Conversion of Allylic Alcohols to Carbonyl Compounds Catalyzed by Alkoxy-Bridged Dinuclear Areneruthenium Complexes

Abstract

Visible light irradiation of an azobenzene-bridged dinuclear ruthenium complex ligated by a η6-arene group having a pendant alkoxy ligand, [Ru2{η6:η1:μ-C6H5(CH2)3O}2(μ-C6H5NNC6H4OMe)]BF4, led to generation of an active species capable of catalyzing isomerization of allyl alcohols to the corresponding carbonyl compounds under mild conditions. Treatment of the chloro-bridged dinuclear complex [Ru2{η6:η1:μ-C6H5(CH2)3O}2(μ-Cl)]BF4 with 1 equiv AgOTf or that of the methoxy-bridged complex [Ru2{η6:η1:μ-C6H5(CH2)3O}2(μ-OMe)]BF4 with HOTf also resulted in generation of catalyst for the isomerization, while these dinuclear complexes themselves were inactive as the isomerization catalyst. Reaction of the hydride-bridged dinuclear complex [Ru2{η6:η1:μ-C6H5(CH2)3O}2(μ-H)]BF4 with methyl vinyl ketone gave the allyloxy-bridged dinuclear complex [Ru2{η6:η1:μ-C6H5(CH2)3O}2(μ-OCHMeCHCH2)]BF4 rather sluggishly, while the same reactants in the presence of an equimolar amount of HOTf rapidly gave CH3COCH2CH3 and the triflate complex [Ru2{η6:η1:μ-C6H5(CH2)3O}2(μ-OTf)]BF4. A mechanistic scheme for the isomerization of allyl alcohols involving the dinuclear acceptor [Ru2{η6:η1:μ-C6H5(CH2)3O}2]2+ as a key species has been discussed.