exo,exo-Bis(isodicyclopentadienyl)titanium and -zirconium Dichlorides: Conformational Characterization of the Homogeneous Ziegler Catalyst Precursors in Solution

Conformational Analysis of Nonbridged Bent Metallocene Ziegler-Catalyst PrecursorsDetection of the Third Torsional Isomer

“…In this study the conformational analysis of the 1-substituted bis(indenyl)zirconocene dichloride complexes was carried out by dynamic 1 H NMR spectroscopy. We had previously observed that the rapid rotation about the zirconium-Cp vector in bis(tetrahydroindenyl)zirconocene dichloride complexes exhibiting bulky secondary alkyl substituents at their indenyl 1-positions could be “frozen” on the 1 H NMR time scale using a sufficiently high field NMR spectrometer. ,, Typically, the corresponding (1-neomenthyl-4,5,6,7-tetrahydroindenyl)zirconium rotational activation barrier was determined at Δ G ⧧ (200 K) ≈ 11 ± 0.5 kcal mol -1 . The here presented series of investigation has now revealed that the analogous bis(1-terpenylindenyl)ZrCl 2 systems exhibit similar barriers of η 5 -indenyl-zirconium rotation; their conformational analysis can thus be carried out by simply “freezing” the ligand-metal rotation at low temperature on the NMR time scale.…”

Some New exo,exo-Bis(isodicyclopentadienyl)titanium and -zirconium Dichloride Derivatives: Synthesis, Characterization, and Evaluation as Propene Polymerization Catalysts

“…In the case of suitably substituted group 4 metallocenes, three different favored conformations may be observed in solution . In the case of the diisodicyclopentadienyltitanium and -zirconium complexes, these could be described as follows: the rotamer characterized by the localization of the two norbornyl groups outside of the Cl−M−Cl angle is termed the bis-lateral (anti) conformation and exhibits C 2 symmetry. The bis-central (syn) conformation with C 2 v symmetry is adopted when each norbornane segment is inside of the Cl−M−Cl angle.…”

“…For the isodicyclopentadienyl ligand, group 4 metals can be selectively coordinated to the diastereotopic exo or endo faces, respectively, by carefully selecting the experimental conditions . In the presence of methylalumoxane, some of these complexes exhibit interesting activity and selectivity as homogeneous Ziegler−Natta catalysts . It was demonstrated by dynamic NMR spectroscopy 3 that exo,exo -bis(isodicyclopentadienyl)titanium dichloride exhibits a chiral C 2 -symmetric structure in solution that is characterized by a bis-lateral (anti) orientation of the annulated bicyclo[2.2.1]heptene moieties at the bent-metallocene wedge.…”

Remarkably Active Non-Metallocene Ethylene Polymerization Catalysts

“…While Ziegler and Natta discovered the first commercially useful examples of metal-catalyzed production of polyolefins some 45 years ago, the relatively recent advance of single-site catalyst technology is revolutionizing the polyolefin business. 1 The chemistry of metallocenes (Cp 2 MX 2 ) [2][3][4][5][6][7][8][9] and more recently the "constrained geometry catalysts (CGC)" (CpSiR 2 NR)MX 2 ) [10][11][12][13] have been the subject of intense experimental 6,[14][15][16][17][18][19] and theoretical study. [20][21][22][23][24][25] While these systems are being used commercially, efforts to uncover alternative systems that better the extensively patented cyclopentadienyl compounds have drawn considerable attention.…”