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-<i>O</i>-3,5- ^<i>t</i> Bu₂-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.