- A safe and scalable procedure for preparation of α-picoline-borane from sodium mono-acyloxyborohydrides and α-picoline
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Sodium monobenzoxyborohydride, which is easily prepared from sodium borohydride and benzoic acid in THF in situ, is treated with α-picoline in THF under mild conditions to give α-picoline-borane in an excellent yield. This method can be a practical preparation for α-picoline-borane.
- Kawase, Yasushi,Yamagishi, Takehiro,Kutsuma, Teruo,Zhibao, Huo,Yamamoto, Yoshinori,Kimura, Tomohiro,Nakata, Tadashi,Kataoka, Tadashi,Yokomatsu, Tsutomu
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- Coordination Chemistry of Borane in Solution: Application to a STING Agonist
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Equilibrium constants were determined for ligand exchange reactions of borane complexes with various oxygen, sulfur, nitrogen, and phosphorus nucleophiles in solution, and a binding affinity scale was built spanning a range of 12 orders of magnitude. While the Keq are minimally dependent on the solvent, the rate of ligand exchange varies significantly. The fastest and slowest rates were observed in THF and CDCl3, respectively. Moreover, the ligand exchange rate differs in a very broad range depending on stability of the starting complex. Binding of BH3 was found to be much more sensitive to steric factors than protonation. Comparing nitrogen bases having equal steric properties, a linear correlation of BH3 binding affinity vs. Br?nsted acidity was found. This correlation can be used to quickly estimate the BH3 binding affinity of a substrate if pKa is known. Kinetic studies suggest the ligand exchange to occur as a bimolecular SN2 reaction unless other nucleophilic species were present in the reaction mixture.
- Lemaire, Sébastien,Zhdanko, Alexander,van der Worp, Boris A.
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- A Lewis Base Nucleofugality Parameter, NFB, and Its Application in an Analysis of MIDA-Boronate Hydrolysis Kinetics
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The kinetics of quinuclidine displacement of BH3 from a wide range of Lewis base borane adducts have been measured. Parameterization of these rates has enabled the development of a nucleofugality scale (NFB), shown to quantify and predict the leaving group ability of a range of other Lewis bases. Additivity observed across a number of series R′3-nRnX (X = P, N; R′ = aryl, alkyl) has allowed the formulation of related substituent parameters (nfPB, nfAB), providing a means of calculating NFB values for a range of Lewis bases that extends far beyond those experimentally derived. The utility of the nucleofugality parameter is explored by the correlation of the substituent parameter nfPB with the hydrolyses rates of a series of alkyl and aryl MIDA boronates under neutral conditions. This has allowed the identification of MIDA boronates with heteroatoms proximal to the reacting center, showing unusual kinetic lability or stability to hydrolysis.
- García-Domínguez, Andrés,Gonzalez, Jorge A.,Leach, Andrew G.,Lloyd-Jones, Guy C.,Nichol, Gary S.,Taylor, Nicholas P.
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supporting information
(2022/01/04)
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- Activation of sodium borohydride via carbonyl reduction for the synthesis of amine- And phosphine-boranes
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A highly versatile synthesis of amine-boranes via carbonyl reduction by sodium borohydride is described. Unlike the prior bicarbonate-mediated protocol, which proceeds via a salt metathesis reaction, the carbon dioxide-mediated synthesis proceeds via reduction to a monoformatoborohydride intermediate. This has been verified by spectroscopic analysis, and by using aldehydes and ketones as the carbonyl source for the activation of sodium borohydride. This process has been used to produce borane complexes with 1°-, 2°-, and 3°-amines, including those with borane reactive functionalities, heteroarylamines, and a series of phosphines.
- Hamann, Henry J.,Lin, Randy,Veeraraghavan Ramachandran, P.
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supporting information
p. 16770 - 16774
(2021/12/08)
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- Amine-boranes bearing borane-incompatible functionalities: Application to selective amine protection and surface functionalization
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The first general open-flask synthesis of amine-boranes with inexpensive and readily available reagents, such as sodium borohydride, sodium bicarbonate, water, and the desired amines is described. Even amines bearing borane-reactive functionalities, such as alkene, alkyne, hydroxyl, thiol, ester, amide, nitrile, and nitro are well tolerated. Some of these novel amine-boranes represent stable molecules containing potentially incompatible electrophilic and nucleophilic centers in proximity. This convenient scalable synthesis provides a novel class of organic ligands for surface functionalization, as demonstrated by the formation of self-assembled layers of thiol- and alkoxysilane-bearing amine-boranes on gold and silica surfaces, respectively.
- Veeraraghavan Ramachandran,Kulkarni, Ameya S.,Zhao, Yan,Mei, Jianguo
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supporting information
p. 11885 - 11888
(2016/10/09)
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- Open-Flask Synthesis of Amine-Boranes via Tandem Amine-Ammonium Salt Equilibration-Metathesis
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An amine-ammonium salt equilibration-metathesis sequence provides high-purity amine-boranes in excellent yields from sodium borohydride in refluxing reagent-grade tetrahydrofuran in an open flask.
