Kinetics of propylene polymerization initiated by rac‐Me2Si(1‐C5H2‐2‐Me‐4‐tBu)2Zr(NME2)2/MAO catalyst

The kinetics of propylene polymerization initiated by ansa‐metallocene diamide compound rac‐Me₂Si(CMB)₂Zr(NMe₂)₂ (rac‐1, CMB = 1‐C₅H₂‐2‐Me‐4‐^tBu)/methylaluminoxane (MAO) catalyst were investigated. The formation of cationic active species has been studied by the sequential NMR‐scale reactions of rac‐1 with MAO. The rac‐1 is first transformed to rac‐Me₂Si(CMB)₂ZrMe₂ (rac‐2) through the alkylation mainly by free AlMe₃ contained in MAO. The methylzirconium cations are then formed by the reaction of rac‐2 and MAO. Small amount of MAO ([Al]/[Zr] = 40) is enough to completely activate rac‐1 to afford methylzirconium cations that can polymerize propylene. In the lab‐scale polymerizations carried out at 30°C in toluene, the rate of polymerization (R_p) shows maximum at [Al]/[Zr] = 6,250. The R_p increases as the polymerization temperature (T_p) increases in the range of T_p between 10 and 70°C and as the catalyst concentration increases in the range between 21.9 and 109.6 μM. The activation energies evaluated by simple kinetic scheme are 4.7 kcal/mol during the acceleration period of polymerization and 12.2 kcal/mol for an overall reaction. The introduction of additional free AlMe₃ before activating rac‐1 with MAO during polymerization deeply influences the polymerization behavior. The iPPs obtained at various conditions are characterized by high melting point (approximately 155°C), high stereoregularity (almost 100% [mmmm] pentad), low molecular weight (MW), and narrow molecular weight distribution (below 2.0). The fractionation results by various solvents show that iPPs produced at T_p below 30°C are compositionally homogeneous, but those obtained at T_p above 40°C are separated into many fractions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 737–750, 1999     

MAO‐free polymerization of propylene by rac‐ Me2Si(1‐C5H2‐2‐Me‐4‐tBu)2Zr(NMe2)2 compound

Ansa‐zirconocene diamide complex rac‐Me₂Si(CMB)₂Zr(NMe₂)₂ (rac‐1, CMB = 1‐C₅H₂‐2‐Me‐4‐^tBu) reacts with AlR₃ (R = Me, Et, i‐Bu) and then with [CPh₃]⁺[B(C₆F₅)₄]⁻ (2) in toluene in order to in situ generate cationic alkylzirconium species. In the sequential NMR‐scale reactions of rac‐1 with various amount of AlMe₃ and 2, rac‐1 transforms first to rac‐Me₂Si(CMB)₂Zr(Me)(NMe₂) (rac‐3) and rac‐Me₂Si(CMB)₂ZrMe₂ (rac‐4) by the reaction with AlMe₃, and then to [rac‐Me₂Si(CMB)₂ZrMe]⁺ (5⁺) cation by the reaction of the resulting mixtures with 2. The activities of propylene polymerizations by rac‐1/Al(i‐Bu)₃/2 system are dependent on the type and concentration of AlR₃, resulting in the order of activity: rac‐1/Al(i‐Bu)₃/2 > rac‐1/AlEt₃/2 > rac‐1/MAO ≫ rac‐1/AlMe₃/2 system. The bulkier isobutyl substituents make inactive catalytic species sterically unfavorable and give rise to more separated ion pairs so that the monomers can easily access to the active sites. The dependence of the maximum rate (R_{p, max}) on polymerization temperature (T_p) obtained by rac‐1/Al(i‐Bu)₃/2 system follows Arrhenius relation, and the overall activation energy corresponds to 0.34 kcal/mol. The molecular weight (MW) of the resulting isotactic polypropylene (iPP) is not sensitive to Al(i‐Bu)₃ concentration. The analysis of regiochemical errors of iPP shows that the chain transfer to Al(i‐Bu)₃ is a minor chain termination. The 1,3‐addition of propylene monomer is the main source of regiochemical sequence and the [mr] sequence is negligible, as a result the meso pentad ([mmmm]) values of iPPs are very high ([mmmm] > 94%). These results can explain the fact that rac‐1/Al(i‐Bu)₃/2 system keeps high activity over a wide range of [Al(i‐Bu)₃]/[Zr] ratio between 32 and 3,260. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1071–1082, 1999     

