Mononuclear and Terminal Zirconium and Hafnium Methylidenes

The dimethyl aryloxide complexes [(PNP)M(CH₃)₂(OAr)] (M=Zr or Hf; PNP^?=N[2‐P(CHMe₂)₂‐4‐methylphenyl]₂); Ar=2,6‐iPr₂C₆H₃), which were readily prepared from [(PNP)M(CH₃)₃] by alcoholysis with HOAr, undergo photolytically induced α‐hydrogen abstraction to cleanly produce complexes [(PNP)M=CH₂(OAr)] with terminal methylidene ligands. These unique systems have been fully characterized, including the determination of a solid‐state structure in the case of M=Zr.     

Mixed Chloro(dialkylamido) Complexes of Zirconium and Hafnium

Chloro(dialkylamido) complexes of the type (R₂N)₂MCl₂(THF)₂ (R = Me, Et; M = Zr and R = Me; M = Hf) were synthesized in a conproportionation reaction by adding an equimolar amount of the corresponding M(NR₂)₄ to an ether slurry of MCl₄ in the presence of THF. X-ray crystal structure determinations of (Et₂N)₂ZrCl₂(THF)₂ ( 1 a ) and (Me₂N)₂ZrCl₂ · (THF)₂ ( 1 b ) reveal a distorted octahedral coordination geometry where the sterically demanding dialkylamide ligands force the chloride and the THF ligands out of their ideal position. Dynamic NMR investigations indicate an equilibrium of complexes with coordinated THF at low temperature in accordance with the structure determined by X-ray crystallography and of chloro-amido complexes that do not bind THF (at higher temperature).     

Periodic Trends in the Agostic Interaction in Zirconium and Hafnium Methylidene Hydride Halide Complexes

The reactions of methyl chloride and bromide with laser‐ablated Zr and Hf atoms during deposition in excess Ne, Ar, or Kr are investigated, and the products are examined by matrix IR spectroscopy and density functional theory calculations. The methylidene complexes, [CH₂?MHX] (M=Zr and Hf, X=Cl and Br), are formed along with the methyl metal halide complexes, [CH₃? MX]. The amounts of both types of complexes increase upon photolysis and in the early stages of annealing. Two sets of methylidene absorptions observed in Ar and Kr matrices form a persistent photoreversible system. The most stable C₁ and slightly higher energy planar structures of the methylidene complex in the singlet ground state trapped in the matrix reproduce the characteristics of the two sets of absorptions. Agostic distortion of the methylidene complexes decreases in the order Ti, Zr, Hf and increases in the order F, Cl, and Br; the C?Zr and Zr? H stretching frequencies increase, and the bonds become shorter. This observation favors the characterization of the agostic interaction as a reorganization of charge.     

Thermodynamic Characteristics of Zirconium and Hafnium Hydroxides in Aqueous Solution

The enthalpies of dissolution of ZrCl₄, ZrBr₄, HfCl₄ and HfBr₄ in water in weakly acidic and alkaline solutions were measured at 25°C in a calorimeter provided with an isothermal cover. The standard enthalpies of formation of Zr(OH)₄ and Hf(OH)₄ in solution were measured. The thermodynamic characteristics of the reactions which resulted in the formation of tetrahydroxy complexes of Zr and Hf in aqueous solution were also determined. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Metallocene Carbene Complexes and Related Compounds of Titanium,Zirconium, and Hafnium

The structure and creativity spectrum of transition-metal carbene complexes has been widened significantly by the bent metallocenes of titanium, zirconium, and hafnium. Proceeding from metal carbonyls and reactive (butadiene)-, (aryne)-, or (olefin) MCp₂ complexes, many new Fischer-type metaloxycarbene complexes of Zr, Hf, V, Nb, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Ni, and Rh have been synthesized. The incorporation of titanocene, zirconocene, or hafnocene fragments allows new types of carbene complexes to be prepared. For the (alkylidenamido)metallocene complexes , metallocene ylides , and binuclear (μ-alkynyl)metallocene compounds, some metalligand π bonding is indicated. Metallocene complexes with metallaoxirane units, , show similar chemical behavior to that of binuclear (μ-methylene)complexes . The methylene groups of zirconaoxirane complexes, which are derived from carbon monoxide, may be expelled as ethylene by thermally induced CC coupling. With metal hydrides, CH₂ transfer with insertion into the metal–hydride bond occurs. In one case, methylene insertion into a metal–carbon bond can even be observed. These reactions of Ti-group metallaoxiranes could be models for postulated intermediates in the Fischer–Tropsch synthesis.     

