New Low-Temperature NMR Studies Establish the Presence of a Second Equatorial−Apical Isomer of [(R,S)-Binaphos](CO)2RhH

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• 作者：Dante A. Castillo Molina ; Charles P. Casey ; Imke Mller ; Kyoko Nozaki ; Christoph Jkel
• 刊名：Organometallics
• 出版年：2010
• 出版时间：August 9, 2010
• 年：2010
• 卷：29
• 期：15
• 页码：3362-3367
• 全文大小：830K
• 年卷期：v.29,no.15(August 9, 2010)
• ISSN：1520-6041

文摘

The important enantioselective hydroformylation catalyst [(R,S)-Binaphos](CO)₂RhH has been reexamained by low-temperature NMR spectroscopy. Both p>1p>H and p>31p>P NMR spectroscopy at −90 °C allow direct observation of a mixture of two apical−equatorial chelates. The major chelate, 1_eq,ap, was shown to have an equatorial phosphine and an apical phosphite. Its structure was unambiguously assigned using low-temperature p>31p>P NMR spectroscopy with selective decoupling of aromatic hydrogens but not of the rhodium hydride, which showed a 225 Hz trans phosphite to RhH coupling. The equilibrium constant for [1_eq,ap]/[1_ap,eq] was determined over a wide temperature range.