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 β-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 η2-bound β-diketiminato ligand. A series of novel ethylene- and cyclohexyl-linked bis(β-diketiminato) ligands [C2H4(BDIAr)2]H2 and [Cy(BDIAr)2]H2 [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(β-diketiminato) yttrium and lanthanum complexes were obtained via amine elimination. The X-ray crystal structure analysis of the ethylene-bridged bis(β-diketiminato) complex [{C2H4(BDIMes)2}YN(SiMe3)2] (3b) and cyclohexyl-bridged complexes [{Cy(BDIMes)2}LaN(SiHMe2)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 β-diketiminato moieties form the basis. The geometry of the bis(β-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 β-diketiminato moieties are tilted out of the η2 coordination mode, resulting in close Ln⋯C contacts. The β-diketiminato and linked bis(β-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(β-diketiminato) complex [{C2H4(BDIMes)2}LaN(SiHMe2)2] (4).

The first homogeneous rare earth metal based catalysts for the copolymerization of cyclohexene oxide and CO2 is reported. A series of β-diketiminato and novel ethylene- and cyclohexyl-linked bis(β-diketiminato) yttrium and lanthanum complexes were prepared via facile amine elimination.Figure optionsDownload as PowerPoint slide