Neighboring Pd single atoms surpass isolated single atoms for selective hydrodehalogenation catalysis

Single atom catalysts have been found to exhibit superior selectivity over nanoparticulate catalysts for catalytic reactions such as hydrogenation due to their single-site nature. However, improved selectively is often accompanied by loss of activity and slow kinetics. Here we demonstrate that neighboring Pd single atom catalysts retain the high selectivity merit of sparsely isolated single atom catalysts, while the cooperative interactions between neighboring atoms greatly enhance the activity for hydrogenation of carbon-halogen bonds. Experimental results and computational calculations suggest that neighboring Pd atoms work in synergy to lower the energy of key meta-stable reactions steps, i.e., initial water desorption and final hydrogenated product desorption. The placement of neighboring Pd atoms also contribute to nearly exclusive hydrogenation of carbon-chlorine bond without altering any other bonds in organohalogens. The promising hydrogenation performance achieved by neighboring single atoms sheds light on a new approach for manipulating the activity and selectivity of single atom catalysts that are increasingly studied in multiple applications.

CO-CYCLIZATION OF ETNCO AND ME2CO AS THE RESULTS OF THEIR SELECTIVE INSERTION INTO THE NIOBIUM-CHLORINE BOND

Development of the new methods for drug production is impossible without reliance on the novel and unorthodox approaches to the synthesis of heterocyclic complexes and compounds.The method is based on the study of new aspects of the of two types of behavior of the coordinated molecules in reaction - their ability to insert into the same transition metal-halogen bond, and their ability to form the unusual heterocyclic ligands, or even molecules after leaving the complex’s coordination sphere. This will make it possible not only to synthesize the already-known compounds under milder conditions, but to also obtain new ones as products of such mixed condensation reactions. On the one hand, this opens up new possibilities for designing and performing the intraspherical "stitching" of ligands and their synthesis with high efficiency and selectivity. On the other hand, these reactions can be considered a significant contribution to the fundamental coordination chemistry in terms of illustration of the new modalities of the mutual influence of ligands, namely their ability to stimulate each other for a mutual insertion, and sheds light on the mechanisms of the intraspheric condensation. Oxadiazine derivatives, just like the derivatives of triazine we synthesized and reported previously, could become a foundation for the generation of biologically-active compounds, often containing heterocyclic fragments and frequently used for the treatment of malignant tumors. It can be expected that the developed method will find use in the synthesis of the new classes of potential antitumor compounds. We have previously found that organic isocyanate not only themselves insert into M-Hal bond, but can also activate the insertion of acetonitrile, the resulting heteromolecular chain of inserted molecules being composed of two MeNCO and one MeCN fragments. Such a structure of this complexes was confirmed be synthesis of striazine derivatives on their base. In this work was to determine optimum condition for the insertion of ethyl isocyanate with acetone into niobium-chlorine bond, as well as their subsequent mixed co-cyclization with obtaining of oxadiazine derivative.

CO-CYCLIZATION OF ETNCO AND ME2CO AS THE RESULTS OF THEIR SELECTIVE INSERTION INTO THE NIOBIUM-CHLORINE BOND

Development of the new methods for drug production is impossible without reliance on the novel and unorthodox approaches to the synthesis of heterocyclic complexes and compounds.The method is based on the study of new aspects of the of two types of behavior of the coordinated molecules in reaction - their ability to insert into the same transition metal-halogen bond, and their ability to form the unusual heterocyclic ligands, or even molecules after leaving the complex’s coordination sphere. This will make it possible not only to synthesize the already-known compounds under milder conditions, but to also obtain new ones as products of such mixed condensation reactions. On the one hand, this opens up new possibilities for designing and performing the intraspherical "stitching" of ligands and their synthesis with high efficiency and selectivity. On the other hand, these reactions can be considered a significant contribution to the fundamental coordination chemistry in terms of illustration of the new modalities of the mutual influence of ligands, namely their ability to stimulate each other for a mutual insertion, and sheds light on the mechanisms of the intraspheric condensation. Oxadiazine derivatives, just like the derivatives of triazine we synthesized and reported previously, could become a foundation for the generation of biologically-active compounds, often containing heterocyclic fragments and frequently used for the treatment of malignant tumors. It can be expected that the developed method will find use in the synthesis of the new classes of potential antitumor compounds. We have previously found that organic isocyanate not only themselves insert into M-Hal bond, but can also activate the insertion of acetonitrile, the resulting heteromolecular chain of inserted molecules being composed of two MeNCO and one MeCN fragments. Such a structure of this complexes was confirmed be synthesis of striazine derivatives on their base. In this work was to determine optimum condition for the insertion of ethyl isocyanate with acetone into niobium-chlorine bond, as well as their subsequent mixed co-cyclization with obtaining of oxadiazine derivative.

