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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 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 series of Me2Si-bridged bis(2-Me-indenyl) ansa-zirconocenes containing N-pyrrolyl, N-indolyl, N-carbazolyl, and P-dibenzophospholyl substituents in position 4 of the indenyl moieties has been syn...

A series of C2–symmetric SiMe2-bridged bis-indenyl zirconium complexes containing 2-methyl-4-aryl/isopropyl-5-amino/pyrrolyl-6-alkylindenyl fragments have been synthesized and unambiguously characterized. These complexes activated by MAO demonstrated high catalytic activity in homo- and heterogeneous polymerization of propylene outperforming the traditional Spaleck system. The degree of electronic interaction of aminogroup in pos. 5 with indenyl ring system was tested via computational investigations, and notable influence of aminogroup on electronic structure of the complexes is witnessed by C (indenyl) N bond order and a sum of NAC of the ZrCl2 fragment.

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. Certain zirconocenes among the 21 tested in propylene polymerization at 70 and 100 °C under MAO or borate activation outperformed the parent catalyst in molecular weight capability, regio- or stereoselectivity.

Absolute rigidity is rare in the "soft" world of organometallics. Here we introduce two cyclopenta[a]triptycyl ansa-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. Stereodefective units are hardly detectable by 13C NMR in the polymer produced at 120 °C; this corresponds to an enantioselectivity exceeding 6-7 kcal/mol: i.e., less than 1 propene misinsertion every 4000 (and at room temperature, one every ∼40000!).

For a set of 40 silicon-bridged C2-symmetric ansa-zirconocenes, reactivity ratios in ethene/1-hexene copolymerization were experimentally determined by means of an accurate high-throughput experimentation (HTE) approach, and used to develop quantitative structure-activity relationship (QSAR) models for comonomer affinity using chemically meaningful descriptors. These QSAR models rely almost exclusively on steric descriptors, with the single most important descriptor being the 'openness' of the open quadrants. Catalysts with an unobstructed main insertion pathway, i.e. without substituents affecting the open quadrant, show a remarkable insensitivity to further substituent effects, be it in 2-, 4-, 5-, 6- or 7-position or the bridge. We attribute this insensitivity to a shift in rate-limiting step for the comonomer incorporation, from insertion to olefin capture, with the latter being much less sensitive to modulation of the active pocket than the former. This indicates that our best incorporators are already close to the upper limit for comonomer affinity within this catalyst class. This journal is

Compared to heterogenous Ziegler–Natta systems (ZNS), ansa-metallocene catalysts for the industrial production of isotactic polypropylene feature a higher cost-to-performance balance. In particular, the C2-symmetric bis(indenyl) ansa-zirconocenes disclosed in the 1990s are complex to prepare, less stereo- and/or regioselective than ZNS, and lose performance at practical application temperatures. The golden era of these complexes, though, was before High Throughput Experimentation (HTE) could contribute significantly to their evolution. Herein, we illustrate a Quantitative Structure – Activity Relationship (QSAR) model trained on a robust and highly accurate HTE database. The clear-box QSAR model utilizes, in particular, a limited number of chemically intuitive 3D geometric descriptors that screen various regions of space in and around the catalytic pocket in a modular way thus enabling to quantify individual substituent contributions. The main focus of the paper is on the methodology, which should be of rather broad applicability in molecular organometallic catalysis. Then again, it is worth emphasizing that the specific application reported here led us to identify in a comparatively short time novel zirconocene catalysts rivaling or even outperforming all previous homologues which strongly indicates that the metallocene story is not over yet.

The zirconium rac- and meso-complexes of the ansa-type that contain a 3-phenyl-6,7,8,9-tetrahydrocyclopenta[a]naphthalene fragment and a dimethylsilylene bridge are synthesized. The compounds obtained are characterized by NMR spectroscopy; the structure of rac-complex is studied by X-ray diffraction, which maked it possible to evaluate the steric availability of the zirconium center in the corresponding catalysts for the olefin polymerization.

Compared to heterogenous Ziegler&ndash, Natta systems (ZNS), ansa-metallocene catalysts for the industrial production of isotactic polypropylene feature a higher cost-to-performance balance. In particular, the C2-symmetric bis(indenyl) ansa-zirconocenes disclosed in the 1990s are complex to prepare, less stereo- and/or regioselective than ZNS, and lose performance at practical application temperatures. The golden era of these complexes, though, was before High Throughput Experimentation (HTE) could contribute significantly to their evolution. Herein, we illustrate a Quantitative Structure &ndash, Activity Relationship (QSAR) model trained on a robust and highly accurate HTE database. The clear-box QSAR model utilizes, in particular, a limited number of chemically intuitive 3D geometric descriptors that screen various regions of space in and around the catalytic pocket in a modular way thus enabling to quantify individual substituent contributions. The main focus of the paper is on the methodology, which should be of rather broad applicability in molecular organometallic catalysis. Then again, it is worth emphasizing that the specific application reported here led us to identify in a comparatively short time novel zirconocene catalysts rivaling or even outperforming all previous homologues which strongly indicates that the metallocene story is not over yet.