Potentiometric Investigation of Fluoride Complexes of Zirconium(IV) and Hafnium(IV) in 1 <Emphasis Type="Italic">M</Emphasis> (H,Na)ClO<Subscript>4</Subscript> Medium Using a Fluoride Ion Selective Electrode

The stability constants of zirconium(IV) and hafnium(IV) fluoride complexes in 1 M (H,Na)ClO₄ medium were measured potentiometrically at 293 K for the first time using a fluoride ion selective electrode (F-ISE). This technique has been recommended by IUPAC as the best tool for studying fluoride complexes. A number of precautions were taken to ensure the stabilization of zirconium or hafnium in 1 M (H,Na)ClO₄ medium and to prevent the formation of polynuclear hydroxo complexes. The formation of only mononuclear complexes was indicated. The average log values of the overall stability constants of zirconium(IV)-fluoride complexes, ₁, ₂, ₃ and ₄ were computed by varying the concentration of metal ion and were found to be 8.49 ± 0.11, 15.76 ± 0.15, 21.57 ± 0.10, and 26.68 ± 0.16, respectively, whereas the corresponding values for hafnium(IV)-fluoride complexes were 8.22 ± 0.06, 15.48 ± 0.15, 21.76 ± 0.14, and 27.42 ± 0.15, respectively. The thermodynamic stability constant, ₁, calculated for these complexes follows the same trend as expected from the linear correlation based on the Brown Sylva Ellies (BSE) model for metal-fluoride complexes provided the effective charge on Zr is taken as +4.1 instead of the formal charge of +4. Without considering this adjustment of formal charge, an attempt has also been made to explain the trend in ₁ values of group(IV) metal-fluoride complexes based on electronegativity values. A good linear correlation was obtained that could explain the ability of these group(IV) ions to form different fluoride complexes with varying number of fluoride ions.     

Einkristalle von (NH4)ZrF5 und (NH4)HfF5 durch Oxidation von Zirconium und Hafnium mit (NH4)HF2

Synthesis and Crystal Structure of (NH₄)ZrF₅ and (NH₄)HfF₅ by Oxidation of Zirconium and Hafnium with (NH₄)HF₂ Colourless single crystals of NH₄ZrF₅ ( 1 ) and NH₄HfF₅ ( 2 ) are obtained by reaction of the respective metal powders with NH₄HF₂ (4 weeks) in sealed Monel metal containers at 450 °C. They crystallize with the monoclinic space group P2₁/c with ( 1 / 2 ) a = 778.16(14)/786.35(12), b = 790.75(9)/786.64(8), c = 792.44(12)/786.01(12), β = 119.177(12)/119.828(10) isotypic to TlZrF₅.     

锆和铪的色谱分离

介绍了用二甲基硅酮作固定相的毛细管气相色谱法分离三氟乙酰丙酮合锆和三氟乙酰丙酮合铪的混合物及乙酰丙酮合锆和乙酰丙酮合铪的混合物。用Ｃ＿（１８）键合固定相的反相高效液相色谱法分离上述β－二酮合锆和铪的混合物;讨论了色谱分离中的问题。     

