Hexagonal terpyridine-ruthenium and -iron macrocyclic complexes by stepwise and self-assembly procedures

Article abstract of DOI:10.1002/1521-3765(20020703)8:13<2946::AID-CHEM2946>3.0.CO;2-M

Methods for the self-assembly, as well as directed construction, of hexaruthenium metallomacrocycles employing bisterpyridine building blocks are described. Self-assembly is effected by a combination of equimolar mixtures of bismetalated and nonmetalated

Full text of DOI:10.1002/1521-3765(20020703)8:13<2946::AID-CHEM2946>3.0.CO;2-M

FULL PAPER
Hexagonal Terpyridine Ruthenium and Iron Macrocyclic Complexes by
Stepwise and Self-Assembly Procedures
George R. Newkome,*[a] Tae Joon Cho,[b] Charles N. Moorefield,[a] Randy Cush,[c]
Paul S. Russo,[c] Luis A. GodÌnez,[d] Mary Jane Saunders,[e] and Prabhu Mohapatra[a]
Abstract: Methods for the self-assem-
bly, as well as directed construction, of
hexaruthenium metallomacrocycles em-
ploying bisterpyridine building blocks
are described. Self-assembly is effected
by a combination of equimolar mixtures
of bismetalated and nonmetalated bis-
(terpyridinyl) monomers each possessing
the requisite planar, 608, terpyridine
metal terpyridine connectivity. Step-
wise synthesis of the identical hexamer
is also discussed and used to aid in
verification of the self-assembled prod-
uct. Preparation and analysis of the
related FeII metallomacrocycle are de-
tailed and its TEM image confirms the
hexameric structure. Characterization of
the metalated products includes cyclic
voltammetry along with the routine
analytical techniques.
Keywords: iron
¥ metallomacro-
cycles ¥ metallocycle ¥ N ligands ¥
self-assembly ¥ ruthenium
polyelectrolyte films,[9] grids,[10] racks,[11] RuII-based dendri-
mers,[12] helicating ligands,[13] and photoactive molecular-scale
wires.[14] Progress in directed synthesis of cyclic rigid struc-
tures[15] can be found in ''shape-persistent'' phenylacety-
lenes,[16 18] diethynylbenzene macrocycles,[19] and a 24-phenyl-
ene hexagon.[20] Whereas advances through self-assembly
have yielded, for example, chiral[21] and achiral[22] circular
helicates, cylindrical cage structures,[23] Pt-coordinated bipyr-
Introduction
Contemporary, eloquent work in the area of self-assembly by
Stang et al.,[1] Lehn et al.,[2] and many others,[3 prompted
7]
our investigation of the self-assembly of (macro)molecules
through formation of stable transition metal complexes. More
specifically, our goal involved the design and preparation of
polyterpyridinyl ligands that would form the basis of ''mod-
ular building block sets''[8] capable of forming stable, irrever-
sible, and non-H-bonding ''higher order'' (fractal) architec-
tures. We herein report the construction of a series of
bis(terpyridine) monomers that facilitate the preparation of
hexametallomacrocycles.
28]
idyl squares,[24] metal-templated catenanes,[25 [2]catenanes
with metals in their backbones,[29, 30] and cyclic porphyrin
trimers.[31]
Our strategy for macrocycle formation involved the prep-
aration of a bis(terpyridine) monomer possessing a 608 angle
with respect to the two ligating moieties. This would facilitate
the assembly of six building blocks with six connecting metals
in the ubiquitous benzenoid architecture. The potential to
synthesize such constructs, with little equilibration (metal
ligand exchange) under mild physicochemical conditions, is
predicated on the unique strength of the terpyridine(tpy) Ru
coordination.[32] It was also envisioned that these rigid
structures, which possess an overall ‡12 charge, would be
an ideal counterion to dendritic macromolecular series
composed of 12, 36, or 108 carboxylate surface groups;
preliminary gel-like materials support a complementary
interaction. A timely, comprehensive review of 2,2':6',2''-
terpyridine ligands has also appeared.[33]
Linear bis(terpyridyl) monomers have been used in the
formation of numerous ordered assemblies, such as layered
[a] Prof. G. R. Newkome, Dr. C. N. Moorefield, Dr. P. Mohapatra
Departments of Polymer Science and Chemistry
The University of Akron, Akron, OH 44325-4717 (USA)
Fax : (‡1)330972-2413
E-mail: newkome@uakron.edu
[b] Dr. T. J. Cho
Chong Kun Dang Pharmaceutical Co.
Chonan (Korea)
[c] R. Cush, Prof. P. S. Russo
Department of Chemistry, Louisiana State University
Baton Rouge, LA 70803 (USA)
[d] Dr. L. A. GodÌnez
¬
¬
Centro de Investigacion y Desarrollo Tecnologico en ElectroquÌmica
¬
¬
Parque Tecnologico Queretaro Sanfandila
Results and Discussion
¬
Apdo. Postal 064, Pedro Escobedo, C. P. 76700, Queretaro (Mexico)
[e] Prof. M. J. Saunders
Synthesis of the key bis(terpyridine) monomer 3 (Scheme 1)
began by treatment of the known dialdehyde 1[34] (prepared
Institute for Biomolecular Sciences, University of South Florida
4202 E. Fowler Avenue, Tampa, FL 33620 (USA)
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Chem. Eur. J. 2002, 8, No. 13

2946 2954
cording to literature.[37] An ethanolic solution of toluylterpyr-
idine 6 and RuCl3 ¥ 3H2O was refluxed for 12 h to afford
(87%) the metalated adduct 8, which was used without
further purification. Mono-complex 8 was then treated with
mono(terpyridine) ligand 6 in MeOH and refluxed for 12 h
under reducing conditions (N-ethylmorpholine) to give the
desired homoleptic complex 9 [Ru(6)2(PF6)2] (67%), which
exhibited a downfield shift (1H NMR) of the 3',5'-pyrH singlet
(d ˆ 9.19 ppm; Dd ˆ ‡0.36) and an upfield shift of the 6,6''-
pyrH doublet (d ˆ 7.62 ppm; Dd ˆ À1.15) compared to the
free ligand 6; mass spectral data (ESI-MS) were also in accord
with the assigned structure. Analogous treatment of the RuIII
complex 8 with free ligand 7[38] afforded the heteroleptic
complex 10 [Ru(6)(7)(PF6)2], which was evidenced by two
close but still distinct singlets (1H NMR) at d ˆ 8.99 and 9.00
for the 3',5'-pyrH and 3a',5a'-pyrH characteristic of structural
dissymmetry. Mass spectral data (ESI-MS) further supported
the heteroleptic structure. There was no evidence of ligand
scrambling, which would have been obvious by the presence
R
R
i)
N
N
N
N
N
N
H
H
ii)
O
O
1 (R = CH3)
2 (R = Br)
3 (R = CH3)
4 (R = Br)
R
N
N
N
RuCl3
N
iii)
N
N
Cl3Ru
5 (R = CH3)
Scheme 1. Synthesis of the key monomers 3, 4, and bis(RuIII) adduct 5: i) 2-
acetylpyridine, NaOH, EtOH, 20h, room temperature; ii) AcO ÀNH4
AcOH, 4 h, reflux; iii) RuCl3 ¥ 3H2O, EtOH, 12 h, reflux.
