Active center determination of ethylene polymerisation catalysts using a quenching method with tritiated methanol

The subject of this work is ethylene polymerisation using Kaminsky type catalysts: Cp₂MR₂=methylaluminoxane [M=Zr, W, Nb; R=Cl, CH₃]. Active center determination and kinetic studies of the (Cp₂WCl₂+methylaluminoxane) and Cp₂ZrCl₂+methylaluminoxane) systems are described, using a quenching method with tritiated methanol. The activity of the polymer was determined by liquid scintillation counting. We have found 0.5% and 87% of active centers, respectively for W and Zr system. The catalytic activity of complexes Cp₂WCl₂ and Cp₂NbCl₂ was compared with that of Cp₂ZrCl₂. The W and Nb complexes are found to be less active than the Zr complex.     

Synthesis and structure of the phosphinophosphide niobocene complex Cp2Nb(PPh2)(PHPh2)

The phosphinophosphido niobocene complex Cp₂Nb(PHPh₂)(PPh₂) (2) was prepared by deprotonation of the cationic diphosphino complex [Cp₂Nb(PHPh₂)₂]Cl (3). Complex 2 is thermally unstable and readily dissociates phosphine to give the ortho-metallated complex Cp₂Nb(PHPhC₆H₄−). Crystal structure determination of 2 supported its formulation as the phosphinophosphido compound. The Nb–P(1) (phosphino) bond length is 2.524(2) Å and Nb–P(2) (phosphido) bond length is 2.610(2) Å.     

Allyl complexes of dicyclopentadienyl-niobium(III) and -tantalum(III)

The synthesis and the properties of the complexes Cp₂TaCl₂, Cp₂M(allyl), Cp₂M(1-methylallyl) and Cp₂M(2-methylallyl) with M  Nb, Ta are described. The complex Cp₂TaCl₂ has one unpaired electron per tantalum atom, while the allyl complexes are diamagnetic. The IR and PMR spectra indicate that the allyl group is π-bonded to the metal. The mass spectra of the complexes are discussed; the thermal stability of the Cp₂Nb- and Cp₂Ta-(allyl) complexes was investigated by differential thermal analysis. The properties of the niobium and tantalum complexes are compared with those of the corresponding titanium complexes.     

Toward the catalytic synthesis of phosphiranes. A computational study

Reaction pathways for the formation of zirconocene phosphinidene complex Cp₂Zr(PR₃)PR from Cp₂ZrCl₂ and LiH and LiPRH and its reactivity to 1,2-dichloroethane are explored with density functional theory using model structures that are devoid of substituents. After the initial Cp₂Zr(Cl)PH₂ is generated with LiPH₂ reaction with LiH is likely to eliminate HCl in a single step to give directly the 16-electron complex Cp₂ZrPH, which is stabilized by the PH₃ phosphine ligand. The intermediate formation of a phosphine hydride complex, Cp₂Zr(H)PH₂ resulting from hydride substitution, is unlikely both on the basis of unfavorable reaction energies and calculated ³¹P NMR chemical shifts that indicate that such a species cannot have been observed experimentally. It is likely that a diphosphine complex, Cp₂Zr(PH₂)₂, results on using an excess of the lithium phosphide, which on H-transfer gives directly the phosphine-stabilized phosphinidene complex. The reactivity of this species is dominated by the release of its stabilizing phosphine ligand to give a highly reactive 16-electron phosphinidene complex, Cp₂ZrPH, which reacts with 1,2-dichloroethane after coordination to one of the chlorine atoms in two asynchronous metathesis steps to the three-membered phosphirane ring. In this process, ZrCl₂ is reformed enabling its recycling to regenerate the phosphinidene complex. This study highlights the special reactivity of the 16-electron Cp₂ZrPH and suggests that related complexes may be generated similarly, thereby expanding the synthetic potential of these nucleophilic reagents.     

