Synthesis and structural features of indium(III) furan-2-thiocarboxylates showing efficient catalytic activity toward multicomponent reactions via Knoevenagel condensation.

A series of furan-2-thiocarboxylate complexes of indium(III), Et3NH[In(SCOf)4] (1), iPr2NH2[In(SCOf)4] (2), [In(2,2'-bipy)(SCOf)3] (3a), and [In(1,10-phen)(SCOf)3] (3b), have been synthesized and structurally characterized. Complex 4, [In(TMEDA)(SCOf)(SH)2], was obtained by the partial hydrolysis of [In(TMEDA)(SCOf)3] (3). Heterobimetallic complexes [(SCOf)2In(µ-SCOf)2Cu(PPh3)2] (5) and [(SCOf)2In(µ-SCOf)2Ag(PPh3)2] (6), were also synthesized and characterized. In an attempt to synthesize the binary compound, In(SCOf)3 (7), a thioester fCOSCH2SCOf (8) was obtained serendipitously; thus, a novel convenient approach for thioester synthesis is introduced. The catalytic activities of all the complexes were assessed for Knoevenagel condensation and Knoevenagel initiated MCRs for the synthesis of chromene and imidazopyrimidine derivatives and it was found that complex 2 is a very efficient catalyst (much superior to the previously reported ones).