Reaction Of Zr Research Articles

Nafion/ZrSPP composite membrane for high temperature operation of proton exchange membrane fuel cells

Abstract To extend the proton conductivity of Nafion at high temperatures above 100 °C zirconium sulphophenyl phosphate (ZrSPP) particles were used as a solid proton conductor and hygroscopic material. ZrSPP was obtained by the reaction of Zr 4+ ion and m -sulphophenyl phosphonic (SPP) acid with a stoichiometric ratio P/Zr = 2. The synthesis of ZrSPP was confirmed by phosphonate (P–O) stretching band, assigned at 900–1300 cm −1 in FT-IR spectra. Nafion/ZrSPP composite membranes almost maintained the maximum conductivity of Nafion even at 110 °C when hydrated at 98% RH. The Nafion/ZrSPP membrane showed four times better cell performance than recast Nafion at 100 °C.

Exploring Alternative Synthetic Routes for the Preparation of Five-Coordinate Diamidoamine Group 4 Metal Complexes

Efficient synthetic routes for the preparation of electrophilic titanium and zirconium complexes featuring a tridentate diamidoamine ligand have been developed. The five-coordinate titanium dichloride complexes [(MesNCH2CH2)2NR]TiCl2 (R = H (3), SiMe3 (4)) are conveniently prepared from the amine elimination reactions of the triamines (MesNHCH2CH2)2NR (R = H (1), SiMe3 (2)) with Ti(NEt2)2Cl2. Treatment of Ti(NEt2)4 with 2 equiv of SiMe3Cl offers an effective method for the preparation of Ti(NEt2)2Cl2. The corresponding five-coordinate zirconium homologues [(MesNCH2CH2)2NR]ZrCl2 (R = H (5), SiMe3 (6)) are synthesized via the toluene elimination reactions of Zr(benzyl)2Cl2(Et2O)2 with 1 and 2, respectively. The thermally unstable and photosensitive Zr(benzyl)2Cl2(Et2O)2 species may be prepared in situ from the reaction of Zr(benzyl)4 with 2 equiv of [NEt3H]Cl in diethyl ether at 0 °C in the dark. The toluene elimination reaction of Hf(benzyl)4 with 1 affords the dibenzyl Hf complex [(MesNCH2CH2)2NH]Hf(benzy...

Azide Addition To Give a Tetra-azazirconacycle Complex

Addition of the dilithium salt, ortho-(Me3SiNLi)2C6H4, to ZrCl4 affords a base-free, D2d-symmetric complex Zr(IV)[ortho-(Me3SiN)2C6H4]2 (2), with rigorously planar ortho-phenylenediamine ligands. Lewis acidic 2 readily coordinates donor ligands such as NHEt2 to give the five-coordinate complex, Zr(IV)(NHEt2)[ortho-(Me3SiN)2C6H4]2 (3), which is also accessible by the reaction of Zr(NEt2)4 with 2 equiv of ortho-(Me3SiNH)2C6H4. Aryl azides react with 2 and 3 to give an unusual tetra-azametallacycle complex, 4, via 1,2-addition of a ligand N-Si bond to the organic azide. An X-ray crystal structure of 4 reveals a planar, five-membered metallacycle comprising the zirconium atom, one nitrogen atom of the ortho-(Me3SiN)2C6H4 ligand, and all three nitrogen atoms of the aryl azide.

The C−H Activation of Methane by Laser-Ablated Zirconium Atoms: CH2ZrH2, the Simplest Carbene Hydride Complex, Agostic Bonding, and (CH3)2ZrH2

Reaction of laser-ablated Zr with CH(4) ((13)CH(4), CD(4), and CH(2)D(2)) in excess neon during condensation at 5 K forms CH(2)=ZrH(2), the simplest alkylidene hydride complex, which is identified by infrared absorptions at 1581.0, 1546.2, 757.0, and 634.5 cm(-)(1). Density functional theory electronic structure calculations using a large basis set with polarization functions predict a C(1) symmetry structure with agostic C-H- - -Zr bonding and distance of 2.300 A. Identification of the agostic CH(2)=ZrH(2) methylidene complex is confirmed by an excellent match of calculated and observed isotopic frequencies particularly for the four unique CHD=ZrHD isotopic modifications. The analogous reactions in excess argon give two persistent photoreversible matrix configurations for CH(2)=ZrH(2). Finally, methane activation by CH(2)=ZrH(2) gives the new (CH(3))(2)ZrH(2) molecule.

