Helicity in Self-Assembled H-Bonded Chains of Chiral CuII Complexes
FULL PAPER
phenoxyl)-2-pyridinecarbaldehyde (1.000 g, 3.54 mmol) followed
by the addition of solid sodium triacetoxyborohydride (0.902 g,
4.25 mmol). The resulting white suspension was stirred for 12 h un-
der nitrogen to give a yellow suspension, which was washed twice
with a saturated NaHCO3 solution (Ϸ 10 cm3), dried with magne-
sium sulfate and the solvent remove under vacuum to give the tetra-
hydropyranyl (THP)-protected precursor, THP-L1, as a viscous yel-
alternate in handedness parallel to the z-axis, so that each
helix is surrounded by six neighbours, two of the same han-
dedness and four of the opposite handedness.
Conclusion
1
low-brown oil (1.130 g). H NMR (CDCl3): δ = 7.93 (d, 2 H, Ar),
Three new helical copper() coordination polymers have
been prepared and characterised. These examples serve to
demonstrate that a weak inter-ion, noncovalent recognition
element, hydrogen bonds involving a phenol or water OH
group within the complex species, in concert with the chiral
twist of the complex cation is perfectly sufficient to cause
aggregation into spirals. Zigzag chains[7,8] of hydrogen-
bonded complexes alternating in chirality were not ob-
served in this work. In the three crystal structures, the spon-
taneous enantioselective self-assembly of the complexes
within each helix suggests a self-recognition process must
play a role in each crystallisation just as hydrogen bonding
between complimentary bases dictates DNA double strand
formation. Notably, the adjacent copper() complexes are
crystallographically inter-related by a 21 screw. Given the
weak directionality of the phenol OH···Cl–Cu or Cu–
7.67 (d, 1 H, py), 7.54 (t, 1 H, py), 7.33 (d, 1 H, py), 7.12 (d, 2 H,
Ar), 5.49 (m, 1 H, CH2), 3.92 (m, 2 H, CH2), 3.77 (s, 2 H, CH2),
3.62 (m, 2 H, CH2), 2.60 (m, 2 H, CH2CH2), 2.49 (m, 2 H,
CH2CH2), 2.35 (s, 3 H, CH3), 2.23 (s, 6 H, 2 CH3), 2.08 (m, 2 H,
CH2), 1.90 (m, 2 H, CH2) ppm. ESI-MS: m/z (%) = 370 (100)
[(THP)-L1 + H]+, 286 (10) [H2L]+. Removal of the THP protecting
group was effected by heating pyridinium p-toluenesulfonate
(75.3 mg, 0.30 mmol) and THP-L1 (1.105 g, 3.00 mmol) in ethanol
(50 cm3) at 60 °C for 6 h. The solvent was removed and the re-
sulting solid purified by column chromatography on silica gel with
dichloromethane as the eluent; the main yellow band afforded the
product, a clear light golden oil (0.810 g, 95%; Ͼ 98% purity by
1H NMR spectroscopy). 1H NMR (CDCl3): δ = 7.90 (d, 2 H, Ar),
7.68 (d, 1 H, py), 7.55 (t, 1 H, py), 7.33 (d, 1 H, py), 7.15 (d, 2 H,
Ar), 3.88 (m, 2 H, CH2), 2.70 (m, 4 H, CH2CH2), 2.38 (s, 9 H,
CH3) ppm. ESI-MS: m/z (%) = 286 (100) [H2L3]+. UV (CH3CN):
λmax (ε/dm3mol–1 cm–1) = 263 (12400), 284 nm (13400).
–
OH2···O (H2O or ClO4 ) hydrogen bonds, this is not sur-
N-4-(Hydroxybenzyl)methyl-N,NЈ,NЈ-trimethylethylenediamine
(HL2): The literature method[9] was adapted as follows. A mixture
of N,N,NЈ-trimethylethylenediamine (1.502 g, 14.73 mmol), 4-hy-
droxybenzaldehyde (1.800 g, 14.73 mmol), and sodium triacetoxy-
borohydride (3.751 g, 17.70 mmol), in 1,2-dichloroethane (70 cm3)
was stirred overnight for 16 h under nitrogen. The solvent was re-
moved to give an orange oil that partially dissolved in acetonitrile
(Ϸ 2×20 cm3) leaving an off-white solid that was removed by filter-
ing the solution through a short silica plug. Removal of the solvent
in vacuo gave the product as an orange-yellow oil (2.822 g, 92%;
prising – it is the simplest possible symmetry relationship
between the adjacent hydrogen-bonded complexes in a he-
lix. Likewise, a majority of the recently reported coordina-
tion polymer helices[7,8] align along a twofold screw axis.
