Addition of Alkynes to a Gallium Bis‐Amido Complex: Imitation of Transition‐Metal‐Based Catalytic Systems

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(R 1 CCR 2 )]Ga–Ga[(R 2 CCR 1 )dpp‐bian]. The alkyne adds across the GaNC section, which results in new carbon–carbon and carbon–gallium bonds. The adducts were characterized by electron absorption, IR, and 1 H 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(PhCCH)]Ga–Ga[(HCCPh)dpp‐bian] and [(dpp‐bian)Ga–Ga(dpp‐bian) + 2 PhCCH] in toluene solution was studied by 1 H 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 (Δ G °=2.4 kJ mol −1 , Δ H °=46.0 kJ mol −1 , Δ S °=146.0 J K −1 mol −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 PhNH 2 and PhCCH into PhNC(Ph)CH 3 was achieved in 16 h at 90 °C. Under similar conditions, the reaction of 1‐aminoanthracene with PhCCH catalyzed by (dpp‐bian)Ga–Ga(dpp‐bian) formed a carbon–carbon bond to afford 1‐amino‐2‐(1‐phenylvinyl)anthracene in 99 % yield.