Aluminium hydrido complexes

While investigating the oligomerization of ethene by aluminium alkyls (p. 80), Ziegler and coworkers noticed that in the presence of traces of nickel dimerization to 1-butene occurs instead. Very active catalysts can be generated by adding an alkylaluminium halide to [(f/ -CjHJNiCl]. The phosphine complexes NiL are also effective in the presence of acids. A nickel hydrido complex is first formed which adds to ethene to give an ethyl intermediate which can either eliminate 1-... 

The Amine Complexes of Aluminium Hydride, V. Hydrido Aluminium Borohydride Derivatives. Inorg. Chem. 2, 515 (1963). 

Semmelhack et al. chose CuBr, together with either Red-Al or LiAl(OMe)3H in a 1 2 ratio, to afford presumed hydrido cuprates, albeit of unknown composition [llj. In THF, both the former Na complex and the latter Li complex are heterogeneous (and of differing reactivities), yet each is capable of 1,4-reductions of unsaturated ketones and methyl esters (Eq. 5.4). Commins has used a modified version, prepared from lithium tri-t-butoxy-aluminium hydride and CuBr (in a 3 4.4 ratio), to reduce a 3-substituted-N-acylated pyridine regioselectively at the a-site [12]. 

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