A DFT Quantum‐Chemical Study of Ion‐Pair Formation for the Catalyst Cp2ZrMe2 /MAO

A process of ion‐pair formation in the system Cp₂ZrMe₂/methylaluminoxane (MAO) has been studied by means of density functional theory quantum‐chemical calculations for MAOs with different structures and reactive sites. An interaction of Cp₂ZrMe₂ with a MAO of the composition (AlMeO)₆ results in the formation of a stable molecular complex of the type Al₅Me₆O₅Al(Me)O–Zr(Me)Cp₂ with an equilibrium distance r(Zr–O) of 2.15 Å. The interaction of Cp₂ZrMe₂ with “true” MAO of the composition (Al₈Me₁₂O₆) proceeds with a tri‐coordinated aluminum atom in the active site (OAlMe₂) and yields the strongly polarized molecular complex or the μ‐Me‐bridged contact ion pair ( d ) [Cp₂(Me)Zr(μMe)Al≡MAO] with the distances r(Zr–μMe) = 2.38 Å and r(Al–μMe) = 2.28 Å. The following interaction of the μ‐Me contact ion pair ( d ) with AlMe₃ results in a formation of the trimethylaluminum (TMA)‐separated ion pair ( e ) [Cp₂Zr(μMe)₂AlMe₂]⁺–[MeMAO]^– with r[Zr–(MeMAO)] equal to 4.58 Å. The calculated composition and structure of ion pairs ( d ) and ( e ) are consistent with the ¹³C NMR data for the species detected in the Cp₂ZrMe₂/MAO system. An interaction of the TMA‐separated ion pair ( e ) with ethylene results in the substitution of AlMe₃ by C₂H₄ in a cationic part of the ion pair ( e ), and the following ethylene insertion into the Zr–Me bond. This reaction leads to formation of ion pair ( f ) of the composition [Cp₂ZrCH₂CH₂CH₃]⁺–[Me‐MAO]^– named as the propyl‐separated ion pair. Ion pair ( f ) exhibits distance r[Zr–(MeMAO)] = 3.88 Å and strong C_γ‐agostic interaction of the propyl group with the Zr atom. We suppose this propyl‐separated ion pair ( f ) to be an active center for olefin polymerization.     

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     

Olefin polymerization with Me4Cp–Amido complexes with electron‐withdrawing groups

A series of Me₄Cp–amido complexes {[η⁵:η¹‐(Me₄C₅)SiMe₂NR]TiCl₂; R = t‐Bu, 1 ; C₆H₅, 2 ; C₆F₅, 3 ; SO₂Ph, 4 ; or SO₂Me, 5 } were prepared and investigated for olefin polymerization in the presence of methylaluminoxane (MAO). X‐ray crystallography of complexes 3 and 4 revealed very long Ti N bonds relative to the bonds of 1 . These complexes were employed for ethylene–styrene copolymerizations, styrene homopolymerizations, and propylene homopolymerizations in the presence of MAO. The productivities of the catalysts derived from 3 – 5 were much lower than the productivity of the catalyst derived from 1 for the propylene polymerizations and ethylene–styrene copolymerizations, whereas the styrene polymerization activities were much higher for the catalysts derived from 3 – 5 than for the catalyst derived from 1 . The polymerization behavior of the catalysts derived from the metallocenes 3 – 5 were more reminiscent of monocyclopentadienyl titanocene Cp′TiX₃/MAO catalysts than of CpATiX₂/MAO catalysts such as 1 containing alkylamido ligands. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4649–4660, 2000     

Pressure and trimethylaluminum effects on ethene/1‐hexene copolymerization with methylaluminoxane‐activated (1,2,4‐Me3Cp)2ZrCl2: Trimethylaluminum suppression of standard termination reactions after 1‐hexene insertion

