Despite the widespread occurrence of intramolecular C-H activating1, 2 cyclometalation processes3(eq 1) and the possibility that they may enjoy an “intramolecular advantage”4, 5 over competing intermolecular processes, relevant comparative thermodynamic (ΔH, AS) and kinetic (ΔH*, ΔS*) information is surprisingly sparse. For one rhodium system, Jones and Feher6 showed that an intramolecular process enjoyed a slight thermodynamic (only AG° could be measured) advantage but also a slight kinetic disadvantage (only in AH*). We recently reported kinetic/mechanistic studies of intermolecular alkane activation7 and closely related intramolecular cyclometalation8 at thorium centers (eq 2–4). C-H scission was found to be rate-limiting, and thermochemical data (ΔH)9suggest that eq 3 and 4 are entropically driven. We now report that the reversibility of eq 4 can be rendered observable, presenting a unique opportunity to quantify, in toto, thermodymamic and kinetic aspects of the in tramolecular cyclometalation process vis-á-vis its intermolecular microscopic reverse.
ASJC Scopus subject areas
- Colloid and Surface Chemistry