Sekundäre Hydroxyalkylphosphane: Synthese und Charakterisierung mono‐, bis‐ und trisalkoxyphosphan‐substituierter Zirconiumkomplexe und des heterobimetallischen Dreikernkomplexes [Cp2Zr{O(CH2)3PHMes(AuCl)}2]

Secondary Hydroxyalkylphosphanes: Synthesis and Characterization of Mono‐, Bis‐ and Trisalkoxyphosphane‐substituted Zirconium Complexes and the Heterobimetallic Trinuclear Complex [Cp₂Zr{O(CH₂)₃PHMes(AuCl)}₂] The secondary hydroxyalkylphosphanes RPHCH₂OH [R = 2,4,6‐Me₃C₆H₂ (Mes) ( 1 ), 2,4,6‐ⁱPr₃C₆H₂ (Tipp) ( 2 )], 1‐AdPH‐2‐OH‐cyclo‐C₆H₁₀ ( 3 ) and RPH(CH₂)₃OH [R = Ph ( 4 ), Mes ( 5 ), Tipp ( 6 ), Cy ( 7 ), ^tBu ( 8 )] were obtained from primary phosphanes RPH₂ and formaldehyde ( 1 , 2 ) or from LiPHR and cyclohexene oxide ( 3 ) or trimethylene oxide ( 4 ‐ 8 ). Starting from 5 or 7 and [Cp^R₂ZrMe₂] [Cp^R = C₅EtMe₄ (Cp°), C₅H₅ (Cp), C₅MeH₄ (Cp′)], the monoalkoxyphosphane‐substituted zirconocene complexes [Cp^R₂Zr(Me){O(CH₂)₃PHMes}] [Cp^R = Cp° ( 9 ), Cp ( 10 )] were prepared. With [Cp^R₂ZrCl₂], the bisalkoxyphosphane‐substituted complexes [Cp′₂Zr{O(CH₂)₃PHMes}₂] ( 11 ) and [Cp₂Zr{O(CH₂)₃PHCy}₂] ( 12 ) are obtained, and with [Tp^RZrCl₃], the trisalkoxyphosphane‐substituted zirconium complexes [Tp^RZr{O(CH₂)₃PHMes}₃] [Tp^R = trispyrazolylborato (Tp) ( 13 ), Tp^R = tris(3,5‐dimethyl)pyrazolylborato (Tp*) ( 14 )] are prepared. The reaction of 5 with [AuCl(tht)] (tht = tetrahydrothiophene) yielded the mononuclear complex [AuCl{PHMes(CH₂)₃OH}] ( 15 ). The trinuclear complex [Cp₂Zr{O(CH₂)₃PHMes(AuCl)}₂] ( 16 ) was obtained from [Cp₂ZrCl₂] and 15 . Compounds 1 ‐ 16 were characterized spectroscopically (¹H‐, ³¹P‐, ¹³C‐NMR; IR; MS) and compound 2 also by crystal structure determination. The bis‐ and trisalkoxyphosphane‐substituted complexes 11‐14 and 16 were obtained as mixtures of two diastereomers which could not be separated.     

Metallocene–methylaluminoxane catalysts for olefin polymerizations. IV. Active site determinations and limitation of the 14CO radiolabeling technique

The initial active site concentrations, [C^*]₀, have been determined with CH₃OT radiolabeling for the Cp₂ZrCl₂/MAO and CpZrCl₃/MAO catalysts (Cp = η⁵ : cyclopentadienyl, MAO = methyl aluminoxane). Almost all the Zr are found to be catalytically active in 70°C ethylene polymerizations; [C^*]₀ = [Zr] and [C^*]₀ = 0.8[Zr] at Al/Zr ratios of 10⁴ and 10³, respectively. Lowering the temperature to 50°C and Al/Zr to 5.5 × 10² reduces [C^*]₀ to 0.2[Zr]. The rate constant of propagation at 70°C was calculated to be 1.6 × 10³(M s)^?1 for both catalysts at Al/Zr = 1.1 × 10⁴; the values are decreased fivefold and tenfold, respectively, for the CpZrCl₃ and Cp₂ZrCl₂ systems. The usage of ¹⁴CO to determine the propagating Zr–P species was investigated. With regard to the time of reaction of ¹⁴CO with the polymerization mixture, the initial phase is attributed to reversible CO complexation and reversible migratory insertion. The second slower phase may be due to the formation of enediolate. During the course of a batch polymerization the ¹⁴C radioactivity incorporated is small compared to the number of active sites found by CH₃OT determination; it is only ca. 10% of [C^*]₀ at maximum rate of polymerization. Therefore, ¹⁴CO radiolabeling cannot be used to count C^*.     

