A rigid metallohexameric macrocycle composed of endo- and exo-cyclic bisterpyridine-metal complexes

Article abstract of DOI:10.1039/c1nj20195f

Synthesis of terpyridine-based building blocks has allowed the self-assembly of a nanosized metallomacrocycle with precisely positioned, peripheral metal complexes. Construction of the precursors included the assembly of a heteroleptic bisterpyridine-Ru(ii) complex possessing a diiodoaryl moiety that was subsequently reacted with two equivalents of 4′-ethynyl-2, 2′:6′,2′′-terpyridine via a Pd(0)-catalyzed Sonagashira coupling, to generate the requisite monomer with two, 120°-juxtaposed metal coordination sites. Addition of one equivalent of Fe(ii) to one equivalent of the bisligand afforded the metallocycle with 12 metals [6 internal Fe(ii) ions and 6 external Ru(ii) ions] measuring ca. 7 nm in diameter.

Full text of DOI:10.1039/c1nj20195f

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PAPER
A rigid metallohexameric macrocycle composed of endo- and exo-cyclic
bisterpyridine-metal complexesw
Sinan Li,a Charles N. Moorefield,b Carol D. Shreiner,c Pingshan Wang,d
Rajarshi Sarkare and George R. Newkome*be
Received (in Montpellier, France) 2nd March 2011, Accepted 9th May 2011
DOI: 10.1039/c1nj20195f
Synthesis of terpyridine-based building blocks has allowed the self-assembly of a nanosized
metallomacrocycle with precisely positioned, peripheral metal complexes. Construction of
the precursors included the assembly of a heteroleptic bisterpyridine-Ru(II) complex
possessing a diiodoaryl moiety that was subsequently reacted with two equivalents of
40-ethynyl-2,20 : 60,200-terpyridine via a Pd(0)-catalyzed Sonagashira coupling, to generate the
requisite monomer with two, 1201-juxtaposed metal coordination sites. Addition of one
equivalent of Fe(II) to one equivalent of the bisligand afforded the metallocycle with
12 metals [6 internal Fe(II) ions and 6 external Ru(II) ions] measuring ca. 7 nm in
diameter.
directionality. Additionally, novel utilitarian properties, based
on metal ion selection, can be instilled.26 Notably, some of
Introduction
The construction of shape-persistent architectures is of great
these terpyridine-metal complexes are reversible under specific
conditions, suggesting their use as protecting groups;27
interest to the design and creation of supramolecular nano-
devices,1–4 as well as smart materials.5 In part, rigid macro-
whereas, others are totally irreversible under typical environ-
cycles possessing dimensions within the nanoregime, in contrast
mental conditions.
to their open-ended chain/hyperbranched analogues,6,7 are
Most shape-persistent macrocycles are constructed as
playing an increasingly important role in the supramolecular
regular convex polygons that include triangles, rectangles,
pentagons, and hexagons, to mention but a few.28 Based on
construction of molecular building blocks as well as affording
easy access to the development of new versatile synthetic
methodologies.8–12
a purely geometric viewpoint, regular polygons can be divided
into subunits that possess identical shape and size; these
Stang13–16 and Lehn17–19 have prompted an extensive and
subunits provide the design criteria for the building blocks
continuing examination of transition metal binding self-assem-
used in their construction. For example, a regular triangle
bling precursors to form shape-persistent macrocycles20–22
consists of three objects each possessing two terminally connected
possessing unique electronic and photonic properties. In the
1930s, Morgan and Bustall23,24 synthesized the first terpyri-
arms juxtaposed to form a 601 angle. Analogously, a regular
hexagon possesses six identical subunits characterized by
dines; however, more recently these monomers have been
used in predesigned macromolecular constructs.25,26 Their
1201 angles forming a hexameric cycle, or three subunits each
possessing a net 601 between terminal ligands. Notably, in
some cases, the polygons are only equiangular, and not
equilateral, but are still geometrically symmetric.14
stable coordination chemistry is a particularly powerful tool
for the assembly of supramolecular architectures, due to their
pseudo-octahedral geometry that easily imparts framework
Our strategy for macrocycle self-assembly is predicated
on this geometric ‘‘retroconstruction’’ and is ideally suited
a Lubrizol Advanced Materials, 9911 Brecksville Rd., Cleveland,
for bis(terpyridinyl) monomers that can be designed and
OH 44141-3201, USA
b Maurice Morton Institute for Polymer Science, 170 University Cr.,
The University of Akron, Akron, OH 44325. Fax: 330-972-2368
c Chemistry Department, Hiram College, P.O. Box 67, Hiram,
OH 44234. Fax: 330-569-5448
constructed with angles up to 1801 with respect to the two
ligating termini.29 Hence, our previous work has focused
predominately on the synthesis of triangular-,30 pentagonal-,31
hexagonal-,32–35 and decameric-macrocycles.36 Herein, we report
the design and construction of a hexagon-based, star-shaped
macrocycle possessing both exo- and endo-cyclic bisterpyridinyl-
metal ion complexes; six Fe(II) ions bind the cyclic core and six
bisterpyridine-Ru(II) complexes radiate from the hexagonal
vertices.
