Issue 0, 1982

Organometallic compounds in organic synthesis. Part 12. Methods of determination of the stereochemistry of tricarbonylcyclohexa-1,3-dieneiron complexes

Abstract

The steric configuration (α- or β-) of a substituent attached to an sp3 carbon atom in tricarbonylcyclohexadieneiron complexes can be determined by 1H n.m.r. spectroscopy if both epimers are available. With only one epimer present, the most useful method involves examination of the vicinal coupling constants of hydrogens attached to sp3 carbon atoms. The β-H atoms have a vicinal coupling constant of 10–12 Hz and the corresponding α-H atoms have a value of ca. 8 Hz. The CH2 splitting patterns are indicative of stereochemistry when flanked by two vicinal protons. In some cases simplification of the spectrum by use of a paramagnetic shift reagent is necessary for evaluation. Usually δ(β-substituent) > δ(α-substituent). The CO2Me substituents show δ(β-CO2Me) > 3.63 > δ(α-CO2Me) and often, but not invariably, δ(β-H) > δ(α-H). Computer simulation confirms the expected pattern. Aromatic solvent induced shifts are not useful; 13C n.m.r. have only a limited usefulness and require both isomers; mass spectrometric fragmentation is intepretable in steric terms, but is not useful for definition. 1H N.m.r. spectra of the isomeric cations (45), (46), and the alkyl analogue (47) show indications of utility in connection with 6-H, but more examples are needed. The vicinal coupling of CH2 seems to be at present the only reliable method for the assignment of configuration in neutral diene complexes.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 1, 1982, 1745-1753

Organometallic compounds in organic synthesis. Part 12. Methods of determination of the stereochemistry of tricarbonylcyclohexa-1,3-dieneiron complexes

B. M. R. Bandara, A. J. Birch and W. D. Raverty, J. Chem. Soc., Perkin Trans. 1, 1982, 1745 DOI: 10.1039/P19820001745

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Spotlight

Advertisements