Synthesis,characterization and polymerization of the novel carbazole‐based monomer 9‐(bicyclo[2.2.1]hept‐5‐en‐2‐ylmethyl)‐9H‐carbazole

Synthesis and characterization of a novel carbazole‐based monomer, 9‐(bicyclo[2.2.1]hept‐5‐en‐2‐ylmethyl)‐9H‐carbazole (BHMCZ) and its copolymerization with ethylene by using two metallocene/MAO catalyst systems are presented. The monomer was characterized by means of NMR spectroscopy, MS and elementary analysis. Copolymerization studies were conducted using [Ph₂C(Ind)(Cp)ZrCl₂] and [Ph₂C(Flu)(Cp)ZrCl₂] catalysts. The [Ph₂C(Ind)(Cp)ZrCl₂] catalyst gave a copolymer containing as much as 4.6 mol‐% of BHMCZ. Polymers were characterized using NMR spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC).     

Exploring the Limits of Frustrated Lewis Pair Chemistry with Alkynes: Detection of a System that Favors 1,1‐Carboboration over Cooperative 1,2‐P/B‐Addition

The zirconocene complex [{(C₆F₅)₂B‐(CH₂)₃‐Cp}(Cp‐PtBu₂)ZrCl₂] ( 6 ; Cp=cyclo‐C₅H₄) was prepared by hydroboration of [(allyl‐Cp)(Cp‐PtBu₂)ZrCl₂] ( 5 ) with HB(C₆F₅)₂ (“Piers’ borane”). It represents a frustrated Lewis pair (FLP) in which both the Lewis acid and the Lewis base were attached at the metallocene framework. Its reaction with 1‐pentyne did not result in the 1,2‐addition of or deprotonation reaction by the FLP, but rather in the 1,1‐carboboration of the triple bond, thereby obtaining a Z/E mixture (1.2:1) of the respective organometallic substituted alkenes 7 . The analogous reaction of 1‐pentyne with the phosphorous‐free system [{(C₆F₅)₂B‐(CH₂)₃‐Cp)}CpZrCl₂] ( 9 ) gave the respective 1,1‐carboboration products ( Z‐10 / E‐10 ≈1.3:1).     

Study on chemisorption of H<Subscript>2</Subscript>, O<Subscript>2</Subscript>, CO and C<Subscript>2</Subscript>H<Subscript>4</Subscript>on Pt-Ag/SiO<Subscript>2</Subscript>catalysts by microcalorimetry and FTIR

Adsorption microcalorimetry has been employed to study the interaction of ethylene with the reduced and oxidized Pt-Ag/SiO₂catalysts with different Ag contents to elucidate the modified effect of Ag towards the hydrocarbon processing on platinum catalysts. In addition, microcalorimetric adsorption of H₂, O₂, CO and FTIR of CO adsorption were conducted to investigate the influence of Ag on the surface structure of Pt catalyst. It is found from the microcalorimetric results of H₂and O₂adsorption that the addition of Ag to Pt/SiO₂leads to the enrichment of Ag on the catalyst surface which decreases the size of Pt surface ensembles of Pt-Ag/SiO₂catalysts. The microcalorimetry and FTIR of CO adsorption indicates that there still exist sites for linear and bridged CO adsorption on the surface of platinum catalysts simultaneously although Ag was incorporated into Pt/SiO₂. The ethylene microcalorimetric results show that the decrease of ensemble size of Pt surface sites suppresses the formation of dissociative species (ethylidyne) upon the chemisorption of C₂H₄on Pt-Ag/SiO₂. The differential heat vs. uptake plots for C₂H₄adsorption on the oxygen-preadsorbed Pt/SiO₂and Pt-Ag/SiO₂catalysts suggest that the incorporation of Ag to Pt/SiO₂could decrease the ability for the oxidation of C₂H₄.     

