Aluminum Reagents Research Articles

Ligand-Free, Copper-Catalyzed Coupling Reaction of Aryl Aluminum Reagents with N-Aryl Thiosuccinimides

: A highly efficient and simple cross-coupling reaction of N-aryl aluminum reagents with Naryl thiosuccinimides for the synthesis of diarylsulide derivatives using CuCl (20 mol%) as a catalyst is reported. Under the optimum reaction conditions, the coupling reaction between aryl aluminum reagents with different substituents and N-aryl thiosuccinimides with different substituents can be carried out smoothly with 18-94% isolated yields of diarylsulides. The method avoids the use of expensive transition metals, such as Pd, Ir, or Rh, phosphine ligands, and has the advantages of simple operation and high reaction efficiency. The structures of all the target compounds are confirmed by 1HNMR and 13CNMR.

The Ether‐Adduct of a Lewis Superacidic, Dicoordinate Aluminum Hydride Cation and the Ion Affinities of Solvent‐Adducts

AbstractAluminum reagents are widely used as strong Lewis acids for organic transformations and catalysis. In recent years, a variety of Al‐Lewis superacids could be accessed by preparation of aluminum cations paired with weakly‐coordinating anions or by use of perfluorinated substituents at the metal. While the majority of these Al‐Lewis superacids is composed of a tricoordinate Al‐metal atom, examples for dicoordinate Al species are very scarce. In this study, we report the preparation of [(Mes*)Al(H)(OEt2)]+[Al(ORF)4]− (Mes*=2,4,6‐tBu3‐C6H2, RF=C(CF3)3) by reaction of protonated ether [H(OEt2)2]+[Al(ORF)4]− with [Mes*AlH2]2. Structural analysis supported by computed frontier orbitals and atomic charges reveals that the cation is best described as diethylether adduct of dicoordinate [(Mes*)Al(H)]+ and acts as synthon to this low‐coordinate cation. To incorporate the masking of the coordination site by the ether, the enthalpy of dissociation is included in the computed fluoride‐ and hydride ion affinities (XIA) and entropic effects are treated by defining a “free ion affinity” (fXIA), basing on the Gibbs energy change. Hereby, the Lewis acidity of free Lewis acids as well as their solvent adducts can be estimated.

Synthesis of the 2-alkynyl benzo[b]furanes/benzo[b]thiophenes from the cross-coupling reaction of benzo[b]furanyl/ benzo[b]thiophene aluminum reagents with gem-dibromoolefin derivatives catalyzed by palladium

A PdCl2(dppf)2/MePhos catalyzed synthesis of 2-alkynylbenzo[b]furanes/benzo[b]thiophenes by the cross-coupling of benzo[b]furan/benzo[b]thiophene aluminums with gem-dibromoviny derivatives at 80 °C in DMF solvent was developed. The aryls bearing electron-donating or -withdrawing groups in gem-dibromoviny derivatives give the corresponding coupling products 2-alkynylbenzo[b]furanes/benzo[b]thiophenes in moderate to good isolated yields up to 74 %. For electrically neutral, electron rich or electron deficient benzo[b]furanyl/benzo[b]thiophene aluminum reagents, corresponding 2-alkynylbenzo[b]furane/benzo[b]thiophene compounds can also be obtained with moderate to good isolated yields. This process was simple and easily performed, which provides an efficient method for the synthesis of 2-alkynyl benzo[b]furane/benzo[b]thiophene derivatives. On the basis of the experimental results, a possible catalytic cycle has been proposed.

Development of Efficient Synthetic Reactions Using Enamines and Enamides Carrying Oxygen Atom Substituent on Nitrogen Atom.

