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

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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.

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