Catalytic Carbon−Carbon Bond Activation and Functionalization by Nickel Complexes

The nickel alkyne complexes (dippe)Ni(PhC⋮CPh), 1, (dippe)Ni(MeC⋮CMe), 2, (dippe)Ni(MeO 2 CC⋮CCO 2 Me), 3, (dippe)Ni(CH 3 OCH 2 C⋮CCH 2 OCH 3 ), 4, and (dippe)Ni(CF 3 C⋮CCF 3 ), 5, were synthesized (dippe = bis(diisopropylphosphino)ethane) and characterized by 1 H, 31 P, and 13 C{ 1 H} NMR spectroscopy. Complexes 1, 2, and 3 were characterized by X-ray crystallography. The thermolysis of complex 1 or 2 (120 °C) in the presence of excess biphenylene and excess alkyne results in very slow catalytic formation of the corresponding 9,10-disubstituted phenanthrene. However, addition of ∼6 mol % O 2 (based on the metal complex) to the reaction mixture results in an acceleration in catalysis at lower temperatures (∼70−80 °C). The thermolysis of complexes 3 or 4 with excess biphenylene and excess alkyne leads to the alkyne cyclotrimerization product as the major organic species formed in the reaction. Fluorenone was catalytically produced by heating (dippe)Ni(CO) 2, biphenylene, and CO. Catalytic insertion of 2,6-xylylisocyanide into the strained C−C bond of biphenylene was also achieved by heating (dippe)Ni(2,6-xylylisocyanide) 2, excess biphenylene, and 2,6-xylylisocyanide. Mechanistic schemes are proposed for these reactions.