The structure and formation of niobocene carbonyl heteronuclear derivatives. The molecular structures of Cp2Nb(CO)(μ-CO)Mn(CO)4, Cp2Nb(CO)(μ-H)Ni(CO)3 and [Cp2Nb(CO)(μ-H)]2Mo(CO)4

The heteronuclear Cp₂Nb(CO)(μ-CO)Mn(CO)₄ (I), Cp₂Nb(CO)(μ-H)Ni(CO)₃ (II) and [Cp₂Nb(CO)(μ-H)]₂M(CO)₄ (III, M = Mo;IV, M = W) complexes were prepared by reaction of Cp₂NbBH₄/Et₃N with Mn₂(CO)₁₀ in refluxing toluene, direct reaction of Cp₂NbBH₄ with Ni(CO)₄ in ether, and reaction of Cp₂NbBH₄/Et₃N with M(CO)₅. THF complexes (M = Mo or W) in THF/benzene mixture. An X-ray investigation of compounds I–III was performed. It is established that in I the bonding between Mn(CO)₅ and Cp₂Nb(CO) (with the angle (α) between the ring planes being 44.2(5)°) fragments takes place via a direct NbMn bond (3.176(1) Å) and a highly asymmetric carbonyl bridge (MnC_co 1.837(5) Å, NbC_co 2.781(5) Å). On the other hand, in complex II the sandwich Cp₂Nb(CO)H molecule (angle α = 37.8°) is combined with the Ni(CO)₃ group generally via a hydride bridge (NbH 1.83 Å, NiH 1.68 Å, NbHNi angle 132.7°) whereas the large Nb?Ni distance, 3.218(1) Å, shows the weakening or even absence of the direct NbNi bond. Similarly, in complex III two Cp₂Nb(CO)H molecules (with α angles equal to 41.4 and 43.0°, respectively) are joined to the Mo(CO)₄ group via the hydride bridges (NbH 1.83 and 1.75 Å and MoH 2.04 and 2.06 Å) producing a cis-form. The direct NbMo bonds are probably absent, since the Nb?Mo distances are rather long (3.579 and 3.565 Å). The effect of electronic and steric factors on the structure of heteronuclear niobocene carbonyl derivatives is discussed.     

Dicyclopentadienylniobium, (C5H5)2Nb; Evidence for its existence and description of its properties

Monomeric dicyclopentadienylniobium, Cp₂Nb, was shown to form in high yield in solution by the action of electron donors on Cp₂NbCl₂. Two compounds Cp₂NbCl₂ and [Cp₂Nb(Me)I]I are obtained from niobocene in oxidative addition reactions.     

Synthesis,molecular structures and PMR spectra of heteronuclear niobocene derivatives containing a niobium-tin bond

Treatment of niobocene carbonylhydride, Cp₂Nb(CO)H (I), with Ph_nSnCl_4?n and Et₂SnCl₂ in THF in the presence of Et₃N leads to the respective heteronuclear complexes Cp₂Nb(CO)SnR_nCl_3?n (R = Ph, n = 3 ÷ 1 (II–IV), R = Et, n = 2 (V)). Treatment of II with HCl in ether gives Cp₂Nb(CO)SnCl₃ (VI). Complex VI and its analog (MeC₅H₄)₂Nb(CO)SnCl₃ (VIII) were prepared by an alternative synthesis using direct reaction of I or (MeC₅H₄)₂Nb(CO)H with an equimolar quantity of SnCl₄ in THF in the presence of Et₃N. Complex VI is also generated by insertion of SnCl₂ into the NbCl bond in Cp₂Nb(CO)Cl (VII). X-Ray analysis of complexes II and VIII was performed: for II, space group P2₁/n, a = 10.1021(21), b = 17.4633(32), c= 14.2473(29) Å, β = 95.578(16)°, Z = 4; for VIII, space group. P2₁/n, a= 8.9369(15), b = 13.3589(12), c = 13.9292(20) Å, β = 99.490(14)°, Z = 4. The NbSn bond in VIII (2.764(9) Å) is shorter than that in II (2.825(2) Å). In both cases the NbSn bond is significantly shorter than the sum of Nb and Sn covalent radii (1.66 + 1.40 = 3.06 Å). It is probably partly multiple in character owing to an additional interaction of the lone electron pair of the Nb^III ion (d² configuration) with the antibonding Sn orbitals. The PMR spectra of II–VI exhibit two satellites of the singlet of C₅H₅ protons because of HSn¹¹⁷ and HSn¹¹⁹ spin-spin coupling (SSC). The SSC constant correlates with the number of electronegative chlorine atoms on the Sn atom.     

