Synthesis and stereochemistry of long-chain quinoxaline metallocyclophanes

Article abstract of DOI:10.1021/jo7021839

(Figure Presented) Condensation of 1,2-diamino-4,5-bis(n-alkoxy)arenes with an oligopyridyl-type α-diketone afforded a series of long-chain pyridine-quinoxaline hybrids. These were evaluated for their ability to self-assemble with tetrahedral Cu(I) and Ag

Full text of DOI:10.1021/jo7021839

Synthesis and Stereochemistry of Long-Chain Quinoxaline
Metallocyclophanes
Mark J. Howard,† Fenton R. Heirtzler,*,‡,§ and Sandra I. G. Dias‡
Chemical Laboratory, UniVersity of Kent, Canterbury, Kent, UK CT2 7NH, and Department of
Biosciences, UniVersity of Kent, Canterbury, Kent, UK CT2 7NJ
fentonh@ualberta.ca
ReceiVed October 16, 2007
Condensation of 1,2-diamino-4,5-bis(n-alkoxy)arenes with an oligopyridyl-type R-diketone afforded a
series of long-chain pyridine-quinoxaline hybrids. These were evaluated for their ability to self-assemble
with tetrahedral Cu(I) and Ag(I) to form dimeric, double-decker amphiphillic complexes having a flattened
metallocyclophane topology. Detailed NOESY and T1 relaxation time experimentation showed that the
configuration of the dicopper(I) complexes corresponds to inversion (meso) symmetry, which leads to an
extended molecular shape, wherein the alkoxy chains of the individual ligand components lie on opposite
sides of the metallocyclophane core, as opposed to the same side. Preliminary measurements show that
n
n
the disilver(I) complexes having C12H25 and C18H37 chains exhibit reversible melting processes and
undergo two endothermic transitions each, at 189/237 and 59/80 °C, respectively.
Introduction
ization along the stacking direction.7 This affords optical and
electronic device functionality for photocopiers, laser printers,
solar cells, organic light-emitting diodes, and field effect
transistors.8,9 The strategies employed by synthetic chemists to
achieve this ordering include expansion of π-conjugated surfaces
in extended arenes,1,5,10 chalcogen-chalcogen interactions
between main group heteroatoms,3,11 hydrogen-bonded net-
A face-to-face, π,π-stacked packing arrangement of arenes
is a key feature of organic materials for molecular electronics
applications.1-5 This geometry permits efficient intermolecular
overlap of parallel π-orbitals, which in turn facilitates one- and
two-dimensional charge carrier transport.4-6 Long-range, hier-
archical ordering on this basis may lead to electronic delocal-
(6) Curtis, M. D.; Cao, J.; Kampf, J. W. J. Am. Chem. Soc. 2004, 126,
4318-4328.
† Department of Biosciences.
(7) Kastler, M.; Pisula, W.; Laquai, F.; Kumar, A.; Davies, R. J.;
Baluschev, S.; Garcia-Gutierrez, M. C.; Wasserfallen, D.; Butt, H. J.; Riekel,
C.; Wegner, G.; Mu¨llen, K. AdV. Mat. 2006, 18, 2255-2259; Don Park,
Y.; Lim, J. A.; Lee, H. S.; Cho, K. Mater. Today 2007, 10, 46-54; Hoeben,
F. J. M.; Jonkheijm, P.; Meijer, E. W.; Schenning, A. P. H. J. Chem. ReV.
2005, 105, 1491-1546.
‡ Chemical Laboratory.
§ Current address: Department of Chemistry, University of Alberta, 11227
Saskatchewan Drive, Edmonton, Alberta T6G 2G2, Canada; Fax: +1-780 492-
8231.
(1) Anthony, J. E. Chem. ReV. 2006, 106, 5028-5048.
(2) Facchetti, A.; Yoon, M. H.; Marks, T. J. AdV. Mat. 2005, 17, 1705-
1725.
(3) Kobayashi, K.; Masu, H.; Shuto, A.; Yamaguchi, K. Chem. Mat. 2005,
17, 6666-6673.
(4) Moon, H.; Zeis, R.; Borkent, E. J.; Besnard, C.; Lovinger, A. J.;
Siegrist, T.; Kloc, C.; Bao, Z. J. Am. Chem. Soc. 2004, 126, 15322-15323.
(5) Wu, J. S.; Pisula, W.; Mu¨llen, K. Chem. ReV. 2007, 107, 718-747.
