Controlled monodefluorination and alkylation of C(sp 3 )-F bonds by lanthanide photocatalysts: importance of metal-ligand cooperativity.

The controlled functionalization of a single fluorine in a CF 3 group is difficult and rare. Photochemical C-F bond functionalization of the sp 3 -C-H bond in trifluorotoluene, PhCF 3 , is achieved using catalysts made from earth-abundant lanthanides, (Cp Me4 ) 2 Ln(2- O -3,5- t Bu 2 -C 6 H 2 )(1-C{N(CH) 2 N( i Pr)}) (Ln = La, Ce, Nd and Sm, Cp Me4 = C 5 Me 4 H). The Ce complex is the most effective at mediating hydrodefluorination and defluoroalkylative coupling of PhCF 3 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.