Preparation of hydrido [CNC]-pincer cobalt complexes via selective C–H/C–F bond activation and their catalytic performances

Abstract

Polyfluorinated aryl imines 2,4,5-R₁,R₂,R₃-C₆H₂-HCN-1-C₁₀H₇ (R₁ = F, R₂ = F, R₃ = H (1); R₁ = F, R₂ = H, R₃ = F (2) and R₁ = F, R₂ = F, R₃ = F (3)) and F₅C₆-HCN-1-C₁₀H₇ (7) reacted with CoMe(PMe₃)₄ to give rise to hydrido [CNC]-pincer cobalt(III) complexes (2,4,5-R₁,R₂,R₃-C₆H-HCN-1-C₁₀H₆)Co(H)(PMe₃)₂ (R₁ = F, R₂ = F, R₃ = H (4); R₁ = F, R₂ = H, R₃ = F (5); R₁ = F, R₂ = F, R₃ = F (6)) and (F₄C₆-HCN-1-C₁₀H₆)Co(H)(PMe₃)₂ (8) via selective C–F/C–H bond activation. Penta-coordinate dicarbonyl cobalt(I) complexes (2,4,5-R₁,R₂,R₃-C₆H-HCN-1-C₁₀H₇)Co(CO)₂(PMe₃) (R₁ = F, R₂ = H, R₃ = F (9); R₁ = F, R₂ = F, R₃ = F (10)) were obtained from reactions of hexa-coordinate cobalt(III) complexes 5 and 6 with carbon monoxide through reductive elimination. Cobalt(III) halides (2,4,5-R₁,R₂,R₃-C₆H-HCN-1-C₁₀H₆)Co(I)(PMe₃)₂ (R₁ = F, R₂ = F, R₃ = H (11); R₁ = F, R₂ = H, R₃ = F (12); R₁ = F, R₂ = F, R₃ = F (13)) and (2,4,5-R₁,R₂,R₃-C₆H-HCN-1-C₁₀H₆)Co(Br)(PMe₃)₂ (R₁ = F, R₂ = F, R₃ = H (14); R₁ = F, R₂ = H, R₃ = F (15); R₁ = F, R₂ = F, R₃ = F (16)) were prepared by the interaction between hydrido cobalt(III) complexes 4–6 and MeI or EtBr. The molecular configurations of complexes 4, 8, and 11 were determined by single crystal X-ray diffraction. We then confirmed that the four hydrido cobalt(III) complexes 4–6 and 8 could be used as catalysts for reduction of aldehydes and ketones. Complex 8 is the best catalyst among the four complexes and can selectively catalyze the carbonyl groups of α,β-unsaturated aldehydes and ketones.