Quadruply BN-Fused Tetrathia[8]circulenes with Flexible Frameworks: Synthesis,Structures and Properties

Quadruply BN-fused tetrathia[8]circulenes were synthesized through four-fold electrophilic borylation. The single-crystal X-ray diffraction analysis revealed that the BN-fused tetrathia[8]circulene with peripheral phenyl groups exhibits crystal polymorphism, in which the circulene core adopts both planar and saddle conformations in the solid state. The experimental and theoretical studies revealed that the weaker aromaticity of azaborine compared with benzene renders the flexibility of the BN-fused tetrathia[8]circulenes.     

Pd-Senphos Catalyzed trans-Selective Cyanoboration of 1,3-Enynes

The first trans-selective cyanoboration reaction of an alkyne, specifically a 1,3-enyne, is described. The reported palladium-catalyzed cyanoboration of 1,3-enynes is site-, regio-, and diastereoselective, and is uniquely enabled by the 1,4-azaborine-based Senphos ligand structure. Tetra-substituted alkenyl nitriles are obtained providing useful boron-dienenitrile building blocks that can be further functionalized. The utility of our method has been demonstrated with the synthesis of Satigrel, an anti-platelet aggregating agent.     

BN Heterosuperbenzenes: Synthesis and Properties

Replacement of C?C unit with its isoelectronic B?N unit in aromatics provides a new class of molecules with appealing properties, which have attracted great attention recently. In this Concept, we focus on BN‐substituted polycyclic aromatics with fused structures, and review their synthesis, photophysical, and redox properties, as well as their applications in organic electronics. We also present challenging synthetic targets, large BN‐ substituted polycyclic aromatics, such as regioregular BN heterosuperbenzenes, which can be viewed as BN‐doped nanographenes. Finally, we propose an atomically precise bottom‐up synthesis of structurally well‐defined BN‐doped graphenes.     

B2N2-Embedded Polycyclic Aromatic Hydrocarbons with Furan and Thiophene Derivatives Functionalized in Crossed Directions

A series of polycyclic aromatic hydrocarbons (PAHs), consisting of two pairs of BN units, have been designed and their synthesis has been achieved by electrophilic C−H borylation. Two conjugation extension directions can be found in these B₂N₂-embedded PAHs. The B₂N₂-containing backbone with shorter effective conjugation length is isoelectronic with diaryl-fused anthracene, whereas the second derivative, with longer effective conjugation length, is isoelectronic with bis(trans-arylvinyl)benzene. By incorporating different aryl groups, i.e., furyl, thienyl, benzo[b]furyl, and benzo[b]thienyl groups, into the two crossed directions of the B₂N₂-embedded PAHs, their electronic and optical properties have been comparatively investigated by photophysical, electrochemical, and theoretical approaches. It is found that both the substituents and their conjugation extension directions have significant effects on the aromatic and photophysical properties of the B₂N₂-embedded PAHs. The conjugation extension in the shorter backbone is more pronounced on the effective conjugation length than the longer backbone. Moreover, all the B₂N₂-embedded PAHs behave as both Lewis acids and Lewis bases, and reversible photoluminescence switching can be observed by simply neutralizing the added Lewis acid or Lewis base.     

BN‐Embedded Polycyclic Aromatic Hydrocarbon Oligomers: Synthesis,Aromaticity, and Reactivity

BN‐embedded oligomers with different pairs of BN units were synthesized by electrophilic borylation. Up to four pairs of BN units were incorporated in the large polycyclic aromatic hydrocarbons (PAHs). Their geometric, photophysical, electrochemical, and Lewis acidic properties were investigated by X‐ray crystallography, optical spectroscopy, and cyclic voltammetry. The B?N bonds show delocalized double‐bond characteristics and the conjugation can be extended through the trans‐orientated aromatic azaborine units. Calculations reveal the relatively lower aromaticity for the inner azaborine rings in the BN‐embedded PAH oligomers. The frontier orbitals of the longer oligomers are delocalized over the inner aromatic rings. Consequently, the inner moieties of the BN‐embedded PAH oligomers are more active than the outer parts. This is confirmed by a simple oxidation reaction, which has significant effects on the aromaticity and the intramolecular charge‐transfer interactions.     

Pd‐Senphos Catalyzed trans‐Selective Cyanoboration of 1,3‐Enynes

The first trans‐selective cyanoboration reaction of an alkyne, specifically a 1,3‐enyne, is described. The reported palladium‐catalyzed cyanoboration of 1,3‐enynes is site‐, regio‐, and diastereoselective, and is uniquely enabled by the 1,4‐azaborine‐based Senphos ligand structure. Tetra‐substituted alkenyl nitriles are obtained providing useful boron‐dienenitrile building blocks that can be further functionalized. The utility of our method has been demonstrated with the synthesis of Satigrel, an anti‐platelet aggregating agent.     

Diels–Alder Reactions of 1,2‐Azaborines

Diels–Alder reactions employing 1,2‐azaborine heterocycles as 1,3‐dienes are reported. Carbocyclic compounds with high stereochemical and functional complexity are produced, as exemplified by the straightforward two‐step synthesis of an amino allyl boronic ester bearing four contiguous stereocenters as a single diastereomer. Whereas electron‐deficient dienophiles undergo irreversible Diels–Alder reactions, a reversible Diels–Alder reaction with the less electron‐deficient methyl acrylate is observed. Both the N and the B substituent of the 1,2‐azaborine exert significant influence on the [4+2] cycloaddition reactivity as well as the aromatic character of the heterocycle. The experimentally determined thermodynamic parameters of the reversible Diels–Alder reaction between 1,2‐azaborines and methyl acrylate correlate with aromaticity trends and place 1,2‐azaborines approximately between furan and thiophene on the aromaticity scale.     

Computation and analysis of molecular Hartree—Fock momentum intracules

An efficient general algorithm for the computation of molecular momentum intracule densities from Hartree-Fock wavefunctions using Gaussian basis functions is described. The momentum intracules for a number of systems are examined, and comparison with their position space counterparts discussed.