Bis(diphenylphosphinyl)-functionalized dipyrido-annulated NHC towards copper(i) and silver(i)

Abstract

The coordination chemistry of our recently isolated bis(diphenylphosphinyl)-functionalized dipyrido-annulated NHC (N-heterocyclic carbene), dpa^P2-NHC, towards copper(I) and silver(I) has been studied. Based on dpa^P2-NHC, two dinuclear silver and copper complexes [2, (Ag₂L₂) and 3, (Cu₂L₂)], two tetranuclear copper complexes {4, [Cu₄L₂(NCMe)₂] and 6, (Cu₄LBr₄)} and a pentanuclear copper complex [5, (Cu₅L₂Br₃)] exhibiting strong intramolecular metal–metal interactions were achieved and characterized. All the complexes exhibited dynamic behavior in solution, in which the NMR coalescence of 2 was well resolved at low temperature (below 208 K) and dissociation for 2 was observed according to the calculated Eyring plot. Ag₂L₂ (2) shows a similar coordination sphere to that of our previously reported gold complex Au₂L₂; Cu₂L₂ (3) features a rare μ₂-bridging carbene and a terminal carbene; Cu₄LBr₄ (6) is neutral and monomeric, in which four copper atoms were rigidly fixed by the tridentate dpa^P2-NHC ligand and bromide anions. All the complexes (2–6) were luminescent at room temperature, in which 4–6 provided phosphorescence at 77 K. Based on the comparison of the emission bands with dpa^P2-NHC, we conclude that the electronic transitions of 2–6 can be attributed to the ligand-centered (LC) transitions.