stirred
for 6 h at 25 °C. Following Method 6, complex 35 was isolated (97%)
as a red solid: 560 mg; mp > 190 °C (dec); 1H NMR (MeOD) δ 1.12
(m, CH3, CH3, 48H), 1.45-1.95 (br m, 40H), 2.20-2.85 (br m, 64H),
3.15-3.65 (br m, overlap H2O, 72H), 4.00 (br s, 24H), 4.45 (br s, 16H),
7.12 (br s, 5,5′′-tpyH, 16H), 7.45 (br s, 6,6′′-tpyH, 16H), 7.70-8.25
(br m, ArH, 4,4′′-tpyH, 28H), 8.45-8.80 (br m, 3,3′′,3′,5′-tpyH, 32H);
13C NMR (MeOD) δ 14.9 (CH2CH3), 24.4, 24.5, 25.9 (CH2CH2CH2-
CONH, CH2CH2CH2Otpy, CH3), 29.6, 30.2, 30.6 (CH2CH2CH2CH2-
Otpy, CH2CH2CO2), 33.8 (CH2CH2CO2), 34.8 (CH2CH2CH2CONH),
36.2 (OCH2CH2CO2), 37.8 (OCH2CH2CONH), 42.4 (CONHCH2), 46.4
(4°C), 57.3 (4°C), 61.8, 61.9 (4°C, OCH2CH3), 68.3 (OCH2CH2CO2),
70.1 (CH2OCH2CH2CO2), 70.7-71.3 (m, CH2Opy, tpyOCH2CH2CH2-
CONH, CH2OCH2CH2CONH), 112.6 (5,5′′-tpyC), 122.7 (4-ArC), 125.8
(4,4′′-tpyC), 129.1 (3,3′′-tpyC), 137.1, 138.1 (2,3,5,6-ArC), 139.3 (3′,5′-
tpyC), 140.7 (ArCNHCO), 153.7 (6, 6′′-tpyC), 157.9 (2,2′′-tpyC), 160.0
(2′,6′-tpyC), 167.7,167.9, 169.1 (CONH, CONH, 4′-tpyC), 172.9
(CONHAr), 173.6 (CO2Et), 175.4 (OCH2CH2CH2CONH), 177.5 (CO2H);
IR (KBr) 3412, 3067, 2934, 1733, 1657, 1613, 1544, 1462, 1210, 1109
cm-1; UV-vis λmax 214 (ꢀ ) 2.56 × 105), 242 (2.59 × 105), 266 (2.26
× 105), 304 (2.28 × 105), 484 nm (6.36 × 104 dm3 mol-1 cm-1);
MALDI-TOF-MS m/z 6380 (M - 8HCl)+, IAA matrix. Anal. Calcd
for C313H380Cl8N40O80Ru4: C, 56.36; H, 5.74; N, 8.40; Cl, 4.25. Found
C, 56.18; H, 5.86; N, 8.46; Cl, 4.62.
a (i) Et3N, THF, 12 h, -5 °C then 25 °C; (ii) DCC, 1-HOBT, DMF,
24 h, 25 °C; (iii) 10% Pd/C, HCO2NH4, MeOH, 0.5 h, 50 °C.
(4°C), 57.6 (4°C), 61.8, 61.9 (4°C, OCH2CH3), 68.3 (OCH2CH2CO2),
70.2 (CH2OCH2CH2CO2), 71.0-71.3 (m, CH2Otpy, tpyOCH2CH2CH2-
CONH, CH2OCH2CH2CONH), 112.5 (5,5′′-tpyC), 122.6 (4-ArC), 126.1
(4,4′′-tpyC), 129.3 (3,3′′-tpyC), 137.2, 138.5 (2,3,5,6-ArC), 139.3 (3′,5′-
tpyC), 140.8 (ArCNHCO), 153.6 (6,6′′-tpyC), 157.9 (2,2′′-tpyC), 160.1
(2′,6′-tpyC), 167.6,167.8, 169.2 (CONH, CONH, 4′-tpyC), 172.5
(CONHAr), 173.6 (CO2Et), 175.3 (OCH2CH2CH2CONH), 181.7 (CO2-);
IR (KBr) 3425, 3066, 2934, 1733, 1657, 1619, 1556, 1462, 1216, 1109
cm-1; UV-Vis λmax 212 (ꢀ ) 2.57 × 105), 242 (2.58 × 105), 266 (2.22
× 105), 306 (2.22 × 105), 486 nm (5.98 × 104 dm3 mol-1 cm-1):
MALDI-TOF-MS m/z 6381 (M + H)+, IAA matrix. Calcd for
C313H372N40O80Ru4: C, 58.94; H, 5.88; N, 8.78; Cl, 0.00. Found C,
58.94; H, 5.86; N, 8.71; Cl, 0.00.
