Biphenyl tricarbonylchromium complexes. Part 7. Preparation, static and dynamic stereochemistry of mono- and bis-tricarbonylchromium complexes of o,o′-bridged biphenyls
- 1 January 1983
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 1
- p. 1723-1729
- https://doi.org/10.1039/p19830001723
Abstract
Mono- and bis-Cr(CO)3 complexes of 9,10-dihydrophenanthrene (1) and the corresponding ketone (3)(with a CH2COCH2 bridge) and their o,o′-dimethyl derivatives (2) and (4) have been prepared. Compounds (1) and (3) give exo-complexes whereas (2a) and (4) afford a 50:50 mixture of exo- and endo-isomers separable by medium pressure chromatography. According to lanthanide induced shift n.m.r. spectroscopy (LIS) complexation does not change the torsional angles of the biphenyl system to a significant degree. Isomeric ratios and relative (exo, endo) configurations were determined from 1H n.m.r. spectra. The exoendo equilibria are determined by steric interactions between bridge, ring (methyl) protons and the Cr(CO)3 groups. Kinetic studies on the interconversion rate of the isomeric monocomplexes of dimethyldihydrophenanthrene (2) revealed that complexation decreases the inversion barrier from ca. 97 [in (2)] to ca. 91 kJ mol–1(in the complex).Keywords
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