Synthesis and properties of the pentacarbonylmetalates of the group 6 metals

Article abstract of DOI:10.1021/om00127a009

Reduction of the amine complexes [M(CO)₅(NMe₃)] (M = Cr, Mo, W) with sodium naphthalenide in THF provides a convenient route to the pentacarbonylmetalates of the group 6 metals in an innocuous solvent. The synthetic utility of the method has been demonstrated by reaction of the dianions with Ph₃SnCl to give [NEt₄][M(CO)₅SnPh₃] (M = Cr, Mo, W) in 76, 92, and 62% yield, respectively, after counterion exchange. The sodium salts of [Mo(CO)₅]^2- and [W(CO)₅]^2- cannot be handled in the solid state but can be readily separated from the NMe₃ and C₁₀H₈ byproducts of the reduction. Naphthalenide reduction has also been used to prepare [W(CO)₅]^2- with Li⁺ and K⁺ counterions, and crystalline salts of [W(CO)₅]^2- and [Mo(CO)₅]^2- have been prepared by adding pentamethyldiethylenetriamine to Li₂[W(CO)₅] and a cryptand (K-2.2.1) to Na₂[M(CO)₅] (M = Mo, W). Crystals of the encrypted sodium salts are indefinitely stable, and a brief account is given of an X-ray diffraction study which establishes a slightly distorted trigonal-bipyramidal structure for the tungsten anion in the solid state. The IR spectra of the [Na(K-2.2.1)]⁺ salts in CH₃CN exhibit the two band patterns expected in the carbonyl stretching region if the anions have D_3h structures without counterion contact ion pairing, but ion pairing has a marked effect on solution spectra of simple alkali-metel salts of [W(CO)₅]²⁺. The Li⁺ salt exhibits isocarbonyl absorptions indicating interaction with two of the equatorial carbonyls, while Na₂[W(CO)₅] and K₂[W(CO)₅] have high-energy carbonyl stretches indicative of contact ion pairing with direct M-W interaction.