We have developed efficient synthetic reactions using enamines and enamides carrying oxygen atom substituent on nitrogen, such as N-alkoxyenamines, N,α-dialkoxyenamines, N-alkoxyanamides, and N-(benzoyloxy)enamides. The umpolung reaction by polarity inversion at the β-position of N-alkoxyenamines afforded α-alkyl-, α-aryl-, α-alkenyl-, and α-heteroarylketones by using aluminum reagent as nucleophiles. Furthermore, one-pot umpolung α-phenylation of ketones has been also developed. We applied this method to umpolung reaction of N,α-dialkoxyenamine, generated from N-alkoxyamide to afford α-arylamides. The vicinal functionalization of N-alkoxyenamines has been achieved with the formation of two new carbon-carbon bonds by using an organo-aluminum reagent and subsequent allyl magnesium bromide or tributyltin cyanide. A sequential retro-ene arylation has been developed for the conversion of N-alkoxyenamides to the corresponding tert-alkylamines. The [3,3]-sigmatropic rearrangement of N-(benzoyloxy)enamides followed by arylation afforded cyclic β-aryl-β-amino alcohols bearing a tetrasubstituted carbon center. The resulting products were converted into the corresponding sterically congested cyclic β-amino alcohols, as well as the dissociative anesthetic agent Tiletamine.

Unveiling the mutual effects of hydroxyl and dibenzhydryl groups in α‐diimino‐nickel precatalysts for direct synthesis of polyethylene elastomers

The properties and practical applications of polyethylene are closely associated with the polymer molecular weight, polydispersity, degree of branching, and the type of branches and its arrangement within microstructure. In this study, a set of structurally diverse unsymmetrical 1‐(2,6‐dibenzhydryl‐4‐hydroxylphenylimino)‐2‐(2,6‐(R)‐4‐(R1)phenylimino)acenaphthene‐nickel dibromide precatalysts (where Ni2Me [R = Me, R1 = H], Ni2Et [R = Et, R1 = H], Ni2iPr [R = iPr, R1 = H], Ni3Me [R, R1 = Me], Ni2Et,Me [R = Et, R1 = Me]) has been prepared and studied for ethylene polymerization. Molecular structure analysis of Ni2Me and Ni2Et complexes revealed distorted tetrahedral geometries at nickel. The polymerization activities are extremely high for all precatalysts upon activation with either EASC or MMAO aluminum reagents, a trend notably pronounced in the case of the EASC‐activated systems, entering activity in the range of 10 million g mol−1 h−1 at 30°C. The Ni2Me demonstrated exceptional performance at higher temperatures, achieving an activity of 2.4 × 106 g mol−1 h−1 at 100°C and generated high molecular weight polyethylene (Mw = 105 g mol−1) with narrow polymer dispersity across all reaction temperatures (Ð ≈ 1.5). High temperature 13C NMR spectra identified 97–142/1000C branches in resulting polyethylene, a feature significantly dependent on the reaction temperature. In terms of mechanical properties, stress–strain analysis indicated that polyethylene synthesized at lower temperatures displayed superior tensile strength compared with that produced at higher reaction temperatures, while a reverse trend was observed in strain recovery analysis. The high strain recovery (up to 72%) of these polyethylene highlights the characteristic properties of thermoplastic elastomers.

Copper-assisted palladium catalyzed the cross-coupling reaction of Alknylalane reagents with 2-Thiobenzo[d]thiazoles via C–S bond cleavage

A highly efficient and simple route for the synthesis of 2-alknyl benzo[d]thiazoles has been developed by palladium and copper catalyzed the cross-coupling reaction of 2-thiobenzo[d]thiazoles with (hetero)aromatic and aliphatic alkynylaluminum reagents. Various 2-alkynyl benzo[d]thiazole derivatives can be obtained in 19–97 % isolated yields using 1 mol% PdCl2(dppf)/5 mol% xanthpos as the catalyst and CuI (3 equiv.) as desulfurization agent. The cross-coupling reaction can be carried out smoothly with electron-donating or -withdrawing groups on the aromatic ring of the organo aluminum reagents or the 2-thiobenzo[d]thiazoles. Furthermore, the broad substrate scope and the maintenance of high efficiency on a gram scale make this protocol a potentially practical method to synthesize 2-alkynylbenzo[d]thiazole derivatives. On the basis of the experimental results, a possible catalytic cycle has been proposed.2009 Elsevier Ltd. All rights reserved.

