Effect of catalyst aging on catalyst activity and stereospecificity for MgCl2/ethyl benzoate or dioctyl phthalate/TiCl4-triethylaluminium for propene polymerization

The aging of the MgCl₂/dioctyl phthalate (DOP) or ethyl benzoate (EB)/TiCl₄ catalyst was studied. Because of the strong complexation of DOP with the catalyst, only a small fraction of DOP was extracted by cocatalyst triethylaluminium (TEA) during aging, resulting in converting some highly isospecific sites into aspecific ones. No change of the overall number of sites was detected. EB, on the other hand, could be readily removed by TEA, resulting in a large increase in aspecific sites. Clustering of those sites facilitated catalyst deactivation.     

Structures of 18-crown-6, 15-crown-5 and their metal complexes in methanol solution as studied by Raman spectroscopy

Raman spectra of 18-crown-6, 15-crown-5, and their complexes with Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, Ca²⁺ and Ba²⁺ have been investigated in methanol solution. Normal coordinate calculations are presented for the D_3d⁻ and C_i-symmetric structures of 18-crown-6. Analysis of the Raman spectra gives information on the ring conformations of the crown ethers and the stoichiometry of complexation. The uncomplexed ethers adopt diverse conformational states in methanol at room temperature, the D_3d state being the most stable in 18-crown-6 and various states equally stable in 15-crown-5. Most of the cations form 1:1 or 2:1 crown—metal complexes depending on the cation size relative to the hole size of crown. Exceptionally, Cs⁺ forms both 1:1 and 2:1 complexes with 18-crown-6. The ring structures in complexes of 18-crown-6 are not much distorted from the D_3d one, though the distortion is rather large in the 2:1 Cs²⁺ and 1:1 Ca⁺ complexes. Complexes of 15-crown-5 exhibit for types of ring structure depending on the size and charge of the cation. These structures are likely to involve distortion from the gauche or gauche′ conformation about the CC bonds and various conformation about the CO bonds.     

Comparative characterization of MgCl2/ethyl benzoate/TiCl4 and MgCl2/2,2,6,6 tetramethylpiperidine/TiCl4 Ziegler-Natta precatalysts

In this article we present the results of the preparation and characterization of two Ziegler–Natta precatalysts: MgCl₂/Ethyl benzoate (EB)/TiCl₄ and MgCl₂/2,2,6,6 tetramethylpiperidine (TMPiP)/TiCl₄ by means of FTIR, X-ray diffraction, SEM, BET surface area measurements, and other techniques applied at different steps of their preparation procedures. The precatalysts were prepared by impregnating with TiCl₄ a given amount of MgCl₂, which was previously ball-milled with the electron donor chosen. Prior to impregnation, the ball-milled material presented different surface compounds depending on the electron donor used: [(MgCl₂)₂] · 2EB, MgCl₂ · EB, or a salt of the amine. The solid milled with EB is more homogeneous than the one milled with the TMPiP. Titanium is better retained in the solid milled with EB. This precatalyst has better morphological properties and larger BET surface area. By means of FTIR, we found evidences that an adequate surface structure for the formation of stereospecific sites in MgCl₂/TMPiP/TiCl₄ was formed. © 1994 John Wiley & Sons, Inc.     

FT-i.r. and Raman spectra of ethyl benzoate. Assignment based on differences between phases,complexation to titanium tetrachloride,isotopic shifts and normal coordinate analysis

Vibrational spectra are given for ethyl benzoate (EB) as liquid, gas and amorphous solid. Assignation is made for the vibrational spectra of the three phases of EB, with the help of data for crystalline EB given in the literature and the crystalline equimolar ethyl benzoate—titanium tetrachloride complex, and assisted with force field calculations.All fundamental vibrations in EB between 100 and 1800 cm⁻¹ are found. The observed frequencies fit a valence force field, developed for five isotopic congeners of EB, with an average deviation of less than 5 cm⁻¹.     

