Synthesis of zirconium, hafnium, and tantalum complexes with sterically demanding hydrazide ligands

The bulky hydrazine t-BuN(H)NMe2 was synthesized via hydrazone and t-BuN(H)N(H)Me intermediates as the major component in a 90:5:5 mixture consisting of t-BuN(H)NMe2, t-BuN(Me)N(H)Me, and t-BuN(Me)NMe2. Reacting the mixture with n-BuLi followed by distillation and fractional crystallization led to the isolation of the ligand precursor LiN(t-Bu)NMe2. Lithium hydrazides, LiN(R)NMe2, were reacted with metal chlorides to afford the hydrazide complexes M(N(Et)NMe2)4 (M = Zr or Hf), MCl(N(R)NMe2)3 (M = Zr, R = i-Pr or t-Bu; M = Hf, R = t-Bu), and TaCl3(N(i-Pr)NMe2)2. The X-ray crystal structures of [LiN(i-Pr)NMe2]4, [LiN(t-Bu)NMe2.THF]2, ZrCl(N(R)NMe2)3 (R = i-Pr or t-Bu), and TaCl3(N(i-Pr)NMe2)2 were determined. The structural analyses revealed that the hydrazide ligands in ZrCl(N(R)NMe2)3 (R = i-Pr or t-Bu) and TaCl3(N(i-Pr)NMe2)2 are eta2 coordinated.     

Crystal structures of crown and aza-crown ether complexes with zirconium,hafnium, niobium,and tantalum fluorometallates

A systematic X-ray diffraction study of the interaction products of Zr(IV), Hf(IV), Nb(V), and Ta(V) oxides (fluorides) with crown-ethers (CEs) in aqueous solutions of hydrofluoric acid is performed. It is shown that oxygen-containing CEs form oxonium complexes with [NbF6]^s- and [TaF6]^s- hexafluorometallate anions. In two systems, [cis-syn-cis-DCH18C6-H₃O][TaF₆] and [B18C6·H₃O][TaF₆], the phenomenon of supramolecular isomerism is found, which is caused by a change in the conformation of the macrocycle or by a partial redistribution of intermolecular hydrogen bonds. The use of aza-crown ethers as extractants made it possible to extract unique hydrolytically unstable anions, the products of incomplete fluorine substitution for oxygen atoms in the starting oxides in the form of crystalline complexes with a composition of [(HA15C5)₂][Ta₂F₁₀O] and [(HA18C6·H₂O)(A18C6·H₂O)] [(H₂O)Nb₂F₉O]. In [(18C6)(H₇O₃)₂×(Hf₂F₁₀·2H₂O)], [(HA18C6)(M₂F₁₀·2H₂O)·(H₃O)·H₂O], and [(H₂DA18C6) (M₂F₁₀·2H₂O)·2H₂O] (M=Zr, Hf) complexes, the metals are extracted in the form of identical (M₂F₁₀·2H₂O)^2s- anions with a similar topology. The performed study demonstrates that macrocyclic complexones are undoubtedly promising to extract Zr(IV), Hf(IV), Nb(V), and Ta(V) from fluorine-containing aqueous solutions.     

Separation of niobium and tantalum from zirconium with salicylhydroxamic acid

Salicylhydroxamic acid can be used for the separation of zirconium from niobium above pH 2 5 in presence of hydrogen peroxide. Niobium can be precipitated from the filtrate with N-benzoyl-N-phenylhydroxylamine.     

Mixed hydrazido amido/imido complexes of tantalum, hafnium and zirconium: potential precursors for metal nitride MOCVD

The coordination chemistry of the hydrazine derivatives dimethylhydrazine (Hdmh) and N-trimethylsilyl-N'N'-dimethylhydrazine (Htdmh) at Ta, Zr and Hf was investigated aiming at volatile mixed ligand all-nitrogen coordinated compounds. The hydrazido ligands were introduced either by salt metathesis employing the Li salts of the hydrazines and the tetrachlorides MCl(4) (M = Zr, Hf) or by amine substitution using M(NR(2))(4) (R = Me, Et) and [(t-BuN)Ta(NR(2))(3)]. The new complexes were fully characterised including (1)H/(13)C NMR, mass spectrometry and a study of their thermal behaviour. The crystal structures of [ZrCl(tdmh)(3)] and the all-nitrogen coordinated complex [Ta(N-t-Bu)(NMe(2))(2)(tdmh)] are discussed as well as the structure of the by-product [Li(tdmh)(py)](2). Preliminary MOCVD experiments of the liquid compound [Ta(NEt(2))(2)(N-t-Bu)(tdmh)] were performed and the deposited TaN(Si) films were analysed by RBS and SEM.     