Borane chain transfer reaction in olefin polymerization using trialkylboranes as chain transfer agents

This article discusses a new borane chain transfer reaction in olefin polymerization that uses trialkylboranes as a chain transfer agent and thus can be realized in conventional single site polymerization processes under mild conditions. Commercially available triethylborane (TEB) and synthesized methyl‐B‐9‐borabicyclononane (Me‐B‐9‐BBN) were engaged in metallocene/MAO [depleted of trimethylaluminum (TMA)]‐catalyzed ethylene (Cp₂ZrCl₂ and rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂ as a catalyst) and styrene (Cp*Ti(OMe)₃ as catalyst) polymerizations. The two trialkylboranes were found—in most cases—able to initiate an effective chain transfer reaction, which resulted in hydroxyl (OH)‐terminated PE and s‐PS polymers after an oxidative workup process, suggesting the formation of the B‐polymer bond at the polymer chain end. However, chain transfer efficiencies were influenced substantially by the steric hindrances of both the substituent on the trialkylborane and that on the catalyst ligand. TEB was more effective than TMA in ethylene polymerization with Cp₂ZrCl₂/MAO, whereas it became less effective when the catalyst changed to rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂. Both TEB and Me‐B‐9‐BBN caused an efficient chain transfer in the Cp₂ZrCl₂/MAO‐catalyzed ethylene polymerization; nevertheless, Me‐B‐9‐BBN failed in vain with rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂/MAO. In the case of styrene polymerization with Cp*Ti(OMe)₃/MAO, thanks to the large steric openness of the catalyst, TEB exhibited a high efficiency of chain transfer. Overall, trialkylboranes as chain transfer agents perform as well as B? H‐bearing borane derivatives, and are additionally advantaged by a much milder reaction condition, which further boosts their applicability in the preparation of borane‐terminated polyolefins. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3534–3541, 2010     

Derivatization of propene/methyloctadiene copolymers: A flexible approach to side‐chain‐functionalized polypropenes

The copolymerization of propene with 7‐methyl‐1,6‐octadiene (MOD) catalyzed by Cp*TiMe₃/B(C₆F₅)₃ ( A ) and rac‐C₂H₄(Ind)₂ZrCl₂/methylaluminoxane ( B ) in toluene under 1 bar propene gave copolymers with unsaturated side chains. Under these conditions, catalyst A produced copolymers with an atactic backbone structure of type 1 , with 3.5–19.6 mol % MOD incorporation and weight‐average molecular weight = 0.7–2.7 × 10⁵. Using catalyst B , copolymers 2 with 0.4–3.8 mol % MOD incorporation were prepared. The comonomer incorporation was a linear function of the feed ratio. The titanium catalyst A had a significantly higher affinity for MOD than the sterically more hindered zirconocene B . Postpolymerization modification of the side‐chain C?C bond allowed the facile introduction of a wide variety of functional groups. Epoxidation and especially ozonolysis of the C?C bond, to give ? CHO and ? COOH functionalized copolymers, proved to be very facile routes to functionalized polypropenes. According to monitoring by NMR, most of these transformations proceed in an essentially quantitative conversion. As an example of potential applications of such polymers, polypropenes with covalently attached dyes were prepared that are suitable for blending. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1484–1497, 2002     

Supported metallocene catalysts prepared by impregnation of MAO modified silica by a metallocene/monomer solution

Silica supported (butylcyclopentadienyl)₂ZrCl₂/MAO catalysts were synthesized according to the “incipient wetness” method from a solution of metallocene in a liquid monomer. The monomer was allowed to polymerize yielding a catalyst containing polyhexene (PH), polystyrene (PS) or polyoctadiene (PO). One catalyst containing no polymer was also synthesized. The catalysts were used to polymerize ethene at 70°C and 4 bar total pressure. The measured average activities were 5 300 kg PE/(mol Zr · h) for (BuCp)₂ZrCl₂/MAO/PH/SiO₂, 8 600 kg PE/(mol Zr · h) for (BuCp)₂ZrCl₂/MAO/PS/SiO₂, 3 400 kg PE/(mol Zr · h) for (BuCp)₂ZrCl₂/MAO/PO/SiO₂ and 5 700 kg PE/(mol Zr · h) for (BuCp)₂ZrCl₂/MAO/SiO₂. The polyhexene, polystyrene or polyoctadiene in the catalyst forms a protective layer around the active sites. Even after exposure to air for five hours these catalysts retain some polymerization activity.     