(8) Laschat, S.; Baro, A.; Steinke, N.; Giesselmann, F.; Ha¨gele, C.; Scalia,
G.; Judele, R.; Kapatsina, E.; Sauer, S.; Schreivogel, A.; Tosoni, M. Angew.
Chem., Int. Ed. 2007, 46, 4832-4887; Kumar, S. Chem. Soc. ReV. 2006,
35, 83-109.
(9) Pucci, D.; Barberio, G.; Bellusci, A.; Crispini, A.; Donnio, B.;
Giorgini, L.; Ghedini, M.; La Deda, M.; Szerb, E. D. Chem. Eur. J. 2006,
12, 6738-6747.
10.1021/jo7021839 CCC: $40.75 © 2008 American Chemical Society
Published on Web 03/12/2008
2548
J. Org. Chem. 2008, 73, 2548-2553

Long-Chain Quinoxaline Metallocyclophanes
works,12 self-assembly of metallocyclophanes13 or other posi-
tively charged coordination complexes,14 as well as long-range
association of amphiphillic molecules in solvophobic environ-
ments.15
The design of columnar liquid crystal arrays along the
preceding lines necessitates a combination of intercore attraction
and hydrophobic contacts between aliphatic chains16 to achieve
a molecular face-on orientation. The alkyl residues guarantee a
minimal spacing between the columns, such that interactions
between neighboring molecules within the same column are
much stronger than between neighboring columns.17 Metal-
lomesogens potentially unite the luminescent, charge-transport
and electrochemical properties of metal-containing compounds
with the order and mobility of the liquid crystalline state.18 Our
previous work showed that quinoxaline-pyridine hybrids like
1, 21, and related compounds19-21 self-assemble in the presence
of appropriate metal ions into π-stacked, double-decker com-
FIGURE 1. Previous (1) and current (2n) metallocyclophane ligands,
as well as the [2n Cu2]2+dications according to (a) C2- and (b) inversion
plexes [12Cu2][PF6]2 and [21 Cu2][PF6]2 in which inter- and
2
2
(meso) symmetry.
intramolecular stacking separations are identical.22 This is
significant, since the charge-transport or luminescent properties
of copper(I) and silver(I) complexes are appropriate for pho-
tonic-based applications.23 Also, we anticipate that the extension
of this self-assembly motif will lead to long alkyl chain
substituted mesogenic dicopper(I) compexessin spite of the
tetrahedral ligand field of those metal centers.9
material is available and shows the C2-symmetric form to be
1
preferred in the solid state.20,22 In solution, H and 13C NMR
spectroscopy indicate the aromatic shifts of both forms to be
coincident at all temperatures.19 In this report, we consequently
document the synthesis of such long-chain ligands and their
metallocyclophane complexes, in addition to assignment of their
solution-state stereochemistry, and provide an initial description
of their thermotropic behavior.
These goals must take into account metallocyclophane
diastereomerism; in principle, our metallocyclophanes may exist
as either a C2-symmetric or ∆,Λ/Λ,∆-meso-configurational
isomers.19 (Figure 1). Depending on the size of the alkoxy
groups tethered to the heteroarene core, drastic differences in
the molecular dimensions and dipoles of the metallocyclophane
dication may exist. Distinguishing the diastereomers, or even
identifying a dynamically equilibriating mixture thereof, usually
depends on X-ray single-crystal determination, when crystalline
Results and Discussion
The preparation of the target molecules necessitated 1,2-
diamino-4,5-bis(n-alkoxy) arenes 3n (n ) 6, 12, and 18), and
Scheme 1 reports their syntheses. Thus, alkylation of catechol
with the corresponding alkyl bromines either in (a) acetone with
a catalytic amount of KI or (b) 2-butanone and dibenzo-18-
crown-6 ether as catalyst afforded the diethers in respectable
yields (Table 1). The nitration of 3n, using nitric acid/acetic
acid in dichloromethane, efficiently provided the matching
dinitro-ethers 4n (n ) 6, 12, and 18; see Table 2). The reduction
of 4n to the diamino diethers 5n (n ) 6, 12, and 18), availed
itself of hydrazine hydrate and 5% palladium on charcoal. In
agreement with findings from the literature,24,25 the diamines
(10) Payne, M. M.; Parkin, S. R.; Anthony, J. E. J. Am. Chem. Soc.