A Tailored Approach to Isomeric Metallomacromolecules
The ideal starting material to construct the dendritic cores
11 or 12 would be an appropriately trisubstituted benzene, such
that one site is attached to a branched monomer, which can be
further expanded to higher generations; another site possesses
a terpyridine unit, which can be used as metal complex ligand
for the networks; and the third site is connected to a four-
directional core. The candidate chosen was 5-nitroisophthalic
acid, which was converted (23%) with 1 equiv of PCl5 in cold
Et2O into the desired monoacyl chloride36 1 by our modified
literature procedure (Scheme 1). Its treatment with amine 235
afforded N-{tris[(2-tert-butoxycarbonyl)ethyl]methylnitroiso-
phthalamide monocarboxylic acid (3) in 54% yield. Amidation
of 1 was supported (13C NMR) by the shift of the signal assigned
to the quaternary carbon moiety (CONHC) of amine 2 from
The Second Generation of Neutral Metallodendrimer (36). To a
stirred solution of acid 35 (420 mg, 63.0 µmol) in MeOH (5 mL) and
H2O (50 mL) was added KOH (3.526 mg, 63.0 µmol) in H2O (30 mL).
The solution was sealed into a membrane (cutoff mass ) 3500) to
dialyze for 24 h, and the solution was concentrated and dried in vacuo
to give (97%) neutral metallodendrimer 36, as a red solid: 391 mg;
1
mp > 210 °C (dec); H NMR (MeOD) δ 1.10-1.30 (m, CH3, 48H),
1.55-2.20 (br m, 72H), 2.50-2.65 (br m, 32H), 3.25-3.75 (br m,
overlap H2O, 72H), 4.15 (q, J ) 7.0 Hz, CO2CH2, 24H), 4.50 (br s,
16H), 7.12 (br s, 5,5′′-tpyH, 16H), 7.45 (br d, 6,6′′-tpyH, 16H), 7.90-
8.15 (br m, ArH, 4,4′′-tpyH, 28H), 8.45-8.90 (br m, 3,3′′,3′,5′-tpyH,
32H); 13C NMR (MeOD) δ 14.9 (CH2CH3), 24.4, 24.5, 26.2 (CH2CH2-
CH2CONH, CH2CH2CH2Otpy, CH3), 29.6, 30.2, 30.4 (CH2CH2CH2-
CH2Otpy, CH2CO2), 33.8, 33.9 (CH2CH2CO2, CH2CH2CH2CONH),
36.2 (OCH2CH2CO2), 38.2 (OCH2CH2CONH), 42.2 (CONHCH2), 46.5

10000 J. Am. Chem. Soc., Vol. 122, No. 41, 2000
He et al.
Scheme 2. Construction of the Second Tier Building Block
Scheme 3. Construction of the Dendritic Coresa
for the Dendritic Corea
a (i) HCOOH, 24 h, 25 °C; (ii) DCC, 1-HOBT, DMF, 48 h, 25 °C;
(iii) 10% Pd/C, HCO2NH4, MeOH, 0.5 h, 50 °C.
52.8 to 58.7 ppm and the appearance (ESI-IT) of a molecular
peak at m/z 631.7 ([M + Na]+ m/z 631.7). Monoacid 3 was
subsequently treated with 5-aminopentyl 4′-(2,2′: 6′,2′′-terpy-
ridinyl) ether37 (4) by the DCC coupling32 procedure generating
(84%) N-{tris[(2-tert-butoxycarbonyl)ethyl]methyl}-N′-[4′-oxa-
(2,2′:6′,2′′-terpyridinyl)]-nitroisophthalamide (5). A downfield
shift (13C NMR) for the CONHCH2 observed in the spectrum
of nitro-terpyridyl 5 from 42.0 to 40.5 ppm along with a
molecular peak at m/z 947.8 ([M + Na]+ m/z 948.1) in ESI-
MS support its structural assignment. Reduction40 of the aryl
nitro moiety of 5 with 10% Pd/C and a large excess HCO2NH4
afforded (87%) the arylamine monomer 6, which was supported
by the chemical shift (13C NMR) for the 1-ArC from 148.6 to
147.5 ppm and the molecular peaks at m/z 917.5 ([M + Na+]
m/z 918.1). Alternative reduction conditions using Raney nickel
catalyst35 were also attempted for the conversion of nitro group,
but the reaction was not successful.
