Solvent- free synthesis and reactivity of nickel( II) borohydride and nickel( II) hydride plus circle plus

Transition metal-hydrides are highly useful in organic transformations of industrial importance yet synthesizing them or their precursor metal-borohydrides in high yield is cumbersome due to their high reactivity and sensitivity towards air and many common solvents. Reported is the development of a mechanochemical protocol for the solvent-free high-yield synthesis of nickel(ii) borohydrides as precursors of nickel(ii) hydrides. The Ni(ii)-chelates ((LNi)-Ni-H) were prepared by manually grinding Ni(ii)-halides with a tetradentate macrocyclic N4 chelating ligand in the presence of air. The Ni(ii)-chelates obtained were further ground with sodium borohydride to yield nickel(ii)-borohydrides [(LNi)-Ni-H((2)-BH4)](+), which in turn upon dissolution in solvents lost BH3 to yield homodinuclear nickel(ii)--hydrides [(LNi)-Ni-H(-H)(2)NiL](2+). Representative reactions of the fully characterized nickel-hydride with alcohols, disulphides, benzyl bromide, trityl cation, air and SO2 yielding alkoxide, thiols, toluene, triphenylmethane, carbonate and sulfate, respectively, are presented. These results open a new avenue in handling sensitive borohydrides and provide a new route for high yield synthesis of hydrides and their precursors.