Tungsten ethylidene

This particular thiocarbenoid complex and the analogous tungsten derivative are more conveniently synthesized by an initial reaction of [Cr(CO)5 C(CH3)(OCH3) ] or [W(CO)5 C(CH3)(OCH3) ] with benzene-thiolate ion at room temperature followed by acidification with hydrochloric acid. This synthetic route has also been used to prepare a series of pentacarbonyl[(l-phenylthio)ethylidene]tungsten(0) complexes substituted in the 4-position of the phenyl rings.4... 

Pentacarbonyl[l-(phenylthio)ethylidene]tungsten(0) is an air-stable, dark-red, crystalline solid mp 76°. It can be handled in the presence of light with no decomposition. It may be stored for several months at 5°. It is soluble in aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, and other common laboratory solvents such as benzene, 1,4-dioxane, tetra-hydrofuran, chloroform, dichloromethane, and methanol it is slightly soluble in ethanol. The infrared spectrum (cyclohexane solution) shows v(CO) bands at 2065, 1980, and 1953 cm-1. The H nmr spectrum in chloroform- shows the methyl proton resonance at t6.96. Other physical properties are reported in the literature.4... 

The term alkylidene refers to carbenes, CR2 with alkyl substituents for example, MeCH=ML is an ethylidene complex but alkylidene is sometimes used as a synonym for Schrock carbene in the older literature because the first alkylidenes were of the Schrock type. There are electrophilic Fischer alkylidenes as well as nucleophilic Schrock ones, however, so the terms should be kept separate. For example, [Cp2W(=CH2)Me], and Cp2Ta(=CH2)Me are isoelectronic, but the former is electrophilic and the latter nucleophilic at the carbene carbon the net positive charge on the tungsten complex must stabilize the M(d,) levels and is therefore probably the main reason for the difference. 

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