Five examples of bis(pyrazolyl)borate Ni(II) complexes 2-5, containing the C-H···Ni interaction, were readily prepared from reactions of K[BBN(3-R1-4-R2-pz)2] with Ni(II) precursors (Ni(acac)2 or NiCl2(PPh3)2) in dichloromethane or toluene. When R1 = R2 = H, complex 2a with square-planar geometry around the Ni centre and showing an unusual C-H···Ni anagostic interaction was obtained. In constast, when R1 = Me, R2 = H, or R1 = Me, R2 = Br, tetrahedral complexes 3 or 4 were formed preferentially with strong C–H···Ni agostic interactions, respectively. Additionally, some differences in the formation and transformation of 3 and 4 were also found including a 1,2-borotropic shift during the fromation of 3 and a further geometrical transformation from tetrahedral 3 to square-planar 2b by the second 1,2-borotropic shift under continuous heating, in contrast, no ligand change and further conversion were found in 4. When the more hindered 3-iPr substituted ligand 1d was introduced in the reaction, the hydrolysis and cleavage of one B-N bond in the ligand occurred, leading to the singly hydroxo-bridged complex 5. The experimental and theoretical results indicate that the preferential to form a thermodynamically stable complex and then balancing with orbital energy should be the intrinsic reason for the reaction selectivity.

链接地址：https://pubs.rsc.org/en/content/articlelanding/2019/DT/C9DT02287B#!divAbstract