Preparation and properties of dinitrogen trimethylphosphine complexes of molybdenum and tungsten—II: Synthesis and crystal structures of [MCl(N2)(PMe3)4] (M = Mo,W) and trans-[MoCl2(PMe3)4]

Sodium amalgam reduction of the complexes MCl₃(PMe₃)₃] (M = Mo, W) in tetrahydrofuran, under dinitrogen, yields dark red-brown suspensions from which red-orange crystals of composition trans-MCl(N₂)· (PMe₃)₄] can be collected. Spectroscopic and chemical evidence indicate the compounds are best formulated as mixtures of trans-M(N₂)₂(PMe₃)₄] and trans-MCl₂(PMe₃)₄] species, but attempts to isolate the pure bis(dinitro derivatives have proved unsuccessful. Single crystals of analytical composition MCl(N₂)(PMe₃)₄] have been studied by X-ray crystallography, and the structure of trans-MoCl₂(PMe₃)₄] has been determined for comparison. trans-MCl(N₂)(PMe₃)₄] (M = Mo, W) and trans-MoCl₂(PMe₃)₄] are all isostructural, crystallizing in the tetragonal space group I$\text{4}$2 trans-MoCl(N₂)(PMe₃)₄] has a = 9.597(5), b = 12.294(6) Å, D_c = 1.36g cm^?3 Z = 2 and was refined to a final R value of 0.021 based on 319 independent observed reflections. The tungsten analogue has a = 9.573(4), b = 12.278(5) Å, D_c = 1.63g cm^?3 for Z = 2 and was refined to R = 0.19 with 322 independent observed reflections. trans-MoCl₂(PMe₃)₄] has cell parameters a = 9.675(5), b = 12.311(6) Å D_c = 1.36 g cm^?3 for Z = 2 and was refined to R = 0.043 with 316 independent observed reflections. In each case the metal atom resides on a crystallographic $\text{4}$2m position. For trans-MoCl(N₂)(PMe₃)₄] (M = Mo, W) the chlorine and dinitrogen ligands are disordered. M-N distances of 2.08(1) ? (M = Mo) and 2.04(2) ? (M = W) and M-Cl bond lengths of 2.415(8) Å (M = Mo) and 2.46(1) Å (M = W) are observed. In trans-MoCl₂(PMe₃)₄], where there is no disorder, the Mo-Cl distance is 2.420(6) Å.