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.

Luminescent PtII and PtIV Platinacycles with Anticancer Activity Against Multiplatinum‐Resistant Metastatic CRC and CRPC Cell Models

“…Both the platinacycle and the chelate rings are nearly coplanar with the coordination plane leading to more rigid structurest han those previously reported for 2a [17] and 2b [18] containing ap ropylene chain. 2a' [17] 277 (7524) Pt II cyclometallated compounds show severala bsorption bands in the UV/Visible range ( Figure S8, Supporting Information). 2a' [17] 277 (7524) Pt II cyclometallated compounds show severala bsorption bands in the UV/Visible range ( Figure S8, Supporting Information).…”

“…In compounds 2a' and 2b' the Pt II centrala tom adopts as quare-planar coordination completed with at ridentate (C,N,N')l igand and an halido (Cl for 2a or Br for 2a') ligand trans to the imine. Both the platinacycle and the chelate rings are nearly coplanar with the coordination plane leading to more rigid structurest han those previously reported for 2a [17] and 2b [18] Absorption and emissions pectra for all compounds were recorded in 5 10 À5 m dichloromethanes olutions at 298 K. The resultsa re summarized in Table 1. 2a' [17] 277 (7524) [18] 287 (3831) 349 0.051 [a] 3b [18] 286 ( Pt II cyclometallated compounds show severala bsorption bands in the UV/Visible range ( Figure S8, Supporting Information).…”

“…[14,15,16] An additional interesting feature of these (C,N,N')-cycloplatinated compounds relies on their luminescence properties since we have unveiled that the intensity and the energy of the emission can be easily modulated by altering the nature of the ligands, the size of the (N,N')-chelate ring and the substituents in the aryl ring. [17,18] Indeed, this property of the reported compounds can also be of remarkable interest for in vivo cell imaging and flow cytometry applications.…”

“…Although no clear trends are observed for Pt IV compounds, the higher quantum yield is obtained for compound 3a' containing chlorido ligandsa nd the more rigid ethylene fragment. [17,18] The stabilityofthe Pt IV compound 3a in the aqueous biological mediumw as evaluated by 1 HNMR spectroscopyi nD 2 O and two drops of [D 6 ]DMSO. It can be attributed to phosphorescence 3 IL emission due to the observation of al arge Stokes' shift and the quenching of the emission in the presence of oxygen ( Figure S11, Supporting Information).…”

“…It can be attributed to phosphorescence 3 IL emission due to the observation of al arge Stokes' shift and the quenching of the emission in the presence of oxygen ( Figure S11, Supporting Information). [17,18] The stabilityofthe Pt IV compound 3a in the aqueous biological mediumw as evaluated by 1 HNMR spectroscopyi nD 2 O and two drops of [D 6 ]DMSO. The obtained spectra ( Figure S12, Supporting Information) suggests the formationo famixture of solvato complexes,w hich is in line with recent observations of aquation of equatorial ligandsofP t IV compounds.…”