Structural and catalytic aspects of copper(II) complexes containing 2,6-bis(imino)pyridyl ligands

The synthesis, structure, and ligand substitution mechanism of a new five-coordinate trigonal-bipyramidal copper(II) complex, [Cu^II(py ^tBuMe₂N₃)Cl₂] (1), with a sterically constrained py ^tBuMe₂N₃ chelate ligand, py ^tBuMe₂N₃?=?2,6-bis-(ketimino)pyridyl, are reported. The kinetics and mechanism of chloride substitution by thiourea, as a function of nucleophile concentration, temperature, and pressure, were studied in detail and compared with an earlier study reported for the analogous complex [Cu^II(py ^tBuN₃)Cl₂] (2) [py ^tBuN₃?=?2,6-bis-(aldimino)pyridyl]. Catalysis of the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone by 1 and 2 was studied. Correlations between the reactivity, chloride substitution behavior, and reduction potentials of both complexes were made. These show that the rate of oxidation is independent of the rate of chloride substitution, indicating that the substitution of chloride by catechol as substrate occurs in a fast step. Spectral data show a non-linear relationship between the ability of the complexes to oxidize 3,5-DTBC and the Lewis acidity of their copper(II) centers. Electrochemical data demonstrate that the most effective complex 1 has a E ⁰ value that approaches the E ⁰ value of the natural tyrosinase enzyme.     

Light promoted aqueous phase amine synthesis via three-component coupling reactions

By applying a simple TiO₂–(NH₄)₂S₂O₈ system and promoted by UV light, the three-component reactions of cyclic ether, aniline and aldehyde can be progressed efficiently. 29 substituted amines with different structures were synthesized with up to 97% isolated yields. Isotope effect study revealed that the rate-determining step might be the nucleophilic addition step but not radical generation.     

Catalytic aerobic photooxidation of primary benzylic amines using hindered acridinium salts

Hindered acridinium cations, simply prepared by the addition of primary amines to the known methylium tris(2,6-dimethoxyphenyl) cation, catalyze the aerobic photooxidation of primary benzyl amines into benzylimines. A mechanistic rationale for the electron-transfer process is proposed.     

Synergistic Photoredox Catalysis and Organocatalysis for Inverse Hydroboration of Imines

The first catalytic inverse hydroboration of imines with N‐heterocyclic carbene (NHC) boranes has been realized by means of cooperative organocatalysis and photocatalysis. This catalytic combination provides a promising platform for promoting NHC‐boryl radical chemistry under sustainable and radical‐initiator‐free conditions. The highly important functional‐group compatibility and possible application in late‐stage hydroborations represent an important step forward to an enhanced α‐amino organoboron library.