Self-Assembled Molecular Gear: A 4:1 Complex of Rh(III)Cl Tetraarylporphyrin and Tetra(p-pyridyl)cavitand.
The components of a 4:1 mixture of Rh(III)Cl tetrakis(4-methylphenyl)porphyrin 1 and a bowl-shaped tetra(4-pyridyl)cavitand 4 self-assemble into a 4:1 complex 14•4 via Rh-pyridyl axial coordination bonds. The single-crystal X-ray diffraction analysis and variable-temperature (VT) (1)H NMR study of 14•4 indicated that 14•4 behaves as a quadruple interlocking gear with an inner space, wherein (i) four subunits-1 are gear wheels and four p-pyridyl groups in subunit-4 are axes of gear wheels, (ii) one subunit-1 and two adjacent subunits-1 interlock with one another cooperatively, and (iii) four subunits-1 in 14•4 rotate quickly at 298 K on the NMR time scale. Together, the extremely strong porphyrin-Rh-pyridyl axial coordination bond, the rigidity of the methylene-bridge cavitand as a scaffold of the pyridyl axes, and the cruciform arrangement of the interdigitating p-tolyl groups as the teeth moiety of the gear wheels in the assembling 14-unit make 14•4 function as a quadruple interlocking gear in solution. The gear function of 14•4 was also supported by the rotation behaviors of other 4:1 complexes: 24•4 and 34•4 obtained from Rh(III)Cl tetrakis[4-(4-methylphenyl)phenyl]porphyrin 2 or Rh(III)Cl tetrakis(3,5-dialkoxyphenyl)porphyrin 3 and 4 also served as quadruple interlocking gears, whereas 14•5 obtained from 1 and tetrakis[4-(4-pyridyl)phenyl]cavitand 5 did not behave as a gear. The results of activation parameters (ΔH(⧧), ΔS(⧧), and ΔG(⧧)) obtained from Eyring plots based on line-shape analysis of the VT (1)H NMR spectra of 14•4, 24•4, and 34•4 also support the interlocking rotation (geared coupled rotation) mechanism.
Department of Chemistry, Faculty of Science, Shizuoka University , 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan.
Munechika
M
Nakamura
Department of Chemistry, Faculty of Science, Shizuoka University , 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan.
Kazuki
K
Kishimoto
Department of Chemistry, Graduate School of Science, Kobe University , 1-1 Rokkodaicho, Nada-ku, Kobe 657-8501, Japan.
Yasuhiro
Y
Kobori
Department of Chemistry, Graduate School of Science, Kobe University , 1-1 Rokkodaicho, Nada-ku, Kobe 657-8501, Japan.
Tomoka
T
Abe
Bruker axs , 3-9-B Moriya, Kanagawa-ku, Yokohama 221-0022, Japan.
Kenji
K
Yoza
Department of Chemistry, Faculty of Science, Shizuoka University , 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan.
Kenji
K
Kobayashi