Synthesis and Coordination Chemistry of an Integrated Binucleating Ligand Based on Bidentate NacNac and NCN Pincer Frameworks

A new binucleating “Janus” ligand based on the betadiketiminato (“NacNac”) donor combined with an NCN pincer ligand framework has been designed and synthesized. By incorporating pyridyl donors on the imino carbons of the NacNac ligand, two binding sites for metals are introduced. The ligand’s binucleating capabilities are demonstrated by ligating BF2 in the NacNac pocket and NiBr into the NCN pincer bay. The resulting binuclear boron-nickel complexes chemistry was explored by substitution of the bromide ligand on nickel and one fluoride ion on boron with the weakly coordinating triflimide anion [N(SO2CF3)2]- (NTf2). The bromide is replaced preferentially with AgNTf2 and further treatment with Me3SiNTf2 produces a borenium ion by abstracting F- from the BF2 unit. Semiquantitative assessment of the Lewis acidity at the nickel center using the Gutmann-Beckett method shows a substantial increase in Lewis acidity upon conversion of the BF2 to the [BF]+ borenium moiety.