Borate Complexes Research Articles

Rhenium Tris(pyrazolyl)borate Complexes with O-Donor Ligands: Synthesis and Structures

Rhenium Tris(pyrazolyl)borate Complexes with O-Donor Ligands: Synthesis and Structures

Influence of boron on the properties of basic magnesium sulfate cement

Magnesium hydroxide was calcined at different temperatures to prepare different active magnesia, and 3% and 5% B was added to the magnesia precursor to prepare basic magnesium sulfate cement (BMSC). The phase composition of the hydration products and the development of the pore structure were analysed to investigate the effect of the salt lake coexisting B impurity on the performance of BMSC. The results showed that the hydration rate of the BMSC prepared by adding B is slower, the setting and hardening times were longer, and the compressive strength was lower than those of the control group. Furthermore, B significantly affected the early compressive strength of the BMSC prepared using high-activity magnesium oxide. Mainly because the specific surface area of the magnesia calcined at a low temperature (700 °C) increased, the crystal grain size reduced, the degree of crystallinity reduced, and the number of internal defects increased. In the case of the magnesia obtained by calcining at a high temperature (1000 °C) and adding boric acid, a large number of rough magnesium borate complexes were formed on the surface, and the adjacent magnesium oxide continuously agglomerated and underwent sintering, which improved the degree of crystallinity and reduced the number of internal defects.

Towards Elucidating Structure-Spectra Relationships in Rhamnogalacturonan II: Computational Protocols for Accurate 13C and 1H Shifts for Apiose and Its Borate Esters.

Apiose is a naturally occurring, uncommon branched-chain pentose found in plant cell walls as part of the complex polysaccharide Rhamnogalacturonan II (RG-II). The structural elucidation of the three-dimensional structure of RG-II by nuclear magnetic resonance (NMR) spectroscopy is significantly complicated by the ability of apiose to cross-link via borate ester linkages to form RG-II dimers. Here, we developed a computational approach to gain insight into the structure–spectra relationships of apio–borate complexes in an effort to complement experimental assignments of NMR signals in RG-II. Our protocol involved structure optimizations using density functional theory (DFT) followed by isotropic magnetic shielding constant calculations using the gauge-invariant atomic orbital (GIAO) approach to predict chemical shifts. We evaluated the accuracy of 23 different functional–basis set (FBS) combinations with and without implicit solvation for predicting the experimental 1H and 13C shifts of a methyl apioside and its three borate derivatives. The computed NMR predictions were evaluated on the basis of the overall shift accuracy, relative shift ordering, and the ability to distinguish between dimers and monomers. We demonstrate that the consideration of implicit solvation during geometry optimizations in addition to the magnetic shielding constant calculations greatly increases the accuracy of NMR chemical shift predictions and can correctly reproduce the ordering of the 13C shifts and yield predictions that are, on average, within 1.50 ppm for 13C and 0.12 ppm for 1H shifts for apio–borate compounds.

Hydroboration reactions using transition metal borane and borate complexes: an overview.

In recent years, the chemistry of transition metal borane and borate complexes has advanced fast with reasonable growth. Frequent utilisation of these complexes in hydrofunctionalisation reactions is one of the key driving forces for their development. As a result, the important role of borate complexes in the hydroboration/hydrosilylation/hydroamination of unsaturated organic species has been successfully demonstrated together with the isolation of many different boron-containing transition metal complexes such as borataallyl, vinylborane, silyl complexes featuring the known bonding modes of boron. Both the uncatalysed and catalysed hydroboration reactions using the transition metal borane/borate complexes are known, which show these complexes' huge potential. Careful investigation and fine-tuning of the electronic and steric properties of the borane/borate ligands has facilitated the synthesis of these transition metal complexes which are convenient for use in the hydroboration reactions. Furthermore, the systematic development of this field has established the connection between the structure and reactivity of these complexes and their utilisation in hydroboration reactions. This Frontier sheds light on the recent developments that have been made with hydroboration reactions using transition metal borane/borate complexes. Also, in this Frontier we have provided meaningful synthetic methods to make new boron-containing transition metal complexes together with mechanistic insights for some of these reactions.

Ruthenium tris(σ-B-H) borate complexes: synthesis, structure, and reactivity.