The obvious implication, of course, is that a recognition
element(s) of greater complexity with inbuilt directionality
in the non-covalent interaction – i.e. more information con-
tent – is necessary for predictable self-assembly of helices of
higher symmetry.
1
1
Ϸ 95% purity by H NMR spectroscopy). H NMR (CDCl3): δ =
7.10 (d, 2 H, Ar), 6.80 (d, 2 H, Ar), 3.59 (s, 2 H, CH2), 2.92 (t, 2
H, CH2CH2), 2.79 (t, 2 H, CH2CH2), 2.52 (s, 6 H, CH3), 2.32 (s,
3 H, CH3); δC (CDCl3) 157.9 (Ar), 131.8 (Ar), 126.7 (Ar), 116.3
(Ar), 62.1 (CH2), 54.7 (CH2CH2), 52.0 (CH2CH2), 44.3 (CH3), 41.9
(CH3) ppm. ESI-MS: m/z (%) = 209 (100) [H2L2]+. UV (CH3CN):
λmax (ε/dm3mol–1 cm–1) = 278 (6200), 283 (5900), 314 nm (2900).
Experimental Section
General: 1H and 13C{1H} NMR spectra were recorded at 300 K
with a Bruker AC 300F spectrometer (300 MHz) operating at
300.13 MHz. Electrospray Ionisation (ESI) mass spectra were ac-
quired with a VG Quattro mass spectrometer operating with a cap-
illary voltage of 4 kV and a cone voltage of 30 V at 60 °C with a
feed solvent of CH3CN/water (1:1, v/v). Electronic spectra of the
complexes were recorded between 220 and 2000 nm with a CARY
5 spectrometer in the dual beam mode; solution spectra were re-
corded in sealed 1-cm quartz cuvettes and solid-state spectra were
recorded in reflectance mode on powdered samples. X-band EPR
spectra of both solids and frozen solutions and were recorded at
77 K (using a liquid nitrogen dewar) with a Bruker EMX 10 EPR
spectrometer. Elemental analyses for C, H and N were carried out
at the Australian National University Microanalytical Laboratory.
Prior to being sent for analysis, samples were dried at 40 °C for
48 h under vacuum (0.2 Torr) over phosphorus pentoxide.
N-2-Hydroxybenzylmethyl-N,NЈ,NЈ-trimethylethylenediamine
(HL3):[10] A mixture of N,N,NЈ-trimethylethylenediamine (1.530 g,
15.00 mmol), 2-hydroxybenzaldehyde (1.832 g, 14.99 mmol), and
sodium triacetoxyborohydride (3.820 g, 18.03 mmol), in 1,2-dichlo-
roethane (40 cm3) was stirred for 16 h under nitrogen. Workup as
for L1 afforded HL2; a straw-coloured oil (2.780 g, 89%; Ͼ 98%
1
1
purity by H NMR spectroscopy). H NMR (CDCl3): δ = 7.16 (t,
1 H, Ar), 7.00 (d, 1 H, Ar), 6.83 (d, 1 H, Ar), 6.77 (t, 1 H, Ar),
3.68 (s, 2 H, CH2), 2.74 (m, 4 H, CH2CH2), 2.42 (s, 6 H, CH3),
2.32 (s, 3 H, CH3) ppm 13C NMR (CDCl3): δ = 158.2 (Ar), 129.7
(Ar), 122.5 (Ar), 119.8 (Ar), 117.0 (Ar), 61.2 (CH2), 56.1
(CH2CH2), 53.3 (CH2CH2), 44.7 (CH3), 42.6 (CH3) ppm. ESI-MS:
m/z (%) = 209 (100) [H2L3]+. UV (CH3CN): λmax (ε/dm3mol–1 cm–1)
= 277 (6400), 330 nm (600).
Caution: Although no problems were encountered in the course of
this work, perchlorate salts are potentially explosive materials and
appropriate precautions should be taken when handling them.
[Cu(HL1)Cl2]2[CuCl4]: Methanol solutions, 5 cm3 each, of HL1
(140 mg, 0.49 mmol) and CuCl2 (66 mg, 0.49 mmol) were stirred
N-[6-(4-Hydroxyphenyl)-2-pyridylmethyl]-N,NЈ,NЈ-trimethylethyl- overnight. The resulting dark green solution when placed under
enediamine (HL1): A solution of N,N,NЈ-trimethylethylenediamine
(363 mg, 3.55 mmol) in 1,2-dichloroethane (15 cm3) was added to
a 1,2-dichloroethane (10 cm3) solution of 6-(2-tetrahydropyranyl-4-
diethyl ether produced a green precipitate, which was twice recrys-
tallised, firstly from dichloromethane/acetonitrile (3:1) under di-
ethyl ether and then from methanol/acetonitrile (1:1). This pro-
Eur. J. Inorg. Chem. 2006, 1190–1197
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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