Synthesis, characterization, and application in asymmetric catalysis of dendrimers containing chiral ferrocenyl diphosphines

Abstract

Starting from the functionalized Josiphos derivatives (R)-1-[(S)-2-(diphenylphosphino)-1'-(dimethyl-3''-aminopropylsilyl)-ferrocenyl]ethyldicyclohexylphosphine ((R)-(S)-3), (R)-1-[(S)-2-(diphenylphosphino)-1'-(hydroxy methyl) ferrocenyl]ethyldicyclohexylphosphine ((R)-(S)-4), and (R)-1-[(S)-2-(diphenylphosphino)-1'-(3''-hydroxy propyl)ferrocenyl]ethyldicyclohexylphosphine ((R)-(S)-5), a series of dendrimers containing up to sixteen ferrocenyl diphosphine units were prepared. Dendrimer cores are based on benzene 1,3,5-tricarboxylic acid and 1,3,5,7-adaman tanetetracarboxylic acid, with 5-substituted isophthalic acid derivatives constituting the branching units. The dendrimers have been used in three different asymmetric catalytic reactions: Rh-catalyzed hydrogenation of dimethyl itaconate, Pd-catalyzed allylic substitution, and Rh-catalyzed hydroboration of styrene with catecholborane. In all three reactions the selectivity obtained with the dendrimers was very similar to the one obtained with the parent ligand Josiphos.Key words: dendrimer, asymmetric catalysis, ferrocenyl ligands, hydrogenation.