Chelated Boronate–Imine and Boronate–Amine Complexes as Chiral Dopants for Nematic Liquid Crystals

Abstract

Enantiomerically and diastereomerically pure chelated boronate-imine complexes 5 and a library of boronate-amine complexes 8 have been synthesized by taking advantage of a modular concept based on aromatic aldehydes, aminoethanols and boronic acids. The configuration of the amine complexes 8 featuring stable stereogenic boron and nitrogen centers are assigned based upon crystal structure analyses of the representative compounds 8aaa and 8acj and the comparison of the CD spectra of all complexes 8. They serve as colorless, stable dopants for nematic liquid crystals and pro-

The Diaryl(oxy)methyl Group: More than an Innocent Bystander in Chiral Auxiliaries, Catalysts, and Dopants

“…These complexes were shown to contain configurationally stable stereogenic boron and nitrogen atoms. Their HTP values, as shown in Figure 12, were determined in the nematic phases 5‐CB and ZLI‐1840 69c. NMR spectroscopic studies in combination with crystal‐structure analyses led to the identification of two different types of host–guest interactions: Firstly, a π–π stacking between the aryl residue at the boron atom and the aryl group of the nematic compounds 42 and, secondly, a hydrogen bridge between the coordinated NH group and the nitrile group of the nematic compounds.…”

“…NMR spectroscopic studies in combination with crystal‐structure analyses led to the identification of two different types of host–guest interactions: Firstly, a π–π stacking between the aryl residue at the boron atom and the aryl group of the nematic compounds 42 and, secondly, a hydrogen bridge between the coordinated NH group and the nitrile group of the nematic compounds. This led to a model being proposed69c that correlates the sign of the induced helix (−) with the structure of the dopant, as determined by crystal‐structure analyses and known absolute configuration. It is assumed in this model that the arylboronic residue prevents the nematic compound from forming a stack towards the front side.…”

Iodo‐Functionalized Salicylideneimine‐Boron Complexes: Synthesis and Photosensitized Degradation of Organic Water Pollutants

“…The overlap of the empty p‐orbital of boron with the organic moieties in such compounds leads to the delocalization of the electron cloud and planarization of the π‐systems, thereby resulting in interesting photophysical properties. Several tri‐ and tetra‐coordinated boron compounds have been synthesized by the complexation of boron with organic ligands containing hetero atoms . Four‐coordinate boron compounds based on an imine scaffold are reported to have higher stability compared with tricoordinate boron compounds .…”

“…Severalt ri-andt etra-coordinated boron compounds have been synthesized by the complexation of boron with organic ligands containing hetero atoms. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Fourcoordinate boronc ompounds based on an imine scaffold are reported to have higher stabilityc ompared with tricoordinate boron compounds. [18] Although the luminescentp roperties of boranils are well documented, [18] the photosensitizationp rop-ertieso fs uch molecules have rarely been explored.…”

Stereogenic boron in 2-amino-1,1-diphenylethanol-based boronate–imine and amine complexes

“…By comparison, stereogenic tetrahedral-coordinated boron has been studied to a much lesser extent. This is partly because it was incorporated in a chiral environment generated by enantiomerically pure ligands [ 5 – 9 ] or counter-ions [ 10 ], although some of these complexes have been obtained in a diastereoselective manner [ 6 – 9 ]. On the other hand, enantiomerism at boron has been observed in acyclic tetra-coordinated complexes 1 [ 11 ] and 2 [ 12 ], in acyloxyboranes 3 [ 13 – 16 ] with electron with-drawing substituents X ( Scheme 1 ) that turned out to be crucial to the configurational stability at boron, and recently, in boronate complexes of boradiazaindacene [ 17 ].…”