Cyclopentadienyls MeCp

In the case of propylene polymerisation with class III catalysts based on rac.-dimethylsilylenebis[l-(3-methylcyclopentadienyl)]zirconium dichloride [rac.-Me2Si(MeCp)2ZrCl2] (Table 3.1) or rac.-dimethylsilylenebis[l-(3-methyl-cyclopentadienyl)]hafnium dichloride [rac.-Me2Si(MeCp)2HfCl2] as a procatalyst, isoblock polypropylene is obtained [132]. 

By reacting LaCl3 with excess Na(MeCp) in THF gives (MeCp )3Ln which crystallizes as a tetramer. The structure differs from that of Cp3Ln. The methyl substituent on the cyclopentadienyl ring forces the mode of coordination from an rj2 rj5 polymer for Cp3Ln to a t]1 ri5 tetramer for (MeCp)3Ln. The geometry of the tetrameric (MeCp)3Ln is nearly identical with the compounds of Ce and Nd. The structure [46] of [(MeCp)3Ce]4 is shown in Fig. 6.4. 

Compounds containing one or more cyclopentadienyl-type ligands are much more robust. (Throughout this section, C5H5 is abbreviated to Cp CsMes is abbreviated to Cp C5H4.CH3 is MeCp.)... 

Bis(r -cyclopentadienyl)titanium pentasulfide was prepared first by Samuel and Schmidt from TiCp2Cl2 (Cp = cyclopentadienyl) and polysulftde salts. It can also be prepared from the reaction of TiCp2(CO)2 or TiCp2(CH2R)2 with elemental sulfur. The method presented here is a modification of Kopf s procedure and is equally applicable to the Cp, MeCp, and i-PrCp ((-Pr = isopropyl) derivatives. This reaction has been successfully conducted at 40 times... 

He-I and He-ll photoelectron spectra of (MeCp)3Pr and (MeCp)jDy show the first bands between 7 and 8.5 eV, which are assigned to ionization from the cyclopentadienyl ej orbitals. Ionizations for the 5f-electrons are not identified (Green et al., 1981). 

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