Synthesis and Characterization of New Boron Compounds Using Reaction of Diazonium Tetraphenylborate with Enaminoamides

A family of oxazaborines, diazaborinones, triazaborines, and triazaborinones was prepared by reaction of polarized ethylenes, such as β-enaminoamides, with 4-methylbenzenediazonium tetraphenylborates. The reaction conditions (stirring in CH2Cl2 at room temperature (Method A) or stirring with CH3COONa in CH2Cl2 at room temperature (Method B) or refluxing in the CH2Cl2/toluene mixture (Method C)) controlled the formation and relative content of these compounds in the reaction mixtures from one to three products. Substituted oxazaborines gradually rearranged into diazaborinones at 250 °C. The prepared compounds were characterized by 1H NMR, 13C NMR, IR, and UV–Vis spectroscopy, HRMS, or microanalysis. The structure of individual compounds was confirmed by 11B NMR, 15N NMR, 1D NOESY, and X-ray analysis. The mechanism of reaction of enaminoamides with 4-methylbenzenediazonium tetraphenylborate was proposed.

Effects of Glymes on the Distribution of Mg(B10H10) and Mg(B12H12) from the Thermolysis of Mg(BH4)2

We examined the effects of concentrations and identities of various glymes, from monoglyme up to tetraglyme, on H2 release from the thermolysis of Mg(BH4)2 at 160–200 °C for 8 h. 11B NMR analysis shows major products of Mg(B10H10) and Mg(B12H12); however, their relative ratio is highly dependent both on the identity and concentration of the glyme to Mg(BH4)2. Selective formation of Mg(B10H10) was observed with an equivalent of monoglyme and 0.25 equivalent of tetraglyme. However, thermolysis of Mg(BH4)2 in the presence of stoichiometric or greater equivalent of glymes can lead to unselective formation of Mg(B10H10) and Mg(B12H12) products or inhibition of H2 release.

Solid-State 11B NMR Studies of Coinage Metal Complexes Containing a Phosphine Substituted Diboraantracene Ligand

Transition metal interactions with Lewis acids (M→Z linkages) are fundamentally interesting and practically important. The most common Z-type ligands contain boron, which contains an NMR active 11B nucleus. We measured...

Anion recognition by anthracene appended ortho-aminomethylphenylboronic acid: a new PET based sensing mechanism

Interactions of anthracene appended ortho-aminomethylphenylboronic acid 1 with 20 organic and inorganic anions have been studied by fluorescence, 1H and 11B NMR titrations in DMSO. Carboxylate, phosphate and sulphate anions...

Surface-Controlled Conversion of Ammonia Borane from Boron Nitride

“One-pot regeneration”, which is simple regneneration method of ammonia borane (AB) using hydrazine and liquid ammonia, enables conversion of AB from hexagonal boron nitride (h-BN) after milling hydrogenation. Solution 11B-NMR revealed the presence of AB after NH3/N2H4 treatment of milled h-BN (BNHx) although the yield of AB was less than 5%. The conversion mechanism was clarified as B-H bonds on the h-BN surface created by ball-milling under hydrogen pressure have an ability to form AB, which was confirmed by Thermogravimetry-Residual Gas Analysis (TG-RGA) and Infrared (IR) analysis. The reaction routes are also the same as regeneration route of polyborazylene because intermediates of AB such as (B(NH2)3 and hydrazine borane were found by solution 11B-NMR after soaking BNHx in liquid NH3 and hydrazine, respectively. Because of the fact that all reactions proceed on the h-BN surface and no reaction proceeds when neat h-BN is treated, breaking of B3N3 ring structure and then creation of B-H bond is the key issue to increase conversion yield of AB.

