Trityl Borate Research Articles

Coplanar binuclear group 4 post-metallocene complexes supported by chelating μ-(σ2-aryl) ligands: characterisation and olefin polymerisation catalysis.

The report concerns expansion of the previously developed M-[O,N,C] [pyridine-2-phenolate-6-(σ-aryl)] catalyst system into rigid, coplanar bimetallic assemblies, which afford metal-metal distances that are predetermined yet amenable for cooperativity, as well as locked-in "syn" orientation of binding sites that offer the same direction of access for substrates. The binuclear complexes are generated in a regioselective manner to yield para hydrogen atoms (not ortho) at the central μ-aryl moiety, and have been characterised by multinuclear NMR spectroscopy. The "anti" (showing opposite directions of access) and mononuclear analogues have also been prepared for comparison purposes. Six syn-type bimetallic derivatives of Ti, Zr and Hf have been characterised by X-ray crystallography, to reveal metal-metal separations of 6.3-6.7 Å. For ethylene and ethylene/1-octene polymerisation reactions in conjunction with trityl borate, the syn-Ti2 catalysts display superior efficiencies and produced polymers with higher Mw values than for the anti and mono-Ti congeners, thus indicating the possibility of favourable enchainment interactions and cooperative reactivity.

Dinuclear Group 4 Metal Complexes Bearing Anthracene-Bridged Bifunctional Amido-Ether Ligands: Remarkable Metal Effect and Cooperativity toward Ethylene/1-Octene Copolymerization.

Two types of bifunctional amido-ether ligands (syn-L and anti-L) with the rigid anthracene skeleton were designed to support dinuclear group 4 metal complexes. All organic ligands and organometallic complexes (syn-M2 and anti-M2; M = Hf, Zr, and Ti) were fully characterized by 1H and 13C NMR spectroscopies and elemental analyses. The anti-Hf2 complex showed two confirmations at room temperature with C2-symmetry or S2-symmetry that can inter-exchange, as indicated by VT NMR, while only a C2-symmetric isomer was observed for syn-Hf2 complex at room temperature. However, for Zr and Ti analogues, both syn and anti complexes exhibited only one conformation at room temperature. The molecular structures of complexes syn-Hf2, anti-Hf2, and syn-Ti2 in the solid state were further determined by single-crystal X-ray diffraction, revealing the distances between two metal centers in syn-M2 from 7.138 Å (syn-Ti2) to 7.321 Å (syn-Hf2) but a much farther separation in anti-M2 (8.807 Å in C2-symmetric anti-Hf2). The mononuclear complex (2-CH3O-C6H4-N-C14H9)Zr(NMe2)3 (mono-Zr1) was also prepared for control experiments. In the presence of alkyl aluminum (AlEt3) as the alkylating agent and trityl borate ([Ph3C][B(C6F5)4]) as the co-catalyst, all metal complexes were tested for copolymerization of ethylene with 1-octene at high temperature (130 °C). The preliminary polymerization results revealed that the activity was highly dependent upon the nature of metal centers, and syn-Zr2 showed the highest activity of 9600 kg(PE)·mol-1 (Zr)·h-1, which was about 17- and 2.2-fold higher than those of syn-Hf2 and syn-Ti2, respectively. Benefitting from both steric proximity and electronical interaction of two metal centers, syn-Zr2 exhibited significant cooperativity in comparison to anti-Zr2 and mono-Zr1, with regard to activity and molecular weight and 1-octene incorporation of resultant copolymers.

Mixed Low-Valent Alanes from the Bis(4-methyl-benzoxazol-2-yl)methanide Ligand.