Relative reactivity enhancement of (Me5Cp)2ZrCl2 in mixture with (1,2,4-Me3Cp)2ZrCl2 during ethene/1-hexene copolymerization

Dual-site ethene/1-hexene copolymerizations with MAO-activated (1,2,4-Me₃Cp)₂ZrCl₂ and (Me₅Cp)₂ZrCl₂ catalysts were performed. Copolymers with narrow molecular weight distributions and bimodal short chain branching distributions could be produced. The combined catalyst system demonstrates a number of discrepancies from an expected average behavior of the individual sites. Dual-site (1,2,4-Me₃Cp)₂ZrCl₂/(Me₅Cp)₂ZrCl₂ systems produce copolymers with lower incorporation than expected. Clear evidences for relative activity enhancement of the (Me₅Cp)₂ZrCl₂ catalyst in the mixture were observed in melting endotherms and Crystaf profiles. Molecular weights obtained by the mixture were higher than for any of the individual catalysts. A similar effect is observed for a dual-site system of the (1,2,4-Me₃Cp)₂ZrCl₂ catalyst together with the Me₄Si₂(Me₄Cp)₂ZrCl₂ catalyst as an alternative to (Me₅Cp)₂ZrCl₂.     

Influence of copper precursors in the steam reforming of methanol over Cu/SnO2/SiO2 catalysts

Cu/SnO₂/SiO₂ catalysts, prepared with three different copper precursors (copper nitrate, sulfate and chloride), were characterized and investigated for the steam reforming of methanol. Cu/SnO₂/SiO₂ catalyst, prepared with copper nitrate, showed the highest activity among the tested catalysts. The highest activity of the catalyst prepared with copper nitrate was ascribed to the highly dispersed Cu particles from CO adsorption experiment. The selectivity of methanol to H₂ decreased with an increase in the amount of acid on the surface of Cu/SnO₂/SiO₂ catalysts from FT-IR experiments.This revised version was published online in December 2005 with corrections to the Cover Date.     

Novel use of mesoporous aluminas as supports for Cp2ZrCl2 and Cp*ZrMe3: Ethylene polymerization and formation of polyethylene nanofibers

Mesoporous aluminas with average pore sizes of 4.3–7.8 nm were prepared by anodization of an aluminum film (AAO), and by a sol–gel templating method (TPL). In addition to a commercial alumina and sulfated TPL, the aluminas were used as supports for cyclopentadienyl zirconocene dichloride (Cp₂ZrCl₂) and trimethyl(η5‐pentamethylcyclopentadienyl)zirconium (Cp*ZrMe₃) and tested in the polymerization of ethylene. The metallocenes supported on the alumina prepared with the templating method and its sulfated modification exhibited polymerization activities of 440 and 350 kg_PE/(mol_Zr × h × bar), respectively, comparable to that obtained with silica‐supported metallocenes (390 kg_PE/(mol_Zr × h × bar)). The acid site distribution of the aluminas was studied with FTIR and temperature programmed desorption (TPD) of pyridine, and also the amount of medium and strong acid sites was determined gravimetrically from the adsorption of pyridine. Relative to the surface area, AAO with the highest amount of acid sites (2.10 μmol_py/m) adsorbed Cp₂ZrCl₂ and Cp*ZrMe₃ the most. Study of the polymers' morphology with a scanning electron microscope revealed polyethylene nanofibers in all the polymer samples, also in those obtained from the reference polymerizations with homogeneous Cp₂ZrCl₂ and Cp*ZrMe₃. This finding suggests that a catalyst support with a tubular pore structure is not a prerequisite for the formation of polymer nanofibers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4002–4012, 2007     

Preparation of Au Nanoparticles on Surface of Two Supports by Adsorption Phase Synthesis

By utilizing adsorption phase synthesis (APS), Au nanoparticles were prepared on the surface of SiO₂ with or without modification by Ni(OH)₂. TEM, XRD, and UV‐vis were employed to characterize the morphology of Au particles on the surface of two kinds of supports. The results showed that the average size of Au particles on the SiO₂ surface modified by Ni(OH)₂ was less than 5 nm. Due to high surface isoelectric point, Au particles formed in the adsorption layer were prone to distribute on the surface of SiO₂ modified by Ni(OH)₂. With content of Ni(OH)₂ in samples increasing, more Au particles with small size appeared on the support surface.     