Preparation of functionalized montmorillonites and their application in supported zirconocene catalysts for ethylene polymerization

Ethylene polymerization was carried out with zirconocene catalysts supported on montmorillonite (or functionalized montmorillonite). The functionalized montmorillonite was from simple ion exchange of [CH₃O₂CCH₂NH₃]⁺ (MeGlyH⁺) ions with interlamellar cations of layered montmorillonites. The functionalized montmorillonites [high‐purity montmorillonite (MMT)‐MeGlyH⁺] had larger interlayer spacing (12.69 Å) than montmorillonites without treatment (9.65 Å). The zirconocene catalyst system [Cp₂ZrCl₂/methylaluminoxane (MAO)/MMT‐MeGlyH⁺] had much higher Zr loading and higher activities than those of other zirconocene catalyst systems (Cp₂ZrCl₂/MMT, Cp₂ZrCl₂/MMT‐MeGlyH⁺, Cp₂ZrCl₂/MAO/MMT, [Cp₂ZrCl]⁺[BF₄]/MMT, [Cp₂ZrCl]⁺[BF₄]^?/MMT‐MeGlyH⁺, [Cp₂ZrCl]⁺[BF₄]^?/MAO/MMT‐MeGlyH⁺, and [Cp₂ZrCl]⁺[BF₄]^?/MAO/MMT). The polyethylenes with good bulk density were obtained from the catalyst systems, particularly (Cp₂ZrCl₂/MAO/MMT‐MeGlyH⁺). MeGlyH⁺ and MAO seemed to play important roles for preparation of the supported zirconocenes and polymerization of ethylene. The difference in Zr loading and catalytic activity among the supported zirconocene catalysts is discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1892–1898, 2002     

Synthesis and properties of poly‐1‐olefins

The oligomerization and polymerization of 1‐pentene using Cp₂ZrCl₂, Cp₂HfCl₂, [(CH₃)₅C₅]₂ZrCl₂, rac‐[C₂H₄(Ind)₂]ZrCl₂, [(CH₃)₂Si(Ind)₂]ZrCl₂, (CH₃)₂Si(2‐methylbenz[e]indenyl)₂ZrCl₂, Cp₂ZrCl{O(Me)CW(CO)₅}, Cp₂ZrCl(OMe) and methylaluminoxane (MAO) has been studied. The degree of polymerization was highly dependent on the metallocene catalyst. Oligomers ranging from the dimer of 1‐pentene to polymers of poly‐1‐pentene with a molar mass M_w = 149000 g/mol were formed. Cp₂ZrCl{O(Me)CW(CO)₅} is a new highly active catalyst for the oligomerization of 1‐pentene to low molecular weight products. The activity decreases in the order Cp₂ZrCl{O(Me)CW(CO)₅} > Cp₂ZrCl₂ > Cp₂ZrCl(OMe). Furthermore, poly‐1‐olefins ranging from poly‐1‐pentene to poly‐1‐octadecene were synthesized with (CH₃)₂Si(2‐methyl‐benz[e]indenyl)₂ZrCl₂ and methylaluminoxane (MAO) at different temperatures. The temperature dependence of the molar mass can be described by a common exponential decay function irrespective of the investigated monomer.     

