Ethylene polymerization using an asymmetric dinuclear titanocene catalyst carrying a novel 3-oxa-pentamethylene bridge

The asymmetric 3-oxa-pentamethylene bridged dinuclear titanocenium complex (CpTiCl₂)₂ (η⁵-C₉H₆(CH₂CH₂ OCH₂CH₂)-η⁵-C₅H₃ CH₃) (1) has been prepared, characterized by ¹H NMR spectroscopy and elemental analysis, and after activation with MAO tested as a homogenous catalyst for the polymerization of ethylene. The results show that the catalytic activity of 1 as well as the molecular weight of the produced polyethylene are higher than those using the alkylidene bridged asymmetric dinuclear metallocenes (CpTiCl₂)₂ (η⁵-C₉H₆(CH₂) _n-η⁵-C₅H₄), n = 3 (4), 4 (5). The molecular weight distribution of polyethylene produced with 1/MAO reaches 11.00 and the HT-GPC curve shows a bimodal distribution. The melting point of the polyethylene obtained by 1/MAO is higher than 135 °C and the ¹³C NMR spectrum of PE shows only one strong signal at 30 ppm for the methylene units indicating a highly linear and crystalline polymer.     

Semi-rigid N-para-ferrocenyl(benzoyl)amino-acid esters for biomaterials: synthesis and characterization of Fc-C6H4CONHCH(R)CO2Me where Fc = (η5-C5H5)Fe(η5-C5H4) and R=H,CH3,CH2CH(CH3)2,CH2C6H5 and the X-ray crystal structures of Fc-C6H4CO2Me and the l-alanine derivative Fc-C6H4CONHCH(CH3)CO2Me

A series of N-para-(ferrocenyl)benzoyl amino-acid esters, para-Fc(C₆H₄)CONHCH(R)CO₂CH₃ {Fc = (η⁵-C₅H₅)Fe(η⁵-C₅H₄); R = H, CH₃, CH₂CH(CH₃)₂, CH₂C₆H₅}, 3–6 have been prepared by coupling para-(ferrocenyl)benzoic acid to the amino-acid esters (gly, l-Ala, l-Leu, l-Phe) using the standard 1,3-dicyclohexylcarbodiimide (DCC), 1-hydroxybenzotriazole (HOBt) protocol. The compounds were fully characterized by a range of spectroscopic techniques including FAB-MS. The X-ray crystal structures of the parent para-(ferrocenyl)benzoyl methyl ester, Fc-C₆H₄CO₂Me, 1 and a chiral derivative N-{para-(ferrocenyl)benzoyl}-l-alanine methyl ester, Fc-C₆H₄CONHCH(CH₃)CO₂Me, 4 have been determined.     

Synthesis,characterization and compared reactivity of asymmetrical ansa-metallocenes

Rac and meso ansa-zirconocenes [Zr{1-Me₂Si(3-R-(η⁵-C₉H₅))(3-R′-(η⁵-C₉H₅))}Cl₂] (R = Et, R′ = H; R = Pr, R′ = H; and R = Et, R′ = Pr) 4–9 have been prepared by the reaction of ZrCl₄ with the corresponding dilithiated derivatives from the ligands {1-Me₂Si(3-R-(η⁵-C₉H₅))(3-R′-(η⁵-C₉H₅))} (R = Et, R′ = H 1; R = Pr, R′ = H 2; and R = Et, R′ = Pr 3) in diethyl ether/toluene at ?78 °C. The molecular structure of rac [Zr{1-Me₂Si(3-Et-(η⁵-C₉H₅))(3-Pr-(η⁵-C₉H₅))}Cl₂] 8 has been determined by single crystal X-ray diffraction studies, which show a pseudotetrahedral environment formed by the two chlorine ligands and two η⁵-coordinated indenyl ligands. The activity in homogeneous and heterogeneous polymerization is compared and discussed.     

