Synthesis, Properties, and Reactivity of Diketiminate-Supported Cobalt Fluoride Complexes

Reaction of the three-coordinate cobalt(II) methyl complex L^tBuCoCH₃ (L^tBu = bulky β-diketiminate ligand) with (CH₃)₃SnF gives an interesting trimetallic complex, [L^tBuCo(μ-F)₂]₂Sn(CH₃)₂ (1). Magnetic susceptibility studies indicate that 1 consists of two mixed-valence cobalt(II/III) fluoride units bridged by the organometallic tin(III) fragment [SnF₂(CH₃)₂]⁻. The addition of pyridine releases the tin bridge, and the cobalt fluoride species can be isolated as the high-spin cobalt(II) complex L^tBuCoF(py) (2). Treating 2 with triethylsilane in an effort to form L^tBuCoH(py) gave instead the high-spin cobalt(I) complex L^tBuCo(py), with elimination of H₂. Attempts at catalytic or stoichiometric hydrodefluorination of fluorinated aromatics with silane using 2 as a catalyst were unsuccessful. The lack of hydrodefluorination activity may be due to H₂ elimination from low-coordinate cobalt hydride complexes or from inhibition by a fourth donor to the metal.