In contrast to their transition-metal analogues (which have long been known as active catalysts for olefin polymerisation), the chemistry of cationic rare-earth metal alkyl species has only recently been developed. 1 The use of nitrogen-based facial tridentate ligand moieties (such as 1,4,7-triazacyclononane, tris(pyrazolyl)methane and tris(oxazolinyl)methane) has played an important role in opening up this chemistry. 2 A disadvantage of these ligand systems is ...
