Synthesis, Structure, Reactivity and Catalytic Implications of a Cationic, Acetylide-Bridged Trigold-JohnPhos Species.

The cationic complex [(JohnPhos-Au) ₃ (acetylide)][SbF ₆ ] (JohnPhos=(2-biphenyl)di-tert-butylphosphine, L1) has been characterised structurally and features an acetylide-trigold(I)-JohnPhos system; the trinuclear-acetylide unit, coordinated to the monodentate bulk phosphines, adopts an unprecedented μ,η ¹ ,η ² ,η ¹ coordination mode with an additional interaction between distal phenyl rings and gold centres. Other cationic σ,π-[(gold(I)L1) ₂ ] complexes have also been isolated. The reaction of trimethylsilylacetylene with various alcohols (iPrOH, nBuOH, n-HexOH) catalysed by cationic [Au ^I L1][SbF ₆ ] complexes in CH ₂ Cl ₂ at 50 °C led to the formation of acetaldehyde acetals with a high degree of chemo- and regioselectivity. The reaction mechanism was studied, and several organic and inorganic intermediates have been characterised. A comparative study with the analogous cationic [Cu ^I L1][PF ₆ ] complex revealed different behaviour; the copper metal is lost from the coordination sphere leading to the formation of cationic vinylphosphonium and copper nanoparticles. Additionally, a new catalytic approach for the formation of this high-value cationic vinylphosphonium has been established.
(© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)