Rare earth metal complexes based on β-diketiminato and novel linked bis(β-diketiminato) ligands:: Synthesis, structural characterization and catalytic application in epoxide/CO2-copolymerization

Mesityl substituted beta-diketiminato lanthanum and yttrium complexes [(BDI)Ln{N(SiRMe2)}(2)] (BDI = ArNC(Me)CHC(Me)-NAr, Ar = 2,4,6-Me3C6H2, Ln = La, R = Me (1), H (2a); Ln = Y, R = H (2b)) can be prepared via facile amine elimination starting from [La(N(SiMe3)(2)}(3)] and [Ln{N(SiHMe2)(2)}(3)(THF)(2)] (Ln = Y, La), respectively. The X-ray crystal structure analysis of 1 revealed a distorted tetrahedral geometry around lanthanum with a eta(2)-bound beta-diketiminato ligand. A series of novel ethylene- and cyclohexyl-linked bis(beta-diketiminato) ligands [C2H4(BDAr)(2)]H-2 and [Cy(BDIAr)(2)]H-2 [Ar = Mes (=2,4,6-Me3C6H2), DEP (=2,6-Et2C6H3), DIPP (=2,6-i-Pr2C6H3)] were synthesized in a two step condensation procedure. The corresponding bis(beta-diketiminato) yttrium and lanthanum complexes were obtained via amine elimination. The X-ray crystal structure analysis of the ethylene-bridged bis(beta-diketiminato) complex [{CyH4(BDIMes)(2)}YN(SiMe3)(2)] (3b) and cyclohexyl-bridged complexes [{Cy(BDIMes)(2)}LaN(SiMe2)(2)] (7) and [{Cy(BDIDEP)(2)} LaN(SiMe3)(2)] (8) revealed a distorted square pyramidal coordination geometry around the rare earth metal, in which the amido ligand occupies the apical position and the two linked beta-diketiminato moieties form the basis. The geometry of the bis(beta-diketiminato) ligands depends significantly on the linker unit. While complexes with an ethylene-linked ligand adopt a cisoid arrangement of the two aromatic substituents, complexes with cyclohexyl linker adopt a transoid arrangement. Either one (3b) or both (7, 8) of the beta-diketiminato moieties are tilted out of the eta(2) coordination mode, resulting in close Ln(...)C contacts. The beta-diketiminato and linked bis(beta-diketiminato) complexes were moderately active in the copolymerization of cyclohexene oxide with CO2. A maximum of 92% carbonate linkages were obtained using the ethylene-bridged bis(beta-diketiminato) complex [{C2H4(BDIMes)(2)}LaN(SiHMe2)(2)] (4). (c) 2005 Elsevier B.V. All rights reserved.