Manganese-catalyzed synthesis of polyketones using hydrogen-borrowing approach.

We report here a method of making polyketones from the coupling of diketones and diols using a manganese pincer complex. The methodology allows us to access various polyketones (polyarylalkylketone) containing aryl, alkyl, and ether functionalities, bridging the gap between the two classes of commercially available polyketones: aliphatic polyketones and polyaryletherketones. Using this methodology, 12 polyketones have been synthesized and characterized using various analytical techniques to understand their chemical, physical, morphological, and mechanical properties. Based on previous reports and our studies, we suggest that the polymerization occurs via a hydrogen-borrowing mechanism that involves the dehydrogenation of diols to dialdehyde followed by aldol condensation of dialdehyde with diketones to form chalcone derivatives and their subsequent hydrogenation to form polyarylalkylketones

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

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

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..

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