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

Visible light irradiation of an azobenzene-bridged dinuclear ruthenium complex ligated by a η 6 -arene group having a pendant alkoxy ligand, [Ru 2 {η 6 :η 1 :μ-C 6 H 5 (CH 2 ) 3 O} 2 (μ-C 6 H 5 N=NC 6 H 4 OMe)]BF 4 , 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 [Ru 2 {η 6 :η 1 :μ-C 6 H 5 (CH 2 ) 3 O} 2 -(μ-Cl)]BF 4 with 1 equiv AgOTf or that of the methoxy-bridged complex [Ru 2 {η 6 :η 1 :μ-C 6 H 5 -(CH 2 ) 3 O} 2 (μ-OMe)]BF 4 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 [Ru 2 {η 6 :η 1 :μ-C 6 H 5 (CH 2 ) 3 O} 2 (μ-H)]BF 4 with methyl vinyl ketone gave the allyloxy-bridged dinuclear complex [Ru 2 {η 6 :η 1 :μ-C 6 H 5 (CH 2 ) 3 O} 2 -(μ-OCHMeCH=CH 2 )]BF 4 rather sluggishly, while the same reactants in the presence of an equimolar amount of HOTf rapidly gave CH 3 COCH 2 CH 3 and the triflate complex [Ru 2 {η 6 : η 1 :μ-C 6 H 5 (CH 2 ) 3 O} 2 (μ-OTf)]BF 4 . A mechanistic scheme for the isomerization of allyl alcohols involving the dinuclear acceptor [Ru 2 {η 6 :η 1 :μ-C 6 H 5 (CH 2 ) 3 O} 2 ] 2 + as a key species has been discussed.