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 C_sp³–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 M^II-(TPY˙˙)²⁻ electronic structure featuring divalent metals and TPY diradical dianions. We believe that site isolation stabilizes novel M^II-(TPY˙˙)²⁻ (M = Co or Fe) species in the MOLs to endow them with unique and enhanced catalytic activities for C_sp³–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.