Transition-metal complexes of two valence tautomers of a bulky phenoxide, 2,6-Bu-t2-4-MeC6H2O− (ArO−); preparation and crystal and molecular structure of a phenoxytitanium(III) and a cyclohexadienonylrhodium(I) complex, [Ti(η-C5H5)2 OAr] and [Rh(ArO-η5)(PPh3)2]

The 2,6-di-t-butyl-4-methylphenoxo ligand (ArO^?) is ambidentate, giving rise to the O-bonded 15-electron d¹ [Ti(η-C₅H₅)₂OAr] and the η⁵ -[C(2)-C(6)]-bonded 18-electron d⁸ complex [Rh(ArO-η⁵)(PPh₃)₂], obtained from [{Ti(η-C₅H₅)₂Cl}₂]-LiO Ar and [Rh{N(SiMe₃)₂}(PPh₃)₂]-ArOH, respectively; the average TiC(η) distance is 2.362(10) Å, TiO 1.892(2) Å, and O:C(of Ar) 1.352(3) Å, and TiOC 142.3(2)°; in the Rh^I complex, C(2)C(6) are coplanar (with CC(av.) 1.38(2) Å). C(1)O 1.28 Å, and Rh to C(2) C(6) bond lengthsare in the range 2.19–2.65 Å.     

Zweikernige η5-pentamethylcyclopentadienyl-rhenium-komplexe mit einer chalkogenbrücke. Die molekülstruktur von [(η5-C5Me5)Re(CO)2]2(μ-Se)

We report the synthesis and characterisation of binuclear η⁵-pentamethylcyclopentadienylrhenium complexes, [(η⁵-C₅Me₅)Re(CO)₂]₂(μ-E) (E = S (2), Se (3), Te (4)), containing a chalcogen bridge in addition to a ReRe bond. According to the X-ray structural analysis, 3 possesses approximately C₂ molecular symmetry; the C₅Me₅ ring ligands occupy trans positions with respect to the central Re₂Se unit [d(ReRe) 3.032(1) Å, ∢ ReSeRe 74.9(1)°]. As expected, the complexes of the now complete series [CpRe(CO)₂]₂(μ-E) (E = O (1), S (2), Se (3), Te (4)) show a high degree of similarity in their corresponding mass, IR, ¹H and ¹³C NMR spectra.     

The syntheses and coordination properties of M(CO)3X(DAB) (M = Mn,Re; X = Cl,Br, I; DAB = 1,4-diazabutadiene)

M(CO)₅X (M = Mn, Re; X = Cl, Br, I) reacts with DAB (1,4-diazabutadiene = R₁N=C(R₂)C(R₂)′=NR′₁) to give M(CO)₃X(DAB). The ¹H, ¹³C NMR and IR spectra indicate that the facial isomer is formed exclusively. A comparison of the ¹³C NMR spectra of M(CO)₃X(DAB) (M = Mn, Re; X = Cl, Br, I; DAB = glyoxalbis-t-butylimine, glyoxyalbisisopropylimine) and the related M(CO)₄DAB complexes (M = Cr, Mo, W) with Fe(CO)₃DAB complexes shows that the charge density on the ligands is comparable in both types of d⁶ metal complexes but is slightly different in the Fe-d⁸ complexes. The effect of the DAB substituents on the carbonyl stretching frequencies is in agreement with the A′(cis) > A″ (cis) > A′(trans) band ordering.Mn(CO)₃Cl(t-BuNCHCHNt-Bu) reacts with AgBF₄ under a CO atmosphere yielding [Mn(CO)₄(t-BuNCHCHN-t-Bu)]BF₄. The cationic complex is isoelectronic with M(CO)₄(t-BuNCHCHNt-Bu) (M = Cr, Mo, W).     

Preparation and structural characterization of [(η5-C5H5)2Zr(SC6H5)]2O. A qualitative description of the bonding in oxo-bridged dicyclopentadienyl-transition metal dimers

