Structural Varieties in Heterobimetallic Lanthanide Disiloxanediolates: “Inorganic Metallocenes” versus In-Plane Metallacrowns

The previously proposed concept of “inorganic metallocenes” of group 3 and rare-earth elements has been tested
by preparing a series of novel disiloxanediolates with metals displaying different ionic radii. For the smaller scandium
and yttrium, approximately planar arrangements of the disiloxanediolate frameworks with solvent and chloride ligands
in trans positions were found. Thus, the compounds [{(Ph2SiO)2O}2{Li(DME)}2]ScCl(THF/DME) (2; DME = 1,2-dimethoxyethane and THF = tetrahydrofuran) and [{(Ph2SiO)2O}2{Li(THF)2}2]YCl(THF) (3) can be described as
heterobimetallic inorganic ring systems or metallacrown complexes with “in-plane” coordination of the metal. In
contrast, “out-of-plane” geometries with cis coordination of additional ligands were identified in the praseodymium
derivatives [{(Ph2SiO)2O}2{Li(THF)2}{Li(THF)}]Pr(μ-Cl)2Li(THF)2 (4) and [{(Ph2SiO)2O}2{Li(DME)}2]PrCl(DME)
(5). These compounds can be viewed as analogues of the known metallocene derivatives (C5Me5)2Pr(μ-Cl)2Li(THF)2 and (C5Me5)2PrCl(THF). The molecular structures of 2−5 have been determined by X-ray diffraction.