Two new Ru-based metathesis catalysts, 3 and 4, have been synthesized for the purpose of comparing their catalytic properties to those of their cis-selective nitrate analogues, 1 and 2. Although catalysts 3 and 4 exhibited slower initiation rates than 1 and 2, they maintained high cis-selectivity in homodimerization and ring-opening metathesis polymerization reactions. Furthermore, the nitrite catalysts displayed higher cis-selectivity than 2 for ring-opening metathesis polymerizations, and 4 delivered higher yields of polymer.

Pribisko Melanie A.    Ahmed Tonia    Robert H.Grubbs    

Polyhedron

2014

The past 5 years have witnessed an enormous growth in the field of Z-selective olefin metathesis. The development of a new class of cyclometalated ruthenium-based catalysts has extended the utility of olefin metathesis to the synthesis of useful Z-olefin-containing small molecules, polymers, and natural products. This review highlights the recent advances in the area of Z-selective olefin metathesis employing cyclometalated ruthenium alkylidene catalysts, with particular focus on its applications and mechanistic basis. A deeper understanding of structure-activity relationships should aid in the future design of even more active and selective olefin metathesis catalysts.

Marx Vanessa M.    Rosebrugh Lauren E.    Herbert Myles B.    Robert H.Grubbs    

Topics in Organometallic Chemistry

2014

The Z-selective ethenolysis activity of chelated ruthenium metathesis catalysts was investigated with experiment and theory. A five-membered chelated catalyst that was successfully employed in Z-selective cross metathesis reactions has now been found to be highly active for Z-selective ethenolysis at low ethylene pressures, while tolerating a wide variety of functional groups. This phenomenon also affects its activity in cross metathesis reactions and prohibits crossover reactions of internal olefins via trisubstituted ruthenacyclobutane intermediates. In contrast, a related catalyst containing a six-membered chelated architecture is not active for ethenolysis and seems to react through different pathways more reminiscent of previous generations of ruthenium catalysts. Computational investigations of the effects of substitution on relevant transition states and ruthenacyclobutane intermediates revealed that the differences of activities are attributed to the steric repulsions of the anionic ligand with the chelating groups. © 2013 American Chemical Society.

Miyazaki Hiroshi    Herbert Myles B.    Peng Liu    Dong Xiaofei    Xiufang Xu    Benjamin keith Keitz    Ung Thay    Mkrtumyan Garik    Kendall Houk    Robert H.Grubbs    

Journal of the American Chemical Society

2013

Chung Hoyong    Robert H.Grubbs    

Macromolecules

2013

Benjamin keith Keitz    Endo Koji    Patel Paresma R.    Herbert Myles B.    Robert H.Grubbs    

Journal of the American Chemical Society

2013

We report a transition-metal-free protocol for the efficient reductive cleavage of diaryl and aryl alkyl ethers. The combination of triethylsilane with common bases forms an unusually powerful reductive couple that regioselectively ruptures lignin- and coal-related C–O bonds in aromatic ethers. Interestingly, with certain bases and temperature regimes ortho-directed C–H silylation efficiently competes with the latter process. However, careful tuning of the reactions conditions allows for the selective reductive cleavage of lignin model compounds to their corresponding phenolic and aromatic constituents. © 2013 The Royal Society of Chemistry.

Alexey Fedorov    Toutov Anton A.    Swisher Nicholas A.    Robert H.Grubbs    

Chemical Science

2013

Wacka wacka: The title reaction makes use of a wide range of directing groups (DG) to enable the highly regioselective oxidation of alkenes, and occurs predictably at the distal position. Both E and Z alkenes afford valuable functionalized ketones and cross-metathesis was shown to facilitate the preparation of the starting materials. BQ=benzoquinone. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Morandi Bill    Wickens Zachary K.    Robert H.Grubbs    

Angewandte Chemie - International Edition

2013

A series of ruthenium catalysts bearing five-membered chelating NHC architectures that exhibit very high Z-selectivity in a variety of metathesis reactions have recently been reported. It was envisioned that catalysts possessing six-membered chelates could similarly exhibit high Z-selectivity and address limitations of this methodology. We thus prepared a number of new catalysts and systematically investigated the impact of the NHC and anionic ligand on their stereoselectivity. In standard metathesis assays, only catalysts containing six-membered chelated NHC structures and η-bound anionic ligands favored the Z-olefin products. In addition, substitution with bulkier N-aryl groups led to improved Z-selectivity. The effect of ligand structure on stereoselectivity discovered in this study will be useful in the future design of highly active and Z-selective ruthenium catalysts. © 2013 American Chemical Society.

Endo Koji    Herbert Myles B.    Robert H.Grubbs    

Organometallics

2013

Robert H.Grubbs    

Nature

2013

Kaneyoshi Hiromu    Haruyuki Makio    Fujita Terunori    Robert H.Grubbs     Jun Okuda    Eugene you xian Chen   

Organic Chemistry - Breakthroughs and Perspectives

2012