Dichlorido[(1,2,3,3a,8b-η)-2,4-dimethylcyclopenta[b]indolyl)(η5-pentamethylcyclopentadienyl)zirconium(IV)

In the structure of the title compound, [Zn(C13H12N)(C10H15)Cl2], the dihedral angle between the planes of rings coordinating to Zr is 51.6 (2)°. The Cl—Zr—Cl angle is 97.52 (4)°. The crystal structure is stabilized by H...Cl and C—H...π interactions

Crystal structures of di-μ-bromido-bis{dibromido[η5-2-(dimethylamino)indenyl]zirconium(IV)} and dibromidobis[η5-2-(dimethylamino)indenyl]zirconium(IV)

In the title compounds, [Zr2Br6(C11H12N)2], (I) and [ZrBr2(C11H12N)2], (II), the positions of the η5-binding 2-dimethylaminoindenyl units are fixed by intramolecular C—H...Br interactions involving aromatic or dimethylamino H atoms. The binuclear molecule of (I) is located on a general position, while the mononuclear molecule of (II) is situated on a twofold rotation axis. Both ZrIV atoms in (I) are ligated by one cyclopentadienyl (CP) ring and four Br ligands (two bridging, two terminal), while in (II) the ZrIV atom is ligated by two CP rings and two terminal Br ligands. The crystal structures of both (I) and (II) comprise of strands of π–π- and N–π-bonded molecules, which in turn are linked by C—H...Br interactions

C1-Symmetric Si-bridged (2-indenyl)(1-indenyl) ansa-metallocenes as efficient ethene/1-hexene copolymerization catalysts

In the search for more efficient single-center ethene/α-olefin copolymerization catalysts, metallocenes bearing a 2-indenyl substituent pattern have largely been ignored in the past. Here, we show that such a structural motif yields competent linear low-density polyethylene (LLDPE) catalysts. They are also relatively easy to synthesize, allowing for a wide structural amplification. A screening of 28 catalysts reveals that the lead catalyst in this study displays high comonomer affinity and molecular weight capability at industrially relevant temperatures. QSAR models show that steric factors likely contribute stronger than electronic factors to the observed substituent trends, both for comonomer affinity and MW capability

Hafnium vs. Zirconium, the Perpetual Battle for Supremacy in Catalytic Olefin Polymerization: A Simple Matter of Electrophilicity?

The performance of C2-symmetric ansa-hafnocene catalysts for isotactic polypropylene typically deteriorates at increasing temperature much faster than that of their zirconium analogues. Herein, we analyze in detail a set of five Hf/Zr metallocene pairs—including some of the latest generation catalysts—at medium- to high-polymerization temperature. Quantitative structure–activity relationship (QSAR) models for stereoselectivity, the ratio allyl/vinyl chain ends, and 2,1/3,1 misinsertions in the polymer indicate a strong dependence of polymerization performance on electrophilicity of the catalyst, which is a function of the ligand framework and the metal center. Based on this insight, the stronger performance decline of hafnocenes is ascribed to electrophilicity-dependent stabilization effects

A Systematic Study of the Temperature-Induced Performance Decline of ansa-Metallocenes for iPP

Highly accurate high-throughput experimentation (HTE) data for a set of 21 silicon-bridged C2-symmetric ansa-zirconocenes in propene homopolymerization were collected and were used to develop quant..

Octahedral Zirconium Salan Catalysts for Olefin Polymerization: Substituent and Solvent Effects on Structure and Dynamics

: Group 4 metal-Salan olefin polymerization catalysts typically have relatively low activity, being slowed down by a pre-equilibrium favoring a non-polymerization active resting state identified as a mer-mer isomer (MM); formation of the polymerization active fac-fac species (FF) requires isomerization. We now show that the chemistry is more subtle than previously realized. Salan variations bearing large, flat substituents can achieve very high activity, and we ascribe this to the stabilization of the FF isomer, which becomes lower in energy than MM. Detailed in situ NMR studies of a fast (o-anthracenyl) and a slow (o-tBu) Salan precursors, suitably activated, indicate that preferred isomers in solution are different: the fast catalyst prefers FF while the slow catalyst prefers a highly distorted MM geometry. Crystal structures of the activated o-anthracenyl substituted complex with a moderately (chlorobenzene) and, more importantly, a weakly coordinating solvent (toluene) in the first coordination sphere emphasize that the active FF isomer is preferred, at least for the benzyl species. Site epimerization (SE) barriers for the fast catalyst (ΔS > 0, dissociative) and the slow catalyst (ΔS < 0, associative) in toluene corroborate the solvent role. Diagnostic NMe 13C chemical shift differences allow unambiguous detection of FF or MM geometries for seven activated catalysts in different solvents, highlighting the role of solvent coordination strength and bulkiness of the ortho-substituent on the isomer equilibrium. For the first time, active polymeryl species of Zr-Salan catalysts were speciated. The slow catalyst is effectively trapped in the inactive MM state, as previously suggested. Direct observation of fast catalysts is hampered by their high reactivity, but the product of the first 1-hexene insertion maintains its FF geometry

The Interplay of Backbone Stiffening and Active Pocket Design in Bis(phenolate-ether) Zr/Hf Propene Polymerization Catalysts

For [OOOO]-type catalysts, the introduction of two methyl substituents behind the active site, at the backbone C3 linker, can substantially impact performance in propene polymerization catalysis depending also on the nature of the R1 substituent neighboring the active pocket. Catalyst molar mass capability and productivity can increase by 2–3 orders of magnitude; also, regioselectivity and stereoselectivity increase (2–3 fold). The results highlight (a) the importance of stiffening catalyst backbones of post-metallocene catalysts for high-temperature applications and (b) the complex interplay between backbone and active pocket design in post-metallocene olefin polymerization catalysis

Amine-Catalysed Suzuki–Miyaura-Type Coupling? the Identification and Isolation of the Palladium Culprits.

A recent report in Nature Catalysis detailed the potentially paradigm-shifting organocatalysis of Suzuki cross-coupling of aryl halides with aryl boronic acids, catalysed by simple amine species. We have conducted a reinvestigation of key claims in this paper across multiple academic and industrial laboratories that shows that the observed catalytic activity cannot be due to the amine, but rather is due to tricyclohexylphosphine palladium complexes that are readily entrained during the purification of the amine.</b