Nitrogen-15 nuclear magnetic resonance spectroscopy of dinitrogen-bridged complexes

Abstract

Dinitrogen-bridged complexes of trans-[ReCl(N₂)(PMe₂Ph)₄] with NbCl₅ and TaCl₅(1 : 1 adducts) and ZrCl₄(2 : 1 adduct) have been characterised and a corresponding complex of HfCl₄ observed in solution. Nitrogen-15 chemical shifts are compared for three types of dinitrogen bridge: complexes of Mo, W, Re, and Os with a main-group acceptor (AlMe₃), complexes of trans-[ReCl(N₂)(PMe₂Ph)₄] with a π acceptor (TiCl₄, ZrCl₄, HfCl₄, NbCl₅, or TaCl₅), and symmetrical transition-metal complexes, [{W(N₂)₂(PR₂Ph)₃}₂(µ-N₂)](R = Et or Prⁿ), [{Ru(NH₃)₅}₂(µ-N₂)]⁴⁺, etc. The variation in the shielding is related by simple molecular orbital arguments to the variation in electronic (charge-transfer) absorption, to the periodicities observed for mononuclear dinitrogen complexes, and to the activation of dinitrogen by co-ordination.