Nickel Catalysts [Cross-coupling Reaction using Transition Metal Catalysts]

On the other hand, similar to iron and cobalt catalysts, nickel catalysts are used for the cross coupling reactions of alkyl halides with organometallic species such as organomagnesium, organozinc and organoboric acid compounds. This synthetic means is effective for producing the carbon (sp³)–carbon (sp³) bond. In this reaction, phosphine ligands are less effective and an optimization of the reaction conditions suitable for each substrate was investigated. In a case using primary alkyl halides as a reactant, the coupling reactions are accelerated by using NMP as a solvent and addition of alkenes with electron-withdrawing groups. It is also effective to add butadienes as additives because the reactivity of the coupling reactions improves through the formation of nickel - bis-allyl complexes. The proceeding of cross-coupling reactions with secondary alkyl halides is harder relative to primary alkyl halides, so pyridyl-type chelate ligands such as phenanthrolines, Pybox, and diamines are used for promoting those reactions. This has been applied to asymmetric reactions and natural products synthesis.³⁾