Mechanism and Regioselectivity of Rh(III)-Catalyzed Intermolecular Annulation of Aryl-Substituted Diazenecarboxylates and Alkenes: DFT Insights

The mechanism of Rh-catalyzed intermolecular annulation of aryl-substituted diazenecarboxylates and alkenes was investigated using density functional theory (DFT) (PCM-M062X/6-311+G­(d,p)//M062X/6-31G­(d)). The acetate ligand (OAc)-assisted C–H activation via the formation of a five-membered rhodacycle (<b>I-TS</b>_<b>1</b>; Δ<i>G</i>^⧧ = 19.4 kcal/mol) is more favorable compared to that via a four-membered intermediate (<b>II-TS</b>_<b>1</b>; Δ<i>G</i>^⧧ = 27.8 kcal/mol). Our results also revealed that the seven-membered intermediate (<b>I-3</b>, Δ<i>G</i>_rel = −6.8 kcal/mol) formed after the alkene insertion could undergo a coordination switch with the adjacent nitrogen atom (via <b>TS</b>_<b>cs</b>; Δ<i>G</i>^⧧ = 16.5 kcal/mol) to produce a thermodynamically stable six-membered intermediate (<b>II-3</b>, Δ<i>G</i>_rel = −10.4 kcal/mol), eventually leading to a cyclization process followed by a barrierless ligand-assisted protonation to yield the final product. The β-hydride elimination product was found to be kinetically and thermodynamically undesirable. The rate-determining step is identified as the initial C–H activation, consistent with the previous kinetic studies. Notably, DFT studies offered important insights on the ability of the substrate (diazene carboxylate) to promote the switchable coordination site selectivity during the reaction to achieve a lower energy pathway

Molecular Dynamics Simulations on Gate Opening in ZIF-8: Identification of Factors for Ethane and Propane Separation

Gate opening of zeolitic imidazolate frameworks (ZIFs) is an important microscopic phenomenon in explaining the adsorption, diffusion, and separation processes for large guest molecules. We present a force field, with input from density functional theory (DFT) calculations, for the molecular dynamics simulation on the gate opening in ZIF-8. The computed self-diffusivities for sorbed C1 to C3 hydrocarbons were in good agreement with the experimental values. The observed sharp diffusion separation from C₂H₆ to C₃H₈ was elucidated by investigating the conformations of the guest molecules integrated with the flexibility of the host framework

Selective Catalytic Hydrogenation of Arenols by a Well-Defined Complex of Ruthenium and Phosphorus–Nitrogen PN³–Pincer Ligand Containing a Phenanthroline Backbone

Selective catalytic hydrogenation of aromatic compounds is extremely challenging using transition-metal catalysts. Hydrogenation of arenols to substituted tetrahydronaphthols or cyclohexanols has been reported only with heterogeneous catalysts. Herein, we demonstrate the selective hydrogenation of arenols to the corresponding tetrahydronaphthols or cyclohexanols catalyzed by a phenanthroline-based PN³-ruthenium pincer catalyst

Selective Catalytic Hydrogenation of Arenols by a Well-Defined Complex of Ruthenium and Phosphorus–Nitrogen PN³–Pincer Ligand Containing a Phenanthroline Backbone

Selective catalytic hydrogenation of aromatic compounds is extremely challenging using transition-metal catalysts. Hydrogenation of arenols to substituted tetrahydronaphthols or cyclohexanols has been reported only with heterogeneous catalysts. Herein, we demonstrate the selective hydrogenation of arenols to the corresponding tetrahydronaphthols or cyclohexanols catalyzed by a phenanthroline-based PN³-ruthenium pincer catalyst

Unusual Intramolecular Hydrogen Transfer in 3,5-Di(triphenyl­ethylenyl) BODIPY Synthesis and 1,2-Migratory Shift in Subsequent Scholl Type Reaction

The straightforward synthesis of 3,5-di­(triphenyl­ethylenyl) BODIPYs <b>1</b>–<b>3</b> from the condensation of 2-(triphenyl­ethylenyl) pyrrole with aryl aldehydes are surprisingly found to produce side products that are hydrogenated at one of the two triphenylethylene substituents. It was also observed that the subsequent Scholl type reaction of <b>1</b> resulted in a “1,2-migratory shift” of one triphenyl­ethylene substituent in addition to a ring closing reaction. Preliminary investigations, including DFT calculations and isolation of intermediates, were conducted to study these unusual observations on BODIPY chemistry

Unusual Intramolecular Hydrogen Transfer in 3,5-Di(triphenyl­ethylenyl) BODIPY Synthesis and 1,2-Migratory Shift in Subsequent Scholl Type Reaction

The straightforward synthesis of 3,5-di­(triphenyl­ethylenyl) BODIPYs <b>1</b>–<b>3</b> from the condensation of 2-(triphenyl­ethylenyl) pyrrole with aryl aldehydes are surprisingly found to produce side products that are hydrogenated at one of the two triphenylethylene substituents. It was also observed that the subsequent Scholl type reaction of <b>1</b> resulted in a “1,2-migratory shift” of one triphenyl­ethylene substituent in addition to a ring closing reaction. Preliminary investigations, including DFT calculations and isolation of intermediates, were conducted to study these unusual observations on BODIPY chemistry

Synthesis of Highly Reactive Polyisobutylene Catalyzed by EtAlCl₂/Bis(2-chloroethyl) Ether Soluble Complex in Hexanes

The polymerization of isobutylene (IB) to yield highly reactive polyisobutylene (HR PIB) with high exo-olefin content using GaCl₃ or FeCl₃·diisopropyl ether complexes has been previously reported. In an effort to further improve polymerization rates and exo-olefin content, we have studied ethylaluminum dichloride (EADC) complexes with diisopropyl ether, 2-chloroethyl ethyl ether (CEEE), and bis­(2-chloroethyl) ether (CEE) as catalysts in conjunction with <i>tert</i>-butyl chloride as initiator in hexanes at different temperatures. All three complexes were readily soluble in hexanes. Polymerization, however, was only observed with CEE. At 0 °C polymerization was complete in 5 min at [<i>t</i>-BuCl] = [EADC·CEE] = 10 mM and resulted in PIB with ∼70% exo-olefin content. Studies on complexation using ATR FTIR and ¹H NMR spectroscopy revealed that at 1:1 stoichiometry a small amount of EADC remains uncomplexed. By employing an excess of CEE, exo-olefin contents increased up to 90%, while polymerization rates decreased only slightly. With decreasing temperature, polymerization rates decreased while molecular weights as well as exo-olefin contents increased, suggesting that isomerization has a higher activation energy than β-proton abstraction. Density functional theory (DFT) studies on the Lewis acid·ether binding energies indicated a trend consistent with the polymerization results. The polymerization mechanism proposed previously for Lewis acid·ether complexes adequately explains all the findings