Synthesis, Structure, and Local Molecular Dynamics for Crystalline Rotors Based on Hecogenin/Botogenin Steroidal Frameworks

The synthesis and solid-state characterization of a series of cyclic/acyclic molecular rotors derived from naturally occurring steroidal 12-oxosapogenins are described. The bridged molecular rotors with rigid steroidal frameworks were obtained by employing ring-closing metathesis (RCM) as a key step. The X-ray diffraction technique was employed for determination and refinement of the crystal and molecular structure of selected models giving good quality single crystals. In the case of the bridged hecogenin molecular rotor <b>11</b><i><b>E</b></i> for which poor quality crystals were obtained, an NMR crystallography approach was used for fine refinement of the structure. Solid state NMR spectroscopic techniques were applied for the study of local molecular dynamics of the featured acyclic/cyclic molecular rotors. Analysis of ¹³C principal components of chemical shift tensors and chemical shift anisotropy (CSA) as well as heteronuclear ¹H–¹³C dipolar couplings (DC) unambiguously proved that aromatic rings located in the space within the rigid steroidal framework both for cyclic and acyclic rotors are under kHz exchange regime. Experimental results were confirmed by theoretical calculations of rotation barrier on the density functional theory level. Small distinctions in the values of CSA and DC for the rotors under investigation are explained on the basis of differences in their molecular structures

Synthesis and Evaluation of Molecular Rotors with Large and Bulky <i>tert</i>-Butyldiphenylsilyloxy-Substituted Trityl Stators

The search for voluminous stators that may accommodate large rotator units and speed rotational dynamics in the solid state led us to investigate a simple and efficient method for the synthesis of molecular rotors with <i>tert-</i>butyldiphenylsilyl-protected (TBDPS) triphenylmethyl stators. Additionally, solid state characterization of these systems with two-, four-, and six-TBDPS groups provided us with a description of their crystallinity and thermal stability. Among them, molecular rotor <b>7c</b> with the largest and most symmetric stator resulting from six peripheral silyl groups showed the best tendency to crystallize, and the study of its isotopologue <b>7c</b>-<i>d</i>₄ by solid state ²H NMR revealed a 2-fold motion of the 1,4-diethynylphenylene-<i>d</i>₄ rotator in the kHz regime

Synthesis and Evaluation of Molecular Rotors with Large and Bulky <i>tert</i>-Butyldiphenylsilyloxy-Substituted Trityl Stators

The search for voluminous stators that may accommodate large rotator units and speed rotational dynamics in the solid state led us to investigate a simple and efficient method for the synthesis of molecular rotors with <i>tert-</i>butyldiphenylsilyl-protected (TBDPS) triphenylmethyl stators. Additionally, solid state characterization of these systems with two-, four-, and six-TBDPS groups provided us with a description of their crystallinity and thermal stability. Among them, molecular rotor <b>7c</b> with the largest and most symmetric stator resulting from six peripheral silyl groups showed the best tendency to crystallize, and the study of its isotopologue <b>7c</b>-<i>d</i>₄ by solid state ²H NMR revealed a 2-fold motion of the 1,4-diethynylphenylene-<i>d</i>₄ rotator in the kHz regime

Synthesis and Evaluation of Molecular Rotors with Large and Bulky <i>tert</i>-Butyldiphenylsilyloxy-Substituted Trityl Stators

The search for voluminous stators that may accommodate large rotator units and speed rotational dynamics in the solid state led us to investigate a simple and efficient method for the synthesis of molecular rotors with <i>tert-</i>butyldiphenylsilyl-protected (TBDPS) triphenylmethyl stators. Additionally, solid state characterization of these systems with two-, four-, and six-TBDPS groups provided us with a description of their crystallinity and thermal stability. Among them, molecular rotor <b>7c</b> with the largest and most symmetric stator resulting from six peripheral silyl groups showed the best tendency to crystallize, and the study of its isotopologue <b>7c</b>-<i>d</i>₄ by solid state ²H NMR revealed a 2-fold motion of the 1,4-diethynylphenylene-<i>d</i>₄ rotator in the kHz regime

Synthesis and Evaluation of Molecular Rotors with Large and Bulky <i>tert</i>-Butyldiphenylsilyloxy-Substituted Trityl Stators

The search for voluminous stators that may accommodate large rotator units and speed rotational dynamics in the solid state led us to investigate a simple and efficient method for the synthesis of molecular rotors with <i>tert-</i>butyldiphenylsilyl-protected (TBDPS) triphenylmethyl stators. Additionally, solid state characterization of these systems with two-, four-, and six-TBDPS groups provided us with a description of their crystallinity and thermal stability. Among them, molecular rotor <b>7c</b> with the largest and most symmetric stator resulting from six peripheral silyl groups showed the best tendency to crystallize, and the study of its isotopologue <b>7c</b>-<i>d</i>₄ by solid state ²H NMR revealed a 2-fold motion of the 1,4-diethynylphenylene-<i>d</i>₄ rotator in the kHz regime