Diazofluorene reacts with Ni(0) and Pd(0) complexes, M(t-BuNC)2 or M(PPh3)2(C2H4) (M = Ni or Pd), to give the corresponding diazofluorene complexes, ML2(diazofluorene). The reduction in the C=N=N stretching frequency from 2055 cm-1 in free diazofluorene to ca. 1500 cm-1 in these complexes suggests a side-on, π-coordination of the diazofluorene ligand. Reaction of these diazofluorene complexes with substituted olefins (methyl acrylate or diethyl maleate) at 100 °C produces cyclopropanation products. In the absence of any Ni(0) or Pd(0) catalysts, diazofluorene reacts with the substituted olefins at 30 °C to produce 1-pyrazoline derivatives which slowly undergo ring contraction to form the corresponding cyclopropane derivatives. Diazomethane does not form a stable complex with Ni(0) or Pd(0) systems even at -78°C. However, in the presence of Ni(0) or Pd(0) compounds, diazomethane readily reacts with substituted olefins to produce substituted cyclopro-panes. In the absence of the metal compounds, diazomethane and substituted olefins produce 2-pyrazoline derivatives which do not undergo ring contraction to the corresponding cyclopropane derivatives, even in the presence of Ni(0) or Pd(0) catalysts. The structure of one diazofluorene complex, Ni(t-BuNC)2(diazofluorene), has been confirmed by x-ray diffraction studies. The diazofluorene molecule is π-bonded to the Ni atom through the N-N multiple bond such that the N atoms are essentially equidistant from the Ni atom and the complete molecule, with the exception of the methyl groups of the tert-butyl ligands, is nearly planar. Some relevant metrical parameters are: Ni-N(diazofluorene), 1.874 (3) and 1.834 (3); Ni-C(t-BuNC), 1.844 (4) and 1.844 (5); N-N(diazofluorene), 1.245 (4); N-C(diazofluorene), 1.334 (4) A; N-Ni-N(diazofluorene), 39.2 (1); N-N-C(diazofluorene), 133.8 (3)°. The compound crystallizes in the orthorhombic space group D2h l5-Pbca in a cell of dimension a = 17.748 (3), b = 18.999 (4), c = 14.295 (2) Å, and Z = 8. Based on 3022 unique reflections, the structure was refined by full-matrix, least-squares techniques to agreement indices (on F2) of R = 0.076 and Rw = 0.129. The conventional agreement index (on F) for the 2095 reflections having Fo2 > σ(F02) is R = 0.046. An interesting correlation between the Ni-C distances, the vc≡n values, and the C-Ni-C angles of the t-BuNC ligands and the π acidity of the ligand, AB, in a series of complexes, Ni(t-BuNC)2(AB), is noted.
ASJC Scopus subject areas
- Colloid and Surface Chemistry