1209-83-2Relevant academic research and scientific papers
Steric Effects. Inversion of 4,5-Disubstituted 9,10-Dihydrophenanthrenes
Cosmo, Robert,Sternhell, Sever
, p. 35 - 47 (2007/10/02)
Six 4,5-di-X-9,10-dihydrophenanthrenes (X = H, F, OCH3, Cl, CH3, CF3) were synthesized and their inversion rates were investigated by n.m.r spectroscopy.The barriers to inversion at a standard temperature (ΔG340) ranged from 120 kJ mol-1 and showed good correlation with the van der Waals radii of the interacting substituents at C4 and C5 and with the previously proposed 'apparent overlap' parameter.
Biphenyl Tricarbonylchromium Complexes. Part 8. Optical Resolutions, Chiroptical Properties, Kinetics and Absolute Chiralities of Monotricarbonylchromium Complexes of o,o'-Bridged Biphenyls
Schloegl, Karl,Werner, Andreas,Widhalm, Michael
, p. 1731 - 1735 (2007/10/02)
Chiral biphenyls and their tricarbonylchromium complexes can be conveniently resolved by medium pressure chromatography on triacetylcellulose in ethanol or ether.Thereby the mono-Cr(CO)3 exo-complexes of 9,10-dihydrophenanthrene (1) and of the corresponding o,o'-bridged ketone (3) were separated into enantiomers whereas the mixtures of the dimethylated biphenyls (2) and (4) could be separated in one run into all four stereoisomers, i.e. the enantiomers of exo- and endo-forms.The chiroptical properties of these complexes are reported.From kinetic studies based on the relative intensities of diagnostic bands in the circular dichroism spectra a barrier of ΔG ca. 90 kJ mol-1 was found for the interconversion exo endo-(2m) a (S)a around the biphenyl axis without affecting the metallocene chirality (R)m or (S)m>.From the results of the photochemical decomplexation of the optically active complexes (2m) and (4m) (to give the active ligands of known configurations) and by optical comparison with the corresponding complexes (1m) and (3m) the axial chiralities and (on the basis of general stereochemical considerations) also the metallocene chiralities were deduced.
