Lewis bases overview

Polyfluorooxiranes rearrange to carbonyl compounds in the presence of a wide range of catalysts. The nature of the product carbonyl compound depends on the structure of the epoxide and the catalyst an overview is given in Scheme 8. Monosubstituted perfluorooxiranes generally give acyl fluorides with Lewis bases, and trifluoromethyl ketones with Lewis acids. Symmetrically 2,3-disubstituted perfluorooxiranes give ketones with either Lewis acids or Lewis bases. In the presence of Lewis acids, unsymmetrically 2.3-disubstituted perfluorooxiranes give a 1 1 mixture of the two possible ketones. 

Abstract. Within the context of Lewis base catalysis /V-heterocyclic carbenes represent an extremely versatile class of organocatalyst that allows for a great variety of different transformations. Starting from the early investigations on benzoin, and later Stetter reactions, the mechanistic diversity of /V-hctcrocyclic carbenes, depending on their properties, has led to the development of several unprecedented catalytic reactions. This article will provide an overview of the versatile reactivity of A-heterocyclic carbenes. 

The preparation and properties of halides of the actinides have been described fully. As most of these complexes are solid state, rather than molecular in nature, only overview information on classes of compounds will be provided. Adducts of the halide complexes will be discussed in the context of compounds of the respective Lewis bases vide infra). 

An overview of recent work from the Takats laboratory deals with divalent Ln(Tp Bu Me) complexes and preparation, molecular structure, NMR characteristics and reactivity of [Yb( x-H)(TptBu,Me)]2. Reactions of this compound with Lewis bases and Lewis acids, such as the perfluoroaryl boranes, a-bond metathesis reactions generally involving acidic H-X bonds, but also an example of C-Si bond cleavage, and insertion chemistry, primarily involving alkynes have been described. The molecular structures of representative complexes have been determined by X-ray crystallography.110... 

Abstract Carbohydrates generally possess multiple hydroxyl groups of similar reactivity, and selective monofunctionalizatimi is often difficult. Catalysis provides a versatile and potentially general solution to this problem. This chapter provides an overview of catalyst-controlled methods for the regioselective activation of carbohydrate derivatives. The catalysts discussed include organocatalysts (Lewis bases, Brpnsted acids/bases, and others) as well as those based on main group and transition metal elements. 

For an overview of indium trihydride complexes, see C. Jones (2001) Chem. Commun., p. 2293. See also S.G. Alexander and M.L. Cole (2008) Eur. J. Inorg. Chem., p. 4493 - Lewis base adducts of heavier group 13 halohydrides - not just aspiring trihydrides ... 

The international symposium on Recent Developments in Olefin Polymerization Catalysts was held in Tokyo in October 1989. This volume includes 38 i>apers fi"om the 31 lectures and 18 posters presented at the symposium, which covered the following topics Overview of super-active homogeneous and heterogeneous catalysts, kinetic profile of olefin polymerization including copolymerization, characterization of catalysts and polymers, methods for the determination of active center concentration, role of Lewis bases on the catalyst isospecificity, polymerization mechanisms, and synthetic pathways for functionalized polyolefins. We believe the contents are well balanced between fundamental research and application as well as between homogeneous and heterogeneous catalyst systems. 

Overview Cationic polymerizations proceed via a chain growth process which involves a carbenium ion (R3C+) at the chain end [19, 28]. Most examples of living cationic polymerizations utilize low temperatures (-90 °C to -30 °C) and electrophilic solvents, such as dichloromethane. In contrast to anionic polymerizations that require Lewis bases as initiators, cationic polymerizations employ Brpnsted acids or Lewis acids as initiators or coinitiators. For example, common Lewis acids include the halides of aluminum, boron, tin, and titanium. 

This chapter will give first an overview of silyl cations. Thereafter, very briefly, hypervalent sihcon compounds will be discussed. Strictly speaking, the concept of hypervalent sihcon compounds is part of Lewis base catalysis and will be discussed there in detail. However, since in this type of reachon a Lewis base forms in situ with a sihcon atom containing reagent or SiCh an intermediate, which functions as a Lewis acid to achvate substrates during the reaction, we also give here a few examples. Notably, sihcon is a semimetal. Hence, we leave it up to the reader to decide whether sihcon catalysts should be considered as organocatalysts. 

W. B. Jensen, The Lewis Acid-Base Concepts, An Overview, John Wiley Sons, Hoboken, NJ, 1980. 

This graduate-level text presents the first comprehensive overview of modern chemical valency and bonding theory, written by internationally recognized experts in the held. The authors build on the foundation of Lewis- and Pauling-like localized structural and hybridization concepts to present a book that is directly based on current ab initio computational technology. 

Manson (72,) expanded the concept to the solid state by observing that the strength of composite materials also depended upon the acid-base interaction between continuous and dispersed phases. More directly, Vanderhoff et al. (21) addressed the issue of adhesion of polymeric materials to corroded steel. They synthesized eight corrosion products of iron, and used the interaction scheme developed by Fowkes and Manson first to characterize the iron corrosion products as Lewis acids or bases and then to select polymer vehicles for practical coating systems. Such results were employed to enhance the adhesion of epoxy systems to substrates which were predominantly iron oxide in nature. A good overview of these Issues was presented by Fowkes in 1983 (74). ... 

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