Isomeric Bis Research Articles

Zn(II)-Coordination Polymers Constructed from Isomeric Bis(Imidazole) Derivative Ligands and Tetracarboxylic Acid for the Detection of Iron Ions

AbstractThree Zn(II)-coordination polymers, namely, {[Zn2(µ4-L)(µ-obix)2]·4DMF}n (1), {[Zn2(µ4-L)(µ-mbix)2]·6H2O}n (2) and {[Zn2(µ4-L)(µ-pbix)2]·5H2O}n (3), (L4−: 5,5’-(terephthaloylbis(azanediyl))diisophthalate and obix (y = 2), mbix (y = 3), pbix (y = 4): 1,y-bis((1H-imidazol-1-yl)methyl)benzene) were prepared with a tetracarboxylic acid and flexible isomeric bis(imidazole) linkers and characterized. The compounds displayed structural diversity depending on the rotation of imidazole rings around the –CH2- groups on bis(imidazole) ligands. Compounds 1–3 showed 2-fold interpenetrated 3D framework, 2D structure and 3D framework, respectively. The compounds showed high emissions in solid-state and solutions. Luminescence experiments showed that compounds 1–3 displayed sensitive detection towards Fe3+ ions with detection limits of 2.31 ppm, 5.17 ppm and 2.61 ppm, respectively. Moreover, the compounds could selectively detect Fe3+ ions over the other interfering metal ions via luminescence quenching. The detection mechanism could be ascribed to the competitive light absorption between Fe3+ ions and the compounds.

Gold(III), Mercury(II), and Palladium(II) Complexes of a Series of Isomeric Bis(mono- and dialkoxyphenyl)pyridines: Introduction of Gold through Transmetalation and Catalysis.

A series of isomeric bis-2,6-(monoalkoxyphenyl)pyridine and bis-2,6-(dialkoxyphenyl)pyridine ligands were synthesized and characterized. In order to prepare their chlorogold(III) complexes, intermediate chloromercury(II) complexes were first prepared, but unlike observations from previous studies where they were obtained impure and at best in moderate yield, here pure complexes were synthesized, many in rather high yields. Depending on the substitution pattern of the alkoxy chains on the ligands, mono- and/or dimercurated complexes were obtained, characterized by 1H, 13C{1H}, and 199Hg NMR spectroscopy as well as, in several cases, by X-ray crystallography. Factors that may explain this unusual reactivity are discussed. In most cases, transmetalation to the related chlorogold(III) complex proceeded smoothly, although lower yields were obtained when starting from doubly mercurated precursors. Prompted by the propensity of these ligands to mercurate, attempts were made to effect direct auration, but none was successful. However, dimeric, orthometalated complexes of palladium(II) could be prepared and were also amenable to transmetalation to the chlorogold(III) complex, providing for a mercury-free synthesis.

Synthesis, molecular docking, and antimicrobial activity of novel scaffolds based on bis(thiazole) linked to 2-phenoxy-N-arylacetamide as new hybrid molecules

The reaction of the appropriate bis(α-haloketones) with the corresponding thiosemicarbazones in EtOH at reflux in the presence of a few drops of TEA produced good yields of novel bis-thiazoles linked to 2-phenoxy-N-arylacetamide as novel hybrid molecules. The isomeric bis(thiazoles) were prepared under similar reaction conditions by reacting the appropriate bis(thiosemicarbazone) with the corresponding α-haloketones. All of the newly synthesized compounds were tested against four bacterial strains. Compounds 8g and 8i have the most antibacterial activity against S. aureus and Bacillus subtilis. The molecular docking studies supported our findings, which demonstrated that compounds 8g and 8i could fit with favorable binding energies in the active sites of bacterial DNA gyrase B and thymidylate kinase, respectively.

Novel Scaffolds Based on Bis-thiazole Connected to Quinoxaline or Thienothiophene through 2-Phenoxy-N-arylacetamide Groups as New Hybrid Molecules: Synthesis, Antibacterial Activity, and Molecular Docking Investigations.

