Two U(VI)-Containing Silicotungstates with Sandwich Structures: Lewis Acid-Base Synergistic Catalyzed Synthesis of Benzodiazepines and Pyrazoles

Two new U(VI)-containing silicotungstates with similar sandwiched polyanions but different space structures, two-dimensional Na10.5H3.5(H2O)(36)[Na(UO2)(alpha-SiW9O34)](2)center dot 2.5H(2)O (1) and three- dimensional Na-14(H2O)(36)[ Na(UO2)(alpha-SiW9O34)](2)center dot 4H(2)O (2), have been synthesized by the reactions of UO2(OAc)(2) and Na-10[alpha-SiW9O34]center dot 18H(2)O in aqueous solution at different pH values. Structure analyses demonstrated that different reaction conditions may provide different self-assembly conditions and result in the different coordination environments of Na(I)-H2O clusters with different disorders, which are the keys to the differences between 1 and 2. Compound 2 was demonstrated to show excellent catalytic activity for the synthesis of 3H-benzo[b]-[1,4]diazepines and pyrazoles via the intermolecular cyclization reactions, and the yields of the desired products reached 99%. This work illustrates the catalytic properties for U(VI)-containing POMs.

Automated summary

Two U(VI)-containing silicotungstates with similar sandwiched polyanions but different space structures were synthesized. The structures of these compounds were influenced by the reaction conditions, resulting in different coordination environments of Na(I)-H2O clusters. One of the compounds showed excellent catalytic activity for the synthesis of certain organic compounds.