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

Abstract

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.