Towards (C,C)‐cyclometalated N‐(9‐alkylfluorenyl)NHC Ruthenium Complexes for Z‐selective Olefin Metathesis

Abstract

Three Hoveyda‐Grubbs complexes supported by N‐(9‐alkylfluorenyl)imidazol‐2‐ylidene ligands (alkyl=methyl, ethyl or benzyl) have been synthesized. With the aim to generate chelating, cyclometalated (C,CNHC) ruthenium complexes for Z‐selective olefin metathesis, the C(sp3)‐H activation of the dangling alkyl group has been studied. While the methyl derivative leads to the expected cyclometalated complex, a C(sp2)‐H activation of the fluorenyl moiety and no evolution/transformation are observed for the ethyl and benzyl derivatives, respectively. Although highly fragile under catalytic conditions, the cyclometalated complex leads to Z/E stereoselectivity up to 94/6. An unprecedented insertion of the alkylidene moiety into the Ru‐CNHC bond leading to ruthenium N‐heterocyclic olefin complexes is also observed and supported by calculations of the corresponding reaction pathway.

An Anthracene-Thiolate-Ligated Ruthenium Complex: Computational Insights into Z-Stereoselective Cross Metathesis

“…To achieve this goal, we have proposed a Ru-based or C 6 H 5 ), they conducted thorough investigations of olefin metathesis reactions, with a specific focus on achieving Zselectivity with Z/E ratios of up to 94/6. 55 Furthermore, Rubased catalysts incorporating sulfurated chelates have also been reported by Lemcoff et al 56−58 Therefore, we have formulated a possible synthesis route to the precatalyst in question (details in Figure S1 in the Supporting Information), which involves the preparation of thioether-imidazolium chlorides, 59 anilines, 60,61 and modifications to the Grubbs first-generation catalyst. 34,62 3.1.…”

“…In the context of polycyclic aromatic hydrocarbons, Grela et al previously synthesized Ru-based catalysts characterized by either a thiophene-based or a 10-phenyl-9-phenanthryl ligand bonded to an unsymmetrical NHC moiety. In fact, in the case of Hoveyda–Grubbs complexes bearing N -(9-alkylfluorenyl)­imidazol-2-ylidene ligands (alkyl: CH 3 , C 2 H 5 , or C 6 H 5 ), they conducted thorough investigations of olefin metathesis reactions, with a specific focus on achieving Z-selectivity with Z/E ratios of up to 94/6 . Furthermore, Ru-based catalysts incorporating sulfurated chelates have also been reported by Lemcoff et al − Therefore, we have formulated a possible synthesis route to the precatalyst in question (details in Figure S1 in the Supporting Information), which involves the preparation of thioether-imidazolium chlorides, anilines, , and modifications to the Grubbs first-generation catalyst. , …”