The first discrete seven-membered cyclic zinc(II) complex catalyzed room temperature Knoevenagel condensation reactions, and the synthesis of perimidine derivatives has been reported under mild reaction conditions. The cyclic zinc(II) complex [(L)ZnBr2] (1) was isolated from the reaction between 1-(2-hydroxyethyl)-3-isopropyl-benzimidazol-2-thione (L) and ZnBr2. Complex 1 was characterized by different analytic techniques such as FT-IR, CHNS, TGA, NMR, and SCXRD. The mononuclear zinc(II) complex 1 was utilized as a catalyst for Knoevenagel condensation reactions to isolate twenty different substituted methylene malononitriles with excellent yield. Besides, the zinc(II) thione complex 1 was utilized for the synthesis of 2,4-dihydroperimidine derivatives in a highly efficient manner. Catalyst 1 depicted wide substrate scopes. Overall, twenty different substituted methylene malononitriles and nine different perimidine derivatives were synthesized using catalyst 1 at room temperature. The present investigation features a mild and fast synthetic approach along with excellent functional group tolerance. © 2022 Wiley-VCH GmbH.