Richtlinien und Bemerkungen der Redaktion und des Verlages für Abfassung von Manuskripten für die Zeitschrift für anorganische und allgemeine Chemie

Reaction of Trimethylsilylethers of Unsaturated Alcohols with Schwartz Reagent – Stabilisation of Cyclic Zirconiumorganic Compounds by the Moiety Cp₂ZrH₂ Besides the normal product of hydrozirconation the reaction of allyltrimethylsilylethers CH₂? CHC(R¹R²)OSi(CH₃)₃ ( I : R¹ = R² = H, VIII : R¹ = R² = CH₃, X : R¹ = H, R² = CH₃) with Cp₂Zr(H)Cl yields, as a result of a hydrogenation of the Si? O bond, trimethylsilane and a series of compounds with a Zr? O bond. Depending on the substitution of the α-C atom either dimeric chelates ( III ) or binuclear complexes of the type Cp₂Zr(Cl)CH₂CH₂C(R¹R²)OZr(Cl)Cp₂ ( IX : R¹ = R² = CH₃; XII : R¹ = H, R² = CH₃) are formed. Starting with X and excess Cp₂Zr(H)Cl the binuclear compound XIII is obtained which may be considered as an adduct of Cp₂ZrH₂ to the unsaturated chelate Compound XVII with a structure analogous to XIII is synthesized by the reaction of IX with Cp₂ZrH₂. The ¹H-NMR spectrum is in accordance with the existence of cis-trans-isomers of this complex.     

Synthesis and structure of [Cp2Zr(OPr)(HOPr)] and its activity in the polymerisation of propene oxide

The reaction of Cp₂Zr(OPrⁱ)₂ with [H(OEt₂)₂][H₂N{B(C₆F₅)₃}₂] in dichloromethane at room temperature gives [Cp₂Zr(OPrⁱ)(HOPrⁱ)]⁺[H₂N{B(C₆F₅)₃}₂]⁻ · Et₂O in high yield. The crystal structure is reported. The complex contains a short Zr-alkoxide and a longer Zr-alcohol bond; the OH group of the coordinated isopropanol is hydrogen-bonded to a diethyl ether molecule. The complex initiates the polymerisation of propylene oxide, most probably via a cationic mechanism.     

Titanium and Zirconium Complexes with Non‐Salicylaldimine‐Type Imine–Phenoxy Chelate Ligands: Syntheses,Structures, and Ethylene‐Polymerization Behavior

New Ti and Zr complexes that bear imine–phenoxy chelate ligands, [{2,4‐di‐tBu‐6‐(RCH=N)‐C₆H₄O}₂MCl₂] ( 1 : M=Ti, R=Ph; 2 : M=Ti, R=C₆F₅; 3 : M=Zr, R=Ph; 4 : M=Zr, R=C₆F₅), were synthesized and investigated as precatalysts for ethylene polymerization. ¹H NMR spectroscopy suggests that these complexes exist as mixtures of structural isomers. X‐ray crystallographic analysis of the adduct 1 ?HCl reveals that it exists as a zwitterionic complex in which H and Cl are situated in close proximity to one of the imine nitrogen atoms and the central metal, respectively. The X‐ray molecular structure also indicates that one imine phenoxy group with the syn C?N configuration functions as a bidentate ligand, whereas the other, of the anti C?N form, acts as a monodentate phenoxy ligand. Although Zr complexes 3 and 4 with methylaluminoxane (MAO) or [Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ displayed moderate activity, the Ti congeners 1 and 2 , in association with an appropriate activator, catalyzed ethylene polymerization with high efficiency. Upon activation with MAO at 25 °C, 2 displayed a very high activity of 19900 (kg PE) (mol Ti)^?1 h^?1, which is comparable to that for [Cp₂TiCl₂] and [Cp₂ZrCl₂], although increasing the polymerization temperature did result in a marked decrease in activity. Complex 2 contains a C₆F₅ group on the imine nitrogen atom and mediated nonliving‐type polymerization, unlike the corresponding salicylaldimine‐type complex. Conversely, with [Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ activation, 1 exhibited enhanced activity as the temperature was increased (25–75 °C) and maintained very high activity for 60 min at 75 °C (18740 (kg PE) (mol Ti)^?1 h^?1). ¹H NMR spectroscopic studies of the reaction suggest that this thermally robust catalyst system generates an amine–phenoxy complex as the catalytically active species. The combinations 1 /[Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ and 2 /MAO also worked as high‐activity catalysts for the copolymerization of ethylene and propylene.     

