A Structure Comparison of Ni(II) Complexes Supported by PNCNP and POCOP Pincer Ligands

In order to compare the structure and property of the same metal center supported by different types of pincer ligands, a series of Ni(II) pincer complexes, [2,6‐( i Pr 2 PNH) 2 C 6 H 3 ]NiX (X=SH, 1 a ; SPh, 1 b ; SBn, 1 c ; BH 4 , 1 d ), were synthesized based on m ‐( i Pr 2 PNH) 2 C 6 H 4 (PNCNP) and fully characterized by multinuclear NMR, FTIR, X‐ray crystallography and elemental analysis. The structures of complexes 1 a – d were compared with those of the corresponding Ni(II) complexes supported by a bis(phosphinite) (POCOP) pincer ligand, [2,6‐( i Pr 2 PO) 2 C 6 H 3 ]NiX (X=SH, 2 a ; SPh, 2 b ; SBn, 2 c ; BH 4 , 2 d ). It was found that the Ni‐C ipso and Ni−S bond lengths and the Ni⋅⋅⋅B distance in complexes 1 a – d are comparable to those in complexes 2 a – d ; however, the Ni−P bond lengths in complexes 1 a – d are longer than those in complexes 2 a – d . As a result, the nickel center is less tightly chelated by the PNCNP backbone compared with the POCOP framework. Natural population analysis (NPA) of complexes 1 a , 2 a , 1 b and 2 b indicated that the nickel center supported by a PNCNP pincer ligand is less electron‐rich. Cyclic voltammetry study of 1 a and 2 a showed that 2 a is easier to be oxidized.