Borate Cocatalysts Research Articles

Effect of Borate Cocatalysts toward Activity and Comonomer Incorporation in Ethylene Copolymerization by Half-Titanocene Catalysts in Methylcyclohexane.

Ethylene copolymerizations with 2-methyl-1-pentene, 1-dodecene (DD), vinylcyclohexane (VCH), [Me2Si(C5Me4)(N t Bu)]TiCl2 (1), Cp*TiMe2(O-2,6- i Pr2-4-RC6H2) [R = H (2), SiEt3 (3)]-borate, and [A(H)]+[BAr4]- [Ar = C6F5; A(H)+ = N+(H)Me(n-C18H37)2, N+(H)(CH2CF3)(n-C18H37)2, HO+(n-C14H29)2·O(n-C14H29)2, HO+(n-C16H33)2·O(n-C16H33)2; Ar = C10F7, A(H)+ = HO+(n-C14H29)2·O(n-C14H29)2 (B5), N+(H)(CH2CF3)(n-C18H37)2] catalyst systems conducted in methylcyclohexane (MCH) exhibited better comonomer incorporation than those conducted in toluene (in the presence of methylaluminoxane (MAO) or borate cocatalysts). The activity was affected by the borate cocatalyst and 1,3-B5 catalyst systems in MCH and showed the highest activity in the ethylene copolymerizations with VCH and DD.

Synthesis of Ethylene/1-Octene Copolymers with Ultrahigh Molecular Weights by Zr and Hf Complexes Bearing Bidentate NN Ligands with the Camphyl Linker

Ultrahigh molecular weight polyethylene (UHMWPE) is a class of high-performance engineering plastics, exhibiting a unique set of properties and applications. Although many advances have been achieved in recent years, the synthesis of UHMWPE is still a great challenge. In this contribution, a series of zirconium and hafnium complexes, [2,6-(R1)2-4-R2-C6H2-N-C(camphyl)=C(camphyl)-N-2,6-(R1)2-4-R2-C6H2]MMe2(THF) (1-Zr: R1 = Me, R2 = H, M = Zr; 2-Zr: R1 = Me, R2 = Me, M = Zr; 1-Hf: R1 = Me, R2 = H, M = Hf; 2-Hf: R1 = Me, R2 = Me, M = Hf), bearing bidentate NN ligands with the bulky camphyl backbone were synthesized by the stoichiometric reactions of α-diimine ligands with MMe4 (M = Hf or Zr). All Zr and Hf metal complexes were analyzed using 1H and 13C NMR spectroscopy, and the molecular structures of complexes 1-Zr and 1-Hf were determined by single-crystal X-ray diffraction, revealing that the original α-diimine ligand was selectively reduced into the ene-diamido form and generated an 1,3-diaza-2-metallocyclopentene ring in the metal complexes. Zr complexes 1-Zr and 2-Zr showed moderate activity (up to 388 kg(PE)·mol−1(M)·h−1), poor copolymerization ability, but unprecedented molecular weight capability toward ethylene/1-octene copolymerization. Therefore, copolymers with ultrahigh molecular weights (>600 or 337 × 104 g∙mol−1) were successfully synthesized by 1-Zr or 2-Zr, respectively, with the borate cocatalyst [Ph3C][B(C6F5)4]. Surprisingly, Hf complexes 1-Hf and 2-Hf showed negligible activity under otherwise identical conditions, revealing the great influence of metal centers on catalytic performances.

Structural Monitoring of NiBi Modified BiVO4 Photoanodes Using in Situ Soft and Hard X-ray Absorption Spectroscopies

Photoelectrochemical (PEC) water splitting, a process using solar light and a semiconductor to split water, is proposed as a potentially scalable method to store solar energy through renewable H2 fuels. Obtaining the electronic structure information on co-catalyst is a crucial step toward gaining a mechanistic understanding of the water oxidation reaction of this catalyst. In the present work, we show that the PEC performance of BiVO4 photoanodes can be enhanced by the deposition of a nickel–borate co-catalyst layer (NiBi). We investigate the electronic structure of the NiBi by in situ soft and hard X-ray absorption spectroscopies (XAS) at the Ni L- and K-edges as well as at the O K-edge under different potential and illumination conditions. We discuss the involvement of the active oxygen species related to the hybridized O 2p Ni 3dt2g orbitals in the oxygen evolution reaction (OER) and further correlate the changes at the O K-edge with that of at the Ni L-edge. In situ soft XAS measurements show that Ni ...