Terminal Zirconium Imides Prepared by Reductive C−N Bond Cleavage

Toluene reflux of ZrCl4 with Li(Nacnac) (Nacnac- = [Ar]NC(tBu)CHC(tBu)N[Ar], Ar = 2,6-[CH(CH3)2]2C6H3) provides the complex (Nacnac)ZrCl3 in 75% yield. Cl- substitution for OTf- is readily achieved with 3 equiv of AgOTf to yield 77% of the complex (Nacnac)Zr(OTf)2(η2-OTf). The coordination mode of the three triflato groups was determined by a combination of single-crystal X-ray analysis and 19F COSY experiments. Addition of 2 equiv of LiCH2XMe3 (X = C, Si) to (Nacnac)ZrCl4 in Et2O affords the bis(alkyl) systems (Nacnac)Zr(CH2XMe3)2Cl in good yield (X = C, 86%; X = Si, 91%). In contrast, reaction of (Nacnac)Zr(OTf)2(η2-OTf) with 2 equiv of LiCH2CMe3 leads instead to formation of the terminal zirconium−imido complex [(NactBu)ZrNAr(μ2-OTf)]2 (NactBu- = [2,6-(CHMe2)2C6H3]NC(tBu)CHC(tBu)). Likewise, reduction of (Nacnac)ZrCl3 with 2 equiv of KC8 in THF also affords a terminal zirconium−imido species, (NactBu)ZrNAr(Cl)(THF). The zirconium−imido compounds described herein result from reductive cleavage of the C−...

Enantioselective Synthesis of ansa-Zirconocenes

The reaction of the chiral chelated bis-amide complex Zr{(2R,4R)-PhNCHMeCH2CHMeNPh}Cl2(THF)2 (R,R-7) with lithium ansa-bis-indenyl reagents Li2[SBI](Et2O) (8a, SBI = (1-indenyl)2SiMe2) or Li2[EBI](Et2O) (8b, EBI = 1,2-(1-indenyl)2ethane) in THF affords the corresponding ansa-zirconocenes S,S-(SBI)Zr{(2R,4R)-PhNCHMeCH2CHMeNPh} (S,S,R,R-9a) or S,S-(EBI)Zr{(2R,4R)-PhNCHMeCH2CHMeNPh} (S,S,R,R-9b) in >95% isolated yield and >99% enantiomeric excess. Compound 9b was converted to the corresponding enantiomerically pure dichloride S,S-(EBI)ZrCl2 (S,S-10b) in 91% isolated yield by reaction with HCl in Et2O. The chiral diamine (2R,4R)-HPhNCHMeCH2CHMeNHPh (R,R-5) was recovered from this reaction.

Nafion/ZrSPP composite membrane for high temperature operation of PEMFCs

Nafion/zirconium sulphophenyl phosphate (ZrSPP) composite membranes were prepared to maintain proton conductivity at elevated temperatures. ZrSPP was precipitated by the reaction of Zr 4+ ion and m-sulphophenyl phosphonic (SPP) acid with a stoichiometric ratio P/Zr = 2. The synthesis of ZrSPP was confirmed by phosphonate (P O) stretching band, assigned at 900–1300 cm −1 in FTIR spectra. The sharp diffraction pattern at 2 θ = 5° indicated crystalline α-layered structure of ZrSPP. The proton conductivity of Nafion/ZrSPP (12.5 wt.%) composite membrane reached ca. 0.07 S/cm at 140 °C without extra humidification.

