1,3-Dihydro-1,3,2-diazaborole- and 1,3,2-diazaborolidine compounds from alkali metal complexes of aromatic nitrogen heterocycles and dichloro(diisopropylamino)borane 1)

Reactions of complexes of isoquinoline, 2,2'-dlpyridyl and phenanthridine and sodium or potassium with dichloro(diisopropylamino)borane lead to new heterocycles containing diazaborole and diazaborolidine ring systems. The corresponding reaction starting from quinoline gives bis(1,4-dihydro-quinolinyl-1)diisopropylaminoborane, while with indole bis(1-indolyl)diisopropylaminoborane is the product. The new compounds are characterized by spectroscopic (MS; NMR ¹H, ¹¹B, ¹³C, ¹⁵N) data and elemental analyses.     

Synthesis and molecular structure of 2,4,6‐tri[bis(diisopropylamino)boryl(methylamino)]borazine, [(NiPr2)2B(Me)N]3B3N3H3

Reaction of bis(diisopropylamino)(methylamino)borane, (NHⁱPr)₂B(NHMe), with 2,4,6‐trichloroborazine (ClBNH)₃ affords 2,4,6‐tri[bis(diisopropylamino)boryl(methylamino)]borazine, 2,4,6‐[(NⁱPr₂)₂B(Me)N]₃B₃N₃H₃, which is the first boryl‐borazine structurally characterized. According to the X‐ray single crystal structure and the chemical shifts of ¹¹B NMR resonances of boron atoms, compared with the aminoborane and borazine analogs, the borazine and boryl π‐systems are not coplanar either in the solid state or in organic solution. Copyright © 2002 John Wiley & Sons, Ltd.     

Reaktion von konjugierten doppelbindungsystemen mit dihalogen(diorganylamino)boranen und Na/K-legierung

The reaction of 2,3-dimethylbuta-1,3-diene or 2-methylbuta-1,3-diene with Na/K-alloy and dichloro(diisopropylamino)borane in n-hexane yielded the 1-bora-cyclopent-3-enes, A and II, and 1-bora-cyclonona-1,3-diene, I, respectively. Cycloocta-3,7-diene reacts with dibalogeno(diorganylamino)boranes and Na/K-alloy in n-hexane to yield the 9-bora-bicyclo[4,2,1]non-7-enes III, V, VI and the 1,6-bis(diorganylaminofluoroboryl)-cyclooct-7-enes IV and VH. When 1,2-dimethoxyethane was the solvent, only the dimeric cyclooctene, C, was obtained. The compounds were characterized by elemental analyses and spectroscopy [MS; NMR (¹H, ¹¹B, ¹³C, ¹⁹F)]. An X-ray analysis is presented for I, MNDO-calculations have been carried out for III and III.     

Dichloro(diisopropylamino)phosphonio[5(4H)oxopyrazol‐4‐ylide‐5‐one]: Synthesis and properties

Chlorination of the 4‐[chloro(diisopropylamino)phosphino]pyrazole 1 leads to the dichlorophosphonium chloride 2 , which immediately after its formation transforms into the dichloro(diisopropylamino)phosphonio[5(4)oxopyrazol‐4‐ylide‐5‐one] 3 , as a result of dealkylation through loss of ethyl chloride. Reactions of 3 with various nucleophilic reagents were studied. The partial hydrolysis of 3 in the presence of nitriles, resulting in new phosphorus‐containing cyclic systems, is of particular interest. It was demonstrated that chlorination of the P‐dichloropyrazolylphosphine A leads to the stable tetrachlorophosphorane 12 . The C P bond of 12 is broken upon heating. An X‐ray structure determination of compound 11b revealed a planar central heterocycle (mean deviation 0.029 Å). © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:452–458, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10177     

Reaction of Hexamethyldisilazane with Borane in Tetrahydrofuran

Hexamethyldisilazane 1 reacts with borane in tetrahydrofuran (THF? BH₃, 2 ) first by formation of an adduct (Me₃Si)₂NH? BH₃ ( 3 ), and then either to the N,N-bis-(trimethylsilyl)-μ-aminodiborane 5 or to the mixture of 5 and N-trimethylsilyl-μ-aminodiborane(6) 6 , depending on the reaction conditions. The compounds 5 and 6 can be quantitatively converted to the N,N′,N″-tris(trimethylsilyl)borazine 4 . Three intermediates can be identified, namely N,N-bis(trimethylsilyl)borane 7 , N,N-bis(trimethylsilyl)amino(N′-trimethylsilylamino)borane 8 and N-trimethylsilylaminoborane-trimer. All products and intermediates were characterized by multinuclear NMR spectroscopy, and coupling constant ¹J(²⁹Si, ¹⁵N) were measured from ²⁹Si NMR spectra by using the Hahn-echo-extended (HEED) INEPT pulse sequence.     

