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.     

Study of the cytotoxic activity of alkenyl-substituted ansa-titanocene complexes

The cytotoxic activity on tumour cell lines, human adenocarcinoma HeLa, human myelogenous leukemia K562, human malignant melanoma Fem-x and normal immunocompetent cells, was tested for four different ansa-titanocene dichloride derivatives with potentially reactive substituents [Ti{Me(CH₂CH)Si(η⁵-₅Me₄) (η⁵-C₅H₄)}Cl₂] (1), [Ti{Me(H)Si(η⁵-C₅Me₄)₂}Cl₂] (2), [Ti{Me{(CH₂CH)Me₂SiCH₂CH₂}Si(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] (3) and [Ti{Me₂Si(η⁵-C₅Me₄)(η⁵-C₅H₃(CMe₂(CH₂CH₂CHCH₂)))}Cl₂] (4), showing a very promising activity and opening up the possibility of extensive investigation in this field.     

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.     

The synthesis of (η5-cyclopentadienyl)titanium(IV) alkoxides by alcoholysis of the Ti–π-ligand bond in permethyl η3:η4-allyldiene-(η5-cyclopentadienyl)titanium(II)

The η³:η⁴-allyldiene-(η⁵-cyclopentadienyl)titanium(II) complex [Ti(η⁵-C₅Me₅){η³:η⁴-C₅Me₃(CH₂)₂}] (1) reacts with three molar equivalents of substituted propargylic alcohols FcCCCMe₂(OH) (2a) and PhCCCH₂OH (2b) at elevated temperature to give (η⁵-pentamethylcyclopentadienyl)titanium(IV) alkoxides [Ti(η⁵-C₅Me₅)(FcCCCMe₂O-κO)₃] (3a) and [Ti(η⁵-C₅Me₅)(PhCCCH₂O-κO)₃] (3b), respectively. The crystal structure of 3a has been determined by single-crystal X-ray diffraction.     

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.     

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).     

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.     

Catalytic N−N bond cleavage of hydrazine by thiolate-bridged iron-ruthenium heteronuclear complexes

The novel thiolate-bridged iron-ruthenium heteronuclear complex [(PPh₃)(bdt)Ru(μ-η²:η⁴-bdt)FeCp*] (1, Cp* = η⁵-C₅Me₅, bdt = benzene-1,2-dithiolate) was prepared by one-electron reduction of complex [(PPh₃)(bdt)Ru(μ-η²:η⁴-bdt)FeCp*][FeCl₃] (1[FeCl₃]) using CoCp₂ as reducing agent. Meanwhile, complex 1 can also be one-electron oxidized by Fc·PF₆ or HBF₄ to regenerate the ionic complex 1[PF₆] or 1[BF₄]. Importantly, complex 1 shows good reactivity toward the catalytic N−N bond cleavage of hydrazine into ammonia.     

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.     

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).     

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.     

Formation of a binuclear titanocene hydride–magnesium hydride carbyl-bridged complex in the (C5Me4Ph)2TiCl2/Mg/THF system

The reduction of (C₅Me₄Ph)₂TiCl₂ by magnesium in tetrahydrofuran affords a mixture of the diamagnetic doubly tucked-in titanocene complex (C₅Me₄Ph)[C₅Me₂(CH₂)₂Ph]Ti (1), the paramagnetic trinuclear Ti–Mg–Ti hydride bridged complex [(C₅Me₄Ph)₂Ti(μ-H)₂]₂Mg (2) and the paramagnetic binuclear titanocene hydride–magnesium hydride complex (C₅Me₄Ph)[C₅Me₄(o-C₆H₄)]Ti(μ-H)₂Mg(THF)₂ (3). The X-ray diffraction analysis of 3 revealed that the magnesium atom forms the σ-bond to the ortho-carbon atom of one of the phenyl rings and binds 2 molecules of THF.     

Thermal dehydration of Y(TFA)3(H2O)3: Synthesis and molecular structures of [Y(μ,η1:η1-TFA)3(THF)(H2O)]1∞ · THF and [Y4(μ3-OH)4(μ,η1:η1-TFA)6(η1-TFA)(η2-TFA)(THF)3(DMSO)(H2O)] · 6THF (TFA = trifluoroacetate)

