Non-cyclopentadienyl ancillaries in organogroup 3 metal chemistry: a fine balance in ligand design

Over the past decade, several groups have targeted well-defined organometallic Group 3 metal complexes with ancillary ligand supporting environments alternative to the ubiquitous bis-Cp donor set. In addition to a desire to develop the fundamental organometallic chemistry of Group 3 bis-alkyl derivatives, these compounds are of interest as catalyst precursors for olefin and lactide polymerization processes, as well as olefin hydrosilation, amination and hydrogenation cycles. This review surveys the non-Cp organometallic chemistry of the ligands which have so far been explored for this purpose, commenting on the fine balance of steric and electronic properties necessary to stabilize monomeric, base-free organometallic compounds of these metals. While bona fide organometallic compounds have not been explicitly prepared in all cases, promising ligands in this regard are also included. The review covers the literature from about 1994 forward, encompassing 35 new ligand systems.