Alkoxo- and carboxylato-bridged hexanuclear copper(II) complex: Synthesis,structure and magnetic properties

Reaction of copper(II) nitrate trihydrate with N,N-dimethylethanolamine (dmea) and pivalic acid in methanol led to the hexanuclear copper(II) complex Cu₆(η¹:μ₂-C₄H₁₀NO)₄(η¹:η¹:μ₂-C₅H₉O₂)₄(η¹:μ₁-C₅H₉O₂)₂(μ₃-OH)₂ (1). The crystal structure of 1 indicates that hexametallic centers are bridged by the μ₃-alkoxo, dmea oxygens, and the μ₂-dicarboxylato oxygen atoms of pivalate ions. Furthermore, in the asymmetric unit, three types of copper ions have been found labeled as Cu₁, Cu₂ and Cu₃. The Cu₂ takes a distorted octahedral shape, whereas Cu₁ and Cu₃ adopt square pyramidal geometries. The complex 1 shows strong antiferromagnetic interactions through the oxo groups within the dimeric units (J = − 82.6 to − 25.8 cm^− 1) and weak antiferromagnetic couplings between the dimers (J = − 10.9 and 0.8 cm^− 1).     

Structural differences of half-sandwich complexes of scandium and yttrium containing bulky substituents

Scandium and yttrium half-sandwich chloride complexes (η⁵-C₅Me₄R)ScCl₂(THF)₂ R = CH₂Ph (3) or SiMe₂CH₂CH₂Ph (5) and (η⁵-C₅Me₄R)YCl₂(THF)₂ R = CH₂Ph (4) or SiMe₂CH₂CH₂Ph (6) were prepared by metathetic reactions of the corresponding substituted lithium or potassium cyclopentadienides with scandium or yttrium trichloride. A mutual comparison of the determined solid state structures of 4 and 5 revealed the tetranuclear character in the case of scandium complex containing C₅Me₄SiMe₂CH₂CH₂Ph ligand, while a formation of the trinuclear ate-complex 4 incorporating lithium was observed for the combination of yttrium and the benzyl substituted tetramethyl cyclopentadienyl. Moreover, the steric effect of addition of another differently substituted cyclopentadienyl ring into the molecule was evaluated.     

Organometallic boxes built from 5,10,15,20-tetra(4-pyridyl)porphyrin panels and hydroxyquinonato-bridged diruthenium clips

Self-assembly of 5,10,15,20-tetra(4-pyridyl)porphyrin (tpp-H₂) tetradentate panels with dinuclear arene ruthenium clips [Ru₂(η⁶-arene)₂(dhbq)Cl₂] (arene = C₆H₅Me, p-PrⁱC₆H₄Me, C₆Me₆; dhbq = 2,5-dihydroxy-1,4-benzoquinonato) affords the cationic organometallic boxes [Ru₈(η⁶-C₆H₅Me)₈(tpp-H₂)₂(dhbq)₄]⁸⁺ ([1]⁸⁺), [Ru₈(η⁶-p-PrⁱC₆H₄Me)₈(tpp-H₂)₂(dhbq)₄]⁸⁺ ([2]⁸⁺) and [Ru₈(η⁶-C₆Me₆)₈(tpp-H₂)₂(dhbq)₄]⁸⁺ ([3]⁸⁺). These octanuclear cations have been isolated as their triflate salts and characterised by mass spectrometry, NMR and IR spectroscopy. The molecular structure of these systems was deduced by one-dimensional and two-dimensional NMR experiments (ROESY, COSY, HSQC).     

Polynuclear copper(II) carboxylates with 2,2′-bipyridine or 1,10-phenanthroline: Synthesis,characterization, X-ray structures and magnetism

