Alkyl halides with metal cations

Methods to generate the unsaturated intermediate that adds alkane include photolysis of metal-carbonyl or -dihydride complexes, thermolysis of alkyl hydride complexes, and abstraction of halide with a cationic reagent or protonation of an alkyl group with an acid containing a weakly coordinating anion. For example, the photolysis of Cp Ir(CO)j or Cp IrfPMejJHj generates Cp Ir(L) (L = CO or and photolysis of the... 

Anionic complexes [R2Au] are present in salts with metal or large quaternary cations, but only a few compounds of this type have been isolated.1,2 Solutions of the lithium salts generated in situ are substrates for addition reactions with alkyl halides leading to alkylgold(m) compounds.26... 

We have recently shown that metal-exchanged zeolites give rise to carbocationic reactions, through the interactions with alkylhalides (metal cation acts as Lewis acid sites, coordinating with the alkylhalide to form a metal-halide species and an alkyl-aluminumsilyl oxonium ion bonded to the zeolite structure, which acts as an adsorbed carbocation (scheme 2). We were able to show that they can catalyze Friedel-Crafts reactions (9) and isobutane/2-butene alkylation (70), with a superior performance than a protic zeolite catalyst. 

It is in many ways unfortunate that the study of cationic polymerization has, from its very start, been so intimately linked with the very complicated and ill-understood chemistry of the metal halides. This connection is largely fortuitous and there is the promise of much progress in this field when these two problems can be attacked independently. On the one hand, we need to know much more about the complex acids and esters which are formed when water, alcohols, carboxylic acids, and alkyl halides react with metal halides on the other hand, a study of olefin polymerizations catalysed by simple acids such as HBr [14], HC104 [25], and H2S04 [26] should be rewarding, because they would presumably be unobscured by the complications and uncertainties accompanying the formation of the initiating species when this involves a metal halide. 

The alkylation of primary nitramines with alkyl halides is of little preparative value for the synthesis of secondary nitramines. Such reactions often result in a mixture of N- and 0-alkylated products. The product distribution appears to be very dependent on the nature of the cation of the nitramine used, with silver salts ° favouring 0-alkylation and alkali metal salts usually giving A-alkylation as the predominant product. However, this is not always the case. 

Compounds with a low HOMO and LUMO (Figure 5.5b) tend to be stable to selfreaction but are chemically reactive as Lewis acids and electrophiles. The lower the LUMO, the more reactive. Carbocations, with LUMO near a, are the most powerful acids and electrophiles, followed by boranes and some metal cations. Where the LUMO is the a of an H—X bond, the compound will be a Lowry-Bronsted acid (proton donor). A Lowry-Bronsted acid is a special case of a Lewis acid. Where the LUMO is the cr of a C—X bond, the compound will tend to be subject to nucleophilic substitution. Alkyl halides and other carbon compounds with good leaving groups are examples of this group. Where the LUMO is the n of a C=X bond, the compound will tend to be subject to nucleophilic addition. Carbonyls, imines, and nitriles exemplify this group. 

Acidic clay catalysts can also be used in alkylation with alcohols 98 The main advantages of these catalysts are the reduced amount necessary to carry out alkylation compared with conventional Friedel-Crafts halides, possible regeneration, and good yields. Natural montmorillonite (K10 clay) doped with transition metal cations was shown to be an effective catalyst 200... 

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