Experimental and Computational Evidence for 1,4-Diradical Intermediates in Reactions of Cobalt Fluorocarbene Complexes with Terminal Aryl-alkynes to give Metallacyclobutenes

Abstract

Cobalt fluorocarbene complex CpCo(=CF(CF3))(PPh2Me) (Cp = n5-cyclopentadienyl) reacts with para-substituted phenylacetylenes to furnish partially fluorinated cobaltacyclobutene complexes [Cp(PPh2Me)Co{ΰ2-C(Ar)=CHCF(CF3)}], which were isolated and characterized by elemental analysis, multinuclear NMR and UV-vis spectroscopy, and X-ray crystallography. The scope of reactivity between CpCo(=CFRF)(L) and various alkynes was explored. The detailed pathway for the [2 + 2] cycloaddition reaction was investigated using a combination of kinetic studies and DFT computational chemistry (M06/def2-TZVP), with a 1,4 diradical species identified as the key intermediate.