Organometallics最新文献

In this work, we computationally studied the influence of the change in the substrate structure on the course of the heterofunctional cross-metathesis reaction between azo compounds and olefins catalyzed by the first-generation Grubbs catalyst. The highest reaction rates were predicted for symmetric, bulky diazenes and sterically uncrowded olefins. Other studied azo compounds have much higher energy barriers in the crucial steps in the catalyst initiation phase, while larger olefins are characterized by high energy barriers in the second part of the catalytic cycle. Our analysis suggests that Grubbs-like catalysts can be efficiently used in heterofunctional azo metathesis only for a limited number of olefin-azo compound combinations, such as 1,2-diphenyldiazene and ethylene to produce N-phenylmethanimine.

We computationally explored the influence of two Lewis bases (N-heterocyclic carbene (NHC) and trimethylphosphine (PMe₃) and four metal cations (Li⁺, Na⁺, K⁺, and Mg²⁺) used in experiments on the isomerizations of disilyne Si₂Ph₂ (Ph = C₆H₅) and Si₂Tip₂ (Tip = 2,4,6-iPr₃C₆H₂) in this work. Computations demonstrated that kinetically, both NHC and PMe₃ increase the energy barriers and thus stabilize disilavinylidene. Thermodynamically, however, NHC can reduce the energy gap between disilyne and disilavinylidene, while PMe₃ stabilizes disilavinylidene or slightly influences the relative stability. Further analyses showed that it is polarization that governs the energy barriers and gaps. When metal cations are further introduced, they tend to adopt the end-on bonding mode and cooperate with Lewis bases via a push–pull effect. The electrostatic interaction between Mg²⁺ and NHC-stabilized disilyne can even improve the relative stability of disilyne. Therefore, the synergy between NHC and Mg²⁺ can help the preparation of disilyne if the energy barrier from Lewis base-stabilized disilavinylidene to disilyne is overcome, but to obtain disilavinylidene, it might be better to use phosphine alone without metal cations.

Ruthenium CNC pincer complexes, comprised of N-heterocyclic carbenes (NHCs) and a pyridyl ring, are highly active catalysts for carbon dioxide reduction. We hypothesized that the addition of long chain aliphatic groups with an olefin terminus as wingtips on these CNC pincers could be used to form macrocyclic catalysts by ring closing metathesis (RCM). We have synthesized three new ruthenium pincer catalysts, [(CNC)Ru(CH₃CN)₂Cl]OTf, containing a long chain olefin wingtip (where the substituent para to N on the pyridine ring is H, Me, or OMe) and performed RCM on one compound with R = Me, followed by hydrogenation, to form a novel macrocyclic ruthenium catalyst. These four catalysts were tested for the photocatalytic reduction of carbon dioxide (CO₂) in the presence (sensitized) and absence (self-sensitized) of an external photosensitizer. With a photosensitizer, these catalysts produced mostly CO (775 to 1210 TON) with smaller amounts of H₂ also formed. The methyl substituted macrocyclic catalyst showed a TON of 1185 for CO over 72 h compared to a TON of 775 for CO for the analogous nonmacrocyclic catalyst. The remote substituents at the para-position of the central pyridine ring significantly influence catalyst activity with R = OMe > H ≈ Me.

Selective functionalization has numerous potential applications in the modification of bioactive compounds and pharmaceuticals. Herein, we advance a new approach for the selective reductive N-formylation of N-heteroarenes and transfer hydrogenation using Ir^III complexes as catalysts. The combination of solvent, equivalent of formic acid (FA), reaction temperature, and iridium catalyst exerts high product selectivity, delivering divergent selective formations of reductive N-formylation and transfer hydrogenation products in excellent yields. In this process, FA can be employed as not only the hydrogen source but also the reductive N-formylation reagent under different reaction conditions.

The design of a rigidified macrocyclic N-heterocyclic carbene (NHC) ligand led to the formation and structural characterization of in- and out-Ru carbene complexes. In this study, the introduction of a conformational lock was used to rigidify heteroaryl–aryl bonds and thereby enforce a more perpendicular dihedral angle. A forcing metalation step was needed to form the isomeric Ru carbene complexes (Grubbs complexes). The major isomer had the Ru carbene fragment located outside the macrocyclic ring, whereas the minor isomer had the Ru carbene inside the macrocyclic ring. The two new Ru carbene complexes are the first examples of in- and out-isomers of a Grubbs-type complex. The solid-state structures of each isomeric ruthenium carbene complex were determined by X-ray diffraction (XRD) studies. The two Ru complexes showed significantly different catalytic reactivities in the ring-closing metathesis (RCM) of the benchmark substrate, diethyl diallylmalonate. We performed computational studies to determine rotational barriers; scalable energetic barriers were found in the unmetalated NHC ligand, favoring the in-isomer by 2.4 kcal/mol. These calculations, coupled with the attempted interconversion of isomers, support a mechanism featuring rotational isomerization of the NHC nucleophile in a pre-equilibrium step before metalation.