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 ZrIVatoms in (I) are ligated by one cyclopentadienyl (CP) ring and four Br ligands (two bridging, two terminal), while in (II) the ZrIVatom 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.

Nickel catalysts with diazabutadiene ligands promote cross-coupling of benzaldehydes with aryl halides in the presence of zinc as reducing agent, which leads to the corresponding benzhydrols and benzophenones. The benzophenone percentage considerably increases when lithium chloride additive is used.

Quantitative structure–property relationships in group 4 metallocene olefin polymerization catalysts were constructed for a dataset of 8 zirconocenes in a combined experimental and quantum chemical study. A total of 45 descriptors measuring the steric and electronic influence of the rac-SiMe2[Ind]2 based ligand framework were correlated with the observed polymerization activities, together with the molecular weights, melting temperatures, stereoerrors and regioerrors of the produced isotactic polypropene. Direct correlations between the calculated descriptors and observed catalytic properties turned out to be relatively weak due to the combined steric and electronic effects of multiple descriptors. Multiple regression models based on ordinary least squares linear regression and principal component regression techniques typically led to significant improvements, particularly for the molecular weights, melting temperatures and regioerrors, providing R2 of up to 0.92. The results provide a solid starting point for an extension of the methodology for a greater variety of catalyst structures, and thereby for the development of new high-performance catalysts for this industrially important process.

A novel protocol for efficient coupling of nitrobenzene and aniline in poly(ethylene glycol) medium in the presence of KOH giving diphenylamine derivatives has been developed, to enable the exclusion of the toxic tetramethylammonium hydroxide catalyst commonly used in the rubber antidegradant industry.

Mol­ecules of di[(μ-bromido)(η5-2-di­methyl­amino­inden­yl)di­bromido­zirconium(IV)], (I), and bis­(η5-2-di­methyl­amino­inden­yl)di­bromido­zirconium(IV), (II), are dinuclear with one CP ligand and four Br ligands for each of the ZrIV atoms and mononuclear with two CP and two Br ligands for the ZrIV atom, respectively., 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.

The structure of the title compound [systematic name: 8-butyl-8-(2-methyl-1H-inden-1-yl)-8-silatricyclo[7.4.0.02,3]trideca-1(13),2,4,6,9,11-hexaene], C26H26Si, at 110 K has orthorhombic (Pbca) symmetry. In the molecule, the butyl group displays an extended conformation with the C—C—C—C torsion angle of 176.8 (2)°. The dihedral angle between the biphenyl group and the indole group is 60.04 (2)°. The structure exhibits a weak intramolecular C—H...π interaction.

Pd-catalyzed Negishi reactions of Zr and Hf complexes bearing η5-4-bromo-2-methylindenyl and η5-2-bromoindenyl ligands with MeZnCl and various aryl- and heteroarylzinc reagents (RZnCl) give in high yields the respective complexes bearing η5-4-R-2-methylindenyl and η5-2-R-indenyl ligands, respectively.

The Pd-catalyzed cross-coupling reactions of readily available 2-bromo-1H-indene with 1H-pyrrole, 1H-indole, 9H-carbazole, and their derivatives were shown to be convenient methods to obtain novel ligands containing azole fragments bonded with cyclopentadienyl via nitrogen. An alternative protocol using enol triflates of 1-indanone or 2-indanone is also useful, particularly for synthesizing indenes bearing the N-azolyl fragment in position 1. On the other hand, the synthesis of 2-(1H-benzimidazol-1-yl)-1H-indene can be achieved via the Cu-catalyzed reactions only. The substituted indenes with the N-azolyl fragment in position 2 were further used for obtaining several semisandwich complexes of zirconium, [η5-2-(N-azolyl)indenyl]zirconium tribromides, as well as symmetrical and unsymmetrical Waymouth-type zirconium and hafnium complexes containing indenyl ligands bearing planar N-azolyl or aryl fragments in position 2. These metallocenes were unambiguously characterized, including by X-ray crystal structure...

