A soft acid-soft base interaction is highly predictable. However, we demonstrate how the crystal packing of the newly synthesized zinc framework [Zn 2 (5-AIA) 2 (DPTTZ)]•DMF (where 5-AIA = 5-aminoisophthalic acid, DPTTZ = N,N′-di(4-pyridyl)thiazolo- [5,4-d]thiazole, DMF = N,N′-dimethylformamide) directs an unexpected interaction between the soft acid Hg(II) and the hard base oxygen instead of having a soft center like nitrogen and sulfur in the system attributed to a strong solvent interaction and a favorable ionic radius of Hg(II) ion for oxygen chelation. This engenders selective Hg(II) ion sensing through a "turn-off" emission quenching in water (limit of detection = (2.174 ± 0.06) × 10 −9 M) along with natural water resources and in a broad pH range. A quantum-chemical calculation elucidates the turn-off quenching mechanism and favorable Hg(II) interaction with encompassed oxygen atoms inside the framework.
A series of azo-aromatic copper(II) complexes, [1ag] and a Cu(I) complex, [1h], with varying amine-functionalized hemilabile pincer-like [HL 1−3 ] and [L 1,2 ], methyl-substituted azo [L 3 ], and imine [L 4 ] ligands, were synthesized and characterized. These complexes were investigated for aerobic oxidation of a variety of aromatic alcohols in the presence of 2.0 mol % precatalysts [1a-g], cobaltocene (2.0 mol %), N-methyl imidazole (NMI) (8.0 mol %), and TEMPOH (2.0 mol %) at room temperature. The Cu(I) complex (1h) acted as a catalyst in the absence of cobaltocene. To understand the mechanism, detailed experimental and theoretical studies have been performed with the representative complex [1a], which has suggested a new kind of mechanism involving a Cu(II)/Cu(I) redox couple. Cobaltocene acts as a reductant to [1a] to generate a Cu(I) complex, which activates dioxygen in the presence of NMI. TEMPOH transfers a hydrogen atom to the activated dioxygen with the generation of TEMPO•, which further participates in α-C−H bond activation in the Cu(II)-alkoxide intermediate in an intermolecular fashion in the catalytic cycle. The amine sidearm in the ligand backbone of the complexes has a significant role in catalytic activity. Complexes with amine sidearms are more effective than complexes without them. Moreover, the aliphatic secondary amine sidearm is more efficient among the amine sidearm than the aromatic secondary amine and tertiary amines. The amine sidearm that remained coordinated to the Cu(II) center is hemilabile, and it facilitates alcohol coordination in the catalytic process. Alcohol coordination was the rate-limiting step, and it was supported by the isotope effect study on benzyl alcohol, substitution effect on the amine moiety of the ligands, and DFT calculation. The hemilabile amine sidearm of the coordinated ligand also acted as a base in deprotonating the alcoholic O−H proton and acted as an acid in releasing H 2 O 2 during the catalysis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.