ORGANOMETALLIC NITROSYL CHEMISTRY .43. SYNTHESIS, CHARACTERIZATION, AND PHYSICAL-PROPERTIES OF UNUSUAL CYCLOPENTADIENYL BIS(BENZYL) NITROSYL COMPLEXES OF MOLYBDENUM AND TUNGSTEN

{Treatment of either the dichloro or diiodo nitrosyl precursors Cp’M(NO)X2 (Cp’ = Cp (eta-5-C5H5) or Cp* (eta-5-C5Me5); M = Mo or W; X = Cl or I) in THF/Et2O with 2 equiv of a benzyl Grignard reagent, Ph’CH2MgCl (Ph’ = C6H5 or 2,4,6-Me3C6H2), at 0-degrees-C affords the corresponding bis(benzyl) nitrosyl complexes, Cp’M(NO)(CH2Ph’)2, isolated yields typically being 50-65%. All the bis(benzyl) nitrosyl complexes are relatively high melting (143-163-degrees-C), orange-red, diamagnetic solids that are soluble in most common organic solvents. They are all stable to air in the solid state for at least 2 months, and only solutions of the tungsten species react with O2 to produce moderate yields of the corresponding dioxo benzyl complexes, Cp’W(O)2(CH2Ph’). The spectroscopic properties of the bis(benzyl) complexes are consistent with their possessing 18-electron, monomeric Cp’M(NO)(eta-1-CH2Ph’)(eta-2-CH2Ph’) molecular structures. Variable-temperature H-1 and C-13{H-1} NMR spectra of all the compounds in CD2Cl2 establish that they are stereochemically nonrigid in solutions at ambient temperatures, the principal fluxionality involving the two benzyl ligands exchanging their modes of attachment to the metal centers. C-13 NMR spectroscopy also establishes that the low-temperature limiting structures of the complexes in solution are identical with their solid-state molecular structures. Interestingly, the tungsten bis(benzyl) complexes exhibit the more facile fluxional processes in solution, this increased nonrigidity apparently rendering the tungsten complexes more reactive to Lewis bases. Crystal structure analyses of the five bis(benzyl) nitrosyl complexes have been performed in order to establish their solid-state molecular structures. Crystals of CpMo(NO)(CH2Ph)2 (1a) are orthorhombic, Pbca, with a = 10.122 (1) angstrom