Comparison of the Full Catalytic Cycle of Hydroformylation Mediated by Mono- and Bis-Ligated Triphenylphosphine-Rhodium Complexes by Using DFT Calculations

The coordination mode of triphenylphosphine to rhodium is considered to be important for the outcome of hydroformylation catalysis. The difference in reactivity between mono- and bis-ligated rhodium species has not been investigated systematically, mostly because it is impossible to obtain pure mono-ligated rhodium under hydroformylation conditions. Therefore, we performed detailed computational studies to get an insight into the effect of the coordination of triphenylphosphine to rhodium on hydroformylation catalysis. The DFT-calculated catalytic pathway of the monophosphine-based catalyst shows a lower free energy barrier (24.5kcalmol(-1)) compared to the pathway of the bisphosphine catalyst (28.9kcalmol(-1)). This confirms that monophosphine catalysts have an intrinsically higher activity than bisphosphine catalysts and indicates that the rate enhancement seen with the tetraphenylporphyrin-based catalyst reported by our group previously is at least partly due to the monocoordination enforced by this encapsulating ligand.