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 Na 10.5 H 3.5 (H 2 O) 36 [Na(UO 2 )(α-SiW 9 O 34 )] 2 ·2.5H 2 O ( 1 ) and three-dimensional Na 14 (H 2 O) 36 [Na(UO 2 )(α-SiW 9 O 34 )] 2 ·4H 2 O ( 2 ), have been synthesized by the reactions of UO 2 (OAc) 2 and Na 10 [α-SiW 9 O 34 ]·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)-H 2 O 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 3 H -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.