Highly branched polyethylene oligomers via group IV-catalysed polymerization in very nonpolar media

Early transition metal catalysts produce high-density and linear low-density polyethylenes with spectacular efficiency. Nevertheless, these catalysts are ineffective in producing low-density polyethylene homopolymers with large –(CH2)xCH3 branch densities (x ≥ 5) or low-molecular-mass (Mn < 1,200 g mol−1) highly branched polyethylenes (HBPEs). The latter are potential alternative synthetic lubricants that have eluded efficient catalytic synthesis. Here we report the synthesis of low-Mn HBPEs with 61–93 branches per 1,000 carbon atoms from abundant ethylene as the primary feedstock using a soluble, highly active ion-paired organozirconium catalyst in a saturated hydrocarbon solvent. The unprecedented activity and branch selectivity reflect previously unrecognized aspects of the cationic catalyst–counteranion pairing in nonpolar media and are characterized spectroscopically and quantum mechanically. The HBPE products are rheologically and tribologically attractive candidates for synthetic lubricants. Low-molecular-weight, highly branched polyethylenes are attractive candidates for synthetic lubricants, but their efficient production is constrained by a lack of effective catalytic methods. While conventional group IV transition metal catalysts produce diverse polyethylenes on a huge scale, they are unable to produce highly branched polyethylenes. Here a hydrocarbon-soluble organozirconium precatalyst and borate cocatalyst produce the desired polyethylenes with excellent activity and branch selectivity.

Scandium‐Catalyzed Self‐Assisted Polar Co‐monomer Enchainment in Ethylene Polymerization

AbstractDirect coordinative copolymerization of ethylene with functionalized co‐monomers is a long‐sought‐after approach to introducing polyolefin functionality. However, functional‐group Lewis basicity typically depresses catalytic activity and co‐monomer incorporation. Finding alternatives to intensively studied group 4 d0 and late‐transition‐metal catalysts is crucial to addressing this long‐standing challenge. Shown herein is that mono‐ and binuclear organoscandium complexes with a borate cocatalyst are active for ethylene + amino olefin [AO; H2C=CH(CH2)nNR2] copolymerizations in the absence of a Lewis‐acidic masking reagent. Both activity (up to 4.2×102 kg mol−1⋅h−1&gt; atm−1&gt;) and AO incorporation (up to 12 % at 0.2 m [AO]) are appreciable. Linker‐length‐dependent (n) AO incorporation and mechanistic probes support an unusual functional‐group‐assisted enchainment mechanism. Furthermore, the binuclear catalysts exhibit enhanced AO tolerance and enhanced long chain AO incorporation.

Rare-earth metal formamidinate complexes from [(C5Me5)LnMe2]3 and [LnMe3]n precursors

The equimolar reaction of [(C5Me5)LnMe2]3 (Ln = Y, Lu) with (DippForm)AlMe2 gave the ligand-rearranged complexes (C5Me5)Ln(AlMe4)(DippForm) in quantitative yields. The half-sandwich complexes were fully characterized including X-ray structure analyses. Donor solvent (THF)-induced alkylaluminate cleavage of (C5Me5)Lu(AlMe4)(DippForm) gave complex [(C5Me5)LuMe(DippForm)(thf)] exclusively, as evidenced by 1H‒13C HSQC NMR spectroscopy. Treatment of polymeric [LuMe3]n with formamidine DippFormH produced a mixture of two compounds, namely, the bis(formamidinate) complex (DippForm)2LuMe and the methyl methylidene complex [{(DippForm)Lu(μ2-Me)}3(μ3-Me)(μ3-CH2)]. While monomeric (DippForm)2LuMe revealed a very short Lu–C terminal methyl bond lengths of 2.314(3) Å in the solid state, the structure of the trimetallic methylidene complex could be assigned unambiguously on the basis of a 1H‒13C HSQC NMR spectrum. Preliminary studies on the performance of complex (C5Me5)Y(AlMe4)(DippForm) in isoprene polymerization revealed that upon activation with borate co-catalysts [Ph3C][B(C6F5)4] and [PhNMe2H][B(C6F5)4] highly active catalyst systems are obtained, producing polyisoprenes with dominant 3,4-units (57% and 58%).

