3 years ago

Intramolecular C–H Activation Reactions of Ru(NHC) Complexes Combined with H2 Transfer to Alkenes: A Theoretical Elucidation of Mechanisms and Effects of Ligands on Reactivities

Intramolecular C–H Activation Reactions of Ru(NHC) Complexes Combined with H2 Transfer to Alkenes: A Theoretical Elucidation of Mechanisms and Effects of Ligands on Reactivities
Katharina Marie Wenz, K. N. Houk, Peng Liu
Recent experimental studies have identified Ru(II) NHC complexes that are highly reactive in the tandem intramolecular C(sp3)–H activation of an N-alkyl substituent to form a metallacycle and transfer hydrogenation of alkenes. These complexes are promising candidates for tandem catalytic processes that depend on a reversible uptake of hydrogen (“borrowing hydrogen catalysis”). We have elucidated the reaction mechanisms by density functional theory calculations and investigated ligand effects on reactivity. The reaction of ruthenium dihydride complex [Ru(H)2(NHC)(CO)(PPh3)2] (1) with ethylene occurs via dissociative ligand exchange to replace one of the phosphine ligands with ethylene, followed by hydride migration and reductive elimination to form a Ru(0) intermediate. Subsequent C–H activation occurs via an oxidative addition mechanism. Bulkier NHC and phosphine ligands facilitate the dissociation of phosphine, which leads to a lower overall barrier. In addition, the N-iPr substituted NHC ligand promotes the C–H oxidative addition/ruthenacyclization due to the release of steric strain caused by the N-iPr group and the substituents on the NHC backbone. The reaction with the monohydride monochloride complex [RuHCl(NHC)(PPh3)2] (2) occurs via ligand exchange and hydride migration to form an alkyl ruthenium(II) complex. The type of phosphine ligand determines whether the subsequent intramolecular C–H activation proceeds via an associative or a dissociative mechanism. In the associative pathway, C–H activation occurs via a concerted σ-bond metathesis mechanism, which directly transfers the hydrogen atom from the C–H bond of the N-alkyl group on the NHC to the alkyl ligand on ruthenium. In the dissociative pathway, C–H activation occurs via stepwise C–H oxidative addition to form a Ru(IV) intermediate followed by reductive elimination of the alkane product.

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00531

DOI: 10.1021/acs.organomet.7b00531

You might also like
Discover & Discuss Important Research

Keeping up-to-date with research can feel impossible, with papers being published faster than you'll ever be able to read them. That's where Researcher comes in: we're simplifying discovery and making important discussions happen. With over 19,000 sources, including peer-reviewed journals, preprints, blogs, universities, podcasts and Live events across 10 research areas, you'll never miss what's important to you. It's like social media, but better. Oh, and we should mention - it's free.

  • Download from Google Play
  • Download from App Store
  • Download from AppInChina

Researcher displays publicly available abstracts and doesn’t host any full article content. If the content is open access, we will direct clicks from the abstracts to the publisher website and display the PDF copy on our platform. Clicks to view the full text will be directed to the publisher website, where only users with subscriptions or access through their institution are able to view the full article.