We report the synthesis and full characterization for a series of cyclometallated complexes of Pt(ii) and Pd(ii) incorporating the fluxional trithiacrown ligand 1,4,7-trithiacyclononane (aneS3). Reaction of [M(C^N)(µ-Cl)]2 (M = Pt(ii), Pd(ii); C⁁N = 2-phenylpyridinate (ppy) or 7,8-benzoquinolinate (bzq)) with aneS3 followed by metathesis with NH4PF6 yields [M(C⁁N)(aneS3)](PF6). The complexes [M(C⁁P)(aneS3)](PF6) (M = Pt(ii), Pd(ii); C⁁P = (CH2C6H4P(o-tolyl)2-C, P)−) were synthesized from their respective [Pt(C⁁P)(µ-Cl)]2 or [Pd(C⁁P)(µ-O2CCH3)]2 (C⁁P) starting materials. All five new complexes have been fully characterized by multinuclear NMR, IR and UV-Vis spectroscopies in addition to elemental analysis, cyclic voltammetry, and single-crystal structural determinations. As expected, the coordinated aneS3 ligand shows fluxional behavior in its NMR spectra, resulting in a single13C NMR resonance despite the asymmetric coordination environment of the cyclometallating ligand. Electrochemical studies reveal irreversible one-electron metal-centered oxidations for all Pt(ii) complexes, but unusual two-electron reversible oxidations for the Pd(ii) complexes of ppy and bzq. The X-ray crystal structures of each complex indicate an axial M–S interaction formed by the endodentate conformation of the aneS3 ligand. The structure of [Pd(bzq)(aneS3)](PF6) exhibits disorder in the aneS3 conformation indicating a rare exodentate conformation as the major contributor in the solid-state structure. DFT calculations on [Pt(aneS3)(ppy)](PF6) and [Pd(aneS3)(ppy)](PF6) indicate the HOMO for both complexes is primarily dz2 in character with a significant contribution from the phenyl ring of the ppy ligand and p orbital of the axial sulfur donor. In contrast, the calculated LUMO is primarily ppy π* in character for [Pt(aneS3)(ppy)](PF6), but dx2−y2 in character for [Pd(aneS3)(ppy)](PF6).
|Original language||English (US)|
|Number of pages||11|
|Journal||Journal of the Chemical Society. Dalton Transactions|
|State||Published - Jan 15 2008|
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