Metal-organic layers stabilize earth-abundant metal-terpyridine diradical complexes for catalytic C-H activation

Abstract

We report the synthesis of a terpyridine-based metal-organic layer (TPY-MOL) and its metalation with CoCl2 and FeBr2 to afford CoCl2·TPY-MOL and FeBr2·TPY-MOL, respectively. Upon activation with NaEt3BH, CoCl2·TPY-MOL catalyzed benzylic C-H borylation of methylarenes whereas FeBr2·TPY-MOL catalyzed intramolecular Csp3-H amination of alkyl azides to afford pyrrolidines and piperidines. X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy, UV-Vis-NIR spectroscopy, and electron paramagnetic spectroscopy (EPR) measurements as well as density functional theory (DFT) calculations identified M(THF)2·TPY-MOL (M = Co or Fe) as the active catalyst with a MII-(TPY)2- electronic structure featuring divalent metals and TPY diradical dianions. We believe that site isolation stabilizes novel MII-(TPY)2- (M = Co or Fe) species in the MOLs to endow them with unique and enhanced catalytic activities for Csp3-H borylation and intramolecular amination over their homogeneous counterparts. The MOL catalysts are also superior to their metal-organic framework analogs owing to the removal of diffusion barriers. Our work highlights the potential of MOLs as a novel 2D molecular material platform for designing single-site solid catalysts without diffusional constraints.