Haptotropic Shift of [5]Cumulenes in Zirconocene Complexes and Effects of Steric Factors

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• 作者：Noriyuki Suzuki ; Takao Yoshitani ; Shota Inoue ; Daisuke Hashizume ; Hajime Yoshida ; Meguru Tezuka ; Keisuke Ida ; Sayoko Nagashima ; Teiji Chihara ; Osamu Kobayashi ; Shinkoh Nanbu ; Yoshiro Masuyama
• 刊名：Organometallics
• 出版年：2014
• 出版时间：October 13, 2014
• 年：2014
• 卷：33
• 期：19
• 页码：5220-5230
• 全文大小：644K
• ISSN：1520-6041

文摘

Zirconium complexes of some [5]cumulene derivatives were studied for their variable coordination modes and haptotropic shifts. Some [5]cumulene compounds reacted with zirconocene(II) species to afford 1-zirconacyclopent-3-yne complexes that have five-membered cycloalkyne structures. Only a few [5]cumulene compounds afforded 畏²-coordinated complexes in the presence of neutral ligands such as trimethylphosphine and tert-butyl isocyanide. Interconversion between the five-membered structure and the 畏²-complex was observed. Investigation of [5]cumulene derivatives of various cycloalkylidene moieties indicated that the 畏²-complex was preferred when the [5]cumulene has bulkier substituents. A [5]cumulene with 2,2,6,6-tetramethylcyclohexylidene groups much preferred the 1-zirconacyclopent-3-yne structure to 畏²-coordination. In sharp contrast, the 畏²-coordinated complex was favored for a [5]cumulene with 2,2,7,7-tetramethylcycloheptylidene groups in the presence of PMe₃. Small differences in steric environments caused totally different reactivity in [5]cumulene complexes. DFT calculations on the formation enthalpy were consistent with the experimental results, although that cannot fully rationalize the difference.