Sixty Years of the Chemistry of Rare-earth Organometallic Complexes

Abstract

Rare-earth elements include scandium, yttrium and fifteen lanthanides. Since Wilkinson and Birmingham reported the fist example of rare-earth organometallic complex, the chemistry of rare-earth organometallic complexes has had a great advance during the past sixty years. A variety of Cp containing rare-earth metal complexes, including mono-Cp, bis-Cp, and tri-Cp complexes, have been synthesized. Variation of the size of substituent on Cp ring, introducing the nitrogen or oxygen containing pendant arm to Cp ring or using ansa bis-Cp ligands make the synthesis and stabilization of these three types of rare-earth metal Cp complexes available. The Cp related ligands, such as indenyl and fluorenyl, also have been applied for the rare-earth organometallic complexes. From 1990's, there was a tendency to explore the rare-earth organometallic complexes with ancillary ligands beyond Cp and its derivatives in order to search for more efficient rare-earth metal catalysts. Non-Cp ligands, such as biphenolates, β-diketiminates, amidinates, guanidinates, etc. have been introduced into the chemistry of rare-earth organometallic complexes, and a larger number of non-Cp rare-earth organometallic complexes have been synthesized and characterized. The application of non-cyclopentadienyl ligands not only resulted in the rare-earth organometallic complexes with new structural features, but also the catalysts with high activity and high selectivity for the polymer synthesis and organic synthesis. The rare-earth organometallic complexes catalyze homo-and co-polymerization of olefins as well as specific polymerization of dienes and polar monomers. The discovery of the catalytic system composed of the neutral rare-earth metal dialkyls/borate enables to synthesize some interesting polymers which are difficult to be prepared by using other catalytic system. The rare-earth organometallic complexes are also able to catalyze some important organic reactions, such as hydroamination, hydrophosphinylation, and hydroalkoxylation, etc. Different from the late-translation metal catalyzed organic reactions, most of the rare-earth metal catalyzed ones do not involve oxidative addition and reductive elimination steps. The review describes some important developments of the chemistry of rare-earth organometallic complexes in the past sixty years.

Lanthanide‐Coordinated Black Phosphorus

“…Although other strategies have been suggested to protect BP, this strategy is still attractive due to the following points. First, compared to transition metal elements, Ln elements have bigger atomic radii and larger coordination numbers conducive to coordination of LnL 3 on BP . Secondly, since the 4f electrons do not contribute to bonding between lanthanide and phosphorus, the physical properties of the lanthanide ions are maintained .…”

“…First, compared to transition metal elements, Ln elements have bigger atomic radii and larger coordination numbers conducive to coordination of LnL 3 on BP. [38] Secondly, since the 4f electrons do not contribute to bonding between lanthanide and phosphorus, the physical properties of the lanthanide ions are maintained. [39] Thirdly, considering the multifunctionality of different lanthanide ions, the strategy may endow special functionalities as discussed in the following section.…”

Molecular Complexes of Emerging Tetravalent Rare‐Earth Metals

“…Exploring new oxidation state of rare‐earth metals (scandium, yttrium and lanthanides) is an important and challenging research subject for inorganic and organometallic chemists. Rare‐earth metals all exhibit the stable +3 oxidation state, [ 1 ] while it is more than a century of exploration before the +2 oxidation state is accessible for all rare‐earth elements except radioactive promethium. [ 2 ] Besides, cerium has the +4 oxidation state in molecular complexes, in which its electronic configuration adopts the noble gas xenon (4f 0 ).…”

Recent Advances in Rare‐Earth Polypnictides

“…These 17 elements have been widely explored in many research fields, including material, coordination, and organometallic chemistry . Since the first rare earth organometallic complex was prepared by Wilkinson and Birmingham in 1954, great advances of rare earth coordination chemistry with mono‐, bis‐, tri‐, and non‐cyclopentadienyl (Cp) ligands have been achieved in the past five decades, comprising a large portion of modern coordination chemistry of rare earth elements. In recent years, polypnictides, the Zintl clusters comprised of pentel elements, have arisen as prevalent new ligand scaffolds for rare earth cations, affording opportunities toward novel structural motif as well as new thermoelectronic devices and catalysts .…”