Aluminium and Gallium Silylimides as Nitride Sources.

Terminal aluminium and gallium imides of the type K[(NON)M(NR)], bearing heteroatom substituents at R, have been synthesised via reactions of anionic aluminium(I) and gallium(I) reagents with silyl and boryl azides (NON=4,5-bis(2,6-diisopropyl-anilido)-2,7-di-tert-butyl-9,9-dimethyl-xanthene). These systems vary significantly in their lability in solution: the N(Sii Pr3 ) and N(Boryl) complexes are very labile, on account of the high basicity at nitrogen. Phenylsilylimido derivatives provide greater stabilization through the π-acceptor capabilities of the SiR3 group. K[(NON)AlN(Sit BuPh2 )] offers a workable compromise between stability and solubility, and has been completely characterized by spectroscopic, analytical and crystallographic methods. The silylimide species examined feature minimal π-bonding between the imide ligand and aluminium/gallium, with the HOMO and HOMO-1 orbitals effectively comprising orthogonal lone pairs centred at N. Reactivity-wise, both aluminium and gallium silylimides can act as viable sources of nitride, [N]3- , with systems derived from either metal reacting with CO to afford cyanide complexes. By contrast, only the gallium system K[(NON)Ga{N(SiPh3 )}] is capable of effecting a similar transformation with N2 O to yield azide, N3 - , via formal oxide/nitride metathesis. The aluminium systems instead generate RN3 via transfer of the imide fragment [RN]2- .

Redox Reorganization: Aluminium Promoted 1,5‐Hydride Shifts Allow the Controlled Synthesis of Multisubstituted Cyclohexenes

AbstractAn efficient synthesis of cyclohexenes has been achieved from easily accessible tetrahydropyrans via a tandem 1,5‐hydride shift–aldol condensation. We discovered that readily available aluminium reagents, e.g. Al2O3 or Al(OtBu)3 are essential for this process, promoting the 1,5‐hydride shift with complete regio‐ and enantiospecificity (in stark contrast to results obtained under basic conditions). The mild conditions, coupled with multiple methods available to access the tetrahydropyran starting materials makes this a versatile method with exceptional functional group tolerance. A wide range of cyclohexenes (>40 examples) have been prepared, many in enantiopure form, showing our ability to selectively install a substituent at each position around the newly forged cyclohexene ring. Experimental and computational studies revealed that aluminium serves a dual role in facilitating the hydride shift, activating both the alkoxide nucleophile and the electrophilic carbonyl group.

Ring-expansion and desulfurisation of thiophenes with an aluminium(I) reagent.

Reactions of thiophene, 2-methylthiophene, 2-methoxythiophene, 2,3-dimethylthiophene, and benzothiophene with the aluminium(I) complex [{ArNC(Me)2H}Al] (Ar = 2,6-di-isopropylphenyl) are reported. In all cases, carbon-sulfur bond activation and ring-expansion of the heterocycle is observed. For thiophene, we identify a reaction network for desulfurisation that includes an unusual second carbon-sulfur bond activation step.

Lanthanoid Biphenolates as a Rich Source of Lanthanoid-Main Group Heterobimetallic Complexes.