New effective reagent [Cp2ZrH2 · ClAlEt2]2 for alkene hydrometallation

New bimetallic complex [Cp₂ZrH₂ · ClAlEt₂]₂ (1) was synthesized, and its reactivity in hydrometallation reaction with the following alkenes was studied: hept-1-ene, okt-1-ene, α-methylstyrene, (1S)-β-pinene, (+)-camphene. Complex 1 shows the highest reactivity among the other known Al,Zr-bimetallic complexes: [Cp₂ZrH₂ · ClAlBuⁱ₂]₂ (2), [Cp₂ZrH₂ · AlEt₃]₂ (3), [Cp₂ZrH₂ · AlBuⁱ₃]₂ (4) and [Cp₂ZrH₂ · HAlBuⁱ₂] (5) as well as organoaluminium compounds (OAC): ⁱBu₂AlH, ⁱBu₃Al and ⁱBu₂AlCl in presence of Zr catalysts. Chlorine containing complexes 1 and 2 appear to be more effective in alkene hydrometallation, and relative hydrometallation rates are (1S)-β-pinene ? (+)-camphene < α-methylstyrene < oct-1-ene < hept-1-ene. Hydrometallation of (1S)-β-pinene and its subsequent oxidation with I₂ run with high diastereoselectivity and yield trans-myrtanol. However, the diastereoselectivity of (+)-camphene hydrometallation is less than that for (1S)-β-pinene, and the reaction gives predominately endo-camphanol.     

Synthesis and Structure of Amido‐ and Imido(pentafluorophenyl)borane Zirconocene and Hafnocene Complexes: N?H and B?H Activation

Treatment of Me₂S ? B(C₆F₅)_nH_3?n (n=1 or 2) with ammonia yields the corresponding adducts. H₃N ? B(C₆F₅)H₂ dimerises in the solid state through N? H???H? B dihydrogen interactions. The adducts can be deprotonated to give lithium amidoboranes Li[NH₂B(C₆F₅)_nH_3?n]. Reaction of the n=2 reagent with [Cp₂ZrCl₂] leads to disubstitution, but [Cp₂Zr{NH₂B(C₆F₅)₂H}₂] is in equilibrium with the product of β‐hydride elimination [Cp₂Zr(H){NH₂B(C₆F₅)₂H}], which proves to be the major isolated solid. The analogous reaction with [Cp₂HfCl₂] gives a mixture of [Cp₂Hf{NH₂B(C₆F₅)₂H}₂] and the N? H activation product [Cp₂Hf{NHB(C₆F₅)₂H}]. [Cp₂Zr{NH₂B(C₆F₅)₂H}₂] ? PhMe and [Cp₂Hf{NH₂B(C₆F₅)₂H}₂] ? 4(thf) exhibit β‐B‐agostic chelate bonding of one of the two amidoborane ligands in the solid state. The agostic hydride is invariably coordinated to the outside of the metallocene wedge. Exceptionally, [Cp₂Hf{NH₂B(C₆F₅)₂H}₂] ? PhMe has a structure in which the two amidoborane ligands adopt an intermediate coordination mode, in which neither is definitively agostic. [Cp₂Hf{NHB(C₆F₅)₂H}] has a formally dianionic imidoborane ligand chelating through an agostic interaction, but the bond‐length distribution suggests a contribution from a zwitterionic amidoborane resonance structure. Treatment of the zwitterions [Cp₂MMe(μ‐Me)B(C₆F₅)₃] (M=Zr, Hf) with Li[NH₂B(C₆F₅)_nH_3?n] (n=2) results in [Cp₂MMe{NH₂B(C₆F₅)₂H}] complexes, for which the spectroscopic data, particularly ¹J(B,H), again suggest β‐B‐agostic interactions. The reactions proceed similarly for the structurally encumbered [Cp′′₂ZrMe(μ‐Me)B(C₆F₅)₃] precursor (Cp′′=1,3‐C₅H₃(SiMe₃)₂, n=1 or 2) to give [Cp′′₂ZrMe{NH₂B(C₆F₅)_nH_3?n}], both of which have been structurally characterised and show chelating, agostic amidoborane coordination. In contrast, the analogous hafnium chemistry leads to the recovery of [Cp′′₂HfMe₂] and the formation of Li[HB(C₆F₅)₃] through hydride abstraction.     

