Controlled monodefluorination and alkylation of C(sp3)–F bonds by lanthanide photocatalysts: importance of metal–ligand cooperativity

Abstract

The controlled functionalization of a single fluorine in a CF₃ group is difficult and rare. Photochemical C–F bond functionalization of the sp³-C–H bond in trifluorotoluene, PhCF₃, is achieved using catalysts made from earth-abundant lanthanides, (Cp^Me4)₂Ln(2-O-3,5-^tBu₂-C₆H₂)(1-C{N(CH)₂N(ⁱPr)}) (Ln = La, Ce, Nd and Sm, Cp^Me4 = C₅Me₄H). The Ce complex is the most effective at mediating hydrodefluorination and defluoroalkylative coupling of PhCF₃ with alkenes; addition of magnesium dialkyls enables catalytic C–F bond cleavage and C–C bond formation by all the complexes. Mechanistic experiments confirm the essential role of the Lewis acidic metal and support an inner-sphere mechanism of C–F activation. Computational studies agree that coordination of the C–F substrate is essential for C–F bond cleavage. The unexpected catalytic activity for all members is made possible by the light-absorbing ability of the redox non-innocent ligands. The results described herein underscore the importance of metal–ligand cooperativity, specifically the synergy between the metal and ligand in both light absorption and redox reactivity, in organometallic photocatalysis.