2005, 127, 8028-8029; Zhu, S. S.; Swager, T. M. J. Am. Chem. Soc. 1997,
119, 12568-12577.
(11) Briseno, A. L.; Miao, Q.; Ling, M. M.; Reese, C.; Meng, H.; Bao,
Z.; Wudl, F. J. Am. Chem. Soc. 2006, 128, 15576-15577; Mas-Torrent,
M.; Rovira, C. J. Mater. Chem. 2006, 16, 433-436.
(12) Sokolov, A. N.; Friscic, T.; MacGillivray, L. R. J. Am. Chem. Soc.
2006, 128, 2806-2807; Gearba, R. I.; Lehmann, M.; Levin, J.; Ivanov, D.
A.; Koch, M. H. J.; Barbera, J.; Debije, M. G.; Piris, J.; Geerts, Y. H. AdV.
Mater. 2003, 15, 1614-1618; Schenning, A. P. H. J.; Jonkheijm, P.; Peeters,
E.; Meijer, E. W. J. Am. Chem. Soc. 2001, 123, 409-416; Lin, C. H.; Tour,
J. J. Org. Chem. 2002, 67, 7761-7768.
TABLE 1. Yields of Catechol Diethers 3n According to Synthetic
Methoda
(13) Nohra, B.; Graule, S.; Lescop, C.; Re´au, R. J. Am. Chem. Soc. 2006,
128, 3520-3521; Huang, P. H.; Lin, J. T.; Yeh, M. C. P. J. Organomet.
Chem. 2006, 691, 975-982; Dinolfo, P. H.; Coropceanu, V.; Bredas, J. L.;
Hupp, J. T. J. Am. Chem. Soc. 2006, 128, 12592-12593; Ghedini, M.;
Pucci, D.; Crispini, A.; Aiello, I.; Barigelletti, F.; Gessi, A.; Francescangeli,
O. Appl. Organomet. Chem. 1999, 13, 565-581.
n ) 6 (%)
n ) 12 (%)
n ) 18 (%)
method a
method b
64
-
22
57
5
79
a See Scheme 1 for details of synthetic method.
(14) Zheng, S. L.; Zhang, J. P.; Wong, W. T.; Chen, X. M. J. Am. Chem.
Soc. 2003, 125, 6882-6883; Gregg, D. J.; Fitchett, C. M.; Draper, S. M.
Chem. Commun. 2006, 3090-3092.
TABLE 2. Yields of Dinitrodiethers 4n and
(15) Che, Y.; Datar, A.; Balakrishnan, K.; Zang, L. J. Am. Chem. Soc.
2007, 129, 7234-7235.
Oligopyridine-quinoxaline Diethers 2n a
(16) Collings, P. J.; Hird, M. Introduction to Liquid Crystals; Taylor
and Francis: London, 1997.
n ) 6 (%)
n ) 12 (%)
n ) 18 (%)
4n
2n
75
71
73
74
80
37
(17) Kumar, S. Liq. Cryst. 2004, 31, 1037-1059.
(18) Binnemans, K. Chem. ReV. 2005, 105, 4148-4204.
(19) Cragg, P. J.; Heirtzler, F. R.; Howard, M. J.; Prokes, I.; Weyher-
mu¨ller, T. Chem. Commun. 2004, 280-281.
a See Scheme 1 for reaction details.
(20) Bark, T.; Weyhermu¨ller, T.; Heirtzler, F. Chem. Commun. 1998,
1475-1476.
(21) Heirtzler, F.; Weyhermu¨ller, T. J. Chem. Soc., Dalton Trans. 1997,
3653-3654.
(24) Ong, C. W.; Liao, S. C.; Chang, T. H.; Hsu, H. F. J. Org. Chem.
2004, 69, 3181-3185.
(25) Antonisse, M. M. G.; Snellink-Ruel, B. H. M.; Yigit, I.; Engbersen,
J. F. J.; Reinhoudt, D. N. J. Org. Chem. 1997, 62, 9034-9038.
(22) Heirtzler, F.; Dias, S. I. G.; Neuburger, M. Eur. J. Inorg. Chem.
2004, 685-688.
(23) Xu, Z. T. Coord. Chem. ReV. 2006, 250, 2745-2757.
J. Org. Chem, Vol. 73, No. 7, 2008 2549

Howard et al.