‡
,
from 1,3-bis(bromomethyl)-5-methylbenzene)[35] with at least
three molar equivalents of 2-acetylpyridine[36] under basic
conditions at 258C for 20h, followed by addition of excess
NH4OAc in AcOH and reflux for 4 h to afford the desired
2‡
2‡
of the Ru(6)2 (i.e., 9) or Ru(7)2 complexes. This confirmed
the previous report,[39] but also demonstrated the structural
integrity of the molecular assembly.
To aid in the characterization of the resultant hexameric
architecture in the self-assembled construct, formation and
proof of the similar components for that used in a stepwise
assembly process were undertaken. Thus, an ethanolic sol-
ution of bisterpyridine monomer 3 with two equivalents of
RuCl3 ¥ 3H2O was refluxed for 12 h, which produced (92%)
the minimally soluble, paramagnetic bis(RuIII) adduct 5
(Scheme 1), which when reacted with two equivalents of free
monoterpyridine ligand 6 afforded the bis(ruthenium com-
angular
1,3-bis(2,2':6',2''-terpyridin-4'-yl)-5-methylbenzene
(3) in 22% overall yield. The structure of 3 was confirmed
by singlets (1H NMR) at d ˆ 2.59 ppm for the arylCH3, at d ˆ
7.82 pm for the 4,6-ArH, and at d ˆ 8.83 ppm for the 3',5'-
pyrH (these signals integrate in the expected 3:2:4 ratio), and
‡
a mass peak (ESI-MS) at m/z 555 [M ‡ H ]. The related 3,5-
bis(2,2':6',2''-terpyridin-4'-yl)-1-bromobenzene (4) was simi-
larly prepared (35%) from bromodialdehyde 2,[34] whose
structure was verified by the observation of singlets (1H NMR)
at d ˆ 8.15 ppm (2,6-ArH) and d ˆ 8.81 ppm (3',5'-pyrH) that
integrated in a 1:2 ratio as well as a mass peak (ESI-MS) at
1
plex) 11 [Ru2(5)(6)2(PF6)2] (Scheme 3). The H NMR spec-
trum for 11 showed a 1:2 proton integration ratio for the
central (d ˆ 2.96 ppm) and terminal (d ˆ 2.68 ppm) methyl
groups supporting the bis(capped) structure. As in the case of
dimer 9, complex 11 exhibited a downfield shift (1H NMR) of
the 3',5'-proton resonance (d ˆ 9.17 ppm; Dd ˆ ‡0.34 ppm)
and an upfield shift for the 6,6''-proton signal (d ˆ 7.62 ppm;
Dd ˆ À1.15 ppm). Alternatively, treatment of the bis-ligand 3
with two equivalents of mono-complex 8 afforded the
identical diamagnetic bis-complex 11; no evidence for ligand
scrambling was detected.
‡
m/z 620[ M ‡ H ].
Confirmation of the specificity and stability of the Ru(tpy)2
motif was obtained from a combination of selected simple
ligands (6 or 7) and the RuIII complex 8 (Scheme 2). The 4'-(4-
methylphenyl)-2,2':6',2''-terpyridine (6) was synthesized ac-
The self-assembled, diamagnetic, hexameric RuII complex
14 [Ru6(3)6(PF6)12] was prepared (Scheme 4) by reaction of
the free bisterpyridine monomer 3 with one equivalent of the
activated bis(RuIII) adduct 5 in MeOH for 12 h at reflux under
reducing conditions (N-ethylmorpholine). The hexamer was
initially obtained in 85% yield but possessing chloride
counterions which, after chromatography and counterion
N
N
N
N
i)
R
N
H3C
N
RuCl3
(R = CH3)
6 (R = CH3)
7 (R = Br)
8
2+
-
exchange (ClÀ to PF6 ), afforded macrocycle 14 in an overall
À
2PF6
H6
3'H
5'H
N
N
N
H'3a
H'5a
yield of 43% overall, that was structurally confirmed by
diverse spectral methods. The 1H NMR spectrum of 14
revealed a single absorption at d ˆ 2.93 ppm (CH3) suggesting
the presence of a single monomeric unit in contrast to that of a
linear oligomer such as in the case of bisruthenium complex
11, which displayed two distinct methyl singlets in the
1H NMR spectrum. Other diagnostic spectral attributes
(1H NMR) included the singlet at d ˆ 8.41 ppm for the 4,6-
ArH as well as the notable upfield and downfield shifts for the
ii)
Ru
H3C
N
N
R
N
9 (R = CH3)
10 (R = Br)
Scheme 2. Synthesis of mono(RuII) complexes 9 and 10: i) RuCl3 ¥ 3H2O,
EtOH, 12 h, reflux; ii) a) N-ethylmorpholine, MeOH, 12 h, reflux,
‡
À
b) methanolic NH4 PF6
.
Chem. Eur. J. 2002, 8, No. 13
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2947

G. R. Newkome et al.
FULL PAPER
CH3
CH3
CH3
N
N
N
N
N
N
N
N
N
N
+
N
N
N
N
N
N
N
Cl3Ru
RuCl3
N
3
5
3
i)
N
N
i) H3C
N
RuCl3
R
12+
12PF6
-
2 equiv
N
N
N
N
N
N
N
N
8
M
N
M
N
N
N
CH3
R
R
4+
4PF6
-
N
N
N
N
N
M
N
N
N
M
N
N
N
N
N
N
N
N
N
N
N
N
N
Ru
Ru
N
N
N
11
H3C
CH3
R
N
M
N
N
M
N
R
N
N
N
N
N
N
N
N
N
i) H3C
N
N
2 equiv
R
14 R = CH3, M = Ru
6
18 R = CH2OH, M = Fe
ii)
CH3
N
N
N
N
N
N
N
N
N
N
N
Cl3Ru
RuCl3
N
17
5
CH2OH
Scheme 3. Synthesis of complex 11 by different routes to verify the
structure of bis(RuIII) adduct 5; i) a) N-ethylmorpholine, MeOH, 12 h,
Scheme 4. Synthesis of metallomacrocycles 14 by self- and directed-
assembly; i) a) N-ethylmorpholine, MeOH, 12 h, reflux, b) methanolic
‡
À
‡
À
reflux, b) methanolic NH4 PF6
.
NH4 PF6
.
the expected 1:2 ratio. Finally, reaction of oligomer 12 with
two equivalents of RuCl3 ¥ 3H2O afforded the corresponding
paramagnetic bis(terminal RuIII) adduct 13, which when
treated with one equivalent of 12 yielded (ca. 80%) a sample
of crude hexamer, subsequent chromatography and counter-
ion exchange generated 14 which possesses identical spectral
and physical characteristics to those for 14 derived from the
self-assembled procedure. The UV spectrum of 14 exhibited
extinction coefficients (e) of a 5.1-, 5.5-, and 5.8-fold increase
for lmax at 290, 312, and 496 nm, respectively (Table 1), when
doublet (d ˆ 7.62 ppm; Dd ˆ À1.15 ppm) of the 6,6''-pyrH and
for the 3',5'-pyrH signals (d ˆ 9.37 ppm; Dd ˆ ‡0.54 ppm),
respectively, when compared to corresponding absorptions
that characterize the uncomplexed bisterpyridine. COSY and
HETCOR spectra of the bisterpyridine 3 and the self-
assembled macrocycle 14 verified the peak assignments as
well as coupling patterns. This hexameric structure was
further established by MALDI-TOF mass spectrometry,
which was measured in the linear mode with the use of a
trans-3-indoleacrylic acid matrix. The peaks at m/z 5544
[À1PF5], 5400 [À1PF6 À 1PF5], 5292[À3PF5], 5166[À4PF5],
5020[À4PF5 À 1PF6] were calculated as the loss of either PF5
alone or as both PF5 and PF6 together, which is a known
phenomena.[40] Hexamer 14, initially isolated as the 12ClÀ
salt, exhibited solubility in MeOH and hot H2O, while
Table 1. CV data for RuII complexes 9 and 14 (potentials versus ferrocene/
ferrocenium; reversible signal experiments were carried out at 100 mVsÀ1
in 0.1 m nBu4BF4/DMF solution at 298 K).
