Redistribution halides

Halide redistribution is the best known and most often observed type of transfer between organometallic complexes. Thus halide transfer is often observed during the transfer of other ligands such as Cp, R, H, and CO. Studies concerned with multiple exchanges are covered under other headings. The following studies have been concerned mainly with halide exchange. 

Discuss these reactions in terms of redox processes and halide redistributions. 

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). 

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... 

Organotin halides are commonly prepared by the Kocheshkov redistribution reaction, where an organic group on tin (e.g., in SnR4) exchanges (reversibly) with a halide group on tin (e.g., in SnCLt).64 Two recent examples are shown in Equations (125) and (126). The first reaction exploits the high reactivity of the Sn-Me bonds, and the second... 

Nucleophilic attack by iV-methylaniline is favoured by electron-withdrawing groups on the amide and acyloxyl side chains. A series of / ara-substituted Af-acetoxy-Af-butoxy-benzamides (138) (Table 6) gave a weak but positive Hammett correlation with a constants (p = 0.13, r = 0.86) °. The analogous reactions of pyridine with para-substituted phenacyl halides in methanol afforded a similar Hammett correlation a, p = 0.25) . The bimolecular rate constants for the limited series of Ai-benzoyloxy-A-benzyloxybenzamides (139) in Table 6 correlated strongly with Hammett a constants (p = 1.7, r = 0.97) °. Stabilization of developing carboxylate character supported the computed charge redistribution in the transition state ... 

Use of di-M-butylstannyl dichloride along with an acyl or silyl halide leads to addition of allylstannanes to the aldehydes.106 Reaction is also promoted by butylstannyl trichloride.107 Both SnCl4 and SnCl2 also catalyze this kind of addition. Reactions of tetraallyl-stannane with aldehydes catalyzed by SnCl4 also appear to involve a halostannane intermediate. It can be demonstrated by NMR that there is a rapid redistribution of the allyl group.108... 

The second route (Scheme 1) is a redistribution reaction, in fact the Schlenk equilibrium. This route may be used in the reverse direction for the preparation of pure diorganomagnesium compounds from organomagnesium halides. Addition of a ligand, usually dioxane, that forms an insoluble complex with magnesium dihalide, shifts the Schlenk equilibrium completely to the left side and allows isolation of pure diorganomagnesium compounds from the remaining solution. ... 

Attempts to isolate mixed halides of tin from mixtures of tin tetrahalides have been unsuccessful because of apparent rapid redistribution of halogen atoms. Existence of such mixed species has been suggested by extra lines ob-... 

In general M and M may differ or be the same and X may be NR2, OR, a halide, SR, S, 0, etc. The use of Group I metal amides in the synthesis of other metal amides (equations 12-19) provides one class of this type of reaction. A four-center transition state can in most cases be invoked and in studies of the ligand redistributions between Ti(NMe2)4 and Ti(OR)4 compounds (R = Bu and Pr ) activation parameters are consistent with this view.226,227... 

In addition to the redistributions discussed above which involve exchanges on aluminum atoms only, there is a great deal of literature available on the exchange reactions of aluminum alkyls with halides, oxides, and alkoxides of other elements which undoubtedly are also equilibrium reactions. These, however, have found great interest as methods for the syntheses of organometallic compounds in general 129, 130). It appears that the equilibria in these systems lie almost completely at the side of the alkyl compound of the other element. 

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. 

Intermolecular redistribution of CO, halide, and phosphine ligands has been observed in various [MX(CO)(PR3)2] (M = Rh or Ir, X = Cl or Br) systems using i.r. and n.m.r. spectroscopy.127 The authors suggested that CO and halide exchange occurs via the doubly five-co-ordinate, bridged intermediates (28a) and (28b) (M =... 

A complication to the formation of a single compound from halide displacement reactions is the ability of the main group element center to undergo redistribution reactions. Examples are given in Eqs. (166)— (169).41 45 These reactions probably account for why the complexes [Co(CO)4]2EC1 and [Co(CO)4]EC12 (E = P, As, Sb) have not been isolated.57... 

Chemical Properties. The most important reactions which tetraorganotins undergo are heterolytic, ie, electrophilic and Kocheshkov redistribution (81—84). The tin—carbon bond in tetraorganotins is easily cleaved by halogens, hydrogen halides,... 

The most widely utilized reaction of tetraorganotins is the Kocheshkov redistribution reaction, by which the tri-, di-, and in some cases the monoorganotin halides can be readily prepared ... 

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