The hydrolysis of (η⁵-C₅H₅)₂Zr(SC₆H₅)₂ was shown previously by IR spectroscopy to produce an oxo-bridged complex. The molecular structure of this material has been determined by X-ray diffraction methods and consists of two (η²-C₅H₅)₂Zr(SC₆H₅) units linked by an oxo bridge. The ZrOZr bond is nonlinear at 165.8(2)° with a Zr?Zr interatomic separation of 3.902(1)Å. The two independent SZrO bond angles of 98.7(1) and 103.3(1)° are consistent with a d° electronic structure for each zirconium atom. The relatively short ZrO distances of 1.968(3) and 1.964(3) Å support the presence of partial double-bond character arising from the donation of electron density from filled p_π-orbitals on the oxygen atom to unfilled d-orbitals on the electron deficient d⁰ metal atoms. This bonding feature requires based upon orbital symmetry arguments that the (ML)₂O molecular core in [(η⁵-C₅H₅)₂ML]₂O complexes must be nonplanar with a dihedral angle between the two LMO planes less than 90°. For [(η⁵-C₅H₅)₂Zr(SC₆H₅)]₂O, dihedral angle of 61.7° was observed. The compound crystallizes in an orthorhombic space group, Pbca, with refined lattices parameters a 16.458(4), b 20.281(5), and c 17.016(4) Å. Full-matrix least-squares refinement of 2613 diffractometry data I > σ(I) led to a final discrepancy index R(F₀²) = 0.044.     

Crystal structure of olanzapinium benzoate (1:1)

Olanzapinium benzoate, 1-methyl-4-(2-methyl-10H-thieno[2,3-b][1,5]benzodiazepin-4-yl)-piperazin-1-ium benzoate, (C₁₇H₂₁N₄S)⁺(C₇H₅O₂)^? (I), crystallizes in triclinic space group P-1 with unit cell dimensions a = 9.2957(6) Å, b = 11.2416(7) Å, c = 12.0003(8) Å; α = 64.585(1)°, β = 87.568(1)°, γ = 83.248(1)°; V = 1124.8(1) ų. The asymmetric part of the structure comprises a singly charged olanzapinium cation and a singly charged benzoate anion. The central 1,5-diazepine ring adopts the expected boat conformation, while the piperazine ring favors the chair conformation. The olanzapinium and benzoate ions are linked by intermolecular N-H...O hydrogen bonds forming infinite chains running along the c-axis of the crystal.     

Steric control in the stereospecific complexation of chiral α-olefins to platinum(II)

The complexes trans-dichloro[R(CH₃)C^*HCH=CH₂](pyridine)platinum-(II), R = C₂H₅, i-C₃H₇, t-C₄H₉, have been prepared and their ¹H NMR and CD spectra investigated. The two diastereomers formed in the complexation of the chiral α-olefin to Pt^II are present in different concentrations in solution, the diastereomer of opposite absolute configuration at the two chiral centres being the prevailing one. The extent of stereoselectivity, evaluated both by NMR and CD, varies from 32% to 75% by changing the bulkiness of the R group. The preferred conformation of the two diastereomers for each complex has been established by NMR, taking into account the deshielding effect on the protons bound to saturated carbon atoms as well as J(HH) and J(PtH) coupling constants.     

Fluorooxoperoxo complexes of vanadium(V)

Substances crystallizing under various conditions from the MVO₃(MF, HF)H₂O₂H₂O (M = NH₄, K) systems have been characterized by elemental analysis, infrared and Raman spectra and X-ray powder patterns. Besides the known M₂[VO(O₂)₂F] complexes, complexes of two new types have been obtained: M₃[HV₂O₂(O₂)₃F₄·2H₂O and (NH₄)₃[V₂O₂(O₂)₄F]·nH₂O (n≈2). Vibrational spectra of new complexes are consistent with the presence of dimeric anions containing V(μ₂O₂)V and VFV bridges, respectively.     

Lineare oligophosphaalkane: XVIII. Addition Ph-funktioneller methylenbisphosphane an die MoMo-Dreifachbindun in (η5-C5H5)2Mo2(CO)4