The resistance of microorganisms to antimicrobials has endangered the health of many people across the world. Overcoming the resistance problem will require the invention of molecules with a new mechanism of action so that no cross-resistance with existing therapies occurs. Because of their powerful antibacterial activity against a wide spectrum of Gram-positive and Gram-negative bacterial strains, heterocyclic compounds are appealing candidates for medicinal chemists. In this regard, as unique hybrid compounds, we synthesized a novel family of bis-thiazoles linked to quinoxaline or thienothiophene via the 2-phenoxy-N-arylacetamide moiety. The target compounds were synthesized by reacting the relevant bis(α-haloketones) with the corresponding thiosemicarbazones in EtOH at reflux with a few drops of TEA. Under comparable reaction conditions, the isomeric bis(thiazoles) were synthesized by reacting the appropriate bis(thiosemicarbazone) with the respective α-haloketones. The structures of the novel compounds were confirmed using elements and spectral data. All of the synthesized compounds were tested for antibacterial activity in vitro. With an inhibitory zone width of 12 mm, compound 12a had the same activity as the reference medication tobramycin against Staphylococcus aureus. Compound 12b showed 20 mg/mL as a minimum inhibitory concentration (MIC) against Bacillus subtilis. Some of the synthesized compounds were tested via molecular docking against two bacterial proteins (dihydrofolate reductase and tyrosyl-tRNA synthetase).

Ligand and Linkage Isomers of Bis(ethylthiocarbamato) Copper Complexes with Cyclic C6H8 Backbone Substituents: Synthesis, Characterization, and Antiproliferation Activity.

A series of isomeric bis(alkylthiocarbamate) copper complexes have been synthesized, characterized, and evaluated for antiproliferation activity. The complexes were derived from ligand isomers with 3-methylpentyl (H2L2) and cyclohexyl (H2L3) backbone substituents, which each yield a pair of linkage isomers. The thermodynamic products CuL2a/3a have two imino N and two S donors resulting in three five-member chelate rings (555 isomers). The kinetic isomers CuL2b/3b have one imino and one hydrazino N donor and two S donors resulting in four-, six-, and five-member rings (465 isomers). The 555 isomers have more accessible CuII/I potentials (E1/2 = -811/-768 mV vs. ferrocenium/ferrocene) and lower energy charge transfer bands than their 465 counterparts (E1/2 = -923/-854 mV). Antiproliferation activities were evaluated against the lung adenocarcinoma cell line (A549) and nonmalignant lung fibroblast cell line (IMR-90) using the MTT assay. CuL2a was potent (A549EC50 = 0.080 μM) and selective (IMR-90EC50/A549EC50 = 25) for A549. Its linkage isomer CuL2b had equivalent A549 activity, but lower selectivity (IMR-90EC50/A549EC50 = 12.5). The isomers CuL3a and CuL3b were less potent with A549EC50 values of 1.9 and 0.19 μM and less selective with IMR-90EC50/A549EC50 ratios of 2.3 and 2.65, respectively. There was no correlation between reduction potential and A549 antiproliferation activity/selectivity.

Binuclear metal ruthenium complexes bridged by isomeric bis(ethynyl)pyridine: Syntheses, characterization and electronic coupling properties

Isomeric diruthenium complexes with bis(ethynyl)pyridine as bridge core [2,6-bis(ethynyl)pyridine (1), 3,5-bis(ethynyl)pyridine (2), 2,5-bis(ethynyl)pyridine (3)] were successfully prepared and characterized by 1H NMR, 13C NMR and elemental analysis. The electrochemical properties of complexes 1–3 were investigated by cyclic voltammetry (CV) and square-wave voltammetry (SWV), and different potential difference values were revealed and affected by N atom position and distance between redox metal centers. Electron absorption spectra showed that the absorption of the linear molecule 3 displayed a red shift relative to that of complexes 1 and 2. The broad near-infrared absorption characteristic of the singly-oxidized complex 3+ revealed the existence of a mixed-valence state, which can be classified as a class II mixed-valence system according to the intervalence charge transfer (IVCT) absorption parameter Hab and Г. These results indicated that 3 has higher conjugation and charge delocalization ability than isomers 1 and 2. Density functional theory (DFT) calculations spin density distribution analysis further confirmed the above results, and time-dependent DFT showed the NIR multi-absorption of complex 3+, and effectively attributed to Ru–CC→Ru IVCT absorption characteristics.

Bis[cyclic (alkyl)(amino)carbene] isomers: Stable trans-bis(CAAC) versus facile olefin formation for cis-bis(CAAC).

