Methylaluminoxane‐free ethylene polymerization with in situ activated zirconocene triisobutylaluminum catalysts and silica‐supported stabilized borate cocatalysts

Heterogenization of tris(pentafluorophenyl)borane [B(C₆F₅)₃] on a silica support stabilized with chlorotriphenylmethane (CICPh₃) and N,N‐dimethylaniline (HNMe₂Ph) creates the following supported borane cocatalysts: [HNMe₂Ph]⁺[B(C₆F₅)₃‐SiO₂]^? and [CPh₃]⁺[B(C₆F₅)₃‐SiO₂]^?. These supported catalysts were reacted with Cp₂ZrCl₂ TIBA in situ to generate active metallocene species in the reactor. Triisobutylaluminum (TIBA) was a good coactivator for dichloro‐zirconocene, acting as the prealkylating agent to generate cationic zirconocene (Cp₂ZrC₄H₉⁺). The catalytic performances were determined from the kinetics of ethylene‐consumption profiles that were independent of the time dedicated to the activation of the catalysts. The scanning electron microscopy‐energy dispersive X‐ray measurements showed that B(C₆F₅)₃ dispersed uniformly on the silica support. Under our reaction conditions, the [CPh₃]⁺[B(C₆F₅)₃‐SiO₂]^? system had higher productivity and weight‐average molecular weight than the [HNMe₂Ph]⁺[B(C₆F₅)₃‐SiO₂]^? system. For the [CPh₃]⁺[B(C₆F₅)₃‐SiO₂]^? system, the productivity increased with the amount catalyst; however, the polydispersity index of polyethylene synthesized did not change. The final shape of polymer particles was a larger‐diameter version of the original support particle. The polymer particles synthesized with supported [CPh₃]⁺[B(C₆F₅)₃‐SiO₂]^? catalysts had larger diameters. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3240–3248, 2002     

Alkylation of toluene with dichloromethane in the presence of triisobutylaluminum and perfluorophenylborates

¹H NMR method showed that in systems based on triisobutylaluminum (TIBA) and triphenylcyclopropenylium [Ph₃C₃]⁺[B(C₆F₅)₄]–(CPB) or triphenylmethylium [Ph₃C]⁺[B(C₆F₅)₄]–(TB) perfluorophenylborates in a toluene–dichloromethane mixture the Friedel–Crafts process occurs with the formation of ditolylmethane (DTM) accompanied by the complete decomposition of TIBA to form isobutane. ¹⁹F NMR spectroscopy showed that the [B(C₆F₅)₄]–anion decomposes in the systems to form B(C₆F₅)₃ and HC₆F₅. The short-living [AlBu₂ ⁱ]+ cation formed in the reaction of perfluorophenylborates with TIBA is assumed to be the species initiating the process. It has been shown that CPB is less reactive than TB. The addition of a stoichiometric amount of Ph₂CCpFluHfMe₂ exerts no effect on the process with the CPB-containing system but inhibits the reaction in the case of TB.     

Cationic Zinc Organyls as Precatalysts for Hydroamination Reactions

The cationic zinc triple‐decker complex [Zn₂Cp*₃]⁺[BAr^F₄]^? (BAr^F₄=B(3,5‐(CF₃)₂C₆H₃)₄) exhibits catalytic activity in intra‐ and intermolecular hydroamination reactions in the absence of a cocatalyst. These hydroaminations presumably proceed through the activation of the C?C multiple bond of the alkene or alkyne by a highly electrophilic zinc species, which is formed upon elimination of the Cp* ligands. The reaction of [Zn₂Cp*₃]⁺[BAr^F₄]^? with phenylacetylene gives the hydrocarbonation product (Cp*)(Ph)CCH₂, which might be formed via a similar reaction pathway. Additionally, several other structurally well‐defined cationic zinc organyls have been examined as precatalysts for intermolecular hydroamination reactions without the addition of a cocatalyst. These studies reveal that the highest activity is achieved in the absence of any donor ligands. The neutral complex [ZnCp^2S₂] (Cp^2S=C₅Me₄(CH₂)₂SMe) shows a remarkably high catalytic activity in the presence of a Brønsted acid.     

