Studies on the mechanism for stereoisomerization of 1-zirconacyclopent-3-yne compounds |
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Authors: | Noriyuki Suzuki Kosuke Nishimura Nozomu Ohara Masayoshi Nishiura Yoshiro Masuyama |
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Institution: | 1. Department of Materials and Life Sciences, Faculty of Science and Technology, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan;2. Organometallic Chemistry Laboratory, RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan |
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Abstract: | The stereoisomerization of 2,5-disubstituted 1-zirconacyclopent-3-yne compounds, stable five-membered cycloalkynes, has been studied with regard to the mechanism. The bimetallic complex of 1,4-bis(trimethylsilyl)butatriene was synthesized and structurally characterized, although it seems unimportant for the stereoisomerization reactions. The isomerization of trans-1,1-bis(η5-cyclopentadienyl)-2,5-bis(trimethylsilyl)-1-zirconacyclopent-3-yne 2a into the cis-form in benzene-d6 solution were observed using 1H NMR spectroscopy at 50 °C in various concentrations. The reaction was first order with respect to trans-2a. This ruled out the possibility that a bimetallic complex was responsible for the isomerization. A kinetic isotope effect was observed (kH/kD = 1.8), suggesting that C–H activation is involved in the rate-determining step. A mechanism via hydrogen elimination from the complex of η4-π,π-coordination mode is proposed. |
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