The coordination of the B-H bond to a transition metal is fundamentally intriguing due to its connection with the transition metal-mediated B-H bond activation mechanism and catalysis. Most of the reported examples are σ-borane/borate complexes containing one or two σ-B-H bonds. However, examples of compounds containing three σ-B-H bonds are still much rarer. Herein, we report a facile approach for the synthesis of rare transition metal tris(σ-B-H) borate complexes by the salt elimination protocol using [Cp*RuCl]4 and lithium trihydroborates Li[ArBH3] containing 2,6-disubstituted aryl groups. These complexes have remarkable thermal stability in solution. In addition, this novel class of compounds has the unusual σ-complex that features three labile σ-B-H bonds. Our studies on these new species demonstrate that the coordination σ-B-H bond can undergo H/D exchange with D2 and ligand substitution reactions with PPh3, PCy3 and IPr2Me2. These results provide new approaches for the synthesis of both tris(σ-B-H) borates and bis(σ-B-H) borates.

Electrophilic and nucleophilic displacement reactions at the bridgehead borons of tris(pyridyl)borate scorpionate complexes.

Although a wide variety of boron-based "scorpionate" ligands have been implemented, a modular route that offers facile access to different substitution patterns at boron has yet to be developed. Here, we demonstrate new reactivity patterns at the bridgehead positions of a ruthenium tris(pyrid-2-yl)borate complex that allow for facile tuning of steric and electronic properties.

Chalcogen stabilized borate complexes of tantalum

In an attempt to isolate some electron precise early transition metal borate complexes, we have explored the reactions of [Cp*TaCl4] (Cp* = η5-C5Me5) with chalcogen-based borate ligand Li[BH3(SPh)]. The room-temperature reaction yielded bimetallic borate complex [(Cp*Ta)2(μ-SPh){S(BH3)}{SPh(BH3)}] (1) that present two types of borate ligands, i.e., {BH3(SPh)} and {BH3(S)} ligands having unique coordination with the tantalum atoms. Interestingly, the {BH3(S)} ligand is coordinated to both the Ta centers in µ-η1:η2 fashion. On the other hand, thermolysis of [Cp*TaCl4] in the presence of Li[BH3(SPh)] yielded a bimetallic borate species [(Cp*Ta)2(µ-η3:η3-B2H4S){µ-η2:η2-S(C6H4)BH3}] (2). Compound 2 contains a triborane analog and a borate ligand, which are coordinated to two Ta atoms. This can also be considered as a notable example of CH activated molecule, in which a B-C bond formation took place. Both the borate species have been characterized by mass spectrometry, IR spectroscopy, NMR spectroscopy, and single-crystal X-ray diffraction studies. The density functional theory (DFT) calculations further provided insights into the bonding and electronic structures of these bimetallic borate species.

The optimization of table beet cultivation by using a boron-containing chelate

In the field experiment, the possibility of optimizing the cultivation of table beet Beta vulgaris L. using a borate complex based on ethylenediamine disuccinic acid (B-EDDS) was investigated. Before sowing, beet seeds were soaked for a day in a solution of this compound, as well as in solutions of boric acid and a borate complex based on ethylenediaminetetraacetic acid (B-EDTA), taken for comparison, with a concentration of solutes of 1.5·10-3 mol/L. During the growing season, the plants were sprayed twice with experimental solutions at a rate of 100 ml/m2. In the first decade of August, the content of photosynthetic pigments in plant leaves and microbial carbon in the soil was determined, after harvesting, sugars and betanin in root crops were determined by spectrophotometric methods. The boron content in beet root crops was analyzed by the fluorometric method. According to the results of the two-year experiment, all three boron-containing compounds, to varying degrees, had a positive effect on the experimental plant. In decreasing efficiency, they can be arranged in a row: B-EDDS > H3BO3> B-EDTA. Treatment with the solution of borate-ethylenediamine disuccinate complex increased the boron content in root crops by 65% in comparison with treatment with boric acid. In comparison with the control variant, the sugar content in root crops increased by 37%, the content of betanin increased by 25% and the yield of root crops increased by 39%. At the same time, the mass of microbial carbon in the soil increased by 20%, which serves as one of the arguments confirming the ecological safety of the compound under study. Judging by the results of the experiment, borate-ethylenediamine disuccinate has good prospects for use as boron micronutrient fertilizer.

