SELECTIVE HOMOGENEOUS PRODUCTION OF ALKYL FORMATE FROM CO AND ALCOHOL USING METAL-CARBONYL ALKOXIDE CATALYST SYSTEMS
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The homogeneously catalyzed production of alkyl formates from alcohols and carbon monoxide by transition metal carbonyl complexes in the presence of alkali metal alkoxides is reported. A significant increase in the number of turnovers of this reaction by Group VI metal carbonyl/alkoxide catalysts over the alkali metal alkoxide-catalyzed process is due to the dual role of the metal carbonyl to provide a more electrophilic source of carbon monoxide and to promote the removal of trace water impurities through water-gas shift chemistry. The key intermediate in the proposed catalytic cycle is a short-lived metallo-ester derivative which at elevated temperatures (100 C) is protonated by alcohol to afford the alkyl formate product. The reactivity of the metal carbonyl with alkali metal alkoxides is sharply affected by the solvent system employed, e.g., tetrahydrofuran is much more effective than alcohols. Similarly, reactions of triruthenium dodecacarbonyl with alcohols in the presence of alkoxides and CO have led to the production of alkyl formates. In addition, a convenient route to 13CO-enriched Ru3(CO)12 is achieved in the presence of trace quantities of alkoxides. In the absence of CO, XRu3(CO)10Y (X = H or OR; Y = OR) derivatives are produced by direct reaction of Ru3(CO)12 with alcohols. 1987.