Isomeric bis(aldiminium) salts with a 1,4-cyclohexylene framework were synthesized. The first isolable bis(CAAC) was prepared from the trans-stereoisomer and its ditopic ligand competency was proven by conversion to iridium(I) and rhodium(I) complexes. Upon deprotonation, the cis-isomer yielded an electron rich olefin via a classic, proton-catalyzed pathway. The CC bond formation from the desired cis-bis(CAAC) was shown to be thermodynamically very favorable and to involve a small activation barrier. Compounds that can be described as insertion products of the cis-bis(CAAC) into the E-H bonds of NH3, CH3CN and H2O were also identified.

Binuclear Metal Ruthenium Complexes Bridged by Isomeric Bis(Ethynyl)Pyridine: Syntheses, Characterization and Electronic Coupling Properties

Binuclear Metal Ruthenium Complexes Bridged by Isomeric Bis(Ethynyl)Pyridine: Syntheses, Characterization and Electronic Coupling Properties

Room-Temperature Spin Crossover in a Solution of Iron(II) Complexes with N,N'-Disubstituted Bis(pyrazol-3-yl)pyridines.

Here, we report a combined study of the effects of two chemical modifications to an N,N′-disubstituted bis(pyrazol-3-yl)pyridine (3-bpp) and of different solvents on the spin-crossover (SCO) behavior in otherwise high-spin iron(II) complexes by solution NMR spectroscopy. The observed stabilization of the low-spin state by electron-withdrawing substituents in the two positions of the ligand that induce opposite electronic effects in SCO–active iron(II) complexes of isomeric bis(pyrazol-1-yl)pyridines (1-bpp) was previously hidden by NH functionalities in 3-bpp precluding the molecular design of SCO compounds with this family of ligands. With the recent SCO-assisting substituent design, the uncovered trends converged toward the first iron(II) complex of N,N′-disubstituted 3-bpp to undergo an almost complete SCO centered at room temperature in a less polar solvent of a high hydrogen-bond acceptor ability.

Isomeric bis(pyrazolyl)sulfones based on bis(1,1-dihydropolyfluoroalkyl)sulfones. A new type of ligands for metal-polymer complexes with silver cation

The work is devoted to the methods of synthesis of bis(polyfluoroalkenyl)sulfones and bis(polyfluoromethoxyalkenyl)sulfones as well as to the study of their reactions with diazomethane, resulting in the formation of N-methylated bis(pyrazolyl)sulfones isomers. Methods for the preparation of bis(polyfluoromethoxyalkenyl)sulfones not described previously in the literature have been developed by the addition of triethylamine and trimethylchlorosilane to a solution of the respective bis(polyfluoroalkyl)sulfones and methanol in diethyl ether in an argon atmosphere. A new method for the preparation of a previously unknown bis(3,3-difluoro-2,2-dimethoxypropyl)sulfone was suggested. The reaction occurs at room temperature in methanol in the presence of lithium hydroxide monohydrate. It was found that different regioisomeric bis(polyfluoroalkylpyrazolyl)sulfones are formed when using different methoxy derivatives of bis(polyfluoroalkenyl)sulfones in reaction with diazomethane, depending on the length of the polyfluoroalkyl moiety. These experimental data suggest that the attack of the double bond of methoxy-derived bis(polyfluoroalkenyl)sulfones by a molecule of diazomethane is influenced not only by the presence of an alkoxyl group, but also by the length of the polyfluoroalkyl substituent. The obtained bis(pyrazolyl)sulfones were investigated for the possibility of their use as ligands in the chemistry of metal complexes. It was shown that 5,5'-sulfonylbis[4-(difluoromethyl)-1-methyl-1H-pyrazole] forms a polymeric metal complex with silver nitrate. The results of X-ray structural analysis of the prepared coordination compound are presented. According to these results, the silver atom coordinates with two nitrogen atoms of pyrazole cycles of different molecules in the crystal of the obtained metal-complex compound, forming a supramolecular structure. In our opinion, an important role in this arrangement is played by the nitrate group that is coordinated with two silver atoms. As a result, we observed a supramolecular structure in the crystal that had a spiral structure with some free space in the middle. The paper also presents the results of spectral and X-ray diffraction analysis of a new regioisomeric compound of bis(3-hexafluoropropyl-1-methylpyrazolyl)sulfone.

Radical cations and dications of bis[1]benzothieno[1,4]thiazine isomers

Radical cations and dications of three isomeric bis[1]benzothieno[1,4]thiazines are (electro)chemically generated, spectroscopically characterized and assigned by (TD)DFT calculations.