Boranils: Versatile Multifunctional Organic Fluorophores for Innovative Applications

Multifunctional stimuli-responsive fluorophores showing bright environment-sensitive emissions have fueled intense research due to their innovative applications in the fields of biotechnologies, optoelectronics, and materials. A strong structural diversity is observed among molecular materials, which has been enriched over the years with a growing responsiveness to stimuli. Boron dipyrromethene (BODIPY) dyes have long been the flagship of emissive boron complexes due to their outstanding properties until a decade ago when analogues based on N^O, N^N, or N^C π-conjugated chelates emerged. The finality of developing borate dyes was to compensate for BODIPYs’ lack of solid-state fluorescence and small Stokes shifts while keeping their excellent optical properties in solution. Among them, the borate complexes based on a salicylaldimine ligand, called by the acronym boranils appear as the most promising, owing to their facile synthesis and dual-state emission properties. Boranil dyes have proven to be good alternatives to BODIPY dyes and have been applied in applications such as bioimaging, bioconjugation, and detection of biosubstrates. Meanwhile, ab initio calculations have rationalized experimental results and provided insightful feedback for future designs. This review article aims at providing a concise yet representative overview of the chemistry around the boranil core with the subsequent applications.

The Study of Degradation of Complexones, Derivatives of Succinic Acid, and their Boron-Containing Complexes Under the Influence of Microbiological Preparations

The results of the study of the possibility of degradation of complexones, derivatives of succinic acid (CDSA), iminodisuccinic acid (IDSA), ethylenediaminedisuccinic acid (EDCSA), trans-1, 2-diaminocyclohexanedisuccinic acid (DCHDSA) and complexones taken for comparison, derivatives of iminodiacetic acid (IDSA) and ethylenediaminetetraacetic acid (EDTAA) under the influence of microbiological preparations “Baikal EM-1” and “Rhizoplane L”, as well as borate complexes of CDSA: B-IDSA, B-EDCSA and B-DCHDSA under the influence of the preparation Rhizoplane L at a temperature 22±1oC in an aqueous medium. It was found that within 4.5 months of the compounds taken for research under the action of Rhizoplane L preparation, B-IDSA was degraded to greatest extent (by 88%), and under the action of Baikal EM-1 preparation more than other degraded CDSA (by 86%) and EDTAA. Simultaneous destruction of DCHDSA and B-DCHDSA when exposed to the preparation taken for the experiment was not noted.

A Robust Vanadium(V) Tris(2-pyridyl)borate Catalyst for Long-Lived High-Temperature Ethylene Polymerization

Soluble vanadium catalysts are highly coveted for their selectivity in olefin polymerization. However, their utility is limited by rapid deactivation, especially at scalable temperatures under which the polymer remains soluble (>100 °C). Reasoning that a highly σ-donating scorpionate ligand would stabilize the vanadium(V) against reductive deactivation, we developed vanadium tris(2-pyridyl)borate complexes and studied their reactivities in high-temperature homogeneous ethylene polymerization. Complex 1 shows exceptional ethylene polymerization longevity at high temperatures, with 1 h of activity at 105 °C. The low polydispersity, vinyl end groups, and concentration effects indicate single-site catalysis involving chain transfer to the monomer. These results provide a new platform for studying high-valent vanadium catalysts under demanding conditions.

Asymmetric hetero-Michael addition to α,β-unsaturated carboxylic acids using thiourea–boronic acid hybrid catalysts

The first catalytic asymmetric Michael addition of heteroatomic nucleophiles to α,β-unsaturated carboxylic acids is summarized. Direct Michael addition is one of the most straightforward and atom-economical methods for constructing pharmaceutically beneficial building blocks and intermediates, although unsaturated carboxylic acids are known to be inactive Michael acceptors. We designed hybrid catalysts comprising arylboronic acid, thiourea, and tertiary amine to activate the unsaturated carboxylic acids. This review describes the aza- and thia-Michael additions using chiral multifunctional hybrid catalysts, their synthetic applications to biologically active compounds, and the mechanistic consideration of multicomponent borate complexes.

The role of monodentate tetrahedral borate complexes in boric acid binding to a soil organic matter analogue

Boron is an essential plant micronutrient responsible for several important functions. Boron availability in soils may be influenced by binding with soil organic matter (SOM), particularly with aromatic diol and polyphenol groups on SOM. The mechanism by which aromatic diols bind boron, however, remains unclear. The objective of this work is to further investigate interaction between boric acid and varying concentrations of an aromatic, polyphenolic SOM analogue (tannic acid at 5, 10 and 20 g L−1) from pH = 5–9. UV/Visible spectroscopy showed boric acid enhanced tannic acid deprotonation at pH = 7.0 and 9.0, resulting in singly deprotonated tannic acid subunits. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) showed boric acid/tannic acid binding for all concentrations at pH = 7 and 9, whereas binding at pH = 5.0 was observed only at 20 g L−1 tannic acid. Uncomplexed boron species were not evident at pH = 9.0, but were detectable at pH = 7.0 at lower tannic acid concentrations and prevalent at pH = 5.0, qualitatively indicating binding affinity increases from pH = 5.0 to 9.0. ATR-FTIR results indicated tetrahedral coordination of boron upon complexation to tannic acid with a monodentate mechanism. These results collectively highlight a transition of solution planar boric acid to a tetrahedral, monodentate coordination with a single phenol group in tannic acid polyphenols. This contrasts with previous spectroscopic studies, which indicated bidentate tetrahedral or monodentate trigonal planar orientations prevail at aromatic diol sites. This work presents a previously unobserved boric acid coordination mechanism to an SOM analogue and, therefore, may better inform prediction and modeling of boron behavior in soils.