Insight into Oxide‐Bridged Heterobimetallic Al/Zr Olefin Polymerization Catalysts

Reaction of (TBBP)AlMe ? THF with [Cp*₂Zr(Me)OH] gave [(TBBP)Al(THF)?O?Zr(Me)Cp*₂] (TBBP=3,3’,5,5’‐tetra‐tBu‐2,2'‐biphenolato). Reaction of [DIPPnacnacAl(Me)?O?Zr(Me)Cp₂] with [PhMe₂NH]⁺[B(C₆F₅)₄]^? gave a cationic Al/Zr complex that could be structurally characterized as its THF adduct [(DIPPnacnac)Al(Me)?O?Zr(THF)Cp₂]⁺[B(C₆F₅)₄]^? (DIPPnacnac=HC[(Me)C=N(2,6‐iPr₂?C₆H₃)]₂). The first complex polymerizes ethene in the presence of an alkylaluminum scavenger but in the absence of methylalumoxane (MAO). The adduct cation is inactive under these conditions. Theoretical calculations show very high energy barriers (ΔG=40–47 kcal mol^?1) for ethene insertion with a bridged AlOZr catalyst. This is due to an unfavorable six‐membered‐ring transition state, in which the methyl group bridges the metal and ethene with an obtuse metal‐Me‐C angle that prevents synchronized bond‐breaking and making. A more‐likely pathway is dissociation of the Al‐O‐Zr complex into an aluminate and the active polymerization catalyst [Cp*₂ZrMe]⁺.     

过渡金属氢化物和聚集双键化合物反应的研究——Ⅴ.Cp2MH2(M=Zr,Hf)与RNCS(R=n-Bu,c-C6H11,C6H5,2-C10H7)、CS2的反应

本文研究了Cp₂ZrH₂与CS₂、RNCS(R=n-Bu,c-C₆H₁1,C₆H₅,2-C₁₀H₇)和Cp₂HfH₂与c-C₆H₁₁NCS的反应,探讨了在这类新型脱硫反应中锆氢与铪氢配合物化学反应性能上的差异.从以上反应中分     

Kinetic model of olefin hydroalumination by HAlBui2 and AlBui3 in the presence of Cp2ZrCl2 catalyst

The mechanism of α‐olefin hydroalumination by HAlBuⁱ₂, ClAlBuⁱ₂, and AlBuⁱ₃ in the presence of Cp₂ZrCl₂ catalyst has been studied. It was established that the key intermediate of the reaction is a bimetallic complex [Cp₂ZrH₂ · ClAlBuⁱ₂]₂, which reacts with olefins and yields higher diisobutylalkylalanes. In parallel with this stage, the key complex can readily react with XAlBuⁱ₂ (X = H, Cl, Buⁱ) and form a stable trihydride complex Cp₂ZrH₂ · ClAlBuⁱ₂ · HAlBuⁱ₂, which does not exhibit reactivity in olefin hydroalumination. A kinetic model of α‐olefin hydroalumination with HAlBuⁱ₂ and AlBuⁱ₃ has been developed. The model explains the causes of the low stability of the key intermediate [Cp₂ZrH₂ · ClAlBuⁱ₂]₂ and of the different activities of organoaluminum compounds (OACs) in the olefin hydroalumination reaction. Moreover, the model gives information about the limit stages of the reaction and explains the influence of the length of the initial olefins on the rate of the whole catalytic process. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 333–339, 2007     

