Synthesis of Ni(II) complexes with unsymmetric [O,N,O′]-pincer ligands and their use as precatalysts in carbon–carbon bond formations to access diarylmethanes

•Ni(II) complexes with unsymmetric [O,N,O′]-pincer ligands have been studied.•A square planar geometry with triphenylphosphane as co-ligand have been observed.•The Ni(II) complexes were applied as precatalysts in cross-coupling reactions to access diarylmethanes.

1-Acetyl-[1a,3,5-CF3,1-C(=O)CH3] and 1-benzoyl-5-hydroxypyrazolines [1b, 3,5-CF3, 1-C(=O)C6H5] have been synthesized and reacted with Ni(OAc)2·4H2O in the presence of PPh3 to form square planar nickel complexes, which revealed a O,N,O′-coordination. An additional coordination site on the nickel center is occupied by one triphenylphosphane ligand. After having investigated the properties of the complexes, catalytic experiments have been carried out to synthesize diarylmethanes. Applying the complexes in the nickel-catalyzed carbon–carbon cross coupling of aryl halides with benzylzinc bromide excellent yields and selectivities of the corresponding diarylmethane have been obtained. Moreover, various experiments have been performed to shed light on the underlying reaction mechanism.

Graphical abstract1-Acetyl-[1a, 3,5-CF3, 1-C(=O)CH3] and 1-benzoyl-5-hydroxypyrazolines [1b, 3,5-CF3, 1-C(=O)C6H5] have been synthesized and reacted with Ni(OAc)2·4H2O in the presence of PPh3 to form square planar nickel complexes, which revealed a O,N,O′-coordination. An additional coordination site on the nickel center is occupied by one triphenylphosphane ligand. After having investigated the properties of the complexes, catalytic experiments have been carried out to synthesize diarylmethanes. Applying the complexes in the nickel-catalyzed carbon–carbon cross coupling of aryl halides with benzylzinc bromide excellent yields and selectivities of the corresponding diarylmethane have been obtained. Moreover, various experiments have been performed to shed light on the underlying reaction mechanism.Figure optionsDownload full-size imageDownload as PowerPoint slide