Tetraethylammonium fluoride as a convenient source of hydroxide ions in acetonitrile solution. Its reaction with [Fe(η-C5H5)(CO)2(L)]+ salts and [Fe(η-C5H5)(CO)2X] complexes

In acetonitrile solution, [Et4N]F·2.5H2O acts as a convenient source of hydroxide ions for use in organometallic chemistry. Within 20 min, at room temperature, it converts [Fe(η-C5H5)(CO)2(L)]+ salts (molar ratio 1:1) to [Fe2(η-C5H5)2(CO)3(L)] (L=CO, CNMe and PPh3) complexes in good yields with the evolution of CO2 and, when L=CO, CO. Under the same conditions it converts [Fe(η-C5H5)(CO)2Cl] (molar ratio 1:2 or, better, 1:3) to [Fe2(η-C5H5)2(CO)3(NCMe)]. Other [Fe(η-C5H5)(CO)2X] (X=Br or I) react only slowly to give [Fe2(η-C5H5)2(CO)4]. Other routes to [Fe2(η-C5H5)2(CO)3(PPh3)] and [Fe2(η-C5H5)2(CO)3(NCMe)] involve prolonged photolysis and give impure or non-isolable products. This route gives them as analytically pure solids in high yields. It is proposed that in acetonitrile solutions, the F− ions react with H2O to give HF and OH− in a reaction driven by the strength of the HF bond and the lack of anion solvation in acetonitrile. The OH− ions then attack the [Fe(η-C5H5)(CO)2(L)]+ cations at CO with the evolution of CO2 to give the [Fe(η-C5H5)(CO)(L)]− which subsequently displaces L from the cations.