d ChemNano Materials, 2220 High St., Suite 605, Cuyahoga Falls,
OH 44221
e Departments of Polymer Science and Chemistry, 170 University Cr.,
The University of Akron, Akron, OH 44325.
E-mail: newkome@uakron.edu; Fax: 330-972-2368
w Dedicated to Professor Didier Astruc on the occasion of his
65th birthday.
c
2130 New J. Chem., 2011, 35, 2130–2135
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Results and discussion
Assembly (Scheme 1) began with commercially available
3,5-diaminobenzoic acid (1) that was initially transformed
(70%) to 3,5-diiodobenzoic acid (2),37 which was subsequently
reduced with BH3ꢀTHF to give (88%) the intermediate alcohol
338 that was then oxidized with PCC to afford (490%) the
1
desired 3,5-diiodobenzaldehyde (4);39 their H and 13C NMR
data were identical to literature. 3,5-Diiodobenzaldehyde 4
was subsequently treated with 2.1 eq. of 2-acetylpyridine at
25 1C under basic conditions (NaOH) for 12 h, followed by
refluxing with excess NH4OAc in HOAc for 8 h. The desired
40-(3,5-diiodophenyl)-2,20 : 60,20 0-terpyridine (5) was isolated
in 34% yield and confirmed by peaks (1H NMR) at 8.64
(30,50-tpyH) and 8.76 ppm (6,60 0-tpyH) along with an absorption
(13C NMR) at 95.05 ppm assigned to the CAr-I, and the mass
signal at m/z = 561.9 (M+H)+ supported the assignment.
The paramagnetic, Ru(III) capping agent adduct 40-(p-methoxy-
phenyl)-2,20 :60,20 0-terpyridine (8) was then obtained by refluxing
(EtOH, 4 h) a mixture of 40-(p-methoxyphenyl)-2,20 : 60,200-
terpyridine40 (7), generated from para-methoxybenzaldehyde
(6) with 2-acetylpyridine and excess NH4OAc in HOAc, with
RuCl3ꢀnH2O.
Scheme 2 (i) RuCl3ꢀnH2O, MeOH, reflux; (ii) N-ethylmorpholine,
MeOH, reflux; (iii) Pd0, CuI, Et3N.
Two routes to produce the intermediate diiodo complex 13
were employed (Scheme 2). To a mixture of methoxy adduct 8
(1 eq.) and diiodoterpyridine 5 (1 eq.) in MeOH, N-ethyl-
morpholine, as a reducing agent, was added. After refluxing,
the desired dimer 13 was isolated (84%), as a dark red solid;
however, for structural verification, it was also prepared
(77%) by refluxing the diiodoRu(III) adduct 12 (1 eq.; accessed
by treatment of diiodo-terpyridine ligand 5 with RuCl3ꢀnH2O)
with methoxyterpyridine 7 in MeOH with added N-ethyl-
morpholine. In each instance, the structure of the Ru(II) complex
13 was characterized (1H NMR) by signals at 8.98 and 8.96 ppm,
which were assigned to 30,50 0-tpyHs of the diiodo (5) and
methoxy (7) components, respectively; while the 13C NMR
spectrum displayed a prominent absorption at 96.78 ppm for
C
Ar-I. Further confirmation of the structure of complex 13
was provided by the ESI-MS data [1146.9 (M – PF6)1+, 501.0
(M ꢁ 2PF6)2+].