High Solid‐State Near Infrared Emissive Organic Fluorophores from Thiadiazole[3,4‐c]Pyridine Derivatives for Efficient Simple Solution‐Processed Nondoped Near Infrared OLEDs

AbstractMany efforts have been dedicated to developing near infrared (NIR) fluorescent emitters with strong emission especially in the range of 700–1000 nm due to their potential applications in biomedical and optoelectronic fields. However, high solid state NIR emission fluorophores are still rare for applications. Herein, two efficient donor‐π‐acceptor type NIR emitters, C3HTP and C4HTP, are designed and synthesized by end‐capping two isomeric bis(n‐hexylthienyl)thiadiazole[3,4‐c]pyridines as π‐acceptor with structural bulky, electron rich tercarbazole moiety. They exhibit excellent solid state NIR emission with an emission peak at 725 nm, especially C3HTP, reaching a record high photoluminescence quantum yield (ΦPL) of 34% for NIR organic fluorescent materials. By taking advantage of their ΦPL values in the film state (ΦPL = 10–34%), suitable energy levels (highest occupied molecular orbital (HOMO) level ≈ −5.3 eV), high hole mobility (5.49 × 10−8 cm2 V−1 s−1) as well as good amorphous film forming ability by solution casting, they are used to fabricate a nondoped emissive layer (EML) in simple double‐layer solution processed NIR electroluminescent (EL) devices. The device containing C3HTP as the EML shows a NIR emission peaking at 726 nm and excellent EL performance with a high external quantum efficiency of 1.51%, which is the best solution processed nondoped NIR organic light‐emitting diodes reported to date. Importantly, this represents an advance in near infrared organic fluorescent materials and EL devices that meet the requirements of many applications.

Exceptional Substrate Diversity in Oxygenation Reactions Catalyzed by a Bis(μ-oxo) Copper Complex.

The enzyme tyrosinase contains a reactive side‐on peroxo dicopper(II) center as catalytically active species in C−H oxygenation reactions. The tyrosinase activity of the isomeric bis(μ‐oxo) dicopper(III) form has been discussed controversially. The synthesis of bis(μ‐oxo) dicopper(III) species [Cu2(μ‐O)2(L1)2](X)2 ([O1](X)2, X=PF6 − , BF4 −, OTf−, ClO4 −), stabilized by the new hybrid guanidine ligand 2‐{2‐((dimethylamino)methyl)phenyl}‐1,1,3,3‐tetramethylguanidine (L1), and its characterization by UV/Vis, Raman, and XAS spectroscopy, as well as cryo‐UHR‐ESI mass spectrometry, is described. We highlight selective oxygenation of a plethora of phenolic substrates mediated by [O1](PF6)2, which results in mono‐ and bicyclic quinones and provides an attractive strategy for designing new phenazines. The selectivity is predicted by using the Fukui function, which is hereby introduced into tyrosinase model chemistry. Our bioinspired catalysis harnesses molecular dioxygen for organic transformations and achieves a substrate diversity reaching far beyond the scope of the enzyme.

Two entangled Cd(II) MOFs of sebacic acid and bis(2-methyl-imidazole) ligands for selective sensing of Fe3+

Two new entangled Cd(II) MOFs, [Cd(Seb)(1,2-mbix)]·H2O (1) and [Cd(Seb)(1,4-mbix)] (2), based on sebacic acid (Seb) mixed with 1,2-bis(2-methyl-imidazol-1-ylmethyl)benzene (1,2-mbix) and 1,4-bis(2-methyl-imidazol-1-ylmethyl)benzene (1,4-mbix) ligands, have been hydrothermally prepared and characterized by single-crystal X-ray diffraction, IR and UV–Vis spectra, thermogravimetric and photoluminescent analyses. In 1, the Cd(II) centers are connected by Seb2− and 1,2-mbix into a 3D framework with a 4-fold interpenetrating dia topology. When 1,2-mbix was replaced by 1,4-mbix, a distinct structure for 2 was constructed, which is a 2D interpenetrating network containing both polyrotaxane and polycatenane features. This result demonstrates the important role of the two position isomeric bis(2-methyl-imidazole) ligands to their structural diversity. 1 and 2 dispay photoluminescence at 368 nm (λex = 247 nm) and 401 nm (λex = 306 nm), respectively. And both MOFs exhibit selective sensing toward Fe3+ through the luminescent quenching experiments.

Experimental and Theoretical Insights into Molecular and Solid-State Properties of Isomeric Bis(salicylaldehydes).