By means of the addition of the PH-functional methylenebisphosphanes R¹R²-PCH₂PR³H (PCP) to the MoMo triple bond in (η⁵-C₅H₅)₂Mo₂(CO)₄(MoMo) the complexes (η⁵-C₅H₅)₂Mo₂(CO)₄(PCP) containing a five-membered ring system Mo₂P₂C are obtained. Starting with unsymmetrically substituted methylenebisphosphanes R′₂PCH₂PRH only one isomer is formed, while the disecondary derivatives RHPCH₂PHR (as the diastereomeric mixture) gave two isomers of (η⁵-C₅H₅)₂Mo₂(CO)₄(PCP) (A₂ and AB) as indicated by the ³¹P{¹H} and ¹³C{¹H} NMR spectra.X-ray structural analysis of the derivative of the racemate of t-BuHPCH₂PH(t-Bu) space group C2/c, monoclinic, a 18.034(2), b 14.909(1), c 11.106(1) Å, α 90, β 99.788(8), γ 90°) reveals a puckered Mo₂P₂C five-membered ring system (dihedral angle PMoMo′P′ 54.4(2)°) with square-pyramidal coordination geometry at the Mo atoms. Two of the CO ligands (C(6)O(1) and C(6′)O(1′)) are almost coplanar with the molybdenum atoms, while the terminal CO groups (C(7)O(2) and C(7′)O(2′)) are about orthogonal (dihedral angle C(7)MoMo′C(7′) 88.4(3), MoMo′ 3.2109(4), MoP 2.4567(8), PC(8) 1.834(3), PH(P) 1.37(3) Å).     

Laser induced fluorescence spectroscopy of van der Waals complexes of aniline with N2, H2, and CH4 formed in a supersonic free jet

The laser induced fluorescence spectra for the Ã(¹B₂)X̃(¹A₁) transition of van der Waals (vdW) complexes of aniline with N₂, H₂, and CH₄ have been observed. Based on the analysis of the rotational structure of the spectra, it is suggested that two vdW conformers exist for the N₂aniline complex though only one conformer is identified for the other complexes. In the electronically excited state of the CH₄aniline complex, energy level splittings are observed and attributed to the intramolecular rotation of CH₄.     

Molecular structure of two dicyclopentadienylmolybdenum derivatives containing a four-membered ring [Mo(η5-C5H5)2(2-NHNC5H4)][PF6] and [Mo(η5C5H5)2(2-ONC5H4)][PF6]

The structure of the new compound [Mo(η⁵-C₅H₅)₂(2-NHNC₅H₄)][PF₆] (1) has been determined. The crystals are orthorhombic, space group Pca2₁ with a 20.807(1), b 8.0030(8), c 10.056(3) Å, V 1674.5 ų, Z = 4. The structure of [Mo(η⁵-C₅H₅)₂(2-ONC₅H₄)][PF₆] (2) has also been determined. The crystals are orthorhombic, space group Pnma with a 12.727(3), b 10.174(2), c 12.918(1) Å, V 1672.8 ų, Z = 4. The structures were solved by Patterson and difference electron density syntheses and refined by least-squares to R of 0.028 for 1287 reflections for 1 and 0.059 for 1178 reflections for 2.Although not isostructural the two cationic complexes have equivalent geometries with the normal bent bismetallocene structure. For 1 the MoN bond lengths are 2.160(8) and 2.142(9) Å, with a NMoN bond angle of 59.8(3)°, whereas for 2 MoO is 2.142(10), MoN is 2.138(11) Å, the NMoO angle is 61.2(4)°. These parameters are discussed and compared with the corresponding data for similar biscyclopentadienyl complexes of molybdenum(IV). Extended Hückel molecular orbital calculations have been carried out to throw light on the nature of the bonding between the metal and the bidentate ligand.     

Adsorption of TiCl4 and electron donor on defective MgCl2 surfaces and propylene polymerization over Ziegler-Natta catalyst: A DFT study

The formations of defective MgCl₂ surfaces, and subsequent adsorption of Ti species and electron donor, as well as propylene polymerization over the Ziegler-Natta catalyst have been investigated using density functional theory (DFT) method. Twelve possible support models of regular and defective MgCl₂ (110) and (100) surfaces were built. The individual adsorptions of titanium chlorides as mononuclear or dinuclear, and ethyl benzoate (EB) as electron donor, on these models were evaluated. The analysis of energies presented the cases of EB adsorption were generally more stable than titanium chlorides on both surfaces. Thus, EB as internal electron donor mainly prevented TiCl₄ from coordinating on the MgCl₂ surfaces where mostly non-stereospecific active sites could be formed. Exceptionally, A5 the site model with terminal Cl-vacancy on the MgCl₂ support, presented stronger adsorption of TiCl₄ than that of EB on (110) surface. Since the TiCl₄ and ethyl benzoate (EB) would compete to adsorb on the support surface, it seems reasonable to assume that TiCl₄ might predominately occupy this site, which can act as the most plausible active site for propylene polymerization. The first insertion of propylene monomer into the A5 active site model showed that it exhibited good regioselectivity but poor stereospecificity in the absence of electron donor.     

