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

The coordination chemistry of our recently isolated bis(diphenylphosphinyl)-functionalized dipyrido-annulated NHC (N-heterocyclic carbene), dpaP2-NHC, towards copper(i) and silver(i) has been studied. Based on dpaP2-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 dpaP2-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 dpaP2-NHC, we conclude that the electronic transitions of 2-6 can be attributed to the ligand-centered (LC) transitions.