Effect of cocatalyst on the chain microstructure of polyethylene made with CGC‐Ti/MAO/B(C6F5)3

This investigation studied the solution polymerization of ethylene in Isopar E in a semibatch reactor using CGC‐Ti as catalyst and methylalumoxane (MAO) and tris(pentaflourophenyl)borane [B(C₆F₅)₃] as cocatalysts. The effects of cocatalyst type and amount on the chain microstructure were investigated. ¹³C NMR and gel permeation chromatography were used to determine the long‐chain branching (LCB) content and molecular weight distribution (MWD), respectively, of the samples. It was observed that higher concentrations of MAO increased the LCB content and decreased the molecular weight of the polymer. On the other hand, increasing the amount of B(C₆F₅)₃ lowered the LCB content, increased the molecular weight, and broadened MWD significantly. We believe that this approach can be used as an efficient way to control the microstructure of polyolefins made with these catalytic systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3055–3061, 2004     

Polymerization of higher α‐olefins using a Cs‐symmetry hafnium metallocene catalyst. Kinetics of the polymerization and microstructural analysis

The C_s‐symmetry hafnium metallocene [(p‐Et₃Si)C₆H₄]₂C(2,7‐di‐tert‐BuFlu)(C₅H₄)Hf(CH₃)₂ and tetrakis(pentafluorophenyl) borate dimethylanilinium salt ([B(C₆F₅)₄]^?[Me₂NHPh]⁺) were used as the catalytic system for the polymerization of higher α‐olefins (from hexene‐1 to hexadecene‐1) in toluene at 0 °C. The evolution of the polymerization was studied regarding the variation of the molecular weight, molecular weight distribution and yield with time. The effect of the monomer structure on the polymerization kinetics was established. The role of trioctylaluminum in accelerating the polymerization was investigated. ¹³C NMR spectroscopy was used to study the microstructure of the poly(α‐olefins) by the determination of the pentad monomer sequences. The thermal properties of the polymers were obtained by differential scanning calorimetry, DSC. The results were discussed in connection with the polymer microstructure. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4314–4325, 2009     

Preparation of High-Purity Ammonium Tetrakis(pentafluorophenyl)borate for the Activation of Olefin Polymerization Catalysts

Homogeneous olefin polymerization catalysts are activated in situ with a co-catalyst ([PhN(Me)₂-H]⁺[B(C₆F₅)₄]⁻ or [Ph₃C]⁺[B(C₆F₅)₄]⁻) in bulk polymerization media. These co-catalysts are insoluble in hydrocarbon solvents, requiring excess co-catalyst (>3 eq.). Feeding the activated species as a solution in an aliphatic hydrocarbon solvent may be advantageous over the in situ activation method. In this study, highly pure and soluble ammonium tetrakis(pentafluorophenyl)borates ([Me(C₁₈H₃₇)₂N-H]⁺[B(C₆F₅)₄]⁻ and [(C₁₈H₃₇)₂NH₂]⁺[B(C₆F₅)₄]⁻) containing neither water nor Cl⁻ salt impurities were prepared easily via the acid–base reaction of [PhN(Me)₂-H]⁺[B(C₆F₅)₄]⁻ and the corresponding amine. Using the prepared ammonium salts, the activation reactions of commercial-process-relevant metallocene (rac-[ethylenebis(tetrahydroindenyl)]Zr(Me)₂ (1-ZrMe₂), [Ph₂C(Cp)(3,6-^tBu₂Flu)]Hf(Me)₂ (3-HfMe₂), [Ph₂C(Cp)(2,7-^tBu₂Flu)]Hf(Me)₂ (4-HfMe₂)) and half-metallocene complexes ([(η⁵-Me₄C₅)Si(Me)₂(κ-N^tBu)]Ti(Me)₂ (5-TiMe₂), [(η⁵-Me₄C₅)(C₉H₉(κ-N))]Ti(Me)₂ (6-TiMe₂), and [(η⁵-Me₃C₇H₁S)(C₁₀H₁₁(κ-N))]Ti(Me)₂ (7-TiMe₂)) were monitored in C₆D₁₂ with ¹H NMR spectroscopy. Stable [L-M(Me)(NMe(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻ species were cleanly generated from 1-ZrMe₂, 3-HfMe₂, and 4-HfMe₂, while the species types generated from 5-TiMe₂, 6-TiMe₂, and 7-TiMe₂ were unstable for subsequent transformation to other species (presumably, [L-Ti(CH₂N(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-type species). [L-TiCl(N(H)(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-type species were also prepared from 5-TiCl(Me) and 6-TiCl(Me), which were newly prepared in this study. The prepared [L-M(Me)(NMe(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-, [L-Ti(CH₂N(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-, and [L-TiCl(N(H)(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-type species, which are soluble and stable in aliphatic hydrocarbon solvents, were highly active in ethylene/1-octene copolymerization performed in aliphatic hydrocarbon solvents.     

