Syntheses of disubstituted, tetramethylethanediyl-bridged titanocene derivatives (CH3)4C2(1-CsHr3-RhTiCI2' with R = t-butyl, trimethylsilyl, isopropyl, a,a-dimethylbenzyl and I-phenylcyc1ohexyl, by reductive coupling of the appropriately substituted 6,6-dimethylpentafulvenes with Mg/CCl 4 and reaction of the resulting di-Grignard compounds with TiC1 3-3THF are described along with those of several zirconium analogues. The reaction sequence in each case gives, together with the desired racemate, comparable amounts of the corresponding meso-configurated complex. The NMR data for the racemic and meso diastereomers of these compounds and crystal structures of one meso and several racemic representatives are reported.
The NMR signals of cyc10pentadienyl ring protons and C atoms in ansa-metallocene derivatives of general type (CH3)4C2(CsH4hM(X,L)n' with a 16-electron configuration, i.e. with MX n = TiF2' TiCI 2 , TiBr2' TiI2 or Ti(CH3h, and with an 18-electron configuration, i.e. with MLn = Ti(COh, Ti(P(CH 3 hh, Cr(CO) or Fe, have been assigned to the a-and /1-ring positions by nuclear Overhauser effect and selective decoupling studies. Whereas the a-proton resonances appear at higher fields than those for the /1-protons in all the complexes with the 16..:electron configuration, the opposite is the case for the 18-electron ansa-metallocene derivatives studied. * For part XIX see ref. 3.
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