Funktionelle trimethylphosphanderivate: XIX. Phosphinomethylsubstituierte zirconiuimverbindungen als nucleophile: Synthese,reaktion mit CO und molekülstruktur von [(C5H5)2Zr(CH2PMe2)2]2Ni

The organozircomum-substituted phosphines Cp₂Zr(X)CH₂PMe₂ (Cp = η⁵-C₅H₅; X = Cl, CH₂PMe₂) have been prepared from Cp₂ZrCl₂ and LiCH₂PMe₂. In these compounds, the phosphinomethyl group acts as a monohapto (η¹-) ligand. On reaction with CO, the bis(phosphinomethyl)zirconium complex forms a red complex, which by means of NMR spectroscopy is shown to contain a novel zircona heterocycle. With Ni(COD)₂, Cp₂Zr(CH₂PMe₂)₂ forms the 2:1 complex [Cp₂Zr(CH₂PMe₂)₂]₂Ni. Crystals (from tetrahydrofuran) are triclinic, space group P$\text{1}$, with parameters a 13.433(5), b 18.062(3), c 19.505(2) Å, α 64.35(2), β 76.82(1), γ 71.28(2)°, V 4018.12 ų, d_x 1.445 g cm^?3 for Z = 4, μ(Mo-K_α) 11.5 cm^?1, T 21°C. Refinement of 743 parameters on 8826 reflections converged at R = 0.055. The molecular structure consists of monomeric units with two bidentate C₂Zr(CH₂PMe₂)₂ molecules acting as chelating ligands to a tetrahedral Ni⁰ centre. The six-membered Zr(CH₂PMe₂)₂Ni rings adopt a chair conformation. Steric strain by interaction of the axial cyclopentadienyl and methyl ligands at Zr and P, respectively, causes these rings to be considerably flattened.     

Super‐Bulky Penta‐arylcyclopentadienyl Ligands: Isolation of the Full Range of Half‐Sandwich Heavy Alkaline‐Earth Metal Hydrides

Hydrogenolysis of the half‐sandwich penta‐arylcyclopentadienyl‐supported heavy alkaline‐earth‐metal alkyl complexes (Cp^Ar)Ae[CH(SiMe₃)₂](S) (Cp^Ar=C₅Ar₅, Ar=3,5‐ⁱPr₂‐C₆H_3; S=THF or DABCO) in hexane afforded the calcium, strontium, and barium metal–hydride complexes as the same dimers [(Cp^Ar)Ae(μ‐H)(S)]₂ (Ae=Ca, S=THF, 2‐Ca ; Ae=Sr, Ba, S=DABCO, 4‐Ae ), which were characterized by NMR spectroscopy and single‐crystal X‐ray analysis. 2‐Ca , 4‐Sr , and 4‐Ba catalyzed alkene hydrogenation under mild conditions (30 °C, 6 atm, 5 mol % cat.), with the activity increasing with the metal size. A variety of activated alkenes including tri‐ and tetra‐substituted olefins, semi‐activated alkene (Me₃SiCH=CH₂), and unactivated terminal alkene (1‐hexene) were evaluated.     

Insertions of nitriles and pyridine into the ZrSi bond of (η5-C5H5)(η5-C5Me5)Zr[Si(SiMe3)3]Me

The zirconium silyl complex CpCpZr[Si(SiMe₃)₃]Me (1; Cp = η⁵-C₅H₅; Cp = η⁵-C₅Me₅) reacts with nitriles RCN (R = Me, CHCH₂, Ph) to form the azomethine derivatives CpCpZr[NC(R)Si(SiMe₃)₃]Me (2, R = Me; 3, R = CHCH₂; 4, R = Ph). Pyridine reacts with 1 to give a 75% yield of CpCpZr[NC₅H₅Si(SiMe₃)₃]Me (5), which results from 1,2-addition of the ZrSi bond of 1 to pyridine. These reactions provide the first examples of nitrile and pyridine insertions into a transition metal-silicon bond. The related silyl complexes Cp₂Zr[Si(SiMe₃)₃]Me and CpCpZr[Si(SiMe₃)₃]Cl are much less reactive toward nitriles and pyridine.     

