Mechanistic comparison of ruthenium olefin metathesis catalysts: DFT insight into relative reactivity and decomposition behavior

• Published in: Journal of organometallic chemistry Vol. 691; no. 24; pp. 5312 - 5325
• Main Authors: van Rensburg, Werner Janse, Steynberg, Petrus J., Kirk, Megan M., Meyer, Wolfgang H., Forman, Grant S.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-12-2006
• Subjects: Decomposition; DFT; Mechanism; Metathesis; Phoban catalyst; Decomposition; DFT; Phoban catalyst; Mechanism; Metathesis
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/j.jorganchem.2006.08.075

Gibbs free energy surfaces are calculated from DFT for the olefin metathesis mechanism catalyzed by three ruthenium catalysts, viz (PCy
3)
2Cl
2Ru
CHPh, (IMes)(PCy
3)Cl
2Ru
CHPh and (Phoban-Cy)
2Cl
2Ru
CHPh. A substrate-induced decomposition mechanism for all three catalysts is also investigated and compared. Relative calculated reactivity trends are correlated to available experimental data.
The reaction mechanism and substrate-induced decomposition behavior of three ruthenium olefin metathesis catalysts, viz. first- and second-generation catalysts and the recently developed Phoban catalyst (“Phobcat”) are compared by constructing Δ
G surfaces at 298.15
K and 1
atm for the complete ligand systems. From these calculations fundamental insight is gained into the reactivity and stability observed experimentally for the three catalysts. In particular, the higher conversions obtained for the first-generation derived Phobcat catalyst, compared to conventional first-generation catalysts, is attributed to its similarity to the second-generation catalysts instead of first-generation catalyst. Important differences between the calculated Δ
G surfaces and previously reported total electronic energy (Δ
E) surfaces for the metathesis mechanism with complete ligand complexes are discussed.