Determination of niobium and tantalum in binary alloys and zirconium alloys

Recent developments in the metallurgy of niobium, tantalum and zirconium have necessitated provision of analytical procedures for determining niobium and tantalum in the presence of each other and in the presence of zirconium. For this purpose, absorptioinetric procedures based on the formation of yellow coloured complexes, between pyrogallol and niobium or tantalum, have been critically examined. Direct absorptiometric procedures are described, which are suitable for determining niobium or tantalum in the range 2 to 7%; when either of these metals exceeds 7%, differential absorptiometric procedures are recommended. Corrections must lie made for absorption due to the presence of other metals which form complexes with pyrogallol. In tlie determination of niobium or tantalum up to 5%, the precision of the method is about ±0.05%. About 12 determinations can be made in a day, by one analyst.     

Arylaminopyridinato complexes of zirconium

A range of 2-arylaminopyridines (HL) are synthesised readily from bromopyridines and amines using palladium-catalysed amination. Protonolysis reactions of these proligands with ZrX(4)(X = NMe(2), CH(2)Ph, CH(2)Bu(t)) yield zirconium complexes of the type [ML(n)X(4-n)], several of which have been characterised by X-ray crystallography. Control of metal/ligand stoichiometry and structure is pursued by investigation of the effects on substitution patterns of the pyridine and aryl rings. Some distinct patterns emerged; (i) the 6-methyl position on the pyridine appears to be particularly important with regards to control of stoichiometry, although there are co-ligand effects; (ii) structures of the metal alkyl derivatives [Zr(n)(CH(2)R)(4-n)] are dominated by aromatic pi-pi stacking, even when bulky arene substituents are employed at. This leads to the complexes adopting a C(2v)-symmetric core; (iii) the amides [Zr(2)(NMe(2))(2)] have structures for which aromatic pi-pi stacking is unfeasible, and correspondingly C(2)-symmetric or similar structures are adopted. All the structural data presented is consistent with a trans influence order at zirconium Me(2)N > RCH(2) > py.     

Formation of niobium and tantalum ylide complexes

The reactions of tri(bis(ethyl)amino)phosphorus ylide (Et₂N)₃PCH₂ with cyclopentadienyl (Cp) metal (V) tetrachloride CpMCl₄ (M = Nb 1; Ta 3) and pentamethylcycopentadienyl (Cp^∗) metal (V) tetrachloride Cp^∗MCl₄ (M = Nb 2; Ta 4) were investigated. The hexa-coordinate ylide adducts complexes 5 (CpNbCl₄(H₂CP(NEt₂)₃)), 6 (Cp^∗NbCl₄(H₂CP(NEt₂)₃)) and 8 (Cp^∗TaCl₄(H₂CP(NEt₂)₃)) with pseudo-octahedral geometry were structurally analyzed with X-ray diffraction. Compound 4 (Cp^∗TaCl₄) reacted with three molar equivalent of phosphorus ylide to form one ionic complex 9 ([H₃C-P(NEt₂)₃][Cp^∗TaCl₅]) which was also structurally analyzed with X-ray diffraction. The possible formation mechanism of compound 9 has been discussed.     

2-Methoxyethanol complexes of niobium and tantalum

The reactions of Et₄NMCl₆ and MCl₅ (M  Nb, Ta) with 2-methoxyethanol have been studied and complexes MCl₃(OCM₂CH₂OMe)₂ and Et₄N TaCl_5−x (OCH₂CH₂OMe)_x (x = 1,2) have been isolated, and characterised by i.r. and NMR spectra. The reactions of Et₄NMCl₆ with MeOH are also reported.     

Anionic zirconium and hafnium borohydride complexes

Zirconium and hafnium tetrachlorides react with NaBH₄, in dimethoxyethane (DME) to give [Na(DME)₃][M(BH₄)₅]. These compounds react with Bu₄NBH₄ and Ph₄PBH₄ to give (R₄E)[M(BH₄)₅]. Bidentate and tridentate BH ₄ ^– occur in [M(BH₄)₅]^– according to IR spectroscopy. Data from¹H and¹H-{¹¹B} NMR spectra are consistent with intermolecular exchange of BH₄ ligands in solutions of complexes (I)–(VI). The BH₄groups and the bridging and terminal protons in each BH₄ group equilibrate rapidly. Heating the complexes (I)–(VI) reduces the central atom, releases diborane, and decomposes the outer-sphere cation. The neutral borohydrides M(BH₄)₄, can be prepared by thermolysis of the sodium salts (I) and (II).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1207–1214, June, 1990.     