Within this work, an aluminum dihydride complex ([(4-MeBox2CH)AlH2]) (1) based on the bis(4-methyl-benzoxazol-2-yl)methanide ligand was synthesized and characterized by spectroscopic methods (NMR, ATR-IR, and fluorescence), DSC (differential scanning calorimetry), mass spectrometry (LIFDI), and single crystal X-ray diffraction. The reactivity of alane 1 was investigated toward the reducing agents [DippNacNacAlI] and [(MesNacNacMgI)2], which gave the dialane compounds [(4-MeBox2CH)HAlII-AlIIH(DippNacNac)] (2) and [{(4-MeBox2CH)AlIIH}2] (4a), respectively. Furthermore, dialuminoxanes [{(4-MeBox2CH)AlH}2(μ-O)] (4b) and [({(MesNacNac)Mg}2(μ-H)){H3AlII-AlIIH(4-MeBox2CH)}] (4c) were isolated as byproducts, with 4b co-crystallizing with 4a. The hydricity of both hydrides in the mixed-ligated dialane 2 were examined by a reaction with 1 equiv of trityl borate ([Ph3C][B(C6F5)4]), which resulted in [(4-MeBox2CH)HAlII-AlII(DippNacNac)][B(C6F5)4] (3). Due to the formation of 4b, complex 1 was reacted with 0.5 equiv of water, which causes the likely synthesis of insoluble oligomeric alumoxanes. To prevent this reaction and support the formation of well-defined dialumoxanes, 1 was initially converted to [(4-MeBox2CH)(DippO)AlH] (5) by the deprotonation of 2,6-diisopropylphenol (propofol). This sterically encumbered compound 5 was subsequently reacted with 0.5 equiv of water, which resulted in defined molecules of [{(4-MeBox2CH)(DippO)Al}2(μ-O)] (6). All these compounds exemplify the versatility of the 4-MeBox2CH ligand in low-valent aluminum chemistry.

Dichlorovanadium(IV) diamine-bis(phenolate) complexes for ethylene (co)polymerization and 1-olefin isospecific polymerization

Two vanadium complexes bearing amine-bis(phenolate) ligands with the amino side-arm donor, [V{Me2NCH2CH2N(CH2-2-O-3,5-tBu2-C6H2)2}Cl2] (1) and [V{Me2NCH2CH2N(CH2-2-O-3,5-tBu2-C6H2)(CH2-2-O-C6H4)}Cl2] (2), were synthesised and characterized by FTIR and 1HNMR spectroscopy. Upon activation with Al(iBu)3/Ph3CB(C6F5)4, these complexes became active catalysts for 1-octene polymerization giving highly stereoregular polymers (mmmm ∼ 90%) having regioirregularly arranged units. The catalytic activity of the catalysts in ethylene homo- and copolymerization, and their ability to incorporate a comonomer were highly dependent on both the activator type and the complex structure. 1/EtAlCl2 exhibited very high activity (up to 3.3 · 107 g/(molV h)) in ethylene polymerization and produced copolymers with the highest comonomer content (up to 9.1 mol%), moderate molecular weight and narrow chemical composition distribution (CCD). Both vanadium complexes, when combined with trityl borate activator, led to ethylene copolymers with lower 1-octene content and broad CCD. In addition, the copolymers were characterized by very high molecular weight (∼1 · 106 g/mol) and narrow dispersity (Mw/Mn = 1.4–2.0).

Scandium and gadolinium complexes with aryldiimine NCN pincer ligands: Synthesis, characterization, and catalysis on isoprene and 1,5-hexadiene polymerization

Several scandium and gadolinium complexes bearing tridentate aryldiimine NCN pincer ligands Ar[NCNH]ScCl2(THF)2 (Ar = Ph (1a); Ar = 2,6-Me2C6H3 (1b), Ar = 2,6-Et2C6H3 (1c), Ar = 2,6-iPr2C6H3 (1d), Ar = p-MeC6H4 (1e), Ar = 2,4,6-Me3C6H2 (1f)), Ar[NCNMe]MCl2(THF)2 (M = Sc, Ar = 2,6-Me2C6H3 (2b); M = Gd, Ar = 2,6-Me2C6H3 (3b), Ar = 2,6-iPr2C6H3 (3d)), and iPrPh[NCNMe]ScCl2 (2d) were synthesized via lithiation of the corresponding ligands with nBuLi and subsequent addition of ScCl3(THF)3 or GdCl3(THF)3 respectively. These complexes were well characterized by elemental analysis and the solid structures of 1c, 1d, 1f, and 2b were confirmed by X-ray diffraction analysis to be monomeric with N,C,N-tridentate ligands coordinating to the metal center in a typical meridional manner. In the presence of alkylaluminium and trityl borate, these well-defined complexes showed moderate to high activities in isoprene polymerization affording cis-1,4 enriched polymers (up to 98.3%). Moreover, the NCN pincer scandium complexes can also catalyze the 1,5-hexandiene polymerization giving methylene-1,3-cyclopentane enriched polymers (MCP content up to 99.3%).

