Platinum(IV) Complexes with Tridentate, NNC-Coordinating Ligands: Synthesis, Structures, and Luminescence

Dikova, Yana M.; Yufit, Dmitry S.; Williams, J.A. Gareth

Abstract

Platinum(II) complexes of NNC-cyclometalating ligands based on 6-phenyl-2,2′-bipyridine (HL1) have been widely investigated for their luminescence properties. We describe how PtL1Cl and five analogues with differently substituted aryl rings, PtL2–6Cl, can be oxidized with chlorine and/or iodobenzene dichloride to generate Pt(IV) compounds of the form Pt(NNC-Ln)Cl3 (n = 1–6). The molecular structures of several of them have been determined by X-ray diffraction. These PtLnCl3 compounds react with 2-arylpyridines to give a new class of Pt(IV) complex of the form [Pt(NNC)(NC)Cl]+. Elevated temperatures are required, and the reaction is accompanied by competitive reduction processes and generation of side-products; however, four examples of such complexes have been isolated and their molecular structures determined. Reaction of PtL1Cl3 with HL1 similarly generates [Pt(NNC-L1)2]2+, which we believe to be the first example of a bis-tridentate Pt(IV) complex. The lowest-energy bands in the UV–vis absorption spectra of all the PtLnCl3 compounds are displaced to higher energy relative to the Pt(II) precursors, but they red-shift with the electron richness of the aryl ring, consistent with predominantly 1[πAr → π*NN] character to the pertinent excited state. A similar trend is observed for the [Pt(NNC)(NC)Cl]+ complexes. They display phosphorescence in solution at room temperature, centered around 500 nm for [PtL1(ppy)Cl]+ and [Pt(L1)2]2+, and 550 nm for methoxy-substituted derivatives. The lifetimes are in the microsecond range, rising to hundreds of microseconds at 77 K, consistent with triplet excited states of primarily 3[πAr → π*NN] character with relatively little participation of the metal.

Citation

Dikova, Y. M., Yufit, D. S., & Williams, J. G. (2023). Platinum(IV) Complexes with Tridentate, NNC-Coordinating Ligands: Synthesis, Structures, and Luminescence. Inorganic Chemistry, 62(4), 1306-1322. https://doi.org/10.1021/acs.inorgchem.2c04116

• Journal Article Type: Article
• Acceptance Date: Dec 23, 2022
• Online Publication Date: Jan 16, 2023
• Publication Date: Jan 30, 2023
• Deposit Date: Jan 18, 2023
• Publicly Available Date: Mar 31, 2023
• Journal: Inorganic Chemistry
• Print ISSN: 0020-1669
• Electronic ISSN: 1520-510X
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 62
• Issue: 4
• Pages: 1306-1322
• DOI: https://doi.org/10.1021/acs.inorgchem.2c04116
• Public URL: https://durham-repository.worktribe.com/output/1182820