Reactions of Dicyclopentadienyltitanium(III) compounds with carbon monoxide

Reactions of Cp₂TiR (R = Cl, C₆F₅, C₆H₅, o-CH₃C₆H₄) with CO give two types of products: terminally coordinated adducts, Cp₂Ti(R)CO, and insertion products, Cp₂TiCOR, i.e. acyl compounds. The acyl ligand is η²-coordinated at the titanium atom. The preparations and properties of the compounds are described.     

二茂锆羧酸配合物的合成——二茂锆氢化物与α,β—不饱和酸或钠盐反应的研究

本文研究了Cp₂ZrH₂与丙烯酸和Cp₂Zr(H)Cl与丙烯酸钠、巴豆酸钠的反应。产物由IR ¹H和¹³CNMR、ESR谱、气相色谱以及化学方法分析鉴定。产物水解得到与底物相应的饱和酸.用¹H NMR方法考察了Cp₂ZrH₂与丙烯酸的反应过程,用IR方法考察了Cp₂Zr(H)Cl与丙烯酸钠的反应过程。实验结果表明,上面两种反应首先消除H₂或NaCl,形成锆氧健,然后碳碳双键还原生成二茂锆羧酸盐配合物,其中羧酸根离子与二茂锆桥式双齿配位。     

Etude electrochimique de complexes organometalliques: XV. Reduction electrochimique du dichlorure de niobiocene

The one electron reduction of Cp₂NbCl₂ at low temperature (−30°C) yields the anionic dimer (Cp₂NbClCl₂NbCp₂)⁻. At room temperature the electro-reduction gives Cp₂NbClL (L = trimethylphosphite or triphenylphosphine) or (Cp₂NbCl)₂. Only the latter compound can be reduced to niobocene “Cp₂Nb”.     

The first evidence for a stereostable centrometalled chirality in a dicyclopentadienyltantalum complex

Reaction of dichlorophenylphosphine with monohydrides Cp₂M(CO)H (M = Nb or Ta) gives the salts [Cp₂M(CO)(PPhClH(]⁺ Cl⁻ in good yields. In a basic medium these salts give the neutral complexes Cp₂M(CO) [P(O)(H)Ph]. In a reaction starting from the chiral hydride Cp^* CpTa(CO)H, (Cp^* = C₅Me₅), two diastereoisomers are obtained, and can be isolated as stereostable structures.     

Synthesis and crystal structures of two (cyclopentadienyl)titanium(III) hydroborate complexes, [CpTiCl(BH4)]2 and Cp2Ti(B3H8)

Treatment of Cp^∗TiCl₃ and Cp₂TiCl₂ with NaB₃H₈ affords the titanium(III) hydroborate compounds [Cp^∗TiCl(BH₄)]₂ and Cp₂Ti(B₃H₈), respectively. The former compound arises by means of a new reaction, the metal-induced fragmentation of the B₃H₈ anion, and can also be made by treating Cp^∗TiCl₃ with LiBH₄. The latter compound has been previously described, but not characterized crystallographically. Both compounds have been studied by single crystal X-ray diffraction. Dimeric [Cp^∗TiCl(BH₄)]₂ has bridging chloride ligands and terminal Cp^∗ and BH₄ ligands. The Ti-Ti distance is 3.452(1) Å, which indicates that there is no metal-metal bonding interaction. The Ti-Cl distances are 2.440(2) Å and the Ti-Cl-Ti and Cl-Ti-Cl angles of 89.97(8) and 90.03(8)° so that the Ti₂Cl₂ unit is nearly a perfect square. The BH₄ groups are each tridentate, with a Ti-B distance of 2.220(9) Å and an average Ti-H distance of 1.98(5) Å. In Cp₂Ti(B₃H₈), the B₃H₈ ligand is bidentate, as is usually seen, and the Ti-B and Ti-H distances are 2.600(3) and 1.96(2) Å. The dihedral angle between the Ti-B(1)-B(2) plane and the B(1)-B(2)-B(3) plane is 123.4°. The Ti-B distances are 0.04 Å longer than those in niobium analog, Cp₂Nb(B₃H₈), despite the fact that the single bond metallic radius of Ti is 0.02 Å smaller than that of Nb. This lengthening of the bond is probably a consequence of the presence of one fewer skeletal bonding electron in Cp₂Ti(B₃H₈).     

