Reduction of the amine complexes [M(CO)6( 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)BSnPh3] (M = Cr, Mo, W) in 76, 92, and 62% yield, respectively, after counterion exchange. The sodium salts of [Mo(CO)B]2~a nd [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)B]2" with Li+ and K+ counterions, and crystalline salts of [W(CO)5]2' and [Mo(CO)B]2~h ave been prepared by adding pentamethyldiethylenetriamine to Li2[W(CO)6] and a cryptand (K-2.2.1) to Na2[M(CO)s] (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 Dy, structures without counterion contact ion pairing, but ion pairing has a marked effect on solution spectra of simple alkali-metal salts of [W(CO)6]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.
1053protonated carbonyl compounds can relax to their ground states. In this context, the photoreactions of 3 and 4 described here can perhaps be better compared to those of 1,3-dienes rather than conjugated enones.'Secondly, it is of interest to consider the mechanism of the thermal isomerization about the C -0 bonds. Several possibilities can be eliminated from consideration. Thus, the minimal effect of introducing a methyl group a t C3 on the rate of isomerization about the C-0 bond renders a direct rotation process unlikely as this involves a large change in the charge distribution in the system. The absence of any appreciable medium effect eliminates any base addition route, while the substantially different activation energies for isomerism about the C-0 and C2-C3 bonds rules out the intervention of a common 0-methyloxetium ion in these two rearrangements.Rather, it appears that the most likely process occurring is an inversion or "lateral shift" mechanism8 as has also been found with the isoelectronic aldimines and k e t i m i n e~.~ Acknowledgment.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.