Substituted 4-/7-halo-1H-indenes and 5-methyl-3-bromo-4-/6H-cyclopenta[b]thiophenes were shown to be convenient starting materials for Suzuki−Miyaura, Negishi, and Murahashi protocols to give the corresponding aryl-subsituted indenes and cyclopenta[b]thiophenes of importance for further synthesis of ansa-metallocenes. Alternatively, (2-methyl-1H-inden-4-yl)boronic acid and (1-methoxy-2-methyl-2,3-dihydro-1H-inden-4-yl)boronic acid as well as the respective organozinc and -magnesium reagents can be used for synthesizing aryl-subsituted indenes via the Pd-catalyzed reactions with aryl halides. These synthetic methods were shown to have a very broad scope to afford libraries of aryl-substituted indenes. Finally, synthesis and structure characterization of several representative chiral ansa-zirconocenes, potentially useful as components of highly active and stereoselective olefin polymerization catalysts, have been performed.

A series of 2-R2P-substituted indenes, where R2P = Ph2P, Cy2P, iPr2P, and tBu(H)P, were obtained via Pd-catalyzed reactions of 2-bromo-1H-indene (or 1H-inden-2-yl trifluoromethane sulfonate) with R2PH/Et3N. Analogous indenes bearing Me2P, tBu(Cl)P, and tBu2P substituents at position 2 were obtained through the reaction of 1H-inden-2-ylphosphonous dichloride with MeLi, tBuMgCl, and tBuMgCl/tBuLi−CuCN, respectively. Diethyl 1H-inden-2-ylphosphonate, prepared via the Ni-catalyzed Arbuzov reaction of 2-bromo-1H-indene with P(OEt)3, was found to be a convenient starting material for the synthesis of 2-H2P-substituted indene. 1H-Inden-2-yl(phenyl)phosphine, prepared via the Pd-catalyzed arylation of 2-H2P-substituted indene by PhI, turned out to react with 2-bromo-1H-indene in the presence of Pd(PPh3)4 and Et3N to form di(1H-inden-2-yl)(phenyl)phosphine in almost quantitative yield. Analogously, di(1H-inden-2-yl)(tert-butyl)phosphine was prepared via catalytic reaction of tBuPH2 with 2 equiv of 2-bromo-1H-inden...

The following cyclopentadienes (Cp‘H) with fused thiophene and benzothiophene fragments were synthesized: 4,5-dimethyl-6H-cyclopenta[b]thiophene (2), 5,6-dimethyl-4H-cyclopenta[b]thiophene (4), 1,...

A new single-step approach to cyclopenta[a]naphthalenes through TiCl4-catalyzed reactions of 1-trimethylsilyloxycyclopentene with arylacetaldehydes was proposed. 8-Methoxy-5-methyl-2,3-dihydro-1H-cyclopenta[a]naphthalene and its derivatives were studied in oxidation and bromination reactions, as well as in hydrolytic cleavage of the O-Me bond.

Vinylation of various azoles (pyrrole, indole, carbazole, and their derivatives) and phenothiazine with vinyl bromides catalyzed by palladium−phosphine complexes results in the respective N-vinylaz...

Substituted 4-/7-halo-1H-indenes and 5-methyl-3-bromo-4-/6H-cyclopenta[b]thiophenes were shown to be convenient starting materials for Suzuki−Miyaura, Negishi, and Murahashi protocols to give the corresponding aryl-subsituted indenes and cyclopenta[b]thiophenes of importance for further synthesis of ansa-metallocenes. Alternatively, (2-methyl-1H-inden-4-yl)boronic acid and (1-methoxy-2-methyl-2,3-dihydro-1H-inden-4-yl)boronic acid as well as the respective organozinc and -magnesium reagents can be used for synthesizing aryl-subsituted indenes via the Pd-catalyzed reactions with aryl halides. These synthetic methods were shown to have a very broad scope to afford libraries of aryl-substituted indenes. Finally, synthesis and structure characterization of several representative chiral ansa-zirconocenes, potentially useful as components of highly active and stereoselective olefin polymerization catalysts, have been performed.

[reaction: see text] Vinylation of various azoles (pyrrole, indole, carbazole, and their derivatives) and phenothiazine with vinyl bromides catalyzed by palladium-phosphine complexes results in the respective N-vinylazoles in 30-99% yields. This reaction with cis- and trans-beta-bromostyrenes is stereospecific giving the respective products with full retention of configuration.

By treatment of Cp*ZrCl3 with the lithium salt of cyclopenta[b]pyridine (LiCpPy) in toluene, the unsymmetrical complex Cp*(η5-CpPy)ZrCl2 was prepared in 32% yield. On the evidence of X-ray crystal structure analysis, the bifunctional CpPy ligand coordinates Zr in an η5-manner rather than via nitrogen. Cyclopenta[b]pyridine turned out to react with Zr(NMe2)4 in toluene to form mono-cyclopentadienyl complex (η5-CpPy)Zr(NMe2)3(Me2NH) in 70% yield. The polymerization of ethylene and the copolymerization of ethylene with 1-hexene or propene catalyzed by Cp*(η5-CpPy)ZrCl2 activated with MAO was studied in detail.