Molecular gyroscope having a halogen-substituted p-phenylene rotator and silaalkane chain stators

Article abstract of DOI:10.1246/cl.2010.468

2,3-Halophenylene-bridged polysilaalkane macrocages lb and Ic were synthesized as novel molecular gyroscopes. X-ray crystallographic data showed that the structures of the macrocages were deformed to avoid contact between the halogens and the silaalkane cage. The 2,3-dichlorophenylene derivative 1c shows restricted rotation of the phenylene in solution as observed by variable temperature 1HNMR spectroscopy.

Full text of DOI:10.1246/cl.2010.468

doi:10.1246/cl.2010.468
468
Published on the web March 31, 2010
Molecular Gyroscope Having a Halogen-substituted p-Phenylene Rotator
and Silaalkane Chain Stators
Wataru Setaka,*1,3 Soichiro Ohmizu,2 and Mitsuo Kira*2
1Faculty of Pharmaceutical Sciences at Kagawa Campus, Tokushima Bunri University, 1314-1 Shido, Sanuki 769-2193
2Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578
3PRESTO, JST, 4-1-8 Honcho, Kawaguchi 332-0012
(Received February 22, 2010; CL-100172; E-mail: setaka@kph.bunri-u.ac.jp, mkira@m.tains.tohoku.ac.jp)
2,3-Halophenylene-bridged polysilaalkane macrocages 1b
si
si
siH
siH
si
siH
and 1c were synthesized as novel molecular gyroscopes. X-ray
crystallographic data showed that the structures of the macro-
cages were deformed to avoid contact between the halogens and
the silaalkane cage. The 2,3-dichlorophenylene derivative 1c
shows restricted rotation of the phenylene in solution as
Si
X
NaOH
H2O / DME
si = SiMe2
siH
siH
si
X
si
Si
siH
1
si
observed by variable temperature H NMR spectroscopy.
2a-2d
Macrocyclic molecules having bridged ³-electron systems
have attracted much attention in terms of their unique structures,
dynamics, and functions.1-5 Especially phenylene-bridged mac-
rocages are expected to have functions of gyroscopes and
compasses as first proposed by Garcia-Garibay et al.3 Recently,
such cage molecules were reported as molecular gyroscopes.3-5
We have applied polysilaalkane chains of novel cyclo-
phanes.2a,5 These chains are easily constructed, chemically
stable, and exhibit good crystallinity. Recently we reported the
synthesis and structure of a molecular gyroscope having a
bridged phenylene encased in a large silaalkane cage.5 Cage
compound 1a was found by X-ray crystallography to show
remarkable disorder at 30 °C. The phenylene ring was observed
at three positions around the threefold molecular axis, suggest-
ing the phenylene rotates around the axis even in crystals. We
report herein the synthesis and structure of 2,3-halophenylene-
bridged polysilaalkane macrocages 1b and 1c and reveal steric
effects on the structure and dynamics of the corresponding
macrocages.
si
si
si
si
si
si
O
O
si
si
Si
Si
Si
si
X
si
si
O
si
O
si
O
si
X
si
si
O
X
X
si
si
si
si
si
Si
si
si
si
1a; X = H, y. 38%5)
1b; X = F, y. 8%
1c; X = Cl, y. 6%
1d; X = Br, y. 0%
3a; X = H, y. 54%5)
3b; X = F, y. 24%
3c; X = Cl, y. 19%
3d; X = Br, y. 11%
Scheme 1.
The 2,3-halophenylene-bridged molecular gyroscopes were
synthesized by hydrolysis reactions of hydrosilanes 2a-2d
(Scheme 1).6,7 Statistically, the ratio of the formation of a cage
structure to its isomer is calculated to be 1:3; therefore, the yield
of the cage structure is lower than that of the isomer. In this
reaction, a remarkable dependence of the yields on the bulkiness
of the internal rotator was observed. The yields of the cage
compounds decreased with increasing atomic size of the
halogens on the rotator. Indeed, there was no observation of a
1,2-dibromophenylene-bridged molecular gyroscope 1d due to
the steric hindrance in the reaction. Compounds 1b and 1c were
identified by 1H, 29Si, and 13C NMR spectroscopy, and mass
spectrometry.
The molecular structures of the molecular gyroscopes 1b
and 1c were confirmed by X-ray crystallography (Figure 1).8 In
the 2,3-difluorophenylene-bridged molecular gyroscope 1b, the
shape of the frame was slightly deformed from that of the
phenylene-bridged derivative, and the molecule 1b has C2
symmetry. This deformation was most likely due to steric
hindrance of the fluorines on the phenylene ring. The phenylene
ring was observed at two positions around the molecular axis.
Figure 1. Molecular structure of (a) compound 1b at 0 °C and (b)
compound 1c at ¹120 °C. Left: equatorial view with 30% thermal
probability ellipsoid; Right: axial view. Hydrogen atoms and
structural disorder on the side chains are omitted for clarity.
Structural disorder of phenylene ring in 1b is shown, and ratio of
occupancy factor is 0.5:0.5.
Chem. Lett. 2010, 39, 468-469
© 2010 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

