Recyclable Polymer-Supported Organolanthanide Hydroamination Catalysts. Immobilization and Activation via Dynamic Transamination

Abstract

A series of divinylbenzene cross-linked, amino-functionalized polystyrene resins such as aminomethylated polystyrenes of varying mesh size, piperazinomethyl polystyrene, 1,12-diaminododecanetrityl resin, 1,7-diaminoheptanetrityl resin, 1,2-diaminoethanetrityl resin, 1,4-bis-(aminomethyl)benzenetrityl resin, N -(2-aminoethyl)aminomethyl polystyrene, cis -1,2-diaminocyclohexanetrityl resin, and trans -1,2-diaminocyclohexanetrityl resin are used as supports for the intramolecular hydroamination/cyclization precatalysts Cp‘ 2 SmCH(SiMe 3 ) 2, Cp‘ 2 LaCH(SiMe 3 ) 2 (Cp‘ = η 5 -Me 5 C 5 ), and CGCSmN(SiMe 3 ) 2 (CGC = Me 2 Si[(η 5 -Me 4 C 5 )( t BuN)]). It is shown that these catalyst precursors can be immobilized on the polymer supports via transaminative protonolysis to give the corresponding bound precatalysts, which, in the presence of aminoalkene substrates, are transaminatively released for efficient homogeneous intramolecular hydroamination/cyclization processes. Upon substrate consumption, the catalysts are readsorbed on the supports. In many cases, these catalysts exhibit activities comparable to the homogeneous precursors and are recoverable/recyclable with only minor to moderate loss of activity, depending on the particular resin amino substituents.