Competitive Carbon−Sulfur vs Carbon−Carbon Bond Activation of 2-Cyanothiophene with [Ni(dippe)H]₂

The processes of C−C and C−S bond cleavage have been studied with the homogeneous organometallic compound [Ni(dippe)H]2 (1). When 1 is reacted with 2-cyanothiophene at room temperature, cleavage of the nitrile-substituted C−S bond occurs, forming the Ni−metallacycle complex (dippe)Ni(κ2-S,C-SCHCHCHC(CN)) (2a), which has been fully characterized by NMR spectroscopy and X-ray diffraction. 2a was converted to the C−CN cleavage product (dippe)Ni(CN)(2-thiophenyl) (3) when heated in solution. On closer inspection, four other intermediates were observed by 31P NMR spectroscopy at low temperature. Structures for the intermediates were elucidated through a combination of independent synthesis, theoretical calculations, chemical characterization, and experimental precedent. A kinetic product (dippe)Ni(κ2-S,C-SC(CN)=CHCHCH) (2b) was formed from cleavage of the nonsubstituted C−S bond, as well as a Ni(0) η2-nitrile intermediate, (dippe)Ni(η2-C,N-2-cyanothiophene) (4), and a dinuclear mixed Ni(0)−Ni(II) product (6b). A complete DFT analysis of this system has been carried out to reveal comparative details about the two bond cleavage transition states.