SCHEME 1. Synthesis of Oligopyridine-Quinoxaline Diethers 26, 212, and 218
56 and 512 and, by analogy, 518 are air-sensitive materials; thus,
they were used immediately upon preparation, and merely
preliminary characterization is reported. Subsequently, conden-
sation of 5n with R-diketone26 6 in acetic acid/ethanol produced
2n (n ) 6, 12, and 18) in moderate to good yields (Table 2).
[2182Cu2][PF6]2 is very poorly soluble in acetonitrile (proton
NMR spectra of this compound were only suitable after
overnight data collection).
The aromatic regions of these compounds’ 1H NMR spectra
are presented in Figure 2. Whereas only [2122Cu2][PF6]2 has
been completely assigned using two-dimensional methods, the
1
The results of H- and 13C NMR, IR, UV-vis, and EI-MS
spectroscopic characterization of 2n are in accord with their
anticipated structures. In all cases, 2n displayed clean melting
points; no secondary endothermic processes were observed.
Treatment of 2n with one equivalent of copper(I)tetrakis-
(acetonitrile) hexafluorophosphate in degassed methanol and at
ambient temperature gave purple- or brown-colored solutions,
from which the complexes were deposited in quantitative yields.
The results of these materials’ combustion analyses bespoke a
1:1 metal/ligand ratio, and their ESI-MS spectra contained peaks
corresponding to successive loss of two PF6- ions or one metal
aromatic shifts from [26 Cu2][PF6]2 and [2182Cu2][PF6]2 closely
2
correspond to those of the dodecyl-substituted complex as well
as related compounds.19,20,22 Their spectra also display the
shielding effects that are particular to this family of dicopper-
(I) metallocyclophanes:19,20,22 the protons adjacent to the alkoxy
substitution points (H-5 and H-8) appear ∼0.7 ppm upfield,
relative to the bare ligands, and the resonance of H-3′′ on the
stacked pyridine ring is shielded from an edge-on interaction
with the 2,6′-bipyridyl group of the same ligand equivalent. The
-OCH2- methylene protons exhibit diastereotopic splitting, as
is to be expected from their proximity to stereogenic, tetrahedral
Cu(I) centers. Hence, there is no real uncertainty regarding the
center; these findings agreed with their formulation as [2n Cu2]-
2
[PF6]2. The solubility of these complexes in polar solvents
expectedly drops with increasing alkyl chain length of 2n;
1
FIGURE 2. Overlap plot of H NMR spectra of [2n Cu2][PF6]2 (n ) 6, 12, and 18); recorded at 270 MHz in acetonitrile-d3.
2
2550 J. Org. Chem., Vol. 73, No. 7, 2008

Long-Chain Quinoxaline Metallocyclophanes
FIGURE 3. NOESY spectrum of [2122Cu2][PF6]2 (CD3CN, 600 MHz; mixing time of 2 s).
existence of the metallocyclophane cores in all three compounds.
The aromatic shifts of these complexes display no concentration
dependence.
relaxation times of [2122Cu2][PF6]2 using the inversion-recovery
method at 600 MHz. The values thereby obtained indicated a
significant difference between the opposite ends of the dode-
cyloxy chains, which is consistent with ∆,Λ/Λ,∆-[2122Cu2][PF6]2
(Figure 4). This consistency stems from the anisotropic structure
of this complex, which allows a visual estimate for the T1 values
of the methylene protons. We would expect an increase in T1
with distance from the principal axis of rotation passing through
the long axis of the molecule, and this is indeed what is observed
following resonance assignment.
Examination of molecular models indicates that the lengths
of ∆,∆/Λ,Λ- and ∆,Λ/Λ,∆-configurations for [2122Cu2][PF6]2
should be ∼23 and 44 Å, respectively. To investigate these
configurational preferences, two-dimensional NOE correlation
experiments were carried out on [2122Cu2][PF6]2 (Figure 3).
Numerous short-range, through-space interactions are evident
between the flanking 2,2′-bipyridyl groups and the pyridyl
quinoxaline “decks” of [2122Cu2][PF6]2; these are anticipated
to be present in either of the two conceivable dimeric complex
stereochemistries. However, these studies also revealed a close
contact between H-5′′ of the solitary “deck” pyridyl ring and
H-8 on the quinoxaline ring, and this is only consistent with
meso-[2122Cu2][PF6]2 (cf. Figure 1).
