Defense: Synthesis, Characterization, and Photophysics of Symmetric and Unsymmetric CCC-NHC Pincer Platinum Halide Complexes and Derivatives

Tuesday, September 18, 2018

Min Zhang

Department of Chemistry

Mississippi State University

A series of 24 new photoluminescent symmetric and unsymmetric CCC-NHC pincer Pt complexes was synthesized and characterized, including collection of their 195Pt NMR chemical shifts. In total 18 new X-ray crystal structures, and photophysical studies of these photoluminescent CCC-NHC pincer Pt complexes are reported. CCC-NHC pincer Pt complexes were synthesized and characterized using new CCC-NHC pincer based proligands [(RChetChetCRH3)X2, X = Cl, Br, or BPh4, where het represents imidazolyl, benzimidazolyl, and 1,2,4-triazolyl moieties; R = n-butyl, 3,3-dimethylbutyl, n-hexyl] as starting materials. A new method to synthesize Pt-Cl complexes to prevent halogen mixing was developed using tetraphenylborate salts as proligands. CCC-NHC pincer complexes Pt(II) were oxidized to Pt(IV) complexes by reaction with Br2, I2, or iodobenzene dichloride. Photophysical studies showed emission of blue to red-orange wavelengths for the Pt(II) complexes when irradiated with long wavelength UV light (360 nm). No visible emission for Pt(IV) complexes was observed upon irradiation at 360 nm. X-ray crystal structures of five CCC-NHC pincer Pt complexes are reported. The tunable photoluminescence of the synthesized CCC-NHC pincer Pt(II) complexes can be used as the materials for OLEDs.

Parameters and scales that provide understanding of steric and electronic effects are essential to predicting properties, and, therefore, to systematically designing new ligands. Meridional tridentate pincer ligands are neither conveniently nor accurately described by existing options. A scale has been developed based on 195Pt NMR chemical shift that is reflective of the total donor ability of a multi-dentate ligand in a square planar complex and that does not suffer from cis/trans stereochemical issues. This scale, Platinum Electronic Parameter (PtEP) and defined as PtEP = –(195Pt NMR shift) in CDCl3 revealed significant deviations of CCC-NHC pincer ligands, PCP and POCOP donor abilities from predicted extrapolations using existing TEP parameters. This initial data set demonstrates the applicability and broad potential of the PtEP scale.

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