Ethene homopolymerizations and copolymerizations with 1‐hexene were catalyzed by methylaluminoxane‐activated (1,2,4‐Me₃Cp)₂ZrCl₂. Investigations of the effects of various pressures on the homopolymerizations and copolymerizations and of the effects of different concentrations of trimethylaluminum (TMA) on the copolymerizations were performed. The characteristics of the ethene/1‐hexene copolymers agreed with expectations for changes in the ethene concentration: the incorporation of 1‐hexene decreased, whereas the melting point and crystallinity increased, with increasing pressure. The main termination mechanism of the homopolymerizations was β‐hydrogen transfer to the monomer. Termination mechanisms resulting in vinylidene unsaturations dominated in the copolymerizations. Standard termination mechanisms producing vinyl and trans‐vinylene unsaturations occurred in parallel and were not influenced by the ethene or TMA concentration. In addition, some chain transfer to TMA, producing saturated end groups after hydrolysis, occurred. Copolymerizations with different additions of TMA, with the other polymerization conditions kept constant, showed that the catalytic productivity [tons of polyethylene/(mol of Zr h)], the 1‐hexene incorporation, and the molecular weight (from gel permeation chromatography) were independent of the TMA concentration. Surprisingly, the vinylidene content decreased almost linearly with increasing TMA concentration. TMA might have coordinated to the catalytic site after 1‐hexene insertion and rotation to the β‐agostic state and, therefore, suppressed the standard termination reactions after 1‐hexene insertion. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2584–2597, 2005     

Stabilization of a Silaaldehyde by its η2 Coordination to Tungsten

Treatment of pyridine‐stabilized silylene complexes [(η⁵‐C₅Me₄R)(CO)₂(H)W?SiH(py)(Tsi)] (R=Me, Et; py=pyridine; Tsi=C(SiMe₃)₃) with an N‐heterocyclic carbene ^MeIⁱPr (1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene) caused deprotonation to afford anionic silylene complexes [(η⁵‐C₅Me₄R)(CO)₂W?SiH(Tsi)][H^MeIⁱPr] (R=Me ( 1‐Me ); R=Et ( 1‐Et )). Subsequent oxidation of 1‐Me and 1‐Et with pyridine‐N‐oxide (1 equiv) gave anionic η²‐silaaldehydetungsten complexes [(η⁵‐C₅Me₄R)(CO)₂W{η²‐O?SiH(Tsi)}][H^MeIⁱPr] (R=Me ( 2‐Me ); R=Et ( 2‐Et )). The formation of an unprecedented W‐Si‐O three‐membered ring was confirmed by X‐ray crystal structure analysis.     

Ethylene/hexene copolymerization with the heterogeneous catalyst system SiO2/MAO/rac‐Me2Si[2‐Me‐4‐Ph‐Ind]2ZrCl2: The filter effect

The main focus of this study is the ethylene/hexene copolymerization with the silica supported metallocene SiO₂/MAO/rac‐Me₂Si[2‐Me‐4‐Ph‐Ind]₂ZrCl₂. Polymerizations were carried out in toluene at a reaction temperature of 40°C–60°C and the cocatalyst used was triisobutylaluminium (TIBA). The kinetics of the copolymerization reactions (reactivity ratios r_E/H, monomer consumption during reaction) were investigated and molecular weights M_w, molecular weight distributions MWD and melting points T_m were determined. A schematic model for the blend formation observed was developed that based on a filtration effect of monomers by the copolymer shell around the catalyst pellet.     

