Insight into Binding of Alkanes to Transition Metals from NMR Spectroscopy of Isomeric Pentane and Isotopically Labeled Alkane Complexes
- 1 March 2005
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 127 (12) , 4134-4135
- https://doi.org/10.1021/ja044208m
Abstract
Alkane complexes of the type Cp‘Re(CO)2(alkane) (Cp‘ = cyclopentadienyl or (isopropyl)cyclopentadienyl; alkane = isotopomers of n-pentane and cyclopentane) have been characterized using NMR spectroscopy following photolysis of Cp‘Re(CO)3 in the appropriate alkane at 163−193 K. In the case of n-pentane, three different complexes are observed corresponding to binding of the three different types of carbon in this alkane. ROESY NMR experiments indicate that these isomeric complexes are slowly interconverting intramolecularly at 173 K. The order of the energetically preferred site of coordination is methylene (C2) ≈ central methylene (C3) > methyl (C1) but with a spread of CH2D > CHD2. This suggests that the alkane coordinates in an η2-C,H fashion with a rapid exchange of bound hydrogen or deuterium within a methyl or methylene group, and that binding of a hydrogen atom is preferred over a deuterium by an amount of 0.23 ± 0.03 kcal mol-1.Keywords
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