The Versatile Coordination Modes of Monophosphine‐o‐Carborane in the Formation of Iridium and Rhodium Complexes: Synthesis,Reactivity, and Characterization

Monophosphine‐o‐carborane has four competitive coordination modes when it coordinates to metal centers. To explore the structural transitions driven by these competitive coordination modes, a series of monophosphine‐o‐carborane Ir,Rh complexes were synthesized and characterized. [Cp*M(Cl)₂{1‐(PPh₂)‐1,2‐C₂B₁₀H₁₁}] (M=Ir ( 1 a ), Rh ( 1 b ); Cp*=η⁵‐C₅Me₅), [Cp*Ir(H){7‐(PPh₂)‐7,8‐C₂B₉H₁₁}] ( 2 a ), and [1‐(PPh₂)‐3‐(η⁵‐Cp*)‐3,1,2‐MC₂B₉H₁₀] (M=Ir ( 3 a ), Rh ( 3 b )) can be all prepared directly by the reaction of 1‐(PPh₂)‐1,2‐C₂B₁₀H₁₁ with dimeric complexes [(Cp*MCl₂)₂] (M=Ir, Rh) under different conditions. Compound 3 b was treated with AgOTf (OTf=CF₃SO₃^?) to afford the tetranuclear metallacarborane [Ag₂(thf)₂(OTf)₂{1‐(PPh₂)‐3‐(η⁵‐Cp*)‐3,1,2‐RhC₂B₉H₁₀}₂] ( 4 b ). The arylphosphine group in 3 a and 3 b was functionalized by elemental sulfur (1 equiv) in the presence of Et₃N to afford [1‐{(S)PPh₂}‐3‐(η⁵‐Cp*)‐3,1,2‐MC₂B₉H₁₀] (M=Ir ( 5 a ), Rh ( 5 b )). Additionally, the 1‐(PPh₂)‐1,2‐C₂B₁₀H₁₁ ligand was functionalized by elemental sulfur (2 equiv) and then treated with [(Cp*IrCl₂)₂], thus resulting in two 16‐electron complexes [Cp*Ir(7‐{(S)PPh₂}‐8‐S‐7,8‐C₂B₉H₉)] ( 6 a ) and [Cp*Ir(7‐{(S)PPh₂}‐8‐S‐9‐OCH₃‐7,8‐C₂B₉H₉)] ( 7 a ). Compound 6 a further reacted with nBuPPh₂, thereby leading to 18‐electron complex [Cp*Ir(nBuPPh₂)(7‐{(S)PPh₂}‐8‐S‐7,8‐C₂B₉H₁₀)] ( 8 a ). The influences of other factors on structural transitions or the formation of targeted compounds, including reaction temperature and solvent, were also explored.     

Homogeneous tandem catalysis of the bis‐(diphenylphosphino)‐amine/chromium tetramerization catalyst with metallocene catalysts

Homogeneous tandem catalysis of the bis(diphenylphoshino)amine‐chromium oligomerization catalyst with the metallocenes Ph₂C(Cp)(9‐Flu)ZrCl₂ and rac‐EtIn₂ZrCl₂, is discussed. GC, CRYSTAF, and ¹³C NMR analysis of the products obtained from reactions at constant temperatures show that during tandem catalysis, α‐olefins, mainly 1‐hexene and 1‐octene, are produced from ethylene by the oligomerization catalyst and subsequently built into the polyethylene chain. At 40 °C the Cr/PNP catalyst acts as a tetramerization catalyst while the polymerization catalyst activity is low. Copolymerization of ethylene and the in situ produced α‐olefins have also been carried out by increasing the temperature from 40 °C, where primarily oligomerization takes place, to above 100 °C, where polymerization becomes dominant. The melting temperature of the polymer is dependent on the catalyst and cocatalyst ratios as well as on the temperature gradient followed during the reaction, while the presence of the oligomerization catalyst reduces the activity of the polymerization catalyst. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6847–6856, 2006     

Some mixed cyclopentadienyl–indenyl zirconium complexes with PhCH2 or PhCH2CH2 substituents in ethylene polymerization

(RCp)(R′Ind)ZrCl₂ complexes 1 – 6 (Cp = cyclopentadienyl; Ind = indenyl; 1 , R = PhCH₂ and R′ = H; 2 , R = PhCH₂ and R′ = PhCH₂; 3 , R = PhCH₂CH₂ and R′ = H; 4 , R = PhCH₂CH₂ and R′ = PhCH₂; 5 , R = o‐Me? PhCH₂CH₂ and R′ = H; 6 , R = o‐Me? PhCH₂ and R′ = H) were synthesized and characterized with ¹H NMR, elemental analysis, mass spectrometry, and infrared spectroscopy. Their catalytic behaviors were compared with those of (Et₃SiCp)(PhCH₂CH₂Cp)ZrCl₂, (PhCH₂Cp)₂ZrCl₂, (PhCH₂‐ CH₂Cp)₂ZrCl₂, (o‐Me? PhCH₂CH₂Cp)₂ZrCl₂, and (Ind)₂ZrCl₂ in ethylene polymerization in the presence of methylaluminoxane. Complex 5 showed high activity up to 2.43 × 10⁶ g of polyethylene (PE)/mol of Zr h, and complex 4 produced PE with bimodal molecular weight distributions. The methyl group at the 2‐position of phenyl in complex 5 increased the activity greatly. The relationships between the polymerization results and the structures were analyzed with NMR spectral data. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1261–1269, 2005     

