INDENYL AND FLUORENYL TRANSITION METAL COMPLEXES XIII. DETERMINATION OF GEOMETRIC CONFIGURATION OF (9-SUBSTITUTED FLUORENES)CHROMIUM TRICARBONYL COMPLEXES BY ASIS-EFFECT IN 1H NMR SPECTRA

Article abstract of DOI:10.1016/0022-328X(85)88051-7

A method to determine the geometric configuration of chromium tricarbonyl complexes of 9-substituted fluorenes (η⁶-9-RC13H9)Cr(CO)3 which allows one to distinguish between exo-isomers (IIIa-e) and endo-isomers (Va-e) is proposed; a, R = CH3; b, R = CH2C6H5, c, R = D; d, R = t-C4H9; e, R = C6H5.This method is based on measuring chemical shifts induced in 1H NMR spectra by aromatic solvents when passing from CDCl3 to C6D6 solutions (ASIS effect).The validity of the criterion is confirmed by X-ray analysis of IIIb.Exo-isomers, IIIb,c were obtained by alkylation of the η⁶-fluorenylchromium tricarbonyl anion (I) with the corresponding halides RX in tetrahydrofuran (THF) at low temperature.Endo-isomers (Vb,c) have been obtained by alkylation of the η⁵-fluorenylchromium tricarbonyl anion (II) with subsequent thermal rearrangement of intermediate ?-organometal derivatives (IV) without their isolation.Endo-isomers, Vd,e have been formed by stereoselective protonation of substituted complex anions <(η⁶-9-RC13H8)Cr(CO)3>^-.