NHC-Ni-catalyzed Suzuki-Miyaura and Negishi Cross-couplings

3 NHC-Ni-catalyzed Suzuki-Miyaura and Negishi Cross-couplings 

In 1999, Cavell and co-workers reported that the Suzuki coupling reaction could be catalyzed by NHC-Ni complexes, although not as efficiently as observed with Pd. The introduction of a bulky NHC on the catalyst precursor led to a significant increase in activity, although not as pronounced as in the Pd case. In fact, Blakey and MacMillan described the first efficient Suzuki-Miyaura cross-coupling reaction mediated by NHC-Ni in 2003. The original reaction used aryltrimethyl ammonium triflates as coupling partners and in the presence of CsF, the authors showed that IMes-Ni [1 1] led to the efficient preparation of various biphenyl derivatives (Equation (10.15)). 

Radius and co-workers next reported examples of Suzuki-type cross-coupling reactions of perfluorinated arenas i.e. octafluorotoluene or per-fluorobiphenyl) (Equation (10.16)). Again, [(IiPr)4Ni2(COD)] was used to activate the C-F bond (see Section 10.4.2). 

In 2004, Liu and Robbins demonstrated that a Ni/SIPr [1 1] system allowed the synthesis of 6-arylpurine 2 -deoxynucleosides and nucleosides from 6-(imidazol-l-yl)- and 6-(l,2,4-triazol-4-yl)purine derivatives by a Suzuki coupling (Equation (10.17)). These reactions were not observed with classical pPd(PPh3)4] while [Ni(dppp)Cl2] (dppp = l,3-bis(diphenylphosphino)propane) only led to 30% of desired product. 

Two other contributions from Hiroya and Chen , respectively, reported the use of pyridine-functionalized NHC, supported or not, for Suzuki-Miyaura cross-coupling reactions. 

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