Platinum(II) Compounds Containing Cyclometalated Tridentate Ligands: Synthesis, Luminescence Studies, and a Selective Fluoro for Methoxy Substitution

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.