"Sandwich" Diimine‐Copper Catalyzed Trifluoroethylation and Pentafluoropropylation of Unactivated C(sp3)−H Bonds by Carbene Insertion.

We report here "sandwich"‐diimine copper complex‐catalyzed trifluoroethylation and pentafluoropropylation of unactivated C(sp3)−H bonds in alkyl esters, halides, and protected amines by employing CF3CHN2 and CF3CF2CHN2 reagents. Reactions proceed in dichloromethane solvent at room temperature. Identical C−H functionalization conditions and stoichiometries are employed for generality and convenience. Selectivities for C−H insertions are higher for compounds possessing stronger electron‐withdrawing substituents. Preliminary mechanistic studies point to a mechanism involving a pre‐equilibrium forming a "sandwich"‐diimine copper‐CF3CHN2 complex followed by rate‐determining loss of nitrogen affording the reactive copper carbene. It reacts with trifluoromethyldiazomethane about 6.5 times faster than with 1‐fluoroadamantane explaining the need for slow addition of the diazo compound. [ABSTRACT FROM AUTHOR]