Hydrolysis of 5 with formic acid gave (95%) the triacid 7
(Scheme 2), whose assignment was confirmed by the signal at
174.6 ppm (CO2H) in the 13C NMR spectrum and the molecular
peak at m/z 757.3 ([M + H]+ m/z 757.8) in the ESI-MS. Iterative
amidation41 of 7 gave (90%) the desired nonaester 8, which
was structurally established by the new signal for the additional
quaternary carbon (CONHC) at 57.5 ppm and the molecular
peak (ESI-IT) at m/z 1972.0 ([M + Na]+ m/z 1972.8).
Reduction40 of the aryl nitro moiety of 8 with 10% Pd/C and a
large excess of HCO2NH4 afforded (83%) the key arylamine
monomer 9, which was supported by the chemical shift (13C
NMR) for the 1-ArC from 148.6 to 147.5 ppm and the molecular
peak at m/z 1,942.8 ([M + Na]+ m/z 1,942.5).
a (i) Et3N, THF, 24 h, 0 °C then 25 °C.
THF in the presence of Et3N. In the 13C NMR spectra of 11 or
12, a significant upfield shift of the signal at 147.5 to 139.2
(138.7 for 12) ppm corresponding to the ArCNHCO cor-
roborates amidation, as well as the peak at m/z 1988.7 [M +
2Na]2+ (ESI-IT) for 11, or m/z 8075 [M + 2Na - H]+ (MALDI-
TOF) for 12, respectively.
The first and second tier metalloappendages 13 and 14 were
prepared by a simple divergent process15 (Figure 3). The
complementary metallo-donor and receptor dendritic molecules
were readily assembled via four [- Ru -] connections to
generate a methane-type motif. Reductive assemblage of 11 with
4 equiv of 13 in hot MeOH in the presence of 4-ethylmorpholine
afforded (97%) the desired microcrystalline, red dendritic
assembly 15 (Scheme 4). Based on its 13C NMR spectra, the
absence of any free terpyridine moiety and the presence of two
very similar complexed terpyridine moieties (i.e., core vs
terminal directed terpyridines) indicated the four, symmetrical
attachments. MALDI-TOF mass spectrum gave a molecular
peak at m/z 8283 ([M - PF6]+ m/z 8283) for 15.
Novel isomeric “dendritic methane-type” metallomacromol-
ecules 16 (93%), formed from 11 and 4 equiv of metalloap-
pendages 14, and 17 (80%), prepared from 12 and 13, were
constructed (Scheme 5) by the same manner as for 15. MALDI-
TOF mass spectrum of each showed a broad molecular peak at
m/z 12 235 ([M - 2PF6]+ m/z 12 236) for 16, and at m/z 12 234
([M - 2PF6]+ m/z 12 236) for 17; these results strongly support
the isomeric relationship between these two structures. Normal
spectroscopic and analytical analyses were indiscernible for
these two obviously similar structures; however, electrochemical
The first and second tier dendritic cores 11 or 12 were
prepared (72 or 24%, respectively) via a coupling reaction of
tetraacid chloride38 10 (Scheme 3) with 4 equiv of 6 or 9 in
(40) Ram, S.; Ehrenkaufer, R. E. Tetrahedron Lett. 1984, 25, 3415-
3418.
(41) Young, J. K.; Baker, G. R.; Newkome, G. R.; Morris, K. F.; Johnson,
C. S., Jr. Macromolecules 1994, 27, 3464-3471.

Synthesis of Isomeric Metallodendrimers
J. Am. Chem. Soc., Vol. 122, No. 41, 2000 10001
di-tert-butyl 4-amino-4-methylheptanedicarboxylate (19) in 96%
yield. The large upfield shift of the carbon peak (13C NMR) of
CNO2 to CNH2 (∆ ) -39 ppm) clearly indicated the success
of reduction and the molecular peak (ESI-IT) at m/z 324.7 ([M
+ Na]+ m/z 324.4) further supported the expected structure.
Reaction of 19 with 5-nitroisophthalic acid monoacyl chloride
(1) in the presence of Et3N at -5 °C gave (58%) monocar-
boxylic acid 20. The downfield shift (13C NMR) of CNH2 to
CNHCdO (∆ ) 5.50 ppm) along with the molecular peak (ESI-
IT) at m/z 517.7 ([M + Na]+ m/z 517.9) supported the desired
the structure. DCC coupling of acid 20 with 1-HOBT and
5-aminopentyl 4′-(2,2′:6′,2′′-terpyridinyl) ether (4) in DMF at
25 °C afforded nitro precursor 21, which possessed the correct
mass peak (ESI-IT) at m/z 812.0 ([M + H]+ m/z 812.0) and
was subsequently reduced with 10% Pd/C and ammonium
formate in MeOH at 50 °C to afford the desired branched
monomer 22. The clear upfield shift (13C NMR) of 4-ArC (∆
) -17.5 ppm) and ArCNO2 to ArCNH2 (∆ ) -0.7 ppm)
supported the structure of 22, which was further confirmed by
the molecular peak (ESI-IT) at m/z 782.2 ([M + H]+ m/z 782.0).
