Reversible C-C bond formation in group 4 metal complexes: nitrile extrusion β-aryl elimination.

Pyridylamides of zirconium and hafnium with [C,N,N]-ligands reversibly insert nitriles into M-C bonds leading to an observable equilibrium between the starting [C,N,N]-complexes and newly formed [N,N,N]-complexes with a ketimide moiety in a 7-membered metallacycle. The discovered reversible insertion of nitriles into M-C bonds represents an unprecedented example of β-aryl elimination from a ketimide ligand in early transition metal complexes. Experimental and computational studies suggest thermodynamic and electronic reasons for this reactivity.

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.

Triptycene as a scaffold in metallocene catalyzed olefin polymerization.

A set of metallocene olefin polymerization catalysts bearing triptycene moieties in either position 4-5 (complexes Ty1-Ty5) or in position 5-6 (complexes Ty6-Ty8) of the basic dimethylsilyl-bridged bis(indenyl) system has been tested in propene polymerization and in ethene/1-hexene copolymerization. Comparison of the results with QSPR (quantitative structure-property relationship) predictions not parametrized for these exotic ligand variations demonstrates that trends can still be identified by extrapolation. Interestingly, Ty7, upon suitable activation, provides a highly isotactic polypropylene with an exceptional amount of 2,1 regio-errors (8%).

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 isomer (MM); formation of the polymerization active 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 in energy than MM.

-Zirconocene Catalysts for Isotactic-Selective Propene Polymerization at High Temperature: A Long Story Finds a Happy Ending.

Absolute rigidity is rare in the "soft" world of organometallics. Here we introduce two cyclopenta[]triptycyl -zirconocene catalysts for isotactic-selective propene polymerization, designed by means of an integrated high-throughput experimentation/quantitative structure-activity relationship modeling approach. An ultrarigid ligand precisely wrapped around the Zr center enforces an enzyme-like lock and key fit, effectively hampering undesired reactive events, even at high temperature.

Multisubstituted -symmetric -metallocenes bearing nitrogen heterocycles: influence of substituents on catalytic properties in propylene polymerization at higher temperatures.

In this work we systematically studied the effects of modifications of substituents on the performance of the isospecific zirconocene-based catalyst family, Me2Si(2-Alk-4-(N-carbazolyl)Ind)ZrX2 (X = Cl, Me), wherein the progenitor was shown to be particularly suitable in high-temperature propylene polymerization processes. In order to obtain the required zirconocenes, we developed a novel synthetic pathway to 4-(N-carbazolyl)indenes through Pd-catalyzed cyclizations of 2,2'-dibromobiaryls with 4-aminoindenes, which were synthesized via Buchwald-Hartwig reaction or electrophilic amination of 4-indenyl Grignard reagents with trimethylsilylmethyl azide. By a number of examples, the anion-promoted rac-to-meso isomerization method was shown to work reliably well for preparation of rac-ZrMe2-complexes.

Pyridylamido hafnium complexes with a silylene bridge: synthesis and olefin polymerization.

The synthesis and characterisation of six novel Cs-symmetric pyridylamido hafnium complexes with a silylene bridge of the type [ArPy(R2Si)NAr']HfAlk2 are reported. Four complexes have been structurally characterised using single crystal X-ray diffraction. Appreciable differences between the solid state structures of these complexes and the pyridylamido hafnium complexes with a CRR' bridge were noted.

Reactivity of C -Symmetric Heteroarylamido Hafnium Complexes towards Unsaturated Electrophilic Molecules: Development of New Families of Olefin Polymerization Catalysts.

Heteroarylamido hafnium post-metallocenes with [C,N,N] ligands were functionalized by the insertion of small electrophilic unsaturated molecules into the C -Hf bond of the ligand, which gave rise to various 1,1- and 1,2-insertion complexes with the modified ligands of previously unknown [O,N,N], [N,N,N], [O,N,N,N], and [N,N,N,N] types. It was found that C symmetry of the starting complexes, in some cases, results in the formation of two diastereoisomers after 1,1- or 1,2-insertion. Most of the obtained novel complexes were shown to form active catalysts for olefin polymerization in the presence of MAO (methylaluminoxane).

Crystal structures of di-μ-bromido-bis{di-bromido-[η-2-(di-methyl-amino)-inden-yl]zirconium(IV)} and di-bromido-bis-[η-2-(di-methyl-amino)-inden-yl]zirconium(IV).

In the title compounds, [ZrBr(CHN)], (I) and [ZrBr(CHN)], (II), the positions of the η-binding 2-di-methyl-amino-indenyl units are fixed by intra-molecular C-H⋯Br inter-actions involving aromatic or di-methyl-amino H atoms. The binuclear mol-ecule of (I) is located on a general position, while the mononuclear mol-ecule of (II) is situated on a twofold rotation axis. Both Zr atoms in (I) are ligated by one cyclo-penta-dienyl (CP) ring and four Br ligands (two bridging, two terminal), while in (II) the Zr atom is ligated by two CP rings and two terminal Br ligands.