Dinitrogen complexes of tungsten with bulky phosphine co-ligands. Preparation and crystal structures of [{W(N2)2(PEt2Ph)3}2(µ-N2)],trans-[W(N2)2(PEt2Ph)4]·C4H8O, and [W(η6-C6H5PPrn2)(N2)(PPrn2Ph)2] and their reactions to give hydrazine or ammonia

Abstract

Reduction of WCl₆ or [WCl₄(PR₂Ph)₂](R = Et or Prⁿ) with Mg in the presence of PR₂Ph under N₂ in tetrahydrofuran (thf) gives a mixture of dinitrogen complexes: [{W(N₂)₂(PR₂Ph)₃}₂(µ-N₂)](1), trans-[W(N₂)₂(PR₂Ph)₄](2), and [W(η⁶-C₆H₅PR₂)(N₂)(PR₂Ph)₂](3) which can be observed in the ¹⁵N n.m.r. spectra of the reaction solutions and isolated in most cases in moderate yield. Compound (1a)(R = Et) is shown to be a dimer by X-ray analysis but the structure could be refined only with constraints on interatomic distances. Compounds (1) react with anhydrous HCl (thf, 20 °C) to give hydrazine (0.2 mol/W atom) and dinitrogen (2 mol/W atom). Compound (2a)(R = Et) crystallises as a thf solvate with W–N = 1.986(6) and 1.994(6), N–N = 1.146(7) and 1.139(7)Å. Complex (2a) gives ammonia (1.8 mol/W atom) and N₂(1 mol/W atom) on treatment with H₂SO₄–MeOH. Compound (3b)(R = Prⁿ) has W–N = 1.980(8) and N–N = 1.126(10)Å and loses N₂ quantitatively on treatment with anhydrous HCl in thf.