Unexpected solvent-induced Cis/Trans isomerization and catalytic application of a bis-bidentate Nickel(II) complex with n-heterocyclic carbene and amido functionalities

A series of bis-bidentate nickel(II) complexes with bifunctional ligands of N-heterocyclic carbene and amido moieties were prepared from the ligand precursors, [(LHH2)-H-1-H-1]Cl and [L-2 (H2H2)-H-1]CI (H-1 = NHC=O, H-2 = NCHN), in 48-82% yields. The complexes. NiL21 and Ni((LH1)-H-2)(2) are stable in the air and toward moisture. They are characterized by NMR (1D 2D)and single-crystal X-ray diffraction studies. According to the NMR, crystallographic, and PXRD studies, one of the NiL21 omplexes undergoes an intriguing reversible solvent-induced cis/trans transformation process, producing the cis form with DMSO and trans with CHCl3. The exchange process is highly specific and can be explained by the higher polarity of cis-NiL21, which favors the polar DMSO solvent, whereas the less polar trans form due to cancellation of polarity from the trans disposition of ligands favors the less polar CHCl3 solvent. A DFT calculation is in support of the experimental findings. Unlike the previous reported palladium analogues, NiL21 and Ni(L 2 HI)2, in the presence of PPh3 as cocatalyst, are highly efficient in catalyzing the Suzuki cross-coupling reaction of aryl chlorides with phenylboronic acid. A 3 mol % of NiL21 (Ni:PPh3 = 1:2) was sufficient to mediate the formation of 4-methoxy-1,1 '-biphenyl from 4-chloroanisole in 95% yield in 12 h.