Asymmetric Hetero-Michael Additions to α,β-Unsaturated Carboxylic Acids by Multifunctional Boronic Acid Catalysts

Several direct asymmetric Michael additions to α,β-unsaturated carboxylic acids with integrated catalysts comprising chiral bifunctional thiourea and arylboronic acid were developed. First, the asymmetric aza-Michael addition of hydroxylamine derivatives efficiently afforded a variety of optically active β-amino acid derivatives. Furthermore, upon detailed investigation of the reaction, tetrahedral borate complexes, comprising two carboxylate molecules, were found to serve as reaction intermediates. Based on this observation, a drastic improvement in product enantioselectivity was achieved upon benzoic acid addition. Second, on merely changing the solvent, the asymmetric thia-Michael addition of arylthiols afforded both enantiomers of the adducts, which are important building blocks for biologically active compounds.

Recent Advances in the Synthesis and Reactivity of Transition Metal σ-Borane/Borate Complexes

The coordination of an element-element σ bond to a transition metal (TM) is both a fundamentally intriguing binding mode and of critical importance to metal-mediated bond activation mechanisms and catalysis, particularly the hotly contested field of C-H activation. TM σ complexes of dihydrogen (i.e., H-H) and silanes (H-SiR3) have been extensively studied, the latter being of interest as models for the (generally unstable and unisolable) σ complexes of alkanes (i.e., H-CR3). TM σ complexes of hydroboranes and hydroborates (i.e., H-BR2, H-BR3, (H-)2BR2) are somewhat less well studied but similarly have relevance to catalytic borylation reactions that are of high current interest to organic synthesis. Our two research groups have made significant contributions to elaborating the family of σ-borane/-borate complexes using two distinct approaches: while the Ghosh group generally starts from hydrogen-rich tetracoordinate boron species such as borates, the Braunschweig group starts from hypovalent and/or hypocoordinate boron building blocks. Through these two approaches, a wide range of species containing one or two σ-bound B-H ligands have been prepared, some with additional chelating donor sites. Over the past 2 years, the body of work on σ-borane/-borate complexes from our two research groups has significantly expanded, with a combined nine published articles in 2019-2020 alone. Very recent work from the Braunschweig group has led to the synthesis of the first bis(σ)-borane complexes of group 6 metals, as well as the synthesis of a series of novel bis(σ)-borane and bis(σ)-borate complexes of ruthenium and iridium, the former being useful precursors for pentacoordinate borylene complexes of Ru. Recent work from the Ghosh group has uncovered a remarkable diversity of structures with σ(B-H)-bound ligands from the combination of borohydrides and nitrogen/chalcogen-containing groups and heterocycles. These reactions, while in some cases producing conventional scorpionate-type chelating products, more frequently undergo fascinating rearrangements with unpredictable outcomes. This Account aims to highlight this recent acceleration of research progress in this area, particularly the distinct but related approaches of-and complexes produced by-our two research groups, in addition to relevant works from other groups where appropriate.

Rapid capillary gel electrophoresis analysis of human milk oligosaccharides for food additive manufacturing in-process control

Industrial production of human milk oligosaccharides (HMOs) represents a recently growing interest since they serve as key ingredients in baby formulas and are also utilized as dietary supplements for all age groups. Despite their short oligosaccharide chain lengths, HMO analysis is challenging due to extensive positional and linkage variations. Capillary gel electrophoresis primarily separates analyte molecules based on their hydrodynamic volume to charge ratios, thus, offers excellent resolution for most of such otherwise difficult-to-separate isomers. In this work, two commercially available gel compositions were evaluated on the analysis of a mixture of ten synthetic HMOs. The relevant respective separation matrices were then applied to selected analytical in-process control examples. The conventionally used carbohydrate separation matrix was applied for the in-process analysis of bacteria-mediated production of 3-fucosyllactose, lacto-N-tetraose, and lacto-N-neotetraose. The other example showed the suitability of the method for the in vivo in-process control of a shake flask and fermentation approach of 2′-fucosyllactose production. In this latter instance, borate complexation was utilized to efficiently separate the 2′- and 3-fucosylated lactose positional isomers. In all instances, the analysis of the HMOs of interest required only a couple of minutes with high resolution and excellent migration time and peak area reproducibility (average RSD 0.26% and 3.56%, respectively), features representing high importance in food additive manufacturing in-process control.Graphical abstract

Chalcogen Stabilized bis-Hydridoborate Complexes of Cobalt: Analogues of Tetracyclo[4.3.0.02,4 .03,5 ]nonane.