Four equiv of 22 were treated with tetraacyl chloride 10 in
the presence of excess of Et3N at -5 °C to provide (67%) the
tetrakisterpyridine core 23 (Scheme 7). The downfield shift (13C
NMR) of 4-ArC (∆ ) 6.8 ppm) and upfield shift of ArCNH2
to ArCNH(CdO) (∆ ) -8.4 ppm) indicated that the tetraami-
dation had occurred. The desired structure of 23 was further
confirmed by the mass peak (ESI-IT) at m/z 1740.7 ([M + 2H]2+
m/z 1739.1).
Figure 3. Metallodendritic building blocks.
Scheme 4. Construction of the “Dendritic Methane”a
A simple capping reagent was prepared from 4′-chloro-2,2′:
6′,2′′-terpyridine (4′-Cl-tpy, 24),39 by heating with 1-propanol
and powered KOH in DMSO at 60 °C to give propyl 4′-(2,2′:
6′,2′′-terpyridinyl) ether (25) in 93% yield (Scheme 8). The
significant chemical shifts (1H NMR) for 3′,5′-tpyH and 5′,5′′-
tpyC, as well as for tpy 4′-tpyC (13C NMR) confirmed the
formation of 4′-ethereal bond and the molecular peak at m/z
292.4 ([M + H]+ m/z 292.4) further supported the structure.
Terpyridine ether 25 was then refluxed with RuCl3‚3H2O in
EtOH to give (89%) the unbranched building block appendage
26. Its structure was only supported by combustion analysis;
NMR spectra were not measured due to the presence of the
paramagnetic Ru(III) metal center.
Branched metalloappendages possessing a formic acid stable
functionality were based on the use of Lin’s amine.38 Thus, DCC
coupling of 4-[4′-oxa-(2,2′:6′,2′′-terpyridinyl)]butanoic acid
(28)37 with 1,11-diethyl 6-amino-6-(4-ethoxycarbonyl-2-oxabu-
tyl)-4,8-dioxaundecane-dicarboxylate38 (27) and 1-HOBT in
DMF at 25 °C afforded desired terpyridine monomer 29 in 86%
yield (Scheme 9). The amidation of 29 was confirmed by the
downfield (∆ ) 3.9 ppm) shift (13C NMR) of 4°CNH(CdO).
The molecular mass (ESI-IT) at m/z 739.8 ([M + H]+ m/z 739.8)
clearly indicated the correct composition. The branched terpy-
ridine ester 29 was refluxed with RuCl3‚3H2O in EtOH to give
(86%) the branched metalloappendage 30. Both Ru(III) ap-
pendage molecules (26 and 30) were carried on to the coupling
stage without further purification.
a (i) 4-Ethylmorpholine, MeOH, 4 h, reflux.
data (described below) offered insight to the different packing
arrays as related to an external electrode surface.
Construction of Neutral Metallodendrimers
To construct neutral metallodendrimers, a dendritic core that
has eight covalently attached internal carboxylate groups and
four terpyridine ligands was envisioned; thus, the resultant
macromolecule will possess the requisite number of internal
octacarboxylate counterions. Thematically, the overall procedure
is as previously demonstrated, except that there can be only
eight internal tert-butyl ester moieties and the metalloappendages
must possess formic acid-stable substituents. Initially then,
EtNO2 was treated with 2 equiv of tert-butyl acrylate in liquid
NH3 at -78 °C to give (95%) di-tert-butyl 4-nitro-4-methyl-
heptanedicarboxylate (18) (Scheme 6). The characteristic carbon
signal (13C NMR) for CNO2 at 89.9 ppm strongly supported
the desired structure, which is further confirmed by the
molecular peak (ESI-IT) at m/z 332.6 ([M + H]+ m/z 332.4).
Treatment of 18 with Raney Nickel under H2 at 25 °C afforded
One equiv of core 23 was refluxed with 4 equiv of 26 in
EtOH in the presence of 4-ethylmorpholine, as reducing agent,
to assemble metallodendrimer 31 in 93% yield (Scheme 10).
Although appendage 26 possessed a limited initial solubility, it
quickly went into the solution upon addition of the reducing
agent, to give the deep-red color of the [- Ru -] complex. After
dialysis, pure complex 31 was isolated and its structure was
supported by the significant downfield shift (13C NMR) of all

10002 J. Am. Chem. Soc., Vol. 122, No. 41, 2000
He et al.
Scheme 5. Construction of Two Isomeric Metallodendrimersa
a (i) 4-Ethylmorpholine, MeOH, 6 h, reflux.