Polymerization of acrylates and bulky methacrylates with the use of zirconocene precursors: Block copolymers with methyl methacrylate

The polymerization behavior of cyclohexyl methacrylate and trimethylsilyloxyethyl methacrylate with the catalytic system Cp₂ZrMe₂/B(C₆F₅)₃/ZnEt₂ was examined. Block copolymers of these bulky methacrylates with methyl methacrylate (MMA), having high molecular weights and relatively narrow molecular weight distributions, were prepared. n‐Butyl acrylate and tert‐butyl acrylate were polymerized with various catalytic systems based on zirconocene complexes. These polymerizations seemed to proceed to a nonquantitative yield, producing polymers with high molecular weights and relatively low polydispersities. This behavior indicated the presence of termination reactions in the initiation step, which appeared to be faster than the propagation step. Block copolymers of these acrylates with MMA were synthesized with the catalytic system rac‐Et(Ind)₂ZrMe₂/[B(C₆F₅)₄]⁻[Me₂NHPh]⁺/ZnEt₂, starting from the polymerization of MMA. The block copolymers produced were well defined in most cases, as indicated by size exclusion chromatography, NMR, and differential scanning calorimetry measurements. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3337–3348, 2005     

Addition polymerization of norbornene using bis(β‐ketoamino)nickel(II)/tris(pentafluorophenyl)borane catalytic systems

Norbornene polymerizations proceeded in toluene with bis(β‐ketoamino)nickel(II) {Ni[CH₃C(O)CHC(NR)CH₃]₂ [R = phenyl ( 1 ) or naphthyl ( 2 )]} complexes as the catalyst precursors and the organo‐Lewis compound tris(pentafluorophenyl)borane [B(C₆F₅)₃] as a unique cocatalyst. The polymerization conditions, such as the cocatalyst/catalyst ratio (B/Ni), catalyst concentration, monomer/catalyst ratio (norbornene/Ni), polymerization temperature, and polymerization time, were studied in detail. Both bis(β‐ketoamino)nickel(II)/B(C₆F₅)₃ catalytic systems showed noticeably high conversions and activities. The polymerization activities were up to 3.64 × 10⁷ g of polymer/mol of Ni h for complex 1 /(B(C₆F₅)₃ and 3.80 × 10⁷ g of polymer/mol of Ni h for complex 2 /B(C₆F₅)₃, and very high conversions of 90–95% were maintained; both polymerizations provided high‐molecular‐weight polynorbornenes with molecular weight distributions (weight‐average molecular weight/number‐average molecular weight) of 2.5–3.0. The achieved polynorbornenes were confirmed to be vinyl‐addition and atactic polymers through the analysis of Fourier transform infrared, ¹H NMR, and ¹³C NMR spectra, and the thermogravimetric analysis results showed that the polynorbornenes exhibited good thermal stability (decomposition temperature > 410 °C). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4733–4743, 2007     

