18130-07-9Relevant academic research and scientific papers
Molecular and electronic structures of two 16-electron complexes of tungsten(II): WBr2(CO)2(C7H8) (C7H8 = Norbornadiene) and WBr2(CO)2(PPh3)2
Cotton,Meadows
, p. 4688 - 4693 (2008/10/08)
The previously reported reaction of WBr2(CO)4 with norbornadiene has been reinvestigated and found to give monomeric WBr2(CO)2(C7H8) (1). Compound 1 crystallizes from CH2Cl2 in the monoclinic space group P21/n with lattice dimensions a = 7.506 (7) ?, b = 12.643 (8) ?, c = 12.296 (6) ?, β = 99.60 (7)°, V = 1150 (2) ?3, and Z = 4. The structure was refined to R1 = 0.032 and R2 = 0.038. Compound 1 is a diamagnetic d4 complex having a pseudo-octahedral geometry with its CO ligands trans to each other. Compound 1 also has relatively short W-Br (2.493 (1) and 2.489 (1) ?) bond lengths. Another 16-electron d4 tungsten complex, WBr2(CO)2(PPh3)2 (2), was also structurally characterized. Compound 2 crystallizes in the triclinic space group P1 with lattice dimensions a = 9.418 (5) ?, b = 10.021 (4) ?, c = 19.898 (6) ?, α = 90.54 (3)°, β = 112.80 (3)°, γ = 92.02 (4)°, V = 1730 (1) ?3, and Z = 2. The structure was refined to R1 = 0.064 and R2 = 0.072. Compound 2 has an overall geometry greatly distorted from octahedral. Fenske-Hall type molecular orbital calculations were performed on models of 1 and 2 to determine the principal factors responsible for the removal of t2g orbital degeneracy. The calculational results predict a lowest energy allowed transition between orbitals separated by ca. 3 eV for both 1 and 2. This transition is assigned to visible transitions observed at 565 and 545 nm for 1 and 2, respectively. The calculations indicate that the LUMO-HOMO separation in 1 can be attributed to metal d to CO π* and olefin π* back-donation, which results in the lowering of two orbitals preferentially. In 2 it appears that the strong distortions from octahedral symmetry, especially the P-M-P angle of only 128°, are as important as π bonding in giving the singlet ground state.
Stabilization of RN=NN=PR3. Preparation and structural characterization of stable tetraarylphosphazide complexes containing molybdenum and tungsten
Hillhouse, Gregory L.,Goeden, Gary V.,Haymore, Barry L.
, p. 2064 - 2071 (2008/10/08)
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 Rw(F) = 0.037 for 4066 unique data with Fo2 > 3σ(Fo2).