The key bisterpyridine ligand 14 for the desired heteronuclear
macrocycle was synthesized via the Sonagashira coupling41–43
of diiodoaryl complex 13 with 40-ethynyl-2,20 : 60,200-terpyri-
dine44,45 (11), which was prepared (Scheme 3) by the transfor-
mation of 2-carboethoxypyridine (9) to the terpyridine triflate
10, then treatment with trimethylsilylacetylene and deprotec-
tion. The solubility of bis-ligand-Ru(II) complex 14 was poor
1
in most common organic solvents. The H NMR spectrum of
complex 14 showed the expected downfield shifts for the
complexed 30,50-tpyHs (9.19 ppm, Dd = +0.21) for the
dialkynylterpyridine portion and (9.04 ppm, Dd = +0.08)
for the methoxyterpyridine portion along with additional
esonances at 8.86–8.70 ppm assigned to the 30,50-tpyHs,
6,60 0-tpyHs, and 3,30 0-tpyHs of the two free terpyridines.
Scheme 1 (i) NaNO2, H2SO4, urea, H2O, 0 1C, 2 h, then KI, 5 h, 25 1C;
(ii) BH3ꢀTHF; (iii) PCC; (iv) 2-acetylpyridine, NaOH, then NH4OAc,
HOAc; (v) RuCl3ꢀnH2O, MeOH, D.
Scheme 3 (i) acetone, NaH, anh. THF, reflux, 2 h; (ii) NH4OAc,
EtOH, reflux, 8 h; (iii) (CF3SO2)2O, anh. pyridine, 25 1C, 48 h; (iv) Pd0;
(v) KF.
c
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The 13C NMR spectrum displayed distinct signals at 94.10,
89.72, and 56.84 ppm assigned to the unsymmetrical CRC
and OCH3 moieties, respectively. The structure of bisterpyridine
14 was further confirmed by the ESI-MS data [m/z 1405.6
(M ꢁ PF6)1+ and 630.6 (M ꢁ 2PF6)2+].
Complex 14 was subsequently subjected to macrocyclic-
zation,27,29,33,34,46 in which 14 was treated with 1 eq. of FeCl2
in refluxing MeOH for 24 h to afford the desired homonuclear
hexameric macrocycle 15, which was isolated in 36% as a
purple solid (Scheme 4). The resultant hexamer 15, possessing 24
positive charges, exhibited improved solubility compared to that
ꢁ
of the starting ligand 14; it waꢁs freely soluble in MeCN (PF6
counterion) and MeOH (NO3 or Clꢁ counterion). Pertinent
observations confirming the structure included a downfield
1H NMR shift of the singlet assigned to the Fe(II)-complexed,
30,50-tpyHs (9.25 ppm, Dd = +0.45) and the presence of signals
(13C NMR) at 96.67, 89.31, and 56.50 ppm corresponding to the
unsymmetrical CRC and OCH3 moieties, respectively.
Fig. 1 UV-vis and XPS spectra of metallomacrocycle 15.
is the higher oxidatꢁion state of N, was attributed to the
presence of the NO3 counterion. The exact atomic Fe : Ru
ratio of 1 : 1 provided excellent support for hexamer 15.
Based on initial molecular modeling, the predicted structure
of heteronuclear-Fe(II)Ru(II) macrocycle 15 possesses 7 nm
and 2.5 nm outer and internal diameters, respectively (Fig. 2A).