Complex
E1/2(DEp), [V]
terpyridines
RuIII/RuII
À
conversion to the 12PF6 salt facilitated solubility in MeCN,
acetone, and DMSO.
9
14
À 1.800 (0.061)
À 1.580 (0.061)
À 1.622 (0.075)
0.832 (0.062)
0.798 (0.091)
adsorption peak
To further confirm and insure the structural character-
ization of macrocycle 14 [Ru6(3)6(PF6)12], an alternative
stepwise, directed route was undertaken (Scheme 5). The
diamagnetic bis-complex 12 was prepared by treatment of bis-
complex 5 with two equivalents of unmetalated bisterpyridine
3. The 1H NMR spectrum of 12 showed a complex pattern of
broadened absorptions in the aromatic region (d ˆ 9.76
7.40ppm) as well as two anticipated singlets arising from the
nonequivalent methyl groups (d ˆ 2.79, 2.94 ppm) present in
compared to coefficients for the mono(RuII) complex 9
measured analogously. The equilibrium analytical ultracen-
trifugation absorption profiles[41] for hexamer 14, (obtained
from the self-assembly procedure) at a concentration of 0.5%
in MeCN has been conducted and further support the
molecular weight range. It is also notable that the chromato-
2948
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Chem. Eur. J. 2002, 8, No. 13

Hexagonal Terpyridine Ruthenium and Iron Macrocyclic Complexes
2946 2954
CH3
CH3
N
N
N
N
N
N
N
N
N
N
N
N
+
2 equiv
Cl3Ru
RuCl3
3
5
i)
CH3
4+
4Cl-
N
N
N
N
N
N
N
N
Ru
Ru
N
N
N
H3C
N
CH3
N
N
N
N
N
N
N
N
12
ii)
Cl3
Ru
Cl3
Ru
N
N
N
N
Figure 1. Cyclic voltammograms of 1 mm solutions of a) mono(RuII)
complex 9, and b) and c) macrocycle 14 (performed in 0.1m nBu4NBF4 in
DMF at 298 K with a scan rate of 100 mVsÀ1).
H3C
N
N
CH3
N
N
N
N
N
N
N
N
Ru
Ru
4+
4Cl-
reduction peak. In this way, the incorporation of a second
electron into each one of the Ru tpy moieties would form a
large neutral species that, as opposed to its smaller counter-
part (mono-complex 9), would be readily adsorbed on the
electrode surface. This idea was further supported by CV
experiments in which the cathodic scan reached more
negative potentials than those showed in Figure 1a and 1b.
As can be observed in Figure 1c, the CV response of 14 in a
slightly wider potential window is characterized by an
irreversible reduction at very negative potentials that resulted
in the absence of the sharp oxidation peak observed in
Figure 1b during the anodic scan. This suggests that there is
an irreversible reaction at about 2.1 V versus ferrocenium/
ferrocene that, either disconnected some high percentage of
metal complex, or formed a chemically different species that
did not adsorb on the electrode surface. Another interesting
comparison that could be made with the CV curves presented
in Figure 1a and b is related to the half-wave potentials and to
the peak-to-peak splitting that characterize them. Close
inspection of the data (Table 2) for complexes 9 and 14,
reveals that the reduction of macrocycle 14 requires more
energy than its smaller counterpart 9 and that macrocycle 14
has a slightly larger peak-to-peak separation. Whereas the
improved basicity of the terpyridine ligands in 14 could be
rationalized in terms of the ''pseudo''-resonance stabilization
energy provided by its chemical structure;[46] the larger peak-
to-peak splitting of the waves may be due to the nonequiva-
lence effect of the terpyridine units of 14 that, in turn, could be
a consequence of a weak coupling between the electroactive
N
N
CH3
13
iii)
14
Scheme 5. Synthesis of trimeric precursors 12 and 13 for stepwise
preparation of metallomacrocycle 14: i) N-ethylmorpholine, MeOH, 12 h,
reflux; ii) RuCl3 ¥ 3H2O, EtOH, 12 h, reflux; iii) a) 12, N-ethylmorpholine,
‡
À
MeOH, 12 h, reflux, b) methanolic NH4 PF6
.
graphs measured by TLC of the self- versus the stepwise-
assembled hexamers were identical and, as expected, different
from all precursors.
Cyclic voltammetry (CV) experiments with macrocycle 14,
further supported its proposed structure (Figure 1). The
electrochemical response of mono(RuII) complex 9 consid-
ered as a monomeric unit of 14, showed two reversible waves
(Figure 1a) that presumably correspond to the monoelec-
tronic reduction of each one of the two terpyridine ligands
surrounding the Ru atom. As expected, the electrochemical
behavior of the Ru tpy moieties of macrocyclic complex 14,
based on previous electrochemical experiments,[42, 43] was
notably different from that of the simple complex 9. In
Figure 1b, the electrochemical response of hexamer 14 in the
same potential region revealed that the most positive wave
was quasi-reversible and that the most negative one was
characterized by a sharp oxidation peak that increased its size
as the switching potential became more negative. The
observed sharpness of the oxidation peak is typical of
adsorbed electroactive species at an electrode surface[44, 45]
and therefore can reasonably be explained by assuming the
formation of an insoluble reduction product at the second
49]
units.[47
In an effort to modify the solubility of macrocycle 14
[Ru6(3)6(PF6)12], as well as to probe its use as an organiza-
tional scaffolding for nonbonded network formation, the
Chem. Eur. J. 2002, 8, No. 13
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2949

G. R. Newkome et al.
FULL PAPER
Table 2. UV absorption data of complexes.
