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.

(2Sp,4R,8Sp)-4-Methyl-1-phenyl-diferroceno-5-Z-ethylene-1-phosphinoxide

We present a synthesis of the title compound, a homochiral diferroceno cycle intended for use in asymmetric catalysis. We present a hydrovinylation protocol, which allows the production of the title compound in two steps from a known diferrocenyl precursor. We obtained one of two possible diastereomers selectively and propose a plausible regio- and stereoselective reaction mechanism.

Voltammetric characterisation of diferrocenylborinic acid in organic solution and in aqueous media when immobilised into a titanate nanosheet film

Diferrocenylborinic acid (Fc₂BOH, 1) has been synthesized.

Triarylboron Anchored Luminescent Probes: Selective Detection and Imaging of Thiophenols in the Intracellular Environment

The advances in boron incorporated organics have captured overwhelming interest on account of their outstanding properties and promising applications in various fields. Mostly, triarylborane compounds (TAB) are exploited as sensors of F^- and CN^- anions at the expense of the intrinsic Lewis acidic nature of boron. New molecular probes 1 and 2 for detection of toxic thiophenol were designed by conjugating highly fluorescent borylanilines with the luminescent quencher 2,4-dinitrobenzene based sulfonamides (DNBS), wherein the electrophilicity of the DNBS moiety has been modulated by fine-tuning the intrinsic Lewis acidity of boron. The interplay between PET (photoinduced electron transfer) and ICT have been employed for developing the TAB tethered turn-on fluorescent sensor for thiophenol with high selectivity for the first time. The newly developed probes showed very fast response toward thiophenol (within ∼5 min) with limits of detection (LOD) lying in the micromolar range, clearly pointing to their potential. Further, compounds 1 and 2 were explored for detecting thiophenol in the intracellular environment by discriminating biothiols. DFT and TD-DFT calculations were performed to support the sensing mechanism.

Frustrated Lewis pairs incorporating the bifunctional Lewis acid 1,1'-fc{B(C6F5)2}2: reactivity towards small molecules

Applications of the bifunctional ferrocenediyl Lewis acid 1,1'-fc{B(C₆F₅)₂}₂ in frustrated Lewis pair (FLP) chemistry are described. The coordination (or otherwise) of a range of sterically encumbered C-, N- and P-centred Lewis bases has been investigated, with lutidine, tetramethylpiperidine, PPh₃, P^tBu₃ and the expanded ring carbene 6Dipp being found to be sterically incapable of coordinate bond formation. The chemistry of a range of these FLPs in the presence of H₂O, NH₃, CO₂ and cyclohexylisocyanate (CyNCO) has been investigated, with the patterns of reactivity identified including simple coordination chemistry, E-H bond cleavage and C-B insertion.

Borinic Acid Polymer: Simplified Synthesis and Enzymatic Biofuel Cell Application

A simplified one-pot and less harmful method has been introduced for the synthesis of borinic acid monomer. The corresponding borinic acid polymer (PBA) has been prepared by reversible addition-fragmentation chain transfer polymerization. Property investigations confirm the characteristics of PBA as a new type of "smart material" in the field of thermo-responsive polymer. The potential application of PBA in the field of enzymatic biofuel cell has been illustrated with a wide open circuit potential of 0.92 V.

The Effect of Introducing B and N on Pyrolysis Process of High Ortho Novolac Resin

In this contribution, high ortho novolac resins modified with phenylboronic acid were synthesized. The thermal stability of novolac resins cured with hexamethylenetetramine (HMTA) and chemical states of B and N via a pyrolysis process were studied. For the cured o-novolac modified with phenylboronic acid, the temperature with maximum decomposition rate increased by 43.5 °C, and the char yield increased by 5.3% at 800 °C compared with cured o-novolac. Density functional theory (DFT) calculations show the existence of hydrogen bonding between N of HMTA and H of phenol in modified resin. Thus, N could still be found at high temperature and C=N structure could be formed via a pyrolysis process. B₂O₃ was obtained at 400 °C by the cleavage of B–O–C and B–C bonds and it reduces the oxygen loss which may take part in the formation of carbon oxides in the system. The melting B₂O₃ on the surface of the resin will prevent small molecules and carbon oxides from releasing. Moreover, introducing B into the system helps to decrease the interlayer distance and improve graphite structures via a pyrolysis process.

Thermo-responsive rheological behavior of borinic acid polymer in dilute solution

Borinic acid polymer is rheologically thermo-responsive in solution, which expands its application as a new type of “smart” polymer.

Thermo-responsive behavior of borinic acid polymers: experimental and molecular dynamics studies

The thermo-responsive properties of borinic acid polymers were investigated by experimental and molecular dynamics simulation studies. The homopolymer poly(styrylphenyl(tri-iso-propylphenyl)borinic acid) (PBA) exhibits an upper critical solution temperature (UCST) in polar organic solvents that is tunable over a wide temperature range by addition of small amounts of H2O. The UCST of a 1 mg mL(-1) PBA solution in DMSO can be adjusted from 20 to 100 °C by varying the H2O content from ∼0-2.5%, in DMF from 0 to 100 °C (∼3-17% H2O content), and in THF from 0 to 60 °C (∼4-19% H2O). The UCST increases almost linearly from the freezing point of the solvent with higher freezing point to the boiling point of the solvent with the lower boiling point. The mechanistic aspects of this process were investigated by molecular dynamics simulations. The latter indicate rapid and strong hydrogen-bond formation between BOH moieties and H2O molecules, which serve as crosslinkers to form an insoluble network. Our results suggest that borinic acid-containing polymers are promising as new "smart" materials, which display thermo-responsive properties that are tunable over a wide temperature range.

Extension of conjugation: probing anion binding strength and reporter mechanisms in (phenyl)cyclopentadienyl and indenyl receptors

Two families of novel organo-iron functionalized boranes have been developed for anion binding/detection. Synthetically simple phenylferrocene systems, while stable to air and moisture, possess similar binding affinities to FcBMes2 and no workable discrimination between F(-) and CN(-). In addition, reduced electronic communication between receptor and reporter sites brought about by a lack of conformational rigidity means that photochemical and electrochemical responses to anion binding are intrinsically weak. Receptors based on a more rigid indenyl framework are available in two steps from organic precursors (in ca. 50% yield), and feature intrinsically higher binding constants for F(-) and especially CN(-), consistent with the lower LUMO energies implied by extended conjugation. One such system, (4-dimesitylboryl-indenyl)cyclopentadienyl-iron(ii), can be shown to bind cyanide in protic media with an accompanying green to red/pink colour change. Extremely high selectivity over fluoride and hydroxide and a detection limit of ca. 10 ppm represent a highly desirable combination among borane derived cyanide receptors.

Borinic acid block copolymers: new building blocks for supramolecular assembly and sensory applications

Borinic acid functional groups were incorporated into block copolymers via RAFT polymerization and their supramolecular assembly and sensor applications were investigated.