Wesentlich bessere Initiatoren und demzufolge erheblich reaktiver als die Komplexe des Typs A sind die Metathesekatalysatoren B, die durch Umsetzung von [RuCl2 (PPh3)3] mit den entsprechenden Diazoalkanen und nachfolgenden Phosphanaustausch erhältlich sind. Während die PPh3‐Derivate ausgezeichnete Katalysatoren für die lebende ROMP von Norbornen sind, erweist sich der Komplex mit R Cy, R′ Ph zusätzlich als sehr wirksamer Katalysator für die Metathese acyclischer Alkene.
The kinetics of the initiation and propagation of the ring-opening metathesis polymerization of exo, exo-5,6-bis(methoxycarbonyl)-7-oxabicyclo[2.2.1]hept-2-ene catalyzed by Grubbs' catalyst (Cl 2 (PCy 3 ) 2 RuACHPh) were measured by ultravioletvisible and 1 H NMR spectroscopy, respectively. Activation parameters for these processes were also determined. Although the ratio of the rate constant of initiation to the rate constant of propagation was determined to be less than 1 for this system, this polymerization showed many of the characteristics of a living system, including low polydispersities.
EXPERIMENTALAll manipulations were carried out under an inert nitrogen atmosphere with standard Schlenk and
Ring-opening metathesis polymerization (ROMP) of exo,exo-5,6-bis(methoxymethyl)-7oxabicyclo[2.2.1]hept-2-ene (3) catalyzed by Run(H20)e(tos)2 (tos = p-toluenesulfonate) (1) in the presence of terminal acyclic olefins such as 3-buten-l-ol and methyl acrylate affords low molecular weight polymeric materials. Analysis of these oligomer samples by one-and two-dimensional NMR spectroscopy identifies them as resulting from a true metathesis chain transfer mechanism. These data and the identification of the ring-opened monomer units with alkylidene end groups corresponding to the acyclic chain transfer agent by high resolution mass spectrometry confirm this study as the first example of metathesis of an acyclic olefin by 1. A comparison of the chain transfer activities of a series of acyclic esters yields a reactivity order of terminal olefins > deactivated terminal olefins > internal olefins > deactivated internal olefins, consistent with the behavior of well-characterized homogeneous alkylidene complexes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.