Phosphine-assisted C–H bond activation in Schiff bases and formation of novel organo cobalt complexes bearing Schiff base ligands

Abstract

Two novel cobalt Schiff base complexes 3 and 4, ((2-PPh₂)C₆H₄)CN(C₁₀H₇)Co(PMe₃)₂ (3) and ((2-PPh₂)C₆H₄)CHN(C₆H₅)Co(PMe₃)₂ (4) with η²(C–H) coordination, were synthesized by the reactions of Schiff base preligands ((2-PPh₂)C₆H₄)CHN(C₁₀H₇) (1) and ((2-PPh₂)C₆H₄)CHN(C₆H₅) (2) with CoMe(PMe₃)₄via sp² C–H bond activation. Under similar reaction conditions, the reactions of Co(PMe₃)₄ with 1 and 2 gave rise to the simple π-(CN)-coordinated cobalt(0) complexes ((2-PPh₂)C₆H₄)CHN(C₁₀H₇)Co(PMe₃)₂ (5) and ((2-PPh₂)C₆H₄)CHN(C₆H₅)Co(PMe₃)₂ (6). Complex ((2-PPh₂)C₆H₄)CN(C₁₀H₆)CoI(PMe₃)₂ (7) was obtained through the reaction of 3 with iodomethane via the activation of the second C–H bond in 1. The substitution reaction of complex 3 with carbon monoxide afforded the dicarbonyl cobalt(I) complex ((2-PPh₂)C₆H₄)CN(C₁₀H₇)Co(CO)₂(PMe₃) (8). The molecular structures of 4, 5, 7 and 8 were determined by single-crystal X-ray diffraction.