Imine-assisted C–F bond activation using low-valent cobalt compounds supported by trimethylphosphine ligands and formation of novel organic fluorides

Abstract

A cyclometalation reaction involving C–F bond activation at a cobalt(I) center with an aldazine-N atom as anchoring group affords ortho-chelated cobalt(III) complexes containing a [C–Co–F] fragment [CoFMe(PMe₃)₂{(C₆H₃F-ortho)CHN–R}] 5–8. Under similar reaction conditions π-coordinated cobalt(0) complexes [Co(PMe₃)₃((C₆H₃F-ortho)CHN–R)] 12–14 were formed when [Co(PMe₃)₄], instead of [CoMe(PMe₃)₄], was applied. C–F bond activation did not occur. Carbonylation of complexes 6–8 delivered novel organic fluorides 15–17. A proposed formation mechanism of the novel organic fluorides with demetallation and carbonylation of complexes 6–8 by CO is discussed with experimental support. As important intermediates, an acetyl cobalt complex, [CoFMeCO(PMe₃)₂{(C₆H₃F-ortho)CHN–R}] 20, and a 19-electron cobalt(0) complex, Co(CO)₃(PMe₃)₂21, were structurally characterized. The crystal and molecular structures of complexes 5, 6, 8, 12, 20 and 21 were determined by X-ray diffraction.