Phosphine and selenoether peri-substituted acenaphthenes and their transition metal complexes: structural and NMR investigations

A series of peri-substituted acenaphthene-based phosphine selenoether bidentate ligands Acenap(iPr₂P)(SeAr) (L1–L4, Acenap = acenaphthene-5,6-diyl, Ar = Ph, mesityl, 2,4,6-trisopropylphenyl and supermesityl) were prepared. The rigid acenaphthene framework induces a forced overlap of the phosphine and selenoether lone pairs, resulting in a large magnitude of through-space ⁴J_PSe coupling, ranging from 452 to 545 Hz. These rigid ligands L1–L4 were used to prepare a series of selected late d-block metals, mercury, and borane complexes, which were characterized, including by multinuclear NMR and single-crystal X-ray diffraction. The Lewis acidic motifs (BH₃, Mo(CO)₄, Ag⁺, PdCl₂, PtCl₂, and HgCl₂) bridge the two donor atoms (P and Se) in all but one case in the solid-state structures. Where the bridging motif contained NMR-active nuclei (¹¹B, ¹⁰⁷Ag, ¹⁰⁹Ag, ¹⁹⁵Pt, and ¹⁹⁹Hg), J_PM and J_SeM couplings are observed directly, in addition to the altered J_PSe in the respective NMR spectra. The solution NMR data are correlated with single-crystal diffraction data, and in the case of mercury(II) complexes, they are also correlated with the solid-state NMR data and coupling deformation density calculations. The latter indicate that the through-space interaction dominates in free L1, while in the L1HgCl₂ complex, the main coupling pathway is via the metal atom and not through the carbon framework of the acenaphthene ring system.