| Summary: | The Pd(II) complexes [Pd(Cp)(L)<sub>n</sub>]<sub>m</sub>[BF<sub>4</sub>]<sub>m</sub> were synthesized via the reaction of cationic acetylacetonate complexes with cyclopentadiene in the presence of BF<sub>3</sub>∙OEt<sub>2</sub> (<i>n</i> = 2, <i>m</i> = 1: L = PPh<sub>3</sub> (<b>1</b>), P(<i>p</i>-Tol)<sub>3</sub>, <i>tris</i>(<i>ortho</i>-methoxyphenyl)phosphine (TOMPP), <i>tri</i>-2-furylphosphine, <i>tri</i>-2-thienylphosphine; <i>n</i> = 1, <i>m</i> = 1: L = dppf, dppp (<b>2</b>), dppb (<b>3</b>), 1,5-bis(diphenylphosphino)pentane; <i>n</i> = 1, <i>m</i> = 2 or 3: 1,6-bis(diphenylphosphino)hexane). Complexes <b>1</b>–<b>3</b> were characterized using X-ray diffractometry. The inspection of the crystal structures of the complexes enabled the recognition of (Cp<sup>–</sup>)⋯(Ph-group) and (Cp<sup>–</sup>)⋯(CH<sub>2</sub>-group) interactions, which are of C–H…π nature. The presence of these interactions was confirmed theoretically via DFT calculations using QTAIM analysis. The intermolecular interactions in the X-ray structures are non-covalent in origin with an estimated energy of 0.3–1.6 kcal/mol. The cationic palladium catalyst precursors with monophosphines were found to be active catalysts for the telomerization of 1,3-butadiene with methanol (<i>TON</i> up to 2.4∙10<sup>4</sup> mol 1,3-butadiene per mol Pd with chemoselectivity of 82%). Complex [Pd(Cp)(TOMPP)<sub>2</sub>]BF<sub>4</sub> was found to be an efficient catalyst for the polymerization of phenylacetylene (PA) (catalyst activities up to 8.9 × 10<sup>3</sup> g<sub>PA</sub>·(mol<sub>Pd</sub>·h)<sup>−1</sup> were observed)
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