Platinum(II) compounds containing cyclometalated tridentate ligands: Synthesis, luminescence studies, and a selective fluoro for methoxy substitution

Abstract

Two series of potentially tridentate ligands of formula ArCH=N(CH2)2NMe2 and ArCH=N(CH2)3NMe2 (Ar = C6H5, 2-FC6H4, 4-FC6H4, 2,3,4-F3C6H2) were used to prepare [C,N,N′]-cyclometalated platinum compounds containing either a chloro or a methyl ancillary ligand. The synthesis of the compounds [PtCl{Me2N(CH2)xN=CHR}] (3a−h), via the corresponding compounds [PtCl2{Me2N(CH2)xN=CHAr}] (2), requires drastic conditions and proceeds more easily for ligands derived from N,N-dimethylpropylenediamine (x = 3). Along the process, an unexpected selective nucleophilic substitution of a fluoro for a methoxy substituent took place at the aryl ring for ligands 2,3,4-F3C6H2CH=N(CH2)xNMe2. The syntheses of compounds [PtMe{Me2N(CH2)xN=CHR}] (4a−h) using [Pt2Me4(μ-SMe2)2] as a precursor took place for all ligands under relatively mild conditions. All compounds were fully characterized, including molecular structure determination for [PtCl{Me2N(CH2)3N=CH(4-FC6H3)}] (3b) and [PtCl{Me2N-(CH2)3N=CH(2-OMe,3,4-F2C6H)}] (3g). The absorption and emission spectra were also studied for the [C,N,N′]-cyclometalated platinum(II) compounds, and all of the compounds were emissive in the solid state and in dichloromethane solution at room temperature (compounds 3) or at 77 K (compounds 4). The size of the [N,N′]-chelate ring and the number and position of the substituents in the aryl ring modulate the intensity and the energy of the emission.