Alkyl group transfer reactions

Mixed-Metal Systems. Mixed-metal systems, where a zirconium alkyl is formed and the alkyl group transferred to another metal, are a new apphcation of the hydrozirconation reaction. These systems offer the advantages of the easy formation of the Zr—alkyl as well as the versatiUty of alkyl—metal reagents. For example, Cp2ZrRCl (R = alkyl or alkenyl) reacts with AICI3 to give an Al—alkyl species which may then be acylated with... 

The presence of Cu(i) or Cu(n) salts in the aforementioned reactions is critical. It is believed that organozinc reagents undergo transmetallation with copper species to yield more reactive complexes.301 A proposed301 catalytic cycle (Scheme 118) suggests that the alkyl group transferred to the enone from the copper metal in a bimetallic intermediate 207. 

Because mercury is easily reduced, dialkylmercury compounds are useful reagents for preparing a large number of alkyls of other metals by group transfer reactions. This is illustrated by the following equations ... 

Many organoarsenic compounds are prepared by reactions of AsC13 with alkyl group transfer agents such as Grignard reagents, lithium alkyls, or aluminum alkyls. Typical reactions include... 

This process is the result of the stability of trimethylboron. Alkyl group transfer also occurs in the reaction... 

Trialkylstannyl chlorides undergo dealkylation in the presence of iodine chloride, as shown in reaction 27. The alkyl iodide product reacts further very slowly in the case of primary alkyl groups, however, reaction 28 proceeds readily for R = i -Pr. The mechanism involves a charge transfer complex that can be detected in the reaction mixture. The compounds involved in the process can be analysed by GC, NMR and UVV spectroscopy282. 

When isobutene is polymerised in an inert solvent such as w-hexane by a metal halide with water as co-catalyst, the same end-groups are formed [9, 10] However, with other solvents, especially alkyl halides, transfer reactions may also introduce end-groups derived from the solvent [11, 12], for example ... 

Consequently, this reaction could be identified with a process where an alkyl fragment is transferred from one alkane molecule to another. The methyl group is the smallest alkyl fragment and the easiest to be transferred. However, crossmetathesis shows that ethyl and propyl groups can also be transferred. Indeed, heavier homolog alkanes can result from successive reactions or from heavier alkyl group transfer. Consequently, because of the successive reactions, the real product distribution corresponds to the following equation ... 

Whereas additions of carbon radicals to alkene moieties are the best characterized homolytic additions, carbon radicals are known to add to a wide range of unsaturated systems. These include polyenes, alkynes, arenes, heteroarenes, carbon monoxide,isonitriles, °° ° nitriles, ° imines and derivatives, ° ° aldehydes,nitrones, and thiones. ° Many of these reactions, such as addition of an alkyl radical to a carbonyl group, ° are thermodynamically unfavorable and readily reversible, and they form the basis of composite group-transfer reactions discussed below. 

Radical combinations become important for chemi-excitation only when the product can undergo reactions other than stabilization and reformation of the reactants. The alternative reactions require that weaker bonds be present in the new molecule than in the one formed in the combination. The alkyl halides are useful in this respect. Elimination of HX is a competitive secondary reaction106 -110. Our final example of the use of chemi-excitation is drawn from this field111. It shows the application of three techniques group transfer reactions, radical combination, and methylene insertion... 

It is anticipated that all of the complex reactions observed in the boron system and in the studies on indium and gallium derivatives to be discussed below will be found in alkylaluminum systems. There also will be some additional complications which arise from the fact that the A1R3 moiety often occurs in a dimeric form which will alter the energetics of the reaction and may in some instances govern the mechanism of exchange as observed for alkyl group transfer. 

In addition to the magnesium compounds, lithium alkyls are versatile reagents that also function as alkyl group transfer agents. Lithium alkyls are prepared by the reaction of lithium with an alkyl halide using benzene or petroleum ether as a solvent ... 

Alkyl group transfer. When metal alkyls react with compounds of a different metal, the products frequently are those in which one product forms a stable crystal lattice. For example, in the reaction... 

These compounds function as alkyl group transfer agents, particularly when the other compound is a somewhat covalent halide. Some typical reactions that illustrate alkyl... 

Transalkylation An alkylation reaction with an intramolecular alkyl group transfer. 

Complications can arise from accompanying reactions, e.g., alkyl-group transfer, hydridoborate formation and disproportionation. Thus, 2 1 MejSiLi and Me2BOMe includes as products MejB, Li[(Mc3Si)3BMe] and Li[(Me3Si)2BMc2]. 

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