Another important difference between the structures of the
∆,∆/Λ,Λ- and ∆,Λ/Λ,∆-configurations for [2122Cu2][PF6]2
relates to the location of methylene protons on the alkoxy chain
of the ligand relative to the principal (short) axis. In a
hypothetical ∆,∆/Λ,Λ-configuration, the methylene protons
adjacent to the alkoxy-chain termini are at opposite ends to the
complex dication as those next to the metallocyclophane core.
In the ∆,Λ/Λ,∆-configuration, the latter set of protons are
instead adjacent to the center of mass and the principal axis
(Figure 1). Thus, the rates of anisotropic tumblingsand thus
spin-lattice relaxation times (T1)sfor both sets of protons
should be similar for a ∆,∆/Λ,Λ-configuration and dissimilar
for a ∆,Λ/Λ,∆-configuration.19,27 We therefore determined 1H T1
1
FIGURE 4. Assignment of H T1 relaxation times (s) for [2122Cu2]-
[PF6]2, determined at 600 MHz in acetonitrile-d3.
For preparation of the silver complexes of 2n, [2n Ag2][BF4]2,
(n ) 6, 12, and 18) treatment of the ligands with one equivalent
of silver tetrafluoroborate in methanol and at ambient temper-
ature gave yellow-colored solutions, which upon standing
2
J. Org. Chem, Vol. 73, No. 7, 2008 2551

Howard et al.
1
deposited the solid complexes in quantitative yields. The H
on the consequences of this phenomenon on the mesogenic
behavior of these, and other metallocyclophanes, in due course.
NMR spectra of these materials displayed only greatly exchange-
broadened chemical shifts and were therefore of little use in
assigning their structures. However, their IR spectra uniformly
showed absorptions at ν ≈ 1058 cm-1 from the B-F stretch of
BF4-. As well, their ESI-MS spectra were dominated by
fragmentation to form the [2n Ag2(BF4)]+, [2n Ag2]+, and [2n -
Experimental Section
1,2-Bis-dodecyloxy-benzene (312). Catechol (5.00 g, 45.4 mmol),
anhydrous K2CO3 (25.1 g, 182 mmol), 1-bromododecane (24.0 mL,
100 mmol), and dibenzo-18-crown-6 (0.5 g) in 2-butanone (250
mL) were heated overnight under reflux and N2. The mixture was
filtered hot and the solvent evaporated at reduced pressure.
Recrystallization (MeOH) afforded 312 as a white solid in 57% yield
(11.6 g, 25.9 mmol). Mp 43 °C (lit.:30 45-46 °C); Calcd for
C30H54O2: C, 80.65; H, 12.18. Found: C, 80.56; H, 12.38; EI-MS
(70 eV): m/z 446 ([M]+, 10%); 110 ([M - C24H48]+, 100%); IR
(KBr): 2918 (s, ArC-H), 2848 (C-H), 1593 (w, CdC), 1512 (m,
CdC), 1256 (s, C-O-C), 730 (m, C-H) cm-1; 1H NMR (CDCl3,
270 MHz): δ 6.88 (s, 4H), 3.98 (t, J ) 6.6, 6.9 Hz, 4H), 1.80 (m,
4H), 1.26 (m, 36H), 0.88 (t, J ) 6.3, 6.9 Hz, 6H); 13C NMR (CDCl3,
67.5 MHz): δ 149.3 (2C, C), 121.0 (2C, CH), 114.2 (2C, CH),
69.3 (2C, CH2), 31.9 (2C, CH2), 29.7 (2C, CH2), 29.4 (10C, CH2),
29.3 (2C, CH2), 26.1 (2C, CH2), 22.7 (2C, CH2), 14.1 (2C, CH3).
