Synthesis and evaluation of molecular rotors with large and bulky tert-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 tert-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 7c 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 7c-d(4) by solid state (2)H NMR revealed a 2-fold motion of the 1,4-diethynylphenylene-d(4) rotator in the kHz regime.

4-[(E)-(4-Fluoro-benzyl-idene)amino]-benzoic acid.

In the title compound, C(14)H(10)FNO(2), the benzene rings make a dihedral angle of 57.50 (13)°, and the molecule has an E configuration about the C=N bond. In the crystal, molecules are linked via pairs of O-H⋯O hydrogen bonds, forming inversion dimers.

Facile preparation of [4.4]metacyclophane- and [5.5]paracyclophane-type macrocycles from arylboronic acids and salicylideneaminoaryl alcohols.

Four different salicylideneaminoaryl alcohols have been treated with arylboronic acids in order to prepare air-stable cyclophane-type macrocyclic systems. In two cases, this objective could be realized with the high-yield formation of [4.4]metacyclophane and [5.5]paracyclophane derivatives. The skeleton in these macrocycles is held together by two chiral boron atoms. In the other two cases, monomeric boronates or polymeric material were obtained. The title structures were characterized by spectroscopic techniques and X-ray crystallography. They show transannular C-H...O hydrogen bonding, but no intramolecular pi-pi interactions. A synthetic strategy for the preparation of further boron macrocycles is presented.

Preparation and structural characterization of three types of homo- and heterotrinuclear boron complexes: salen[[B-O-B][O2BOH]], salen[[B-O-B][O2BPh]], and salen[[B-O-B][O2P(O)Ph]].

Three types of homo- and heterotrinuclear boron complexes have been obtained in moderate to good yields from reactions of salen-type ligands with boric acid and combinations of boric acid with phenylboronic and phenylphosphonic acid. The products are air-stable and have relatively high melting points (>290 degrees C) but are poorly soluble or insoluble in common organic solvents. They have been characterized as far as possible by elemental analysis, mass spectrometry, IR, (1)H, (11)B, and (31)P NMR spectroscopy, and X-ray crystallography. Furthermore, theoretical calculations have been performed for representative examples to permit a complete comparison of the different structure types. A detailed analysis of the molecular structures showed that the complexes are constructed around a central B(3)O(3) or B(2)PO(3) ring. The salen ligands are attached to two boron atoms of these rings, which have therefore tetrahedral coordination geometries. The complexes contain seven- and eight-membered heterocycles of the B(2)C(n)ON(2) (n = 2, 3) type with chair or twisted-chair and boat-chair or chair-chair conformations, respectively. In the homotrinuclear complexes one of the three boron atoms is three-coordinate and can therefore still act as Lewis acid, thus making these products interesting for catalytic applications, e.g. in asymmetric synthesis. Depending on the substitutents attached to the boron atoms, these complexes show a relationship with either trimetaboric acid, boroxine, or the tetraborate dianion found in Borax.