Chapter 53 Organometallic compounds of the rare earths

Abstract

This chapter discusses the term organometallic compound inchides alkyl and aryl derivafives of the rare earths—the transition metals of group III, scandium, yttrium, lanthanum and the lanthanides cerium to lutetium with covalent metal-to-carbon σ-bonds, as well as the so-called π-complexes with more than monohapto metal-to-carbon bonds, for example cyclopentadienyl and olefin complexes, metal acetylides, but not carbonyls, cyanides and isocyanide complexes. Derivatives of scandium, yttrium and lanthanum are included and discussed together with the compounds of the lanthanides, because of many similarities in the synthesis and the chemistry of these organometallic derivatives of the rare earths. The common oxidation state of the rare earth elements is +3. Therefore organometallic compounds of the type RL 3 (R = rare earth metal, L = ligand) is diamagnetic for R = Sc, Y, La and Lu, but paramagnetic for the other lanthanides. The redox properties of some of the lanthanides, reflecting the electronic situation with an unfilled, half-filled, or completely filled of shell make the existence of organometallic compounds with the lanthanides in the oxidation state +2 and +4 possible, namely EuL 2 , YbL 2 , and CeL 4 . The rare earths are rather electropositive elements and are hard acids following the Pearson concept. This causes, in combination with the contracted nature of the 4f-orbitals of the lanthanides, poor overlap with ligand orbitals, and therefore, high ionic character in the metal-to-carbon bonds.