189813-47-6Relevant articles and documents
A General Route to Labile Niobium and Tantalum d° Monoimides. Discussion of Metal-Nitrogen Vibrational Modes
Korolev, Andrey V.,Rheingold, Arnold L.,Williams, Darryl S.
, p. 2647 - 2655 (1997)
Reaction of TaCl5 with 2 equiv of an amine in the presence of sodium silicate and pyridine affords Ta(NR)Cl3(py)2 in good yield. Reaction of NbCl5 with ZnCl2 followed by addition of an amine RNH2 and pyridine affords M(NR)Cl3(dme) (dme is 1,2-dimethoxyethane). For niobium this reaction proceeds smoothly regardless of the amine but is ineffective with tantalum and alkyl amines. An alternative route involves reaction of TaCl2 with 3 equiv of RNH2 to form [RNH3]2[Ta(NR)Cl5], followed by reaction of this salt with ZnCl2 in the presence of dme. The molecular structure of Nb(NtBu)Cl3(dme) (formula C8H19Cl3NNbO2) was determined by X-ray crystallography (monoclinic space group Cc with a = 30.565(4) ?, b = 7.2406(13) ?, c = 13.915(2) ?, = 90.626(7)°, V = 3079.4(8) ?3, Z = 8). The Nb-N bond length is 1.72 ? with a Nb-N-C bond angle of 177° in a distorted octahedral structure. In order to characterize the M-N stretching frequencies in these compounds, IR data for each compound are compared with calculated stretching frequencies using the commercially available Spartan calculation package. These experiments reveal that there is no real M-N stretching frequency in these imidos. Rather, the M-N modes are strongly coupled to N-C and C-H or C-C modes in these imidos. IR active modes are observed at ～ 260 cm-1 for tantalum alkyl imidos and ～1350 cm-1 for tantalum aryl imidos. These correspond to a Ta-(N-C) stretch coupled to the CR3 umbrella deformation.
