Simple NMR predictors of catalytic hydrogenation activity for [Rh(cod)Cl(NHC)] complexes featuring fluorinated NHC ligands

A series of imidazolium salts precursors for N -heterocyclic carbenes (NHCs) featuring fluoroaryl substituents have been prepared along with their selenides and rhodium complexes. Tests of the catalytic activity of the [Rh(cod)Cl(NHC)] complexes in the transfer hydrogenation of acetophenone with iPrOH shows that the rhodium complexes bearing fluorinated NHCs are better than their non-fluorinated counterparts. The order of activity being 4-F-C 6 H 4 < 2,4-F 2 -C 6 H 3 < 2,4,5-F 3 -C 6 H 2 < 2,6-F 2 -C 6 H 3 < 2,4,6-F 3 -C 6 H 2 . This order of reactivity is consistent with a number of simple NMR measures of the electronic properties of these systems, including 1 J CH of the NHC·HBF 4 salts, δ ( 77 Se) of the NHC selenides and 1 J Rh-C and δ ( 13 C carbene ) of the [Rh(cod)Cl(NHC)] complexes. 13 C and 77 Se NMR parameters for fluorinated NHC ligand precursors provide simple measures of the catalytic transfer-hydrogenation reactivity of the corresponding [Rh(cod)Cl(NHC)] complexes.