Structure-Reactivity Relationship in the Frustrated Lewis Pair (FLP)-Catalyzed Hydrogenation of Imines

The autoinduced, frustrated Lewis pair (FLP)-catalyzed hydrogenation of 16-benzene-ring substituted N-benzylidene-tert-butylamines with B(2,6-F2C6H3)(3) and molecular hydrogen was investigated by kinetic analysis. The pK(a) values for imines and for the corresponding amines were determined by quantum-mechanical methods and provided a direct proportional relationship. The correlation of the two rate constants k(1) (simple catalytic cycle) and k(2) (autoinduced catalytic cycle) with pK(a) difference between imine and amine pairs (Delta pK(a)) or Hammett's sigma parameter served as useful parameters to establish a structure-reactivity relationship for the FLP-catalyzed hydrogenation of imines.