Synthesis, structures, and catalytic reactivity of bis(N-heterocyclic carbene) supported diphenyldiazomethane and 1-azidoadamantane complexes of nickel

• Family of bis(N-heterocyclic carbene)-supported Ni complexes bind N2CPh2 and N3Ad.
• Unique binding modes for N2CPh2 and N3Ad have rarely been observed in group 10 metals.
• Catalytic cyclopropanation with NiN2CPh2 complexes is efficient and high yielding.
• The proposed catalytic cycle does not include formation of a metallacarbene.

Diphenyldiazomethane reacts with Ni(NHC)2 (1, NHC = N-heterocyclic carbene) to afford complexes of the type (NHC)2Ni(κ1-N2CPh2) (3) in which the diazoalkane ligand is bound to the metal in an end-on κ1 fashion. Additionally, 1-IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) reacts with 1-azidoadamantane (N3Ad) to produce (IMes)2Ni(η2-N3Ad) (4) in which the azide ligand is bound to the metal in a side-bound η2-fashion. While thermolysis of 3 and 4 does not induce N2 loss to form terminal carbenes and imidos, respectively, (IMes)2Ni(κ1-N2CPh2) (3-IMes) reacts with olefins at elevated temperatures to give cyclopropane products in excellent yields. Either 3-IMes or 1-IMes can also perform this reaction catalytically with a 1:1 ratio of diphenyldiazomethane to olefin. An olefin activation mechanism is proposed to explain the cyclopropanation reaction.

Complexes of type (NHC)2Ni(κ1-N2CPh2) (3), in which diphenyldiazomethane is bound to an N-heterocyclic carbene-supported nickel center in an unusual κ1 end-on fashion, react with olefins at elevated temperatures to give cyclopropane products in excellent yields. 3-IMes or 1-IMes can also perform this reaction catalytically with an efficient 1:1 ratio of diphenyldiazomethane to olefin.Figure optionsDownload as PowerPoint slide