Ethylene Polymerization by Phenoxy Substituted Tris(pyrazolyl)borate Ti(IV) Methyl Complexes

Ethylene polymerization using Tp*TiMe2(OAr) [Tp* = HB(3,5-Me2-pyrazolyl)3; Ar = O-2,6-Me2C6H3 (2a), O-2,6-iPr2C6H3 (2b)]-cocatalyst systems [cocatalyst: MAO, [Ph3C][B(C6F5)4], or B(C6F5)3 and AliBu3 or Al(n-octyl)3] or[Tp*TiMe(O-2,6-Me2C6H3)]+[MeB(C6F5)3]−·2THF (3a) in the presence of Al alkyls have been explored. The catalytic activity by 2a,b−cocatalyst systems was highly affected by the Al/Ti molar ratios. Ethylene polymerizations by 2a,b−MAO catalyst systems proceeded in a quasi living manner between −30 and 25 °C, whereas certain degree of chain transfer was observed when the polymerizations by 2a,b were conducted in the presence of borate cocatalysts. The activity by the cationic Ti(IV)−methyl complex (3a) in the presence of Al(n-octyl)3 was close to those by 2a−B(C6F5)3−Al(n-octyl)3, AliBu3 catalyst systems and the Mn values in the resultant polymers were close with uniform distributions; the facts clearly indicate that the same catalytically active species play a role in this catalysis.

Polymerization of vinyl ethers using titanium catalysts containing tridentate triamine ligand of the type N[CH2CH(Ph)(Ts)N]22−

Titanium complexes having tridentate triamine of the type N[CH2CH(Ph)(Ts)N]22− in combination with methylaluminoxane (MAO) was able to polymerize ethyl vinyl ether in good yields. The polymers obtained in general were having molecular weight in the order of 105 with narrow molecular weight distributions. Polymerization conditions had an impact on the molecular weight and the polydispersity index (PDI). Using chlorobenzene as the solvent the polymer had an Mn of 350 000 and PDI of 1.21, where as under neat conditions the Mn was 255 000 with PDI of 1.21. The type of solvent and the temperature dictated the polymerization rate and the polymer stereo regularity. The molecular weight of the polymer is distinctly governed by the polymerization temperature. Temperature ranging between −50 and ambient (30°C) resulted in high molecular weight polymers and vice versa at a temperature of 60–70°C resulted in low molecular weight polymers in moderate yields. The polymers obtained below 30°C are highly stereo-regular compared to that of the ones produced at and above ambient temperature. The polymerization of iso-butyl vinyl ether (IBVE) was faster than that of linearly substituted n-butyl vinyl ether (BVE) and less bulky ethyl vinyl ether (EVE). The order of isotacticities of the polymers obtained are polyIBVE>polyBVE>polyEVE. The use of borate cocatalyst for activation generated narrow molecular weight polymers with a linear increase in the yield and molecular weight over time suggesting the living nature of the catalyst system.

Structure−Reactivity Relationships of Amido-Pyridine-Supported Rare-Earth-Metal Alkyl Complexes

Treatment of rare-earth-metal dialkyl complexes with group 13 cocatalysts is a prominent approach to generate homogeneous catalysts active in olefin polymerization. Reaction of Ln(CH2SiMe3)3(THF)2 with monovalent imino-amido-pyridine [2-{(2,6-iPr2C6H3)N═CMe}-6-{(2,6-iPr2C6H3)NHCMe2}C5H3N] (HL2) gives donor solvent-free discrete dialkyl compounds [L2]Ln(CH2SiMe3)2 (Ln = Sc, Y, Lu). In the solid state the scandium derivative is isostructural to the previously reported lutetium complex (Gordon et al.). Activation by borate cocatalysts [Ph3C][B(C6F5)4] and [PhNMe2H][B(C6F5)4] produces ion pairs that polymerize ethylene in moderate yields (activity: Sc > Lu). Cationization with N-[tris(pentafluorophenyl)borane]-3H-indole gives inactive species. 1H/13C/11B/19F NMR spectroscopy is applied to examine the interaction of the rare-earth-metal dialkyl complexes with the boron cocatalysts. In contrast to the monoalkyl diamido-pyridine compounds [L1]Ln(CH2SiMe3)(THF)x (HL1 = [2,6-{(2,6-iPr2C6H3)NHCH2}C5H3N], the dialky...

