Negishi coupling

The Negishi coupling is a widely employed transition metal catalyzed cross-coupling reaction. The reaction couples organic halides or triflates with organozinc compounds, forming carbon–carbon bonds (C–C) in the process. A palladium (0) species is generally utilized as the catalyst, though nickel is sometimes used. A variety of nickel catalysts in either Ni0 or NiII oxidation state can be employed in Negishi cross couplings such as Ni(PPh3)4, Ni(acac)2, Ni(COD)2 etc.

R

−

X

+

R

′

−

Zn

X

′

→

PdL

n

or

NiL

n

R

−

R

′

{\displaystyle {\begin{matrix}{}\\{\color {Red}{\ce {R}}}{-}{\color {Blue}{\ce {X}}}+{\color {Green}{\ce {R}}'}{-}{\ce {Zn}}{\color {Magenta}{\ce {X}}'}\ {\ce {->[{\ce {PdL}}_{n}{\text{ or }}{\ce {NiL}}_{n}]}}\ {\color {Red}{\ce {R}}}{-}{\color {Green}{\ce {R}}'}\end{matrix}}}

The leaving group X is usually chloride, bromide, or iodide, but triflate and acetyloxy groups are feasible as well. X = Cl usually leads to slow reactions.

The organic residue R = alkenyl, aryl, allyl, alkynyl or propargyl.

The halide X′ in the organozinc compound can be chloride, bromine or iodine and the organic residue R′ is alkenyl, aryl, allyl, alkyl, benzyl, homoallyl, and homopropargyl.

The metal M in the catalyst is nickel or palladium

The ligand L in the catalyst can be triphenylphosphine, dppe, BINAP, chiraphos or XPhos.

Palladium catalysts in general have higher chemical yields and higher functional group tolerance.