As a consequence of the high symmetry in hexamer 15 as well
as the repeating htpy-metal(II)-tpyi moieties, the NMR, UV,
and XPS data confirm its macrocyclic architecture. Hence to
better envision its uniformity, atomic force microscopy (AFM)
was conducted. A droplet of a dilute MeCN solution of
hexamer 15 (1 mg mLꢁ1) was deposited on a freshly cleaved,
mica surface, dried under N2. Using a super sharp silicon
probe possessing a typical radius-of-curvature of B2 nm on
the AFM, the collected topographic image of 15 revealed an
obvious ring structure with a discernible central hole, which
has an outer diameter B11 nm supporting both the shape and
size of the modeled macrocycle (Fig. 2B).
The heteronuclear macrocycle 15 (with PF6ꢁ) was observed to
possess moderate thermal stability as measured by thermal
gravimetric analysis (TGA). Unlike that of other related metallo-
macromolecules, the TGA trace of 15 did not exhibit a sharp
decomposition temperature (Fig. 3A). The overall decomposition
process was observed as a curve with a small slope and two
onset temperatures recorded at 174.2 and 591.8 1C. The cyclic
voltammetry (CV) was also conducted to characterize the electro-
chemical properties of 15 (Fig. 3B). Interestingly, the recorded CV
trace did not reveal the expected two oxidative couples of Ru and
Fe,47 but only one at 1.29 V (DE = 18 mV), presumably due to
the very close redox potentials of Fe and Ru.
Scheme 4 (i) FeCl2, MeOH, D, 8 h.
The UV-vis spectrum of hexamer 15 exhibited the expected
absorbance pattern at 582 and 493 nm in MeCN, which was
attributed to the MLCT transitions25 in the two different com-
plexes, htpy-Fe-tpyi and htpy-Ru-tpyi, respectively (Fig. 1A).
X-Ray photoelectron spectroscopy (XPS, using monochro-
matic Mg-Ka radiation at a power of 250 W; Fig. 1B) was
performed to verify the presence of the coordinated metals.
Since the electron binding energies that are commonly used to
characterize Ru (3d1 and 3d5 at B285 eV) and Fe (2p1 and 2p3
at 705–720 eV) are very close to the binding energy peaks of
C 1s (B284 eV) and F 1s (B690 eV), we choose Ru 3p3 as the
characteristic binding energy and the NO3ꢁ counterion rather
than the more common PF6ꢁ. The XPS measurements of this
heteronuclear-polymetal macrocycle showed a binding energy
peak at 462.52 eV attributed to Ru 3p3, as well as peaks
assigned to Fe (2p1 and 2p3 at 720.57 and 707.65 eV, respec-
tively). As expected, the appearance of two N 1s peaks at
407.98 eV and 401.62 eV was observed; there was no evidence
Conclusions
Geometrical ‘‘retroconstruction’’ of a 2D hexagon has been
employed for the design and synthesis of a heteronuclear-
Fe(II)Ru(II) structure in the nanometre size regime. The observed
ꢁ
of any residual PF6 (specifically P 2p at 130.6eV and F 1s at
690 eV). The higher binding energy of N 1s (407.98 eV), which
c
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Fig. 3 Thermogravimetric analysis (A) and cyclic voltammetry (B)
recordings for macrocycle 15 (PF6ꢁ). The CV was conducted in
MeCN/Bu4NPF6 with 0.1 M Bu4NPF6 at 25 1C using a NaCl
reference electrode.
and X-ray photoelectron spectroscopic (XPS, monochromatic
Mg-Ka radiation at power 250 W, 93.90 eV) measurements were
used. Molecular modeling was performed using Material Studio
software available from Accelyrs. Geometry optimization was
achieved using the Forcite module and the conjugate gradient
algorithm with convergence tolerances of 0.0001 kcal molꢁ1
(energy) and 0.005 kcal molꢁ1/A. Energy minimization employed
a universal forcefield with an atom-based summation method
and cubic spline truncation for both the electrostatic and non-
bonded interactions. AFM was conducted in the tapping mode
by adding droplets of dilute solutions of the macrocycle on the
surface of freshly cleaved mica, then dried at 25 1C for 8 h; a
super sharp silicon probe possessing a typical radius-of-curvature
of B2 nm (SSS-NCH-SPL from NANOSENSORS) was used.