[Cu₂(phen)₂(μ-O₂CH)₂(O₂CH)₂]_n (1) and [Cu₆(bpy)₆(μ-O₂CC₂H₅)₇(H₂O)₂)](PF₆)₅ · 2H₂O (2) were synthesized and characterized by elemental analyses, electronic and EPR spectra and X-ray structure analyses. Compound 1 consists of four independent polymeric chains of dinuclear [Cu₂(phen)₂(μ-O₂CH)₂(O₂CH)₂] subunits with the asymmetric bidentate bridging formato groups linking Cu atoms in an anti–anti configuration. All Cu(II) ions are in a distorted square-pyramidal geometry. The hexanuclear copper(II) molecule of compound 2 is constructed from three different dinuclear units connected to each other via two syn–anti-μ₃-η¹;η² carboxylato bridges. All copper(II) ions are in the distorted square-pyramidal geometry. Two terminal dinuclear units are similar in structure in which both Cu(II) ions are doubly bridged by the syn–syn carboxylato anions, while those of the central dinuclear entity are triply bridged by two μ₃-η¹;η² carboxylato anions via monoatomic bridging fashion and one syn–syn carboxylato anion. The magnetic susceptibility (5–350 K) of compound 2 was measured and agree with a weak antiferromagnetic interaction between the Cu(II) centers.     

Synthesis and crystal structure of the singly tucked-in derivative of bis(phenyltetramethylcyclopentadienyl)titanium

Thermolysis of [TiMe₂(η⁵-C₅Me₄Ph)₂] (4) at 145 °C for 5 h afforded the singly tucked-in paramagnetic titanocene [Ti(III)(η⁵-C₅Me₄Ph){η⁵:η¹-C₅Me₃Ph(CH₂)}] (9). In distinction to the singly tucked-in permethyltitanocene [Ti(III)(η⁵-C₅Me₅){η⁵:η¹-C₅Me₄(CH₂)}] (1) which was found crystallographically disordered [J.M. Fischer, W.E. Piers, V.G. Young, Jr., Organometallics 15 (1996) 2410] the single crystal X-ray diffraction analysis of 9 afforded molecular parameters with nearly by one order better precision as measured by esd-values.     

Ethylene polymerization by 3‐oxa‐pentamethylene bridged asymmetric dinuclear titanocene/MAO system

An asymmetric 3‐oxa‐pentamethylene bridged dinuclear titanocenium complex (CpTiCl₂)₂(η⁵‐η⁵‐C₉H₆(CH₂CH₂OCH₂CH₂)C₅H₄) ( 1 ) has been prepared by treating two equivalents of CpTiCl₃ with the corresponding dilithium salts of the ligand C₉H₇(CH₂CH₂OCH₂ CH₂)C₅H₅. The complex 1 was characterized by ¹H‐, ¹³C‐NMR, and elemental analysis. Homogenous ethylene polymerization catalyzed using complex 1 has been conducted in the presence of methylaluminoxane (MAO). The influences ofreaction parameters, such as [MAO]/[Cat] molar ratio, catalyst concentration, ethylene pressure, temperature, and time have been studied in detail. The results show that the catalytic activity and the molecular weight (MW) of polyethylene produced by 1 /MAO decrease gradually with increasing the catalyst concentration or polymerization temperature. The most important feature of this catalytic system is the molecular weight distribution (MWD) of polyethylene reaching 12.4, which is higher than using common mononuclear metallocenes, as well as asymmetric dinuclear titanocene complexes like [(CpTiCl₂)₂(η⁵‐η⁵‐C₉H₆(CH₂)_nC₅H₄)] (n = 3, MWD = 7.31; n = 4, MWD = 6.91). The melting point of polyethylene is higher than 135°C, indicating highly linear and highly crystalline polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Models of intermediates in metallocene-catalyzed alkene polymerizations: observation of a d0 cationic titanium–alkyl-alkene complex and decomposition by β-allyl elimination

