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

Zekai Lin; Nathan C Thacker; Takahiro Sawano; Tasha Drake; Pengfei Ji; Guangxu Lan; Lingyun Cao; Shubin Liu; Cheng Wang; Wenbin Lin

doi:10.1039/c7sc03537c

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

Chem Sci. 2017 Oct 30;9(1):143-151. doi: 10.1039/c7sc03537c. eCollection 2018 Jan 7.

Authors

Zekai Lin¹, Nathan C Thacker¹, Takahiro Sawano¹, Tasha Drake¹, Pengfei Ji¹, Guangxu Lan¹, Lingyun Cao², Shubin Liu³, Cheng Wang², Wenbin Lin^{1

2}

Affiliations

¹ Department of Chemistry , University of Chicago , 929 E. 57th St. , Chicago , Illinois 60637 , USA . Email: wenbinlin@uchicago.edu.
² Collaborative Innovation Center of Chemistry for Energy Materials , State Key Laboratory of Physical Chemistry of Solid Surfaces , Department of Chemistry , College of Chemistry and Chemical Engineering , Xiamen University , Xiamen 361005 , PR China.
³ Research Computing Center , University of North Carolina , Chapel Hill , North Carolina 27599-3420 , USA.

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.