Stabilization of RN=NN=PR3. Preparation and structural characterization of stable tetraarylphosphazide complexes containing molybdenum and tungsten

Article abstract of DOI:10.1021/ic00135a068

The reaction of aromatic azides (R′N₃) with MBr₂(CO)₃(PPh₃)₂ (M = Mo, W; Ph = C₆H₅; tol = p-CH₃C₆H₄) in dry methylene chloride at 20°C affords MBr₂(CO)₃(R′N₃PPh₃), N₂, and R′N =PPh₃ (R′ = Ph, tol). The phosphazide complexes exhibit remarkable stability with respect to N₂ loss. In contrast to the Mo(II) and W(II) complexes, ReCl₃(CH₃CN)(PPh₃)₂ and ReCl₃(PPh₂Me)₃ yield ReCl₄(PR₃)₂ upon treatment with the same aryl azides. Triclinic needles of WBr₂(CO)₃(tolN₃PPh₃) were grown from chloroform - ether and crystallized in space group C₁¹-P1 with Z = 2, a = 13.715 (6) A?, b = 9.904 (5) A?, c = 10.397 (5) A?, α = 100.98 (2)°, β = 83.11 (2)°, and γ = 85.80 (1)°. An X-ray diffraction study at -145 (5)°C showed the complex to be monomeric and seven-coordinate. The tolyl azide had inserted into the W-P bond, forming a phosphazide ligand (tolN₃PPh₃) which is bound to W in a chelating fashion through the α and γ nitrogen atoms; the N₃W metallacycle is nearly planar. Salient metrical parameters of the structure include the following: W-N(1) = 2.163 (4) A?, W-N(3) = 2.220 (5) A?, N(1)-N(2) = 1.279 (6) A?, N(2)-N(3) = 1.364 (6) A?, N(3)-P = 1.672 (5) A?, N(1)-C(41) = 1.423 (7) A?; N(1)-W-N(3) = 56.7 (2)°, W-N(1)-N(2) = 102.4 (3)°, W-N(3)-N(2) = 96.8 (3)°, N(1)-N(2)-N(3) = 103.8 (4)°. The full-matrix, least-squares refinement converged to R(F) = 0.028 and R_w(F) = 0.037 for 4066 unique data with F_o² > 3σ(F_o²).