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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.
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.
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.
The HMBC correlation of 14a confirmed the catalyst structure and showed good correlation of the attached proton signal from indenylidene group with the weak carbenic carbon peak.], they are reliable.
The experiments performed simultaneously with the same batch of reagents in air clearly showed differences in reactivity of 5, 14a, and 14b.
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 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.