Assemblage of Two Different Disk-Shaped Ligands
A R T I C L E S
Figure 6. Plausible mechanism for the relative rotational motion mediated by intramolecular metal-ligand exchange within the Ag31‚2 complex.
then heated at 90 °C for 3 h. After cooling, the colorless solution was
filtered to remove unreacted Ag2O and then evaporated. The resulting
colorless solid was washed with acetone to remove CH3SO3H and then
dried in vacuo to obtain AgCH3SO3 (3.18 g, 91%) as a colorless solid.
1H NMR (500 MHz, CD3OD) δ 2.71 (s); 13C NMR (125 MHz, CD3-
OD) δ 39.5.
(thiazolyl ring (1) from ligand 1 and (A) and (B) from ligand
2; see Figure 6) coordinate to an Ag+ ion with a trigonal
coordination geometry. The negative value of ∆Sq should be
due to the changes in the environment, i.e., solvent ordering
through hydrogen bonding to the complex, association of
counterions with the complex, and additional coordination of a
thiazolyl nitrogen donor to the neighboring Ag+ ion in the
transition state.10 Moreover, it is worth describing that the
metal-ligand exchange should give rise to the (P) a (M)
racemization accompanying a reversible 60°-rotational motion
between the coordinatively paired ligands. In the (P) isomer,
for instance, a thiazolyl ring (1) in ligand 1 and a thiazolyl ring
(B) in ligand 2 coordinate to an Ag+ ion and, after the (P) f
(M) conversion, the thiazolyl ring (A) exchanged by another
thiazolyl ring (B) through the 60° rotation around the helix axis
leading to the (M) isomer (Figure 6).
1,2-Bis(2-thiazolyl)ethylene (5). To a solution of CuI (21 mg, 0.11
mmol, 3 mol %), PdCl2(PPh3)2 (78 mg, 0.11 mmol, 3 mol %), and
2-bromothiazole (0.40 mL, 4.4 mmol) in Et3N (10 mL) was added
2-ethynylthiazole 4 (0.40 g, 3.7 mmol). The mixture was degassed and
heated at 70 °C for 12 h under a nitrogen atmosphere. The resulting
dark brown mixture was filtered, and the solvent was then removed in
vacuo. Purification by silica gel chromatography was performed
(n-hexane/AcOEt (10:1-4:1)) to obtain the desired coupling product
1
5 (226 mg, 32%) as a pale yellow solid: mp 143 °C; H NMR (500
MHz, CDCl3) δ 7.93 (d, J ) 3.5 Hz, 2H), 7.50 (d, J ) 3.5 Hz, 2H);
13C NMR (125 MHz, CDCl3) δ 146.9, 144.1, 122.1, 85.9; IR (KBr) ν
3130, 3100, 3060, 1460, 1360, 1320, 1250, 1130, 1080, 730 cm-1. MS
(ESI-TOF) m/z exact mass [M + Na]+ 214.9697, C8H4N2S2Na requires
214.9714.
Conclusion
In conclusion, the exclusive heterotopic assemblage was
accomplished by the quantitative formation of a heterotopic
Ag31‚2 complex. The reversible rotational motion between the
two ligands 1 and 2 placed in parallel takes place concertedly
through metal-ligand exchange at the three Ag+ ions. Such
intramolecular rotational motion between two different coun-
terparts would be applicable to the development of novel metal-
mediated molecular devices particularly for multicomponent-
based molecular machinery.
Hexa(2-thiazolyl)benzene (2). Co2(CO)8 (27 mg, 78 µmol, 15 mol
%) and 5 (100 mg, 0.52 mmol) in 1,4-dioxane (6.0 mL) were placed
in a sealed tube flask. The mixture was degassed and heated at 100 °C
for 10 h. The solvent was removed in vacuo. Purification by silica gel
column chromatography (CHCl3/CH3OH (50:1)) afforded the desired
2 (56 mg, 56%) as a colorless solid: mp 430 °C (dec); 1H NMR (500
MHz, DMSO-d6) δ 7.67 (d, J ) 3.3 Hz, 6H), 7.58 (d, J ) 3.3 Hz,
6H); 13C NMR (125 MHz, DMSO-d6) δ 161.7, 142.2, 136.8, 123.5;
IR (KBr) ν 3120, 3100, 3060, 1500, 1480, 1360, 1300, 1160, 1090,
1070, 1060, 960, 770, 740 cm-1. Anal. Calcd for C24H12N6S6: C, 49.98;
H, 2.10; N, 14.57. Found: C, 49.77; H, 2.25; N, 14.40.
Experimental Section
General. 2-Ethynylthiazole 4 was prepared according to the
literature.10 All ambient and variable-temperature 1H NMR spectra
were recorded on a Bruker DRX 500 (500 MHz) spectrometer using
TMS as the internal reference. Electrospray ionization-time-of-flight
(ESI-TOF) mass spectra were recorded on a Micromass LCT mass
spectrometer KB 201. IR spectra were recorded on a Jasco IR-Report
100. Melting points were measured on a Yanaco MP-500D.
Formation of Ag31‚2‚(CH3SO3)3 Complex. To a solution of
AgCH3SO3 (1.8 mg, 8.6 µmol) and 1 (3.4 mg, 5.8 µmol) in CD3OD
(0.4 mL) was added a solution of AgCH3SO3 (1.8 mg, 8.6 µmol)
and 2 (3.3 mg, 5.8 µmol) in CD3OD (0.4 mL), and the mixture
1
stood at room temperature for 5 min. Its H NMR spectrum showed
the quantitative formation of the Ag31‚2‚(CH3SO3)3 complex. 1H
NMR (500 MHz, CD3OD, 293 K) δ 7.90 (d, J ) 3.3 Hz, 6H), 7.80
(d, J ) 3.5 Hz, 3H), 7.66 (d, J ) 3.5 Hz, 3H), 7.64 (d, J ) 3.3 Hz,
6H), 7.50 (dd, J ) 1.7, 7.8 Hz, 3H), 7.00 (d, J ) 8.0 Hz, 3H),
6.83 (dd, J ) 1.7, 8.0 Hz, 3H), 6.67 (d, J ) 7.8 Hz, 3H), 2.68
(s, 9H), 2.23 (s, 9H); 13C NMR (125 MHz, CD3OD) δ 170.1,
165.2, 146.8, 144.5, 143.3, 140.6, 138.6, 135.2, 133.7, 131.9, 131.1,
130.8, 130.4, 126.6, 125.6, 39.6, 21.3; MS (ESI-TOF) (CH3OH)
AgCH3SO3. Ag2O (2.0 g, 8.6 mmol) was added to a solution of
CH3SO3H (1.1 mL, 17.3 mmol) in H2O (40 mL), and the solution was
(10) For a similar discussion on the negative entropy change of metal-ligand
exchange was recently reported, see: Kajiwara, T.; Yokozawa, S.; Ito, T.;
Iki, N.; Morohashi, N.; Miyano, S. Angew. Chem., Int. Ed. 2002, 41, 2076-
2078.
(11) Neenan, T. X.; Whitesides, G. M. J. Org. Chem. 1988, 53, 2489-2496.
9
J. AM. CHEM. SOC. VOL. 126, NO. 4, 2004 1217