Fluoroboration of a Schiff-base ligand through nickel tetrafluoroborate

The nickel-assisted equilibrium-fluoroboration of the Schiff-base compound, a 2-pyridinecarboxaldehyde salicylhydrazone (H2L) is reported. Crystal structure of the fluoroborated nickel compound 1 Ni(L-BF2)2 revealed that the boron atom was in a distorted tetrahedral geometry with two of the fluorine atoms, one of the phenol oxygen atom and the uncoordinated hydrazone nitrogen atom occupying the four coordination positions. It was suggested that the coordination abilities of the precursor H2L and the product L–BF2 to the nickel atom are important factors influencing the fluoroboration. The cobalt and nickel compounds Co(HL)2 (2) and Ni(HL)2 (3) of the precursor ligand were also structurally characterized for comparison. The ESI-MS spectra revealed that both sodium and cobalt tetrafluoroborate salt cannot make the precursor fluoroborated, and the fluoroboration of the precursor occurred only in the presence of nickel ion.