| The C-H amination and olefin aziridination chemistry of iron supported by dipyrromethene ligands (RLAr, L=1,9-R2-5-aryldipyrromethene, R = Mes, 2,4,6-Ph3C6H2, tBu, Ad, 10-camphoryl, Ar = Mes, 2,4,6-Cl3C6H2) was explored. The weak-field, pyrrole-based dipyrrinato ligand was designed to generate an electrophilic, high-spin metal center capable of accessing high valent reactive intermediates in the presence of organic azides. Isolation of the reactive intermediate in combination with a series of mechanistic experiments suggest the N-group transfer chemistry proceeds through a rapid, single-electron pathway and maintains an overall S=2 electronic configuration throughout the catalytic cycle. We have established the catalysts' strong preference for allylic amination over aziridination with olefin containing substrates. Aziridination is limited to styrenyl substrates without allylic C-H bonds, while allylic amination has been demonstrated with both cyclic and linear aliphatic alkenes. Notably, the functionalization of alpha-olefins to linear allylic amines occurs with outstanding regioselectivity.;We have applied the complex AdLArFeCl towards the generation of complex pyrrolidines using simple linear aliphatic azides via an intramolecular C-H amination reaction. A series of substrates were synthesized in order to probe the mechanism of cyclization. An intramolecular kinetic isotope effect of 5.3 suggested a stepwise mechanism for benzylic substrates, which is consistent with the intermolecular amination reaction. The stereospecificity of cyclization of an enantiopure substrate and the preservation of the cyclopropyl unit in a radical clock experiment suggest that if a stepwise mechanism is operative, the radical intermediate following H-atom abstraction is extremely short-lived. Efforts to synthesize diastereoselective and enantioselective catalysts have been taken. Exposure of AdLArFeCl to potassium phenoxide generates AdLArFeOPh, which is extremely selective for the formation of cis-2,5-disubstituted pyrrolidines. Incorporation of camphor substituents to the ligand platform has led to the design of a chiral, C2-symmetric Fe-dipyrrinato complex. Application of this complex to the cyclization of 1-azido-4-phenylbutane results in the formation of 2-phenylpyrrolidine with modest levels of enantiomeric excess. |