Several new trivalent dinuclear rare earth 2,2’‐methylenebis(6‐tert‐butyl‐4‐methylphenolate) (mbmp2−) complexes with the general form [Ln2(mbmp)3(thf)n] (Ln=Sm 1, Tb 2 (n=3), and Ho 3, Yb 4 (n=2), and a tetravalent cerium complex [Ce(mbmp)2(thf)2] (5) have been synthesised by RTP (redox transmetallation/protolysis) reactions from lanthanoid metals, Hg(C6F5)2 and the biphenol mbmpH2. These new complexes and some previously reported partially protonated rare earth biphenolate complexes [Ln(mbmp)(mbmpH)(thf)n] react with lithium, aluminium, potassium and zinc organometallic reagents to form lanthanoid‐main group heterobimetallic species. When reaction mixtures containing the Ln biphenolate complexes were treated with n‐butyllithium, both molecular ([Li(thf)2Ln(mbmp)2(thf)n] (Ln=La 6, Pr 7 (n=2) and Er 8, Yb 9, and Lu 10 (n=1)) and charge separated ([Li(thf)4][Ln(mbmp)2(thf)2] (Ln=Y 11, Sm 12, Dy 13, and Ho 14) complexes were isolated. Treatment with trimethylaluminium also led to isolation of molecular ([AlMe2Ln(mbmp)2(thf)2] (Ln=Pr 15, Sm 16, and Tb 17)) and ionic [La(mbmp)(thf)5][AlMe2(mbmp)] (18) complexes. One gadolinium‐potassium ([K(thf)3Gd(mbmp)2(thf)2] (19)), and one ytterbium‐zinc species ([ZnEtYb(mbmp)2(thf)] (20)) were isolated from treatment of reaction mixtures with potassium bis(trimethylsilyl)amide and diethylzinc respectively.

Reactivity studies and structural outcomes of a bulky dialkylaluminium amide in the presence of the N-heterocyclic carbene, ItBu

Aluminium reagent iBu2Al(TMP) (TMP is 2,2,6,6-tetramethylpiperidide) has previously shown interesting synergistic metallation chemistry when paired with alkali metal amides. Here its structural chemistry and reactivity is explored in the presence of the N-heterocyclic carbene, ItBu, 1,3-di-tert-butylimidazol-2-ylidene. Abnormal aItBu structures are obtained with iBu2Al(TMP) on its own and in the co-presence of LiTMP, NaTMP or KTMP. Reaction with phenol is stoichiometric dependent leading to the diphenolate [ItBu(H)]+ [(PhO)2Al(iBu)2]− and triphenolate [ItBu(H)]+ [(PhO)3Al(iBu)]− ionic complexes. Dinuclear aItBu(Ph)CN[Al(iBu)2NC(TMP)Ph]Al(iBu)2 was the surprising product from reaction with benzonitrile, displaying an imidoC- and (iBu)2Al- disubstituted imidazolium ring as well as a second imido unit made by addition of “non-nucleophilic” TMP across the benzonitrile triple bond. Potential insight into the mechanism of this intriguing complicated reaction was gained through the crystallographic characterisation of the ketamide [iBu2AlNC(Ph)TMP]2, a possible intermediate. Reaction with Ph2CHCN, diphenylacetonitrile, proved more straightforward affording the ionic complex [ItBu(H)]+ [Ph2CCN]−.

Mixed-Phase Ion-Exchangers from Waste Amber Container Glass.

This study investigated the one-pot hydrothermal synthesis of mixed-phase ion-exchangers from waste amber container glass and three different aluminium sources (Si/Al = 2) in 4.5 M NaOH(aq) at 100 °C. Reaction products were characterised by X-ray diffraction analysis, Fourier transform infrared spectroscopy, 27Al and 29Si magic angle spinning nuclear magnetic resonance spectroscopy and scanning electron microscopy at 24, 48 and 150 h. Nitrated forms of cancrinite and sodalite were the predominant products obtained with reagent grade aluminium nitrate (Al(NO3)3∙9H2O). Waste aluminium foil gave rise to sodalite, tobermorite and zeolite Na-P1 as major phases; and the principal products arising from amorphous aluminium hydroxide waste were sodalite, tobermorite and zeolite A. Minor proportions of the hydrogarnet, katoite, and calcite were also present in each sample. In each case, crystallisation was incomplete and products of 52, 65 and 49% crystallinity were obtained at 150 h for the samples prepared with aluminium nitrate (AN-150), aluminium foil (AF-150) and amorphous aluminium hydroxide waste (AH-150), respectively. Batch Pb2+-uptake (~100 mg g−1) was similar for all 150-h samples irrespective of the nature of the aluminium reagent and composition of the product. Batch Cd2+-uptakes of AF-150 (54 mg g−1) and AH-150 (48 mg g−1) were greater than that of AN-150 (36 mg g−1) indicating that the sodalite- and tobermorite-rich products exhibited a superior affinity for Cd2+ ions. The observed Pb2+- and Cd2+-uptake capacities of the mixed-product ion-exchangers compared favourably with those of other inorganic waste-derived sorbents reported in the literature.

