Unraveling the Effect of Chemical Environment on Half‐Sandwich Cp*ReO ₃ Complex Stability in Deoxydehydration Reaction

Understanding the identity of catalytically active species remains a central challenge in rhenium‐catalyzed deoxydehydration (DODH) of biomass‐derived vicinal diols. Here we revisit the scarcely studied Cp*ReO 3 complex, despite being the first reported homogeneous DODH catalyst, as a mechanistic model to elucidate catalyst speciation and activity relationships. Using the conversion of 1,2‐propanediol to propylene, a transformation that has received little attention and is shown here to produce pure propylene, we quantitatively analyze reaction kinetics and catalyst speciation. Our results reveal a dynamic equilibrium between intact Cp*ReO 2 complexes, Cp*‐less rhenium species, and polymerized rhenium species. The reaction environment strongly governs catalyst speciation, as nonpolar solvents promote ligand dissociation of Cp*ReO 2 , whereas polar solvents stabilize intact Cp*ReO 2 complexes. Kinetic analysis demonstrates that in d 6 ‐benzene, a common DODH solvent, the Cp*‐less rhenium species are 54‐fold more active than the intact Cp*ReO 2 complexes, identifying them as the dominant catalytic contributors. We further show that substrate coordination stabilizes reduced rhenium centers and prevents catalyst polymerization, while simultaneously promoting ligand dissociation. Extending these insights to other vicinal diols, Cp*ReO 3 also catalyzes the DODH of diethyl tartrate at room temperature. Together, these findings position Cp*ReO 3 as a benchmark platform for mechanistic and stability studies in homogeneous DODH catalysis.