Synthesis, Characterisation of Carbon‐Bridged (Diphenolato)lanthanide Complexes and Their Catalytic Activity for Diels–Alder Reactions

The synthesis and structures of new lanthanide complexes supported by the carbon‐bridged diphenolato ligand 2,2′‐methylenebis(6‐tert‐butyl‐4‐methylphenolato) (MBMP2–) are described. Reactions of anhydrous lanthanide trichlorides with Na2MBMP in a 1:2 molar ratio in THF at room temperature afforded the corresponding “ate” (diphenolato)lanthanide complexes [(THF)nLn(MBMP)2Na(THF)2] [Ln = Nd (1), Sm (2), n = 2; Ln = Yb, n = 1 (3)]. Recrystallisation of complexes 1–3 from toluene in the presence of DME gave the discrete ion‐pair complexes [(MBMP)2Ln(THF)2][Na(DME)2(THF)2] [Ln = Nd (4), Sm (5), Yb (6)]. These complexes have been fully characterised. The single‐crystal structural analyses of 1, 3 and 6 revealed that the coordination geometries of the lanthanide ions can be best described as distorted octahedral in complexes 1 and 6 and distorted trigonal‐bipyramidal in complex 3. It was found that these lanthanide complexes are able to act as Lewis acids to catalyse the Diels–Alder reactions of cyclopentadiene with substituted dienophiles with good activity and stereoselectivity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)