C–Cl bond activation of ortho-chlorinated benzamides by nickel and cobalt compounds supported with phosphine ligands

Abstract

The C–Cl bonds of ortho-chlorinated benzamides Cl-ortho-C₆H₄C(O)NHR (R = Me (1), nBu (2), Ph (3), (4-Me)Ph (4) and (4-Cl)Ph (5)) were successfully activated by tetrakis(trimethylphosphine)nickel(0) and tetrakis(trimethylphosphine)cobalt(0). The four-coordinate nickel(II) chloride complexes trans-[(C₆H₄C(O)NHR)Ni(PMe₃)₂Cl] (R = Me (6), nBu (7), Ph (8) and (4-Me)Ph (9)) as C–Cl bond activation products were obtained without coordination of the amide groups. In the case of 2, the ionic penta-coordinate cobalt(II) chloride [(C₆H₄C(O)NHnBu)Co(PMe₃)₃]Cl (10) with the [C_phenyl, O_amide]-chelate coordination as the C–Cl bond activation product was isolated. Under similar reaction conditions, for the benzamides 3–5, hexa-coordinate bis-chelate cobalt(III) complexes (C₆H₄C(O)NHR)Co(Cl-ortho-C₆H₄C(O)NR)(PMe₃)₂ (11–13) were obtained via the reaction with [Co(PMe₃)₄]. Complexes 11–13 have both a five-membered [C,N]-coordinate chelate ring and a four-membered [N,O]-coordinate chelate ring with two trimethyphosphine ligands in the axial positions. Phosphonium salts [Me₃P⁺-ortho-C₆H₄C(O)NHR]Cl⁻ (R = Ph (14) and (4-Me)Ph (15)) were isolated by reaction of complexes 8 and 9 as a starting material under 1 bar of CO at room temperature. The crystal and molecular structures of complexes 6, 7 and 9–12 were determined by single-crystal X-ray diffraction.