Efficient synthesis and NMR data of N‐ or B‐substituted borazines

The thermolysis of borane‐primary amine complexes RNH₂.BH₃ was reexamined. Excellent yields of N‐substituted borazines were obtained at 200°C, when R is an alkyl group, and at 120°C for R = Ph. B‐alkyl, vinyl, and alkynyl borazines were easily prepared in good to excellent yields by ammonolysis of bis(diisopropylamino)organoboranes at temperatures above 95°C. The ¹H, ¹³C, and ¹⁵N or ¹⁴N NMR data for all borazines prepared are reported for the first time. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:218–225, 2000     

Phenylhydrazine–borane adduct—characterized in the solid state and in solution

The 1:1 phenylhydrazine–borane adduct, obtained from phenylhydrazine and sodium borohydride in acidic solution, was investigated by IR, NMR spectroscopy, and MS spectrometry. Ab initio MO calculations indicated the isomer in which the boron center is attached to the primary amino group as the more stable. This forecast was confirmed by solution‐state ¹H, ¹¹B, ¹³C, and ¹⁵N NMR spectroscopy, in agreement with the molecular structure in the solid state determined by X‐ray analysis. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:366–372, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10049     

Chiral Bora[1]ferrocenophanes: Syntheses,Mechanistic Insights,and Ring‐Opening Polymerizations

A series of new boron‐bridged [1]ferrocenophanes ([1]FCPs) was prepared by salt‐metathesis reactions between enantiomerically pure dilithioferrocenes and amino(dichloro)boranes (Et₂NBCl₂, iPr₂NBCl₂, or tBu(Me₃Si)NBCl₂). The dilithioferrocenes were prepared in situ by lithium–bromine exchange from the respective planar‐chiral dibromides (S_p,S_p)‐[1‐Br‐2‐(HR₂C)H₃C₅]₂Fe (R=Me or Et). In most of the cases, mixtures of the targeted [1]FCPs 4 and the unwanted 1,1′‐bis(boryl)ferrocenes 5 were formed. The product ratio depends on the bulkiness of the amino group, the speed of addition of the amino(dichloro)borane, the alkyl group on Cp rings, and in particular on the reaction temperature. The formation of strained [1]FCPs is strongly favored by increased reaction temperatures. Secondly, CHEt₂ groups at Cp rings favored the formation of the targeted [1]FCPs stronger than CHMe₂ groups. These discoveries open up new possibilities to further suppress the formation of unwanted byproducts by a careful choice of the reaction temperature and through tailoring the bulkiness of CHR₂ groups on ferrocene. Thermal ring‐opening polymerizations of selected boron‐bridged [1]FCPs gave metallopolymers with a M_w of 10 kDa (GPC).     

Spectres de vibrations de pyrimidines tétrasubstituées: Amino et méthylamino-2 et -4 dichloro(méthylthio)-5 pyrimidines

2- and 4-amino, -methylamino, -dimethylamino dichloro 5-methylthio pyrimidines and their deuterated derivatives are studied by i.r and Raman spectroscopies (3600-100 cm⁻¹). X-sensitive ring vibrations, ring out-of-plane vibrations and amino group vibrations are discussed. Spectroscopic data about these latter vibrations allow estimation of the self-association of the studied compounds in solution and in the solid state.     

The first example of a mixed alkoxide hydride of boron: sodium boron isopropoxide trihydride

The title compound, poly[[μ‐trihydro(isopropoxy)borato]sodium(I)], [Na(C₃H₁₀BO)]_n, forms unique polymeric layers normal to the c axis via Na⁺...O [2.3405 (15) Å] and Na⁺...H(borane) [2.22 (3) and 2.28 (3) Å] interactions. This arrangement builds on distorted tetrahedral Na⁺, oxygen and boron environments, with one of the borane hydride units uncoordinated, and highlights potential H₃B—O‐based chemistry.     

