Formation of N-heterocyclic diphosphine ligands from Ag(i)-assisted condensation reactions between bdppeda and formaldehyde and their binuclear silver(i) complexes

The reaction of [Ag(MeCN)4]ClO4 with N,N,N′,N′-tetra(diphenylphosphanylmethyl)ethylenediamine (dppeda) in CH2Cl2/MeOH afforded an unexpected cationic binuclear complex [Ag2(L1)2(η,η-μ-ClO4)2](ClO4)2 (L1 = N,N′-bis(diphenylphosphanylmethyl)-3H-4,5-dihydroimidazole-1-ium) (1). Compound 1 was also prepared in high yield from reactions of [Ag(MeCN)4]ClO4 with N,N′-bis(diphenylphosphanylmethyl)ethylenediamine (bdppeda) in the presence of formaldehyde (HCHO) or formic acid (HCOOH). Analogous reactions of AgCl with bdppeda and HCHO resulted in the formation a neutral binuclear complex [Ag2(L2)2(μ-Cl)2] (L2 = N,N-bis(diphenylphosphanylmethyl)-tetrahydroimidazole) (2). Treatment of 1 with concentrated HCl gave rise to a partially anion-exchanged product [Ag2(L1)2(μ-Cl)2](ClO4)2 (3). Compounds 1 and 3 have a similar cationic binuclear structure, in which a [Ag2(η,η-μ-ClO4)2] or [Ag2(μ-Cl)2] ring is sandwiched by two in situ-formed cationic L1 ligands. The L1 ligand may be generated by the Ag(I)-assisted condensation reaction between bdppeda and HCHO or HCOOH. Compound 2 holds a neutral binuclear structure, in which a [Ag2(μ-Cl)2] ring is connected by two in situ-formed L2 ligands from its top and bottom sites. The neutral ligand L2 may be produced from another Ag(I)-assisted condensation reaction between bdppeda and HCHO. The in situ formation of the L1 and L2 ligands provides a new route to the N-heterocyclic diphosphine ligands, and an interesting insight into the coordination chemistry of their metal complexes.