Comprehensive Study of the Reactions Between Chelating Phosphines and Ni(cod)₂

Abstract

A comprehensive study of the reactions of chelating phosphines with Ni(cod) 2 to form (phosphine)Ni(cod), (phosphine) 2 Ni, or mixtures thereof is presented. A series of (phosphine)Ni(cod) complexes were isolated and characterized. The structural differences between the (phosphine)Ni(cod) and (phosphine) 2 Ni complexes were examined using Xray crystallography and 1 H and 31 P NMR spectroscopy. In addition, the effects of ring size, rigidity, and bulk of the phosphine backbone on the formation of either (phosphine)Ni(cod) or (phosphine) 2 Ni were investigated. These studies show that the Ni−P bond lengths in both the (phosphine)-Ni(cod) and (phosphine) 2 Ni complexes and the size of the ring formed by the chelating phosphine and Ni are crucial in determining whether or not (phosphine)Ni(cod) complexes can be isolated. Other factors such as π-stacking interactions were found to have marginal influence.

Nickel‐Catalyzed Mono‐Selective α‐Arylation of Acetone with Aryl Chlorides and Phenol Derivatives

“…Of note, the same results were observed when the reaction of complex I with chlorobenzene was carried out in the presence of high excess of acetone, showing that acetone does not inhibit the oxidative addition process . Moreover, addition of chlorobenzene to a 1:1 mixture of I and ( L1 ) 2 Ni(0) led to quantitative formation of the oxidative addition product II b (Figure S7), indicating that ( L1 ) 2 Ni(0) is a reactive species …”

“…However, the feasibility of such a mechanism for the challenging α‐arylation of acetone under the developed catalytic conditions raises some questions about (i) the exact structure and the reactivity of Ni 0 species toward aryl chloride and pivalate substrates in the presence of an excess of coordinating and non‐sterically hindered acetone and ( ii ) the stability and reactivity of Ni II intermediates at high temperature (Figure ). The reaction of Ni(COD) 2 with an excess of chelating Josiphos ligands, as carried out in our catalytic protocol, may result in the formation of 4‐coordinate (Josiphos) 2 Ni(0) species, raising the question of its reactivity in catalysis …”

Unexpected Nickel Complex Speciation Unlocks Alternative Pathways for the Reactions of Alkyl Halides with dppf-Nickel(0)

“…When an additional dppf ligand was present, there was a significant increase in reaction rate. Further analysis of [NiCl 2 (dppf)] (4-Cl) by 31 34 Complex 1 is prepared from dppf and [Ni(COD) 2 ], which yields 1 as the major product, 30,35 but the presence of 5 appears to be essential for these reactions with alkyl halides. The equilibrium constant for the formation of 5 from 1 plus dppf was measured (K eq = 6.8).…”

Cross‐Coupling Reaction of Alkenyl Sulfoximines and Alkenyl Aminosulfoxonium Salts with Organozincs by Dual Nickel Catalysis and Lewis Acid Promotion

“…(Table , entry 8). The CCR of ( aR , R )‐ 5 a proceeded with the alleged catalyst Ni(PPh 3 ) 4 in a similar manner (entry 11), whereas no CCR occurred with alleged complex Ni(dppp) 2 (Table , entry 12), which was prepared from Ni(dppp)Cl 2 , dppp (1 equiv), and MeLi (2 equiv) in diethyl ether . Thus, CCR of both alkenyl sulfoximines took place under inversion of the configuration of the chiral axis in the presence of PPh 3 as the ligand for the Ni atom.…”