Fluorenyl Half-Sandwich Bis(tetramethylaluminate) Complexes of the Rare-Earth Metals: Synthesis, Structure, and Isoprene Polymerization

Aiming at half-sandwich complexes of the type (FluR)Ln(AlMe4)2, homoleptic tetramethylaluminates Ln(AlMe4)3 (Ln = Y, La, Nd, and Lu) were treated with equimolar amounts of R-substituted potassium fluorenyls. The salt metathesis reaction of La(AlMe4)3 with K(Flu) (Flu = fluorenyl = C13H9) and K(FlutBu) (FlutBu = di(tert-butyl) fluorenyl) selectively gave the desired half-sandwich complexes (FluR)La(AlMe4)2. The corresponding reactions of Y(AlMe4)3 with K(Flu)/K(FlutBu) and Lu(AlMe4)3 with K(FlutBu) gave mixtures of half-sandwich and sandwich complexes, while treatment of Lu(AlMe4)3 with K(Flu) produced only the lutetocene complex (Flu)2Lu(AlMe4). Sterically more demanding 1-trimethylsilyl fluorenyl (FluSi) allowed for the isolation of half-sandwich complexes for the entire Ln(III) size range (Ln = La, Nd, Y, and Lu), in crystalline yields up to 94%. Upon activation with routinely employed borate or borane activators [Ph3C][B(C6F5)4], [PhNMe2H][B(C6F5)4], and B(C6F5)3, highly active initiators for isoprene polymerization were obtained. The catalyst activity as well as molecular weight (distribution) and stereoregularity of the obtained polyisoprenes are governed by the rare-earth metal size, fluorenyl ligand, and cocatalyst: highest activity for La/FluSi/[Ph3C][B(C6F5)4], lowest Mw/Mn = 1.11 for La/Flu/[PhNMe2H][B(C6F5)4], maximum trans-1,4 selectivity = 85% for La/FlutBu/[PhNMe2H][B(C6F5)4], maximum cis-1,4 selectivity = 78% for Lu/FluSi/[Ph3C][B(C6F5)4]. The formations of the active species were investigated by NMR spectroscopy revealing not only established cationization pathways but also fluorenyl abstraction in lanthanum complexes (Flu)La(AlMe4)2 and (FlutBu)La(AlMe4)2 by trityl borate [Ph3C][B(C6F5)4]. The reaction of half-sandwich complexes (FluR)Ln(AlMe4)2 with equimolar amounts of Me2AlCl did not give access to catalytically active species. Crystallization of binary mixtures (FluSi)Y(AlMe4)2/Me2AlCl in distinct molar ratios of 1:1 and 1:1.7 yielded complexes [(FluSi)Y(AlMe4)(μ-Cl)]2 and (FluSi)6Y6Cl12, respectively.

