Aluminium halides, complexes

Eley, D. D., and H. Watts Aluminium Halide Complexes with Pyridine, Trimethylamine and Triethylamine, Part I. J. chem. Soc. [London] 1952, 1914. 

Research initiated at the CSIRO Division of Materials Science, Melbourne and now being continued at the University of Tasmania, has led to the development of a group of highly active and extremely versatile catalyst systems (refs. 6-8). The systems comprise nickel dithio-e-diketonate phosphine complexes (I) and (II) activated by a suitable cocatalyst such as an alkyl aluminium halide complex. 

A new synthesis giving good yields of highly substituted phosphole oxides (24) is the reaction of aluminium halide complexes of cyclobutadienes (23) with phosphonous dichlorides (Scheme 2). The synthesis of several substituted dibenzophospholes, e.g., (25), has been reported. ... 

It is known that the conducting species in solutions of aluminium halides in alkyl halides are complex for instance solutions of aluminium bromide in ethyl bromide [70] contain the ions Al2Br5+ and Al2Br7 ... 

Having commented briefly on the first two parts of my new theory (the self-ionisation and the initiation by AlX+2), it is appropriate to consider the complex formation between monomer and metal halide, expressed by Equation (ii), which we have mentioned in the previous section. This complex formation actually provides an easy and plausible explanation for some of the hitherto rather obscure phenomenological differences which are observable when monomer and aluminium halide solutions are brought together in different ways we can distinguish three such techniques which give very different results. 

When the aluminium halide solution is added to a solution of monomer, only the aluminium present as cations can initiate (disregarding any active cations that may have been formed by reaction of the initiator with impurities in the solvent) and the unionised aluminium halide becomes complexed with monomer and thus formation of further ions from it stops or becomes at best a very slow process. This is what was called the Esso technique [1] and it was the commonest method of experimentation. If the system is sufficiently free from terminating impurities and if the propagating ions are not occluded in precipitated polymer, all the monomer should be consumed eventually, and so the bound aluminium halide should in the end become free by the shifting of equilibrium (ii). However, these conditions are generally unfavourable for the reaction going to completion, and it comes virtually to a stop at incomplete conversion. 

A quite different situation prevails when the monomer is run into a solution of the aluminium halide. The polymerisation initiated by the AlX+2 ions in solution is very fast so that there is never sufficient monomer to complex an appreciable fraction of the aluminium halide thus there is no obstacle to the continuous formation of AlX+2 ions by reaction (iii), and the polymerisation therefore goes to completion. Such polymerisations are always accompanied by a rapid and large increase in conductivity. 

Proposition 3 Most of the un-ionized aluminium halide becomes complexed with unreacted monomer the resulting complex is not an initiator. The concentration of free aluminium halide is thereby reduced so much, that the rate of the ionogenic reaction (ii) (the formation of A1X2+) becomes negligibly small, and there is thus no further initiation. This accounts for the limited yields which are generally found in this type of polymerisation, and which had defied plausible explanation. 

These experiments provide the most direct evidence so far for the formation of complexes between A1X3 and isobutylene. The formation of such complexes was of course to be expected on the basis of the complex formation between aluminium halides and other olefins [29-33] and between titanium tetrachloride and isobutylene [34], and numerous other examples of complexes formed by an olefin and a metal halide it can be objected... 

Soluble cobalt and nickel catalysts for conjugated diene polymerization are usually prepared in the presence of monomer with the formation of a TT-allylic structure as a relatively stable intermediate, but the nature of attachment of other ligands to the active site is not known. Aluminium halides and cobalt halides react to form complexes of the structure (IX) [57]... 

The dimeric allylic nickel halide complexes are simpler in that no problems of reaction with organo-aluminium compounds are involved. They are of low activity and give polymer of low molecular weight owing to a rapid monomer transfer reaction [61]. The active centre is formed by dissociation of the complex in the presence of monomer and since the rate is proportional to [Ni] and [M] the extent of dissociation is small and the complex with monomer of low stability. 

In the presence of aluminium halides nitronium halides react forming complex nitronium salts [33,40] ... 

Metal Chloride Complexes. Optimum conditions for employing lithium aluminium halide as co-catalyst with tungsten hexachloride have been esta-... 

To avoid the formation of HCl in the synthesis of supported Lewis acidic ILs, ionic liquids bearing an alkoxylsilyl group on the alkyl chain, which can be covalently bound (grafted) to the surface, were used. In this procedure the aluminium halide was introduced subsequently, giving a highly acidic ionic complex on the surface of the support (Scheme 4.13). 

The sigma-complexes of cyclobutadienes and aluminium halides react with activated nitriles (e.g. EtOjCCN) to yield substituted pyridines. The sigma-complexes are themselves formed by aluminium-bromide-promoted cyclodimerization of alkynes (Scheme 3). In an extension of this work, Dewar-... 

The well-known Sm ry -arene complexes are generally prepared by the reaction of arenes with rare-earth trihalides in the presence of aluminium halides. This reaction was also effective with samarium diiodide and was extended to thulium diiodide however, an attempt to react Tml2 with naphthalene in toluene in the presence of aluminium trichloride was not successful but resulted in the isolation of an ry -toluene complex of Tm [77 -(CH3C6H5)Tm(AlCl4)3] (Figure 6) (Fagin et al., 2005). 

Cyanides do form metal complexes, and are important as linking groups between metalsAn important reaction of cyanides is with a molecule already complexed to a metal. This reaction is quite similar to the reaction reported by Hogeveen between aluminium halide a complexes of cyclobutadiene and cyanides, yielding a mixture of pyridines. 

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