Controllable Single and Double Difluoromethylene Insertions into C-Cu Bonds: Copper-Mediated Tetrafluoroethylation and Hexafluoropropylation of Aryl Iodides with TMSCFH and TMSCFBr.

The selective difluoromethylene insertion into a C-Cu bond is a challenging task and is currently limited to either a single CF insertion into CuCF or double CF insertions into CuCF (or ()-CFCF = CFCu). Achieving both selective single and double CF insertions into the same C-Cu bond is even more difficult. Herein, highly controllable single and double CF insertions into CuCFH species with a TMSCFBr reagent have been described, affording two previously unknown fluoroalkylcopper species "Cu(CF)CFH" ( = 1 and 2) independently under different reaction conditions. This work represents the first example of both single and double CF insertions into the same C-Cu bond in a highly selective manner. The synthetic value of the obtained "Cu(CF)CFH" ( = 1 and 2) species is demonstrated by their reactions with aryl iodides, halogenation agents, and cinnamyl chloride, which enables the direct transfer of HCFCF and HCFCFCF moieties into organic molecules. The key to controllable fluorocarbon chain elongation from C to C and from C to C is presumably attributed to the different reactivities of "Cu(CF)CFH" species ( = 0, 1, 2 and 3) and the loading of the TMSCFBr reagent.