Catalytic Synthesis of N-Heterocycles via Direct C(sp3)–H Amination Using an Air-Stable Iron(III) Species with a Redox-Active Ligand
Bagh, Bidraha ; Broere, Daniël L. J. ; Sinha, Vivek ; Kuijpers, Petrus F. ; van Leest, Nicolaas P. ; de Bruin, Bas ; Demeshko, Serhiy ; Siegler, Maxime A. et al.
Citable Link (URL):http://resolver.sub.uni-goettingen.de/purl?gs-1/14461
Coordination of FeCl3 to the redox-active pyridine−aminophenol ligand NNOH2 in the presence of base and under aerobic conditions generates FeCl2(NNOISQ) (1), featuring high-spin FeIII and an NNOISQ radical ligand. The complex has an overall S = 2 spin state, as deduced from experimental and computational data. The ligand-centered radical couples antiferromagnetically with the Fe center. Readily available, well-defined, and air-stable 1 catalyzes the challenging intramolecular direct C(sp3)−H amination of unactivated organic azides to generate a range of saturated N-heterocycles with the highest turnover number (TON) (1 mol% of 1, 12 h, TON = 62; 0.1 mol% of 1, 7 days, TON = 620) reported to date. The catalyst is easily recycled without noticeable loss of catalytic activity. A detailed kinetic study for C(sp3)−H amination of 1-azido-4-phenylbutane (S1) revealed zero order in the azide substrate and first order in both the catalyst and Boc2O. A cationic iron complex, generated from the neutral precatalyst upon reaction with Boc2O, is proposed as the catalytically active species.
Sponsored by EU
Project: ESmart Systems for Small Molecule Activation and Sustainable Homogeneous Catalysis (EuReCat)