VIBRATIONAL-SPECTRA AND STRUCTURE OF STAIRCASE CARBONYL PI-COMPLEXES OF TRANSITION-METALS .2. ROTATIONAL-ISOMERISM

FTIR spectra have been studied for ''staircase'' cyclopentadienyl complexes containing two or three metal carbonyl fragments bound by the metal-carbon bond Cp(CO)(2)Fe-CpmMn(Co)(3) (1), Cp(CO)(2)Fe-CpmFe(CO)(2)CH(2)Ph (2), Cp(CO)(2)Fe-Cpm(CO)(2)Fe-CpmMn(CO)(3) (3), Cp(CO)(2)Mo-Cpm(CO)(2)Fe-CpmMn(CO)(3) (4), Cp(CO)(3)W-Cpm(CO)(2)Fe-CpmMn(CO)(3) (5), Cp(CO)2Fe-Cpm(CO)(2)Fe-BmCr(CO)(3) (6), Cr(CO)(3)Bm-CpmFe(CO)(2)CH(2)Ph (7), where Cp = eta(5)-C5H5, Cpm = eta(1):eta(5)-C5H4, Bm = eta(1):eta(6)-C6H5. Temperature-dependent FTIR spectra were measured in n-pentane solutions over a wide temperature range and in the low-temperature solid matrices of argon and nitrogen. Rotamers, formed due to rotation about the metal-carbon sigma-bond, were found in solutions and matrices. A molecular mechanics calculation of 1 proved the possibility of such rotation.