Fine‐Tuning of Lewis Acidity: The Case of Borenium Hydride Complexes Derived from Bis(phosphinimino)amide Boron Precursors

Reactions of bis(phosphinimino)amines LH and L′H with Me₂S ? BH₂Cl afforded chloroborane complexes LBHCl ( 1 ) and L′BHCl ( 2 ), and the reaction of L′H with BH₃ ? Me₂S gave a dihydridoborane complex L′BH₂ ( 3 ) (LH=[{(2,4,6‐Me₃C₆H₂N)P(Ph₂)}₂N]H and L′H=[{(2,6‐iPr₂C₆H₃N)P(Ph₂)}₂N]H). Furthermore, abstraction of a hydride ion from L′BH₂ ( 3 ) and LBH₂ ( 4 ) mediated by Lewis acid B(C₆F₅)₃ or the weakly coordinating ion pair [Ph₃C][B(C₆F₅)₄] smoothly yielded a series of borenium hydride cations: [L′BH]⁺[HB(C₆F₅)₃]^? ( 5 ), [L′BH]⁺[B(C₆F₅)₄]^? ( 6 ), [LBH]⁺[HB(C₆F₅)₃]^? ( 7 ), and [LBH]⁺[B(C₆F₅)₄]^? ( 8 ). Synthesis of a chloroborenium species [LBCl]⁺[BCl₄]^? ( 9 ) without involvement of a weakly coordinating anion was also demonstrated from a reaction of LBH₂ ( 4 ) with three equivalents of BCl₃. It is clear from this study that the sterically bulky strong donor bis(phosphinimino)amide ligand plays a crucial role in facilitating the synthesis and stabilization of these three‐coordinated cationic species of boron. Therefore, the present synthetic approach is not dependent on the requirement of weakly coordinating anions; even simple BCl₄^? can act as a counteranion with borenium cations. The high Lewis acidity of the boron atom in complex 8 enables the formation of an adduct with 4‐dimethylaminopyridine (DMAP), [LBH ? (DMAP)]⁺[B(C₆F₅)₄]^? ( 10 ). The solid‐state structures of complexes 1 , 5 , and 9 were investigated by means of single‐crystal X‐ray structural analysis.     

Nickel(II) and palladium(II) complexes with α‐dioxime ligands as catalysts for the vinyl polymerization of norbornene in combination with methylaluminoxane,tris(pentafluorophenyl)borane,or triethylaluminum cocatalyst systems

Nickel(II) and palladium(II) complexes with α‐dioxime ligands dimethylglyoxime, diphenylglyoxime, and 1,2‐cyclohexanedionedioxime represent six new precatalysts for the polymerization of norbornene that can be activated with methylaluminoxane (MAO), the organo‐Lewis acid tris(pentafluorophenyl)borane [B(C₆F₅)₃], and triethylaluminum (TEA) AlEt₃. The palladium but not the nickel precatalysts could also be activated by B(C₆F₅)₃ alone, whereas two of the three nickel precatalysts but none of the palladium systems are somewhat active with only TEA as a cocatalyst. It was possible to achieve very high polymerization activities up to 3.2 · 10⁷ g_polymer/mol_metal · h. With the system B(C₆F₅)₃/AlEt₃, the activation process can be formulated as the following two‐step reaction: (1) B(C₆F₅)₃ and TEA lead to an aryl/alkyl group exchange and result in the formation of Al(C₆F₅)_nEt_3?n and B(C₆F₅)_3?nEt_n; and (2) Al(C₆F₅)_nEt_3?n will then react with the precatalysts to form the active species for the polymerization of norbornene. Variation of the B:Al ratio shows that Al(C₆F₅)Et₂ is sufficient for high activation. Gel permeation chromatography indicated that it was possible to control the molar mass of poly(norbornene)s by TEA or 1‐dodecene as chain‐transfer agents; the molar mass can be varied in the number‐average molecular weight range from 2 · 10³ to 9 · 10⁵ g · mol^?1. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3604–3614, 2002     

