Rare-earth dialkyl and dihydride complexes bearing monoanionic ancillary ligands

Abstract

Rare-earth elements, including scandium, yttrium, and the lanthanides (La-Lu), possess unique chemical and physical properties, and constitute one of the last frontiers in the periodic table. Rare-earth elements are vital for many high-tech industry products such as smartphones and electric cars. However, the fundamental chemistry of the rareearth elements has been explored to a far less extent. The first organo rare-earth complexes Cp3Ln (1, Figure 1), which bear three cyclopentadienyl (Cp) ligands, were reported in the early 1950s [1], but these complexes did not receive much attention because of the lack of significant reactivity. In the early 1980s, the alkyl and hydride complexes supported by two cyclopentadienyl ligands (such as 2 in Figure 1) were reported [2]. Since then such metallocene complexes have dominated the research area of the organo rare-earth chemistry, because of their high activity in a series of carbon-carbon and carbon-heteroatom bond formation reactions [3]. Unfortunately, however, the catalytic activity of the monoalkyl (or monohydride) rare-earth metallocene complexes for the polymerization of olefins, in particular higher olefins such as 1-alkenes, styrene, 1,3- conjugated dienes and cyclic olefins, is generally poor [4]. Recently, dialkyl and dihydride rare-earth complexes bearing one cyclopentadienyl or related monoanionic ancillary ligands (such as 3 in Figure 1) have emerged as a new family of organo rare-earth complexes, which show unique structure and reactivity features that are different from those of the monoalkyl (or monohydride) analogues. This article is intended to highlight recent progress in the chemistry of this new class of rare-earth complexes [5].