The commercially available catalyst cis-Caz-1 is extremely robust, especially when reactions are performed in an atmosphere of air. This phosphite-containing ruthenium complex only shows olefin metathesis activity at high temperatures. Herein, we report photoactivation of cis-Caz-1 at room temperature with UVA light. Thus, a wide variety of olefin metathesis reactions was performed under mild conditions with good yields. In addition, we report the synthesis, characterization, and catalytic activity of a phosphite-chelated ruthenium benzylidene complex, cis-PhosRu-1, which can be efficiently activated either by irradiation with visible light (λ = 405 nm) or by heat.

Several olefin metathesis reactions are studied, namely, jojoba oil oligomerization, methyl oleate self-metathesis, ring-closing metathesis (RCM) to form a nitrogen heterocycle, and 1,5-hexadiene acyclic diene metathesis polymerization (ADMET). The catalyst containing the Bertrand−Grubbs cyclic alkyl amino carbene (CAAC) ligand showed high selectivity by diminishing isomerization reactions; this was especially clear at high temperatures where the more widely used nitrogen heterocyclic carbene (NHC)-based catalysts show side reactions. Experimental and computational studies determined that it is much more difficult to produce ruthenium hydrides with CAAC, a property that can explain the improved observed activity. This finding opens a pathway for the development of even more selective olefin metathesis catalysts for reactions that require harsh conditions.

Sulfur-chelated ruthenium olefin metathesis precatalysts that possess cyclic (alkyl)(amino)carbenes (CAAC) can benefit from the synergetic effect of both ligands. Changing the steric bulk of the CAAC ligand by using different substitution patterns was shown to affect the geometry of the complexes produced and determined whether the complexes could be catalytically dormant. The cis-dichloro latent catalysts could be activated both by heat or light, even in the visible region, for representative acyclic diene metathesis and ring-opening metathesis polymerization reactions, olefin cross-metathesis, and ring-closing metathesis without isomerization byproducts. Thus, these complexes were shown to combine the uniqueness of CAAC-containing Ru olefin metathesis catalysts with the advantage of the thermal and photolatency imposed by sulfur chelation of the benzylidene.

No abstract

Efficient light-and thermal-activated metathesis reactions of tetra-substituted olefins were obtained by the Schelated ruthenium precatalyst Tol-SCF 3 . Its reactivity in a series of benchmark olefin metathesis reactions was compared to previously reported Mes-SCF 3 and a novel sterically congested S-chelated complex, Dipp-SCF 3 . Tol-SCF 3 is thus the first latent catalyst proven to be capable of promoting olefin metathesis of demanding substrates upon light stimulation at room temperature.

Adding an external electric field to reactions driven by quantum mechanical tunneling brings a whole new dimension to the idea of switch chemistry.

While the influence of intramolecular electric fields is a known feature in enzymes, the use of oriented external electric fields (EEF) to enhance or inhibit molecular reactivity is a promising topic still in its infancy. Herein we will explore computationally the effects that EEF can provoke in simple molecules close to the absolute zero, where quantum tunnelling (QT) is the sole mechanistic option. We studied three exemplary systems, each one with different reactivity features and known QT kinetics:  bond-shifting in pentalene, Cope rearrangement in semibullvalene, and cycloreversion of diazabicyclohexadiene. The kinetics of these cases depdend both on the field strength and its direction, usually giving subtle but remarkable changes. However, for the cycloreversion, which suffers large changes on the dipole through the reaction, we also observed striking results. Between the effects caused by the EEF on the QT we observed an inversion of the Arrhenius equation, deactivation of the molecular fluxionality, and stabilization or instantaneous decomposition of the system. All these effects may well be achieved, literally, at the flick of a switch.<br>

The ruthenium (cis‐RuCl2(DPPM)2) based catalytic dehydrogenation reaction of formic acid in the presence of an amine base in a biphasic system experimentally tested by Treigerman and Sasson (ChemistrySelect 2017, 2, 5816) was studied computationally to ascertain its mechanism. The energy span model was applied on the double‐hybrid DFT computed energy profile to comprehend its kinetics. The catalytic network includes three possible interconnected cycles depending on the ancillary ligands, going through decarboxylation, protonation and H2 release. The dihydride cycle proves to be the most efficient after pre‐activation steps coming from the other cycles. The turnover frequency (TOF) determining intermediate (TDI) is the formatohydride species, while the TOF determining transition state (TDTS) corresponds to a formate decarboxylation. Herein we include the effect of reactants concentrations to the energy span model, which proved to be essential to comprehend the experimental ESI‐MS results and to propose a more accurate mechanism.