Production of Dihydrogen Using Ammonia Borane as Reagent and Pyrazole as Catalyst

Theoretical chemistry (DLPNO-CCSD(T)/def2-TZVP//M06-2x/aug-cc-pVDZ) was used to design a system based on ammonia boranes catalyzed by pyrazoles with the aim of producing dihydrogen, nowadays of high interest as clean fuel. The reactivity of ammonia borane and cyclotriborazane were investigated, including catalytic activation through 1H-pyrazole, 4-methoxy-1H-pyrazole, and 4-nitro-1H-pyrazole. The results point toward a catalytic cycle by which, at the same time, ammonia borane can initially store and then, through catalysis, produce dihydrogen and amino borane. Subsequently, amino borane can trimerize to form cyclotriborazane that, in presence of the same catalyst, can also produce dihydrogen. This study proposes therefore a consistent progress in using environmentally sustainable (metal free) catalysts to efficiently extract dihydrogen from small B−N bonded molecules.     

The Reaction of Trialkylboranes with Allyl Phenyl Ether. Syntheses of 1-Alkenes and 1,5-Alkadienes

In the organoborane chemistry, the homologation reaction is one of the useful methods for the synthesis of organoboranes not available via hydroboration.¹⁾ The allylic boranes are known to be highly reactive and exhibit specific behaviors,²⁾ but with few exceptions,³) these are difficult to be prepared directly by the hydroboration reaction.⁵⁾ Previously, we reported that in the reaction of the dianion of phenoxyacetic acid with organoborane, the phenoxy group acts as a good leaving group.⁶⁾ This result suggested us a new homologation reaction converting a saturated organoborane to a allylic borane (1) by the treatment with the carbanion of allyl phenyl ether. Here we wish to report the synthesis of 1-alkenes (II) three-carbon-homologated from starting alkenes⁷⁾ and the regioselective synthesis of 1,5-dienes (III) using allylic borane intermediates (1) (eq. 1).     

Rh2[(R)-(+)-MTPA]4 as an NMR auxiliary for the enantiodifferentiation of chiral secondary and tertiary phosphine–borane complexes

The direct chiral recognition of secondary and tertiary phosphine–borane complexes is made possible by applying the dirhodium method (NMR in the presence of Rh₂[(R)-(+)-MTPA]₄, Rh¹). Due to the acid lability of the phosphine–borane complexes, it is advisable to use deuterated benzene as solvent rather than deuterated chloroform. The decomposition of the phosphine–borane complexes and the resulting Rh¹–phosphine adducts are also studied.     

Recent development of aminophosphine chalcogenides and boranes as ligands in s-block metal chemistry

The coordination chemistry of the aminophosphine chalcogenide ligands [Ph₂P(O)NHR], [Ph₂P(S)NHR], and [Ph₂P(Se)NHR] (R = 2,6-Me₂C₆H₃,^tBu, CHPh₂, CPh₃) or corresponding borane derivative [Ph₂P(BH₃)NHR] toward group 1 and 2 metals is reviewed. The structural characterization of a huge number of mono- and bis-aminophosphine chalcogenide/borane complexes with group 1 and 2 metals—in most cases lithium, sodium, potassium, magnesium, calcium, strontium, and barium complexes—reveals a poly-metallacyclic motif in each case. The coordination takes place from adjacent chalcogen/borane and nitrogen as donor atom or group of the ligand confirming the direct bond between metal and chalcogen/borane to develop homoleptic and heteroleptic complexes. The heteroleptic group 2 metal complexes were used as pre-catalysts in hydrophosphination and hydroamination reactions. Similarly, aminophosphine chalcogenide alkaline earth metal complexes were used in the catalytic ring-opening polymerization (ROP) study of ?-caprolactone.     

The stereochemistry of aziridine borane lithiation: diastereoselectivity and enantioselectivity

Lithiation of 1-methylaziridine borane, 1-(tert-butyldimethylsiloxyethyl)aziridine borane, or 1-(tert-butyldimethylsiloxyethyl)-2-methylaziridine borane occurs syn to the boron substituent, while lithiation of 1-(tert-butyldimethylsiloxyethyl)-2-trimethylstannylaziridine borane occurs anti to boron as well as silicon due to the steric effect of trimethylsilyl group (s-butyllithium was used in all cases). Kinetically controlled lithiation in the first three cases results from a combination of steric and electrostatic effects. Enantioselective lithiation occurs in the presence of (−)-sparteine, with product enantioselectivities near 70% ee.     

