Highly Efficient Nickel-Catalyzed Heck Reaction Using Ni(acac)₂/N-Heterocyclic Carbene Catalyst

Abstract

Ni(acac)₂/N-heterocyclic carbene-derived catalysts were shown to be highly efficient in the nickel-catalyzed Heck reaction. Various aryl halides were reacted with acrylate to give the coupled products in good to high yield.

nickel - carbene ligands - Heck reaction - catalysis

References

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NHC precursors were prepared according to modified methods of reported procedures:

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<A NAME="RU11405ST-11A">11a</A>

Other nickel sources such as NiCl₂ and Ni(OAc)₂ were ineffective.

<A NAME="RU11405ST-11B">11b</A>

Reactions in toluene, dioxane, NMP, and DMA proceeded in relatively poor yields.

<A NAME="RU11405ST-12">12</A>

Use of Ag₂CO₃, t-BuOK, CsF, CsOAc, or Et₃N rather than Cs₂CO₃, K₂CO₃ or Na₂CO₃, led to a decreased yield. In addition, after the catalyst optimization (Table 1), it was found that the use of Na₂CO₃ gave similar but slightly better results than Cs₂CO₃ in almost all cases (Table 2).

<A NAME="RU11405ST-13">13</A>

Reactions of aryl bromides in the absence of Bu₄NI resulted in poorer yields. However, the role of such an ammonium salt is obscure at present.

<A NAME="RU11405ST-14">14</A>

Under the optimized conditions we developed here, we have not yet obtained the products in satisfactory yields from the reaction of aryl chlorides.