Effect of substituents on the catalytic properties of bis(cyclopentadienyl) zirconocene dichlorides in polymerization of ethene

Comparative analysis of catalytic activity of substituted bis(cyclopentadienyl)zirconium dichlorides with the general formula (R _n Cp)₂ZrCl₂ (Cp₂ZrCl₂, (MeCp)₂ZrCl₂, (PrⁱCp)₂ZrCl₂, (Prⁱ ₂Cp)₂ZrCl₂, (BuⁿCp)₂ZrCl₂, (BuⁱCp)₂ZrCl₂, (Bu^tCp)₂ZrCl₂, Cp^* ₂ZrCl₂ (Cp^*=Me₅C₅), (Me₃SiCp)₂ZrCl₂, (cyclo-C₆H₁₁Cp)₂ZrCl₂, and [(cyclo-C₆H₁₁)₂Cp]₂ZrCl₂) in ethene polymerization using polymethylalumoxane as the cocatalyst was performed. The molecular mass characteristics of the polyethylene samples obtained were determined. A linear correlation of the specific activity of the catalysts and the turnover number with the electronic and steric characteristics of substituents at the Cp ring of the complexes was established for the first time. Analysis of the polymerization kinetics and the obtained correlation between the specific activity of the complexes and molecular mass characteristics of the polyethylene samples suggest that alkyl substituents participate in reactions responsible for the restriction of the polymer chain growth and regeneration of the active center. These interactions most likely involve associates of AlMe₃ with polymethylalumoxane molecules.     

Synthesis and characterization of ethylene‐propylene‐1‐pentene terpolymers

Ethylene (E), propylene (P), and 1‐pentene (A) terpolymers differing in monomer composition ratio were produced, using the metallocenes rac‐ethylene bis(indenyl) zirconium dichloride/methylaluminoxane (rac‐Et(Ind)₂ZrCl₂/MAO), isopropyl bis(cyclopentadienyl)fluorenyl zirconium dichloride/methylaluminoxane (Me₂C(Cp)(Flu)ZrCl₂/MAO, and bis(cyclopentadienyl)zirconium dichloride, supported on silica impregnated with MAO (Cp₂ZrCl₂/MAO/SiO₂/MAO) as catalytic systems. The catalytic activities at 25 °C and normal pressure were compared. The best result was obtained with the first catalyst. A detailed study of ¹³C NMR chemical shifts, triad sequences distributions, monomer‐average sequence lengths, and reactivity ratios for the terpolymers is presented. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 947–957, 2008     

Ethylene‐Norbornene Terpolymerization with 5‐Vinyl‐2‐norbornene Using Single‐Site Catalysts

The incorporation of 5‐vinyl‐2‐norbornene (VNB) into ethylene‐norbornene copolymer was investigated with catalysts [Ph₂C(Fluo)(Cp)]ZrCl₂ ( 1 ), rac‐[Et(Ind)₂]ZrCl₂ ( 2 ), and [Me₂Si(Me₄Cp)^tBuN]TiCl₂ ( 3 ) in the presence of MAO by terpolymerizing different amounts of 5‐vinyl‐2‐norbornene with constant amounts of ethylene and norbornene at 60°C. The highest cycloolefin incorporations and highest activity in terpolymerizations were achieved with 1 . The distribution of the monomers in the terpolymer chain was determined by NMR spectroscopy. As confirmed by XRD and DSC analysis, catalysts 1 and 3 produced amorphous terpolymer, whereas 2 yielded terpolymer with crystalline fragments of long ethylene sequences. When compared with poly‐(ethylene‐co‐norbornene), VNB increased both the glass transition temperatures and molar masses of terpolymers produced with the constrained geometry catalyst whereas decreased those for the metallocenes.     

