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

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.