Br
CH3
Complex
lmax [nm]
Extinctioncoefficient (e)
N
N
N
N
N
9
284
3106610
486
58900
N
N
N
N
N
N
+
0
0
Cl3Ru
RuCl3
N
24800
56 000
10
11
12
14
16
286
3105970
49023680
5
4
i)
0
29011320
496
490
2+
2Cl-
CH3
120400
47000
N
N
288
310122480
492
135530
N
N
N
N
N
N
Ru
Cl3Ru
50490
N
Br
0
0
29032290
312
496
336800
143400
(not isolated)
29031710
310310
496
N
N
N
0
20
148150
15
counterions in [Ru6(3)6(Cl)12] were exchanged with a dodec-
acarboxylate-terminated dendrimer.[50] Thus, a 1:1 mixture of
macrocycle 14 (dodecachloride) and the dodecacarboxylate
sodium salt [C(CH2OCH2CH2CONHC(CH2CH2CO2Na)3)4]
was dialyzed to give a gelatinous precipitate that possessed no
residual sodium or chloride ions based on elemental analysis;
unfortunately, this 1:1 combination proved to be extremely
insoluble in all common solvents. However, a 1:1 mixture of
hexamer 14 (ClÀ) and a 3rd generation carboxylate-termi-
CH3
12+
12PF6
-
N
N
N
N
N
N
N
N
N
N
Ru
N
Ru
N
Br
Br
N
N
N
À
N
N
N
N
N
nated dendrimer gave an analogous [Ru6(3)6(G3-108-CO2
Ru
Ru
(ca. Na96))] complex, which produced a deep red D2O solution
N
N
N
(258C), owing to the presence of the RuII, which allowed
N
1
verification of the aqueous solubility by H NMR spectros-
copy due to the excess carboxylate component in the
assembly.
H3C
N
N
CH3
N
N
N
N
N
N
N
N
To further investigate the Ru-based self-assembly techni-
que, the construction of heteroleptic macrocycles was under-
taken to ascertain the degree of order in the assembly process
(Scheme 6). A suspension of monomer 4 and bis(RuII)
complex 5 in MeOH was refluxed for 12 h to afford the
alternating Me/Br-based macrocycle 16, which was purified by
preparative TLC (SiO2, Rf ˆ 0.60, eluent; MeCN:saturated
aqueous KNO3:waterˆ 7:1:1, 36%). Evidence for its forma-
tion includes a symmetrically similar, yet expectedly broad-
ened, spectrum (1H NMR) that corresponds to that of the
hexamethyl analogue 14 except for two identical proton peaks
on the benzene ring associated with ligand 4, which were
shifted downfield from those of free ligand 4 ((d ˆ 8.75 ppm,
2,6-ArH (Dd ˆ ‡0.6 ppm, 4), d ˆ 9.18 ppm, 4-ArH (Dd
‡0.88, 4)) with the exact expected proton integration values,
respectively. COSY and HETCOR NMR experiments further
supported the assigned structure. A UV study of 16 gave
extinction coefficients (e) that exhibited a 5.7-, 5.2-, and 6.1-
fold increase for lmax at 290, 310, and 496 nm, respectively,
when compared to coefficients measured for the mono(RuII)
complex 10. Since ligand scrambling has not been observed
(as noted above), the stepwise complexation led to the in situ
generation of intermediate 15, which then assembled to give
rise to macrocycle 16, as supported by the spectral data.
Ru
Ru
N
N
Br
16
Scheme 6. Synthesis of heteroleptic metallomacrocycle 16 by self-assem-
bly: i) a) N-ethylmorpholine, MeOH, 12 h, reflux, b) methanolic NH4 PF6
‡
À
.
Successful construction of homo- and heteroleptic macro-
cycles suggested the creation of rings with easily modifiable
functionality, as well as with different metals, such as FeII
(Scheme 4). Thus, the hydroxymethyl bisterpyridine mono-
mer 17 was accessed starting 3,5-di(formyl)-1-hydroxymeth-
ylbenzene, derived from the incomplete reduction of 1,3,5-
tris(chlorocarbonyl)benzene followed by its treatment under
standard conditions.[34] Reaction of 17 with FeCl2 (1:1, MeOH)
gave the desired [Fe6(17)6(Cl)12] macrocycle 18 in 81% yield.
The complete absence (1H NMR) of extraneous peaks
excluded the presence of starting materials, intermediates,
and oligomeric materials; whereas a slightly broadened
singlet (1H NMR) at d ˆ 5.65 ppm (CH2OH), the singlet at
d ˆ 8.63 ppm for the 4,6-ArH as well as the diagnostic shifts
for the doublet (d ˆ 7.30ppm, Dd ˆ À1.48 ppm) of 6,6''-pyrH,
2950
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Chem. Eur. J. 2002, 8, No. 13

Hexagonal Terpyridine Ruthenium and Iron Macrocyclic Complexes
2946 2954
gel (60 200 mesh) purchased from Fisher Scientific. Melting points were
determined on an Electrothermal 9100 and are uncorrected. 1H and
13C NMR spectra were recorded on a Bruker DPX250NMR spectrometer.
IR spectra were recorded on an ATI Matheson Genesis FTIR spectropho-
tometer. Absorption spectra were measured in MeCN at room temperature
with a Hewlett Packard 8452A Diode Array spectrophotometer. Mass
spectra were obtained on a Bruker Esquire Electrospray Ion Trap mass
and the 3',5'-pyrH (d ˆ 9.51 ppm, Dd ˆ ‡0.67 ppm) signals
were in accord with that expected for ring formation. Trans-
mission electron microscopy (TEM) images of 18
[Fe6(19)6(Cl)12] revealed single, hexagonal-shaped particles
with the predicted diameter of about 37 ä, based on
molecular modeling studies (Figure 2). Close inspection of
spectrometer (ESI-MS) or
a Bruker Reflex II MALDI-TOF mass
spectrometer (MALDI-MS) with trans-3-indoleacrylic acid as the matrix.
Molecular weights for 14 were measured by equilibrium analytical ultra-
centrifugation using a Beckman XLA analytical ultracentrifuge equipped
with an AN60Ti rotor and absorption optics. MeOH or MeCN served as
solvents. A visible wavelength was selected for each sample to produce an
average absorbance of about 0.5; concentration was varied over a wide
range. Rotor speed (typically 25,000 RPM) was selected to produce a
smooth, substantial gradient in concentration. For a single component in
the dilute limit, the absorbance, A, profile is given by Equation (1),where w
is the circular frequency (radsÀ1), M is the molar mass, 1 the solvent density,
the solute partial specific volume, r the radius from the center of the rotor, a
the radius at the meniscus,
temperature.
R the gas constant, and T the Kelvin
w2M(1À1nÄ)r2Àa2)/2RT
A(r) ˆ A(a)e
Figure 2. Transmission electron micrograph of 18‡12 ¥ 12PF6 (magnifica-
À
tion of 200000 Â ) showing an individual, regular hexagon along with its
computer generated CPK model for comparison Darkened metal centers in
hexameric arrangement can be observed.
The absorbance profile of
a multicomponent system has additional
exponential growth terms. A Parr DMA58 precision densitometer was
used to determine the partial specific volume. The electrochemical
experiments were conducted using a PGZ301 Potentiostat programmed
and controlled by means of a computer loaded with the voltamaster 4
software (Radiometer-Copenhagen). Resistance compensation for all
experiments was automatically computed and corrected by the software
in the ''static automatic'' mode. All cyclic voltammetry measurements were
conducted in anhydrous DMF solutions containing approximately a 1.0m m
concentration of the electroactive compound and 0.1m of tetrabutylammo-
nium tetrafluoroborate (nBu4NBF4) as supporting electrolyte. The electro-
chemical cell consisted of a 2.0mL conical vial fitted with a graphite
working electrode (previously polished in sequential steps with diamond
and alumina polishing compounds on a felt surface), a silver pseudo-
reference electrode, and a platinum wire as a counter electrode (Cypress
System, Lawrance, KS). Dry N2 gas was bubbled carefully through the
electroactive solution for at least 10min before each measurement to
deoxygenate the solution. All the potentials reported in this work were
measured against the ferrocene/ferrocenium redox couple. Transmission
electron micrographs were obtained by using a JEOL 200EXII electron
microscope at a magnification of 200000 Â . A 0.03% methanolic solution
of 18 was applied to a carbon-coated glass plate. After removal of the glass
with HF (48%), the coated carbon film was applied to the surface of a Ni
grid and air-dried.
the TEM image reveals an inner star form and six, hexago-
nally juxtaposed dark regions (i.e., the metal centers), which
are also consistent with predicted morphology. The H-bond-
ing functionality and the intial water content were critical
factors in sample preparation Thus, the external functionality
may play an important role in aggregation processes; further
studies are on-going to evaluate intermolecular interactions.
