SEARCH

SEARCH BY CITATION

Keywords:

  • alkynes;
  • gallium;
  • hydroamination;
  • hydroarylation;
  • redox-active ligands

Abstract

Acetylene, phenylacetylene, and alkylbutynoates add reversibly to (dpp-bian)Ga–Ga(dpp-bian) (dpp-bian=1,2-bis[(2,6-diisopropylphenyl)-imino]acenaphthene) to give addition products [dpp-bian(R1C[DOUBLE BOND]CR2)]Ga–Ga[(R2C[DOUBLE BOND]CR1)dpp-bian]. The alkyne adds across the Ga[BOND]N[BOND]C section, which results in new carbon–carbon and carbon–gallium bonds. The adducts were characterized by electron absorption, IR, and 1H NMR spectroscopy and their molecular structures have been determined by single-crystal X-ray analysis. According to the X-ray data, a change in the coordination number of gallium from three [in (dpp-bian)Ga–Ga(dpp-bian)] to four (in the adducts) results in elongation of the metal–metal bond by approximately 0.13 Å. The adducts undergo a facile alkynes elimination at elevated temperatures. The equilibrium between [dpp-bian(PhC[DOUBLE BOND]CH)]Ga–Ga[(HC[DOUBLE BOND]CPh)dpp-bian] and [(dpp-bian)Ga–Ga(dpp-bian) + 2 PhC[TRIPLE BOND]CH] in toluene solution was studied by 1H NMR spectroscopy. The equilibrium constants at various temperatures (298≤T≤323 K) were determined, from which the thermodynamic parameters for the phenylacetylene elimination were calculated (ΔG°=2.4 kJ mol−1, ΔH°=46.0 kJ mol−1, ΔS°=146.0 J K−1mol−1). The reactivity of (dpp-bian)Ga–Ga(dpp-bian) towards alkynes permits use as a catalyst for carbon–nitrogen and carbon–carbon bond-forming reactions. The bisgallium complex was found to be a highly effective catalyst for the hydroamination of phenylacetylene with anilines. For instance, with [(dpp-bian)Ga–Ga(dpp-bian)] (2 mol %) in benzene more than 99 % conversion of PhNH2 and PhC[TRIPLE BOND]CH into PhN[DOUBLE BOND]C(Ph)CH3 was achieved in 16 h at 90 °C. Under similar conditions, the reaction of 1-aminoanthracene with PhC[TRIPLE BOND]CH catalyzed by (dpp-bian)Ga–Ga(dpp-bian) formed a carbon–carbon bond to afford 1-amino-2-(1-phenylvinyl)anthracene in 99 % yield.