Synthesis and characterization of bis(pyrazolyl)borate Ni(ii) complexes: ligand rearrangement and transformation.

Five examples of bis(pyrazolyl)borate Ni(ii) complexes 2-5, exhibiting C-HNi interactions, were readily prepared from the reactions of K[BBN(3-R-4-R-pz)] with Ni(ii) precursors (Ni(acac) or NiCl(PPh)) in dichloromethane or toluene. When R = R = H, complex 2a with square-planar geometry around the Ni centre and showing an unusual C-HNi anagostic interaction was obtained. In contrast, when R = Me, R = H or R = Me, R = Br, tetrahedral complexes 3 or 4 were formed preferentially with strong C-HNi agostic interactions, respectively.