Synthesis of functionalized diarylborinic 8-oxyquinolates via bimetallic boron–lithium intermediates

Recent Advances in the Synthesis of Borinic Acid Derivatives

Borinic acids [R2B(OH)] and their chelate derivatives are a subclass of organoborane compounds used in cross-coupling reactions, catalysis, medicinal chemistry, polymer or optoelectronics materials. In this paper, we review the recent advances in the synthesis of diarylborinic acids and their four-coordinated analogs. The main strategies to build up borinic acids rely either on the addition of organometallic reagents to boranes (B(OR)3, BX3, aminoborane, arylboronic esters) or the reaction of triarylboranes with a ligand (diol, amino alcohol, etc.). After general practical considerations of borinic acids, an overview of the main synthetic methods, their scope and limitations is provided. We also discuss some mechanistic aspects.

Synthesis of tetraarylborates via tetralithio intermediates and the effect of polar functional groups and cations on their crystal structures

The synthesis and X-ray structural characterization of functionalized (COOH, CHO, C(O)NHtBu, B(OH)₂) tetraphenyl- and tetrakis(4′-biphenylyl)borates is reported.

Multicomponent syntheses of functional chromophores

Multicomponent reactions are a valuable tool for the synthesis of functional π-electron systems. Two different approaches can be taken into account for accessing the target structures. In the more conventional scaffold approach an already existing chromophore is coupled with other components to give a complex functional π-system. Here, electronically monotonous components can also be introduced, which may exert synergistic electronic effects within the novel compound. The more demanding chromophore concept generates a complete π-electron system and a scaffold concurrently. The latter approach is particularly stimulating for methodologists since π-systems might be accessible from simple starting materials. This review encompasses the advances in the preparation of functional π-electron systems via multicomponent processes during the past few years, based both on the scaffold and chromophore concepts. Besides the synthetic strategies the most important properties, i.e. redox potentials, absorption and emission maxima or fluorescence quantum yields, of the synthesized molecules are highlighted.

Tuning of the colour and chemical stability of model boranils: a strong effect of structural modifications

An improved approach to luminescent diphenylborinic complexes with functionalized salicydeneaniline ligands was developed. A strong effect of structural modifications on their stability and optical properties was established.

syn-1,2-carboboration of alkynes with borenium cations

The reaction of 8-(trimethylsiloxy)quinoline (QOTMS) with BCl₃ and (aryl)BCl₂ forms QOBCl₂ and QOBCl(aryl). The subsequent addition of stoichiometric AlCl₃ follows one of two paths, dependent on the steric demands of the QO ligand and the electrophilicity of the resulting borenium cation. The phenyl- and 5-hexylthienylborenium cations, QOBPh⁺ and QOBTh⁺, are formed, whereas QOBCl⁺ is not. Instead, AlCl₃ preferentially binds with QOBCl₂ at oxygen, forming QOBCl₂⋅AlCl₃, rather than abstracting chloride. A modest increase in the steric demands around oxygen, by installing a methyl group at the 7-position of the quinolato ligand, switches the reactivity with AlCl₃ back to chloride abstraction, allowing formation of QOBCl⁺. All the prepared borenium cations are highly chlorophilic and exhibit significant interaction with AlCl₄⁻ resulting in an equilibrium concentration of Lewis acidic “AlCl₃” species. The presence of “AlCl₃^” species limits the alkyne substrates compatible with these borenium systems, with reaction of [QOBPh][AlCl₄] with 1-pentyne exclusively yielding the cyclotrimerised product, 1,3,5-tripropylbenzene. In contrast, QOBPh⁺ and QOBTh⁺ systems effect the syn-1,2-carboboration of 3-hexyne. DFT calculations at the M06-2X/6-311G(d,p)/PCM(DCM) level confirm that the higher migratory aptitude of Ph versus Me leads to a lower barrier to 1,2-carboboration relative to 1,1-carboboration.

Charge transfer properties of two polymorphs of luminescent (2-fluoro-3-pyridyl)(2,2′-biphenyl)borinic 8-oxyquinolinate

First example of polymorphism and its impact on the charge transport properties of a model borinic quinolinate system.