N-Heterocyclic Carbene-Based Nickel Complexes: Synthesis and Catalysis in Cross-Couplings of Aryl Chlorides with ArMX (M = Mg or Zn)

Two C,N,N-chelate nickel complexes, [Ni(Cl){2-(CN(Me)(CH)(2)N)C6H4N=P(Ph-2)CH(2)Pyr}]I-+(-) and [Ni(Cl){2-(CN(Pr-i)(CH)(2)N)C6H4N=P(Ph-2)CH2P(Ph-2)=NC6H4Me-4}]I-+(-), were synthesized by reaction of (DME)NiCl2 (DME = 1,2-dimethoxyethane) with 2-(CN(R)(CH)(2)N)C6H4N=P(Ph-2)CH(2)Z (R = Me, Z = 2-Pyr; R = Pr-i, Z = p-MeC6H4N=P(Ph-2)) ligands, which were prepared in situ by reaction of corresponding imidazolium salts with 1 equiv of LiBun. C,N,P-Chelate nickel complex [Ni(Br){2-(CN(CH2Ph)(CH)(2)N)C6H4N=P(Ph-2)CH2PPh2}]Br-+(-) was obtained by a similar reaction between (DME)NiBr2 and 2-(CN(CH2Ph)(CH)(2))C6H4N=P(Ph-2)CH2PPh2 ligand prepared from the imidazolium salt and 1 equiv of LiBun. Tetradentate chelate nickel complex [Ni{2-(CN(CH2Ph)(CH)(2)N)C6H4N=P(Ph-2)}(2)CH]Cl-+(-) was synthesized by transmetalation between (DME)NiCl2 and [Li{2-(CN(CH2Ph)(CH)(2)N)C6H4N=P(Ph-2)}(2)CH] generated in situ from [{2-(CHN(CH2Ph)(CH)(2)N)C6H4N=P(Ph-2)}(2)CH2](2+) [Br-](2) and 3 equiv of LiBun. The complexes were characterized by H-1, C-13, and P-31 NMR spectroscopy and elemental analyses. The C,N,N-chelate nickel complexes and the tetradentate chelate nickel complex were additionally characterized by single-crystal X-ray diffraction techniques. The complexes are active catalysts for the cross-coupling reactions of aryl chlorides with arylzine reagents and aryl Grignard reagents.