The Danishefsky hetero Diels-Alder reaction mediated by organolanthanide-modified mesoporous silicate MCM-41

Silylamides are used as reactive precursors for a high-yield synthesis of b eta-diketonate chelates [M(fod)(3)] (M = Sc, Y, La, Al; fod = 1,1,1,2,2,3,3 -heptafluoro-7,7-dimethyl-4,6-octanedionate). A heterogeneously performed s ilylamide route is employed to graft [M{N(SiHMe2)(2)}(3)(thf)(x)], includin g the novel aluminum derivative, onto mesoporous silicate MCM-41 through te rminal silanol groups, generating stable metal siloxide linkages. Subsequen t surface-confined ligand exchange with Hfod monitored by FTIR spectroscopy yields [MCM-41]M(fod)(x)(thf)(y). The hybrid materials obtained, which wer e further characterized by nitrogen physisorption and elemental analysis, s how promising activity in the catalytic hetero Diels-Alder cyclization of t rans-1-methoxy-3-trimethylsilyloxy-1,3-butadiene and benzaldehyde. The effe cts on the catalytic activity of various parameters such as the Lewis acidi ty of the anchored metal cation or the pore diameter of the support materia l are discussed. The performance of the immobilized catalyst species is com pared with, and found superior to, both known homogeneous systems and mater ials obtained from the reaction of [Ln(fod)(3)] with the dehydrated MCM-41 material, particularly in its deactivation behavior and reuseability.