Scheme 6. Construction of the Building Block for the
32 in 98% yield. The characteristic downfield shift (13C NMR)
of the carbonyl carbon (∆ ) 3.5 ppm) clearly indicated the
transformation to the acid and the retention of the external alkyl
ethyl ester moieties was shown by the presence of the ethyl
signals. A sharp mass peak (MALDI-TOF) at m/z 4902 ([M +
Na]+ m/z 4904) further confirmed the desired conversion.
Formation of the neutral metallodendrimer 33 was accomplished
by adding a slight excess of KOH into an H2O/MeOH solution
of 32. After dialysis for 24 h, the desired neutral complex was
analyzed (0.00% of Cl), and only one downfield shift (13C NMR)
for the internal acid carbonyl carbon (∆ ) 3.4 ppm) supported
the formation of the carboxylate carbon centers. The mass peak
(MALDI-TOF) at m/z 4590 ([M + H]+ m/z 4590) confirmed
the structure of 33.
Dendritic Core in Neutral Complexesa
In the same manner, 1 equiv of core 23 was then treated with
4 equiv of 30 in boiling EtOH in the presence of 4-ethylmor-
pholine as reducing agent to assemble (96%) the second
generation of tetrakis(- Ru -) metallodendrimer 34 (Scheme
10). After purification via dialysis, the structure of 34 was
supported by the significant downfield shift (13C NMR) of all
tpy carbons except 4′-tpyC (similar to the spectrum of 31).
Deprotection of tert-butyl groups of 34 by treatment of formic
acid at 25 °C afforded the second generation of acid metallo-
dendrimer 35 in 97% yield. The same characteristic downfield
shift (13C NMR) of the carbonyl carbon (∆ ) 2.9 ppm) clearly
indicated the transformation of the acid. A sharp mass peak
(MALDI-TOF) at m/z 6380 ([M - 8HCl]+ m/z 6379) further
confirmed the desired conversion. The neutral metallodendrimer
36 was formed by adding a slight excess of KOH into a H2O/
MeOH solution of 35. After dialysis for 24 h, the desired neutral
complex 36 was isolated and analyzed (0.00% of Cl); there was
only one downfield shift (13C NMR) for the internal acid
a (i) NH3 (l), 12 h, -78 °C; (ii) Raney Ni, H2, 4 atm, 12 h, 25 °C;
(iii) Et3N, THF, 12 h, -5 °C then 25 °C; (iv) DCC, 1-HOBT, DMF,
24 h, 25 °C; (v) 10% Pd/C, HCO2NH4, MeOH, 0.5 h, 50 °C.
tpy carbons except 4′-tpyC. The tert-butyl groups were removed
from 31 with formic acid at 25 °C affording metallodendrimer

Synthesis of Isomeric Metallodendrimers
J. Am. Chem. Soc., Vol. 122, No. 41, 2000 10003
Scheme 7. Construction of the Dendritic Core in Neutral
Scheme 10. Syntheses of the Two Generations of Neutral
Complexesa
Metallomacromoleculesa
a (i) Et3N, THF, 12 h, -5 °C then 25 °C.
Scheme 8. Synthesis of the first tier metal donor appendage
building blocka
a (i) 4-Ethylmorpholine, EtOH, 6 h, reflux; (ii) HCOOH, 6 h, 25
°C; (iii) KOH, H2O/MeOH, dialysis, 24 h, 25 °C.
a (i) KOH, DMSO, 24 h, 60 °C; (ii) RuCl3‚3H2O, EtOH, 6 h, reflux.
Scheme 9. Synthesis of the Second Tier Metal Donor
UV-Vis Study of [- Ru -] Metallodendrimers
Appendage Building Blocka
Although correct spectral and analytical analyses of the
components leading to the metallodendritic composites and the
lack of both paramagnetic Ru(III) loose ends, as well as random
mixed [Ru(II)] complexes, were ascertained, it was interesting
to utilize UV data in order to relate the extinction coefficient
to the number of [- Ru -] centers in the structure. These data,
if sensitive enough, could be used to ascertain the successful
coupling within such assemblies. In UV-vis studies, the molar
absorptivity ꢀ ) A/(L‚M), where A is absorbance, L is the path
length, and M is the molar concentration of the solute. Since
the molar absorptivity (ꢀ) is directly related to the molar
concentration (M), it should be proportional to the number of
the metal connections, if all the samples only contain single or
multiple [- Ru -] complexes, which will display intense MLCT
(metal ligand charge transfer) signals in visible region.42 Four
major absorption bands (λmax 240-242, 266-268, 304-306,
484-488 nm) were observed for these [- Ru -]-connected
metallodendrimers. The molar absorptivities (ꢀ) of all the
complexes have similar values (Table 3), indicative that all nine
molecular assemblies have the same number of [- Ru -]
a (i) DCC, 1-HOBT, DMF, 36 h, 25 °C; (ii) RuCl3‚3H2O, EtOH, 6
h, reflux.
carbonyl carbon (∆ ) 4.2 ppm) supporting the formation of
the carboxylate carbon centers. The mass peak (MALDI-TOF)
at m/z 6381 ([M + H]+ m/z 6380) further confirmed the structure
of 36.