Low temperature activation of Cp^*₂Ti[η¹,η¹- CH₂CH(CH₂CHCH₂)CH₂] (3) with [HN(CH₃)(C₆H₅)₂] [B(C₆F₅)₄] led to the formation of Cp^*₂Ti[η¹,η²-CH₂CH(CH₃)CH₂CHCH₂][B(C₆F₅)₄] (6) as determined by ¹H NMR spectroscopy. Cp^*₂Ti[η¹,η²-CH₂CH(CH₃)CH₂CHCH₂][B(C₆F₅)₄] undergoes rapid quantitative β-allyl elimination at temperatures as low as −140 °C. The resulting cationic titanium allyl complex [Cp^*₂Ti(η³-CH₂CHCH₂)][B(C₆F₅)₄] (4) exhibits a static structure at low temperatures, but interconversion of η³–η¹ binding modes can be observed at higher temperatures. Lineshape analysis of this process yielded ΔG³(−10 °C)= 13.7 ± 0.6 kcal mol⁻¹, ΔH³=9.8 ± 0.6 kcal mol⁻¹, and ΔS³=−15 ± 3 eu. The use of neutral borane B(C₆F₅)₃ also resulted in β-allyl elimination with the formation of [Cp^*₂Ti(η³-CH₂CHCH₂)][CH₂=CHCH₂B(C₆F₅)₃] (8).     

Activity of Mo(II) allylic complexes supported in MCM-41 as oxidation catalysts precursors

[Mo(η³-C₃H₅)X(CO)₂(NCCH₃)₂] (X = Br, 1a; X = Cl, 1b) complexes reacted with the bidentate ligand RNC(Ph)–C(Ph)NR, R = (CH₂)₂CH₃ (DAB, 2) affording [Mo(η³-C₃H₅)X(CO)₂(DAB)] (X = Br, 4a; X = Cl, 4b), which were characterized by elemental analysis, FTIR and ¹H and ¹³C NMR spectroscopy. The modified silylated ligand RNC(Ph)C(Ph)NR, R = (CH₂)₃Si(OCH₂CH₃)₃ (DAB–Si, 3), was used to immobilize the two complexes in MCM-41 (MCM) mesoporous silica. The new materials were characterized by powder X-ray diffraction, N₂ adsorption analysis, FTIR and ²⁹Si and ¹³C CPMAS solid state NMR spectroscopy. Both the materials and the complexes were tested in the oxidation of cyclooctene and styrene and behaved as active catalyst precursors for cyclooctene and styrene epoxidation with TBHP (t-butylhydroperoxide), leading selectively to epoxides with high conversions and TOFs. Although the homogeneous systems reach 100% conversion of cyclooctene and slightly less for styrene, the loss of catalytic activity in the heterogeneous systems is small, with a 98% conversion of styrene achieved by the chloride containing material.     

A new organic-inorganic hybrid tetrameric polyoxometalate assembled by monovacant Dawson [α2-P2W17O61]10 − and trivalent cerium cations

A novel octa-nuclear cerium(III)-containing organic-inorganic hybrid polyoxometalate [N(CH₃)₄]₈H₁₆[{Ce(η¹-C₆H₅NO₂)₂(H₂O)₆[Ce(H₂O)₃(α₂-P₂W₁₇O₆₁)]}{Ce(η²-C₆H₅NO₂)₂(H₂O)₅[Ce(H₂O)(α₂-P₂W₁₇O₆₁)]}]₂·90H₂O (C₆H₅NO₂ = isonicotinic acid) (1) was obtained, which had been hydrothermally synthesized and characterized by IR spectrum, thermogravimetric analysis (TGA), and X-ray single-crystal diffraction. Structural analysis indicated at 1 is composed of four lacunary Dawson-type units [α₂-P₂W₁₇O₆₁]^10 − joined together by eight cerium cations forming an uncommon zigzag tetrameric structure with eight isonicotinic acids as the organic pendants coordinating to the cerium cations. Magnetic property studies indicate that obvious antiferromagnetic interactions exist in eight Ce^3 + cations.     