Tacticity of poly‐α‐olefins from poly‐1‐hexene to poly‐1‐octadecene

A systematic study of the influence of the α‐olefin size, the catalyst stereospecificity and the reaction temperature was done on the catalytic activity and tacticity of poly‐α‐olefins from 1‐hexene to 1‐octadecene. The metallocenes used were rac‐Et[Ind₂]ZrCl₂ ( 1 ) and Me₂C[Cp(9‐Flu)]ZrCl₂ ( 2 ) to obtain isotactic and syndiotactic polyolefins. Some catalysts giving atactic polymers were also used in order to study all the possible ¹³C NMR pentades. Catalytic activities increased and isotacticity and syndiotacticity decreased with temperature, but no real trend was found with the α‐olefin size. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4744–4753, 2005     

Syndiotactic polypropene with MCM‐41 supported metallocene [Me2C(Cp)(Flu)]ZrCl2

Mesoporous aluminosilicates – type MCM‐41 – were used as carriers for syndiospecific propene polymerisation using [Me₂C(Cp)(Flu)]ZrCl₂/MAO as catalyst. Alumina‐free mesoporous MCM‐41 reveals a far greater polymerisation activity than the analogous carrier containing alumina. The use of MCM‐41 as carrier material at low propene concentration and high polymerisation temperature produces syndiotactic polypropene (sPP) with higher syndiotacticity and higher melting points than achieved when using a homogenous system or a supported system based on spherical SiO₂.     

Chemistry of Diruthenium and Dirhodium Analogues of Pentaborane(9): Synthesis and Characterization of Metal N,S‐Heterocyclic Carbene and B‐Agostic Complexes

Building upon our earlier results on the synthesis of electron‐precise transition‐metal–boron complexes, we continue to investigate the reactivity of pentaborane(9) and tetraborane(10) analogues of ruthenium and rhodium towards thiazolyl and oxazolyl ligands. Thus, mild thermolysis of nido‐[(Cp*RuH)₂B₃H₇] ( 1 ) with 2‐mercaptobenzothiazole (2‐mbtz) and 2‐mercaptobenzoxazole (2‐mboz) led to the isolation of Cp*‐based (Cp*=η⁵‐C₅Me₅) borate complexes 5 a , b [Cp*RuBH₃L] ( 5 a : L=C₇H₄NS₂; 5 b : L=C₇H₄NOS)) and agostic complexes 7 a , b [Cp*RuBH₂(L)₂], ( 7 a : L=C₇H₄NS₂; 7 b : L=C₇H₄NOS). In a similar fashion, a rhodium analogue of pentaborane(9), nido‐[(Cp*Rh)₂B₃H₇] ( 2 ) yielded rhodaboratrane [Cp*RhBH(L)₂], 10 (L=C₇H₄NS₂). Interestingly, when the reaction was performed with an excess of 2‐mbtz, it led to the formation of the first structurally characterized N,S‐heterocyclic rhodium‐carbene complex [(Cp*Rh)(L₂)(1‐benzothiazol‐2‐ylidene)] ( 11 ) (L=C₇H₄NS₂). Furthermore, to evaluate the scope of this new route, we extended this chemistry towards the diruthenium analogue of tetraborane(10), arachno‐[(Cp*RuCO)₂B₂H₆] ( 3 ), in which the metal center possesses different ancillary ligands.     

New Half‐Metallocene Catalysts Generating Polyethylene with Bimodal Molecular Weight Distribution and Syndiotactic Polystyrene

A new type of half‐metallocene catalyst for the polymerization of ethylene and styrene, Cp*M((O)₃O₉Si₇(c‐C₅H₉)₇) (M = Ti ( 1) ; Zr ( 2 )), is prepared by the reaction of (HO)₃O₉Si₇(c‐C₅H₉)₇ with Cp*MCl₃ in the presence of triethylamine. Complex 1 is stable to heat and air, but its heavier congener 2 is slightly air‐sensitive. The catalytic systems 1 /MMAO and 2 /MMAO, in which MMAO is modified methylaluminoxane, show good activities in ethylene polymerization, with that of 2 /MMAO greater than that of 1 /MMAO. Polyethylenes with bimodal molecular weight distributions were obtained. In addition, the catalytic system 1 /MMAO shows fairly good activities for the syndiospecific polymerization of styrene.