Nitridorhenium(V) Complexes with 1,3‐Dialkyl‐4,5‐dimethylimidazole‐2‐ylidenes

The nitridorhenium(V) complexes [ReNCl₂(PR₂Ph)₃] (R = Me, Et) react with the N‐heterocyclic carbenes (NHC) 1,3‐diethyl‐4,5‐dimethylimidazole‐5‐ylidene (L^Et) or 1,3,4,5‐tetramethylimidazole‐2‐ylidene (L^Me) in absolutely dry THF under complete replacement of the equatorial coordination sphere. The resulting [ReNCl(L^R)₄]⁺ complexes (L^R = L^Me, L^Et) are moderately stable as solids and in solution, but decompose in hot methanol under formation of [ReO₂(L^R)₄]⁺ complexes. With 1,3‐diisopropyl‐4,5‐dimethylimidazole‐5‐ylidene (L^i‐Pr), the loss of the nitrido ligand and the formation of a dioxo species is more rapid and no nitridorhenium intermediate could be isolated. The Re‐C bond lengths in [ReNCl(L^Et)₄]Cl of approximately 2.195Å are relatively long and indicate mainly σ‐bonding in the electron‐deficient d² system under study. The hydrolysis of the nitrido complexes proceeds via the formation of [ReO₃N]^2? anions as could be verified by the isolation and structural characterization of the intermediates [{ReN(PMe₂Ph)₃}{ReO₃N}]₂ and [{ReN(OH₂)(L^Et)₂}₂O][ReO₃N].     

Copolymerization of propylene with 1‐octene catalyzed by rac‐Me2Si(2,4,6‐Me3‐Ind)2ZrCl2/methyl aluminoxane

The copolymerization of propylene with 1‐octene was carried out with rac‐dimethylsilylbis(2,4,6‐trimethylindenyl)zirconium dichloride as a catalyst activated by methylaluminoxane (MAO) and an MAO/triisobutylaluminum mixture. The copolymerization conditions, including the polymerization temperature, Al/Zr molar ratio, and 1‐octene concentration in the feed, significantly influenced the catalyst activity, 1‐octene incorporation, polymer molecular weight, and melting temperature. The addition of 1‐octene to the polymerization system caused a decrease in the activity, whereas the melting temperature and intrinsic viscosity of the polymer increased. The microstructure of the propylene–1‐octene copolymer was characterized by ¹³C NMR, and the reactivity ratios of the copolymerization were estimated from the dyad distribution of the monomer sequences. The amount of regioirregular structures arising from 2,1‐ and 1,3‐misinserted propylene decreased as the 1‐octene content increased. The influence of the propagation chain on the polymerization mechanism is proposed to be the main reason for the changes in the reactivity ratios and regioirregularity with the polymerization conditions. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4299–4307, 2000     

Synthesis and characterization of functional polysilanes [RMe2Si(CH2)x(Me)Si]n (R = 2‐Fu, 5‐Me‐2‐Fu, 2‐Th, 4‐Me‐2‐Th; x = 2, 3) with appended furyl/thienyl groups on the carbosilyl side chains and their application in the generation and stabilization of palladium nanoparticles

The polysilanes [RMe₂Si(CH₂)_x(Me)Si]_n [x = 2, 3; R = 2‐Fu ( 1, 2 ), 5‐Me‐2‐Fu ( 3, 4 )] bearing furyl‐substituted carbosilyl side chains have been synthesized by dehalocondensation reaction (Wurtz coupling) of the corresponding carbosilanes using sodium dispersion in refluxing toluene. On the other hand, analogous polysilanes with appended thienyl groups [x = 2, 3; R = 2‐Th ( 5, 6 ), 4‐Me‐2‐Th ( 7, 8 )] are only accessible by the reaction of the corresponding carbosilane precursors under mild Wurtz coupling conditions (THF, RT). These polysilanes reveal monomodal molecular weight distribution with M_w/PDI = 3.3–5.4 × 10⁴/1.22–1.47 ( 1–4 ) and 9.1–14.4 × 10⁴/1.45–1.61 ( 5–8 ) and are characterized by FT‐IR, multinuclear (¹H, ¹³C{¹H}, ²⁹Si{¹H}) NMR, and UV/PL spectral studies as well as thermogravimetric analysis (TGA). Preliminary studies on the reactivity of polysilane 2 with palladium acetate (toluene, RT) reveal the formation of spherical palladium nanoparticles of size 8.2 ± 0.6 nm, which remain stable in solution for several weeks. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7816–7826, 2008     

A Novel Divalent Ytterbium Complex Supported by a Bridged Diamide Ligand: Synthesis and Structure of [{Me2Si(NPh)2Yb(THF)2}(μ3‐Cl)(μ4‐Cl){Li(THF)}2]2·2THF

