Energetics of C-H bond activation of fluorinated aromatic hydrocarbons using a [Tp'Rh(CNneopentyl)] complex.

ABSTRACT

C-H bond activation of fluorinated aromatic hydrocarbons by [Tp'Rh(CNneopentyl)] resulted in the formation of products of the type Tp'Rh(CNneopentyl)(aryl(F))H. The stability of the Rh-C(aryl) product is shown to be strongly dependent on the number of ortho fluorines and only mildly dependent on the total number of fluorine substituents. Complexes with aryl groups containing two ortho fluorines have barriers to reductive elimination that are approximately 5 kcal mol(-1) higher than for those with a single ortho fluorine. Competition experiments along with DeltaG(re)(double dagger) values allow for the determination of relative Rh-C(aryl) bond strengths and illustrate the large ortho fluorine effect on the strength of the Rh-C(aryl) bond. A large change in Rh-C(aryl) bond strength was measured for small changes in the respective calculated C-H bond strengths. Relating M-C to C-H bond strengths resulted in a line (slope = 2.14) that closely matches the theoretically calculated value (slope = 1.96). This is the first experimental quantization of an ortho fluorine effect as predicted by theory.