Treatment of Li[BH3 ER] (E=Se or Te, R=Ph; E=S, R=CH2 Ph) with [Cp*CoCl]2 led to the formation of hydridoborate complexes, [{CoCp*Ph}{Cp*Co}{μ-EPh}{μ-κ2 -E,H-EBH3 }], 1a and 1 b (1 a: E=Se; 1 b: E=Te) and a bis-hydridoborate species [Cp*Co{μ-κ2 -Se,H-SeBH3 }]2 , 2. All the complexes, 1 a, 1 b and 2 are stabilized by β-agostic type interaction in which 1 b represents a novel bimetallic borate complex with a rare B-Te bond. QTAIM analysis furnished direct proof for the existence of a shared and dative B-chalcogen and Co-chalcogen interactions, respectively. In parallel to the formation of the hydridoborate complexes, the reactions also yielded tetracyclic species, [Cp*Co{κ3 -E,H,H-E(BH2 )2 -C5 Me5 H3 }], 3 a and 3 b (3 a: E=Se and 3 b: E=S), wherein the bridgehead boron atoms are surrounded by one chalcogen, one cobalt and two carbon atoms of a cyclopentane ring. Molecules 3 a and 3 b are best described as the structural mimic of tetracyclo[4.3.0.02,4 .03,5 ]nonane having identical structure and similar valence electron counts.

Optimization of fermentation conditions for production of l-arabinose isomerase of Lactobacillus plantarum WU14.

As a substitute sweetener for sucrose, d‐tagatose is widely used in products, such as health drinks, yogurt, fruit juices, baked goods, confectionery, and pharmaceutical preparations. In the fermentation process of l‐AI produced by Lactobacillus plantarum, d‐tagatose is produced through biotransformation and this study was based on the fermentation process of Lactobacillus plantarum WU14 producing l‐AI to further research the biotransformation and separation process of d‐tagatose. The kinetics of cell growth, substrate consumption, and l‐arabinose isomerase formation were established by nonlinear fitting, and the fitting degrees were 0.996, 0.994, and 0.991, respectively, which could better reflect the change rule of d‐tagatose biotransformation in the fermentation process of L. plantarum WU14. The separation process of d‐tagatose was identified by decolorization, protein removal, desalination, and freeze drying, initially. Finally, the volume ratio of whole cell catalysts, d‐galactose, and borate was 5:1:2 at 60°C, pH 7.17 through borate complexation; then, after 24 hr of conversion, the yield of d‐tagatose was 58 g/L.

Hydrogen atom transfer rates from Tp-containing metal-hydrides to trityl radicals

The H• transfer rate constants for a series of group 6 molybdenum and tungsten pyrazolyl borate complexes are described. The rate constants for these complexes were found to span a range over 1 magnitude. Analysis of the H• transfer rate constants suggests that a combination of steric, electronic, and enthalpic factors are important in these reactions. Further analysis of the components suggests that the generated 17 e– radicals of these complexes are less electrophilic than the more commonly used CpCr(CO)3H complexes. General implications for H• transfer reactions are discussed.

RHEOLOGICAL PROPERTIES STUDY OF FRACTURING FLUIDS USING LOCAL SANDS

A method of extracting natural gas from shale rock formations is hydraulic fracturing. The nearly water-based fracking fluid consists of cross-linking agents, mineral salts, pH-adjusting agents, and other components to control rheological behaviour. The fracturing fluid is pumped deep into a well at high pressure to crack the shale layer in order to access the natural gas. Once the fractures are formed, proppants, usually crystalline silica, keep them open, filling in the cracks created to allow the proper flow of hydrocarbons. This research explores the rheological properties of XLFC-1B polymer (gel-forming) and a borate complex (crosslinker XLW-56) as additives solutions, existing components used in hydraulic fracturing using local sands, including aoelian and quarries sands. Tests have shown that liquids exhibit viscoelastic behavior that allows them to hold the proppants and place them in fractures. It must also be established that these fluids ' minimal stress allows the liquid to flow.