1,2-Bis-dodecyloxy-4,5-dinitro-benzene (412). HNO3 (3.5 mL,
69%) and fuming HNO3 (30 mL) were added to a solution of
benzene derivative 312 (4.50 g, 10.1 mmol) in AcOH (30 mL) over
2 h at 0 °C. The resulting orange solution was stirred for another
2 h at ambient temperature. The mixture was poured over an ice-
water mixture (1.5 L), the precipitate was collected by vacuum
filtration and washed with H2O. Recrystallization (EtOH) afforded
412 as a yellow solid in 73% yield (3.93 g, 7.32 mmol). Mp 80 °C
(lit.:24 81-82 °C); Calcd for C30H52N2O6: C, 67.13; H, 9.76; N,
5.22; Found: C, 68.58; H, 10.04; N, 5.18; EI-MS (70 eV): m/z
537 ([M]+, 10%), 201 ([M - C24H48]+, 30%); IR (KBr): 3068 (w,
ArC-H), 2918 (s, C-H), 1586 (m, CdC), 1537 (s, NdO), 1372
(s, NO2), 1230 (s, C-O-C), 871 (C-N), 751 (m, C-H), 664 (w,
C-H) cm-1; 1H NMR (CDCl3, 270 MHz): δ 7.29 (s, 2H), 4.09 (t,
J ) 6.3, 6.6 Hz, 4H), 1.87 (m, 4H), 1.26 (m, 36H), 0.88 (t, J )
6.6, 7.1 Hz, 6H); 13C NMR (CDCl3, 67.5 MHz): δ 151.7 (2C, C),
136.4 (2C, C), 107.8 (2C, CH), 70.2 (2C, CH2), 31.9 (2C, CH2),
29.6 (2C, CH2), 29.5 (2C, CH2), 29.4 (2C, CH2), 29.3 (2C, CH2),
29.2 (4C, CH2), 28.7 (2C, CH2), 25.8 (2C, CH2), 22.7 (2C, CH2),
14.1 (2C, CH3).
2
2
2
Ag]+ ions, and their combustion analyses furthermore support
dimeric structures.
A preliminary survey of all complexes’ thermotropic behavior
was undertaken using differential scanning calorimetry. For the
dicopper(I) complexes, [26 Cu2][PF6]2 decomposed directly from
2
the solid state before melting (Table 3). On the other hand, both
TABLE 3. Phase Transition Temperatures and Phase Transition
Enthalpies of Dicopper(I) and Disilver(I) Metallomesogens
Tmelt (°C)
Tdecomp (°C)
∆H (kJ mol-1
)
[26 Cu2][PF6]2
214
∼207
∼160
134
2
[2122Cu2][PF6]2
135
113
[2182Cu2][PF6]2
[26 Ag2][BF4]2
2
[2122Ag2][BF4]2
189
237
59
>250
-22.34
-12.16
-35.89
-20.98
[2182Ag2][BF4]2
>140
80
[2122Cu2][PF6]2 and [2182Cu2][PF6]2 reVersibly melted and
solidified below their decomposition temperatures. Among the
disilver(I) complexes, [26 Ag2][BF4]2 decomposed upon heating.
2
Intriguingly, [2122Ag2][BF4]2 and [2182Ag2][BF4]2 each under-
went two endothermic transitions before forming isotropic
phases, and these processes are likewise reversible. Currently,
we are not yet able to conclusively classify these intermediate
states according to traditional mesogen descriptors. However,
the overwhelming majority of silver(I)-containing mesogens
adapt either linear or bent geometries about the metal,28,29 with
few exceptions.29 Since our substances likely have tetrahedral
ligand fields, it is therefore not obvious that their states should
be comparable to those earlier substances.
1,2-Diamino-4,5-bis-dodecyloxy-benzene (512). Hydrazine mono-
hydrate (1.0 mL, 20 mmol) and palladium on carbon (0.2 g, 5%)
were added to a suspension of the dinitroarene 412 (0.30 g, 0.55
mmol) in EtOH (50 mL). The mixture was heated overnight under
reflux and N2. The hot solution was filtered through Celite and
under N2 to give the crude product 512 as a white solid in
Conclusions
The synthesis of quinoxaline-pyridine hybrids disubstituted
with long-chain alkoxy ethers has been demonstrated in three
cases. These compounds self-assemble with tetrahedral metals,
to form double-decker, hydrophobic metallocyclophanes. The
molecular symmetry of the dicopper(I) metallocyclophanes, and
by inference, that of their disilver(I) homologues, is character-
ized by inversion symmetry, which results in the alkoxy chains
lying on opposite sides of the metallocyclophane core. Formation
of a chiral (racemic) configuration, where the alkoxy chains lie
on the same side of the core, is apparently thwarted by steric
interactions between the alkoxy chains. We shall be reporting
1
quantitative yield (0.26 g). H NMR (CDCl3, 270 MHz): δ 6.38
(s, 2H), 3.88 (t, J ) 6.6 Hz, 4H), 1.74 (m, 4H), 1.27 (m, 36H),
0.88 (t, J ) 6.5, 6.9 Hz, 6H). This material was unstable in air and
was used immediately upon preparation.