Conclusion
We have prepared novel, angular bis(terpyridine) derivatives
(3, 4, and 17) as building blocks for the formation of stable,
hexagonal metallomacrocycles. These ligands were employed
for the synthesis of the homo- or heteroleptic hexa(bis(ter-
pyridine)ruthenium) complexes 14 and 16 and the related FeII
analogue 18. The structures of these hexagonal architectures
1,3-Bis(2,2':6',2''-terpyridin-4'-yl)-5-methylbenzene (3): 5-Methylbenzene-
1,3-dicarbaldehyde[34] (1; 400 mg, 2.7 mmol) was dissolved in EtOH
(50mL) then 2-acetylpyridine (1.5 g, 12 mmol) was added, followed after
2 min by aqueous NaOH solution (5 mL, 1m). After the dark pink solution
had been stirred at 258C for 20h, the solvent was evaporated in vacuo to
yield a red oil, which was extracted with CH2Cl2. The combined extracts
were washed with water, dried (MgSO4), and concentrated in vacuo to give
a pink solid, as an intermediate. Ammonium acetate (10g, excess) and
glacial AcOH (50mL) were added; the mixture was refluxed for 4 h. The
dark brown solution was cooled, and neutralized with aqueous Na2CO3 to
afford a deep yellow precipitate, which was filtered, washed with hot
EtOH, and purified by column chromatography (Al2O3). Elution with a
mixture of EtOAc/hexane (1:1), followed by recrystallization gave pure
bis(terpyridine) ligand 3 (320mg, 22% overall yield). M.p. 187 188 8C
(decomp); 1H NMR (CDCl3) d ˆ 2.59 (s, 3H; CH3), 7.38 (dd, J ˆ 6 Hz, 4H;
H5,5''), 7.82 (s, 2H; H4,6Ar), 7.91 (dd, J ˆ 8 Hz, 4H; H4,4''), 8.22 (s, 1H; H2Ar),
1
were characterized by means of H and 13C NMR, UV/Vis
spectroscopy, mass spectrometry, and, in the case of the Fe6
macrocycle, also by electron microscopy. Also it is envisioned
that, based on the simple counterion exchange experiments,
the use of compact, charge-concentrated (pseudo)spherical
dendrimers possessing polyanionic surfaces will facilitate
entry to better control counterion randomness at the organ-
ic inorganic interface. Experiments are currently ongoing to
access larger and more complex macrocycles possessing
different metal connectivities as well as larger fractal archi-
tectures.
8.71 (d, J ˆ 8 Hz, 4H; H3, 3''), 8.77 (d, J ˆ 4 Hz, 4H; H6, 6''), 8.83 (s, 4H;
Experimental Section
H3'5') ppm; 13C NMR (CDCl3): d ˆ 21.60(CH ), 119.24 (C3'), 121.50(C Ar),
5
3
Materials and methods: Chemicals were purchased from Aldrich and used
as received. Thin layer chromatography (TLC) was conducted on flexible
sheets precoated with aluminum oxide IB-F or silica gel IB2-F (Baker-flex)
and visualized with UV light. Column chromatography was conducted
using neutral/basic alumina, Brockman Activity I, 60 325 mesh, or silica
121.71 (C3), 123.53 (C2Ar), 123.94 (C5), 128.94 (C6Ar), 136.97 (C4), 139.48
(C1Ar), 149.20(C 6), 150.31 (C4'), 155.97 (C2), 156.20(C 2') ppm; IR (KBr):
nÄ ˆ 3051, 3013, 2918, 2855, 1589, 1567, 1469, 1379 cmÀ1; ESI-MS: m/z: 555
‡
[‡H ]; calcd C37H26N6 (554); elemental analysis (%): calcd: C 80.14, H
4.69, N 15.16; found: C 79.34, H 4.84, N 14.89.
Chem. Eur. J. 2002, 8, No. 13
¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
0947-6539/02/0813-2951 $ 20.00+.50/0
2951

G. R. Newkome et al.
FULL PAPER
3,5-Bis(2,2':6',2''-terpyridin-4'-yl)-1-bromobenzene (4): Bromo-bis(terpyr-
idine) ligand 4 was synthesized (35% overall yield) by same procedure as
for 3 by using 1-bromo-3,5-dicarboxaldehyde[34] as a starting material. M.p.
308 3098C; 1H NMR (CDCl3): d ˆ 7.41 (dd, J ˆ 6 Hz, 4H; H5, 5''), 7.94 (dd,
124.30, 124.51 ((6 ‡ 3)-C3), 127.50(( 6 ‡ 3)-C5), 127.70(( 6 ‡ 3)-C2Ar),
130.26 (6-C3 ‡ 3-C6Ar), 133.89 (6-C4 ‡ 3-C5Ar), 138.03 ((6 ‡ 3)-C4),
Ar
Ar
141.02 ((6 ‡ 3)-C1Ar), 147.55, 148.39 ((6 ‡ 3)-C4'), 152.46 ((6 ‡ 3)-C6),
155.34, 155.60(( 6 ‡ 3)-C2), 158.23 ((6 ‡ 3)-C2') ppm; IR (KBr):nÄ ˆ 3112,
2923, 2856, 1606, 1547, 1467, 1429, 1405 cmÀ1; UV/Vis (MeCN): lmax ˆ 290
(1.13 Â 105), 310(1.20 Â 105), 490nm (4.70 Â 104); MALDI-TOF: m/z: 1837
[ÀPF6], 1692 [À2PF6], 1547 [À3PF6], calcd for C81H60N12Ru2P4F24 (1982);
elemental analysis (%): calcd (‡2H2O): C 48.16, H 3.17, N 8.32; found: C
48.14, H 3.54, N 8.52.
4
J ˆ 8 Hz, 4H; H4, 4''), 8.15 (s, 2H; H2, 6Ar), 8.30(s, 1H; H Ar), 8.73 (d, J ˆ
8 Hz, 4H; H3, 3''), 8.78 (d, J ˆ 5 Hz, 4H; H6, 6''), 8.81 (s, 4H; H3', 5') ppm;
13C NMR (CDCl3): d ˆ 119.23 (C3'), 121.62 (C3), 123.90(C 4Ar), 124.18 (C5),
125.23 (C1Ar), 130.96 (C2Ar), 137.12 (C4), 141.63 (C3Ar), 148.88 (C4'), 149.33
‡
(C6), 156.10(C 2), 156.33 (C2'); ESI-MS: m/z: 620[ ‡H ]; calcd for
C36H23N6Br (619); IR (KBr): nÄ ˆ 3050, 3012, 1585, 1567, 1469, 1385 cmÀ1
;
[(3)Ru2(6)2][PF6]4 (11): Route 2: Bis(terpyridine)ligand 3 (36 mg, 65 mmol)
was added to a suspension of mono(RuIII) adduct 8 (69 mg, 130 mmol),
following the above method B, to afford 11 as red microcrystals: yield:
100 mg (77%). This sample was spectrally identical to the sample obtained
by Route 1.
elemental analysis (%): calcd (‡1H2O): C 67.82, H 3.93, N 13.19; found: C
67.75, H 3.97, N 13.24.