A series of five bis(salicylaldehydes), including four isomeric compounds based on a benzene scaffold and a closely related naphthalene derivative, were investigated in order to elucidate the impact of resonance effects and intramolecular hydrogen bonds (HBs) on the macroscopic properties of these systems. Density functional theory (DFT) computations revealed important differences between isomers on the molecular level, which was reflected in different charge distributions, aromatic C-C bond orders, and aromaticity characters. The consequences of these features were evidenced by the UV-vis absorption spectra: for 1,3-diformyl-4,6-dihydroxybenzene (2), the longest wavelength absorption band is observed at 285 nm, while its isomers 1,4-diformyl-2,5-dihydroxybenzene (1), 1,4-diformyl-2,3-dihydroxybenzene (3), and 1,2-diformyl-3,6-dihydroxybenzene (4) are characterized by absorption in the visible range (379-407 nm). The specificity of 2 results from simultaneous lowering and elevation of HOMO and LUMO energy levels, respectively. We have found that the HOMO/LUMO energy variations follow trends observed in isomeric dihydroxybenzenes (HOMO) and phthalaldehydes (LUMO), and these effects operate separately to some extent. Furthermore, theoretical calculations indicate that the UV-vis spectral properties of bis(salicylaldehydes) are directly transferable to the corresponding bis(salicylaldimines) and their boron complexes. Finally, the influence of structural and molecular stabilization effects was analyzed by means of X-ray structural analysis and periodic DFT computations.

Disilene-Silylene Interconversion: A Synthetically Accessible Acyclic Bis(silyl)silylene.

Silylenes have recently shown fascinating reactivity patterns, which are normally observed almost exclusively for transition-metal complexes. In particular, very reactive representatives are considered to be promising candidates, which may become powerful and economical alternatives for catalytic applications in the future. Here, we present the isolation of an equilibrium mixture consisting of a tetrasilyldisilene and its isomeric bis(silyl)silylene, the first isolable silylene of this type. Preliminary investigations demonstrate the extreme inherent reactivity via facile small-molecule activation even under very mild conditions. Thus, the oxidative addition of challenging targets such as H2 and NH3 was achieved. In addition, by synthesizing donor-stabilized bis(silyl)silylenes we gained further insights into the disilene-silylene rearrangement by 1,2-silyl migrations. Thorough theoretical calculations support the observed experimental results.

Two new CoII coordination polymers with multifunctional 5-amino-2,4,6-tribromoisophthalic acid and flexible isomeric bis(imidazole) ligands: preparation, crystal structure and characterization.

Two new CoII coordination polymers (CPs), namely, catena-poly[[[(5-amino-2,4,6-tribromobenzene-1,3-dicarboxylato-κO)aquacobalt(II)]-bis[μ-1,3-bis(imidazol-1-ylmethyl)benzene-κ2N:N']] 4.75-hydrate], {[Co(C8H2Br3NO4)(C14H14N4)2(H2O)]·4.75H2O}n, (1), and poly[(μ-5-amino-2,4,6-tribromobenzene-1,3-dicarboxylato-κ2O1:O3)[μ-1,2-bis(imidazol-1-ylmethyl)benzene-κ2N:N']cobalt(II)], [Co(C8H2Br3NO4)(C14H14N4)]n, (2), have been synthesized successfully by the assembly of multifunctional 5-amino-2,4,6-tribromoisophthalic acid (H2ATBIP) and CoII ions in the presence of the flexible isomeric bis(imidazole) ligands 1,3-bis(imidazol-1-ylmethyl)benzene (mbix) and 1,2-bis(imidazol-1-ylmethyl)benzene (obix). The isomeric mbix and obix ligands have a big influence on the structures of CPs (1) and (2). CP (1) is composed of chains of nanometre-sized elliptical rings, in which the CoII atom exhibits a distorted octahedral coordination geometry and ATBIP2- acts as a monodentate ligand. Two adjacent chains are interlinked by π-π stacking interactions and hydrogen bonds, resulting in a supramolecular double chain. Hydrogen-bonded R86(16) rings extend adjacent supramolecular double chains into a two-dimensional supramolecular layer. Halogen bonding and a hydrogen-bonded R42(8) ring further link the two-dimensional supramolecular layers, leading to the formation of a three-dimensional supramolecular network. The CoII ion in CP (2) is tetracoordinated, exhibiting a distorted tetrahedral configuration. The ATBIP2- ligand exhibits a bis(monodentate) coordination bridging mode, linking adjacent CoII ions into zigzag chains, which are further bridged by the auxiliary bridging obix ligand, resulting in a two-dimensional (4,4) topological network. Interlayer hydrogen and halogen-halogen bonding further extend the two-dimensional layers into a three-dimensional supramolecular network. A detailed analysis of the solid-state UV-Vis-NIR diffuse-reflectance spectra of (1) and (2) indicates that a wide optical band gap exists in both (1) and (2). CP (1) exhibits an irreversible dehydration-rehydration behaviour.