Fig. 2 (A) Top and side views of an optimized molecular model of 15
with the counterions omitted for clarity and (B) a tapping mode AFM
image of macrocycle 15 (scale bar: 50 nm).
NMR spectra coupled with the AFM imaging and measured
physical properties provide direct evidence for the proposed
structure. Investigations into the potential to employ and fine-
tune the electronic properties of these unique materials are
currently ongoing.
Experimental section
General comments
3,5-Diaminobenzoic acid, 2-acetylpyridine, trimethylsilyl
acetylene, palladium catalysts [Pd(PPh3)4, Pd(PPh3)2Cl2, and
Pd(dppf)Cl2], 4-methoxy-benzaldehyde, ammonium acetate
(NH4OAc), BH3ꢀTHF, pyridinium chlorochromate (PCC),
RuCl3, FeCl2, CuI, and NH4PF6 were purchased from either
Aldrich or Acros and were used directly without further
purification. Both 740 and 1144,45 were prepared following
literature procedures and their structures were fully characterized.
Column chromatography was performed using SiO2 (60–200
mesh) or basic Al2O3, Brockman Activity I (60–325 mesh).
1H and 13C NMR spectra were recorded using a Mercury
300 MHz (75 MHz) NMR spectrometer using CD3CN, as
solvent, unless otherwise noted. Mass spectra were obtained
using a Bruker Esquire Electrospray Ion Trap mass spectrometer
(ESI-MS). Hewlett-Packard 8452A diode array spectrophoto-
meter for UV/Vis absorption measurement; CHI 440 Electro-
chemical Workstation for cyclic voltammetry measurements;
40-(3,5-Diiodophenyl)-2,20 : 60,20 0-terpyridine (5)
To an aqueous solution of NaNO2 (2.5 M), a H2SO4 solution
of 3,5-diaminobenzoic acid (1; 3 g, 20 mmol) was added at
0 1C. Urea (3 g) and KI (7 g) were added and the mixture was
stirred for 2 h, then poured into ice-cold water. The solid was
filtered and shown to be 3,5-diiodobenzoic acid (2; 5.1 g,
70%),37 which was reduced with BH3ꢀTHF to give (88%)
3,5-diiodobenzyl alcohol (3).38 Subsequent PCC-oxidation of
3 in CH2Cl2 at 25 1C gave (490%) 3,5-diiodobenzaldehyde
(4), as a yellowish solid.39
To a stirred mixture of aldehyde 4 (2.5 g, 7 mmol) and
2-acetylpyridine (1.78 g, 2.1 eq.) in EtOH (80 mL, 95%),
aqueous NaOH (1.5 mL, 2.1 eq., 1.0 M) was added dropwise.
The mixture was stirred at 25 1C for 12 h, then the solvent was
evaporated in vacuo to give a dark red solid. Excess NH4OAc
c
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(5.5 g) in HOAc (50 mL) was added and the resultant mixture
was refluxed for 8 h, after which the HOAc was removed
in vacuo leaving a brown residue that was partitioned between
CHCl3 and H2O (1 : 1, 600 mL). The organic layer was washed
twice with H2O, dried (MgSO4), and concentrated in vacuo to
give the crude product, which was chromatographed (Al2O3)
by elution with an EtOAc/C6H12 (1 : 1) solvent mixture.
