The metathesis reactions were carried out in commercial-grade solvents in air.
The catalysts were also tested in a model CM reaction of allylbenzene with ) of TMS.
We have considered 13 different conformers of each catalysts 14a and 14b.
After geometry optimization some of the conformers converged to a similar local minimum or had very close absolute energies.
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The precursors of free carbenes—imidazolinium salts—were obtained in an easy and environment-friendly way (under aqueous or neat conditions).Despite initial failures in synthesis of catalysts associated with weak nucleophilicity of nitroaryl substituted NHCs, new complexes with nitrobenzyl substituted NHC were obtained.The complexes were tested in model RCM, leading to formation of five-membered cyclic products bearing di-, tri-, or tetrasubstituted double bonds, as well as ene-yne reactions.The exchange of carbene ligands in the commercial complexes failed probably due to poor nucleophilicity of the NHCs bearing nitroaryl substituents [).A methylene spacer should effectively suppress electronic interaction with the imidazolinium ring.This issue will be the subject of further detailed investigations (e.g., including the Nolan and Cavallo method [H NMR spectrum confirmed the structure of the obtained catalysts.The signals derived from the mesityl group protons (three singlets from the methyl groups and two singlets from the aromatic protons) have been well resolved in C NMR spectra signals from the carbenic carbons were weak.The structural parameters of the mentioned H-bonds, that denote their strength, are shown in Supplementary Material.No specific interactions between the -nitro group of complex 14a and the ruthenium atom were identified.Therefore, olefin molecules are restricted to the nitrobenzyl side for binding to the Ru-methylidene center and therefore relatively more of a In summary, the synthesis of two new ruthenium indenylidene-type catalysts bearing unsymmetrical NHC ligand was described.A three-step protocol for the synthesis of unsymmetrical precursors of NHC with mesityl and nitrobenzyl substituents was elaborated.