The reaction of anhydrous YbCl₃ with 1 equiv. of Li₂Me₂Si(NPh)₂ in THF, after workup, yielded a ytterbium(III) chloride [{Me₂Si(NPh)₂Yb}(μ₂‐Cl)(TMEDA)]₂·3PhMe ( 1 ) (TMEDA=tetramethylethanediamine). The same reaction followed by treatment with Na‐K alloy afforded a new ytterbium(II) complex supported by a bridged diamide with four coordinated LiCl molecules, [{Me₂Si(NPh)₂Yb(THF)₂}(μ₃‐Cl)(μ₄‐Cl){Li(THF)}₂]₂·2THF ( 2 ) in high yield. Both complexes were structurally characterized by X‐ray analysis to be dimers. Complex 1 was a chlorine‐bridged dimer with ytterbium in a distorted octahedral geometry. In complex 2 two [Me₂Si(NPh)₂Yb(THF)₂]‐(μ₃‐Cl)[Li(THF)]₂ moieties were connected with each other by two μ₄‐Cl bridges to form a "chair‐form" framework.     

Stopped‐flow polymerizations of ethene and propene in the presence of the catalyst system rac‐Me2Si(2‐methyl‐4‐phenyl‐1‐indenyl)2ZrCl2/methylaluminoxane

The kinetics of ethene and propene polymerization at 20–60°C in the presence of the homogeneous catalyst system rac‐Me₂Si(2‐methyl‐4‐phenyl‐1‐indenyl)₂ZrCl₂/methylaluminoxane was investigated by means of stopped‐flow techniques. The specific rate of chain propagation, measured at the very short reaction times typical of this method, turned out to be ≈10² times higher for ethene than for propene; this suggests that diffusion limitations through the poly(ethylene) precipitating at longer reaction times may be responsible for the fact that the two monomers polymerize instead at comparable rates under “standard” conditions. It was also found that the concentration of active sites is significantly lower than the analytical Zr concentration.     

Higher α‐olefin polymerizations catalyzed by rac‐Me2Si(1‐C5H2‐2‐CH3‐4‐tBu)2Zr(NMe2)2/Al(iBu)3/[Ph3C][B(C6F5)4]

Polymerizations of higher α‐olefins, 1‐pentene, 1‐hexene, 1‐octene, and 1‐decene were carried out at 30 °C in toluene by using highly isospecific rac‐Me₂Si(1‐C₅H₂‐2‐CH₃‐4‐^t Bu)₂Zr(NMe₂)₂ (rac‐1) compound in the presence of Al(iBu)₃/[CPh₃][B(C₆F₅)₄] as a cocatalyst formulation. Both the bulkiness of monomer and the lateral size of polymer influenced the activity of polymerization. The larger lateral of polymer chain opens the π‐ligand of active site wide and favors the insertion of monomer, while the large size of monomer inserts itself into polymer chain more difficultly due to the steric hindrance. Highly isotactic poly(α‐olefin)s of high molecular weight (MW) were produced. The MW decreased from polypropylene to poly(1‐hexene), and then increased from poly(1‐hexene) to poly(1‐decene). The isotacticity (as [mm] triad) of the polymer decreased with the increased lateral size in the order: poly(1‐pentene) > poly(1‐hexene) > poly(1‐octene) > poly(1‐decene). The similar dependence of the lateral size on the melting point of polymer was recorded by differential scanning calorimetry (DSC). ¹H NMR analysis showed that vinylidene group resulting from β‐H elimination and saturated methyl groups resulting from chain transfer to cocatalyst are the main end groups of polymer chain. The vinylidene and internal double bonds are also identified by Raman spectroscopy. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1687–1697, 2000     

Synthesis and characterization of aluminum(III) and tin(II) complexes supported by diiminophosphinate ligands and their application in ring‐opening polymerization catalysis of ε‐caprolactone