Activation of Metallacyclopropenes,five-membered Metallacyclocumulenes and Metallacyclopentynes of Zirconium with iBu2AlH

The recently described reaction products of zirconacyclopropenes Cp^′₂Zr(η²-Me₃SiC₂SiMe₃) and five-membered zirconacyclocumulenes (zirconacyclopenta-2,3,4-trienes) Cp*₂Zr(η⁴-1,2,3,4-RC₄R), Cp* = η⁵-pentamethylcyclopentadienyl, R = Me, Me₃Si and Ph, with i-Bu₂AlH are active catalysts in the polymerization of ethylene and in the ring opening polymerization of ε-caprolactone. Here we describe the different activity of these complexes after thermal activation or if additional i-Bu₂AlH together with water are added. These results are compared to those which were obtained with the complexes Cp₂Zr(η⁴-1,2,3,4-H₂C₄H₂), rac-(EBTHI)ZrF₂, rac-(EBTHI)ZrCl₂, [rac-(EBTHI)Zr(H)(µ-H)]₂ and rac (EBTHI)Zr(F)CH₂-CH₂(2-Py) after activation with i-Bu₂AlH together with water.     

Insertion Reactions of Neutral Phosphidozirconocene Complexes as a Convenient Entry into Frustrated Lewis Pair Territory

Neutral phosphidozirconocene complexes [Cp₂Zr(PR₂)Me] (Cp=cyclopentadienyl; 1a : R=cyclohexyl (Cy); 1b : R=mesityl (Mes); 1c : R=tBu) undergo insertion into the Zr?P bond by non‐enolisable carbonyl building blocks (O=CR′R′′), such as benzophenone, aldehydes, paraformaldehyde or CO₂, to give [Cp₂Zr(OCR′R′′PR₂)Me] ( 3 – 7 ). Depending on the steric bulk around P, complexes 3 – 7 react with B(C₆F₅)₃ to give O‐bridged cationic zirconocene dimers that display typical frustrated Lewis pair (FLP)/ambiphilic ligand behaviour. Thus, the reaction of {[Cp₂Zr(μ‐OCHPhPCy₂)][MeB(C₆F₅)₃]}₂ ( 10a ) with chalcone results in 1,4 addition of the Zr⁺/P FLP, whereas the reaction of {[Cp₂Zr(μ‐OCHFcPCy₂)][MeB(C₆F₅)₃]}₂ ( 11a ; Fc=(C₅H₄)CpFe) with [Pd(η³‐C₃H₅)Cl]₂ yields the unique Zr?Fe?Pd trimetallic complex 13a , which has been characterised by XRD analysis.     

COPOLYMERIZATION OF ETHYLENE AND PROPYLENE WITH CpCH2CH2CH=CH2)2MCl2(M=Zr,Hf)AND Cp2ZrCl2 CATALYSTS

(CpCH_2CH_2CH = CH_2)_2MCl_2(M=Zr, Hf)/MAO and Cp_2ZrCl_2/MAO (Cp=cyclopentadienyl; MAO=methylaluminoxane) catalyst systems have been compared for ethylene copolymerization to investigate the influence of theligand and transition metal on the polymerization activity and copolymer properties. For both CH_2CH_2CH=CH_2 substitutedcatalysts the catalytic activity decreased with increasing propene concentration in the feed. The activity of the hafnocenecatalyst was 6～8 times lower than that of the analogous zirconocene catalyst, ~(13)C NMR analysis showed that the copolymerobtained using the unsubstituted catalyst Cp_2ZrCl_2 has greater incorporatien of propene than those produced byCH_2CH_2CH=CH_2 substituted Zr and Hf catalysts. The melting point, crystallinity and the viscosity-average molecularweight of the copolymer decreased with an increase of propenc concentration in the feed. Both CH_2CH_2CH= CH_2 substitutedZr and Hf catalysts exhibit little or no difference in the melting point and crystallinity of the produced copolymers. However,there are significant differences between the two zirconocene catalysts. The copolymer produced by Cp_2ZrCl_2 catalyst havemuch lower T_m and X_c than those obtained with the (CpCH_2CH_2CH=CH_2)_2ZrCl_2 catalyst. The density and molecular weightof the copolymer decreased in the order: (CpCH_2CH_2CH=CH_2)_2HfCl_2>(CpCH_2CH_2CH=CH_2)_2ZrCl_2>Cp_2ZrCl_2. The kineticbehavior of copolymerizaton with Hf catalyst was found to be different from that with Zr catalyst.     