Diene Dissolution of the Heavier Alkaline Earth Metals

AbstractAlkaline and alkaline earth metals are efficiently activated in the presence of aromatic hydrocarbons (“potassium–naphthalene”, “magnesium–anthracene”) or (substituted) 1,3‐dienes to produce well‐defined organometallic complexes. In this study, mononuclear diene complexes of calcium, strontium, and barium have been synthesized by utilizing tailor‐made 1,3‐dienes. Complexes [M(2,3‐dimethyl‐1,4‐ditolyl‐1,3‐butadiene)(thf)4] (M = Ca, Sr), [Ca(2,3‐dimethyl‐1,4‐dinaphthyl‐1,3‐butadiene)(thf)4], and {Ba[2,3‐dimethyl‐1,4‐bis(2,4‐dimethylphenyl)‐1,3‐butadiene](thf)4} were isolated and fully characterized including X‐ray structure analyses. Whereas the calcium– and strontium–dienes show an approximate metallacylo‐3‐pentene coordination, barium(II) as the largest nonradioactive metal(II) cation reveals metallacyclo‐2,4‐heptadiene bonding in the solid state. It is further shown that barium(II) can accommodate eight thf molecules as evidenced in the dicationic complex {[Ba(thf)8][B(C6F5)4]2}, obtained from the reaction of barium–diene with trityl borate.

Living Polymerization of Naturally Renewable Butyrolactone-Based Vinylidene Monomers by Ambiphilic Silicon Propagators

Naturally renewable butyrolactone-based vinylidene monomers, α-methylene-γ-butyrolactone (MBL) and γ-methyl-α-methylene-γ-butyrolactone (MMBL), have been successfully polymerized in a rapid and living fashion, using ambiphilic silicon propagating species consisting of both the nucleophilic silyl ketene acetal (SKA) initiating moiety and the electrophilic silylium catalyst. Uniquely, the R3Si+ catalyst is derived directly from the SKA initiator upon in situ oxidative activation with a catalytic amount of the trityl borate activator. Investigations into effects of SKA (thus the resulting R3Si+ catalyst) and activator (thus the resulting counteranion) structures have revealed that the Me2C═C(OMe)OSiiBu3/Ph3CB(C6F5)4 combination is the most active and controlled system for (M)MBL polymerizations. Thus, under ambient conditions and with a low catalyst loading (0.05 mol % relative to monomer), this polymerization system rapidly (within 10 min) and completely converts MMBL to PMMBL with controlled low to high (M...

Olefin Polymerization Catalyst Derived by Activation of a Neutral Monoalkyl Titanium Complex with an Aminopyrrole Ligand Using Triisobutylaluminum and Trityl Borate

Abstract A neutral monocyclopentadienyl titanium monobenzyl complex 3a bearing an aminopyrrole ligand can be activated by treating with Al(iBu)3 and [Ph3C][B(C6F5)4] to became a catalyst for olefin polymerization via the methine proton abstraction of Al(iBu)3 by [Ph3C][B(C6F5)4].

Pyridine and phosphine reactions with [CPh 3][B(C 6F 5) 4

Trityl borate salts [4-RPyCPh 3][B(C 6F 5) 4] (R = H 1, t Bu 2, Et 3, NMe 2 4) and [R 3PCPh 3][B(C 6F 5) 4] (R = Me 5, n Bu 6, Ph[1] 7, p-MeC 6H 4 8) are readily prepared via equimolar reaction of the appropriate pyridine or phosphine and trityl borate [CPh 3][B(C 6F 5) 4]. The analogous reactions of P i Pr 3 affords the product [( p- i Pr 3P–C 6H 4)Ph 2CH][B(C 6F 5) 4] ( 9) while the corresponding reactions of Cy 3P and t Bu 3P gave the cyclohexadienyl derivatives [( p-R 3PC 6H 5)CPh 2][B(C 6F 5) 4] (R = Cy 10, t Bu 11). X-ray structures of 5 and 9 are reported.

Dynamic NMR Studies of Cationic Bis(2-phenylindenyl)zirconium Pyridyl Complexes: Evidence for syn Conformers in Solution

