Aluminum compounds structure

Nickel(O) reacts with the olefin to form a nickel(0)-olefin complex, which can also coordinate the alkyl aluminum compound via a multicenter bond between the nickel, the aluminum and the a carbon atom of the trialkylaluminum. In a concerted reaction the aluminum and the hydride are transferred to the olefin. In this mechanistic hypothesis the nickel thus mostly serves as a template to bring the olefin and the aluminum compound into close proximity. No free Al-H or Ni-H species is ever formed in the course of the reaction. The adduct of an amine-stabihzed dimethylaluminum hydride and (cyclododecatriene)nickel, whose structure was determined by X-ray crystallography, was considered to serve as a model for this type of mechanism since it shows the hydride bridging the aluminum and alkene-coordinated nickel center [31]. 

The structure of dimethylberyllium is similar to that of trimethylaluminum except for the fact that the beryllium compound forms chains, whereas the aluminum compound forms dimers. Dimethylberyllium has the structure shown in Figure 12.3. The bridges involve an orbital on the methyl groups overlapping an orbital (probably best regarded as sp3) on the beryllium atoms to give two-electron three-center bonds. Note, however, that the bond angle Be-C-Be is unusually small. Because beryllium is a Lewis acid, the polymeric [Be(CH3)2] is separated when a Lewis base is added and adducts form. For example, with phosphine the reaction is... 

U.S. 5,466,392 Organic electroluminescence device and compound having an aluminum complex structure... 

XXXVII we also see a bridging group with Al—C distances very close to that observed in other bridged aluminum compounds. The distance between the metal centers in this compound is similar to that observed in the simpler aluminum derivatives but greater than the sum of the covalent radii of the two metals (2.54 A), which may be an indication that Ti—Al interactions do not increase the stability of the bridged system. Structures on Cp2MMe2AlMe2 (M = Y, Er, and Yb) have been recently completed and clearly show stable electron-deficient bonds between the aluminum and the transition metal moiety (XXXVIII) (12). 

Syndiotactic 1.2 polybutadiene has also been made by Longiave and Castelli (49) using an anionic cobalt catalyst made from oxygenated aluminum compounds. Less amounts of 1.2-structure were found in polymerizations in hydrocarbon media. Alkyllithium produced only 6.8% 1.2-structure with the remainder being 1.4 cis and trans. 

The known dialkyl(cyclopentadienyl)aluminum compounds are all highly fluxional 124,133) IR and NMR data are therefore not conclusive evidence for their ground-state structures. We restrict ourselves to those compounds where X-ray crystal structure or gas phase electron diffraction data are available. 

The electron diffraction data of this complex are consistent with a structure similar to that of the analogous aluminum compound XXXIII (see Fig. 9). 

In analogy to the synthesis of the aluminum compounds XXXVI and XXXVII the closo gallium carboranes XLIII and XLIV have been prepared (141), but crystal structures are not yet available. From NMR spectroscopic data it appears that they possess icosahedral structures as shown in Fig. 9. 

Meanwhile, awaiting reaction of the chemistry community to such structures, canonical names in both the IUPAC and the proposed system are supplied for this set of compounds. A corresponding description and nomenclature for related aluminum compounds is presented. 

The precipitate prepared at 80° C. at about the stoichiometric AlEta/TiCE ratio of H has a reddish-brown color, and, according to x-ray analysis, consists of 3-TiCla, whereas the product prepared at 170° C. at the same Al/Ti ratio has a purple color and the structure of 7-TiCE (4, 24, 26). Analysis further showed that the TiCE thus formed contains an appreciable amount of aluminum compounds, and if prepared at 80° C., also some ethyl groups. These aluminum compounds, which apparently consist mainly of A1CE, and possibly of some AEEtCE, are taken up in the crystal lattice of the TiCE since they could not be removed by washing and hardly show up in the x-ray diagram (4, 24). About one out of every six titanium atoms is replaced by aluminum in the 80° C. solid reaction product (4), whereas in the 170° C. product, this... 

An operational description is that one reactant (the more ionic compound with the more electropositive metal) transfers alkyl anions to the other. Thus the four methyl groups in Li2BeMe4 form a distorted tetrahedron around the beryllium, with longer distances to the lithium ions. However, this description is oversimplified. The low-temperature nuclear magnetic resonance (NMR) spectrum of Li3MgMe5 has three different methyl resonances, suggesting structure (14), related to the MeLi tetramer. Ate complexes with zinc and aluminum compounds also form. Electron-deficient bridge-bonded structures, exemplified by the X-ray structure of... 

---