Borane‐Catalyzed Cross‐Metathesis Strategy for Facile Transformation of Cyclic (Alkyl)(Amino)Germylenes

A borane B(C₆F₅)₃‐catalyzed metathesis reaction between the Si?C bond in the cyclic (alkyl)(amino)germylene (CAAGe) 1 and the Si?H bond in a silane (R₃SiH; 2 ) is reported. Mechanistic studies propose that the initial step of the reaction involves Si?H bond activation to furnish an ionic species [ 1 ‐SiR₃]⁺[HB(C₆F₅)₃]^?, from which [Me₃Si]⁺[HB(C₆F₅)₃]^? and an azagermole intermediate are generated. The former yields Me₃SiH concomitant with the regeneration of B(C₆F₅)₃ whereas the latter undergoes isomerization to afford CAAGes bearing various silyl groups on the carbon atom next to the germylene center. This strategy allows the straightforward synthesis of eight new CAAGes starting from 1 .     

Aluminum(III) Cations [(NHC) ⋅ AlMes2]+: Synthesis,Characterization, and Application in FLP-Chemistry

The three-coordinate aluminum cations ligated by N-heterocyclic carbenes (NHCs) [(NHC) ⋅ AlMes₂]⁺[B(C₆F₅)₄]⁻ (NHC=IMe^Me 4 , IiPr^Me 5 , IiPr 6 , Mes=2,4,6-trimethylphenyl) were prepared via hydride abstraction of the alanes (NHC) ⋅ AlHMes₂ (NHC=IMe^Me 1 , IiPr^Me 2 , IiPr 3 ) using [Ph₃C]⁺[B(C₆F₅)₄]⁻ in toluene as hydride acceptor. If this reaction was performed in diethyl ether, the corresponding four-coordinate aluminum etherate cations [(NHC) ⋅ AlMes₂(OEt₂)]⁺ [B(C₆F₅)₄]⁻ 7 – 9 (NHC=IMe^Me 7 , IiPr^Me 8 , IiPr 9 ) were isolated. According to a theoretical and experimental assessment of the Lewis-acidity of the [(IMe^Me) ⋅ AlMes₂]⁺ cation is the acidity larger than that of B(C₆F₅)₃ and of similar magnitude as reported for Al(C₆F₅)₃. The reaction of [(IMe^Me) ⋅ AlMes₂]⁺[B(C₆F₅)₄]⁻ 4 with the sterically less demanding, basic phosphine PMe₃ afforded a mixed NHC/phosphine stabilized cation [(IMe^Me) ⋅ AlMes₂(PMe₃)]⁺[B(C₆F₅)₄]⁻ 10 . Equimolar mixtures of 4 and the sterically more demanding PCy₃ gave a frustrated Lewis-pair (FLP), i.e., [(IMe^Me) ⋅ AlMes₂]⁺[B(C₆F₅)₄]⁻/PCy₃ FLP-11 , which reacts with small molecules such as CO₂, ethene, and 2-butyne.     

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     

Triisobutylaluminum as cocatalyst for zirconocenes. I. Sterically opened zirconocene/triisobutylaluminum/perfluorophenylborate as highly effective ternary catalytic system for synthesis of low molecular weight polyethylenes

