Carbene pentacarbonyl Complexes of Chromium and Tungsten

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(methoxymethylcarbene)chromium(0) precipitates from the concentrated solution when the solution is placed in a Dry Ice-acetone slush (—78). The complex may be recrystallized from the minimum amount of a 1 1 mixture of a n-hexane-diethyl ether purity was confirmed by its mp. Yield is 2.0 g (35%). 

Pentacarbonyl(methoxymethylcarbene)chroniiuin(0) is a dull-yellow, crystalline solid mp 34°. It slowly decomposes in the solid state at room temperature in air, but may be stored at 5° for a few days before appreciable decomposition is observed. 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, tetrahydrofuran, chloroform, dichloromethane, and methanol, and is slightly soluble in ethanol. The infrared spectrum (cyclohexane solution) has v(CO) bands at 2065, 1985, 1965, and 1950 cm-1. The H nmr spectrum in chloroform-d shows the methoxy proton resonance at t6.15 and the methyl proton resonance at t7.70. Other physical properties are reported in the literature.6,7 

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