Lewis acids compounds

Negishi previously reported that a wide variety of Lewis-acidic compounds catalyzed hydrozirconation of alkenes such as 1-decene 108 with /-BuZrCp2Cl.126 It was found that the reaction of 1-decene with 1.1 molar equiv. of TIB A, in the presence of 2-5 mol% of chlorine-containing late transition metals, led to the formation of 1-iododecane 110 after treatment of the product with iodine (Table 9). 

Abstract The term Lewis acid catalysts generally refers to metal salts like aluminium chloride, titanium chloride and zinc chloride. Their application in asymmetric catalysis can be achieved by the addition of enantiopure ligands to these salts. However, not only metal centers can function as Lewis acids. Compounds containing carbenium, silyl or phosphonium cations display Lewis acid catalytic activity. In addition, hypervalent compounds based on phosphorus and silicon, inherit Lewis acidity. Furthermore, ionic liquids, organic salts with a melting point below 100 °C, have revealed the ability to catalyze a range of reactions either in substoichiometric amount or, if used as the reaction medium, in stoichiometric or even larger quantities. The ionic liquids can often be efficiently recovered. The catalytic activity of the ionic liquid is explained by the Lewis acidic nature of then-cations. This review covers the survey of known classes of metal-free Lewis acids and their application in catalysis. 

Some common initiators for cationic polymerization reactions are protonic acids, Friedel-Crafts catalysts (Lewis acids), compounds capable of generating cations, or ionizing radiation. 

Another conceivable structure, namely a monomeric four-membered ring, was observed when electron-withdrawing C6P5 substituents were introduced at boron to increase its Lewis acidity (compounds 40a-d).52 53 The presence of intramolecular P-B interaction was unambiguously substantiated by 31P and 11B NMR data (Figure 7). So far, the lack of suitable single crystals prevented structural characterization, but DFT calculations... 

Coordination catalysts, which are usually applied for the polymerisation and copolymerisation of heterocyclic and heterounsaturated monomers, involve a wide range of metal derivatives characterised by a moderate nucleophilicity and relatively high Lewis acidity. Compounds of group 2 and 3 metals, such as zinc, cadmium and aluminium, as well as transition metals, such as iron, are representative coordination catalysts. The appropriate Lewis acidity of the metal and the appropriate nucleophilicity of the metal substituent in the catalyst make the monomer coordination favourable prior to the nucleophilic attack of the metal substituent on the monomer not yet coordinated. 

As a result of their being able to react as Lewis acids, compounds having the formula SnX2 also form many complexes with molecules containing O and N as the electron donor atoms (H20, pyridine, amines, aniline, etc.). 

AlCl3-A-butylpyridinium chloride, AlCl3-l-ethyl-3-methylimidazolium chloride, HCl-l-ethyl-3-methylimidazolium chloride, and AlCl3-LiSCN mixtures have been studied using X-ray and neutron scattering [164-167]. These studies have provided information about the specific interactions between anions and cations within the ILs. Unfortunately, little additional information could be extracted from the data. In particular, no information about the structure of the respective ILs beyond the first coordination sphere could be obtained. Importantly, however, the authors show that in AlCl3-LiSCN, the N and not the S atom of the SCN ion coordinates to the Al ion. This was explained with a hard base/hard acid interaction which can be expected for a Lewis acid compound like A1C13. 

A novel example of this type of SnR2 Lewis acid compound is the product obtained from the transmetallation reaction of bis[3-(dimethyla-mino)propyl]zinc with bis(dibenzoylmethanato)tin(II). 

Many halides and oxides are Lewis acids compounds with lone-pairs are Lewis bases. Bronsted acidity is possible in hydrides and oxoacids. Halide complexes can also be formed by ion transfer. 

Lewis acids Compounds that accepts an electron pair donated by a Lewis base. Some common examples include aluminum chloride, ferric chloride, boron trifluoride, niobium pentachloride, and the lanthanide triflates. 

Use of nonaqueously prepared DEAE celluloses as Lewis bases offers potential for formation of metal ion complexes between transition metal ions such as Cu and Ni 2j formation of charge-transfer complexes with electron acceptor compounds such as ortho-and para-chloranils or bromanils and with other Lewis acid compounds such as BI3. 

One-pot synthesis of helical aromatics 423 was achieved under MWI by the reaction of WA -diphenyl-p-phenylenediamine (421) and dicarboxylic acids 422 under solvent-free conditions in the presence of a Lewis acid. Compounds 423 were obtained within 5 min in 34-84% yields (Scheme 83), but conventional heating required 9h to give 18-80% yields (04JOC7794). 

Recently the chemistry of nucleophilic silylenes has received a lot of attention. Decamethylsilicocene (1) can be considered as a hypercoordinated nucleophilic silylene [1]. Here we report on reactions of 1 with Lewis-acidic compounds of elements of groups 13 to 15. 

Lewis acid compounds SnCU, SnBr4, PbCU, TiCU, ZnCIa, BF3 142-143... 

Lewis acid catalysts are an interesting option for the fatty acid esters production [16,17], However, Lewis acid compounds that are traditionally used in organic synthesis such as BF3 are more expensive than Bronsted acid catalysts, and are more hardly manipulated, in addition to be few water tolerant. Those unfavorable aspects difficult the use of Lewis acid catalysts in FFA esterification at industrial scale [18],... 

Propargyl amines (145) have been used to prepare 3-amino-2,3-dihydro-2-arylmethylidenebenzofurans (146) with the use of Ag (I) catalyst (Scheme 31). At elevated temperatures (100 °C) or with the use of Lewis acids, compound (146) ionizes to the highly stabilized 2-benzofuranmethyl carbocation (147). The resulting salt collapses to provide a good yield (87%) of the 1,3-migration product (148). With the addition of furan or an allylstannane, the cationic intermediate provides products (149) and (150) in 43% and 73% yields, respectively. 

With almost all Lewis acids, compounds (274) prevailed as products, but the use of T1CI4 in diethyl ether resulted in exclusive formation of (275). A proposed mechanism which outlines competitive pathways responsible for the formation of... 

Lewis acids, compounds with empty orbitals capable of accepting electron pairs, initiate cationic polymerization of epoxy resins. In this case the propagating species is a positive ion. The most commonly used Lewis acids are... 

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