One-pot synthesis of four-coordinate boron(III) complexes by the ligand-promoted organic group migration between boronic acids

Luminescent hexagonal microtubes prepared through water-induced self-assembly of a polymorphic organoboron compound: formation mechanism and waveguide behaviour

Tetra-coordinated organoboron (TCOB) compounds are promising candidates for developing high-performance optical devices due to their excellent optoelectronic performance. Fabricating TCOB-based nanomaterials of controlled and defined morphology through rapid and easy-to-execute protocols can significantly accelerate their practical utility in the aforesaid applications. Herein, we report water-induced self-assembly (WISA) to convert a polymorphic TCOB complex (HNBI-B, derived from a 2-(2'-hydroxy-naphthyl)-benzimidazole precursor) into two unique nanomorphologies viz. nanodiscoids (NDs) and fluorescent microtubes with hexagonal cross-sections (HMTs). Detailed electron microscopic investigations revealed that oriented assembly and fusion of the initially formed NDs yield the blue emissive HMTs (SSQY = 26.7%) that exhibited highly promising photophysical behaviour. For example, the HMTs outperformed all the crystal polymorphs of HNBI-B obtained from CHCl3, EtOAc and MeOH in emissivity and also exhibited superior waveguide behaviour, with a much lower optical loss coefficient α' = 1.692 dB mm-1 compared to the rod-shaped microcrystals of HNBI-B obtained from MeOH (α' = 1.853 dB mm-1). Thus, this work reports rapid access to high performance optical nanomaterials through WISA, opening new avenues for creating useful nanomaterial morphologies with superior optical performance.

Empowering boronic acids as hydroxyl synthons for aryne induced three-component coupling reactions

Boronic acids have become one of the most prevalent classes of reagents in modern organic synthesis, displaying various reactivity profiles via C-B bond cleavage. Herein, we describe the utilization of a readily available boronic acid as an efficient surrogate of hydroxide upon activation via fluoride complexation. The hitherto unknown aryne induced ring-opening reaction of cyclic sulfides and three-component coupling of fluoro-azaarenes are developed to exemplify the application value. Different from metal hydroxides or water, this novel hydroxy source displays mild activation conditions, great functionality tolerance and structural tunability, which shall engender a new synthetic paradigm and in a broad context offer new blueprints for organoboron chemistry. Detailed computational studies also recognize the fluoride activation mode, provide in-depth insights into the unprecedented mechanistic pathway and elucidate the reactivity difference of ArB(OH) x F y complexes, which fully support the experimental data.

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.

Recent Progress on Synthesis of N,N'-Chelate Organoboron Derivatives

N,N′-chelate organoboron compounds have been successfully applied in bioimaging, organic light-emitting diodes (OLEDs), functional polymer, photocatalyst, electroluminescent (EL) devices, and other science and technology areas. However, the concise and efficient synthetic methods become more and more significant for material science, biomedical research, or other practical science. Here, we summarized the organoboron-N,N′-chelate derivatives and showed the different routes of their syntheses. Traditional methods to synthesize N,N′-chelate organoboron compounds were mainly using bidentate ligand containing nitrogen reacting with trivalent boron reagents. In this review, we described a series of bidentate ligands, such as bipyridine, 2-(pyridin-2-yl)-1H-indole, 2-(5-methyl-1H-pyrrol-2-yl)quinoline, N-(quinolin-8-yl)acetamide, 1,10-phenanthroline, and diketopyrrolopyrrole (DPP).

Iodine-Catalyzed Synthesis of N,N'-Chelate Organoboron Aminoquinolate

We disclose a novel method for the synthesis of fluorescent N,N'-chelate organoboron compounds in high efficiency by treatment of aminoquinolates with NaBAr₄/R'COOH in the presence of an iodine catalyst. These compounds display high air and thermal stability. A possible catalytic mechanism based on the results of control experiments has been proposed. Fluorescence quantum yield of 3b is up to 0.79 in dichloromethane.

Reunderstanding the Fluorescent Behavior of Four-Coordinate Monoboron Complexes Containing Monoanionic Bidentate Ligands

We demonstrated for the first time that, at temperatures below the melting point of a given polar solvent, the emission of some four-coordinate monoboron complexes containing monoanionic bidentate (NO) ligands shifted to lower wavelengths, but no such shift was observed for studies conducted in nonpolar solvents. This means that the emission from a polar solvent appears at shorter wavelengths if compared with that from a nonpolar solvent when the measurement was performed at low temperatures, a phenomenon totally different from that observed for conventional solvatochromic fluorophores. The finding was rationalized by considering the temperature-dependent conformational relaxation of the tetrahedron monoboron complexes from their local excited (LE) state to their relaxed excited (RE) state. Further studies revealed that variating the structure of the chelating ligands could result in remarkable changes in the fluorescent colors of the monoboron complexes. However, changing the structure of other two monodentate ligands showed little effect upon the fluorescence property of the compounds. Therefore, it is anticipated that the monoboron complexes may be taken as a platform to construct a variety of functional molecular systems via alternating the structure of the chelating ligand and that of the monodentate ligand. As an example, naphthalene was introduced as a monodentate ligand, and independent emissions from naphthalene unit and the other part of the monoboron complex as well as intramolecular energy transfer between them were observed. It is believed that the present work provides a new insight into the monoboron complexes, laying the foundation for them to be explored for developing novel molecular systems.