Hydrogen Elimination from Ethylene by Laser-Ablated Zr Atoms: An Infrared Spectroscopic Investigation of the Reaction Intermediates in a Solid Argon Matrix

Intermediates of the hydrogen elimination reaction of ethylene by laser-ablated Zr atoms have been isolated in an argon matrix and investigated by means of infrared spectroscopy. The strong absorptions in the region of 1500−1660 cm-1 are due to the Zr−H stretching modes of several intermediates. There are at least three different groups of product absorptions based on the behaviors upon broad-band photolysis and annealing. Among them, the insertion and dihydrido complexes, presumed in previous studies of the hydrogen elimination of ethylene by Zr atoms, are identified. In addition, the remaining Zr−H stretching absorptions, along with absorptions in the C⋮C stretching and other regions, suggest that ethynyl zirconium trihydride is also formed in the hydrogen elimination reaction. Formation of this compound is consistent with the fact that C2H2 and C2D2 as well as CHCD are produced in the reaction of Zr + CH2CD2. Density functional theory calculations for the reaction intermediates are also carried out, and the molecular properties and vibrational characteristics are compared with the experimental values.

The Effects of Activators on Zirconium Phosphinimide Ethylene Polymerization Catalysts

Synthetic routes to the species CpZr(NPt-Bu3)2Cl, 7, Cp2Zr(NPt-Bu3)Cl, 8, CpZr(NPt-Bu3)2Me, 9, Cp2Zr(NPt-Bu3)Me, 10, and CpZr(NPt-Bu3)2Bn, 11, were developed in a manner similar to that previously reported for zirconium phosphinimide complexes. Rather than employing metathesis routes, transamination was considered to synthesize bis-phosphinimide zirconium complexes. At ambient temperature, Zr(NPt-Bu3)3(NMe2), 15, was isolated in less than 5% yield, but could be obtained cleanly via reaction of Zr(NPt-Bu3)3Cl, 14, with LiNMe2. However, thermolysis of Zr(NEt2)4 with HNPt-Bu3 afforded Zr(NPt-Bu3)2(NEt2)2, 12, which was subsequently converted to Zr(NPt-Bu3)2Cl2, 13, upon reaction with trimethylsilyl chloride. Cationic products were generated from the reaction of Lewis acids in the presence of a donor to provide the salts [CpZr(NPt-Bu3)Me(THF)][MeB(C6F5)3], 16, [Cp*Zr(NPt-Bu3)((i-PrN)2CMe)][MeB(C6F5)3], 17, and [CpZr(NPt-Bu3)((i-PrN)2CMe)][MeB(C6F5)3], 18. Similarly, reaction of [HNMe2Ph][B(C6F5)4] with 4 generated the salt [CpZr(NPt-Bu3)Me(NMe2Ph)][B(C6F5)4], 19, while reaction of 11 with B(C6F5)3 gave the base-free product [CpZr(NPt-Bu3)2][BnB(C6F5)3], 20. Structural considerations and preliminary MO calculations support the reactivity studies that augur well for olefin polymerization activity. Experimentally, previously reported screening using MAO as a solvent scrubber/activator with 1−4 showed only moderate polymerization activities. However, use of 20 equiv of Al(i-Bu)3 as scavenger and 2 equiv of B(C6F5)3 as cocatalyst resulted in a significant increase in activity relative to that observed upon activation with MAO. Use of [Ph3C][B(C6F5)4] as the cocatalyst led to even higher ethylene polymerization activities.

Control of the ratio of functional and non-functional ligands in clusters of the type Zr6O4(OH)4(carboxylate)12for their use as building blocks for inorganic–organic hybrid polymers

The methacrylate ligands of the cluster Zr6O4(OH)4(methacrylate)12 undergo degenerate exchange with methacrylic acid in solution. Addition of propionic or isobutyric acid allows partial or complete exchange of the methacrylate ligands for propionate or isobutyrate. The mixed-carboxylate cluster Zr6O4(OH)4(OMc)8(isobutyrate)4(BuOH) was independently prepared by reaction of Zr(OnBu)4 with a mixture of methacrylic acid and isobutyric acid. The structures of Zr6O4(OH)4(OMc)8(isobutyrate)4(BuOH) and Zr6O4(OH)4(isobutyrate)12(H2O) consist of an octahedral Zr6(μ3-O)4(μ3-OH)4 core with one of the carboxylate ligands being monodentate. The H2O or ROH molecule is coordinated to the neighbouring zirconium atom and, at the same time, hydrogen bonded to the monodentate carboxylate. A mechanism for the carboxylate exchange is suggested based on the structural observations.