The crystal structure of eulytite Na3Bi5(PO4)6

The crystal structure of Na₃Bi₅(PO₄)₆ was solved using the single-crystal X-ray diffraction technique. The structural refinement has led to a reliability factor of R₁=0.0257 (wR₂=0.0533) for 428 independent reflections. This compound was found to crystallize in the cubic system (space group I4̄3d) with eulytite structure and the lattice parameters: a=10.097 (4) Å, V=1029.38 ų, Z=2, D_calc.=5.43 g cm⁻³ (D_exp.=5.32(5) g cm⁻³). The structure is characterized by the existence of one single general position (48a) for oxygen anions and two distinguished positions (16c) occupied by Na⁺ and Bi³⁺ cations, respectively. The site occupation factors are equal to 3/8 and 5/8 for sodium and bismuth, respectively. Although all PO distances are identical (1.529(4) Å), the OPO angles ranging from 108.06 (15) to 112.32 (31)°, show that [PO₄]³⁻ are rather distorted. Both sodium and bismuth cations are located in octahedral sites with corresponding mean distances of NaO and BiO equal to 2.428 and 2.386 Å, respectively. As expected from the close values of the ionic radii of Na⁺ and Bi³⁺, these distances lie in the same range.     

Studies on novel unsymmetrical azomethines—III : Copper(II) complexes of unsymmetrical tetradentate azomethines

Copper(II) complexes of unsymmetrical bifunctional tetradentate azomethines having the general formulae, (OC₁₀H₆CH:NXN:C(R)C₆H₄O)Cu, (OC₁₀H₆CH:NXN:C(CH₃)CHC(CH₃)OCu, (OC₆H₄CH:NXN:C(CH₃)C₆H₄O)Cu, (OC₆H₄C(R);NXN:C(CH₃)CHC(CH₃)O)Cu (where R = H or CH₃, X = (CH₂)₃, (CH₂)₄, (CH₂)₆ or -oC₆H₄) have been synthesized by the reactions of preformed mixed imine complexes of the type, CuLL′ (where L and L′ are two different imines such as 2-hydroxy-1-naphthaldimine, salicylaldimine, o-hydroxyacetophenonimine or acetylacetonimine) with diamines such as 1,3-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane or o-phenylenediamine. These complexes have been characterized by elemental analyses, TLC, conductance, magnetic measurements, IR and electronic spectra.     

95Mo NMR spectral studies on seven-coordinate molybdenum(II) isocyanide complexes

The ⁹⁵Mo NMR spectra of a series of seven-coordinate molybdenum(II) isocyanide complexes of the types [Mo(CNR)_7-nL_n](PF₆)₂ (R = CH₃, CHMe₂, CMe₃, C₆H₁₁, CH₂Ph; L = py, bpy, Me₂bpy, phen, dppe, P-n-Bu₃; n = 0,1,2) [Mo(CNC-Me₃)₆X]PF₆ (X = Cl, Br, I) and [{Mo(CNCMe₃)₄(NN)}₂(μ-CN)](PF₆)₃ (NN = bpy, Me₂bpy, phen) have been studied. The ⁹⁵Mo chemical shift range for this group of complexes is about 1100 ppm. An increase in the size of the R group attached to the isocyanide ligand generally tends to shield the ⁹⁵Mo nucleus. Replacement of the isocyanide ligand with a phosphorus ligand also increases the shielding, whereas the replacement of isocyanide with a heterocyclic nitrogen donor leads to deshielding by 800–900 ppm. This group of complexes shows a normal halogen dependence, i.e. replacement of Cl^? by Br^? and I^? increases the shielding of the ⁹⁵Mo nucleus. The cyano-bridged cations [{Mo(CNCMe₃)₄(NN)}₂(μ-CN)]³⁺ (NN = bpy, Me₂bpy, or phen) show two ⁹⁵Mo NMR signals, one for the molybdenum coordinated to the carbon of the bridging CN and one for the N-coordinated molybdenum. Comparison of the chemical shifts and linewidths of the cyano-bridged species with those of the corresponding mononuclear molybdenum(II) complexes [Mo(CNCMe₃)₅(NN)](PF₆)₂ leads to the assignment of the more deshielded signal to the N-coordinated molybdenum. The ¹⁴N and ³¹P NMR spectra for these complexes have also been measured, as have the ¹³C NMR spectra of the pairs of complexes [Mo(CNCMe₃)₅(NN)](PF₆)₂ and [{Mo(CNCMe₃)₄(NN)}₂(μ-CN)](PF₆)₃ (NN = bpy or phen). The ¹⁸³W NMR spectra for [W(CNR)₅(bpy)](PF₆)₂ (R = CMe₃ and CH₂Ph), show that the δ(¹⁸³W)/δ(⁹⁵Mo) chemical shift ratios for isocyanide complexes are different from the ratio found for M⁰ and M^VI.     

