Alkyl groups, redistribution

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. 

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]. 

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

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). 

Reactions in which Phosphorus is Electrophilic.—Further study has been made of the reactions between chlorodialkylphosphines (26) and phosphites or phosphonites.28 By appropriate choice of the alkyl groups in (26), redistribution reactions can be inhibited and good yields of products (27) with P—P bonds are obtained.28... 

Above 100° C, thermal redistributions were observed in the trialkylborane systems involving also isomerization of primary alkyl groups to secondary alkyl groups and subsequent equilibration of the primary and secondary alkyl groups on the boron atoms (115,141,171). 

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. 

The redistribution and cleavage reaction of mixtures of tetramethylgermane and tetrabutylgermane with excess of aluminum chloride give di- as well as trichlorogermanes having mixed alkyl groups. 

Data for the analogous ethyl (220) compounds indicate that the equilibrium constants of the type of Eqs. (129)—(131) are very small for this system also. Consequently, it may be concluded that, in redistribution equilibria involving alkyl groups and halogens on tin, the mixed alkyltin halides are preferred. Mixtures having an overall composition corresponding to one of the mixed alkyltin halides contain this species in major amounts. 

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 ... 

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 ... 

If redistribution proceeds through the formation of three-center, two-electron bonds (Scheme 1), alkenyl, aryl, alkynyl, allyl, benzyl and propargyl groups should participate more readily than the alkyl group, but this point is not established. Catalysis by boron hydrides is not applicable where alkenyl or alkynyl groups are present, because the boron hydrides are consumed through hydroboration. 

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. 

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