Ring-Closing Metathesis Reactions: Interpretation of Conversion-Time Data was written by Thiel, Vasco;Wannowius, Klaus-Juergen;Wolff, Christiane;Thiele, Christina M.;Plenio, Herbert. And the article was included in Chemistry – A European Journal in 2013.Reference of 85838-94-4 This article mentions the following:
Conversion-time data were recorded for various ring-closing metathesis (RCM) reactions that lead to five- or six-membered cyclic olefins by using different precatalysts of the Hoveyda type. Slowly activated precatalysts were found to produce more RCM product than rapidly activated complexes, but this comes at the price of slower product formation. A kinetic model for the anal. of the conversion-time data was derived, which is based on the conversion of the precatalyst (Pcat) into the active species (Acat), with the rate constant kact, followed by two parallel reactions: (1) the catalytic reaction, which utilizes Acat to convert reactants into products, with the rate kcat, and (2) the conversion of Acat into the inactive species (Dcat), with the rate kdec. The calculations employ two exptl. parameters: the concentration of the substrate (c(S)) at a given time and the rate of substrate conversion (-dc(S)/dt). This provides a direct measure of the concentration of Acat and enables the calculation of the pseudo-first-order rate constants kact, kcat, and kdec and of kS (for the RCM conversion of the resp. substrate by Acat). Most of the RCM reactions studied with different precatalysts are characterized by fast kcat rates and by the kdec value being greater than the kact value, which leads to quasistationarity for Acat. The active species formed during the activation step was shown to be the same, regardless of the nature of different Pcats. The decomposition of Acat occurs along two parallel pathways, a unimol. (or pseudo-first-order) reaction and a bimol. reaction involving two ruthenium complexes. Electron-deficient precatalysts display higher rates of catalyst deactivation than their electron-rich relatives. Slowly initiating Pcats act as a reservoir, by generating small stationary concentrations of Acat. Based on this, it can be understood why the use of different precatalysts results in different substrate conversions in olefin metathesis reactions. In the experiment, the researchers used many compounds, for example, tert-Butyl 5,6-dihydropyridine-1(2H)-carboxylate (cas: 85838-94-4Reference of 85838-94-4).
tert-Butyl 5,6-dihydropyridine-1(2H)-carboxylate (cas: 85838-94-4) belongs to pyridine derivatives. The ring atoms in the pyridine molecule are sp2-hybridized. The nitrogen is involved in the π-bonding aromatic system using its unhybridized p orbital. The lone pair is in an sp2 orbital, projecting outward from the ring in the same plane as the σ bonds. One of the examples of pyridines is the well-known alkaloid lithoprimidine, which is an A3 adenosine receptor antagonist and N,N-dimethylaminopyridine (DMAP) analog, commonly used in organic synthesis.Reference of 85838-94-4