Nickel(0) Complexes with Fluorinated Alkyne Ligands and their Reactivity towards Semihydrogenation and Hydrodefluorination with Water

Abstract

The current work describes the synthesis and full characterization of zerovalent nickel complexes of the type [(dippe)Ni(η(2)-C,C-F(n)-alkyne)] (dippe = 1,2-bis(di-isopropylphosphino-ethane), F(n)-alkyne = fluorinated aromatic alkyne, n = 1, 3, 5; 3a-c) and [{(dippe)Ni}(2)(μ(2)-C,C-F(n)-alkyne)] (4). Reactions with complexes 3a-c, and water as the hydrogen source, yield selective semihydrogenation of the bound alkyne to the corresponding alkene, accompanied by partial hydrodefluorination of the aromatic ring. Different alkynes were tested; on using the alkyne with five fluorine atoms over the aromatic ring, partial defluorination was achieved under the mildest reaction conditions, followed in reactivity by the alkyne with three fluorine atoms. The alkyne with only one fluorine atom was barely defluorinated. The use of triethylsilane as a sacrificial hydride source resulted in an overall increase in reactivity towards defluorination.