N‑Assisted CPh–H Activation in 3,8-Dinitro-6-phenylphenanthridine. New C,N-Cyclometalated Compounds of Platinum(II): Synthesis, Structure, and Luminescence Studies

• Published in: Organometallics 2013-08, Vol.32 (15), p.4092-4102
• Main Authors: Sicilia, Violeta, Fuertes, Sara, Martín, Antonio, Palacios, Adrián
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om400159g

The activation of a CPh–H bond in the phenyl ring of 3,8-dinitro-6-phenylphenanthridine (HC∧N) can be achieved by refluxing the intermediate [PtCl(η3-2-Me-C3H4)(HC∧N-κN)] (1) (η3-2-Me-C3H4 = η3-2-methylallyl) in 2-methoxyethanol to render the new cyclometalated complex [{Pt(μ-Cl)(C∧N)}2] (2). The cleavage of the bridging system in 2 by the neutral ligands L rendered the mononuclear complexes [PtCl(C∧N)L] (L = tht 3, PPh3 4, CN t Bu 5) with the geometry (trans C, Cl). The air- and temperature-stable cationic compound [Pt(C∧N)(CNXyl)2]ClO4 (6) could be prepared from 2 by addition of CNXyl (1:4 molar ratio) after the Cl abstraction with AgClO4. Compound [Pt(C∧N-κC)(tht)3]ClO4 (7) was prepared similarly to 6 but using a significant excess of tht, which produces the N-dissociation of the C∧N ligand. The photophysical properties of compounds 3–6 have been studied with the help of time-dependent density functional theory (TD-DFT) calculations. In 2-Me-THF at low temperature (77 K) the green emission of the HC∧N ligand turns to red phosphorescence in compounds 3–6, which was assigned to a mixed metal-to-ligand charge transfer/intraligand/ligand-to-ligand charge transfer [3MLCT/3IL/3L′LCT] excited state. In the solid state at low temperature (77 K) the emissive behaviors are quite similar to that observed in glassy solutions with some contribution of excimeric π–π* emissions in the neutral chloro derivatives. Compounds 4–6 are also emissive in the solid state at room temperature with photoluminescence quantum yields (Φ) between 0.032 and 0.05.