Benzyl complexes of rare earth metals

Data on the synthesis, structure, and reactivity of benzyl complexes of rare earth elements in the oxidation state +3 are integrated and analyzed. A variety of methods for the synthesis of homoleptic tris(benzyl) derivatives and heteroleptic mono- and bis(benzyl) complexes containing spectator ligands of various nature and denticity are considered. The attention is focused on the structure of Ln^III benzyl derivatives in the crystalline state. It is shown that the mode of coordination of the benzyl ligand to Ln³⁺ ions depends on the ionic radius and steric congestion of the metal center, as well as on the ligand nature and can vary from κ¹-C_α- to poly-hapta-coordination due to the non-valent interactions of the metal center with the ipso- and ortho-atoms of the aromatic ring.