Catalyst Decomposition during Olefin Metathesis Yields Isomerization-Active Ruthenium Nanoparticles

The second‐generation Grubbs catalyst, RuCl2(H2IMes)(PCy3) (=CHPh) [GII ; H2IMes=1,3‐bis(2,4,6‐trimethylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene, Cy=cyclohexyl], is shown to decompose during olefin metathesis to generate Ru nanoparticles (RuNPs). These RuNPs appear to contribute significantly to competing isomerization during metathesis. Larger, partially oxidized RuNPs are also observed in commercial GII , but these exhibit modest isomerization activity. Removal of RuNPs from the precatalyst does not prevent isomerization, because new, more reactive NPs are generated by catalyst decomposition during metathesis

Tandem ring‐opening–ring‐closing metathesis for functional metathesis catalysts

Use of a tandem ring-opening–ring-closing metathesis (RORCM) strategy for the synthesis of functional metathesis catalysts is reported. Ring opening of 7-substituted norbornenes and subsequent ring-closing metathesis forming a thermodynamically stable 6-membered ring lead to a very efficient synthesis of new catalysts from commercially available Grubbs’ catalysts. Hydroxy functionalized Grubbs’ first- as well as third-generation catalysts have been synthesized. Mechanistic studies have been performed to elucidate the order of attack of the olefinic bonds. This strategy was also used to synthesize the ruthenium methylidene complex

The influence of structure on reactivity in alkene metathesis

Abstract Alkene metathesis has grown from a niche technique to a common component of the synthetic organic chemistry toolbox, driven in part by the development of more active catalyst systems, or those optimized for particular purposes. While the range of synthetic chemistry achieved has been exciting, the effects of structure on reactivity have not always been particularly clear, and rarely quantified. Understanding these relationships is important when designing new catalysts, reactions, and syntheses. Here, we examine what is known about the effect of structure on reactivity from two perspectives: the catalyst, and the substrate. The initiation of the precatalyst determines the rate at which active catalyst enters the catalytic cycle; the rate and selectivity of the alkene metathesis reaction is dependent on how the substrate and active catalyst interact. The tools deployed in modern studies of mechanism and structure/activity relationships in alkene metathesis are discussed

Attention Demand And Short-term Kinesthetic Memory.

Ph.D.Physical educationUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/191129/2/7510240.pd

Towards More Efficient, Greener Syntheses through Flow Chemistry

Technological advances have an important role in the design of greener synthetic processes. In this Personal Account, we describe a wide range of thermal, photochemical, catalytic, and biphasic chemical transformations examined by our group. Each of these demonstrate how the merits of a continuous flow synthesis platform can align with some of the goals put forth by the Twelve Principles of Green Chemistry. In particular, we illustrate the potential for improved reaction efficiency in terms of atom economy, product yield and reaction rates, the ability to design synthetic process with chemical and solvent waste reduction in mind as well as highlight the benefits of the real‐time monitoring capabilities in flow for highly controlled synthetic output

Targeting an Achilles heel in olefin metathesis: A strategy for high-yield synthesis of second-generation Grubbs methylidene catalysts

The first clean, high-yield route is presented to methylidenes RuCl 2(L)(PCy 3)(=CH 2) (L = H 2IMes or IMes), key vectors for catalysis and deactivation in many olefin metathesis reactions. (H 2IMes = N,N′-bis(mesityl)imidazolin-2-ylidene; IMes = N,N′-bis(mesityl)imidazol-2-ylidene)