(42) Constable, E. C.; Harverson, P. Inorg. Chim. Acta 1996, 252, 9-11.

10004 J. Am. Chem. Soc., Vol. 122, No. 41, 2000
He et al.
Table 1. Electrochemical Parameters for Isomers 16 and 17 in
MeCN at 298 K
terpyridines
E
1/2 (∆Ep)a E1/2 (∆Ep)a
Ru(III)/Ru(II)
E1/2 (∆Ep)a E1/2 (∆Ep)a
compound
17
16
-1.923 (0.121) -1.720 (0.087) 0.719 (0.170) 0.919 (0.092)
-1.951 (0.097) -1.751 (0.093) 0.709 (0.109)
a Potentials against internal ferrocene/ferrocenium. Scan rate: 200
mV/s.
Table 2. Electrochemical Parameters for Metallodendrimers
31-36 in DMF at 298 K
terpyridines
Ru(III)/Ru(II)
compound
E
1/2 (∆Ep)a
E1/2 (∆Ep)a
E1/2 (∆Ep)a
31
32
33
34
35
36
-1.945 (0.082)
-1.759 (0.068)
0.627 (0.073)
0.629 (0.057)
0.624 (0.059)
0.640 (0.100)
0.627 (0.097)
0.634 (0.089)
Ib
Ib
-1.950 (0.072)
-1.950 (0.086)
Ic
-1.788 (0.077)
-1.751 (0.088)
Ic
-1.935 (0.102)
-1.767 (0.106)
Figure 4. CV response of 1.0 mM solutions of the isomeric
metallodendrimers. (i) 17 and (ii) 16 in 0.1 M Et4NTFB in CH3CN at
298 K. Potentials are against internal ferrocene/ferrocenium. Scan
rate: 200 mV/s.
a Potentials against ferrocene/ferrocenium. Scan rate: 200 mV/s.
b Irreversible cathodic peak at -1.945 V. c Irreversible cathodic peak
at -1.968 V.
Table 3. Molar Absorptivities of [- Ru -] Metallodendrimers
ꢀ × 104 (dm3 mol-1 cm-1) at λmax (nm)
similar and exhibited two quasi-reversible waves at negative
potentials that correspond to redox processes on two electro-
active terpyridine groups.15 Inspection of the corresponding
electrochemical parameters, that is, the half-wave potential E1/2
and the peak-to-peak splitting ∆Ep (Table 1), revealed interesting
differences between the two structural isomers. On one hand,
the E1/2 values of the two waves of 16 were about 30 mV more
negative than that of 17. Since the reduction of these metallo-
dendrimers generates neutral species that do not require (or
incorporate) counterions from solution, but instead tend to get
rid of them, the observed half-wave potential displacement may
result from either differences of accessibility of counterions, or
from differences in the solvent environment of the electroactive
terpyridine groups. Metallodendrimer 16 features increased
dendritic character on the periphery of the molecule; thus, the
additional thermodynamic difficulty to reduce the terpyridine
groups of 16 compared to 17 coupled with the necessary
participation (loss) of counterions during reduction is consistent
with decreased accessibility of counterions for 16.43-45 Interest-
ingly, the ∆Ep values for two terpyridine redox processes in 16
and for the most positive wave of 17 were similar (within a 10
mV range) and ∼30 mV smaller than the ∆Ep for the most
negative wave of 17. This clearly indicated that the kinetic rate
of electron transfer for one of the terpyridines in 17 was slower
than that of the other terpyridine in 17 and both terpyridines in
16.46 According to the chemical structures of both dendrimers,
the electron-transfer kinetic asymmetry showed by 17 should
be expected on the basis of different chemical environments.