Synthesis of diiron sulfur clusters containing thiolato-1,8-naphthalene imide ligand

Three diiron sulfur clusters containing thiolato-1,8-naphthalene imide ligand, [Cp*Fe(μ-4,5-S₂-ⁿBu-NMI)(μ-CO)FeCp*] (3a), [Cp′Fe(μ-4,5-S₂-ⁿBu-NMI)(μ-CO)FeCp′] (3b), [CpFe(ⁿBu-NMI-S)]₂ (4) (3a: Cp* = η⁵-C₅Me₅; 3b: Cp′ = η⁵-C₅HMe₄; 4: Cp = η⁵-C₅H₅; ⁿBu-NMI = N-butyl-1,8-naphthalene imide) were synthesized via the reaction of N-butyl-4,5-disulfide-1,8-naphthalene imide and [Cp2Fe(μ-CO)CO]₂ (Cp2 = Cp*, Cp′, Cp). A partially desulfurated product [CpFe(ⁿBu-NMI-S)]₂ was determined in the reaction of [CpFe(μ-CO)CO]₂ with ⁿBu-NMI 4,5-dithiolate. The new complexes were structurally characterized by X-ray analysis.     

Two distinct ferroceneyl carboxylate Pb(II) complexes with the same composition prepared by two different synthetic methods: The substitution of precursor and one-pot reaction

Through substituation reaction, one lead ferroceneyl carboxylate polymer, namely [Pb(μ₂-OOCClH₃C₆Fc)₂(phen)]_n 1a [Fc = (η⁵-C₅H₅)Fe(η⁵-C₅H₄)] was synthesized from precursor [Pb(μ₂-η²-OOCClH₃C₆Fc)₂(CH₃OH)₂]_n 1. However, a mononuclear Pb(II) complex {[Pb(η²-OOCClH₃C₆Fc)₂(phen)]·(CH₃OH)·(H₂O)} 2 could be obtained from the traditional one-pot reaction of FcC₆H₃ClCOONa and Pb(OAc)₂ with 1,10-phenantholine (phen). The electrochemical studies of 1, 1a, 2 and FcC₆H₃ClCOOH indicate that the half-wave potentials of the ferrocenyl moieties in these complexes are all shifted to positive potential compared with that of FcC₆H₃ClCOOH.     

Crystal structure and magnetic dynamics of a novel salen type and β-diketonate Dy2 complex

A novel salen type dinuclear dysprosium complex e.g., [Dy₂(H₂L)(acac)₆]·4CH₃OH (1) [H₂L = N,N′-(1.3-propylene)bis(3-methoxysalicylideneimine) has been isolated by reactions of Dy(acac)₃·H₂O (acac = acetylacetonate) with salen type (H₂L), respectively. X-ray crystallographic analyses reveal that asymmetric Dy(III) ions for 1 was bridged by one ligand displaying bicapped trigonal prism coordination geometry. Magnetic measurement shows that complex 1 exhibit slow relaxations under zero dc field. The presence of two magnetic relaxations in complex 1 is associated with the presence of minute differences in bond lengths around Dy(III) center.     

Ethylene polymerization by alkylidene‐bridged asymmetric dinuclear titanocene/MAO systems

Two asymmetric alkylidene‐bridged dinuclear titanocenium complexes (CpTiCl₂)₂(η⁵‐η⁵‐C₉H₆(CH₂)_nC₅H₄), 1 (n = 3) and 2 (n = 4) have been prepared by treating two equivalents of CpTiCl₃ with the corresponding dilithium salts of the ligands C₉H₇(CH₂)_nC₅H₅ (n = 3, 4). Additionally, Ti(η⁵:η⁵‐n‐BuC₅H₄C₅H₅)Cl₂ (3) and Ti(η⁵:η⁵‐n‐BuC₉H₆C₅H₅)Cl₂ (4) were synthesized as corresponding mononuclear complexes. All complexes were characterized by ¹H, ¹³C NMR, and IR spectroscopy. Homogenous ethylene polymerization catalyzation using those complexes has been conducted in the presence of methylaluminoxane (MAO). The influences of reaction parameters, such as [MAO]/[Cat] molar ratio, catalyst concentration, ethylene pressure, temperature, and time have been studied in detail. The results showed that the catalytic activities of both dinuclear titanocenes were higher than those of the corresponding mononuclear titanocenes. Although the two dinuclear complexes were different in only one [CH₂] unit, the catalytic activity of 2 was about 50% higher than that of 1; however, the molecular weight of polyethylene (PE) obtained by 2 was lower than that obtained from 1. The molecular weight distribution of PE produced by these dinuclear complexes reached 6.9 and 7.3, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3317–3323, 2006     

