Diverting Ni-Catalyzed Direct Benzylic C-H Hydroxylation towards Trifluoroethoxylation

Nickel(II) complexes with the simple N4 donor aminopyridine ligands BPMEN (N,N '-dimethyl-N,N '-bis(2-pyridylmethyl)-1,2-diaminoethane) and TPA (tris(2-pyridylmethyl)amine) have been demonstrated to perform as efficient catalysts for the regioselective oxygenation of benzylic C-H groups with m-chloroperoxybenzoic acid under mild conditions (at 20 degrees C), typically ensuring >90 % substrate conversions within 1 h at 1 mol % catalyst loadings. Unprecedentedly, replacing the commonly used mixed reaction solvent CH3CN/CH2Cl2 with 2,2,2-trifluoroethanol diverts the selectivity of the above Ni-based catalyst systems from hydroxylation/ketonization to trifluoroalkoxylation, with the formation of 1-phenylalkyl 2,2,2-trifluoroethyl ethers. The use of 2,2,2-trifluoroethanol ensures high substrate conversion values (up to 97 %), as well as high selectivity for the ether formation (up to 92 %). Preliminary discussion of the reaction mechanism is given based on the catalytic and literature data.