Stereoselective Formation of Facial Tris-Cyclometalated PtIVComplexes: Dual Phosphorescence from Heteroleptic Derivatives

A stereoselective synthetic route to homo- and heteroleptic facial tris-cyclometalated Pt(IV)complexes is reported, involving the oxidative addition of 2-(2-pyridyl)- or 2-(1-isoquinolinyl)benzenediazonium salts tocis-[Pt(C<<^>>N)(2)] precursors, with C<<^>>N=cyclometalated 2-(p-tolyl)pyridine (tpy), 2-phenylquinoline (pq), 2-(2-thienyl)pyridine or 1-phenylisoquinoline (piq), to produce labile diazenide intermediates that undergo photochemical or thermal elimination of N-2. The method allows the preparation of derivatives bearing cyclometalated ligands of low pi-pi* transition energies. The new complexes exhibit phosphorescence in fluid solution at room temperature arising from triplet ligand-centered ((LC)-L-3) excited states, which, in the cases of the heteroleptic derivatives, involve the ligand with the lowest pi-pi* gap. The heteroleptic piq derivatives exhibit fluorescence and dual phosphorescence from different ligand-centered excited states in rigid media, demonstrating the potential of cyclometalated Pt(IV)complexes as multi-emissive materials.