Unexpected formation and conversion: role of substituents of 1,3-ynones in the reactivity and product distribution during their reactions with Ru3(CO)12

Abstract

The reactions of Ru₃(CO)₁₂ with alkynyl ketones R₁CCC(O)R₂ (R₁ = Et, R₂ = Me (1); R₁ = Ph, R₂ = Me (2); R₁ = n-hexyl, R₂ = Ph (3); R₁ = H, R₂ = CH₃ (4); and R₁ = C(O)OCH₃, R₂ = OCH₃ (5)) proceeds in toluene with the formation of three ruthenoles (1a–3a), four CO-inserted binuclear clusters (1b–2b, 1c and 3c), a tetranuclear cluster 4a, a binuclear cluster 5a and a cyclotrimerization product 5b. Clusters 1a–3a, 1b, 2b, 1c and 3c were isolated from the reactions of Ru₃(CO)₁₂ with two equivalents of the corresponding ketones 1–3; 4a and 5a were collected by adding 4 and 5 to Ru₃(CO)₁₂ in molar ratios of 1 : 1 and 1 : 3, respectively; 5b was obtained by adding 5 to 5a in a molar ratio of 2 : 1. All compounds were characterized by NMR, FT-IR, and MS-ESI, and most of them were structurally verified by single crystal X-ray diffraction. Although the reaction products of 1–3 and Ru₃(CO)₁₂ exhibit similar cluster frameworks of usual ruthenoles and CO-inserted binuclear clusters, the isolation of the clusters 1b–2b, 1c and 3c reveals their strong dependence on both electronic and steric effects of the substituents of the 1,3-ynones 1–3. In addition, detailed investigations suggested that the high reactivity of the terminal hydrogen atom and electron-withdrawing property of the carbonyl group in 4 play a key role in the formation of 4a, and that the structurally unusual 5a is an intermediate in the formation of 5b.