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

Abstract

The series of (1-terpenylindenyl) 2 ZrCl 2 bent metallocene complexes (with terpenyl substituents neomenthyl, neoisomenthyl, menthyl, and isomenthyl) were obtained from the reaction of the respective 1-terpenylindenyl lithium reagents with ZrCl 4 . In each case a single racem-like diastereoisomer was isolated pure by crystallization. The conformational analysis of the bent metallocene systems was carried out by variable temperature 1 H NMR spectroscopy. It has revealed the existence and equilibration of three different bent metallocene torsional isomers. Two of these are C 2 -symmetric and carry their bulky terpenyl substituents either in the lateral or the front sector of the bent metallocene wedge (descriptors bis-lateral:anti (conformer A) and bis-central:syn (conformer B)), whereas the rotational isomer C (central,lateral:gauche) is of lower symmetry. The (1-terpenylindenyl) 2 ZrCl 2 /methylalumoxane systems are active propene polymerization catalysts. The equilibrium amount of the "stereochemically productive" C 2 -symmetric bis-lateral:anti bent metallocene conformer A correlates qualitatively with the observed isotacticity of the propene polymerization process at the respective group 4 bent metallocene catalyst system.

Chiral Indenes and Group‐4 Metallocene Dichlorides Containing α‐ and β‐Pinenyl‐Derived Ligand Substituents: Synthesis and Catalytic Applications in Polymerization and Carboalumination Reactions

“…When to this mixture was added cold pentane at -60°C a small sample (0.054 g, 3 %) of 8a/8b was obtained as yellow crystals enriched in one of the racemic-like diastereomers in a 57:43 ratio. CH in 8a and 8b), 106.70 (4 olefinic CH in five-membered ring in 8a and 8b), 48.82 (2 CH in pinenyl ring in 8a and 8b), 48.79 (2 CH in pinenyl ring in 8a and 8b), 40.71 (2 CH in pinenyl ring in 8a and 8b), 40.67 (2 CH in pinenyl ring in 8a and 8b), 39.45 (4 C q in pinenyl ring in 8a and 8b), 30.96 (2 CH in pinenyl ring in 8a and 8b), 30.87 (2 CH in pinenyl ring in 8a and 8b), 26.89 (2 CH 3 attached to pinenyl ring in 8a or 8b), 26.83 (2 CH 3 attached to pinenyl ring in 8a or 8b), 25.86 (2 CH in pinenyl ring in 8a and 8b), 25.80 (2 CH in pinenyl ring in 8a and 8b), 25.05 (2 bridging CH 2 between pinenyl ring and Si in 8a or 8b), 24.96 (2 bridging CH 2 between pinenyl ring and Si in 8a or 8b), 24.86 (4 CH in pinenyl ring in 8a and 8b), 22.95 (2 CH in pinenyl ring in 8a and 8b), 22.92 (2 CH in pinenyl ring in 8a and 8b), 20.00 (2 CH 3 attached to pinenyl ring in 8a or 8b), 19.95 (2 CH 3 attached to pinenyl ring in 8a or 8b), 13.83 (2 CH 3 attached to five-membered ring in 8a or 8b), 13.80 (2 CH 3 attached to five-membered ring in 8a or 8b), -0.52 (2 CH 3 attached to Si in 8a or 8b), -0.86 (2 CH 3 attached to Si in 8a or 8b), -1.03 (2 CH 3 attached to Si in 8a or 8b), -1.45 (2 CH 3 attached to Si in 8a or 8b) ppm. 29 Si NMR (119.3 MHz, CDCl 3 , 25°C): δ = -4.29 (2 Si in 8a or 8b), -4.31 (2 Si in 8a or 8b) ppm.…”

Implications of Indenyl Substitution for the Structural Chemistry of Rare-Earth Metal (Half-)Sandwich Complexes and Performance in Living Isoprene Polymerization

“…Due to the trimethylsilyl substitution at C1, the aromatic protons of the indenyl ligand Ind Si display distinct chemical shifts. Ind Si is prochiral which impacts the formation of sandwich complex 2d , since Ind Si can coordinate with either side ( re - or si -site) of the enantiotopic faces. − Accordingly, the reaction of Lu­(AlMe 4 ) 3 with Li­(Ind Si ) afforded 2d with an approximately 9:1 mixture of meso ( re , si attachment) and rac isomer ( re , re or si , si attachment), as assigned by 1 H NMR spectroscopy at ambient temperature (Figure ). The isomeric mixture could not be separated by fractional crystallization, but we could obtain single crystals of meso - 2d suitable for X-ray structure analysis (vide infra).…”

Asymmetric alkene cycloalumination by AlEt3, catalyzed with neomenthylindenyl zirconium η-complexes

“…Thus, complex 1 shows higher activity in the absence or in the reduced amount of the solvent (for example, entries 3, 4, 7, 10, 12, 15, 20, 22) and reaction runs with 70e99% alkene conversion; however, the cycloalumination enantioselectivity is low and does not exceed 17%ee. The dilution of the reaction media with hydrocarbons dramatically reduces the alkene conversion to 11e42%; nevertheless, it increases the enantiomeric excess of cycloalumination product 4aeg up to 37%ee (for example, entries 1,2,5,8,11,13,14,18,21). The reaction catalyzed with complex 2 runs with decreased alkene conversion and enantioselectivity of 6e26%ee, which are less sensitive to the solvent effect.…”

“…The length increase for the alkyl chain in the linear alkenes, for example, using of 1-nonene (3d) or 1-decene (3e) in the reaction, catalyzed with complex 1, decreases the cycloalumination enantioselectivity to 23e26%ee (entries 11,13,14). Moreover, the involvement of sterically hindered alkenes 4-methylpentene-1 (3f) or vinylcyclohexane (3g) in the reaction provides cyclic OACs with reduced enantiomeric excess of 24e25%ee (entries 18, 21).…”

“…intermediate of the cycloalumination reaction is five-membered complex 12 [12], which is formed from the alkylchloride 11, responsible for the carboalumination pathway (Scheme 2). It is also known that stereoselectivity of zirconocene complexes in alkene polymerization may depend on the conformational behavior of the substituted h 5 -ligands [13,14]. Apparently, the reaction of Zr complexes with AlEt 3 gives the definite rotamers of Zr,Al-complex 12 (Scheme 2), which populations and effective concentration change with the reaction conditions (solvent, temperature, reagent ratio).…”