Fluorescent Heteroleptic Zirconium and Hafnium Complexes

Five new heteroleptic zirconium and hafnium complexes were synthesized. The complexes carry chloro ligands as well as differently substituted phenoxy benzoxazole ligands [ HL1 = 2‐(2′‐hydroxyphenyl)benzoxazole, HL2 = 2‐(2′‐hydroxynaphthyl)benzoxa‐zole, HL3 = 2‐(2′‐hydroxy‐3′,5′‐di‐tert‐butylphenyl)benzoxazole]. They were characterized by ¹H and ¹³C{¹H} NMR spectroscopy as well as by elemental analyses and X‐ray diffraction experiments. The molecular structures in the crystals show distorted octahedral or capped trigonal prismatic coordination spheres. The intermolecular interactions influencing the packing patterns are mainly H ··· Cl contacts. For the hafnium complex [Cl₂Hf( L3 )₂] a dynamic behavior in solution was examined using temperature dependent ¹H NMR spectroscopy. The photo‐physical data show that in all cases fluorescence arises from a short‐lived excited state, the emission maxima being located in the blue spectral region.     

P507萃取分离-二甲酚橙光度法测定锆铪

本文用自合成的P507萃淋树脂对锆铪吸附特性进行研究,并对此树脂的离子交换柱性能进行了研究与测定;在此基础上,对不同配比锆铪混合液进行分离,作出了分离曲线,并采用二甲酚橙分光光度法对锆铪进行了测定.研究了干扰离子存在的允许量及树脂的使用寿命.     

Molecular Recognition of Bases and Nucleosides by Mono－substituted Mononuclear Complexes of 1,4,7,10－Tetraaza－cyclododecane

The mononuclear macrocyclic polyamine metal complexes 5a-5e have been shown to form stable 1 : 1 complexes with bases and nucleosides. Their binding constants (K) were determined by UV-visible spectrometric titration. The results show that recognition ability of the complexes 5a--5e for uracil, U (Uridine), dT (Thymidine) is higher than that for the other bases or nucleosides (such as Cytidine, Guanosine, Adenosine). The metal ion also plays an important role for the recognition ability of complexes.     

FTIR Spectroscopy,SAXS and Electrical Conductivity Studies of the Hydrolysis and Condensation of Zirconium and Titanium Alkoxides

A continuous flowing-rapid mixing technique was combined with FTIR, SAXS and electrical conductivity to study the early stages of polymer formation and growth during the acid-catalyzed hydrolysis and condensation of titanium and zirconium alkoxides. Reaction times as short as 80 milliseconds were investigated. FTIR spectroscopy was used to monitor the water and M−OR concentrations during the reaction. Hydrolysis of ∼25–50% of the alkoxy groups was facile. The FTIR and SAXS data showed that condensation was also very rapid. The activity and mobility of the ions in the solution were monitored by electrical conductivity measurements. The decrease in the normalized solution conductivity during the reaction correlated with the loss of [M−OR]. Furthermore, the radius of gyration of the growing polymers increased rapidly in regimes where the conductivity and [M−OR] decreased fastest. This finding suggests that the mobility of some of the charge carrying species decreases because of the growth in size of the polymers. Managed by Lockheed-Martin Energy Systems, Inc.     

Cyclic Bis-alkylidene Complexes of Titanium and Zirconium: Synthesis,Characterization, and Reaction

Transition-metal alkylidenes have exhibited wide applications in organometallic chemistry and synthetic organic chemistry, however, cyclic Schrock-carbene-like bis-alkylidenes of group 4 metals with a four-electron donor from an alkylidene have not been reported. Herein, the synthesis and characterization of five-membered cyclic bis-alkylidenes of titanium ( 4 a , b ) and zirconium ( 5 a , b ) are reported, as the first well-defined group 4 metallacyclopentatrienes, by two-electron reduction of their corresponding titana- and zirconacyclopentadienes. DFT analyses of 4 a show a four-electron donor (σ-donation and π-donation) from an alkylidene carbon to the metal center. The reaction of 4 a with N,N′-diisopropylcarbodiimide (DIC) leads to the [2+2]-cycloaddition product 6 . Compound 4 a reacted with CO, affording the oxycyclopentadienyl titanium complex 7 . These reactivities demonstrate the multiple metal–carbon bond character. The reactions of 4 a or 5 a with cyclooctatetraene (COT) or azobenzene afforded sandwich titanium complex 8 or diphenylhydrazine-coordinated zirconacyclopentadiene 9 , respectively, which exhibit two-electron reductive ability.