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Ortin, Y,Ahrenstorf, K,O'Donohue, P,Foede, D,Muller-Bunz, H,McArdle, P,Manning, AR,McGlinchey, MJ
2004
May
Journal Of Organometallic Chemistry
An NMR study of the rotational barriers in cobalt-stabilized carbocations: X-ray crystal structures of (eta(4)-C4Ph4)CO-(eta(5)-C5H4R), where R is CH3C = O, CH = O, CH(Bu-t)OH
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cyclobutadiene-cobalt complexes metal-stabilized carbocations NMR X-ray crystallography 3 DIFFERENT CHIRALITIES CARBONIUM-IONS DIFERROCENYLMETHYLIUM ION FERROCENYLCARBONIUM IONS MOLECULAR-STRUCTURE COUPLING-CONSTANTS TRIPODAL ROTATION CHEMICAL-SHIFTS COMPLEXES CATIONS
689
1657
1664
Treatment of the aldehyde (eta(4)-C4Ph4)Co(eta(5)-C5H4-CH=O) (4b) with tert-butyllithium or phenyllithium yields the secondary alcohols (eta(4)-C4Ph4)CO(eta(5)-C5H4-CH(R)OH), where R = tert-butyl (5) or phenyl (6). Protonation of 5 and 6 at -80 degreesC furnishes the deep purple, cobalt-stabilized cations, 7 and 8, respectively, both of which exhibit restricted rotation about the external C5H4-CHR+ linkage on the NMR time-scale. These data indicate a minimum value for the barrier to rotation of 15 kcal mol(-1), but it is certainly much higher, indicating a considerable degree of C-C double bond character. X-ray crystal structures of 4b, 5 and also of the ketone (eta(4)-C4Ph4)Co(eta(5)-C5H4-C(=O)CH3 (4a) are reported. The secondary alcohol 5 exhibits disorder in the solid state because of the presence of diastereomers as a consequence of the stereogenic center at the alpha-carbon and the clockwise or anticlockwise propeller orientations of the tetraphenylcyclobutadiene ligand. (C) 2004 Elsevier B.V. All rights reserved.
DOI 10.1016/j.jorganchem.2004.02.021
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