Ethylene polymerizations with catalytic systems Me₂SiCp*N^tBuZrX₂ ( 1 ) [Cp* = C₅(CH₃)₄; X = Cl ( 1Cl ), Me ( 1Me )], triisobutylaluminum (TIBA), perfluorophenylborate CatB(C₆F₅)₄ [Cat = CPh₃ ( 3 ), Me₂NHPh ( 4 )], or Me₂SiCp₂ZrX₂ [X = Cl ( 2Cl ), Me ( 2Me )]/TIBA/ 3 ( 4 ) were performed within a wide range of ethylene pressures of different Al/Zr ratios, and Zr/B = 1. Catalytic systems 1Cl ( 2Cl )/TIBA/ 3 led to the formation of very high linear molecular weight polyethylene (PE) of M_η ∼2,000,000 with low activity. The replacement of both chlorine ligands in the precatalyst for the methyl ones led to the formation of active species producing low molecular weight PE with high activity. Chain transfer to ethylene was shown to be the main reaction controlling PE chain propagation: k_p/k_tr ∼20–30 for 1Me /TIBA/ 3 and k_p/k_tr ∼350–500 for 2Me /TIBA/ 3 . It was suggested that TIBA was present in the active center first in the form of a neutral heterobimetallic Zr–Al bridged complex followed by the formation of a partially polarized Zr–Al(Cl)R₂ (R = ⁱBu) or an unreactive Zr–AlR₃ cationic complex by abstraction of the alkyl ligand under the action of borate. It was concluded that AlR₃ from the latter cationic complex may be easily reversibly replaced under the specific coordination of ethylene or accumulated α-olefin, giving rise to highly labile and sterically accessible cationic species. Experiments on ethylene polymerization with the catalytic systems 1Cl ( 1Me )/TIBA/ 3 /Ph₂NH, 1Cl ( 1Me )/TIBA/ 4, 2Cl ( 2Me )/TIBA/ 3 /Ph₂NH, and 2Cl ( 2Me )/TIBA/ 4 were performed to confirm the suggestion. Catalytic systems derived from dichloride complexes in the presence of a σ-donor substrate also produced low molecular weight PEs with molecular weight characteristics similar to those of products obtained with the dimethylated precatalysts. The specific feature of active species derived from 2Me complexes to isomerize coordinated α-olefin into trans-vinylene polymer chains was also revealed. The catalytic behavior of the ternary catalytic system based on 2Me relative to 2Me or 2Cl precatalysts activated with polymethylaluminoxane at different Al/Zr ratios was compared. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1901–1914, 2001     

Improvement of Structure and Properties of Polypropylene/Poly(ethylene-co-propylene) In-reactor Alloy by Modifying the Cocatalyst

Summary : A series of polypropylene/poly(ethylene-co-propylene) in-reactor alloy were synthesized by a TiCl₄/MgCl₂/SiO₂/diester type Ziegler-Natta catalyst, using triethylaluminium (TEA), triisobutylaluminium (TIBA) or TEA/TIBA mixtures of different molar ratio as cocatalyst. Mechanical properties of the alloy are strongly influenced by the cocatalyst. Toughness-stiffness balance of the alloy synthesized using a 50/50 TEA/TIBA mixture as cocatalyst is much better than that of the alloy based on pure TEA cocatalyst. Changes in copolymer chain structure and composition distribution are thought to be the main reason for this improvement of properties.     

Synthesis,Properties, and Application of Tetrakis(pentafluoroethyl)gallate, [Ga(C2F5)4]−

Weakly coordinating anions (WCAs) are important for academic reasons as well as for technical applications. Tetrakis(pentafluoroethyl)gallate, [Ga(C₂F₅)₄]^?, a new WCA, is accessible by treatment of [GaCl₃(dmap)] (dmap=4‐dimethylaminopyridine) with LiC₂F₅. The anion [Ga(C₂F₅)₄]^? proved to be reluctant towards deterioration by aqueous hydrochloric acid or lithium hydroxide. Various salts of [Ga(C₂F₅)₄]^? were synthesized with cations such as [PPh₄]⁺, [CPh₃]⁺, [(O₂H₅)₂(OH₂)₂]²⁺, and [Li(dec)₂]⁺ (dec=diethyl carbonate). Thermolysis of [(O₂H₅)₂(OH₂)₂][Ga(C₂F₅)₄]₂ gives rise to a dihydrate of tris(pentafluoroethyl)gallane, [Ga(C₂F₅)₃(OH₂)₂]. All products were characterized by NMR and IR spectroscopy, mass spectrometry, X‐ray diffraction, and elemental analysis. Furthermore, an outlook for the application of [Li(dec)₂][Ga(C₂F₅)₄] as a conducting salt in lithium‐ion batteries is presented.     