[Ru2(3)Cl6] (5): Method A: Bis(terpyridine)ligand 3 (200 mg, 360 mmol)
was added to a solution of RuCl3 ¥ 3H2O (188 mg, 720 mmol) in EtOH
(20mL), then the suspension was refluxed for 12 h. After mixture had been
cooled, the resultant dark brown solid was filtered, washed with cold
EtOH, and dried in vacuo to yield the bis(RuIII) adduct 5 as a dark brown
solid: yield: 320mg (92%); m.p. > 4008C; IR (KBr): nÄ ˆ 3062, 2923, 2852,
1602, 1548, 1472, 1399 cmÀ1. This material was used without further
purification.
[Ru2(3)3][Cl]4 (12): Bis(terpyridine)ligand 3 (114 mg, 200 mmol) was added
to a suspension of the bis(RuIII) adduct 5 (97 mg, 100 mmol), following the
above method B, to yield the free bis(terpyridine)-terminated trimeric
precursor 12 as red microcrystals: yield: 180mg (89%); m.p. >4008C;
1H NMR (CD3OD): d ˆ 2.79(s, 3H; 5-CH3), 2.94(s, 6H; 3-CH3), 7.40 9.76
(m, aromatics and terpyridines, 69H) ppm; 13C NMR (CD3OD): d ˆ 20.89,
122.01, 122.60, 125.19, 125.69, 128.01, 130.54, 136.84, 138.51, 141.32, 148.76,
149.25, 152.40, 156.12, 158.97 ppm; IR (KBr): nÄ ˆ 3069, 2925, 2853, 1605,
1545, 1470, 1396 cmÀ1; UV/Vis (MeCN, PF6 counterion): lmax ˆ 288 (1.35 Â
105), 310(1.22 Â 105), 492 nm (5.0 Â 104); MALDI-TOF: m/z: 1864 [ÀCl4],
calcd for C111H78N18Ru2Cl4 (2006).
[Ru(6)Cl3] (8): 4'-(4-Methylphenyl)-2,2':6',2''-terpyridine[37] (6; 200 mg,
620 mmol) was treated with one equivalent of RuCl3 ¥ 3H2O (160mg,
620 mmol) in EtOH (20mL), as described in the above Method A, to give
the desired 8 as a brown solid: yield 290mg (87%); m.p. > 4008C; IR
(KBr): nÄ ˆ 3066, 3041, 2919, 2854, 1601, 1548, 1467, 1403 cmÀ1. This material
was used without further purification.
[Ru4(3)3][Cl]10 (13): Trimeric precursor 12 (50mg, 25 mmol) was added to a
solution of RuCl3 ¥ 3H2O (13 mg, 50 mmol) in EtOH (10mL), and the
suspension was refluxed for 12 h. After the mixture had been cooled, the
dark red solid was filtered, washed with cold EtOH and dried in vacuo to
yield 13 as a dark brown solid: yield: 45 mg (74%); m.p. >4008C; IR
(KBr): nÄ ˆ 3061, 2923, 2866, 1604, 1540, 1469, 1395 cmÀ1. This material was
used without further purification.
[Ru(6)2][PF6]2 (9): Method B: Mono(terpyridine)ligand
6 (61 mg,
188 mmol) was added to a suspension of mono(RuIII) adduct 8 (100 mg,
188 mmol) in MeOH (20mL), then N-ethylmorpholine (500 mL) was
added; the mixture was refluxed for 12 h. After the mixture had been
cooled, the resulting deep red solution was filtered through celite, then a
slight excess of methanolic ammonium hexafluorophosphate was added to
precipitate 9, which was filtered, sequentially washed with MeOH, Et2O,
and aqueous acetone, then dried in vacuo to afford red microcrystals: yield:
One-pot synthesis of [Ru6(3)6][PF6]12 (14): Bis(terpyridine)ligand
3
(114 mg, 200 mmol) was added to a suspension of the bis(RuIII) adduct 5
(190mg, 200 mmol), following the above method B, to give (85%) a dark
red solid, which was filtered, then purified by TLC (SiO2; eluent: aqueous
MeCN/saturated KNO3 solution (1:7:1)). The major dark band was
collected and extracted, then excess methanolic ammonium hexafluoro-
phosphate was added to precipitate 14, which was sequentially washed with
MeOH, Et2O, and aqueous acetone, and dried in vacuo to yield dark purple
microcrystals: yield: 160mg (43%); m.p. >4008C; Rf ˆ 0.55; 1H NMR
(CD3CN): d ˆ 2.93 (s, 3H; CH3), 7.31 (dd, 4H; H5, 5''), 7.62 (d, 4H; H6, 6''),
8.06 (dd, 4H; H4,4''), 8.41 (s, 2H; H4, 6Ar), 8.87 (d ‡ s, 5 H; H3, 3'' ‡ H2Ar), 9.37
(br, 4H; H3', 5') ppm; 13C NMR ([D6]DMSO): d ˆ 21.54 (CH3), 121.83 (C3'),
1
130mg (67%); m.p. >4008C; H NMR (CD3CN): d ˆ 2.74 (s, 3H; CH3),
7.37 (dd, 2H; H5, 5''), 7.62 (d, 2H; H6,6''), 7.78 (d, 2H; H3, 5Ar), 8.14 (dd, 2H;
H4, 4''), 8.31 (d, 2H; H2, 6Ar), 8.83 (d, 2H; H3, 3''), 9.19 (s, 2H; H3', 5') ppm;
13C NMR (CD3CN): d ˆ 21.91 (CH3), 122.83 (C3'), 125.94 (C3), 128.89 (C5),
129.14 (C2Ar), 131.77 (C3Ar), 135.39 (C4Ar), 139.47 (C4), 142.52 (C1Ar), 149.75
(C4'), 153.91 (C6), 156.88 (C2), 159.74 (C2') ppm; IR (KBr): 3086, 2924, 2854,
1607, 1550, 1479, 1428, 1407 cmÀ1; UV/Vis (MeCN): lmax ˆ 284 (5.89  104),
310(6.60 Â 104), 486 nm (2.48 Â 104); MALDI-TOF: m/z: 892 [ÀPF6], 747
[À2PF6], calcd for C44H34N6RuP2F12 (1037); elemental analysis (%): calcd:
C 50.91, H 3.28, N 8.10; found: C 50.83, H 3.36, N 8.03.
