Aluminum alkyne interactions

Aluminum-alkyne interactions were invoked when hydrosilylation of alkynes proceeded in the presence of catalytic amounts of AICI3 or EtAlCl2 [31]. Although most hydrometalations of alkynes occur in a cis configuration, trans-selective hydrosilylation was consistently observed (Scheme 6.14). 

It has been suggested that alkene or alkyne complexes are mechanistically important intermediates in hydroalumination and carboalumination reactions (124-126). Clear spectroscopic evidence for n interactions stems from investigations of alkenylaluminum compounds having a suitable intramolecular separation between the aluminum center and the double bond (127). IR and NMR data of these compounds show comparably lower alkene stretching frequencies and deshielded vinylic protons. Furthermore, these molecules are monomeric in solution this indicates that the tendency toward 7i-complex formation is stronger than that toward the dimeric bonding usual in aluminum alkyls. 

Lithium trialkylaluminum hydrides, such as lithium diisobutyl(methyl)aluminum hydride (15), which can be readily prepared by the interaction of diisobutylaluminum hydride with methyllithium in DME, are useful for the anti hydroalumination of internal alkynes (equation 9). ... 

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