The determination of zirconium in its binary alloys with niobium and tantalum

A procedure is presented for the determination of zirconium in the presence of niobium or tantalum. The bulk of the niobium or tantalum is first removed by extracting with hexone from a 10M hyclrofluoric acid, 6M sulphuric acid solution of the sample. The zirconium is then. separated from any unextractcd earth, acid element by precipitation with ammonium hydroxide followed by the addition of hydrogen peroxide. Under these conditions, both the niobium and tantalum form soluble peroxy complexes whereas the zirconium is completely precipitated from solution. After the separation of the precipitate by filtration, it is re-dissolved in hydrochloric acid and the zirconium concentration is finally determined by titration with ethylenediaminetetraacetic acid.     

Synthesis and characterization of binuclear tantalum hydride complexes

Reduction of the quadruply-bridged (2Cl, 2H) tantalum(IV) dimer, Ta₂Cl₆ (PMe₃)₄H₂ (2) with sodium amalgam in glyme or THF at 0°C provides deep green Ta₂Cl₄(PMe₃)₄H₂ (3) in 70% yield. Dimer 3 has a D_2d Ta₂Cl₄(PMe₃)₄ substructure which closely resembles that of the quadruply metal-metal-bonded dimer W₂Cl₄(PMe₃)₄. The hydride ligands of 3 are located on a diagonal plane, bridging the two tantalum atoms and the Ta-Ta separation is 2.545(1) Å. 3 reacts cleanly with Cl₂, HCl and H₂ in diethyl ether to provide the quadruply-bridged dimers 2, Ta₂Cl₅(PMe₃)₄H₃ (4), and Ta₂Cl₄(PMe₃)₄H₄ (5), respectively, in high yield. Dimer 5 can also be prepared in high yield via thermolysis of the tantalum(IV) hydride TaCl₂H₂(PMe₃)₄ (6) in refluxing methylcyclohexane. The X-ray structure of 5 shows that the (μ-H)₄ group is staggered by 45° with respect to the eclipsed pyramidal TaCl₂(PMe₃)₂ end groups. The molecular symmetry of 5 is D_2d and the Ta-Ta separation is 2.511(2)Å. Multiple-scattering Xα calculations on the model compounds Ta₂Cl₄(PH₃)₄H₂ and Ta₂Cl₄(PH₃)₄ are used to elucidate the ground-state electronic structures of 3 and 5, and to probe the question of (μ-H)_x rotation about the metal-metal bonds in these complexes. Crystal data (at 160°C) are as follows: for 3, monoclinic space group C2/c, a = 18.371(5) Å, b = 9.520(3) Å, c = 18.942(6) Å, β = 125.36(2)°, V = 2701.8 ų, Z = 4,d_calc. = 1.991 g cm⁻³; for 5, tetragonal space group P4/nbm, a = b = 12.579(2) Å, c = 10.205(2) Å, V = 1614.7 ų, Z = 2, d_calc. = 1.670 g cm⁻³.     

Synthesis and structures of zirconium amide-iodide complexes

Zirconium amide-iodide complexes were synthesized for possible use as chemical vapor deposition precursors to zirconium nitride films. The series of six complexes Zr(NR(2))(4-n)I(n)(R = Me or Et; n = 1-3) was prepared by reacting ZrI(4) and Zr(NR(2))(4) in hot toluene. X-ray crystallographic analyses were performed for Zr(NMe(2))(3)I, Zr(NEt(2))(2)I(2), and Zr(NEt(2))I(3). In the solid state, Zr(NMe(2))(3)I and Zr(NEt(2))(2)I(2) are the discrete dimers [Zr(NMe(2))(2)I(mu-NMe(2))](2) and [Zr(NEt(2))(2)I(mu-I)](2), and Zr(NEt(2))I(3) is the polymer of dimers ([Zr(NEt(2))I(2)(mu-I)](2))(n). In solution, Zr(NEt(2))(3)I is proposed to be monomeric on the basis of NMR data and a molecular weight determination. The complex Zr(NEt(2))(3)I is the most promising precursor candidate because of its physical properties.     