4
124.62 (C5Ar), 125.09 (C3), 127.96 (C2Ar), 130.32 (C5), 137.60(C Ar), 138.24
[(6)Ru(7)][PF6]2 (10): Bromo-mono(terpyridine)ligand 7[38] (39 mg,
100 mmol) was added to suspension of mono(RuIII) adduct 8 (53 mg,
100 mmol), following the above method B, to afford 10 as red microcrystals:
yield: 95 mg (86%); m.p. >4008C; 1H NMR (CD3CN): d ˆ 2.56 (s, 3H; 6-
CH3), 7.19 (m, 4H; (6 ‡ 7)-H5, 5''), 7.44 (dd, 4H; (6 ‡ 7)-H6, 6''), 7.60(d, 2H;
6-H3, 5Ar), 7.96 (m, 6H; (6 ‡ 7)-H4, 4 ‡ (7)-H2, 6Ar), 8.11 (d, 2H; 7-H3, 5Ar), 8.66
(d, 4H; (6 ‡ 7)-H3, 3''), 8.99 (s, 2H; 7-H3', 5'), 9.00 (s, 2H; 6-H3', 5') ppm;
13C NMR (CD3CN): d ˆ 21.22 (6-CH3), 122.15 (7-C3'), 122.29 (6-C3'), 125.29
((6 ‡ 7)-C3), 128.20( 7-C5), 128.30( 6-C5), 128.45 (7-C3Ar), 130.43 (6-C2Ar),
131.08 (7-C2Ar), 133.48 (6-C3Ar), 134.68 (7-C1Ar), 136.85 ((6 ‡ 7)-C4Ar),
138.83 ((6 ‡ 7)-C4), 141.84 (6-C1Ar), 147.74 (7-C4'), 149.20( 6-C4'), 153.22
((6 ‡ 7)-C6), 156.10( 7-C2), 156.38 (6-C2), 158.90( 7-C2'), 159.90( 6-C2') ppm;
IR (KBr): nÄ ˆ 3085, 2925, 2862, 1608, 1545, 1467, 1430, 1408 cmÀ1; UV/Vis
(MeCN): lmax ˆ 286 (5.60  104), 310(5.97  104), 490nm (2.38  104); ESI
MS: m/z: 40 6 z( ˆ 2, without counter ion) calcd for C43H31N6BrRuP2F12
(1102); elemental analysis (%): calcd: C 46.82, H 2.77, N 7.62; found: C
46.72, H 2.82, N 7.52.
(C4), 140.10 (C1Ar), 146.86 (C4'), 152.24 (C6), 155.25 (C2), 158.14 (C2') ppm;
IR (KBr):nÄ ˆ 3074, 2922, 2854, 1603, 1532, 1469, 1394 cmÀ1; UV/Vis
(MeCN): lmax ˆ 290(3.22  105), 312 (3.37  105), 496 nm (1.43  105);
MALDI-TOF: m/z: 5544 [À1PF5], 5400 [À1PF6–1PF5], 5292[À3PF5],
5166[À4PF5], 5020[À4PF5–1PF6], calcd for C222H156N36Ru6P12F72 (5670);
elemental analysis (%)(‡8H2O): calcd: C 45.82, H 2.96, N 8.67; found: C
45.86, H 2.98, N 8.68.
Stepwise synthesis of [Ru6(3)6][PF6]12 (14): Trimeric precursor 12 (33 mg,
17 mmol) was added to a suspension of the bis(RuIII) adduct 13 (40mg,
17 mmol) in MeOH (20mL), then N-ethylmorpholine (500 mL) was added
and the mixture was refluxed for 12 h. The work-up afforded (ca. 80%)
crude hexamer (chloride counterions), which was subjected to the above
and purification processes (method B): yield: 40mg (55% overall); the
sample was identical in all respects to the above.
[(3)3Ru6(4)3][PF6]12 (16): Bromo-bis(terpyridine)ligand 4 (43 mg, 70 mmol)
was added to bis(RuIII) adduct 5 (68 mg, 70 mmol), following the above
method B, to give (ca. 85%) a dark red solid, which was filtered, then
purified with TLC (SiO2; eluent: aqueous MeCN/saturated KNO3 solution
(1:7:1)). The major dark band was collected and extracted, then excess
methanolic ammonium hexafluorophosphate was added to precipitate 17,
which was sequentially washed with MeOH, Et2O, and aqueous acetone,
and dried in vacuo to yield dark purple microcrystals: yield: 50mg (36%);
[(3)Ru2(6)2][PF6]4 (11): Route 1: Mono(terpyridine)ligand
206 mmol) was added to suspension of bis(RuIII
adduct
6
5
(67 mg,
(100 mg,
)
103 mmol), following the above method B, to yield 11 as red microcrystals:
1
yield: 130mg (65%); m.p. 230 8C; H NMR (CD3CN): d ˆ 2.68 (s, 6H; 6-
CH3), 2.96 (s, 3H; 3-CH3), 7.35 (dd, 8H; (6 ‡ 3)-H5, 5''), 7.62 (m, 8H; (6 ‡ 3)-
H6, 6''), 7.74 (d, 4H; 6-H3, 5Ar), 8.12 (m, 8H; (6 ‡ 3)-H4, 4''], 8.28 (d, 4H; 6-
H2, 6), 8.49 (s, 2H; 3-H4, 6Ar), 8.82 (d, 4H; 6-H3, 3''Ar), 8.92 (d ‡ s, 5 H; 3-
H3, 3'' ‡ H2Ar), 9.17 (s, 4H; 6-H3', 5'), 9.40(s, 4H; 3-H3', 5') ppm; 13C NMR
(CD3CN): d ˆ 20.41, 20.77 ((6 ‡ 3)-CH3), 121.35, 121.83 ((6 ‡ 3)-C3'),
1
m.p. >4008C; Rf ˆ 0.60; H NMR (CD3CN): d ˆ 2.90(s, 3H; 3-CH3), 7.30
(m, 8H; (3 ‡ 4)-H5, 5''), 7.60(d, 8H; ( 3 ‡ 4)-H6, 6''), 8.05 (dd, 8H; (3 ‡ 4)-
H4,4''), 8.41 (s, 2H; 3-H4, 6Ar), 8.75 (s, 2H; 4-H2, 6Ar), 8.85 (d ‡ s, 9 H; (3 ‡ 4)-
2952
¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
0947-6539/02/0813-2952 $ 20.00+.50/0
Chem. Eur. J. 2002, 8, No. 13

Hexagonal Terpyridine Ruthenium and Iron Macrocyclic Complexes
2946 2954
H3, 3'' ‡ 3-H2Ar), 9.18 (s, 1H; 4-H4Ar), 9.43 (s, 8H; (3 ‡ 4)-H3', 5') ppm;
13C NMR ([D6]DMSO): d ˆ 22.01 (3-CH3), 122.79 ((3 ‡ 4)-C3'), 124.84 (3-
C5Ar), 125.88 ((3 ‡ 4)-C3), 127.11 (4-C4Ar), 128.50(( 3 ‡ 4)-C5 ‡ 3-C2Ar),
131.05 (3-C6Ar), 132.10( 4-C1Ar), 132.66 (4-C2Ar), 138.47 (4-C3Ar), 138.84
((3 ‡ 4)-C4), 140.49 (3-C1Ar), 146.15 (4-C4'), 147.99 (3-C4'), 153.00 ((3 ‡ 4)-
C6), 156.04 ((3 ‡ 4)-C2), 158.89 ((3 ‡ 4)-C2) ppm; IR (KBr): nÄ ˆ 3124, 2929,
1605, 1533, 1471, 1396 cmÀ1; UV/Vis (MeCN): lmax ˆ 290(3.17  105), 310
(G.R.N.: (N00014 99
acknowleged for financial support. Also acknowledged are the Louisiana
Board of Regents Fellowship (R.C.) and postdoctoral fellowship
provided by the Korea Research Foundation (T.J.C.). We also thank Prof.