Synthesis and characterization of a tert-butyl ester-substituted titanocene dichloride: t-BuOOCCp2TiCl2

Bis[η5-(tert-butoxycarbonyl)cyclopentadienyl]dichloridotitanium(IV), [Ti(C10H13O2)2Cl2], was synthesized from LiCpCOOt-Bu using TiCl4, and was characterized by single-crystal X-ray diffraction and 1H NMR spectroscopy. The distorted tetrahedral geometry about the central titanium atom is relatively unchanged compared to Cp2TiCl2. The complex exhibits elongation of the titanium–cyclopentadienyl centroid distances [2.074 (3) and 2.070 (3) Å] and a contraction of the titanium–chlorine bond lengths [2.3222 (10) Å and 2.3423 (10) Å] relative to Cp2TiCl2. The dihedral angle formed by the planes of the Cp rings [52.56 (13)°] is smaller than seen in Cp2TiCl2. Both ester groups extend from the same side of the Cp rings, and occur on the same side of the complex as the chlorido ligands. The complex may serve as a convenient synthon for titanocene complexes with carboxylate anchoring groups for binding to metal oxide substrates.

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

Where monochloroacetic acid is widely used as a starting material for the synthesis of relevant groups of compounds, many of these synthetic procedures are based on nucleophilic substitution of the carbon chlorine bond. Oxidative or reductive activation of monochloroacetic acid results in radical intermediates, leading to reactivity different from the traditional reactivity of this compound. Here, we investigated the possibility of applying monochloroacetic acid as a substrate for photoredox catalysis with styrene to directly produce γ-phenyl-γ-butyrolactone. Instead of using nucleophilic substitution, we cleaved the carbon chlorine bond by single-electron reduction, creating a radical species. We observed that the reaction works best in nonpolar solvents. The reaction does not go to full conversion, but selectively forms γ-phenyl-γ-butyrolactone and 4-chloro-4-phenylbutanoic acid. Over time the catalyst precipitates from solution (perhaps in a decomposed form in case of fac-[Ir(ppy)3]), which was proven by mass spectrometry and EPR spectroscopy for one of the catalysts (N,N-5,10-di(2-naphthalene)-5,10-dihydrophenazine) used in this work. The generation of HCl resulting from lactone formation could be an additional problem for organometallic photoredox catalysts used in this reaction. In an attempt to trap one of the radical intermediates with TEMPO, we observed a compound indicating the generation of a chloromethyl radical.

Methylene: The Linker of Two Aromatic Iminium Salts

A straightforward synthesis of aromatic iminium salts has been developed by coupling 2-Azido-1,3,5-trimethyl benzene with 1,3-ditert-butylimidazolium tetrafluoroborate in basic conditions, followed by treatment with dichloromethane or iodomethane. Herein, we report the synthetic procedure and full characterization data, including X-ray structure analysis, of the expected bis(triazenyl)methane adduct 5. Moreover, we have discovered what constitutes a double carbon-chlorine bond activation.

Proteogenomics Reveals Novel Reductive Dehalogenases and Methyltransferases Expressed during Anaerobic Dichloromethane Metabolism

ABSTRACTDichloromethane (DCM) is susceptible to microbial degradation under anoxic conditions and is metabolized via the Wood-Ljungdahl pathway; however, mechanistic understanding of carbon-chlorine bond cleavage is lacking. The microbial consortium RM contains the DCM degrader “CandidatusDichloromethanomonas elyunquensis” strain RM, which strictly requires DCM as a growth substrate. Proteomic workflows applied to DCM-grown consortium RM biomass revealed a total of 1,705 nonredundant proteins, 521 of which could be assigned to strain RM. In the presence of DCM, strain RM expressed a complete set of Wood-Ljungdahl pathway enzymes, as well as proteins implicated in chemotaxis, motility, sporulation, and vitamin/cofactor synthesis. Four corrinoid-dependent methyltransferases were among the most abundant proteins. Notably, two of three putative reductive dehalogenases (RDases) encoded within strain RM’s genome were also detected in high abundance. Expressed RDase 1 and RDase 2 shared 30% amino acid identity, and RDase 1 was most similar to an RDase ofDehalococcoides mccartyistrain WBC-2 (AOV99960, 52% amino acid identity), while RDase 2 was most similar to an RDase ofDehalobactersp. strain UNSWDHB (EQB22800, 72% amino acid identity). Although the involvement of RDases in anaerobic DCM metabolism has yet to be experimentally verified, the proteome characterization results implicated the possible participation of one or more reductive dechlorination steps and methyl group transfer reactions, leading to a revised proposal for an anaerobic DCM degradation pathway.IMPORTANCENaturally produced and anthropogenically released DCM can reside in anoxic environments, yet little is known about the diversity of organisms, enzymes, and mechanisms involved in carbon-chlorine bond cleavage in the absence of oxygen. A proteogenomic approach identified two RDases and four corrinoid-dependent methyltransferases expressed by the DCM degrader “CandidatusDichloromethanomonas elyunquensis” strain RM, suggesting that reductive dechlorination and methyl group transfer play roles in anaerobic DCM degradation. These findings suggest that the characterized DCM-degrading bacteriumDehalobacterium formicoaceticumand “CandidatusDichloromethanomonas elyunquensis” strain RM utilize distinct strategies for carbon-chlorine bond cleavage, indicating that multiple pathways evolved for anaerobic DCM metabolism. The specific proteins (e.g., RDases and methyltransferases) identified in strain RM may have value as biomarkers for monitoring anaerobic DCM degradation in natural and contaminated environments.