The new catalysts were prepared by reaction of in situ generated carbenes with a 1st generation indenylidene catalyst, containing pyridine ligands instead of tricyclohexylphosphine.
The new catalysts were prepared by reaction of in situ generated carbenes with a 1st generation indenylidene catalyst, containing pyridine ligands instead of tricyclohexylphosphine.Tags: Theses And DissertationGrade 6 Essay QuestionsSport Classification EssayNew Testament Research Paper TopicsAmerican English Essay WriterCorporate Sponsorships In Schools EssaysLaw Dissertation TitlesProcess Essays Should Be Organized
However, all experiments aimed at the NHC ligand exchange were unsuccessful.
An alternative way involving the NHC carbene generation in situ by thermal decomposition of 2–(pentafluorophenyl)imidazolidine 10 in the presence of 2 was also attempted. The adduct 10 was synthesized by acid-catalyzed condensation of 2,3,4,5,6-pentafluorobenzaldehyde with diaryl substituted ethylenediamine 9, prepared according to our earlier procedure [We assume that coordination of a carbene, containing the nitroaryl group directly connected with an imidazolinium ring, to the ruthenium center is not feasible.
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 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.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 indenylidene-bearing family of complexes has exhibited a rapid growth in use in recent years and is quickly becoming a mainstream catalyst in metathesis-type reactions [-nitroaryl substituents were designed.We believed that unsymmetrical NHCs could affect the geometry of the metallacyclobutane intermediate produced during the reaction with an olefin, thus increasing ).Separating of the electron-deficient aromatic ring from the imidazolinium part might enable coordination of the resulting carbene to the ruthenium center.-nitrobenzaldehyde under neat conditions followed by reduction of the resulting imines gave corresponding ethylenediamines in high yields.The compound 12a was converted to dihydrochloride and subjected to cyclization with trimethyl orthoformate to give the corresponding imidazolinium salt 13a in 77 % yield.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.