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 Advances in Luminescent Annulated Borepins, Silepins, and Phosphepins

This review summarizes recent research on the molecular design, optical, and electronic properties of annulated borepins, silepins, and phosphepins, with emphasis on their structure–property relationships at the molecular level.

1 Introduction

2 Borepins

3 Silepins

4 Phosphepins

5 Summary and Outlook

Effect of the conjugation pathway on the electronic structures of p–π* conjugated polymers with fused borepin units

Borepin, an aromatic ring system with tricoordinate boron, was incorporated into p–π* conjugated polymers. The polymers exhibited characteristic optical responses upon the addition of cyanide anions in solution.

Extended conjugated borenium dimers via late stage functionalization of air-stable borepinium ions

Conjugated dimeric borenium ions exhibit red-shifted absorptions, enhanced emission, and dramatically lower LUMO energies.

Borepin Rings as "Sigma-Free" Reporters of Aromaticity within Polycyclic Aromatic Scaffolds

The definition and measurement of local and global aromaticity in fused ring polycyclic aromatic compounds is a complex issue. Historically, these types of molecules have been explored in this capacity by way of experimental (NMR, thermochemistry) and computational (NICS, HOMA) analyses. We previously showed how borepin rings with [ b, f] arene fusions can be used as experimental magnetic aromaticity reporters via the remaining protons attached to the borepin rings. In this report, we describe a joint experimental and computational analysis of several borepin-containing polycyclic aromatic molecules in order to draw conclusions about the influence of ring fusion on aromaticity. We find that the borepin ring within these extended structures is a unique motif with limited σ-contribution to aromaticity while still displaying a wide range of structural and magnetic aromatic character.

Ring fusion isomers of dithienoborepins: perturbations of electronic structure, aromaticity, and reactivity in boron-containing polycyclic heteroaromatics

Through a combination of rational design and synthetic serendipity, two new structural isomers of the dithienoborepin (DTB) architecture have been realized. Unlike previous members of this family, these boron-containing polycyclic aromatics are unsymmetrical with respect to the fusion orientation of the central borepin and flanking thiophene rings. Characterization of the unsymmetrical dithienoborepins through spectroscopic, crystallographic, electrochemical, and computational methods reveal that the electronics, aromaticity, and chemical reactivity can differ subtly (as for DTB 3) or in dramatic fashion (DTB 4) throughout the series, as dictated by the nature of the unique π-conjugation in each structure. Synthetic elaboration of the three most closely related DTB isomers (1, 2, and 3) into π-extended derivatives by Pd-catalyzed cross-couplings revealed an enhancement in their inherent electronic property differences, demonstrating the feasibility of such an approach for molecular property tuning.