Lanthanide Pybox Complexes as Catalysts for Enantioselective Silylcyanation of Aldehydes

摘要: Complexes of lanthanide chlorides with pybox ligands catalyze the enantioselective silylcyanation aromatic and aliphatic aldehydes ee's up to 91% under mild convenient conditions. Studies catalysts prepared varying enantiomeric purity show no marked nonlinear effects, indicating a monometallic transition state. A mechanism for catalytic reaction is proposed. Crystal structures [LnCl2(S-Pri-pybox)2][LnCl4(S-Pri-pybox)] (Ln = Eu, Yb) are reported. The structure related triflate complex [La(OTf)3(S-Pri-pybox)2] also Diastereoselectivity has been observed in reactions Ln(OTf)3 racemic Pri-pybox:  Ln heterochiral product containing one R- S-pybox ligand observed, whereas Yb mixture homochiral bis(pybox) complexes formed.