Cyclometallated Pt(II) and Pd(II) complexes with a trithiacrown ligand

Area of Science:

• Coordination Chemistry
• Organometallic Chemistry
• Materials Science

Background:

• Cyclometallated platinum(II) and palladium(II) complexes are crucial in catalysis and photophysics.
• The 1,4,7-trithiacyclononane ([9]aneS3) ligand offers unique coordination properties due to its sulfur donors.
• Understanding ligand fluxionality and its impact on complex properties is essential for designing new functional materials.

Purpose of the Study:

• To synthesize and fully characterize novel cyclometallated Pt(II) and Pd(II) complexes incorporating the [9]aneS3 ligand.
• To investigate the structural, spectroscopic, electrochemical, and electronic properties of these new complexes.
• To explore the influence of the fluxional [9]aneS3 ligand on the coordination environment and reactivity of the metal centers.

Main Methods:

• Synthesis of Pt(II) and Pd(II) complexes with 2-phenylpyridinate (ppy), 7,8-benzoquinolinate (bzq), and a cyclometalated phosphine ligand.
• Full characterization using multinuclear NMR, IR, UV-Vis spectroscopy, elemental analysis, cyclic voltammetry, and single-crystal X-ray diffraction.
• Density Functional Theory (DFT) calculations to elucidate frontier molecular orbitals and electronic structures.

Main Results:

• Five new Pt(II) and Pd(II) complexes with the [9]aneS3 ligand were successfully synthesized and characterized.
• The [9]aneS3 ligand exhibited fluxional behavior in NMR spectra, and X-ray structures revealed axial M-S interactions.
• Pt(II) complexes showed irreversible one-electron oxidations, while Pd(II) complexes displayed unusual reversible two-electron oxidations; DFT revealed distinct HOMO/LUMO characteristics.

Conclusions:

• The incorporation of the fluxional [9]aneS3 ligand leads to unique structural and electrochemical properties in Pt(II) and Pd(II) cyclometallated complexes.
• The endodentate conformation of [9]aneS3 is favored, but an exodentate conformation was observed in one Pd(II) complex.
• These findings provide valuable insights into the coordination chemistry of sulfur-rich macrocycles and their potential applications.