In order to obtain a better anhydrous precursor for various applications in materials science and catalysis, thermal dehydration reactions of Y(TFA)₃(H₂O)₃ (TFA = trifluoroacetate) (A) were investigated. Thermal treatment of A at different temperatures under vacuum (5 × 10^?2 mm) for several hours failed to give totally anhydrous yttrium trifluoroacetate (as indicated by IR). Two different complexes, a partially dehydrated [Y(μ,η¹:η¹-TFA)₃(THF)(H₂O)]_1∞·THF (1) and a partially hydrolyzed [Y₄(μ₃-OH)₄(μ,η¹:η¹-TFA)₆(η¹-TFA)(η²-TFA)(THF)₃(DMSO)(H₂O)] · 6THF (2), were obtained with good and moderate yield, respectively, by crystallization of two different thermally treated batches of A from THF (or THF + DMSO) at room temperature. More efficient dehydration of A could be achieved at 200 °C in a furnace, the obtained anhydrous yttrium tris-trifluoroacetate giving Y(TFA)₃(THF)₂ (3) on crystallization from THF. All the products were characterized by elemental analyses, FT-IR and ¹H NMR spectroscopy as well as thermo-gravimetric analysis. In addition, single crystal X-ray structures are reported for 1 and 2, which show either a terminal (η¹ and η²) or bridging (μ,η¹:η¹) bonding behavior of the TFA ligand.     

Controlled synthesis of lanthanide–lithium inverse crown ether complexes

An ytterbium–lithium inverse crown ether complex stabilized by amine-bridged bis(phenolate) ligands (LYbBr)₂(μ₄-O)(μ₃-Li) (1) [L = Me₂NCH₂CH₂N{CH₂-(2-O- C₆H₂-Bu^t₂-3,5)}₂] was isolated as a byproduct from the reaction of LYbCl(THF) with CH₃Li in THF in a very low isolated yield. Further study revealed that the inverse crown ether complexes can be synthesized in a controlled manner by the reaction of bis(phenolate) lanthanide chloride with an in situ mixture of n-BuLi with water in THF. A second inverse crown ether complex (L′YbCl)₂(μ₄-O)(μ₃-Li) (2) [L′ = Me₂NCH₂CH₂N{CH₂-(2-O-C₆H₂-Bu^t-3-Me-5)}₂] was prepared in high isolated yield and well characterized.     

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).     

Molecular structure of [In2(μ,η1-OR)(μ,η2-OR)(η2-OR)3(η1-OR)] R = C2H4NMe2, a pincer ligand

Functional indium [In(OR)₃]_m alkoxides (R = C₂H₄OMe, C₂H₄NMe₂) have been obtained by alcoholysis of In[N(SiMe₃)₂]₃ and characterised by elemental analysis, FT-IR and NMR spectroscopy. The 2-dimethylaminoethoxide was characterised by X-ray diffraction. It corresponds to the association of two InO₆ octahedra giving the unsymmetrical dimer [In₂(μ,η¹-OR)(μ,η²-OR)(η²-OR)₃(η¹-OR)] (2). 2 was used as a pincer ligand toward Cu(acac)₂.     

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.     

Reactivity of cyrhetrenylphosphines: Synthesis and characterization of oxides,boranes and selenides

Reaction of cyrhetrenylphosphines, of general formula (η⁵-C₅H₄PR₂)Re(CO)₂L (R = Ph, L = CO (1); R = Cy; L = CO (2); R = Ph, L = PMe₃ (3) and R = Ph, L = P(OMe)₃ (4)), with H₂O₂, BH₃·THF or selenium gives the respective cyrhetrenylphosphine oxides, boranes and selenides. These species were characterized by standard spectroscopic techniques (FT-IR, ¹H and ³¹PNMR). Based on the ³¹P⁷⁷Se coupling constant (¹J_P-Se) of the phosphine-selenides, we established the following order of basicity of the parent cyrhetrenylphosphine 2 > 3 > 4 > 1. We also confirmed the opposite electronic effects of the cyrhetrenyl and ferrocenyl groups attached to a –PR₂ unit. Finally, phosphine selenides 2c and 4c were structurally characterized by X-ray diffraction.     

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,structure and reactions of triply selenolate-bridged diiron complex [Cp*Fe(μ-SeMe)3FeCp*]

Two new iron–selenolate complexes [Cp*Fe(μ-SeMe)₃FeCp*] (Cp* = η⁵-C₅Me₅) (1) and [Cp*Fe(μ-SeMe)₃FeCp*][FeCl₃] (2) were prepared by the oxidative addition reaction of MeSeSeMe with [Cp*FeCl]₂ in 25% and 20% yields, respectively. In refluxing toluene, the methyl groups in the selenolate ligands of complex 1 were removed, affording a cubane cluster [Cp*₄Fe₄Se₄] (3) in 50% yield. Complex 1 was oxidized by HBF₄ to give [Cp*Fe(μ-SeMe)₃FeCp*][BF₄] (4), and the reverse reduction reaction occurred in the presence of CoCp₂.