Spectroscopy of terminal dinitrogen complexes: nitrogen-15 and phosphorus-31 nuclear magnetic resonance

Abstract

Nitrogen-15 chemical shifts and coupling constants are reported for terminal dinitrogen complexes of Mo, W, Re Fe, Ru, Os, and Rh. The nitrogen shielding shows a periodic variation with the central metal, increasing with increasing atomic number of the metal across the transition-metal series, or down a particular group, the increase being steeper for the metal-bound nitrogen N_α than for N_β. For complexes of metals later in the series N_α is more shielded than is N_β, but there appears to be a crossover at molybdenum, and possibly at or near tungsten. The ¹⁵N shifts show evidence of interaction of adjacent dinitrogen ligands. The majority of compounds have phosphine co-ligands and their ³¹P chemical shifts show a smaller sensitivity to change of the central metal (about half to three-quarters of that of the ¹⁵N shifts) and also show chelate effects. The preparation, n.m.r. and redox properties of the new complexes trans-[M(N₂)₂(depe)(dppe)](M = Mo or W; depe = Et₂PCH₂CH₂PEt₂, dppe = Ph₂PCH₂CH₂PPh₂) are reported.