A series of Al(III) and Sn(II) diiminophosphinate complexes have been synthesized. Reaction of Ph(ArCH₂)P(?NBu^t)NHBu^t (Ar = Ph, 3 ; Ar = 8‐quinolyl, 4 ) with AlR₃ (R = Me, Et) gave aluminum complexes [R₂Al{(NBu^t)₂P(Ph)(CH₂Ar)}] (R = Me, Ar = Ph, 5 ; R = Me, Ar = 8‐quinolyl, 6 ; R = Et, Ar = Ph, 7 ; R = Et, Ar = quinolyl, 8 ). Lithiated 3 and 4 were treated with SnCl₂ to afford tin(II) complexes [ClSn{(NBu^t)₂P(Ph)(CH₂Ar)}] (Ar = Ph, 9 ; Ar = 8‐quinolyl, 10 ). Complex 9 was converted to [(Me₃Si)₂NSn{(NBu^t)₂P(Ph)(CH₂Ph)}] ( 11 ) by treatment with LiN(SiMe₃)₂. Complex 11 was also obtained by reaction of 3 with [Sn{N(SiMe₃)₂}₂]. Complex 9 reacted with [LiOC₆H₄Bu^t‐4] to yield [4‐Bu^tC₆H₄OSn{(NBu^t)₂P(Ph)(CH₂Ph)}] ( 12 ). Compounds 3–12 were characterized by NMR spectroscopy and elemental analysis. The structures of complexes 6 , 10 , and 11 were further characterized by single crystal X‐ray diffraction techniques. The catalytic activity of complexes 5–8 , 11 , and 12 toward the ring‐opening polymerization of ε‐caprolactone (CL) was studied. In the presence of BzOH, the complexes catalyzed the ring‐opening polymerization of ε‐CL in the activity order of 5 > 7 ≈ 8 > 6 ? 11 > 12 , giving polymers with narrow molecular weight distributions. The kinetic studies showed a first‐order dependency on the monomer concentration in each case. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4621–4631, 2006     

Heterobi‐ and ‐trimetallic Ion Pairs of Zirconocene‐Based Isoselective Olefin Polymerization Catalysts with AlMe3

The reactivity towards AlMe₃ of discrete cationic ansa‐zirconocenes 2 a,b that are ubiquitously used in isoselective propylene polymerization and based on [{Ph(H)C(3,6‐tBu₂‐Flu)(3‐tBu‐5‐Et‐Cp)}ZrMe₂)] {Cp‐Flu} and rac‐[{Me₂Si‐(2‐Me‐4‐Ph‐Ind)₂}ZrMe₂] {SBI} was scrutinized. The first example of a structurally characterized Group 4 metallocene AlMe₃ adduct ( 3 b ) is reported. In the presence of excess AlMe₃, the {SBI}‐based AlMe₃ adduct 3 b undergoes a slow decomposition via C? H activation in a bridging methyl unit to yield a new species ( 4 b ) with a trimetallic {Zr(μ‐CH₂)(μ‐Me)AlMe(μ‐Me)AlMe₂} core. EXSY NMR data for the process 2 b ? 3 b → 4 b suggest very rapid and reversible binding of an additional AlMe₃ molecule onto AlMe₃ adduct 3 b . The resulting heterotrimetallic species intermediates exchange of methyl groups between different metal centers and slowly undergoes the C? H activation reaction towards 4 b .     

Neue Synthesen von Me2SbX (X = Cl,I) und Kristallstrukturen von Me2SbI und [(Me3Si)2CH]2SbCl

Novel Syntheses of Me₂SbX (X = Cl, I) and Crystal Structures of Me₂SbI and [(Me₃Si)₂CH]₂SbCl The crystal structures of Me₂SbI (Me = CH₃) and [(Me₃Si)₂CH]₂SbCl have been determined by X‐ray methods. Both molecules are pyramidal. The Me₂SbI molecules are associated to chains through short intermolecular Sb…I distances (366,7(1) pm) with linear I–Sb…I units (171,87(4)°) and bent Sb–I…Sb bridges (116,83(3)°).     