- Ramachandran, P. Veeraraghavan,Kulkarni, Ameya S.
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supporting information
p. 5618 - 5620
(2015/06/25)
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- Molecular addition compounds. 9. Effect of structure on the reactivities of representative borane-amine complexes in typical reactions such as hydrolysis, hydroboration, and reduction
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A number of borane-amine complexes with widely different structural features in the amine portion was prepared and their reactivities toward typical B-H reactions, such as hydrolysis, hydroboration of 1-octene, and reduction of cyclohexanone, were studied. BH3-amine complexes containing an N-phenyl group are hydrolyzed by neutral hydroxylic solvents, while others require a strong acid medium for the hydrolysis. In hydroboration, BH3-N-phenylamine complexes react rapidly with 1-octene in THF at 25°C, while all other types require refluxing THF or toluene for reaction. Again, BH3-N-phenylamine complexes reduce cyclohexanone in THF at 25°C at reasonable rates, while others require acetic acid solvent or mineral or Lewis acids to achieve the desired reduction. Thus, among such borane-amine addition compounds, the BH3-N-phenylamines emerge as unique hydroborating and reducing agents. The results of the present study provide insights into the mechanisms of the hydroboration and reduction reactions. The rates of hydroboration of alkenes with BH3-amine complexes are inversely related to the stability of the adduct, arguing for a prior dissociation of the adduct, followed by the reaction of BH3 with the alkene. The reduction of cyclohexanone with BH3-amine complex in THF proceeds by an analogous dissociation mechanism. In acetic acid or in the presence of mineral or Lewis acids, a bimolecular attack of the BH3-amine complex on the protonated carbonyl group has been considered to be the most viable mechanistic pathway. However, this does not account for the effect of acids on hydrolytic behavior. Consequently, caution is urged in considering possible interpretation of the acid-enhanced reactions of amine-boranes.
- Brown, Herbert C.,Murray, Leo T.
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p. 2746 - 2753
(2008/10/08)
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- A new synthesis of amine- and phosphine-boranes
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A new, rapid, and high-yield synthesis of borane adducts with amines and phosphines has been developed. It is based on the reaction of sodium borohydride and iodine in the presence of the donor. The procedure is applicable to adducts of ammonia, primary, secondary, and tertiary amines, di- and triamines, pyridines, triphenylphosphine, and diphosphines. The following new compounds have been prepared: 2-methoxypyridine-borane, 2,2′-dipyridyl-bis(borane), bis(diphenylphosphino)methane-bis(borane), and 1,2-bis(diphenylphosphino)ethane-bis(borane).
- Nainan,Ryschkewitsch
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p. 2671 - 2674
(2008/10/08)
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- Lewis acid-base reactions among dimethylaminoboron hydrides
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The dimethylaminoboron hydrides related to diborane form a system of Lewis acids and bases, the interconversion of which can be described as addition or removal of BH3 groups. The first-stage action of [(CH3)2N]3B to remove BH3 from (CH3)3N· BH3 is not appreciably reversible, but the second stage, in which [(CH3)2N]2BH and (CH3)3N·BH3 form 2(CH3)2NBH2 and (CH3)3N, is reversible with ΔF° = 13.95 - 0.0330T kcal. Our base·(CH3)2NB2H5 adducts show vapor-phase dissociation increasing in the order pyridine, (CH3)3P, 2-methylpyridine, (CH3)3N; and (CH3)2PH·(CH3)2NB 2H5 fails to exist in the vapor phase but forms a partially dissociated liquid. All five of these adducts on heating react further to form (CH3)2NBH2 and base·BH3, without reversal. The adducts CH3PH2·(CH3)2NB 2H5 and (CH3)2PCF3·(CH3) 2NB2H5 are still more easily dissociated, and their conversion to BH3 complexes and (CH3)2NBH2 is reversible with ΔF° = 10.61 - 0.0268T and 6.59 - 0.01943T kcal., respectively. It is quite apparent that diborane is a much stronger Lewis acid than (CH3)2NB2H5.
- Burg, Anton B.,Sandhu, Jagtar S.
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p. 1467 - 1472
(2008/10/08)
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- Water‐promoted, open‐flask synthesis of amine‐boranes: 2‐methylpyridine‐borane (2‐picoline‐borane)
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A procedure yielding 2‐methylpyridine‐borane as a white solid is presented. Sodium borohydride and powdered sodium bicarbonate are added into a single‐necked, air‐dried round‐bottomed flask with a Teflon‐coated, egg‐shaped magnetic stir bar. A discussion on amine‐boranes, reductive amination with aldehyde bisulfites and carbohydrates, and metathesis of metal borohydrides with alkylammonium salts concludes the chapter.
- Kulkarni, Ameya S.,Ramachandran, P. Veeraraghavan
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