Photoredox Catalysis of Intramolecular Cyclizations with a Reusable Silica‐Bound Ruthenium Complex

Abstract

Photoredox catalysis with the use of a stable, reusable silica‐bound chromophore was applied to the intramolecular cyclization of a series of 2‐benzylidenehydrazinecarbothioamides to give 5‐phenyl‐1,3,4‐thiadiazol‐2‐amines. The catalyst was readily prepared by carbodiimide‐mediated coupling of commercially available amine‐functionalized silica beads to a carboxylic acid functionalized ruthenium complex. The immobilized catalyst was readily removed from the reaction product by filtration and was used eight times without loss of catalytic activity. This simple, safe, and practical method is an attractive alternative to conventional procedures.

I2 Promoted Synthesis of 2‐Aminothiadiazoles Employing KSCN as a Sulfur Source Under Metal‐Free Conditions

“…5‐(4‐Fluorophenyl)‐1,3,4‐thiadiazol‐2‐amine (4e): Yield:86 %; Colorless solid, m.p. 211–213 °C; 1 H NMR (400 MHz, [D 6 ]DMSO) δ = 7.76 (dd, J = 8.7, 5.4 Hz, 2H), 7.38 (br s, 2H), 7.26 (dd, J = 8.8 Hz, 2H).…”

“…Up to date, a variety of methods have been developed to access diazole skeletons . However, the common method for the preparation of 1,3,4‐oxadiazoles and 1,3,4‐thiadiazoles mainly involves dehydrative or oxidative cyclization of the N ′‐acylthiohydrazide, N ′‐acylhydrazine or thiosemicarbazides in the presence of transition metals or hazardous oxidants, such as, Ru(II), Cu(II) or tert ‐butyl hydroperoxide [Scheme , (a)]. These methods usually require the use of pre‐prepared substrates that was prepared from aldehydes and the corresponding hydrazine/urea/semicarbazide/thioure.…”

Photoredox Catalysis Using Heterogenized Iridium Complexes

“…In the photoredox catalysis field, this idea has not been extensively explored. A few examples exist using derivatives of tris(2,2´-bipyridine)-ruthenium coordination complexes immobilized onto silica 30,31 , glass wool 32 , or polymer 33 supports. Other unique examples have also been tested such as Rose Bengal 34 dye or perylene diimide (PDI) 35 molecules immobilized on silica, and porphyrins immobilized onto cotton threads 36 .…”

Insightful understanding of the correlations of the microstructure and catalytic performances of Pd@chitosan membrane catalysts studied by positron annihilation spectroscopy

“…Therefore, the preparation of transition metal heterogeneous catalysts by immobilization of transition metal on inert materials or functional solid materials with high activity, good selectivity, and excellent stability/ recyclability, has been one of the hotspots in green and sustainable chemistry. 6 Inorganic materials, like zeolites, [7][8][9][10][11] alumina, [12][13][14][15] silica, [16][17][18] and clay, [19][20][21] are commonly used supports for the preparation of supported transition metal catalysts. However, the inorganic carries oen need modication to further improve their chelating ability with transition metal catalysts.…”