Grouping Effect of Single Nickel-N₄ Sites in Nitrogen-Doped Carbon Boosts Hydrogen Transfer Coupling of Alcohols and Amines

As a new type of heterogeneous catalyst with "homogeneous-like" activity, single-site transition-metal materials are usually treated as integrated but separate active centers. A novel grouping effect is reported for single Ni-N₄ sites in nitrogen-doped carbon (Ni/NC), where an effective ligand-stabilized polycondensation method endows Ni/NC nanocatalysts with a high content of single-site Ni up to 9.5 wt %. The enhanced electron density at each single Ni-N₄ site promotes a highly efficient hydrogen transfer, which is exemplified by the coupling of benzyl alcohol and aniline into N-benzylaniline with a turnover frequency (TOF) value of 7.0 mol_{N-benzylaniline} mol_metal ^-1 h^-1 ; this TOF outpaces that of reported stable non-noble-metal-based catalysts by a factor of 2.