Syntheses,structures, and magnetic properties of ethoxy-bridged dinuclear iron(III) complexes containing tetradentate ligands

Dinuclear iron(III) complexes, [(phenO)Fe(SO₄)]₂·2CH₃OH (1) and [(bpmapO)Fe(NO₃)]₂(NO₃)₂·3CH₃OH (2) have been prepared by the reaction of phenOH/bpmapOH and FeSO₄·7H₂O/Fe(NO₃)₃·9H₂O in methanol, respectively (phenOH = N-(2-pyridylmethyl)-N′-(2-hydroxyethyl)ethylenediamine, bpmapOH = N-(bis(2-pyridylmethyl)amino)-2-methylpropan-2-ol). Both complexes are ethoxy-bridged dinuclear species and the iron(III) ions in 1 and 2 have distorted octahedral geometries. Both complexes show strong antiferromagnetic interactions through the bridged ethoxy groups within the dimeric units.     

Structural characterization of ferromagnetic bridged-acetato and -dichlorido copper(II) complexes based on bicompartmental 4-t-butylphenol

The reaction of Cu(II) salts with 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-t-butylphenol (L^t-Bu-OH) afforded two bridged-phenoxido/hydroxido complexes. The dinuclear bridged acetate species [Cu₂(μ-L^t-Bu-O)(μ-CH₃COO)](PF₆)₂ (1) and the 1D polymeric doubly-bridged-chlorido {[Cu₂(μ-L^t-Bu-OH)(μ-Cl)₂](ClO₄)₂·4H₂O}_n (2). The two complexes were structurally characterized. Both complexes revealed ferromagnetic interactions; moderate in complex 1 (J = + 30.8 cm^− 1) and very weak (J = + 2.25 cm⁻¹) in 2.     

A novel route to titanium compounds containing cyclopentadienyl ligands with bromoethyl substituents; molecular structure of [(η5-C5H4CH2CH2Br)TiBr(μ-O)]4

Compounds (η⁵-C₅H₄CH₂CH₂OCH₃)TiCl₃, (η⁵-C₅H₄CH₂CH₂OCH₃)₂TiCl₂ and (η⁵-C₅H₄CH₂CH₂OCH₃)(η⁵-C₅H₅)TiCl₂ react with BBr₃ to give a high yield of titanium compounds containing cyclopentadienyl ligands with bromoethyl substituents, (η⁵-C₅H₄CH₂CH₂Br)TiBr₃ (1), (η⁵-C₅H₄CH₂CH₂Br)₂TiBr₂ (3) and (η⁵-C₅H₄CH₂CH₂Br)(η⁵-C₅H₅)TiBr₂ (4), respectively. Hydrolysis of 1 in the presence of tert-butylamine affords cyclo-[(η⁵-C₅H₄CH₂CH₂Br)TiBr(μ-O)]₄ (2) in quantitative yield. The molecular structure of 2 was determined by X-ray diffraction.     

Synthesis,crystal structures and properties of two Pd(II) and Pt(II) complexes involving 3,5-diphenylpyrazole and NO2 donor ligands

A pyrazolate bridged binuclear Pd(II) complex [Pd₂(μ-dppz)₂(Hida)₂] · CH₃OH · 2H₂O (1) (dppz = 3,5-diphenylpyrazolate) with monoprotonated iminodiacetate (Hida) and a mononuclear Pt(II) complex containing Hdppz and 2,6-pyridinedicarboxylate (2,6-dipic) [Pt(Hdppz)(2,6-dipic)] · CH₃OH (2) have been synthesized and characterized by elemental analysis, ¹H NMR, ESI-MS and single crystal X-ray diffraction studies. The molecular packing for 1 shows a 2D network while that for 2 constitutes a left-handed 1D helix. Moderate luminescence property and antimicrobial activity against Bacillus subtilis have been noted for both.