Among the many types of transition-metal-catalysed C–C bond forming reactions, olefin metathesis is without a doubt one of the most thriving fields in modern organic synthetic chemistry.

Formation of tetrasubstituted C–C double bonds via olefin metathesis is considered very challenging for classical Ru-based complexes. In the hope to improve this condition, three ruthenium olefin metathesis catalysts bearing sterically reduced N -heterocyclic carbene (NHC) ligands with xylyl “arms” were synthesized, characterized using both computational and experimental techniques, and tested in a number of challenging reactions. The catalysts are predicted to initiate much faster than the analogue with mesityl N -substituents. We also foreboded the rotation of xylyl side groups at ambient temperature and the existence of all four atropoisomers in the solution, which was in agreement with experimental data. These catalysts exhibited high activity at relatively low temperatures (45–60 °C) and at reduced catalyst loadings in various reactions of sterically hindered alkenes, including complex polyfunctional substrates of pharmaceutical interest, such as yangonin precursors, chrysantemic acid derivatives, analogues of cannabinoid agonists, α-terpineol, and finally a thermally unstable peroxide.

Compatibility of selected, commercially available ruthenium olefin metathesis catalysts with ethyl lactate as solvent was evaluated using a range of substrates and conditions. In addition, the preparation of a metathesis catalyst in simplified manner by using the advantages of ethyl lactate was accomplished. The application of ethyl lactate facilitates product isolation (also allowing for lower ruthenium contamination in crude metathesis products) and improves the overall green angle of olefin metathesis.

The lithium complexes [(WCA-NHC)Li(toluene)] of anionic N-heterocyclic carbenes with a weakly coordinating borate moiety (WCA-NHC, WCA = B(C 6 F 5 ) 3 , NHC = IDipp = 1,3bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were used for the preparation of silver(I) or copper(I) WCA-NHC complexes. While the reactions in THF with AgCl or CuCl afforded anionic mono-and dicarbene complexes with solvated lithium counterions [Li(THF) n ] + (n = 3, 4), the reactions in toluene proceeded with elimination of LiCl and formation of the neutral phosphine and arene complexes [(WCA-NHC)M(PPh 3 )] and [(WCA-NHC)M(η 2 -toluene)] (M = Ag, Cu). The latter were used for the preparation of chlorido-and iodido-bridged heterobimetallic Ag/Ru and Cu/Ru complexes [(WCA-NHC) M(μ-X) 2 Ru(PPh 3 )(η 6 -p-cymene)] (M = Ag, Cu, X = Cl; M = Ag, X = I). Surprisingly, these complexes resisted the elimination of CuCl, AgCl, or AgI, precluding WCA-NHC transmetalation.

A set of six new catalysts possessing quinone moieties in a pyridine ligand was synthesized and fully characterized by standard analytical techniques, including X-Ray crystallography. The results obtained in Suzuki and Mizoroki-Heck cross-coupling reactions catalyzed by quinone-based compounds were comparable to these obtained in the presence of the original PEPPSI complex designed by Organ. DFT calculations allow to see the structural and electronic factors to describe their similarity. On the other hand, steric maps and NCI plots were the tools to have a more global view of the systems studied, leaving the sphere of reactivity around the metal.