Synthesis and group 4 complexes of tris(pyrrolyl-alpha-methyl)amine.

The tetradentate, trianionic ligand tris(pyrrolyl-alpha-methyl)amine (H(3)tpa) is available in 84% yield in a single step by a triple Mannich reaction involving 3 equiv of pyrrole, 3 equiv of formaldehyde, and ammonium chloride. The new ligand is readily placed on titanium by transamination on Ti(NMe(2))(4), which generates Ti(NMe(2))(tpa) (1) in 73% yield. Treating 1 with 1 equiv of 1,3-dimethyl-2-iminoimidazolidine (H-imd) in toluene provided a rare example of a titanium 2-iminoimidazolidinide, which displays some interesting structural features. Of note is the Ti-N(imd) distance of 1.768(2) A, a typical Ti-N double to triple bond distance. Reaction of Zr(NMe(2))(4) with H(3)tpa gave a complex of variable composition, probably varying in the amount of labile dimethylamine retained. However, stable discreet compounds were available by addition of THF, pyridine, or 4,4'-di-tert-butyl-2,2'-bipyridine (Bu(t)bpy) to in situ generated Zr(NMe(2))(NHMe(2))(x)(tpa). Three chloro zirconium complexes were generated using three different strategies. Treating Zr(tpa)(NMe(2))(Bu(t)bpy) (5) with ClSiMe(3) afforded Zr(tpa)(Cl)(Bu(t)bpy) (6) in 92% yield. Reaction of Li(3)tpa with ZrCl(4)(THF)(2) in THF gave a 72% yield of ZrCl(tpa)(THF)(2) (7). In addition, treatment of ZrCl(NMe(2))(3) with H(3)tpa cleanly generated ZrCl(NHMe(2))(2)(tpa) (8) in 95% yield. An organometallic zirconium complex was generated on treatment of 6 with LiCtbd1;CPh; alkynyl Zr(Ctbd1;CPh)(tpa)(Bu(t)bpy) (9) was isolated in 62% yield. 1, Ti(imd)(tpa) (2), 6, and 9 were characterized by X-ray diffraction.

Chelate-Controlled Synthesis of rac- and meso-Me2Si(3-tBu-C5H3)2ZrCl2

The reaction of the chelated bis-amide complex Zr{PhN(CH2)3NPh}Cl2(THF)2 (2) with Li2[Me2Si(3-tBu-C5H3)2] yields meso-Me2Si(3-tBu-C5H3)2Zr{PhN(CH2)3NPh} (meso-3) in >98% yield. In contrast, the reaction of Zr{Me3SiN(CH2)3NSiMe3}Cl2(THF)2 (4) or the related mono-THF adduct Zr{Me3SiN(CH2)3NSiMe3}Cl2(THF) (5) with Li2[Me2Si(3-tBu-C5H3)2] yields rac-Me2Si(3-tBu-C5H3)2Zr{Me3SiN(CH2)3NSiMe3} (rac-6) in quantitative NMR yield and 89% isolated yield. X-ray crystallographic analyses show that the Zr{RN(CH2)3NR} chelate ring in rac-6 has a pronounced twist conformation, while that in meso-3 has a flatter, envelope conformation. It is proposed that the conformations of the Zr{RN(CH2)3NR} chelate rings in the stereodetermining transition states for addition of the second Cp- ring in these reactions are similar to those in the metallocene products and control the diastereoselectivity. meso-3 and rac-6 are converted to meso-Me2Si(3-tBu-C5H3)2ZrCl2 (meso-1) and rac-1, respectively, by reaction with HCl in Et2O.

Reaction of Metal Alkoxides with Lysine: Substitution of Alkoxide Ligands vs . Lactam Formation

Reaction of Ti(OEt)4 with lysine results in the formation of Ti(OEt)3(lysinate), as previously reported. Contrary to that, Al(OsBu)3 only catalyzes the formation of 3-aminocaprolactam, and no substitution product was observed. The reaction of Zr(OBu)4 with lysine at room temperature produced both 3-aminocaprolactam and Zr(OBu)3(lysinate); the lysinate complex was not observed when the reaction was performed at elevated temperatures.