H2 Evolution from H2O via O–H Oxidative Addition Across a 9,10-Diboraanthracene

The boron-centered water reactivity of the boroauride complex ([Au(B2P2)][K(18-c-6)]; (B2P2, 9,10-bis(2-(diisopropylphosphino)- phenyl)-9,10-dihydroboranthrene) and its corresponding twoelectron oxidized complex, Au(B2P2)Cl, are presented. The tolerance of Au(B2P2)Cl towards H2O was demonstrated and subsequent hydroxide/chloride exchange was acheived in the presence of H2O and triethylamine to afford Au(B2P2)OH. Au(B2P2)]Cl and [Au(B2P2)]OH are poor Lewis acids as judged by the Gutmann-Becket method, with [Au(B2P2)]OH displaying facile hydroxide exchange between B atoms of the DBA ring as evidenced by variable temperature 31P NMR and low temperature 1H and 11B NMR. The reaction of the reduced boroauride complex [Au(B2P2)]– with 1 equivalent of H2O produces a hydride/hydroxide product, [Au(B2P2)(H)(OH)]–, that, upon addition of a second equivalent of H2O, rapidly evolves H2 to yield the dihydroxide compound, [Au(B2P2)(OH)2]–. [Au(B2P2)]Cl can be regenerated from [Au(B2P2)(OH)2]– via HCl·Et2O, providing a synthetic cycle for H2 evolution from H2O enabled by O–H oxidative addition at a diboraanthracene unit.

H2 Evolution from H2O via O–H Oxidative Addition Across a 9,10-Diboraanthracene

The boron-centered water reactivity of the boroauride complex ([Au(B2P2)][K(18-c-6)]; (B2P2, 9,10-bis(2-(diisopropylphosphino)- phenyl)-9,10-dihydroboranthrene) and its corresponding twoelectron oxidized complex, Au(B2P2)Cl, are presented. The tolerance of Au(B2P2)Cl towards H2O was demonstrated and subsequent hydroxide/chloride exchange was acheived in the presence of H2O and triethylamine to afford Au(B2P2)OH. Au(B2P2)]Cl and [Au(B2P2)]OH are poor Lewis acids as judged by the Gutmann-Becket method, with [Au(B2P2)]OH displaying facile hydroxide exchange between B atoms of the DBA ring as evidenced by variable temperature 31P NMR and low temperature 1H and 11B NMR. The reaction of the reduced boroauride complex [Au(B2P2)]– with 1 equivalent of H2O produces a hydride/hydroxide product, [Au(B2P2)(H)(OH)]–, that, upon addition of a second equivalent of H2O, rapidly evolves H2 to yield the dihydroxide compound, [Au(B2P2)(OH)2]–. [Au(B2P2)]Cl can be regenerated from [Au(B2P2)(OH)2]– via HCl·Et2O, providing a synthetic cycle for H2 evolution from H2O enabled by O–H oxidative addition at a diboraanthracene unit.

Syntheses and Reactivity of New Zwitterionic Imidazolium Trihydridoborate and Triphenylborate Species

In this study, four new N-(alkyl/aryl)imidazolium-borates were prepared, and their deprotonation reactions were investigated. Addition of BH3•THF to N-benzylimidazoles and N-mesitylimidazoles leads to imidazolium-trihydridoborate adducts. Ammonium tetraphenylborate reacts with benzyl- or mesityl-imidazoles with the loss of one of the phenyl groups yielding the corresponding imidazolium-triphenylborates. Their authenticity was confirmed by CHN analysis, 1H-NMR, 13C-NMR, 11B-NMR, FT-IR spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). 3-Benzyl-imidazolium-1-yl)trihydridoborate, (HImBn)BH3, and (3-mesityl-imidazolium-1-yl)trihydridoborate, (HImMes)BH3, were also characterized by X-ray crystallography. The reactivity of these new compounds as carbene precursors in an effort to obtain borate-NHC complexes was investigated and a new carbene-borate adduct (which dimerizes) was obtained via a microwave-assisted procedure.

Isonitrile-Based Multicomponent Synthesis of β-Amino Boronic Acids as β-Lactamase Inhibitors

The application of various isonitrile-based multicomponent reactions to protected (2-oxoethyl)boronic acid (as the carbonyl component) is described. The Ugi reaction, both in the four components and in the four centers–three components versions, and the van Leusen reaction, proved effective at providing small libraries of MIDA-protected β-aminoboronic acids. The corresponding free β-aminoboronic acids, quantitatively recovered through basic mild deprotection, were found to be quite stable and were fully characterized, including by 11B-NMR spectroscopy. Single-crystal X-ray diffraction analysis, applied both to a MIDA-protected and a free β-aminoboronic acid derivative, provided evidence for different conformations in the solid-state. Finally, the antimicrobial activities of selected compounds were evaluated by measuring their minimal inhibitory concentration (MIC) values, and the binding mode of the most promising derivative on OXA-23 class D β-lactamase was predicted by a molecular modeling study.