As can be seen in Scheme 5, a dense branched cluster must
surround the internal terpyridine groups in 17, whereas the other
three terpyridines (the external terpyridine of 17 and both
terpyridines of 16) were characterized by a relatively similar
solvent-exposed environment. Furthermore, the asymmetry
reflected on the ∆Ep values, presented in Table 1, was also
consistent with the previous studies of similar compounds.15
compound 240 242 266 268 304 306 484 486 488
15
16
17
31
32
33
34
35
36
27.4
25.4
28.2
23.7
21.5
25.4
23.2
21.5
25.8
6.67
6.54
6.73
25.7
25.9
25.0
21.8
21.8
20.7
22.0
22.3
6.03
5.63
21.1
22.2
5.84
5.98
25.7 22.5
25.9 22.6
25.8 22.2
22.2
22.8
6.13
6.36
connectivities. For the highest absorption of a tetra [- Ru -]-
containing complex (λmax ) 484-488 nm), the average molar
absorptivity ꢀ ) 6.21 × 104 dm3 mol-1 cm-1 is about four times
as strong as Constable’s [- Ru -] complex.42 Though the values
of ꢀ in this series of related complexes are smaller than that of
Constable’s, our metal complexes are heavily hindered by
branched organic moieties, which may slightly affect the UV
absorption. Comparison of these data with previous results37
indicated that four - Ru(II) - complexes are present in each
of the dendritic constructs, further supporting the desired
structures.
According to the present data, the UV absorption of the metal
complexes is relatively independent of the dendritic structures.
The bulkiness of the internal and external branches may slightly
shift (2-4 nm) the absorption (λmax) to longer wavelengths, as
evidenced by the larger dendrimers 15, 16, and 17. The loss of
external counterions does affect the UV absorption; both of the
neutral species shifted the signals to longer wavelengths and
slightly decreased the absorptivities. This effect may be related
to their unimolecular behavior and the stability of these neutral
species.
Electrochemistry of Isomeric and Neutral
Metallodendrimers
(43) Dandliker, P. J.; Diederich, F.; Gisselbrecht, J.-P.; Louati, A.; Gross,
M. Angew. Chem., Int. Ed. Engl. 1995, 34, 2725-2728.
(44) Chow, H.-F.; Chan, I. Y. K.; Chan, D. T.; Kwok, R. W. Chem.
Eur. J. 1996, 2, 1085-1091.
(45) Gorman, C. B.; Parkhurst, B. L.; Su, W. Y.; Chen, K.-Y. J. Am.
Chem. Soc. 1997, 119, 1141-1142.
(46) Newkome, G. R.; Narayanan, V. V.; Echegoyen, L.; Pe`rez-Cordero,
E.; Luftmann, H. Macromolecules 1997, 30, 5187-5191.
Isomeric Metallodendrimers. Despite the similarity of these
isomers, the different distributions of the branched building
blocks for the two isomers 16 and 17 should result in different
chemical environments around the [- Ru -] moieties. The
cyclic voltammograms of both compounds (Figure 4) were

Synthesis of Isomeric Metallodendrimers
J. Am. Chem. Soc., Vol. 122, No. 41, 2000 10005
group upon a probable 1,4-reduction of one of the pyridine rings
of each terpyridine ligand. This explanation is further supported
by CV experiments with the second generation of neutral
dendrimer 36 (as seen in Figure 5iii), where the lack of
neighboring acidic protons, readily available in 35, results in
the recovery of the typical “two wave” reversible response of
the terpyridine ligands.
CV experiments on the first generations of the related
dendrimer series of 31, 32 and 33, exhibit similar voltammetric
responses to those discussed above. By careful inspection of
Table 2, however, the second generation complexes 34 and 36
show slightly larger ∆Ep values than those corresponding to
the first tier series 31 and 33. This observation is in strong
agreement with previous reports43,45,50 and has been attributed
to the slower electron-transfer kinetics that characterizes
molecules featuring bulkier dendritic structures around their
electroactive sites.
Figure 5. CV response of 1.0 mM solutions of dendrimers. (i) 34, (ii)
35, (iii) 36, (iv) 31, (v) 32, (vi) 33 (the smaller current observed was
due to the limited solubility of 33 that was presented in DMF) in 0.1
M Et4NTFB in DMF at 298 K. Potentials are against internal ferrocene/
ferrocenium. Scan rate: 200 mV/s.
Conclusions
Inspection of the positive region of the voltammograms also
showed some interesting differences between the isomeric
metallodendrimers 16 and 17.47 Figure 4ii, for instance, shows
that the process involving the Ru3+/Ru2+ couple of 16 corre-
sponding to one quasi-reversible wave; that is, the four metallic
centers were electrochemically equivalent. In contrast, Figure
4i shows that the wave corresponding to the Ru atoms in 17
had split into two waves with the more positive wave somewhat
smaller. The apparent 3:1 ratio may arise from initial oxidation
of three Ru atoms and oxidation of the fourth Ru atom at more
positive potential, and may be indicative of reaction of the
“tetrahedral” dendrimer at a fixed position on the electrode
surface with three Ru centers close to the electrode and one Ru
moiety oriented away from the electrode surface. In this regard,
previous electrochemical studies on compounds bearing multiple
equivalent electroactive units had shown that the corresponding
redox waves split when these moieties were fixed at relatively
short distances from each other. Further electrochemical studies
of these materials are in progress.
