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Methylidene species are used as model complexes for examining the decomposition of a series of ruthenium metathesis catalysts. The decomposition study has provided a basis for design and synthesis of more efficient ruthenium olefin metathesis catalysts.

A highly efficient route to N-tert-buttoxycarbonyl-(N-Boc) protected beta-amino acids through the enentioselective addition of silyl ketene acetals to N-Boc-aldimines catalyzed by thiourea catalyst is presented. The conclusion states that urea derivatives of general structure serve as highly effective catalysts for the asymmetric addition of silyl ketene acetal derivatives to aldimines.

Studies show evidence supporting the bottom-face orientation of ruthenium metallacycles derived from both ethylene and propene, and the metallacycle structures derived from propene represent examples of substituted ruthenacyclobutanes and offer new insight into the preferred stereochemical orientation of metathesis intermediates. It is suggested that ruthenacyclobutanes derived from ethylene and propene are dynamic structures that proceed through a series of nonproductive metallacycle formations prior to olefin exchange.

The reaction of the phosphonium alkylidene [(H2IMes)RuCl2CHP(Cy)3)] BF4 with propene, 1-butene, and 1-hexene at -45 °C affords various substituted, metathesis-active ruthenacycles. These metallacycles were found to equilibrate over extended reaction times in response to decreases in ethylene concentrations, which favored in- creased populations of a-monosubstituted and a,a'-disubsti- tuted (both cis and trans) ruthenacycles. On an NMR timescale, rapid chemical exchange was found to preferentially occur between the j3-hydrogens of the cis and trans stereoisomers prior to olefin exchange. Exchange on an NMR time scale was also observed between thea- and /3-methylene groups of the monosubstituted ruthenacycle (H2IMes)C12Ru(CHRCH2CH2) (R = CH3, CH2CH3, (CH2)3CH3). EXSY NMR experiments at -87 °C were used to determine the activation energies for both of these exchange processes. In addition, new methods have been developed for the direct preparation of metathesis-active ruthenacyclobutanes via the protonolysis of dichloro(1,3-bis(2,4,6-trimethylphenyl)-2- imidazolidinylidene)(benzylidene) bis(pyridine)ruthenium(II) and its 3-bromopyridine analogue. Using either trifluoroacetic acid or silica-bound toluenesulfonic acid as the proton source, the ethylene-derived ruthenacyclobutane (H2IMes)CI2Ru- (CH2CH2CH2) was observed in up to 98% yield via NMR at -40 °C. On the basis of these studies, mechanisms accounting for the positional and stereochemical exchange within ruthenacyclobutanes are proposed, as well as the implications of these dynamics toward olefin metathesis catalyst and reaction design are described. [ABSTRACT FROM AUTHOR]

The article presents two science experiments on metathesis-derived intrinsically conducting polymers (ICP) and metathesis. It notes that the first study utilizes catalyst 5 to polymerize cyclooctatetraene (COT) while in the second study the students generate a telecheluc polymer from COT. It mentions that the study introduced topics of both the 2000 and 2004 Nobel Prizes in Chemistry, conductive organic polymers, and olefin metathesis. It adds that the students who participated in the experiments were able to effectively evaluate the mechanistic and conceptual characteristic of the experiment.

Describes a highly efficient route to N-tert-butoxycarbonyl-(N-Boc) protected beta-amino acids via the enantionselective addition of silyl ketene acetals to N-Boc-aldimines catalyzed by thiourea catalysts. Emergence of urea derivatives as useful catalysts for the asymmetric hydrocyanation of N-allyl or N-benzyl aldimines and ketoimines.

The decomposition of a series of ruthenium metathesis catalysts has been examined using methylidene species as model complexes. All of the phosphine-containing methylidene complexes decomposed to generate methylphosphonium salts, and their decomposition routes followed first-order kinetics. The formation of these salts in high conversion, coupled with the observed kinetic behavior for this reaction, suggests that the major decomposition pathway involves nucleophilic attack of a dissociated phosphine on the methylidene carbon. This mechanism also is consistent with decomposition observed in the presence of ethylene as a model olefin substrate. The decomposition of phosphine-free catalyst (H2IMes)(Cl)2Ru=CH(2-C6H4-O-i-Pr) (H2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) with ethylene was found to generate unidentified ruthenium hydride species. The novel ruthenium complex (H2IMes)(pyridine)3(Cl)2Ru, which was generated during the synthetic attempts to prepare the highly unstable pyridine-based methylidene complex (H2IMes)(pyridine)2(Cl)2Ru=CH2, is also reported.