469
Cl
Sib
Sib
Sia
Sia
Sia'
Sib'
kex
kex
Si
Si
Si
Si
Si
Si
Cl
Si
Si
kex
Cl
Si
Si
Si
Si
Figure 3. Schematic representation of phenylene rotation in 1c.
References and Notes
1
a) V. Balzani, M. Venturi, A. Credi, Molecular Devices and Machines,
Wiley-VCH Verlag, Weinheim, Germany, 2003. b) Molecular Machines in
Topics in Current Chemistry, ed. by T. R. Kelley, Springer, New York,
2005. c) Modern Cyclophane Chemistry, ed. by R. Gleiter, H. Hopf, Wiley-
VCH Verlag, Weinheim, Germany, 2004. d) V. Balzani, A. Credi, F. M.
Raymo, J. F. Stoddart, Angew. Chem., Int. Ed. 2000, 39, 3348. e) G. S.
Kottas, L. I. Clarke, D. Horinek, J. Michl, Chem. Rev. 2005, 105, 1281. f)
M. A. Garcia-Garibay, Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 10771. g)
S. D. Karlen, M. A. Garcia-Garibay, Top. Curr. Chem. 2005, 262, 179. h)
T.-A. V. Khuong, J. E. Nuñez, C. E. Godinez, M. A. Garcia-Garibay, Acc.
Chem. Res. 2006, 39, 413.
Figure 2. Temperature dependence of 1H NMR spectra of 1c
(methyl region). Left: observed spectra. Right: spectra simulated
with designated exchange rate constants (kex).
The frame structure of the 2,3-dichlorophenylene-bridged
derivative 1c was significantly deformed and has no symmetry.
The silaalkane chains of the frame were separated from each
other to avoid steric contact between the chains and chlorines on
the phenylene. The phenylene ring was observed at only one
position around the molecular axis.
2
a) W. Setaka, K. Sato, A. Ohkubo, C. Kabuto, M. Kira, Chem. Lett. 2006,
35, 596. b) S. T. Phan, W. Setaka, M. Kira, Chem. Lett. 2007, 36, 1180. c)
S. T. Phan, W. Setaka, M. Kira, Chem. Lett. 2008, 37, 976. d) T. C. Bedard,
J. S. Moore, J. Am. Chem. Soc. 1995, 117, 10662. e) A. Lüttringhaus, H.
Simon, Justus Liebigs Ann. Chem. 1947, 557, 120. f) G. Schill, K. Rißler,
H. Frits, Chem. Ber. 1983, 116, 1866. g) G. Schill, H. Neubauer, Justus
Liebigs Ann. Chem. 1971, 750, 76.
a) J. E. Nuñez, A. Natarajan, S. I. Khan, M. A. Garcia-Garibay, Org. Lett.
2007, 9, 3559. b) Z. Dominguez, H. Dang, M. J. Strouse, M. A. Garcia-
Garibay, J. Am. Chem. Soc. 2002, 124, 7719. c) C. E. Godinez, G. Zepeda,
M. A. Garcia-Garibay, J. Am. Chem. Soc. 2002, 124, 4701.
a) T. Shima, F. Hampel, J. A. Gladysz, Angew. Chem., Int. Ed. 2004, 43,
5537. b) T. Shima, E. B. Bauer, F. Hampel, J. A. Gladysz, Dalton Trans.
2004, 1012. c) A. J. Nawara, T. Shima, F. Hampel, J. A. Gladysz, J. Am.
Chem. Soc. 2006, 128, 4962. d) L. Wang, F. Hampel, J. A. Gladysz, Angew.
Chem., Int. Ed. 2006, 45, 4372. e) L. Wang, T. Shima, F. Hampel, J. A.
Gladysz, Chem. Commun. 2006, 4075. f) G. D. Hess, F. Hampel, J. A.
Gladysz, Organometallics 2007, 26, 5129. g) K. Skopek, J. A. Gladysz,
J. Organomet. Chem. 2008, 693, 857. h) K. Skopek, M. Barbasiewicz, F.
Hampel, J. A. Gladysz, Inorg. Chem. 2008, 47, 3474.
Internal rotation of the phenylenes in solution is one of the
most important properties of molecular gyroscopes. The dy-
3
4
1
namic behavior of H NMR spectra of 1b and 1c in solution
were investigated. NMR spectra of 1b and 1c in solution at room
temperature (298 K) show only two methyl signals with a highly