A readily available neutral nickel catalyst for accessing linear ultrahigh molecular weight polyethylene in a living manner

It is of great importance and is highly desired in the olefin polymerization catalysis that a simple catalyst derived from cheap starting materials and short synthetic pathways exhibits superior catalytic property towards a polymerization reaction. In this contribution, starting from commercially available and cheap materials, by using a short and simple three-step reaction route we report a readily available neutral phenoxy-imine nickel catalyst, which significantly enables the formation of linear ultrahigh molecular weight polyethylene (~5 brs/1000C, Mn = 1531 kDa) in a living polymerization (PDI = 1.08–1.11). An enhancement of 77 times on the polymer molecular weight occurs compared to the classical 2,6-diisopropyl substituted phenoxy-imine nickel catalyst. This avoids a tedious synthetic procedure and the use of an excess aluminum reagent as the activator and the scavenger.

Highly Efficient Synthesis of 2-Substituted Benzo[b]furan Derivatives from the Cross-Coupling Reactions of 2-Halobenzo[b]furans with Organoalane Reagents

AbstractA highly efficient and simple route for the synthesis of 2-substituted benzo[b]furans has been developed by palladium-catalyzed cross-coupling reaction of 2-halobenzo[b]furans with aryl, alkynyl, and alkylaluminum reagents. Various 2-aryl-, 2-alkynyl-, and 2-alkyl-substituted benzo[b]furan derivatives can be obtained in 23–97% isolated yields using 2–3 mol% PdCl2/4–6 mol% XantPhos as the catalyst under mild reaction conditions. The aryls bearing electron-donating or electron-withdrawing groups in 2-halobenzo[b]furans gave products in 40–97% isolated yields. In addition, aluminum reagents containing thienyl, furanyl, trimethylsilanyl, and benzyl groups worked efficiently with 2-halobenzo[b]furans as well, and three bioactive molecules with 2-substituted benzo[b]furan skeleton were synthesized. Furthermore, the broad substrates scope and the typical maintenance of vigorous efficiency on gram scale make this protocol a potentially practical method to synthesize 2-substituted benzo[b]furan derivatives. On the basis of the experimental results, a possible catalytic cycle has been proposed.

Effect of Small-Scale Box-Fermentation on Catechin and Epicatechin Content of Lampung Cocoa Beans Varieties

Cocoa is one of the food commodities that is favoured by its high in polyphenols. The polyphenol and flavonoid in cocoa beans can prevent arteriosclerosis, diabetes and their related risk factors. This research aimed to analyze the total polyphenolic contents (TPC) and flavonoid contents (TFC) of three cocoa bean varieties, namely LAM, TSH, and SUL1 collected from Lampung, Indonesia. The study also aimed to understand the effect of adding starter culture on TPC and TFC contents during cocoa beans fermentation. The TPC and TFC were extracted using ethanol from ground-dried beans and measured three times using a spectrophotometric method based on the Folin-Ciocalteu method at 760 nm and aluminium reagents at 510 nm. LAM variety contained the highest TPC and TFC among other samples at 62.8 mg GAE/g and 21.9 mg QE/g, respectively. The TPC and TFC decreased during both fermentation treatments with starter culture and non-starter culture. The TPC of cocoa bean with starter culture and with non-starter culture decreased to 58% and 59% after fermentation, respectively. The TFC of cocoa bean with starter culture and with non-starter culture decreased after five days of fermentation, up to 58% and 75%, respectively. Interestingly, the TPC and TFC in fermented cocoa beans with starter culture were higher than those with non-starter culture. Therefore, it is concluded that three days of fermentation with starter culture can produce fermented cocoa beans with the preferred flavour/quality and maintain the TPC and TFC. However, the polyphenols and flavonoids content were reduced during the fermentation process.

