Redistribution of alkyl groups

Rate law and mechanism. The redistribution of alkyl groups on silanes in benzene is catalyzed by aluminum bromide. Suggest a scheme for it on the basis of the rate equation given. 

As shown in Eqs. (4.11) and (4.12), some dealkylation of the starting amine and redistribution of alkyl groups occur. Hydroamination of ethylene with PhNHj affords a low-yield mixture of N-ethylaniUne, N,N-diethylaniline, 2-methylquinoUne, 2-(l-butenyl)aniline, and N-ethyltoluidine [113, 114]. 

Redistribution of alkyl groups between pairs of Group IV atoms occurred only when the central atoms were adjacent members of the group, i.e., Si vs Ge, Ge vs Sn, Sn vs Pb, while the remaining combinations did not undergo reaction (232). However, the possibility exists that the intersystem constant in the latter case is either very large or very small. 

Redistribution of alkyl groups between Hg dialkyls is slow at RT by contrast, the more weakly bonded silyl- and germylmercurials exchange rapidly, yielding an equilibrium concentration of the unsymmetrical compound ... 

In a similar fashion, the redistribution of alkyl groups between organo-alanes and organoboranes proceeds via an alkyl-bridged boron-aluminum species ... 

The product undergoes a redistribution to produce R4A1C12 and R2A1C14. The reaction of aluminum with HgR2 results in transfer of alkyl groups,... 

Some of the reactions (e.g., that of dimethylaluminum chloride in Table 2) involve redistribution of alkyl and halide groups between the metals. The boronic acids, ArB(OH>2, prepared by Sn/B transmetallation, have been used in Suzuki coupling reactions. It is remarkable that the bistributyltin derivative of 1,1 -binaphthyl undergoes... 

Sita and Babcock have also prepared high molecular weight poly(dibutyl-stannane) from dibutylstannane using Rh(H)(CO)(PPh3)3 as catalyst.147 As is common with late metal catalysts, branching of the polymer chains is observed as a result of alkyl group redistribution. 

Since the above reactions proceed almost completely from left to right, it appears that similar to the redistribution of chlorine and hydrogen atoms between various moieties of alkylsilicon, the halogens prefer to be bonded to the tin moiety bearing the larger number of alkyl groups. 

Because of the commercial importance of halosilanes, particularly the dihalo and trihalo derivatives, in the production of silicone polymers, the reaction in which M = Si has received considerable attention. For example, the direct process produces MegSiCl and MeSiClg as part of a complex mixture including the valuable Me2SiCl2, which is diflScult to separate because of similar boiling points. Fortunately, the equilibration of alkyl groups on silicon is not statistical, a fact that permits a very useful application of the redistribution reaction ... 

Reaction is extensive after 2h and complete in 8h. (Some symmetrization of alkyl groups may occur when R = Me.) The reactivity is not markedly altered by the presence of EtjO or McjN however, Na[BeHEt2] adds readily to ethene (<100Nm , 8 h, 84 °C) in the presence of EtjO, but slowly in its absence. Reaction of ethene (5-8 X 10 Nm , 65°-70°C, 2-10 h) with EtBeH, formed in situ by reduction with NaH of the product of redistribution between BeCl2 and AlEtj, is a preparative route to BeEt2. 

H/D exhange in tetrameric iV-alkyl-iminoalanes produces statistical mixtures H4 D (AlNCMe3)4. H/Cl exchange in these and related compounds takes place without any exchange of alkyl groups, proving that redistribution of substituents... 

The cis addition of R BH to a substituted alkene can sometimes be complemented by the photochemical cis addition of a trialkylborane to the unsubstituted olefin, which affords the other geometrical isomer. Redistribution of organic groups about boron occurs very readily. Even though trialkylboranes exist as monomers, alkyl groups readily transfer between boron atoms. Unsym-metrical trialkylboranes are seldom stable above about 100°C. 

Lithium hydride reacts completely with 9-BBN and ThxBHj at room temperature after 48 h (Eq. 22.1), whereas ChXjBH, SiajBH, and IPC BH remain inert. In addition, the reactions of 9-BBN and ThxBHj in THE under reflux condition are completed in 3 h. However, the other organoboranes at reflux undergo rapid redistribution and/or elimination of alkyl group. 

Redistribution reactions are considered as quite important for the preparation of alkyltin halides having mainly identical alkyl groups. Actually, the redistribution reactions are halogenation reactions of organotin halides by SnX4 (X = F, Cl, Br, I). 

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