Lastly, recrystallization (MeOH) gave pure 40-(3,5-diiodo-
7.98 [m, 4H, 4,40 0-tpy(7)H and 4,40 0-tpy(5)H], 7.45 [d, J = 5 Hz,
2H, 6,600-tpy(7)H], 7.37 [d, J = 5 Hz, 2H, 6,60 0-tpy(5)H],
7.32 [d, J = 8 Hz, 2H, 3,5-(5)ArH], 7.21-7.14 [m, 4H, 5,50 0-
tpy(7)H and 5,500-tpy(5)H], 3.97 [s, 3H, (5)ArOCH3]; 13C NMR
(CD3CN): d 163.22, 159.64, 159.44, 157.10, 156.54, 153.80,
149.61, 147.70, 146.03, 141.85, 139.46, 139.43, 137.43, 130.61,
130.17, 128.96, 128.77, 126.01, 125.88, 123.10, 122.32, 116.44,
96.78, 56.79; ESI-MS Calcd. 1291.9 (C43H30F12I2N6OP2Ru):
phenyl)-2,20 : 60,200-terpyridine (5), as
a
yellowish solid:
found: m/z 1146.9 (M–PF6)1+, 501.0 (M–2PF6)2+
.
1
1.33 g (34%); mp 230 1C; H NMR (CDCl3): d 8.76 (d, J =
4 Hz, 2H, 6,600-tpyH), 8.70 (d, J = 8 Hz, 2H, 3,30 0-tpyH),
8.64 (s, 2H, 30,50-tpyH), 8.17 (s, 2H, 2,6-ArH), 8.15 (s, 1H,
4-ArH), 7.93 (t, J = 6 Hz, 2H, 4,40 0-tpyH), 7.41 (t, J = 6 Hz,
2H, 5,50 0-tpyH); 13C NMR (CDCl3): d 156.00, 155.59, 149.03,
147.70, 145.74, 142.31, 137.67, 135.72, 124.46, 121.89, 119.12,
95.51; ESI-MS (560.92 calcd. for C21H13I2N3): m/z 561.9
(M+H)+.
Terpyridine-Ru(II) dimer (14)
To a degassed mixture of 13 (189 mg, 146 mmol), 1144,45
(94.1 mg, 366 mmol), Pd(PPh3)2Cl2 (7.1 mg,10 mmol), and
CuI (4.3 mg, 23 mmol) in a mixed solution of THF/MeCN
(50 mL, 20/30), (Me2CH)2NH (10 mL) was added. After
degassing five times with Argon, the mixture was stirred at
80 1C for 3 d. The solution was concentrated in vacuo to give a
red residue, which was chromatographed (Al2O3) by eluting
with a H2O/KNO3(conc.)/MeCN (1 : 1 : 10) solvent mixture to
afford terpyridine-Ru(II) dimer 14, which was treated with an
NH4PF6 MeOH solution in order to prepare the desired 14
(PF6ꢁ), as a light red solid: mp 4350 1C, 138 mg (61%);
1H NMR (CD3CN): d 9.19 [s, 2H, 30,50-tpy(7)H], 9.04 [s, 2H,
30,50-tpy(5)H], 8.86-8.70 [m, 15H, 3,30 0-tpy(7)H, 3,30 0-tpy(5)H,
3,300-tpy(11)H, 6,60 0-tpy(11)H, 30,50-tpy(11)H and 2,4,6-(7)ArH],
8.27-8.24 [m, 6H, 4,40 0-tpy(11)H and 2,6-(5)ArH], 8.07-7.99
[m, 2H, 4,40 0-tpy(5H and 4,400-tpy(7)H], 7.73 [t, J = 6 Hz, 4H,
5,500-tpy(11)H], 7.54 [d, J = 5 Hz, 2H, 6,60 0-tpy(7)H], 7.49 [d, J =
6 Hz, 2H, 6,60 0-tpy(5)H], 7.37 [d, J = 8 Hz, 2H, 3,5-(5)ArH],
7.30-7.23 [m, 4H, 5,500-tpy(7)H and 5,500-tpy(5)H], 4.03 [s, 3H,
(5)ArOCH3]; 13C NMR (CD3CN): d 163.24, 159.63, 159.42,
157.23, 156.53, 155.36, 154.12, 153.83, 149.68, 149.30, 146.77,
141.20, 139.55, 137.46, 134.64, 133.50, 130.63, 130.09, 129.11,
128.89, 126.99, 125.97, 125.35, 124.93, 123.40, 122.89, 122.31,
116.44, 94.10, 89.72, 56.84; ESI-MS Calcd.1550.3
(C77H50F12N12OP2Ru); found: m/z 1405.6 (M–PF6)1+, 630.6
40-(3,5-Diiodophenyl)-2,20 : 60,20 0-terpyridine-Ru(III) adduct (12)
Was prepared from a stirred solution of 40-(3,5-diiodophenyl)-
2,20 : 60,20 0-terpyridine (5; 77 mg, 137 mmol), RuCl3 (36.4 mg,
14 mmol) in MeOH (20 mL). After stirring at 25 1C for 1 h, the
mixture was refluxed for additional 8 h. After cooling to 25 1C,
the black precipitate was filtered and washed thoroughly with
MeOH and CHCl3 to give 40-(3,5-diiodophenyl)-2,20 : 60,200-
terpyridine-Ru(III) adduct 12, as a black solid (30 mg, 29%),
which was used directly.