Polyolefin recycling by C–C bond alumination

Efficient catalysis that simultaneously cleaves thermodynamically inert C–C bonds and generates functional moieties to stimulate chemical recycling of polyolefins is lacking. In this issue of <i>Chem</i>, Kanbur et al. design an organozirconium catalyst combined with aluminum reagents to enable a clever tandem C–C cleavage and carboalumination process that yields value-added alkylaluminum products.

Complete deconstruction of SF6 by an aluminium(I) compound.

The room-temperature activation of SF6, a potent greenhouse gas, is reported using a monovalent aluminium(i) reagent to form well-defined aluminium(iii) fluoride and aluminium(iii) sulfide products. New reactions have been developed to utilise the aluminium(iii) fluoride and aluminium(iii) sulfide as a nucleophilic source of F− and S2− for a range of electrophiles. The overall reaction sequence results in the net transfer of fluorine or sulfur atoms from an environmentally detrimental gas to useful organic products.

Alumination of aryl methyl ethers: switching between sp2 and sp3 C-O bond functionalisation with Pd-catalysis.

The reaction of [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl) with aryl methyl ethers proceeded with alumination of the sp3 C–O bond. The selectivity of this reaction could be switched by inclusion of a catalyst. In the presence of [Pd(PCy3)2], chemoselective sp2 C–O bond functionalisation was observed. Kinetic isotope experiments and DFT calculations support a catalytic pathway involving the ligand-assisted oxidative addition of the sp2 C–O bond to a Pd–Al intermetallic complex.

C–H Activation Catalyzed by Earth-Abundant Metals

Abstract This account describes our quest for controlling the reactivity of organoiron species, and developing an iron catalyst that can efficiently activate a C–H bond of a substrate possessing a directing group, followed by reaction with nucleophiles (magnesium, zinc, boron, or aluminum reagents), electrophiles (alkyl halides, alkanol derivatives, allyl ethers, alkenes, alkynes, chloroamines), or with another C–H substrate (heteroarenes or electron-deficient arenes). Our forays into C–H activation using cobalt, manganese, and chromium catalysis are also briefly discussed.

Reactions of an Aluminum(I) Reagent with 1,2-, 1,3-, and 1,5-Dienes: Dearomatization, Reversibility, and a Pericyclic Mechanism.

Addition of the aluminum(I) reagent [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl) to a series of cyclic and acyclic 1,2-, 1,3-, and 1,5-dienes is reported. In the case of 1,3-dienes, the reaction occurs by a pericyclic reaction mechanism, specifically a cheletropic cycloaddition, to form aluminocyclopentene-containing products. This mechanism has been examined by stereochemical experiments and DFT calculations. The stereochemical experiments show that the (4 + 1) cycloaddition follows a suprafacial topology, while calculations support a concerted albeit asynchronous pathway in which the transition state demonstrates aromatic character. Remarkably, the substrate scope of the (4 + 1) cycloaddition includes styene, 1,1-diphenylethylene, and anthracene. In these cases, the diene motif is either in part, or entirely, contained within an aromatic ring and reactions occur with dearomatisation of the substrate and can be reversible. In the case of 1,2-cyclononadiene or 1,5-cyclooctadiene, complementary reactivity is observed; the orthogonal nature of the C═C π-bonds (1,2-diene) and the homoconjugated system (1,5-diene) both disfavor a (4 + 1) cycloaddition. Rather, reaction pathways are determined by an initial (2 + 1) cycloaddition to form an aluminocyclopropane intermediate which can in turn undergo insertion of a further C═C π-bond, leading to complex organometallic products that incorporate fused hydrocarbon rings.