Goeffrey A. Ozin and Dr. Srebri Petrov at the University of Toronto, Prof.
Edwin Constable at the University of Birmingham, and Prof. Deiter
Schubert of the Institute for Biophysics at JWG University in Frankfurt for
insightful and helpful comments. Prof. Stephen Chang and Dr. Lei Zhu
(University of Akron) are gratefully acknowledged for help with the TEM
experiments.
1
0 082)). The Ohio Board of Regents are also
a
(3.10 Â 105),
496 nm
(1.48 Â 105);
elemental
analysis
(%):
(C219H147N36Br3Ru6P12F72 ¥ 24H2O): calcd: C 41.73, H 3.09, N 8.00; found:
C 41.62, H 2.81, N 8.29.
1,3-Diformyl-5-hydroxymethylbenzene: Lithium tri-tert-butoxyaluminum
hydride (12.2 g, 48 mmol) was dissolved in dry THF (150mL) and cooled to
-788C, then a THF solution of 1,3,5-tris(chlorocarbonyl)benzene (4; 3.0g,
12 mmol, 50mL) was added dropwise over 30minutes. The mixture was
stirred for an additional 6 h at 258C with TLC monitoring; then water (ca.
20mL) was added to the mixture to destroy the reducing agent, the solid
was filtered and washed with EtOAc. The combined organic solution was
evaporated in vacuo affording a solid, which was purified by column
chromatography (SiO; elution with a (1:1) EtOAc/hexane mixture) to give
5 (33%; 630mg); Rf ˆ 0.4; 1H NMR: d ˆ 2.17 (br, 1H; CH2OH), 4.94 (s,
2H; CH2OH), 8.20(s, 2H; Ar H4, 6), 8.33 (s, 1H; ArH2), 10.15 (s, 2H;
CHO); 13C NMR d 63.51 (CH2OH), 130.03 (ArC2), 132.50(Ar C4, 6), 137.01
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5
‡
(ArC1, 3), 143.49 (ArC ), 191.25 (C O); ESI-MS: m/z: 165 [M ‡ H ], calcd
ˆ
for C9H8O3 (164).
1,3-Bis(2,2':6',2''-terpyridine-4'-yl)-5-(hydroxymethyl)benzene (17): 1,3-Di-
formyl-5-hydroxymethylbenzene (500 mg, 3.05 mmol) was dissolved in
EtOH (50mL), then 2-acetylpyridine (2.25 g, 18 mmol) was added,
followed after 2 min by aqueous NaOH solution (5 mL, 1m). After the
dark pink solution had been stirred at 258C for 20h, the solvent was
evaporated in vacuo to yield a red oil, which was extracted with CH2Cl2.
The combined extracts were washed with water, dried (MgSO4), and
concentrated in vacuo to give a pink solid to which a mixture of NH4OAc
(15 g) and glacial AcOH (50mL) was added; the mixture was refluxed for
4 h. The dark brown solution was cooled, and neutralized with aqueous
Na2CO3 to afford a deep yellow precipitate, which was filtered and purified
by column chromatography (Al2O3; elution with a mixture (1:1) of EtOAc/
hexane) to give pure bis(terpyridine) ligand 17 (23%; 400 mg) as a colorless
solid; 1H NMR: d ˆ 5.34 (s, 2H; CH2OH), 7.40(dd, J ˆ 6 Hz, 4H; H5, 5''),
7.94 (dd, J ˆ 8 Hz, 4H; H4,4''), 7.99 (s, 2H; H4, 6Ar), 8.33 (s, 1H; H2Ar), 8.75 (d,
J ˆ 8 Hz, 4H; H3, 3''), 8.78 (d, J ˆ 4 Hz 4H; H6, 6''), 8.84 (s, 4H; H3'5') ppm;
13C NMR: d ˆ 66.01 (CH3), 119.32 (C3'), 121.53 (C5Ar), 123.98 (C3), 126.24
(C2Ar), 128.10(C 5), 137.15 (C6Ar), 137.45 (C4), 139.93 (C1Ar), 148.94 (C6),
149.81 (C4'), 155.82 (C2 ‡ C2') ppm; IR (KBr): nÄ ˆ 3055, 3014, 2917, 2853,
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‡
1586, 1567, 1471, 1375 cmÀ1; ESI-MS: m/z: 571 [M ‡ H ], calcd for
C37H26N6O (570); elemental analysis (%): calcd: C 77.89, H 4.56, N 14.74;
found: C 77.44, H 4.54, N 14.69.
[Fe6(17)6][PF6] (18): A MeOH solution of one equivalent of FeCl2 ¥ 4H2O
(35 mg, 175 mmol, 1 mL) was added to a solution of 1,3-bis(2,2':6',2''-
terpyridin-4'-yl)-5-(hydroxymethyl)benzene (17; 100 mg, 175 mmol) in
MeOH/THF ((2:1) 20mL) . The mixed solution was refluxed for 12 h.
After the mixture had been cooled, the resultant deep purple solution was
filtered (Celite), then a slight excess of methanolic ammonium hexafluoro-
phosphate was added to precipitate the complex, which was purified by
column chromatography (SiO2; elution with a H2O:MeCN:KNO3 (1:7:1)
solvent mixture) to afford 18 (81%; 130mg) as a purple solid; Rf ˆ 0.6;
1H NMR (CD3CN): d ˆ 5.65 (s, 2H; CH2OH), 7.15 (dd, 4H; H5, 5''), 7.30(d,
4H; H6, 6''), 7.97 (dd, 4H; H4,4''), 8.63 (s, 2H; H4, 6Ar), 8.81 (d, 4H; H3, 3''), 9.46
(s, 1H; H2Ar), 9.51 (br, 4H; H3', 5') ppm; 13C NMR (DMSO): d ˆ 65.56
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Ar
(C4Ar), 138.85 (C4 ‡ C1Ar), 148.51 (C4'), 152.66 (C6), 157.74 (C2), 159.97
(C2') ppm; IR (KBr): nÄ ˆ 3425, 3067, 2932, 1733, 1609, 1474, 1405, 1302,
1246, 1138, 842, 792 cmÀ1; UV/Vis (MeCN): lmax ˆ 290(3.05  105), 322
(2.11 Â 105), 576 nm (1.29 Â 105); elemtal analysis (%) calcd for
C222H156N36O6Fe6P12F72 (5495) ‡ (16 H2O): C 46.07, H 3.25, N 8.72; found:
C 46.15, H 3.45, N 8.86.
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Acknowledgements
We gratefully thank the National Science Foundation (G.R.N.: (DMR-
9901393) and P.S.R.: (BIR-9420253)) and the Office of Naval Research
Chem. Eur. J. 2002, 8, No. 13
¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
0947-6539/02/0813-2953 $ 20.00+.50/0
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2954
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0947-6539/02/0813-2954 $ 20.00+.50/0
Chem. Eur. J. 2002, 8, No. 13