40-(p-Methoxyphenyl)-2,20 : 60,200-terpyridine-Ru(III) adduct (8)
To a solution of RuCl3 (128 mg, 490 mmol) in MeOH (20 mL),
740 (157 mg, 463 mmol) was added. After being stirred
at 25 1C for 1 h, the solution was refluxed for 4 h to afford
40-(p-methoxy-phenyl)-2,20 :60,20 0-terpyridine-Ru(III) adduct 8, as
black solid (247 mg, 88%), which was used directly.
40-(3,5-Diiodophenyl)-2,20 :60,20 0-terpyridine-Ru(II)-40-(p-methoxy-
phenyl)-2,20 : 60,20 0-terpyridine h5-Ru(II)-7i (13)
(M–2PF6)2+
.
Method A. To a mixture of 5 (139 mg, 250 mmol) and 8
(137.5 mg, 250 mmol) in MeOH (50 mL), N-ethylmorpholine
(5 drops) was added. After stirring for 1 h at 25 1C, the mixture
was refluxed for additional 12 h. The solvent was evaporated
in vacuo to give a residue that was chromatographed (SiO2) by
eluting with a H2O/KNO3 (conc.)/MeCN (1 : 1 : 10) solvent
mixture to afford h5-Ru(II)-7i (13), which was treated with
methanolic NH4PF6 in order to prepare the desired 13 (PF6ꢁ),
as a dark red solid (271 mg, 84%), which was identical in all
respects to the sample derived from Method B.
Heteronuclear-Fe(II)Ru(II) hexameric macrocycle 15
A mixture of bisterpyridine ligand 14 (30 mg, 19 mmol) and
FeCl2 (3.8 mg, 1 eq.) in MeOH (30 mL) was refluxed for 12 h.