Light Lanthanide Metallocenium Cations Exhibiting Weak Equatorial Anion Interactions

As the dysprosocenium complex [Dy(Cp^ttt)₂][B(C₆F₅)₄] (Cp^ttt=C₅H₂tBu₃-1,2,4, 1-Dy ) exhibits magnetic hysteresis at 60 K, similar lanthanide (Ln) complexes have been targeted to provide insights into this remarkable property. We recently reported homologous [Ln(Cp^ttt)₂][B(C₆F₅)₄] ( 1-Ln ) for all the heavier Ln from Gd–Lu; herein, we extend this motif to the early Ln. We find, for the largest Ln^III cations, that contact ion pairs [Ln(Cp^ttt)₂{(C₆F₅-κ¹-F)B(C₆F₅)₃}] ( 1-Ln ; La–Nd) are isolated from reactions of parent [Ln(Cp^ttt)₂(Cl)] ( 2-Ln ) with [H(SiEt₃)₂][B(C₆F₅)₄], where the anion binds weakly to the equatorial sites of [Ln(Cp^ttt)₂]⁺ through a single fluorine atom in the solid state. For smaller Sm^III, [Sm(Cp^ttt)₂][B(C₆F₅)₄] ( 1-Sm ) is isolated, which like heavier 1-Ln does not exhibit equatorial anion interactions, but the Eu^III analogue 1-Eu could not be synthesised due to the facile reduction of Eu^III precursors to Eu^II products. Thus with the exception of Eu and radioactive Pm this work constitutes a structurally similar family of Ln metallocenium complexes, over 50 years after the [M(Cp)₂]⁺ series was isolated for the 3d metals.     

Mechanism of olefin polymerization by a soluble zirconium catalyst

A mechanistic study has been carried out on the homogeneous olefin polymerization/oligomerization catalyst formed from Cp₂ZrMe₂ and methylaluminoxane, (MeAlO)_x, in toluene. Formal transfer of CH₃ from Zr to Al yields low concentrations of Cp₂ZrMe⁺ solvated by [(Me₂AlO)_y(MeAlO)_x−y]_y. The cationic Zr species initiates ethylene oligomerization by olefin coordination followed by insertion into the Zr–CH₃ bond. Chain transfer occurs by one of two competing pathways. The predominant one involves exchange of Cp₂Zr–P⁺ (P=growing ethylene oligomer) with Al–CH₃ to produce another Cp₂ZrMe⁺ initiator plus an Al-bound oligomer. Terminal Al–C bonds in the latter are ultimately cleaved on hydrolytic workup to produce materials with saturated end groups. Concomitant chain transfer occurs by sigma bond metathesis of Cp₂Zr–P⁺ with ethylene. Metathesis results in cleavage of the Zr–C bond of the growing oligomer to produce materials also having saturated end groups; and a new initiating species, Cp₂Zr-CHCH₂⁺. The two chain transfer pathways afford structurally different oligomers distinguishable by carbon number and end group structure. Oligomers derived from the Cp₂ZrMe⁺ channel are C_n (n=odd) alkanes; those derived from Cp₂Zr–CHCH₂⁺ are terminally mono-unsaturated C_n (n=even) alkenes. Chain transfer by beta hydride elimination is detectable but relatively insignificant under the conditions employed. Propylene and 1-hexene react similarly but beta hydride elimination is the predominant chain transfer step. The initial Zr-alkyl species produces a Cp₂ZrH⁺ complex that is the principle chain initiator. Chain transfer is fast relative to propagation and the products are low molecular weight oligomers.