Luminescent gold(I) and silver(I) complexes of imidazole and biimidazole phosphines: Design, synthesis and characterization

Gold(I) and silver(I) phosphine and imine compounds are known to exhibit interesting photo-chemical and photo-physical properties. From these compounds has grown a field of chemistry involving the study of closed-shell metal complexes containing short metal-metal interactions. The drive to create new and interesting closed-shell metal complexes has led to the inovation of novel ligand systems, as well as the utilization of existing ligands to produce complexes that range from simple mono-metallic systems, to dimeric complexes, to large, complicated metallocryptates and polymers.; A novel series of bis(diphenylphosphino)-ligands based on 2,2 ′-biimidazole was proposed as the backbone for metallocryptates. The synthesis of this series focused on producing the bis-phosphines of a range of bridged biimidazoles with the intent to create metallocryptates with controlled metal-metal interactions. The synthesis of the bisphosphine was discovered to be unconventional and difficult. Gold(I) complexes of 4,4 ′-bis(diphenylphosphino)-1,1′-tetramethylene-2,2 ′-biimidazole, P₂ButylBiim, were synthesized with the limited quantities of ligand obtained from this synthetic process. The intense luminescent properties of the tentatively assigned metallocryptate, [(P₂ButylBiim)₃Au₂T1](OAc)₃, gives hope that the proposed series will eventually become an interesting system for further study.; The Au(I) and Ag(I) closed-shell metal dimers of 2-diphenylphosphino-1-methylimidazole, dpim, were investigated. Dpim formed the discreet binuclear species [Ag ₂(dpim)₂(CH₃CN)₂]2+ (1) when reacted with appropriate Ag(I) salts. Likewise, [Au ₂(dpim)₂]2+ (3) and [AuAg(dpim) ₃]2+ (4) were produced via reactions with (tht)AuCl, tht is tetrahydrothiophene, and Ag(I). Compound 3 exhibits an intense blue luminescence (λ_maz = 483 nm) in the solid state. However, upon initial formation of 3, a small impurity of Cl− was present giving rise to an orange emission (λ_maz = 548 nm). Attempts to form [Au₂(dpim) ₂]Cl₂ yielded only dpimAuCl (2), which is not visibly emissive. The rare three coordinate heterobimetallic complex [AuAg(dpim) ₃]2+ (4) exhibits intense luminescence in the solid state resembling that of 3. The crystal structures of 1–4 were determined, revealing strong intramolecular aurophilic and argentophilic interactions in the dimeric compounds.