2-(2,6′-Bipyrid-6′-yl-6,7-bis-dodecyloxy)-3-(pyrid-2-yl)-qui-
noxaline (212). Diamino diether 512 (0.47 g, 1.0 mmol) and AcOH
(2 mL) were added to R-diketone 6 (0.03 g, 1 mmol) in EtOH (15
mL). The mixture was heated overnight under reflux and N2. The
solution was cooled to ambient temperature, neutralized with a satd
aq NaHCO3 soln (10 mL), extracted with CH2Cl2 (3 × 20 mL),
and dried (MgSO4), and the solvent was evaporated at atmospheric
pressure. Column chromatography (EtOAc, alumina) and recrys-
tallization (MeOH) afforded 212 as white crystals in 74% yield (0.53
g, 0.74 mmol). Mp 87 °C; Calcd for C47H63N5O2: C, 77.33; H,
8.70; N, 9.59; Found: C, 77.21; H, 8.90; N, 9.27; EI-MS (70 eV):
m/z 729 ([M]·+, 30%), 560 ([M - C12H25]+, 50%), 392 ([M -
C24H50]+, 100%); IR (KBr): 2918 (ArC-H), 2848 (C-H), 1563
(m, CdN), 1496 (s, CdC), 1223 (s, C-O-C), 780 (m, C-H),
745 (m, C-H) cm-1; UV (CH3CN): λ (log ꢀ) 239 (4.48), 268
(26) Heirtzler, F. R. Synlett 1999, 1203-1206.
(27) Kemp, W. NMR in Chemistry: A Multinuclear Introduction;
MacMillan: London, 1986.
(28) Tolochko, B. P.; Chernov, S. V.; Nikitenko, S. G.; Whitcomb, D.
R. Nucl. Instrum. Methods Phys. Res., Sect. A 1998, 405, 428-434; Albeniz,
A. C.; Barbera, J.; Espinet, P.; Lequerica, M. C.; Levelut, A. M.; Lopez-
Marcos, F. J.; Serrano, J. L. Eur. J. Inorg. Chem. 2000, 133-138; Iida,
M.; Inoue, M.; Tanase, T.; Takeuchi, T.; Sugibayashi, M.; Ohta, K. Eur. J.
Inorg. Chem. 2004, 3920-3929; Lee, C. K.; Hsu, K. M.; Tsai, C. H.; Lai,
C. K.; Lin, I. J. B. Dalton Trans. 2004, 1120-1126; Bruce, D. W. Acc.
Chem. Res. 2000, 33, 831-840.
(29) Neve, F.; Ghedini, M.; Levelut, A. M.; Francescangeli, O. Chem.
Mater. 1994, 6, 70-76.
(30) Egri, J.; Halmos, J.; Rakoczi, J. Acta Chim. Acad. Sci. Hung. 1972,
73, 469-473.
2552 J. Org. Chem., Vol. 73, No. 7, 2008

Long-Chain Quinoxaline Metallocyclophanes
(4.44), 370 (4.14) nm; 1H NMR (CDCl3, 270 MHz): δ 8.76 (br d,
J6′′-5′′ ) 4.9 Hz; 1H; H6′′), 8.59-8.65 (m, 4H, H4′′, H3′′′); 8.36
(dd, J3′-5′′) 0.8, J3′-4′′) 7.5 Hz; 2H, H3′), 8.16-8.24 (m, 4H, H4′′′,
H6′′′), 7.56-7.66 (m, 4H, H4′′, H5′′′), 7.47 (br d, J6′′-5′′ ) 6.6 Hz,
2H, H6′′), 7.29 (d, J3′′-4′′ ) 8.1 Hz, 2H, H3′′), 7.19-7.26 (m, 2H,
H5′′), 6.69 (s, 2H, H8), 6.61 (s, 2H, H5), 3.96-4.02 (m, 8H, H2′′′′,
H2′′′′′), 3.70-3.79 (m, 4H, H1′′′′/H1′′′′′), 3.54-3.60 (m, 4H, H1′′′′′/
H1′′′′), 1.20-1.40 (m, 72 H), 0.82-0.94 (m, 12H); 13C NMR
(CDCl3, 67.5 MHz): δ 159.0 (1C, C), 156.4 (1C, C), 155.8 (1C,
C), 154.4 (1C, C), 153.3 (1C, C), 150.1 (1C, C), 149.1 (1C, C),
148.8 (1C, CH), 148.8 (1C, CH), 138.4 (2C, C), 137.7 (1C, C),
136.3 (1C, CH), 136.1 (2C, CH), 124.1 (1C, CH), 123.8 (1C, CH),
123.5 (1C, CH), 122.3 (1C, CH), 120.8 (1C, CH), 119.9 (1C, CH),
107.4 (1C, CH), 107.2 (1C, CH), 69.2 (2C, CH2), 31.9 (2C, CH2),
29.6 (6C, CH2), 29.3 (4C, CH2), 28.8 (4C, CH2), 26.0 (2C, CH2),
22.6 (2C, CH2), 14.1 (2C, CH3).