symmetric (D3) pattern. This indicates that the phenylene group
of 1b and 1c rotates rapidly in solution. The two methyl signals
of the 2,3-difluorophenylene-bridged derivative 1b do not
change even at low temperature.7 However the two methyl
singlets in the 2,3-dichlorophenylene-bridged derivative 1c are
broadened with decreasing temperatures, coalesce at around
220 K, and then separate into six singlets at 193 K (Figure 2),
indicating the internal phenylene rotation is much slower than
5
6
W. Setaka, S. Ohmizu, C. Kabuto, M. Kira, Chem. Lett. 2007, 36, 1076.
1b: colorless crystals; mp 99-100 °C; 1H NMR (400 MHz, CDCl3): ¤
¹0.08 (s, 36H), 0.00 (s, 36H), 0.32-0.34 (m, 24H), 0.36-0.41 (m, 12H),
0.68-0.73 (m, 12H), 7.06 (s, 2H, aromatic protons); 13C NMR (100 MHz,
CDCl3): ¤ ¹4.3, ¹0.6, 4.8, 5.8, 6.9, 10.1, 127.0 (dd, 2JC-F = 16.3 Hz,
3JC-F = 10.6 Hz, aromatic C-H), 130.2 (dd, 3JC-F = 4JC-F = 6.6 Hz, Cipso),
154.1 (dd, 1JC-F = 245.6 Hz, 2JC-F = 18.1 Hz, C-F); 29Si NMR (79 MHz,
CDCl3): ¤ 5.4 (br), 5.7, 8.1; HRMS (ESI) calcd for C54H122Si14O3F2I,
1
the NMR time scale. The dynamic H NMR behavior of 1c is
explained by assuming a three-site exchange model as shown in
Figure 3. The exchange rate constants (kex) were determined by
line-shape analysis. The Eyring parameters for the exchange
determined using linear plots of ln(kex/T) vs. 1/T are ¦Hº =
¹
¹
1375.5182 ([M + I] ); found, 1375.5173 ([M + I] ). 1c: colorless crystals;
mp 86-87 °C; 1H NMR (400 MHz, CDCl3, 298 K): ¤ ¹0.08 (s, 36H), 0.00
(s, 36H), 0.29-0.37 (m, 36H), 0.74-0.82 (m, 12H), 7.25 (s, 2H); 13C NMR
(100 MHz, CDCl3, 298 K): ¤ ¹4.3, ¹0.5, 4.8, 6.0, 7.1, 10.2, 134.2, 138.7,
139.1; 29Si NMR (79 MHz, CDCl3, 298 K): ¤ 5.6, 7.9, 8.1; HRMS (ESI)
¹1
¹1
12.8 « 0.47 kcal mol and ¦Sº = ¹4.61 « 2.02 cal mol¹1 K
for 1c.7
In summary, 2,3-halophenylene-bridged polysilaalkane
macrocages 1b and 1c were synthesized as novel molecular
gyroscopes. Deformation of the frame structures in the crystal
and rate of the phenylene rotation in solution were dependent on
steric hindrance of the phenylene rotator with halogens.
m/z; calcd for
C
54H122Si14O3Cl2Na, 1303.5433 ([M + Na]+); found,
1303.5439 ([M + Na]+); Anal. Calcd for C54H124Si14O3Cl2: C, 50.53; H,
9.58%. Found: C, 50.23; H. 9.50%.
7
8
See the Supporting Information for the details of the synthesis of 1b and 1c,
temperature-dependent NMR data. Supporting Information is available
electronically on the CSJ-Journal Web site, http://www.csj.jp/journals/
chem-lett/index.html.
Crystal data for 1b (273 K): orthorhombic, space group Pbcn, R1 = 0.128
(I > 2·(I)), wR2 = 0.343 for all data, 9803 unique reflections. CCDC-
716908; Crystal data for 1c (150 K): monoclinic, space group P21,
R1 = 0.0556 (I > 2·(I)), wR2 = 0.1510 for all data, 9671 unique reflec-
tions. CCDC-716909.
This work was supported by the Ministry of Education,
Culture, Sports, Science and Technology of Japan [Grant-in-Aid
for Scientific Research on Specially Promoted Research (No.
17002005)].
Chem. Lett. 2010, 39, 468-469
© 2010 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/