Fluoroalkyl Radical Generation by Homolytic Bond Dissociation in Pentacarbonylmanganese Derivatives

Thermal decarbonylation of the acyl compounds [Mn(CO) 5 (COR F )] (R F =CF 3 , CHF 2 , CH 2 CF 3 , CF 2 CH 3 ) yielded the corresponding alkyl derivatives [Mn(CO) 5 (R F )], some of which have not been previously reported. The compounds were fully characterized by analytical and spectroscopic methods and by several single‐crystal X‐ray diffraction studies. The solution‐phase IR characterization in the CO stretching region, with the assistance of DFT calculations, has allowed the assignment of several weak bands to vibrations of the [Mn( 12 CO) 4 ( eq ‐ 13 CO)(R F )] and [Mn( 12 CO) 4 ( ax ‐ 13 CO)(R F )] isotopomers and a ranking of the R F donor power in the order CF 3 <CHF 2 <CH 2 CF 3 ≈CF 2 CH 3 . The homolytic Mn−R F bond cleavage in [Mn(CO) 5 (R F )] at various temperatures under saturation conditions with trapping of the generated R F radicals by excess tris(trimethylsilyl)silane yielded activation parameters Δ H ≠ and Δ S ≠ that are believed to represent close estimates of the homolytic bond dissociation thermodynamic parameters. These values are in close agreement with those calculated in a recent DFT study ( J. Organomet. Chem . 2018 , 864 , 12–18). The ability of these complexes to undergo homolytic Mn−R F bond cleavage was further demonstrated by the observation that [Mn(CO) 5 (CF 3 )] (the compound with the strongest Mn−R F bond) initiated the radical polymerization of vinylidene fluoride (CH 2 =CF 2 ) to produce poly(vinylidene fluoride) in good yields by either thermal (100 °C) or photochemical (UV or visible light) activation.