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.
The first one (type A) is based on earlier reported salts 6–8 as the source of NHC carbene.
Several attempts were undertaken to obtain new catalysts of type A via exchange with the commercial Hoveyda-Grubbs 1 generation complex (2) or complex 3.
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.The tested catalysts very effectively promoted ring-closing ene-yne metathesis (Table selectivity of synthesized complexes 14a and 14b are directly connected with the geometrical parameters and additional intramolecular interactions in a particular isomer.In order to estimate the most probable structure of the indenylidene-type second generation catalysts the static DFT calculations were performed.As a result, we have chosen 6 conformers per isomer (see Supplementary Material) to show the structural diversity of the synthesized catalysts and influence of weak interactions on their catalytic activity.The global minima structures of 14a and 14b are shown in Fig. Weak intramolecular interactions such as C–H···O, C–H···Cl, C–H···π hydrogen bonds and attractive π–π stacking interactions are among them.In a similar way the compound 12b was converted to 13b in 80 % yield (Scheme The synthesis of new ruthenium catalysts of type B bearing a modified NHCs by reaction of in situ generated carbenes (from new salts 13a and 13b) with the commercially available indenylidene 1st generation catalyst 3 was attempted.Unfortunately, the reaction failed probably due to poor nucleophilicity of the NHCs compared to tricyclohexylphosphine ligand in the complex 3.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.