Radical Capture at Ni(II) Complexes: C-C, C-N, and C-O Bond Formation

The dinuclear b-diketiminato NiIItert-butoxide {[Me3NN]Ni}2(μ-OtBu)2 (2), synthesized from [Me3NN]Ni(2,4-lutidine) (1) and di-tert-butylperoxide, is a versatile precursor for the synthesis of a series of NiIIcomplexes [Me3NN]Ni-FG to illustrate C-C, C-N, and C-O bond formation at NiII via radicals. {[Me3NN]Ni}2(μ-OtBu)2 reacts with nitromethane, alkyl and aryl amines, acetophenone, benzamide, ammonia and phenols to deliver corresponding mono- or dinuclear [Me3NN]Ni-FG species (FG = O2NCH2, R-NH, ArNH, PhC(O)NH, PhC(O)CH2, NH2and OAr). Many of these NiII complexes are capable of capturing the benzylic radical PhCH(•)CH3 to deliver corresponding PhCH(FG)CH3 products featuring C-C, C-N or C-O bonds. DFT studies shed light on the mechanism of these transformations and suggest two competing pathways that depend on the nature of the functional groups. These radical capture reactions at [NiII]-FG complexes outline key C-C, C-N, and C-O bond forming steps and suggest new families of nickel radical relay catalysts.