After the solvent was removed in vacuo, the residue was
chromatographed (SiO2) by eluting with
a H2O/KNO3
(conc.)/MeCN (1 : 1 : 10) solvent mixture. After removal of
the solvent in vacuo, the residue was washed with water,
dissolved in MeOH, and excess methanolic NH4PF6 was
added to precipitate the complex. The collected dark purple
solid was washed thoroughly with MeOH to afford the desired
hexameric macrocycle 15, as purple solid: 10.2 mg (36%);
1H NMR (CD3CN): d 9.25-9.20 [m, 36H, 30,50-tpy(Fe)H
and 30,50-tpy(7)H], 9.03 [s, 12H, 30,50-tpy(5)H], 8.85 [m, 24H,
3,30 0-tpy(Fe)H], 8.81 [s, 6H, 4-(7)ArH], 8.71 [d, J = 5 Hz, 12H,
3,30 0-tpy(7)H], 8.65 [m, 24H, 3,30 0-tpy(5)H and 2, 6-(7)ArH],
8.24 [d, J = 5 Hz, 12H, 2,6-(5)ArH], 7.99 [m, 48H, 4,40 0-tpy(5)H,
4,400-tpy(7)H, and 4,40 0-tpy(Fe)H], 7.55 [m, 36H, 6,60 0-tpy(Fe)H
and 3,5-(5)ArH] 7.34-7.17 [m, 72H, 6,60 0-tpy(7)H, 6,60 0-tpy(5)H,
5,500-tpy(7)H, 5,50 0-tpy(5)H, and 5,50 0-tpy(Fe)H], 3.99 [s, 18H,
(5)ArOCH3]; 13C NMR (CD3CN): d 162.95, 161.51, 159.41,
Method B. To a mixture of 12 (16 mg, 20 mmol) and 7 (7 mg,
20 mmol) in MeOH (10 mL), 2 drops of N-ethylmorpholine
was added. After refluxing for 12 h, the solution was concen-
trated in vacuo and the residue was chromatographed (SiO2)
by eluting with a H2O/KNO3(conc.)/MeCN (1 : 1 : 10) solvent
mixture to afford h5-Ru(II)-7i (13), which was treated with
methanolic NH4PF6 in order to prepare the desired 13 (PF6ꢁ),
as a dark red solid: 19.9 mg (77%); 1H NMR (CD3CN): d 8.98
[s, 2H, 30,50-tpy(7)H], 8.96 [s, 2H, 30,50-tpy(5)H], 8.65 [brd, 4H,
3,30 0-tpy(7)H and 3,30 0-tpy(5)H], 8.59 [s, 2H, 2,6-(7)ArH],
8.42 [s, 1H, 4-(7)ArH], 8.21 [d, J = 9 Hz, 2H, 2,6-(5)ArH],
c
2134 New J. Chem., 2011, 35, 2130–2135
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011

View Article Online
159.21, 158.45, 157.09, 156.30, 154.34, 153.60, 149.39, 146.68,
140.46, 140.16, 139.22, 137.39, 133.06, 130.34, 129.88, 128.85,
128.56, 126.42, 125.68, 125.30, 124.97, 122.95, 122.08, 116.16,
96.67, 89.31, 56.50; ESI MS 1480.6 (M-7PF6)7+, 1277.4
(M-8PF6)8+, 1119.5 (M-9PF6)9+, 992.9 (M-10PF6)10+, 889.6
23 G. T. Morgan and F. H. Burstall, J. Chem. Soc., 1931, 20.
24 G. Morgan and F. H. Burstall, J. Chem. Soc., 1937, 1649.
25 U. S. Schubert, H. Hofmeier and G. R. Newkome, Modern
Terpyridine Chemistry, Wiley-VCH, Weinheim, 2006.
26 U. S. Schubert, A. Winter and G. R. Newkome, Terpyridine-Based
Materials-For Catalytic, Optoelectronic and Life Science Applica-
tions, Wiley-VCH, Weinheim, 2011.
(M-11PF6)11+
, , ,
803.4 (M-12PF6)12+ 730.3 (M-13PF6)13+
27 P. Wang, C. N. Moorefield and G. R. Newkome, Angew. Chem.,
Int. Ed., 2005, 44, 1679.
667.9 (M-14PF6)14+
.
28 M. Soler, C. N. Moorefield and G. R. Newkome, Hexameric
Macrocyclic Architectures in Heterocyclic Chemistry, ed. A. R.
Katritzy, Elsevier, New York, 2010, vol. 101.
Acknowledgements
29 G. R. Newkome, T. J. Cho, C. N. Moorefield, G. R. Baker,
M. J. Saunders, R. Cush and P. S. Russo, Angew. Chem., Int.
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O. Lukoyanova, L. Echegoyen and G. R. Newkome, Chem.
Commun., 2005, 713.
We thank the generous support of the National Science
Foundation (DMR-0705015 and DMR-0812337), the Ohio
Board of Regents, and Mr Joshua Chavez for his summer
assistance.
31 S.-H. Hwang, P. Wang, C. N. Moorefield, L. A. Godı
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nez,
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New J. Chem., 2011, 35, 2130–2135 2135