Facile access to the pnictocenium ions [Cp*ECl]+ (E = P, As) and [(Cp*)2P]+: chloride ion affinity of Al(OR(F))3

The pnictocenium salts [Cp*PCl]⁺[μCl]^? ( 1 a ), [Cp*PCl]⁺[ClAl(OR^F)₃]^? ( 1 b ), [Cp*AsCl]⁺[ClAl(OR^F)₃]^? ( 2 ), and [(Cp*)₂P]⁺[μCl]^? ( 3 ), in which Cp*=Me₅C₅, μCl=(^FRO)₃Al? Cl? Al(OR^F)₃, and OR^F=OC(CF₃)₃, were prepared by halide abstraction from the respective halopnictines with the Lewis superacid PhF→Al(OR^F)₃. 1 The X‐ray crystal structures of 1 a , 2 , and 3 established that in the half as well as in the sandwich cations the Cp* rings are attached in an η²‐fashion. By using one or two equivalents of the Lewis acid, the two new weakly coordinating anions [μCl]^? and [ClAl(OR^F)₃]^? resulted. They also stabilize the highly reactive cations in PhF or 1,2‐F₂C₆H₄ solution at room temperature. The chloride ion affinities (CIAs) of a range of classical strong Lewis acids were also investigated. The calculations are based on a set of isodesmic BP86/SV(P) reactions and a non‐isodesmic reference reaction assessed at the G3MP2 level.     

Silylium dual catalysis in living polymerization of methacrylates via In situ hydrosilylation of monomer

Silylium ions (“R₃Si⁺”) are found to catalyze both 1,4‐hydrosilylation of methyl methacrylate (MMA) with R₃SiH to generate the silyl ketene acetal initiator in situ and subsequent living polymerization of MMA. The living characteristics of the MMA polymerization initiated by R₃SiH (Et₃SiH or Me₂PhSiH) and catalyzed by [Et₃Si(L)]⁺[B(C₆F₅)₄]^– (L = toluene), which have been revealed by four sets of experiments, enabled the synthesis of the polymers with well‐controlled M_n values (identical or nearly identical to the calculated ones), narrow molecular weight distributions (? = 1.05–1.09), and well defined chain structures {H? [MMA]_n? H}. The polymerization is highly efficient too, with quantitative or near quantitative initiation efficiencies (I* = 96–100%). Monitoring of the reaction of MMA + Me₂PhSiH + [Et₃Si(L)]⁺[B(C₆F₅)₄]^– (0.5 mol%) by ¹H NMR provided clear evidence for in situ generation of the corresponding SKA, Me₂C?C(OMe)OSiMe₂Ph, via the proposed “Et₃Si^+”‐catalyzed 1,4‐hydrosilylation of monomer through “frustrated Lewis pair” type activation of the hydrosilane in the form of the isolable silylium‐silane complex, [Et₃Si? H? SiR₃]⁺[B(C₆F₅)₄]^–. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1895–1903     

Univalent Gallium Complexes of Simple and ansa‐Arene Ligands: Effects on the Polymerization of Isobutylene

