Solution and solid-state studies of hydrogen and halogen bonding with N-heterocyclic carbene supported nickel(ii) fluoride complexes†

Nickel fluoride complexes of the type [Ni(F)(L)₂(Ar^F)] (L = phosphine, Ar^F = fluorinated arene) are well-known to form strong halogen and hydrogen bonds in solution and in the solid state. A comprehensive study of such non-covalent interactions using bis(carbene) complexes as acceptors and suitable halogen and hydrogen bond donors is presented. In solution, the complex [Ni(F)(iPr₂Im)₂(C₆F₅)] forms halogen and hydrogen bonds with iodopentafluorobenzene and indole, respectively, which have formation constants (K₃₀₀) an order of magnitude greater than those of structurally related phosphine supported nickel fluorides. Co-crystallisation of this complex and its backbone-methylated analogue [Ni(F)(iPr₂Me₂Im)₂(C₆F₅)] with 1,4-diiodotetrafluorobenzene produces halogen bonding adducts which were characterised by X-ray analysis and ¹⁹F MAS solid state NMR analysis. Differences in the chemical shifts between the nickel fluoride and its halogen bonding adduct are well in line with data that were obtained from titration studies in solution.