Pincer‐Type Mesoionic Carbene Nickel(II) Complexes: Synthesis, Properties, Reactions, and Catalytic Application to the Suzuki–Miyaura Coupling Reaction of Aryl Bromides

Abstract

Tridentate pincer-type triazolylidene nickel(II) complexes have been prepared and characterized. Despite increasing interest in the new series of mesoionic carbene (MIC) ligands in the field of homogeneous catalysis, pincer-type MIC metal complexes have rarely been used as catalysts, and there are few studies on MIC nickel complexes. Herein, MIC nickel(II) halide complexes were synthesized from their silver analogues and fully characterized. An anion exchange reaction with silver tetrafluorobo-rate in acetonitrile gave a dicationic acetonitrile complex in good yield. A comparison of the structures and frontier orbitals between the MIC-and NHC-nickel(II) chloride complexes has revealed that these complexes are comparable in nature. However, their use in the Suzuki-Miyaura (SM) cross-coupling reaction of aryl bromides with phenylboronic acid requires different conditions to provide sufficient results.

Application of first-row transition metal complexes bearing 1,2,3-triazolylidene ligands in catalysis and beyond

“…Reaction of the ditriazolium pincer ligand precursor L8 (R = Dipp, Mes; X = BF 4 ) with Ag 2 O and subsequently with [NiCl 2 (dme)] yields the air-stable monocationic nickel complex Ni12 (dme = 1,2-dimethoxyethane; Scheme 37). 122,123 Despite the formally cationic nickel center, the metal-bound chloride is readily abstracted upon reaction with AgBF 4 to yield the dicationic nickel solvento complex Ni13 , which is however unstable under aerobic conditions. The Ni–C trz bond lengths in Ni12 are 1.905(2) and 1.909(2) Å and thus shorter than in the carbazole pincer complex Ni11 .…”