MOESSBAUER STUDIES ON FERROCENE COMPLEXES. X. STERIC AND POLAR FACTORS IN FERROCENYL KETONES AND CARBENIUM IONS

Article abstract of DOI:10.1016/S0022-328X(00)99481-6

A series of new ferrocenyl alcohols of the types and FcCH(OH)R where R=1-adamantyl, 9-anthracyl and mesityl have been synthesised.The 1H NMR spectra of these carbenium ions derived from these alcohols have been measured and discussed, together with those of the ketone precursors in CF3CO2H.Moessbauer spectra were obtained for the above derivatives in frozen solid solution in CF3CO2H.For the protonated ketones only small differences in quadrupole splitting (QS) were observed as the structure of the aryl or alkyl groups was varied, all having QS values of 0.23-0.36 mm s^-1 lower than that of ferrocene.For the aryl carbenium ions the enhanced QS correlated reasonably well with Hammett ?⁺ values (r=0.953, 7 points).No systematic trends in QS were observed for the o, m and p series of substituents.The more sterically hindered carbenium ions show a significant lowering of QS due to the Cp rings twisting out of the carbenium ion sp² plane.In the case of the anthracyl derivative, no appreciable change in QS occurred on forming the carbenium ion indicative of stabilisation of the ion by the anthracyl rather than the ferrocenyl moiety.The different modes of stabilisation of the protonated ketones and the carbenium ions are discussed.