Stereoselective Formation of Facial Tris-cyclometalated Pt(IV) Complexes. 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 to cis -[Pt(C^N) 2 ] precursors, with C^N = cyclometalated 2-( p -tolyl)pyridine (tpy), 2-phenylquinoline (pq), 2-(2-thienyl)pyridine or 1-phenylsioquinoline (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  π-π * transition energies. The new complexes exhibit phosphorescence in fluid solution at room temperature arising from triplet ligand-centred ( 3 LC) excited states, which, in the cases of the heteroleptic derivatives, involve the ligand with the lowest  π-π* gap. The heteroleptic piq derivatives exhibit fluorescence and dual phosphorescence from different ligand-centred excited states in rigid media, demonstrating the potential of cyclometalated Pt(IV) complexes as multi-emissive materials.