Kinetics of Anionic Ligand Exchange in HG-II type and S-chelated Ruthenium Olefin Metathesis Complexes

Metathesis of olefins is a powerful chemical reaction that produces a wide range of materials ranging from polymers to natural products.¹ Olefin metathesis is catalyzed by transition metal complexes, amongst them the ubiquitous Grubbs type ruthenium complexes that contain 2 neutral ligands, two anionic ligands and an active alkylidene.

While a plethora of different NHC and alkylidene ligands have been extensively studied for this type of complexes, the influence of the anionic ligands is much less recognized. Nonetheless, the anionic ligands have a great influence on the efficiency and selectivity of the olefin metathesis reaction² and it has been shown, in a seminal report by Braddock and coworkers, that the anionic ligands exist in a constant dynamic exchange.³

The facile exchange of the labile anionic ligands has been used in the past to prepare pseudo-halide derivatives of Grubbs` type catalysts.⁴ As an interesting example, our group recently reported exchange of the chloro anionic ligand in the HG-2 complex by protected amino acids to achieve enantioselective olefin metathesis.⁵

Herein, we report our preliminary results on a detailed kinetic study of anionic ligand exchange in HG-II and S-chelated type catalysts.

References

1. Handbook of metathesis , volume 3 , 2003 , p. 103-112
2. Torker,S ; R. Kashif M. Khan ; Amir H. Hoveyda Am. Chem. Soc., 2014, 136 (9), p. 3439–3455
3. Tanaka, K.; Böhm, V. P. W.; Chadwick, D.; Roeper, M.; Braddock, D. C. 2006, 25, 5696.
4. Anderson, E. B.; Buchmeiser, M. R. Synlett 2012, 2, 185.
5. Ivry, E.; Ben-Asuly, A.; Goldbergb, I.; Lemcoff, N. G. Commun. 2015, 51, 3870.