Electronic and steric effects of substituents in 1,3-diphenylprop-2-yn-1-one during its reaction with Ru3(CO)12

Abstract

Thermal reaction of Ru₃(CO)₁₂ with alkynyl ketones PhCCC(O)R (RPh (1); 2-Cl-Ph (2); 4-NO₂-Ph (3); 2-NH₂-Ph (4); and 2-CH₃COO-Ph (5)) proceeds in toluene with the formation of Ru₃(CO)₉(μ-CO)(η⁴-triruthenium) derivatives (1a–5a), Ru(CO)₃(η⁴-ruthenole) derivatives (1b–4b, 1c–5c and 4d) and cyclotrimerization products (1e–2e and 1f–3f). Compounds 1a–5a were isolated from the reaction of Ru₃(CO)₁₂ with one equivalent of 1–5, respectively. Ruthenoles 1b–3b and 1c–3c were collected by adding 1–3 to the corresponding 1a–3a in a molar ratio of 1 : 1. Cyclotrimerization products 1e–2e and 1f–3f were obtained when 1–3 were added to their corresponding 1b–2b and 1c–3c, respectively. 4b, 4c and 4d were afforded during the reaction of 4 with 4a, but only 5c was collected during the reaction of 5 with 5a. All compounds were characterized by NMR, FT-IR, and MS-ESI and most of them were structurally confirmed by single crystal X-ray diffraction. The results suggest that electronic and steric effects of the substituents in the phenyl ring of 1,3-diphenylprop-2-yn-1-one play important roles in regulating the reaction pathways. An electron-withdrawing group is beneficial to the formation of b, c and further formation of e and f; an electron-donating group favors the production of ruthenoles b, c and d, but disfavors the formation of e and f; a substituent with large steric-hindrance prefers only the formation of c.