Chiral ansa metallocenes with Cp ring-fused to thiophenes and pyrroles: Syntheses, crystal structures, and isotactic polypropylene catalysts

Syntheses, crystal structures, and polymerization data for new isospecific metallocenes (heterocenes) having cyclopentenyl ligands b-fused to substitu ted thiophenes (Tp) and pyrroles (Pyr) are reported. The C-2-and C-1-symmet ric heterocenes are dimethylsilyl bridged, have methyl groups adjacent to t he bridgehead carbon atoms, and have aryl substituents protruding in the fr ont. rac-Me2Si(2,5-Me-2-3-Ph-6-Cp[b]Tp)(2)ZrCl2/MAO (MAO = methyl alumoxane s) is the most active metallocene catalyst for polypropylene reported to da te. rac-Me2Si(2,5-Me-2-3-Ph-6-Cp[b]Tp)(2)ZrCl2 and rac-Me2Si(2,5-Me-2-1-Ph- 4-Cp[b]Pyr)(2)ZrCl2 have the same structure, and the former is 6 times more active, produces half the total enantiofacial errors, and is 3.5 times les s regiospecific in propylene polymerizations at the same conditions. rac-Me 2Si(2-Me-4-Ph-1-Ind)(2)ZrCl2/ MAO is 3.5 times lower in activity than rac-M e2Si(2,5-Me-2-3-Ph-6-Cp[b]Tp)(2)ZrCl2 catalyst. and while the former is the more stereospecific and the less regiospecific, the sum of these two enant ioface errors is the same for both species. Fine-tuning the heterocene ster ics by changing selected hydrogen atoms on the ligands to methyl groups inf luenced their catalyst activities, stereospecificites, regiospecificites, a nd isotactic polypropylene (IPP) M-w. Thus, both substituting a hydrogen at om adjacent to the phenyl ring with a methyl group on an azapentalenyl liga nd system and replacing one and then two hydrogens on the phenyl ring with methyls on thiopentalenyl ligands provided increased polymer T, and M, with increasing ligand bulk. Polymer molecular weights are sensitive to and inv ersely proportional to MAO concentration, and the catalyst activities incre ase when hydrogen is added for molecular weight control. The polymer T, val ues with the thiopentalenyls as TIBAL/[Ph3C][B(C6F5)(4)] systems were highe r than with MAO as catalyst activator. A racemic C-1, pseudomeso complex wi th a hybrid dimethylsilyl-bridged 2-Me-4-Ph-1-Ind/2,5-Me-2-4-Ph-1-Cp[b]Pyr ligand produced the first sample of IPP with all the steric pentad intensit ies fitting the enantiomorphic site control model. Speculative mechanistic considerations are offered regarding electronic effects of the heteroatoms and steric effects of the ligand structures, the preferred phenyl torsion a ngles, and anion effects.