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

Abstract

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‐(iPr2PNH)2C6H3]NiX (X=SH, 1 a; SPh, 1 b; SBn, 1 c; BH4, 1 d), were synthesized based on m‐(iPr2PNH)2C6H4 (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‐(iPr2PO)2C6H3]NiX (X=SH, 2 a; SPh, 2 b; SBn, 2 c; BH4, 2 d). It was found that the Ni‐Cipso 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.

Coordination mode and stability of the tetrahydroborate ligand in group 10 metal pincer complexes

“…The 11 B NMR spectrum of the reaction mixture also displayed a new quintet at −29.2 ppm, which is quite similar to the 11 B resonance of the related transition metal tetrahydroborate complexes. 5–10,12,13 As a result, the expected platinum tetrahydroborate complex Pt-POCOP was very probably formed cleanly during the reaction. However, several attempts to isolate this complex failed.…”

“…We have been interested in the structures and reactivities of group 10 metal complexes supported by different types of pincer ligands. 5–11 During our investigation, we noticed that the coordination mode and reactivity of the BH 4 − auxiliary ligand in group 10 metal pincer complexes can be significantly influenced by the pincer platforms. In order to rationalize this influence comprehensively, we synthesized and characterized more nickel and platinum complexes supported by bis(phosphinite) POCOP and diphosphino-boryl PBP pincer ligands.…”