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(PMe(3))(2){(C(6)H(3)F-ortho)CH[double bond, length as m-dash]N-R}] 5-8. Under similar reaction conditions π-coordinated cobalt(0) complexes [Co(PMe(3))(3)((C(6)H(3)F-ortho)CH[double bond, length as m-dash]N-R)] 12-14 were formed when [Co(PMe(3))(4)], instead of [CoMe(PMe(3))(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, [CoFMeC[double bond, length as m-dash]O(PMe(3))(2){(C(6)H(3)F-ortho)CH[double bond, length as m-dash]N-R}] 20, and a 19-electron cobalt(0) complex, Co(CO)(3)(PMe(3))(2)21, were structurally characterized. The crystal and molecular structures of complexes 5, 6, 8, 12, 20 and 21 were determined by X-ray diffraction.