Novel synthesis of lanthanoid complexes starting from metallic lanthanoid sources

Abstract

This review focuses on a new simple synthetic approach to prepare a series of novel organometallic and coordination compounds of lanthanoids using metallic sources. This method has some advantages: (1) one-pot reaction, (2) purification by simple crystallization, and (3) formation of salt-free compounds. The preparation of COT (cycloocta-1,3,5,7-tetraene), diene, and azo complexes of lanthanoid metals is demonstrated by direct reactions of the corresponding organic compounds with metallic lanthanoids in organic solutions such as THF. Moreover, homoleptic lanthanoid chalcogenolate complexes, Ln(ER)_n, were prepared by direct oxidative reaction of metallic lanthanoids with REER (R = aryl or pyridyl, E = S or Se) in organic solution. By controlling the stoichiometry of diaryl disulfides, both lanthanoid-(II) and -(III) compounds can selectively be prepared. Chalcogenolate ligands sometimes bridge two lanthanoid centers to form polymeric compounds, which are transformed to mononuclear compounds upon addition of a strong donor HMPA (= hexamethylphosphoric triamide, PO(NMe₂)₃) or introduction of bulkiness on the chalcogenolate ligands. Furthermore, a transannular S–S bond of a hypervalent compound, 1,5-dithioniabicyclo[3.3.0]octane bis(trifluoromethanesulfonate), reacted with metallic samarium to give a salt-free samarium(II) bis(triflate) compound.