Iridium-Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols with the Liberation of Syngas

Iridium-Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols with the Liberation of Syngas:

Abstract

A new iridium-catalyzed reaction in which molecular hydrogen and carbon monoxide are cleaved from primary alcohols in the absence of any stoichiometric additives has been developed. The dehydrogenative decarbonylation was achieved with a catalyst generated in situ from [Ir(coe)₂Cl]₂ (coe=cyclooctene) and racemic 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (rac-BINAP) in a mesitylene solution saturated with water. A catalytic amount of lithium chloride was also added to improve the catalyst turnover. The reaction has been applied to a variety of primary alcohols and gives rise to products in good to excellent yields. Ethers, esters, imides, and aryl halides are stable under the reaction conditions, whereas olefins are partially saturated. The reaction is believed to proceed by two consecutive organometallic transformations that are catalyzed by the same iridium(I)–BINAP species. First, dehydrogenation of the primary alcohol to the corresponding aldehyde takes place, which is then followed by decarbonylation to the product with one less carbon atom.

Step on the syngas! An iridium catalyst promotes two transformations in the same pot by cleaving both molecular hydrogen and carbon monoxide from primary alcohols (see scheme). The reaction does not require any stoichiometric additives and tolerates a variety of functional groups.