Stepwise Strategy to Cyclometallated PtII Complexes with N-Heterocyclic Carbene Ligands: A Luminescence Study on New β-Diketonate Complexes

The imidazolium salt 3-methyl-1-(naphthalen-2-yl)-1H-imidazolium iodide (2) has been treated with silver(I) oxide and [{Pt(mu-Cl)(eta(3)-2-Me-C3H4)}(2)] (eta(3)-2-Me-C3H4 = eta(3)-2-methylallyl) to give the intermediate N-heterocyclic carbene complex [PtCl(eta(3)-2-Me-C3H4)(H (CC) over cap*-kappa C*)] (3) (H (CC) over cap*-kappa C* = 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene). Compound 3 undergoes regiospecific cyclometallation at the naphthyl ring of the NHC ligand to give the five-membered platinacycle compound [{Pt(mu-Cl)((CC) over cap*)}(2)] (4). Chlorine abstraction from 4 with beta-diketonate Tl derivatives rendered the corresponding neutral compounds [Pt((CC) over cap*)(L-O,O')] {L = acac (HL = acetylacetone) 5, phacac (HL = 1,3-diphenyl-1,3-propanedione) 6, hfacac (HL = hexafluoroacetylacetone) 7}. All of the compounds (3-7) were fully characterized by standard spectroscopic and analytical methods. X-ray diffraction studies were performed on 5-7, revealing short Pt-Pt and pi-pi interactions in the solid-state structure. The influence of the R-substituents of the beta-diketonate ligand on the photophysical properties and the use of the most efficient emitter, 5, as phosphor converter has also been studied.