Infrared spectra and methyl group properties in dicyclopentadienyldimethyl-titanium(IV), -zirconium(IV) and -hafnium(IV)

Abstract

Infrared spectra are reported for CH 3-, CD 3- and CHD 2-substituted Cp 2MMe 2 (Cp = η 5-C 5H 5, M = Ti, Zr, Hf) in CCl 4 solution. The isolated CH stretching frequencies, ν( isCH), measured in the CHD 2 species are lower than any previously observed in methylmetal compounds and the methyl CH bonds in Cp 2HfMe 2 are predicted to be the longest and weakest such bonds yet to have been characterised by this method. The methyl groups in Cp 2ZrMe 2 and Cp 2HfMe 2 have all three CH bonds equal, but in Cp 2TiMe 2 each methyl group contains two strong CH bonds and one weak one. This may be the result of steric overcrowding effects around the relatively small titanium atom. The symmetric deformation δ s(CH 3) rises with increasing atomic number of the metal atom, the reverse of the trend observed for methyl derivatives of Main Group elements.