Using [Ga(C₆H₅F)₂]⁺[Al(OR^F)₄]^?( 1 ) (R^F=C(CF₃)₃) as starting material, we isolated bis‐ and tris‐η⁶‐coordinated gallium(I) arene complex salts of p‐xylene (1,4‐Me₂C₆H₄), hexamethylbenzene (C₆Me₆), diphenylethane (PhC₂H₄Ph), and m‐terphenyl (1,3‐Ph₂C₆H₄): [Ga(1,4‐Me₂C₆H₄)_2.5]⁺ ( 2⁺ ), [Ga(C₆Me₆)₂]⁺ ( 3⁺ ), [Ga(PhC₂H₄Ph)]⁺ ( 4⁺ ) and [(C₆H₅F)Ga(μ‐1,3‐Ph₂C₆H₄)₂Ga(C₆H₅F)]²⁺ ( 5²⁺ ). 4⁺ is the first structurally characterized ansa‐like bent sandwich chelate of univalent gallium and 5²⁺ the first binuclear gallium(I) complex without a Ga?Ga bond. Beyond confirming the structural findings by multinuclear NMR spectroscopic investigations and density functional calculations (RI‐BP86/SV(P) level), [Ga(PhC₂H₄Ph)]⁺[Al(OR^F)₄]^?( 4 ) and [(C₆H₅F)Ga(μ‐1,3‐Ph₂C₆H₄)₂Ga(C₆H₅F)]²⁺{[Al(OR^F)₄] ^?}₂ ( 5 ), featuring ansa‐arene ligands, were tested as catalysts for the synthesis of highly reactive polyisobutylene (HR‐PIB). In comparison to the recently published 1 and the [Ga(1,3,5‐Me₃C₆H₃)₂]⁺[Al(OR^F)₄]^? salt ( 6 ) (1,3,5‐Me₃C₆H₃=mesitylene), 4 and 5 gave slightly reduced reactivities. This allowed for favorably increased polymerization temperatures of up to +15 °C, while yielding HR‐PIB with high contents of terminal olefinic double bonds (α‐contents=84–93 %), low molecular weights (M_n=1000–3000 g mol^?1) and good monomer conversions (up to 83 % in two hours). While the chelate complexes delivered more favorable results than 1 and 6 , the reaction kinetics resembled and thus concurred with the recently proposed coordinative polymerization mechanism.     

Silyl‐functionalized polyolefins via co‐polymerization of vinylsilanes with ethylene or propylene catalyzed by group IV metallocene complexes

Vinylsilanes CH₂CHSiR₃ (R = Me, NMe₂, OMe, OTMS) copolymerize with ethylene rapidly in the presence of catalytic amounts of [Cp′₂ZrMe][MeB(C₆F₅)₃] (Cp′ = η⁵‐C₅Me₅) ( I ) to give high molecular weight silyl‐functionalized polyethylene. The molecular weight of the polymer can be controlled by varying the comonomer concentration as well as the reaction temperature. Relatively low molecular weight polymer was produced at a higher silyl monomer concentration and a higher polymerization temperature. The incorporation of silyl monomer in the polymer is in the range of 0.1‐ 6.0%. On the other hands, catalysts [Cp₂ZrMe][MeB(C₆F₅)₃] (Cp′ = η⁵‐C₅H₅) ( II ) and [Cp″₂ZrMe][MeB(C₆F₅)₃] (Cp″ = η⁵‐1,2‐C₅Me₂H₃) ( III ) show much lower activity. With the use of more coordinatively unsaturated constrained geometry catalysts (CGC), Me₂Si(η⁵‐C₅Me₄)(N^tBu)MMe][MeB(C₆F₅)₃] ( IV , M = Zr; V , M = Ti), the silyl monomer incorporation in the polymer was increased to 40%. The Ti catalyst is more active and produces polymer with a higher molecular weight with a higher silyl monomer incorporation at 23 °C. The copolymerization of vinyltrimethylsilane with propylene was also investigated with these catalysts, yielding high silyl‐functionalized propylene copolymer/oligmer. The microstructure of the copolymers/oligomers has been thoroughly investigated by 1D and 2D NMR techniques (¹H, ¹³C, NOE, DEPT, HETCOR, and FLOCK). The results show that the backbone of the copolymers/oligomers is essentially random. Several termination pathways have been identified. In particular, two unsaturated silyl terminations, cis and/or trans‐TMS CHCH , were identified with the constrained geometry catalysts. Their formation was rationalized based on transition state models. It was found that occasional 1,2‐insertion of either propylene or vinyltrimethylsilane into the chain propagation process has a high probability serving as the trigger for polymer chain termination via β‐H elimination. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1308–1321