Phenotellurazine redox catalysts: elements of design for radical cross-dehydrogenative coupling reactions.

Redox active phenotellurazine catalysts have been recently utilized in two different cross-dehydrogenative coupling reactions. In this study, we revisit the design of the phenotellurazine redox catalysts. In particular, we investigate the level of cooperativity between the Te- and N-centers, the effect of secondary versus tertiary N-centers, the effect of heterocyclic versus non-heterocyclic structures, and the effect of substitution patterns on the redox catalytic activity.

Au → M bonds promote catalytic alkyne hydrofunctionalisation.

The impact of metalloligands on Au catalysed alkyne hydrofunctionalisation is studied. Ambiphilic PMP-type ligands (M = CuI, AgI, ZnII) stabilise Au → M bonds including unprecedented AuI → ZnII interactions. The Lewis acidity of Au increases in the order CuI < AgI < ZnII promoting catalytic cycloisomerisation of propargylamide 14. Au/Zn complex 8 is an excellent catalyst for alkyne hydroamination.

Effects of the Chalcogenide Identity in N-Aryl Phenochalcogenazine Photoredox Catalysts.

Phenochalcogenazines such as phenoxazines and phenothiazines have been widely employed as photoredox catalysts (PCs) in small molecule and polymer synthesis. However, the effect of the chalcogenide in these catalysts has not been fully investigated. In this work, a series of four phenochalcogenazines is synthesized to understand how the chalcogenide impacts catalyst properties and performance. Increasing the size of the chalcogenide is found to distort the PC structure, ultimately impacting the properties of each PC. For example, larger chalcogenides destabilize the PC radical cation, possibly resulting in catalyst degradation. In addition, PCs with larger chalcogenides experience increased reorganization during electron transfer, leading to slower electron transfer. Ultimately, catalyst performance is evaluated in organocatalyzed atom transfer radical polymerization and a photooxidation reaction for C(sp2)-N coupling. Results from these experiments highlight that a balance of PC properties is most beneficial for catalysis, including a long-lived excited state, a stable radical cation, and a low reorganization energy.

O2-Mediated Te(II)-Redox Catalysis for the Cross-Dehydrogenative Coupling of Indoles.

Very few elements in the periodic system can catalytically activate O2, such as in the context of cross-dehydrogenative couplings. The development of O2-activating catalysts is essential to enable new and sustainable reactivity concepts to emerge, because these catalysts also often feature specific activating interactions with the target substrates. In this context, the unprecedented Te(II)/Te(III) catalyzed dehydrogenative C3-C2 dimerization of indoles is described herein. The fact that O2 can be directly utilized as a terminal oxidant in this reaction, as well as the absence of any background reactivity without the redox-active Te catalyst, constitute very important milestones for the fields of cross-dehydrogenative couplings and tellurium catalysis.

Te(II)-Catalyzed Cross-Dehydrogenative Phenothiazination of Anilines.

Oxidative clicklike reactions are useful for the late-stage functionalization of pharmaceuticals and organic materials. Hence, novel methodologies that enable such transformations are in high demand. Herein we describe a tellurium(II)-catalyzed cross-dehydrogenative phenothiazination (CDP) of aromatic amines. A key feature of this method is a cooperative effect between the phenotellurazine catalyst and the silver salt, which serves as a chemical oxidant for the reaction. This novel catalysis concept therefore enables a considerably broader scope compared with previous chemical oxidation methods.

Dehydrogenative C-H Phenochalcogenazination.

Heavy-atom-modified chalcogen-fused triarylamine organic materials are becoming increasingly important in the photochemical sciences. In this context, the general and direct dehydrogenative C-H phenochalcogenazination of phenols with the heavier chalcogens selenium and tellurium is herein described. The latter dehydrogenative C-N bond-forming processes operate under simple reaction conditions with highly sustainable O2 serving as the terminal oxidant.

Leucomethylene blue probe detects a broad spectrum of reactive oxygen and nitrogen species.

Reactive oxygen and nitrogen species (ROS, RNS) are ubiquitous in biology with a variety of physiological and pathological functions. Here we describe a broad spectrum ROS/RNS detecting fluorogenic probe with red fluorescence emission and up to 100-fold gain. Hence these modified probes are useful for in vivo non-invasive quantification of ROS/RNS.

Tellurium(II)/Tellurium(III)-Catalyzed Cross-Dehydrogenative C-N Bond Formation.

The TeII /TeIII -catalyzed dehydrogenative C-H phenothiazination of challenging phenols featuring electron-withdrawing substituents under mild aerobic conditions and with high yields is described. These unexpected TeII /TeIII radical catalytic properties were characterized by cyclic voltammetry, EPR spectroscopy, kinetic experiments, and DFT calculations.

Synthesis and properties of heterobimetallic rhodium complexes featuring LiI, CuI or ZnII as a Lewis acidic metalloligand.

A series of [(PMP)Rh(CO)Cl]n+ complexes was synthesised and the impact of the metalloligands CuI, LiI and ZnII on the CO stretching band was analysed.

Phosphorylation-dependent Regulation of Connecdenn/DENND1 Guanine Nucleotide Exchange Factors.

Connecdenn 1/2 are DENN (differentially expressed in normal and neoplastic cells) domain-bearing proteins that function as GEFs (guanine nucleotide exchange factors) for the small GTPase Rab35. Disruption of connecdenn/Rab35 function leads to defects in the recycling of multiple cargo proteins from endosomes with altered cell function, yet the regulation of connecdenn GEF activity is unexplored. We now demonstrate that connecdenn 1/2 are autoinhibited such that the purified, full-length proteins have significantly less Rab35 binding and GEF activity than the isolated DENN domain. Both proteins are phosphorylated with prominent phosphorylation sites between residues 500 and 600 of connecdenn 1. A large scale proteomics screen revealed that connecdenn 1 is phosphorylated at residues Ser-536 and Ser-538 in an Akt-dependent manner in response to insulin stimulation of adipocytes. Interestingly, we find that an Akt inhibitor reduces connecdenn 1 interaction with Rab35 after insulin treatment of adipocytes. Remarkably, a peptide flanking Ser-536/Ser-538 binds the DENN domain of connecdenn 1, whereas a phosphomimetic peptide does not. Moreover, connecdenn 1 interacts with 14-3-3 proteins, and this interaction is also disrupted by Akt inhibition and by mutation of Ser-536/Ser-538. We propose that Akt phosphorylation of connecdenn 1 downstream of insulin activation regulates connecdenn 1 function through an intramolecular interaction.