Examined herein is the basis for outstanding metathesis productivity of leading cyclic alkyl amino carbene (CAAC) catalysts relative to their important N-heterocyclic (NHC) predecessors, as recently demonstrated in topical contexts macrocyclization and ethenolysis renewable oils. The difference traced stability decomposition metallacyclobutane (MCB) intermediate. CAAC are shown undergo little no β-H elimination MCB ring, a pathway which H2IMes highly susceptible. Unexpectedly, however, found...

Access to leading olefin metathesis catalysts, including the Grubbs, Hoveyda, and Grela ultimately rests on nonscaleable transfer of a benzylidene ligand from an unstable, impure aryldiazomethane. The indenylidene can be reliably installed, but date yields much less reactive catalysts. A fast-initiating, dimeric complex (Ru-1) is reported, which reconciles high activity with scaleable synthesis. Each Ru center in Ru-1 stabilized by state-of-the-art cyclic alkyl amino carbene (CAAC, C1)...

Ring-closing metathesis (RCM) offers versatile catalytic routes to macrocycles, with applications ranging from perfumery production of antiviral drugs. Unwanted oligomerization, however, is a long-standing challenge. Oligomers can be converted into the cyclic targets by catalysts that are sufficiently reactive promote backbiting (e.g., Ru complexes N-heterocyclic carbenes; NHCs), but catalyst decomposition limits yields and selectivity. Incorporation hemilabile o-dianiline (ODA) chelate new...

Bimolecular catalyst decomposition is a fundamental, long-standing challenge in olefin metathesis. Emerging ruthenium–cyclic(alkyl)(amino)carbene (CAAC) catalysts, which enable breakthrough advances productivity and general robustness, are now known to be extraordinarily susceptible this pathway. The details of the process, however, have hitherto been obscure. present study provides first detailed mechanistic insights into steric electronic factors that govern bimolecular decomposition....

Ruthenium catalysts for olefin metathesis are widely viewed as water-tolerant. Evidence is presented, however, that even low concentrations of water cause catalyst decomposition, severely degrading yields. Of 11 studied, fast-initiating examples (e.g., the Grela RuCl2(H2IMes)(═CHC6H4-2-OiPr-5-NO2) were most affected. Maximum tolerance was exhibited by slowly initiating iodide and cyclic (alkyl)(amino)carbene (CAAC) derivatives. Computational investigations indicated hydrogen bonding to...

Critical to advancing the uptake of olefin metathesis in leading contexts, including pharmaceutical manufacturing, is identification highly active catalysts that resist decomposition. Amines constitute an aggressive challenge ruthenium catalysts. Examined here impact 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), morpholine, n-butylamine, and triethylamine on Ru represent current state art, cyclic alkyl amino carbene (CAAC) N-heterocyclic (NHC) complexes. Accordingly, amine-tolerance nitro-Grela...

In ruthenium catalysts for olefin metathesis, carbene ligands of high trans influence/effect suppress decomposition via β-H elimination, but increase susceptibility to bimolecular decomposition.

Hydroxide ion is shown to be a potent disruptor of Ru-catalyzed olefin metathesis, in study the Hoveyda catalyst HII. Addition [NnBu4][OH] immediately terminates metathesis via HII, an effect traced formation bis(hydroxide) complex HII–OH. The latter was synthesized for direct study. HII–OH initiates very slowly on reaction with olefins, and decomposes first cycle metathesis. Computational analysis reveals rapid bimolecular coupling between its four-coordinate methylidene derivative....

One possible route for glycerol utilisation is through a reforming process in which clean hydrogen can be produced. This study presents the results of an Alkaline Membrane Electroreforming Reactor operated with KOH-doped polybenzimidazole (PBI). Commercial PtRu/C and Pt/C are used as catalysts anode cathode, respectively. The influence two important operating variables, temperature, composition cathode feed solution studied. A significant enhancement cell performance observed temperature...

Clean, high-yielding routes are described to ruthenium–diiodide catalysts that were recently shown enable high productivity in olefin metathesis. For the second-generation Grubbs and Hoveyda (GII: RuCl2(H2IMes)(PCy3)(═CHPh); HII: RuCl2(H2IMes)(═CHAr), Ar = C6H4-2-OiPr), slow salt metathesis is arise from low lability of ancillary PCy3 or ether ligands, which retards access four-coordinate intermediate required for efficient halide exchange. To exploit first-generation catalysts, diiodide...

Phosphine-scavenging Merrifield resins can significantly facilitate the synthesis of highly active Ru metathesis catalysts, including second-generation Grubbs, Hoveyda, and indenylidene catalysts (<bold>GII</bold>,<bold>HII</bold>,<bold>InII</bold>).

Oxygenation of hydrocarbons offers versatile catalytic routes to more valuable compounds, such as alcohols, aldehydes, and ketones. Despite the importance monometallic copper-oxygen species hydroxylating agents in biology, few synthetic model compounds are known react with hydrocarbons, owing high C-H bond dissociation energies. To overcome this challenge, photoredox chemistry copper (pyrazolyl)borate complexes coordinated by chlorate has been explored presence C

The triplet excited states of ketones are found to effect selective H-atom abstraction from strong amide N-H bonds in the presence weaker C-H through a proton-coupled electron transfer (PCET) pathway. This chemoselectivity, which results differences ionization energies (IEs) between functional groups rather than bond dissociation (BDEs) arises asynchronicity and proton PCET process. We show how this strategy may be leveraged achieve intramolecular anti-Markovnikov hydroamidation alkenes form...