A Simple,Convenient, and Efficient Synthetic Route for The Preparation of (Z)‐3,5‐Dichloro‐N‐(3‐(4‐substitutedphenyl)‐4‐phenylthiazole‐2(3H)‐ylide)benzamide Heterocyclic Compounds from Aroyl Thiourea Derivatives via S‐cyclization Mechanism

A series of variously substituted 1,3‐thiazole heterocyclic compounds ( 3a – 3d ) were prepared by base‐catalyzed S‐cyclization of corresponding 2,4‐dichloro‐N‐{[(4‐substitutedphenyl)amino]carbonothioyl}benzamide ( 2a – 2d ) with acetophenone in the presence of bromine. The structure of all compounds was established by IR, ¹H‐NMR, ¹³C‐NMR, elemental analysis, and X‐ray crystallographic analysis.     

Dichloro and amino acid cobalt(III) complexes of N,N′-diethylethylenediamine-N,N′-Di-α-butyrate ligand

A novel linear flexible ONNO-type tetradentate ligand, N,N′-diethylethylenediamine-N,N′-di-α-butyrate (deedba), and the dichloro, diaqua and amino acid (glycine, -alanine, -phenylalanine) cobalt(III) complexes of deedba have been synthesized via an H₂O₂ oxidation method. During the preparation of these complexes, the ligand has coordinated geospecifically to the cobalt(III) ion to give only one isomer, s-cis, which has been characterized by electronic absorption, ¹H NMR and IR spectra, and elemental analysis. It is of interest that this is one of the few Co^III(edda)X₂-type complex preparations, which gives only one isomer with geoselectivity.     

The Simplest Amino‐borane H2B=NH2 Trapped on a Rhodium Dimer: Pre‐Catalysts for Amine–Borane Dehydropolymerization

The μ‐amino–borane complexes [Rh₂(L^R)₂(μ‐H)(μ‐H₂B=NHR′)][BAr^F₄] (L^R=R₂P(CH₂)₃PR₂; R=Ph, ⁱPr; R′=H, Me) form by addition of H₃B?NMeR′H₂ to [Rh(L^R)(η⁶‐C₆H₅F)][BAr^F₄]. DFT calculations demonstrate that the amino–borane interacts with the Rh centers through strong Rh‐H and Rh‐B interactions. Mechanistic investigations show that these dimers can form by a boronium‐mediated route, and are pre‐catalysts for amine‐borane dehydropolymerization, suggesting a possible role for bimetallic motifs in catalysis.     

Tetramethyl(perfluoroalkyl)cyclopentadienyl rhodium(I) complexes with ethylene or diene ligands. Crystal structure of [(η-C5Me4C6F13)Rh(CO)2]

Tetramethyl(perfluoroalkyl)cyclopentadienyl rhodium(I) complexes with ethylene or diene (norbornadiene, cycloocta-1,5-diene, 2,3-dimethylbuta-1,3-diene, cyclohexa-1,3-diene) ligands were obtained by reduction of tetramethyl(perfluoroalkyl)rhodium(III) dichloro dimers by zinc in THF or by propan-2-ol/sodium carbonate in the presence of the ligands. Reduction in the presence of cycloocta-1,3-diene gave a different product, an η³-cyclooctenyl complex, which was not reduced further. During the reduction in the presence of ethylene, a new tetramethyl(perfluoroalkyl)-η⁴-cyclopentadiene complex was observed by NMR. This compound, formed by hydrogen transfer from the metal to the ligand, is probably in an equilibrium with the parent hydridocyclopentadienyl complex. Crystal and molecular structure of dicarbonyltetramethyl(perfluorohexyl)cyclopentadienylrhodium(I) complex was determined by X-ray diffraction. The structure shows a moderate ring slippage of the rhodium atom which was not observed in the only other known structure of a complex with the same ligand, the rhodium(III) dichloro dimer.     

Reduction of substituted 1H-4,5-dihydroimidazolium salts

Reactions of several substituted 1H-4,5-dihydroimidazolium salts 1 with nucleophilic and electrophilic reducing agents acting via hydride transfer were explored. Reaction of compounds 1 with lithium aluminum hydride in THF afforded the corresponding imidazolidines 2 . When alkaline borohydrides (sodium borohydride, potassium borohydride, sodium cyanoborohydride) in ethanol at room temperature were used, partial or total over-reduction of compounds 2 leading to N,N,N'-trisubstituted ethylenediamines took place on occasion. Results may be explained taking into account that reductive cleavage of 2 proceeds via a stabilized iminium ion present in protic solvents. Treatment of compounds 1 with an excess of borane in THF afforded the corresponding imidazolidines 2 or their borane complexes, according to the substituent type.