Dicyclopentadienyl-yttrium and -aluminium hydridochloride complexes. Crystal and molecular structure of [(η5- C5H5) 2Y(μ2-Cl) (μ3-H) Y(η5-C5H5)2](μ2-H) 2AlH · NEt3 · C6H6: a new type of coordination of the AlH4 moiety

The interaction of two equivalents of Cp₂YCl with one equivalent of LiAlH₄ gives the hydride complex (Cp₂YH)₂(AlH₃OEt₂)₂ (I), described previously, or the hydrido-chloride complexes (Cp₂Y)₂AlH₄Cl · L (L = NEt₃ (II), and L = THF (III)). The complexes II and III can also be obtained from the reaction Cp₂YCl and AlH₃ · L. The X-ray data indicate that complex II is made up of the fragment

linked to the AlH₃ · NEt₃ moiety via two μ₂ and μ₃ hydrogen atoms, and solvated benzene molecules. On the basis of the IR data complex III is assigned the following structure Cp₂Y(μ₂-H)₂Al(Cl)(μ₂-H)₂YCp₂ · 2THF.     

Synthesis and reactivity of bis(trimethylsilylcyclopentadienyl)- niobium compounds with cumulene ligands

The reduction of Nb(η⁵-C₅H₄SiMe₃)₂Cl2 (I) with Na/Hg in a 1/1 molar ratio gives Nb(η⁵-C₅H₄SiMe₃)₂Cl (II). Reactions of II with some cumulenes give the corresponding niobocene derivatives with the functional groups anchored to the bis(trimethylsilylcyclopentadienyl)niobium unit, Nb(η⁵-C₅H₄SiMe₃)₂Cl(CS₂), Nb(η⁵-C₅H₄SiMe₃)₂Cl(PhNCX) (X = O or S) and Nb(η³-C₅H₄SiMe₃)₂Cl(CyCN- Cy). The imido compound Nb(η⁵-C₅H₄SiMe₃)₂Cl(NPh) has been prepared. The chemical properties and structural features of the compounds are described.     

Structural chemistry of titanium and aluminium bimetallic hydride complexes VI. Molecular structure and physico-chemical properties of (η5-C5 H5) 2Ti(μ2-H)2 Al(Cl) (μ2 -H)2Ti(η5-C5H 5)2, a catalyst-precursor for hydrogenation in the [(η5-C5H5)2TiCl]2-LiAIH4 system

The complex (Cp₂Ti)₂AlH₄Cl has been isolated from the catalytic system (Cp₂TiCl)₂-LiAlH₄, which is a precursor of the catalyst for the hydrogenation and isomerization of olefins. This complex has been studied by X-ray diffraction. The complex forms rhomboidal crystals with unit cell dimensions a = 10.414, b = 11.998, c = 16.008 Å, space group P2₁2₁2₁, Z = 4, and density ϱ_calc = 1.40 g/cm³. The Cp₂Ti moieties are linked to the Al atom via double hydrogen bridges; the Cl atom is bonded to the Al atom. Analysis of the EPR spectral data and some chemical properties of (Cp₂Ti)₂AlH₄Cl solutions has led us to suggest a mechanism for the formation of the catalytically active species upon interaction of this compound with olefins and solvating solvents.     

Role of ion-pair equilibria in homogeneous Ziegler-Natta olefin polymerization catalysis

By means of a multinuclear NMR study of the complexes formed between AlCl₃ and either Cp₂TiCl₂ or Cp₂Ti(CH₂SiMe₃)Cl in methylene chloride solution, isomeric forms of the resulting 1:1 complexes have been detected. The influence of temperature, concentration, ratio of the titanocene chloride to aluminum chloride and nature of the solvent upon the ¹H, ¹³C and ²⁷Al NMR spectra has been investigated. The spectral changes caused by the foregoing factors give compelling evidence for a equilibrium in such Cp₂Ti(R)Cl · AlCl₃ complexes (R = Cl, CH₂SiMe₃) between contact ion pairs, Cp₂TiR · Cl · AlCl₃, and solvent-separated ion pairs, Cp₂TiR⁺ AlCl₄⁻. Upon experimental variations in temperature, concentration, solvent and ratio of R_nAlCl_3−n to the titanium catalyst, the polymerization activity of the catalyst system towards ethylene was markedly altered. Such changes in activity support the conclusion that the most active sites for polymerization in such systems are the solvent-separated ion pairs.     

