Abstract
An efficient self-supported Cu(II)Bi(III) bimetallic catalyst with a layered structure was designed and developed. By careful characterization of the as-prepared material, the host structure was identified to exhibit a Sillen-type bismutite framework, with copper(II) ions being loaded as guests. The heterogeneous catalyst enabled C–N and C–S arylations under mild reaction conditions and with high chemoselectivities, thus furnishing valuable phenothiazines via heterocyclization with wide substrate tolerance. As corroborated by detailed catalytic studies, the cooperative, bifunctional catalyst, bearing Lewis acid sites along with copper(II) catalytic sites, facilitated an intriguing concerted C–N/C–S heterocyclization mechanism. The heterogeneous nature of the catalytic reactions was verified experimentally. Importantly, the catalyst was successfully recycled and reused multiple times, persevering its original structural order as well as its initial activity.
Highlights
Representative examples of N-heterocyclic structures with C− N and C−S moieties are phenothiazines and their derivatives
Thermogravimetry/derivative thermogravimetry (TG/DTG) measurements on bismutite (Figure S1) verified this because 12.5% total weight loss was observed compared to a theoretical loss of 8.5%
To other intercalated cations previously reported [e.g., Ag(I) and Ca(II)], copper ions were surrounded by hydroxyl and carbonate groups, which led to the formation of malachite-like complex anions being dispersed among the layers, as identified by various spectroscopic methods
Summary
Representative examples of N-heterocyclic structures with C− N and C−S moieties are phenothiazines and their derivatives. The application of a large amount of added base (10−30 mol %) as well the application of very long reaction time (48−96 h) and harsh conditions such as high reaction temperature (110−150 °C), sequential control of reaction conditions, and high catalyst loading (10−20 mol %) as well as possible side reactions coupled with moderate yields (50−70%) overcast the effectiveness of these systems. Really few elegant, cascade processes were reported; using organic additives and/or high catalyst loading (30 mol %) is necessary to provide good yields (70−85%).[22,24] while the focus has already been shifted toward the use of eco-friendly heterogeneous catalytic systems,[25] no relevant progress has been achieved for producing phenothiazine in a heterogeneous catalytic manner. In view of the abovementioned weaknesses, it is surprising given that numerous modern C−S/C−N/C−C bond-forming reactions are based
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