Di- and Tetranuclear Cationic Silver(I) Complexes Bearing Bis(diphenylphosphino)pyridine Ligands: Synthesis, Structures, and Utility as Precatalysts in Acid-Catalyzed Cyclization Reactions

A series of di- and tetranuclear silver(I) complexes featuring (BPPMP)E₂ [BPPMP: bis(diphenylphosphinomethyl)pyridine] and (BPPP)E₂ [BPPP: bis(diphenylphosphino)pyridine] (2a/6a, E = S; 2b/6b, E = Se) species have been isolated and utilized in cyclization reactions. The reactions of (BPPP)E₂ and (BPPMP)E₂ (2a/6a, E = S; 2b/6b, E = Se) with various silver salts afforded the corresponding cationic complexes of the type [(2a/2b)₃Ag₄(CH₃CN)₃][X]₄ (3/4, X = BF₄ and SbF₆) and [(6a/6b)Ag]₂[BF₄]₂ (7a/7b) as bench-stable solids. The solid-state structures of tetranuclear silver complexes do not exhibit metal–metal interactions; however, the corresponding dinuclear silver complexes (7) display intramolecular argentophilic (Ag···Ag) interactions. Subsequently, the molecular catalytic performances of bench-stable 3a and 7a were explored in the preparation of biologically active polysubstituted 1,3-dihydronaphtho[2,3-c]furan and aminoindolizine derivatives, respectively, with high atom-economic pathways and achieved good to excellent yields by solvent- and additive-free approaches. The newly developed protocols in this study demonstrate a broad substrate scope and utilize nontoxic and cost-effective silver-based molecular catalysts.