An Investigation of Carbon−Fluorine Bond Functionalization. Versatile Reactivity of Tungsten(II) Fluoride Carbonyl Metallacycles with Alkynes

Abstract

Metal-assisted functionalization of aromatic fluorocarbons is reported. Sequential carbon−fluorine oxidative addition and migratory insertion with electron-deficient alkynes are employed to construct novel tungsten(II) η2-vinyl complexes in which net replacement of an aromatic carbon−fluorine bond by a carbon−carbon bond has ensued. A competitive reaction involving the formation of four-electron donor alkyne complexes is favored for electron-rich alkynes. Evidence suggests a two-electron donor alkyne complex may serve as a common intermediate in these transformations, which could either participate in the migratory insertion reaction or lose carbon monoxide to generate the four-electron donor alkyne complex. The observed partitioning of products appears to be controlled by the electronic profile of the coordinated alkyne as well as the nucleophilicity of the migrating aryl group. The migratory insertion reaction is regioselective for 1-phenyl-1-propyne with the insertion taking place at the phenyl-substituted alkyne carbon to afford 17. Reaction of the nucleophilic tungsten(II) metallacycle 4 with the electronically unsymmetrical acetylene 18 affords two distinct and isolable η2-vinyl isomers in a 56:44 ratio and suggests that there is not a significant electronic bias for the nucleophilic migration process. The solid state structures of the four-electron donor alkyne complex 9 and the η2-vinyl complexes 16 and 17 have been determined.