Stereochemically active lone pairs of electrons in subvalent main fourth-group compounds. The crystal and molecular structures of {η5-C5H5Co[P(OC2H5)2O]3}2MII (M = Sn,Pb)

The air-stable, mixed main group-transition metal, trinuclear sandwich oxygen tripod 2/1 complexes, {η⁵-C₅H₅Co[P(OC₂H₅)₂O]₃}₂M, (1, M = Sn): C₃₄H₇₀Co₂O₁₈P₆Sn, a 18.871(12), b 22.461(12), c 12.671(7) Å, β 92.53(5)°, monoclinic space group P2₁/a, d_calc 1.472 g cm⁻³, Z = 4, R = 9.5%: 2 (M = Pb): C₃₄H₇₀Co₂O₁₈P₆Pb, a 18.787(8), b 22.397(9), c 12.674(3) Å, β 92,01(3)°, monoclinic space group P2₁/a, d_calc 1.594 gcm⁻³, Z = 4, R = 7.2%, have been subjected to single crystal X-ray analysis. Both complexes show a stereochemically active lone pair at the metal and coordination to two tridentate η⁵-C₅H₅Co[P(OC₂H₅)₂O]₃ groups. The angles through the MO₆ units are CoMCo 149.04(14)° and 150.96(7)° for M = Sn and Pb, respectively. The tilting of the two tripod ligand moieties is reflected in the MO internuclear distances which range from 2.24(3) to 2.83 (3) Å for M-Sn and 2.40 (2) to 2.66(3) Å for M = Pb, differences of 0.59(3) and 0.26(3) Å, respectively. The average distances are 2.48(3) and 2.51(2) Å for 1 and 2 which are isostructural.     

The preparation,properties and crystal structure of bis(η5-cyclopentadienyldicarbonyliron)dimethylgermyl]oxide, [(η5-C5H5)(CO)2FeGe(CH3)2]2O

One of the main products of oxidation of (η⁵-C₅-H₅)₂Fe₂(CO)₃Ge(CH₃)₂ by air has been shown to be [(η⁵-C₅H₅)(CO)₂FeGe(CH₃)₂]₂O. The infrared, NMR and mass spectra are consistent with this formula and the detailed structure has been established by X-ray crystallography. In polar solvents the NMR suggests the existence of major and minor conformers interconverting only slowly on the NMR time scale at ≈ 25°. The X-ray diffraction study has shown the compound to consist of two (η⁵-C₅H₅)(CO)₂FeGe(CH₃)₂ moieties joined by a bridging oxygen atom. Two rotational isomers are present in the unit cell in a disordered fashion. Some pertinent average distances and angles are: FeGe, 2.372 Å; GeO, 1.785 Å; GeOGe′, 134°. The compound crystallizes in the monoclinic system, space group P2₁/n, with a 8.056(2), b 12.506(2), c 22.631(3) Å, β 98.01(1)°, d_calc 1.692 g cm^?3. Counter data were collected using Mo-K_α radiation. The 1780 reflections above background were used in least-squares refinement which converged at R₁ = 0.051 and R₂ = 0.068.