Two isomeric metallodendrimers were synthesized by a
combination of divergent and convergent strategies. These two
constitutional isomers clearly indicated the differences between
dendrimers and traditional polymers. Due to the large molecular
weight distribution of linear or branched polymers, no known
methods can yield two structural isomeric polymers in pure
form; however, two constitutionally isomeric metallodendrimers
were constructed since each dendrimer possesses a single precise
molecular mass of 12 526 Da. Another important aspect of
construction of these two tailor-made metallomacromolecules
is that we loosely mimicked the topology of simple organic
molecules such as CR4 or SiR4 at nanoscopic scale by forming
these simple dendritic networks. Thus, the dendritic network
concept via envisioned “dendritic methane”-type of assembly
was introduced. Despite their similar physical and chemical
properties, these two isomers displayed distinct CV spectra that
indicted the different internal density and void regions inside
the dendritic networks.
Neutral Metallodendrimers. Electrochemical experiments
with the neutral series of metallodendrimers give further insight
to their electrocatalytic potential. The half-wave potentials for
31-36 in the metal oxidation region are very close to each other
(Table 2); the only difference between the anodic redox waves
of these compounds is a slightly larger peak-to-peak separation
for the larger dendrimers. The terpyridine electrochemical
responses are more varied and interesting; thus, the negative
regions of the studied window are shown in Figure 5. For
instance, Figure 5i shows the two reversible waves that
characterize the cathodic CV response of the two-terpyridine
ligands of 34. After internal deprotection of the tert-butyl groups,
the presence of the carboxylic acid moieties in 35 results in the
merging of the two-redox waves and the virtual disappearance
of the corresponding anodic signal (Figure 5ii). On the basis of
previous studies of the electrochemical reduction of pyridine
and its derivatives,48,49 the irreversibility observed is due to an
electrochemical-chemical reaction in which a proton uptaken
by the aromatic anion radical from the vicinal carboxylic acid
Metallodendrimers are always in association with counterions
that usually are external counterions, such as Cl-, BF4-, NO3
,
-
and PF6-, which may be interchangeable. The physical and
chemical properties very often depend on the different associated
counterions. Construction of metallodendrimers without external
counterions not only added additional synthetic challenge,
but also provided a better understanding of these materials. The
PF6- salts are commonly used to make metal complexes more
stable and less soluble for the purposes of storage and purifica-
tion, but the Cl- salts exhibited advantages in our materials.
Due to the low solubilities of metallodendrimers, the Cl-
counterions maintained the solubilities to the point that mea-
surement of NMR spectra was still quite convenient. The loss
of external counterions in these metallomacromolecules had
marginal effect on their spectra, as well as the stability and most
of the physical properties. However, the solubilities of these
neutral species decreased quite obviously in polar solvents,
such as MeOH and H2O, in comparison to those possessing
external Cl- counterions. These neutral metallodendrimers have
internally balanced carboxylate moieties, which are weaker
counterions than most others, like Cl- and PF6-; the addition
of inorganic salts to these neutral species conveniently gave
the desired external counterions. One interesting and useful
property of these neutral materials is that they tended to ionize
more easily (lower laser power) and gave clearer signals
(47) The pre-waves at ∼0.5 V were also present in background CV
experiments performed on the solvent-supporting electrolyte system used.
This signal remained unaffected by purification of the solvent and supporting
electrolyte salt, and careful polishing of the electrode surface; thus, this
signal does not arise from the electroactivity of the dendrimers studied,
and its presence is not considered in the analysis and interpretation of the
voltammetric responses.
(48) Elliott, C. M. J. Chem. Soc., Chem. Commun. 1980, 261-262.
(49) Tokel-Takvoryan, N. E.; Hemingway, R. E.; Bard, A. J. J. Am.
Chem. Soc. 1973, 95, 6582-6589.
(50) Dandliker, P. J.; Diederich, F.; Gross, M.; Knobler, C. B.; Louati,
A.; Sanford, E. M. Angew. Chem., Int. Ed. Engl. 1994, 33, 1739-1742.

10006 J. Am. Chem. Soc., Vol. 122, No. 41, 2000
He et al.
in MALDI-TOF-MS than those possessing external Cl- or PF6
Acknowledgment. We gratefully acknowledge support of
this work from the National Science Foundation (DMR-99-
01393; BIR-95-12208) and the Office of Naval Research
(N00014-99-1-0082).
-
counterions. This application could be a quite convenient method
to obtain mass spectra of some less stable metal-containing
macromolecules. The observed intramolecular proton transfer
during the redox process also gives insight to the potential
chemistry within such macromolecular constructs.
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