Synthesis and crystallization behavior study of syndiotactic polystyrene‐g‐isotactic polypropylene (sPS‐g‐iPP) graft copolymers

Based on coordination polymerization mechanism only, novel stereoregular graft copolymers with syndiotactic polystyrene main chain and isotactic polypropylene side chain (sPS‐g‐iPP) were synthesized via two steps of catalytic reactions. First, a chain transfer reaction was initiated by a chain transfer complex composed of a styrene derivative, 1,2‐bis(4‐vinylphenyl)ethane, and hydrogen in propylene polymerization mediated by rac‐Me₂Si[2‐Me‐4‐Ph(Ind)]₂ZrCl₂ and MAO, which gave iPP macromonomer bearing a terminal styryl group (iPP‐t‐St). Then the iPP‐t‐St macromonomers of varied molecular mass were engaged in syndiospecific styrene polymerization over a typical mono‐titanocene catalyst (CpTiCl₃/MAO) under different conditions to produce sPS‐g‐iPP graft copolymers of varied structure. With an effective purification process, well‐defined sPS‐g‐iPP copolymers were obtained, which were then subjected to differential scanning calorimetry (DSC) and polarized optical micrograph (POM) studies. The graft copolymers were generally found with dual melting and crystallization temperatures, which were ascribable respectively to the sPS backbone and iPP graft. However, it was revealed that the two segments displayed largely different melting and crystallization behaviors than sPS homopolymer and the precursory iPP‐t‐St macromonomer. Consequently, the graft copolymer exhibited much distinctive crystalline morphologies when compared with their individual components. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Random propene/4‐methyl‐1‐pentene copolymers synthesized with C2 symmetric highly isospecific metallocenes

Propene (P)/4‐methyl‐1‐pentene (Y) copolymers in a wide range of composition were prepared with isospecific single center catalysts, rac‐Et(IndH₄)₂ZrCl₂ ( EBTHI ), rac‐Me₂Si(2‐Me‐BenzInd)₂ZrCl₂ ( MBI ), and rac‐CH₂(3‐^tBuInd)₂ZrCl₂ ( TBI ). ¹³C NMR analysis of copolymers and statistical elaboration of microstructural data at triad level were performed. Unprecedented and surprising results are here reported. Random P/Y copolymers were prepared with the most isospecific catalyst, TBI , that is known to prepare ethene/propene and ethene/4‐methyl‐1‐pentene copolymers with long homosequences of both comonomers, whereas longer homosequences of both comonomers were observed in copolymers from the less enantioselective metallocenes EBTHI and MBI . These findings, which are against what is acknowledged in the field, can pave the way for the preparation on a large scale of random propene‐based copolymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2575–2585     

Syntheses and Characterization of New Vinyl‐Borylene Complexes by the Hydroboration of Alkynes with [(μ3‐BH)(Cp*RuCO)2(μ‐CO)Fe(CO)3]

Room temperature photolysis of a triply‐bridged borylene complex, [(μ₃‐BH)(Cp*RuCO)₂(μ‐CO)Fe(CO)₃] ( 1 a ; Cp*=C₅Me₅), in the presence of a series of alkynes, 1,2‐diphenylethyne, 1‐phenyl‐1‐propyne, and 2‐butyne led to the isolation of unprecedented vinyl‐borylene complexes (Z)‐[(Cp*RuCO)₂(μ‐CO)B(CR)(CHR′)] ( 2 : R, R′=Ph; 3 : R=Me, R′=Ph; 4 : R, R′=Me). This reaction permits a hydroboration of alkyne through an anti ‐ Markovnikov addition. In stark contrast, in the presence of phenylacetylene, a metallacarborane, closo‐[1,2‐(Cp*Ru)₂(μ‐CO)₂{Fe₂(CO)₅}‐4‐Ph‐4,5‐C₂BH₂] ( 5 a) , is formed. A plausible mechanism has been proposed for the formation of vinyl‐borylene complexes, which is supported by density functional theory (DFT) methods. Furthermore, the calculated ¹¹B NMR chemical shifts accurately reflect the experimentally measured shifts. All the new compounds have been characterized in solution by mass spectrometry and IR, ¹H, ¹¹B, and ¹³C NMR spectroscopies and the structural types were unequivocally established by crystallographic analysis of 2 , 5 a , and 5 b .