Fluoroalkyl Radical Generation by Homolytic Bond Dissociation in Pentacarbonylmanganese Derivatives. Issue 1 (13th December 2018)

• Record Type: Journal Article
• Authors: Morales‐Cerrada, Roberto; Fliedel, Christophe; Daran, Jean‐Claude; Gayet, Florence; Ladmiral, Vincent; Améduri, Bruno; Poli, Rinaldo
• Is Part Of: Chemistry. Volume 25:Issue 1(2019)
• Page Start: 296
• Page End: 308
• Publication Date: 2018-12-13
• Subjects: bond dissociation enthalpy -- fluoroalkyl radicals -- manganese -- radical polymerization -- vinylidene fluoride; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201804007
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: Thermal decarbonylation of the acyl compounds [Mn(CO)5 (CORF )] (RF =CF3, CHF2, CH2 CF3, CF2 CH3 ) yielded the corresponding alkyl derivatives [Mn(CO)5 (RF )], 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)(RF )] and [Mn( 12 CO)4 ( ax ‐ 13 CO)(RF )] isotopomers and a ranking of the RF donor power in the order CF3 2 2 CF3 ≈CF2 CH3 . The homolytic Mn−RF bond cleavage in [Mn(CO)5 (RF )] at various temperatures under saturation conditions with trapping of the generated RF 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−RF bond cleavage was further demonstrated by the observation that [Mn(CO)5 (CF3 )] (the compound with the strongest Mn−RF bond) initiated the radical polymerization of vinylidene fluoride (CH2 =CF2 ) to produce poly(vinylidene fluoride) in good yields by either thermal (100 °C) or photochemical (UV or visible light) activation. Abstract : Tough but active : [Mn(CO)5 (RF )] complexes with floroalkyl groups (RF ) that model poly(vinylidene fluoride) dormant chains, although having homolytically strong Mn−RF bonds, are efficient initiators for the radical polymerization of vinylidene fluoride under thermal and photochemical conditions.