Three Co(II)-coordination polymers based on 5-tert-butyl isophthalic acid and isomeric Bis(imidazole) ligands: Synthesis, optical and magnetic properties

Three new Co(II)-coordination polymers, namely {[Co3(µ3-tbip)(µ4-tbip)(µ4-tbip)(µ-H2O)(µ-obix)]·3H2O}n(1), [Co3(Htbip)(µ-Htbip)(µ4-tbip)(µ4-tbip)(H2O)(µ-mbix)]n(2) and [Co2(µ3-tbip)2(µ-pbix)]n(3) (tbip: 5-tert-butyl isophthalate, o, m, pbix: 1,X-bis(imidazol-1ylmethyl)benzene, X = 2, 3, 4) were systematically synthesized with H2tbip and isomeric bis(imidazole) linkers under hydrothermal conditions to investigate the influence of isomeric ligands on the structural diversity. They were characterized by elemental analysis, IR spectroscopy, single and powder X-ray diffractions. X-ray results showed that complexes 1 and 3 possessed 3D framework while complex 2 was 2D layer. In 1 and 2, trinuclear [Co3(COO)6(OH2)] and [Co3(COO)6] units were connected by tbip ligands to form 2D and 1D structures which were extended to form 3D and 2D structures by neutral ligands, respectively. Complex 3 was mutually interpenetrated each other to form 3D + 3D → 3D interpenetrated framework with crs/dia-e topology. In 2, tbip ligand displayed new coordination modes. Moreover, thermal, optical and magnetic properties of the complexes were also studied.

Self-Assembly and Catalytic Reactivity of BINOL-Bridged Bis(phenanthroline) Metallocages.

Upon treatment with ZnII ions, a series of BINOL-bridged bis(phenanthroline) ligands was self-assembled into [M2L3] metallocages, which were carefully characterized by NMR spectroscopy and ESI-MS spectrometry. Among them, a racemic mixture of the BINOL-bridged bis(phenanthrolines) underwent chiral self-sorting to afford two homochiral metallocages. The narcissistic self-sorting process of the metallocages was observed in the complexation reaction of the constitutionally isomeric bis(phenanthrolines) with varying connection positions. Moreover, the endo hydroxyl-functionalized metallocage [Zn2{( S)-L2OH}3] exhibited catalytic activity and substrate selectivity for the Knoevenagel condensation reactions of aromatic tricarbaldehydes with malononitrile.

Unbridged 1- and 2-substituted bis(silylindenyl) zirconium(IV) and hafnium(IV) dichloride complexes as catalyst precursors for ethylene polymerization

Twelve unbridged metallocene dichloride complexes of the types [1-(4-XC6H4SiMe2)-η5-Ind]2MCl2 and [2-(4-XC6H4SiMe2)-η5-Ind]2MCl2 (X=Me, MeO, F; M=Zr, Hf) with differently 1- and 2-substituted indenyl ligands have been synthesized, characterized and applied for catalytic ethylene polymerization. After activation with methylaluminoxane (MAO), all complexes are catalysts for ethylene polymerization. However, in nearly all cases, the species with the silyl substituent in the 1-position show much higher activities than those with the same substituent in 2-position of the indenyl moiety. For instance, the MAO activated complex bis(η5-1-(dimethyl-4-tolylsilyl)idenyl) zirconium(IV) dichloride (3), displayed an almost five times higher activity (3980kg PE/mol cat.h) than the isomeric bis(η5-2-(dimethyl-4-tolylsilyl)indenyl) zirconium(IV) dichloride (19)/MAO catalyst (870kg PE/mol cat.h). The same trend was observed for the para-fluorophenyl silyl indenyl complexes 23 and 17. This behavior may be explained in a way that the same silyl substituent in position 2 can exert more steric hindrance around the metal center compared to the 1-substituted analogues. The GPC characterization of the produced polyethylenes showed that some of the resins have a bimodal molecular weight distribution indicating at least two different active sites that are involved in the polymerization process.