Di(2-pyridyl)-amides and -phosphides: Syntheses, reactivity, structures, Raman-experiments and calculations
The 2-pyridyl containing compounds (2-Py)(2)NH1, (2-Py)(2)PH 2, Me2Al(2-Py)(2)N 3, Me2Al(2-Py)(2)P 4, Et2Al(2-Py)(2)N 5, Et2Al(2-Py)(2)P 6 and Et2Al(2-Py)(2)NAlEt3 7 have been synthesized and analyzed by solid state structure determination, FT-Raman spectroscopy and theoretical calculations in order to elucidate the charge density distribution. All di(2-pyridyl) amides and -phosphides coordinate the R2Al+ fragment via both ring nitrogen atoms, but the Lewis basicity of the central two-coordinated nitrogen atom in 5 is high enough to coordinate a second equivalent AlEt3 to form the Lewis acid base adduct Et2Al(2-Py)(2)NAlEt3 7. Several density functionals (BLYP, B3LYP, BPW91) have been examined in relation to various basis sets (6-31G, 6-31+G, 6-31G(d), 6-31+G(d)). This computational tool facilitates the unambiguous assignment of the Raman ring vibration frequencies. The shift to higher wavenumbers proceeding from the parent di(2-pyridyl)amine 1 and di(2-pyridyl)-phosphane 2 to the metal complexes 3 and 4 indicates partial double bond localization in the ring positions 3 and 5. This effect is more pronounced in the di(2-pyridyl)amide complexes than in the phosphide. Due to the higher electronegativity of the central nitrogen atom in 3, 5 and 7 compared to the bridging two-coordinated phosphorus atom in 4 and 6 the di(2-pyridyl) amide is the harder Lewis base. In the phosphides nearly all charge density couples into the rings leaving the central phosphorus atom only attractive for soft metals.
amides phosphides aluminum pyridyl-ligands ir/raman spectroscopy dft