An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

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.