Titanium and zirconium complexes with aminoiminophosphorane ligands

A series of titanium and zirconium complexes based on aminoiminophosphorane ligands [Ph₂P(Nt‐Bu)(NR)]₂MCl₂ ( 4 , M = Ti, R = Ph; 5 , M = Zr, R = Ph; 6 , M = Ti, R = SiMe₃; 7 , M = Zr, R = SiMe₃) have been synthesized by the reaction of the ligands with TiCl₄ and ZrCl₄. The structure of complex 4 has been determined by X‐ray crystallography. The observed very weak interaction between Ti and P suggests partial π‐electron delocalization through both Ti and P. The complexes 4–7 are inactive for ethylene polymerization in the presence of modified methylaluminoxane (MMAO) or i‐Bu₃Al–Ph₃CB(C₆F₅)₄ under atmospheric pressure, and is probably the result of low monomer ethylene concentration and steric congestion around the central metal. Copyright © 2005 John Wiley & Sons, Ltd.     

Schiff base tantalum(V) complexes

Summary Complexes of pentachlorotantalum with the Schiff bases: bis(vanillin)benzidine, bis(vanillin)-o-dianisidine, bis(acetylacetone)benzidine, bis(p-dimethylaminobenzaldehyde)-o-dianisidine, bis(anisaldehyde)-1, 3-propanediamine and bis(p-dimethylaminobenzaldehyde)-o-phenylenediamine have been prepared and characterized by molar conductance, decomposition temperature, elemental and t.g. analyses and i.r. spectral measurements. The conductances reveal that pentachlorotantalum (1 mole) interacts with all the ligands (1 mole), all five chloride ions thus forming simple adducts. A comparative study of the i.r. spectra of the parent ligands and their complexes allows the coordination sites to be ascertained. The studies show that tantalum(V) chloride prefers to form complexes of high coordination number.     

Synthesis and characterization of methyl-phenyl-substituted cyclopentadienyl zirconium complexes

The trisubstituted methyl-phenyl-silyl-cyclopentadienes [Me-Ph-C₅H₃(SiMe₂X)] (X = Me, Cl, NHt-Bu) and [(Me-Ph-C₅H₃)₂SiMe₂] and the lithium salts Li₂[Me-Ph-C₅H₂(SiMe₂Nt-Bu)] and Li₂[(Me-Ph-C₅H₂)₂SiMe₂] have been isolated by conventional methods and characterized by NMR spectroscopy. Desilylation of [Me-Ph-C₅H₃(SiMe₃)] with ZrCl₄(SMe₂)₂ gave the monocyclopentadienyl complex [Zr(η⁵-1-Ph-3-Me-C₅H₃)Cl₃]. The ansa-metallocene [Zr{(η⁵-2-Me-4-Ph-C₅H₂)SiMe₂(η⁵-2-Ph-4-Me-C₅H₂)}Cl₂] was obtained from the mixture of isomers formed by transmetallation of Li₂[(Me-Ph-C₅H₂)₂SiMe₂] to ZrCl₄ and characterized as the meso-diastereomer by X-ray diffraction methods. Similar transmetallation of Li₂[Me-Ph-C₅H₂(SiMe₂Nt-Bu)] gave the silyl-η-amido complex [Zr{η⁵-2-Me-4-Ph-C₅H₂(SiMe₂-η-Nt-Bu)}Cl₂] that was further alkylated to give [Zr{η⁵-2-Me-4-Ph-C₅H₂(SiMe₂-η-Nt-Bu)}R₂] (R = Me, CH₂Ph) and used as a catalyst precursor, activated with MAO, for ethene and propene polymerization. All of the new compounds were characterized by elemental analysis and NMR spectroscopy.     

Carboxylato complexes of zirconium(IV)

The preparation and thermal decomposition of several trifluoroacetatozirconium chlorides is described. A mechanism for the thermal decomposition is proposed and the formation of zirconium tetrafluoride discussed in terms of composition of the parent compound.

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Zusammenfassung Es wurde die thermische Zersetzung und die Darstellung einiger Trifluoroazetatozirkoniumchloride beschrieben. Für die Zersetzungsreaktion wurde ein Mechanismus vorgeschlagen und die Bildung von Zirkoniumtetrachlorid unter den Gesichtspunkten der Zersetzung der Mutterverbindung erläutert.

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One of us (CMS) wishes to thank the SERC, England, for a maintenance award.