Aluminium dimeric structure

Hydrogen is not unique in forming the middle partner in (3c, 2e) bridge bonds. A number of aluminium alkyls and aryls A1R3 have dimeric structures similar to diborane. The CH3 group behaves very much like an H atom in many circumstances, and furnishes a singly-occupied orbital for the formation of (3c, 2e) bonds. 

AlBr3 in the vapour state as well as in inertorganic solvents exists as dimer. In the dimeric structure, each aluminium atom forms one coordinate bond by accepting a lone pair of electrons from bromine atom of another AlBr3 molecule and thus completes an octet of electrons. 

A model olefin polymerization catalyst previously characterized as [(C5H5)2TiAlEt2]2 has been studied by X-ray diffraction, H n.m.r., and mass spectral techniques. The compound contains (l- -CjHj) and/i(l- dimeric titanium-aluminium hydride structure (3) has been suggested. Alkyl exchange between a polymeric alkyl-titanium compound and alkylaluminium compound, present in excess, is... 

Another approach is by redistribution between R3AI and AlClj. Halogen is a better bridging group than methyl to aluminium. The structure of Me Al Cl (Fig. 3.1) is very similar to that of the Al Cl dimer. 

Akitt and Duncan have provided further Al NMR evidence for the structure of the tetramer in solution. The spectrum consisted of a very broad peak due to tetrahedral aluminium and a sharper peak due to the central octahedral aluminium in the required 3 1 ratio of intensities. Owing to the quadrupole moment of the Al nucleus, the line width of the NMR signal depends on the symmetry of the electric field and gives independent evidence of the coordination of the aluminium. Furthermore, the structures of a number of other aluminium alkoxides were elucidated in 1984 by Al NMR spectroscopy, which supported the earlier proposed structures of a dimer (2-VII) and linear trimer (2-XI). It may be mentioned that a tetrameric structure for aluminium isopropoxide [Al(OPr )3]4 ° and a dimeric structure for aluminium f-butoxide [Al(OBu )3]2 have been confirmed by X-ray crystallography. 

Diborane has a qeometric structure similar to that of dimeric aluminium chloride, namely... 

Yoshino reports a novel and general method for the C-3 acylation of indoles with acyl chlorides in the presence of dialkylaluminium chloride which obviates the need for prior N-protection . Interestingly, as described in this preliminary communication, the unprotected indoles 147 are first treated with the Lewis acids prior to addition of the acid chlorides, yielding the desired 3-acyl derivatives 148. In reactions more typical of indoles under acidic conditions, Nakatsuka determined the structures of the dimers and trimers of 1-trimethylacetylindole produced in the presence of aluminium chloride . 

Recently, reactions of dimeric [Me2Al(/x-NEt2)]2 with different tripodal ligands have been reported. Along with an Al(/x-0)2Al ring, two Al(/i-N)2Al motifs are noted in the core of the crystal structure of the tetra(aluminium)... 

The chemistry of indium complexes of aU types in metal oxidation states lower than +3 has been comprehensively reviewed. Few lower oxidation state mononuclear amido complexes of indium are well characterized, however, and no structure has been reported for an In(I) amide. The compound In N(SiMe3)2 n. which is unstable, " has been characterized NMR spectroscopy but its structure is unknown. The structures of several In(I) complexes, related to amides but outside our current scope, have been described. Like its aluminium and gallium counterparts, the p-diketuninate derivative [ In N(Dipp)C(Me) 2CH] has been characterized, as has the closely related species [ In N(Dipp)C(CF3) 2CH]. ° These feature V-shaped, two-coordination at the metal. The less bulky [(In N(Mes)C(Me) 2-CH)2] ° and 15-2.6-.Vlc,)( (Me) i are dimeric with long In In bonds of... 

Many three-dimensional polymeric substances are particularly refractory, insoluble and unreactive. One- and two-dimensional polymers tend to be more soluble. For example, dichlorides and trichlorides of the 3d elements are generally quite soluble in weakly-polar organic solvents such as alcohols, ethers and ketones. The driving force here is the formation of complexes with the solvent molecules. These compounds are also soluble in water, with some degree of hydrolysis. Aluminium(III) chloride (which has a layer structure similar to that of CrCl3) dissolves in some non polar organic solvents, such as benzene, in which it forms A12C16 dimers. 

Other groups such as CH3 can do this, e.g. in dimeric aluminium methyl, Al2 (CH3)6, which has a structure similar to B2H6 with CH3 in place of H. 

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