Unsaturation in binuclear cyclopentadienylchromium carbonyl thiocarbonyls: Viability of (η-C5H5)2Cr2(CS)2(CO)3 in contrast to (η-C5H5)2Cr2(CO)5

The cyclopentadienylchromium carbonyl thiocarbonyls Cp₂Cr₂(CS)₂(CO)_n (n = 4, 3, 2, 1) have been studied by density functional theory using the B3LYP and BP86 functionals. The lowest energy Cp₂Cr₂(CS)₂(CO)₄ structure can be derived from the experimentally characterized unbridged Cp₂Cr₂(CO)₆ structure by replacing the two terminal carbonyl groups furthest from the Cr-Cr bond with two terminal CS groups. The two lowest energy Cp₂Cr₂(CS)₂(CO)₃ structures have a single four-electron donor η²-μ-CS group and a formal Cr-Cr single bond of length ∼3.1 Å. In contrast to the carbonyl analogue Cp₂Cr₂(CO)₅ these Cp₂Cr₂(CS)₂(CO)₃ structures are viable with respect to disproportionation into Cp₂Cr₂(CS)₂(CO)₄ and Cp₂Cr₂(CS)₂(CO)₂ and thus are promising synthetic targets. The lowest energy Cp₂Cr₂(CS)₂(CO)₂ structures have all two-electron donor CO and CS groups and short CrCr distances around ∼2.3 Å suggesting the formal triple bonds required to give the chromium atoms the favored 18-electron configurations. These Cp₂Cr₂(CS)₂(CO)₂ structures are closely related to the known structure for Cp₂Cr₂(CO)₄. In addition, several doubly bridged structures with four-electron donor η²-μ-CS bridges are found for Cp₂Cr₂(CS)₂(CO)₂ at higher energies. The global minimum Cp₂Cr₂(CS)₂(CO) structure is a triply bridged triplet with a CrCr triple bond (2.299 Å by BP86). A higher energy singlet Cp₂Cr₂(CS)₂(CO) structure has a shorter Cr-Cr distance of 2.197 Å (BP86) suggesting the formal quadruple bond required to give each chromium atom the favored 18-electron configuration.     

Die CuCl-katalysierte Reaktion von Trimethylsilyl(t-butyl)chlorphosphan mit Dimethylzirconocen: Ein Beispiel der Tandem-Katalyse

The CuCl-catalyzed Reaction of Trimethylsilyl(t-butyl)chlorophosphane with Dimethylzirconocene: An Example for Tandem Catalysis t-BuP(SiMe₃)Cl was prepared from t-BuP(SiMe₃)₂ and hexachloroethane and reacted in situ with Cp₂ZrMe₂ in the presence of catalytic amounts of copper(I) chloride yielding t-Bu(Me)P? P(Cl)t-Bu ( 1 ) (2 : 1 reaction) or t-Bu(Me)P? P · (Me)t-Bu ( 2 ) (1 : 1 reaction) and Cp₂ZrCl(Me). To understand the course of reaction, the reaction of dimethylzirconocene with CuCl and the decomposition of t-BuP(SiMe₃)Cl in the presence of CuCl and tetrachloroethene were studied. The results suggest that CuCl reacts with t-BuP(SiMe₃)Cl in the presence of C₂Cl₄ to give t-Bu(Cl)P? P(Cl)t-Bu ( 3 ); simultaneously, CuCl reacts with Cp₂ZrMe₂ with formation of methylcopper, which reacts with 3 to give 1 or 2 , respectively.     

[Cp2Nb(CH3)2]+ [AsF6]− und [Cp2Mo(CH3)2]2+ [AsF6]2−, die ersten Niobocen- und Molybdänocendimethyl-Komplexe mit den Zentralmetallatomen in ihrer maximalen Oxidationsstufe

The preparation of the first niobium(V) and molybdenum(VI) dimethylmetallocene cations is reported. [Cp₂Nb(CH₃)₂]⁺[AsF₆]⁻ (1) and [Cp₂Mo(CH₃)₂]²⁺ [AsF₆]₂⁻ (2) (Cp = η⁵-C₅H₅) are prepared by oxidation of Cp₂Nb(CH₃)₂ and Cp₂Mo(CH₃)₂ with AsF₅ in liquid sulfur dioxide. IR investigations confirm the ionic structure of 1 and 2, and that the AsF₆⁻ is not coordinated to the metal centre.