8.2 Hz, 2H, H5′/H3′), 8.62 (m, 4H, H4′, H3′′′), 8.37 (d, J3′-4′
)
7.4 Hz, 2H, H3′/H5′), 8.23 (m, 4H, H4′′′, H6′′′), 7.60 (m, 4H, H4′′,
H5′′′), 7.48 (br d, J6′′-5′′ ) 5.9 Hz, 2H, H6′′), 7.29 (m, 4H, H5′′,
H3′′), 6.68 (s, 2H, H5/H8), 6.60 (s, 2H, H8/H5), 3.99 (t, 8H, H1′′′′,
H1′′′′′) 3.72 (m, 2H, H2′′′′), 3.57 (m, 2H, H2′′′′), 2.13 (m, 4H,
H2′′′′′), 1.28 (m, 72H, H3′′′′/H11′′′′, H3′′′′′/H11′′′′′), 0.87 (m, 12H,
H12′′′′, H12′′′′′).
[2122Ag2][BF4]2. A solution of quinoxaline 212 (0.020 g, 0.027
mmol) in degassed MeOH (2 mL) under N2 was treated with solid
AgBF4 (0.005 g, 0.03 mmol). The yellow solution was stirred for
1 h, and the precipitated yellow solid was collected by vacuum
filtration, washed with MeOH, and dried under vacuum (P4O10).
Calcd for C94H126Ag2B2F8N10O4: C, 61.05; H, 6.87; N, 7.57;
Found: C, 60.35; H, 6.87; N, 7.55; ESI-MS: m/z 1568 ([2122Ag]+,
15%), 838 ([2122Ag2]2+, 90%); IR (KBr): 2923 (s, ArC-H), 2852
(s, C-H), 1592 (m, CdN), 1497 (s, CdC), 1224 (s, C-O-C),
1058 (s, B-F), 776 (m, C-H) cm-1; UV-vis (CH3CN): λ (log ꢀ)
234 (6.09), 272 (6.01), 372 (5.74) nm.
[2122Cu2][PF6]2. To a solution of quinoxaline 212 (0.020 g, 0.027
mmol) in degassed MeOH (5 mL) under N2 was added [Cu-
(MeCN)4][PF6] (0.010 g, 0.027 mmol). The solution was stirred at
ambient temperature, and after 5 min a solid precipitated. After 1
h the purple precipitate was collected by vacuum filtration, washed
Acknowledgment. We thank the Engineering and Physical
Sciences Research Council (EPSRC) for financial support (Grant
R/R09138) and Mr. K. Howland (Biosciences, University of
Kent) for technical assistance.
with MeOH and dried under vacuum (P4O10). The product [212
Cu2][PF6]2 was obtained in 93% yield. Calcd for C94H126
-
-
2
Cu2F12N10O4P2: C, 60.14; H, 6.76; N, 7.46. Found: C, 60.01; H,
6.80; N, 7.36; ESI-MS: m/z 993 ([2122Cu]+, 5%), 792 ([2122Cu2]2+
,
Supporting Information Available: Standard conditions, re-
maining detailed synthetic procedures, spectroscopic characteriza-
tion, and 1H/13C NMR spectra of selected compounds. This material
is available free of charge via the Internet at http:// pubs.acs.org.
25%), 730.8 ([212 - H]+, 100%); IR (KBr): 2920 (s, ArC-H), 2851
(m, C-H), 1596 (w, CdN), 1497 (s, CdC), 1222 (s, C-O-C),
841 (s, P-F), 780 (w, C-H), 557 (m, F-P-F) cm-1; UV-vis
(CH3CN): λ (log ꢀ) 241 (4.99), 281 (4.80), 381 (4.47), 483 (3.85),
1
582 (3.74) nm; H NMR (CD3CN, 270 MHz): δ 8.75 (d, J5′-4′
)
JO7021839
J. Org. Chem, Vol. 73, No. 7, 2008 2553