Ring‐opening polymerization of lactones using zirconocene catalytic systems: Block copolymerization with methyl methacrylate

AbstractThe ring‐opening polymerization of ε‐caprolactone (ε‐CL) and δ‐valerolactone (δ‐VL) using nine catalytic systems consisting of a combination of three C2v zirconocene complexes and three borate cocatalysts is discussed. The polymerizations proceed in a well‐controlled manner, producing polymers with relatively high molecular weights and narrow molecular weight distributions. Kinetic experiments of the polymerization of ε‐CL with the catalytic system Cp2ZrMe2/B(C6F5)3 (1) showed a linear dependence between polymerization yield and molecular weight with time, as well as between the molecular weight with the molar ratio of the monomer over the catalyst [ε‐CL]/[Zr], indicating sufficient control of the polymerization reaction. The catalytic system (1) was utilized for the synthesis of well‐defined block copolymers of MMA with ε‐CL and δ‐VL. All samples were characterized by size exclusion chromatography, nuclear magnetic resonance, and differential scanning calorimetry. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3524–3537, 2007

Ethylene Tri- and Tetramerization with Borate Cocatalysts: Effects on Activity, Selectivity, and Catalyst Degradation Pathways

Chromium-based ethylene tri- and tetramerization catalysts have been evaluated with a combination of trialkylaluminium and borate cocatalyst activation. A remarkable effect on activity and selectivity has been observed and studied, and a cocatalyst-induced degradation pathway has been identified.

Influence of the cocatalyst structure on the statistical copolymerization of methyl methacrylate with bulky methacrylates using the zirconocene complex Cp2ZrMe2

AbstractStatistical copolymers of methyl methacrylate with cyclohexyl and trimethylsilyloxy ethyl methacrylate were synthesized with two different catalytic systems based on the zirconocene complex Cp2ZrMe2. The reactivity ratios of methyl methacrylate and these methacrylates were calculated with the Finemann–Ross, inverted Finemann–Ross, and Kelen–Tüdos graphical methods. The structural parameters of these copolymers were estimated from the calculation of the dyad monomer sequence fractions. Two different borate cocatalysts were employed, and their effect on the copolymerization process is discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3305–3314, 2005

Bimetallic catalysis for styrene homopolymerization and ethylene-styrene copolymerization. Exceptional comonomer selectivity and insertion regiochemistry.

This communication reports the styrene homopolymerization behavior and ethylene-styrene copolymerization behavior of the covalently linked bimetallic constrained geometry catalyst (mu-CH2CH2-3,3'){(eta5-indenyl)[1-Me2Si(tBuN)](TiMe2)}2 (Ti2), which is the first single-site catalyst that effects not only styrene homopolymerization with high activity, but also efficient ethylene-styrene copolymerization over a broad styrene composition range (0-76% at 20 degrees C, 1.0 atm ethylene pressure). In styrene homopolymerization, a 50x increase in polymerization activity is achieved with Ti2 vs the mononuclear analogue, Ti1, using an identical trityl borate cocatalyst and polymerization conditions. In ethylene + styrene copolymerization, Ti2 enchains approximately 20% more styrene than Ti1 under identical reaction conditions. 13C NMR spectroscopy indicates that greater than two consecutive styrene units are enchained in the copolymer backbone produced by Ti2 + Ph3C+B(C6F5)4-. End group analysis of the styrene homopolymer produced by Ti2 + Ph3C+B(C6F5)4- suggests that 1,2-regiochemistry is installed in approximately 50% of the initiation steps. This unusual microstructure is believed to be related to the bimetallic catalyst structure.

MCM-41 immobilised borate co-catalyst for metallocene catalyzed propene oligomerisation

Reaction of tris(pentafluorophenyl)boron with the silanol groups of MCM-41 resulted in the heterogeneous tris(pentafluorophenyl)borate anion. This immobilised weakly-coordinating anion retains metallocenes, thus yielding a heterogeneous propene oligomerisation catalyst. Activity comparable to the corresponding homogeneous catalyst can be obtained. The products typically consist of over 90% 1-alkenes with Flory–Schulz carbon number distribution.

Synthesis of polymer supported borate cocatalysts and their application to metallocene polymerizations

Polymer supported borate complexes were synthesized using poly(styrene- co-4-bromostyrene) and polystyrene-beads as carriers. These complexes were reacted with rac-Et[Ind] 2ZrCl 2 (Ind=indenyl) or Ph 2C[(Cp)Flu]ZrCl 2 (Cp=cyclopentadienyl, Flu=Fluorenyl) in toluene, at a molar ratio of [Zr]/[B]=1, to obtain polymer supported catalysts. Polymerizations of ethylene and propylene were conducted over them in the presence of Al( i-C 4H 9) 3 as an activator. When poly(styrene- co-4-bromostyrene) was used as the carrier, the resulting soluble catalyst showed high activity comparable to those of the corresponding homogeneous catalysts for ethylene polymerization. For propylene polymerization, however, those catalysts showed low-activity. Even though the insoluble catalysts prepared with polystyrene-beads as carrier displayed far less activities for both ethylene and propylene polymerizations, it was found that the shape of polyethylene obtained at 40°C is a replica of the carrier particle.