Synthesis, Structure, Reactivity and Catalytic Implications of a Cationic, Acetylide‐Bridged Trigold–JohnPhos Species

• Published in: Chemistry : a European journal 2020-07, Vol.26 (40), p.8810-8818
• Main Authors: Grirrane, Abdessamad, Álvarez, Eleuterio, García, Hermenegildo, Corma, Avelino
• Format: Article
• Language: English
• Subjects: Acetaldehyde; Acetals; Alcohols; Biphenyl; Cations; Chemical synthesis; Chemistry; Comparative studies; Coordination; Copper; Dichloromethane; Gold; homogeneous catalysis; Intermediates; multinuclear complexes; Nanoparticles; Phosphines; phosphorus; Reaction mechanisms; Regioselectivity
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202000420

The cationic complex [(JohnPhos–Au)3(acetylide)][SbF6] (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,η1,η2,η1 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 [AuIL1][SbF6] complexes in CH2Cl2 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 [CuIL1][PF6] 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. Multinuclear gold: A new family of tri‐AuI complexes have been characterised as intermediates during the [AuIL][SbF6] catalytic preparation of acetaldehyde acetals. These well‐characterised cationic AuI intermediates lend support to the proposed reaction mechanism. An analogous copper complex revealed different behaviour, leading to a vinylphosphonium and copper nanoparticles.