Synthesis and Reactivity of Cyclohexadienyl-and o-Xylylenetricarbonylmanganese Complexes Obtained from the Deprotonation of [Mn(η⁶-arene)(CO)₃]⁺ Salts

Following deprotonation of [Mn(η⁶-C₆Me₆)(CO)₃]⁺ with K(O^tBu) to give the known exomethylene cyclohexadienyl complex, a second deprotonation was accomplished using the dual base system K(O^tBu)/KH in THF. The product was the anionic o-xylylene complex K{Mn[η⁴-C₆Me₄(CH₂)₂](CO)₃}. The cyclohexadienyl complex from a single deprotonation of [Mn(η⁶-o-xylene)(CO)₃]⁺ was stable only in solution at room temperature, but direct double deprotonation with K(O^tBu)/KH gave the anionic o-xylylene complex K{Mn[η⁴-C₆H₄(CH₂)₂] (CO)₃} as a thermally stable solid. Deprotonation of [Mn(η⁶-toluene)(CO)₃]⁺, [Mn-(η⁶-C₆H₅Et) (CO)₃]⁺, and [Mn-η⁶-C₆H₅-i-Pr)(CO)₃]⁺ salts with excess K(O^tBu) gave the isolable cyclohexadienyl complexes [η⁵-C₆H⁵(CH₂)]Mn(CO)₃, [η⁵-C₆H₅(CHCH₃)Mn(CO)₃, and [η-C₆H₅(CMe₂)Mn(CO)₃, respectively. All deprotonation products were air and moisture sensitive. Reaction of [η⁵-C₆H₅(CH₂)]Mn(CO)₃ with HPF₆ and Br₂ yielded [Mn(η⁶-toluene)(CO)₃]⁺ and {Mn[(η⁶-C₆H₅(CH₂Br)](CO)₃)}⁺, respectively. The anionic o-xylylene complexes gave crystalline solids with ether solvents such as 1,2-dimethoxyethane, diglyme, and dioxane. Mono-and dialkylation of [η⁵-C₆Me₅(CH₂)]Mn(CO)₃ and K{Mn[η⁴-C₆Me₄(CH₂)₂](CO)₃} with CF₃SO₃CH₃ gave the [Mn(η⁶-C₆Me₅Et)(CO)₃]⁺ and [Mn(η⁶-1,2-C₆Me₄Et₂)(CO)₃]⁺ salts, respectively. Attempted alkylation of K{Mn[η⁴-C₆H₄(CH₂)₂](CO)₃)} in a similar fashion gave unidentified solids. Treatment of the cyclohexdienyl or o-xylylene complexes with molecular oxygen gave only the parent hydrocarbons, hexamethylbenzene or o-xylene, as the isolated organic products.