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Salicylaldimine Ruthenium Alkylidene Complexes: Metathesis Catalysts Tuned for Protic Solvents

“…[27] Switching the reaction solvent to hexanes and the base to the more soluble potassium tert-amylate enhanced the synthesis, enabling the clean conversion of 6a to 7a as confirmed by 1 H NMR. Once again, spectral characterization failed to reveal the signals of the proposed imine complex reported by De Clercq & Verpoort, [17] Although these results confirm that 7a is the authentic product of both our synthesis from H 2 IMes complex 8 and the preparation from 6a, the identity of the product reported previously [17] still remains unclear.…”

“…[17] Attempts to prepare reported complex 7a by this published method resulted, however, in decomposition of the ruthenium benzylidene starting material. Faced with this roadblock, we chose to approach 7a-c by introducing salicylaldimine ligands to a complex already bearing the H 2 IMes ligand.…”

“…[17] As listed in Table 1 To resolve this conflict, we sought crystallographic evidence. Suitable crystals of complex 7a were grown by slow diffusion of pentane into a concentrated benzene solution over a few days.…”

“…[15] Aware of the benefits that N-heterocyclic carbene (NHC) ligands provide other ruthenium metathesis catalysts, we chose to investigate salicylaldimine complexes such as 7a and b reported by Verpoort and coworkers. [16][17][18] According to their work, this family of NHC-imine complexes efficiently catalyzes ring-opening metathesis polymerization (ROMP), RCM, and Kharasch addition. Iminebearing ruthenium complexes are proposed to enter the olefin metathesis catalytic cycle with decoordination of the imine nitrogen rather than the phosphine dissociation observed for initiation of 1 and 2.…”

Latent olefin metathesis catalysts

“…Results showed that these complexes exhibit rather low activity towards the ROMP of norbornene and cyclooctene but high activity is observed after chemical activation with TMSD. 15 The isolation of N-heterocyclic carbenes in the early nineties 10a marked an important milestone when incorporated in olefin metathesis catalysts since they function as strong electron-donating and sterically demanding phosphine mimics. Delaude et al reported the visible light-induced ROMP of cyclooctene with complexes 5 (Scheme 4, L = IMes = 1,3-dimesitylimidazol-2-ylidene, Dipp = 1,3-di(2,6-diisopropylphenyl)-imidazol-2-ylidene).…”