The conformationally dynamic unbridged metallocene (2-PhInd)2ZrMe2 (1) was activated with trispentafluorophenylborane (B(C6F5)3, B2) or trityl tetrakispentafluorophenylborate (“trityl borate”, [Ph3C+][B(C6F5)4-], B4) to generate the ion pair [(2-PhInd)2ZrMe+][MeB(C6F5)3-] (2a) or [(2-PhInd)2ZrMe+][B(C6F5)4-] (2b), respectively. Activation parameters for ion-pair separation were determined by line-shape analysis (2a: ΔH⧧ips = 20 ± 1 kcal/mol, ΔS⧧ips = 17 ± 4 eu; 2b: ΔH⧧ips = 15 ± 2 kcal/mol, ΔS⧧ips = 13 ± 7 eu). For 2a, a much slower B(C6F5)3 dissociation−reassociation process was also observed (ΔG⧧83°C = 18.9 ± 0.1 kcal/mol). Both 2a and 2b were treated with a series of o-substituted pyridines, and the behavior of the resulting zirconocenium-pyridyl complexes (3a−8b) was studied by 1H, 13C, and 19F NMR over the temperature range −100 to 100 °C. Below room temperature, 1H NMR NOESY spectra revealed signals characteristic of a Cs-symmetric syn conformation.

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.

Cationic organoscandium beta-diketiminato chemistry: arene exchange kinetics in solvent separated ion pairs.

Abstraction of methide from the beta-diketiminato supported organoscandium complex [L1ScMe2]2 using the trityl borate activator [Ph3C][B(C6F5)4] in arene solvents gives solvent separated ion pairs in which the arene (C6H5Br, 1a; C6H6, 1b; C7H8, 1c; 1,3,5-Me3C6H3, 1d) is coordinated to the cationic scandium center in an eta6 bonding mode. L1 incorporates methyl groups in the 2,4 positions of the ligand backbone and bulky 2,6-diisopropylphenyl groups on the nitrogen atoms. The relative binding strength of the arenes is C6H5Br < C6H6 < 1,3,5-Me3C6H3 < C7H8. Ion pairs 1a and 1c have been characterized crystallographically, and the C6H5Br derivative is notable for its eta6 bonding mode in preference to the more common eta1 bonding mode via the halogen atom. The kinetics of displacement of mesitylene by toluene (1d --> 1c) yield activation parameters of DeltaH = 21.4(6) kcal mol-1 and DeltaS = 6(1) cal mol-1 K-1. In combination with the observed lack of dependence of [toluene] on the rate of displacement, these data suggest a mechanism involving partial dissociation of the coordinated arene, followed by attack of the incoming arene. This chemistry has relevance to the role of these solvent separated ion pairs in olefin polymerization processes and presents a rare opportunity for the detailed study of these ephemeral species.

Methane Loss from Cationic μ-Methyl Dimers Formed via Trityl Borate Activation of Monocyclopentadienyl Ketimide Complexes Cp[(tBu)2CN]Ti(CH3)2 (Cp = C5H5, C5Me5, C5Me4SiMe3)

The reactions of the monocyclopentadienyl titanium dimethyl compounds Cp(L)TiMe2 (L = tBu2CN; Cp = C5H5, 1a; C5Me5, 1b; C5Me4SiMe3, 1c) with the trityl borate activator [Ph3C]+[B(C6F5)4]- are described. Formation of μ-methyl dimers of formula {[Cp(L)TiMe]2(μ-Me)}+[B(C6F5)4]- as a 1:1 mixture of rac and meso diastereomers is observed when 0.5 equiv of [Ph3C]+[B(C6F5)4]- is employed (−25 °C, C6D5Br; Cp = C5H5, rac/meso 2a; C5Me5, rac/meso 2b; C5Me4SiMe3, rac/meso 2c). Dynamic NMR and crossover experiments suggest that the dimers 2 are relatively nonlabile with respect to dissociation, intramolecular methyl group exchange, or diastereomer interconversion. Dimers 2 are observed to undergo methane loss in solution at room temperature, affording the new dimeric compounds 3a−c, {[Cp(L)Ti]2(μ-CH2)(μ-CH3)}+[B(C6F5)4]-. For the less sterically demanding C5H5 ligand, 3a is formed as a mixture of rac/meso diastereomers (7:3), but for the bulkier C5Me5 and C5Me4SiMe3 ligands, the rac isomers of 3b and 3c are formed exclusively. In contrast to μ-methyl dimers 2, in which rac/meso interconversion is not observed, the diastereomers of 3 do undergo interchange, as determined by EXSY spectroscopy, and thus the rac/meso ratios observed are thermodynamic.