Activation of CH4 by Gas-Phase Zr+ and the Thermochemistry of Zr−Ligand Complexes

The kinetic energy dependence of the reaction of Zr + ( 4 F) with methane has been studied using guided ion beam mass spectrometry. At low energies, the only process observed is dehydrogenation, which is slightly endothermic such that it exhibits a strong isotope effect when CD 4 is used as the reactant. At high energies, products resulting from C-H cleavage processes are appreciable. Modeling of the endothermic reaction cross sections yields the 0 K bond dissociation energies (in eV) of D 0 (Zr + -CH) = 5.96 ′ 0.22, D 0 (Zr + -CH 2 ) = 4.62 ′ 0.07, and D 0 (Zr + -CH 3 ) = 2.30 ′ 0.24. The experimental thermochemistry is favorably compared with density functional theory calculations (B3LYP), which also establish the electronic structures of these species and provide insight into the reaction mechanism. The results for Zr + are compared with those for the first-row transition metal congener Ti + , and the differences in behavior and mechanism are discussed.

Cationic benzyl zirconium heteroscorpionates: synthesis and characterization of a novel ethylene polymerisation catalyst showing an unusual temperature dependent polymerisation mechanism.

The reaction of (bpzmp)Zr(CH2Ph)3 with B(C6F5)3 produces the active ethylene polymerisation catalyst [(bpzmp)Zr(CH2Ph)2]+[PhCH2B(C6F5)3]- which showed a temperature dependent polymerisation mechanism identified by variable temperature 1H NMR analysis of the catalyst solution.

Synthesis and characterisation of novel zirconium(iv) derivatives containing the bis-amido ligand SiMe2(NRR′)2

The silicon compounds SiMe2(NRR′)2 [NRR′ = NMe2 (1), NEt2 (2), NC4H8 (3), NHEt (4), NHiPr (5), NHtBu (6), NMeBu (7)] have been synthesised via aminolysis of the dichloro species SiMe2Cl2 and their ligating ability has been investigated towards zirconium(IV). The dimer zirconium compound {Zr[(NiPr)2SiMe2]2}2 (8) has been synthesised by reacting ZrCl4 with the lithium salt Li2[(NiPr)2SiMe2] and its molecular structure has been determined in the solid state by X-ray diffraction analysis. The reaction of ZrCl4 with SiMe2(NRR′)2 yields the Lewis adducts ZrCl4[(NRR′)2SiMe2] [NRR′ = NMe2 (10), NC4H8 (11), NHEt (12), NHiPr (13), NHtBu (14), NMeBu (15)]. On the other hand, the mixed amido derivative Zr(NMe2)3(NHMe)[(NtBu)SiMe2(NHtBu)] (9) has been obtained from the reaction of Zr(NMe2)4 with SiMe2(NHtBu)2. The solution molecular structure and dynamics of the zirconium derivatives have been elucidated by 1D and 2D multinuclear NMR spectroscopy.

Isolation and characterisation of transition and main group metal complexes supported by hydrogen-bonded zwitterionic polyphenolic ligands.

Reaction of Zr(O(i)Pr)4 or Sn[N(SiMe3)2]2 with the tris-phenol amine ligand H3L(Me/Me) results in the formation of zirconium or tin complexes containing the new C3-symmetric zwitterionic ammonium-trisphenolate ligand HL2-, while increasing the steric bulk of the ligand results in the isolation of a zirconium complex containing the known trianionic ligand L3-.

Solution structure and decomposition pathway of zwitterionic zirconium (IV) benzyl complexes

Reaction of the chelating diamido complexes Zr(ABA n )(CH 2Ph) 2 [ABA 1= N, N′-(SiMe 3) 2-2-amidobenzylamido, ABA 2= N, N′-(SiMePh 2)(SiMe 3)-2-amidobenzylamido] with B(C 6F 5) 3 leads to formation of the unstable zwitterionic adducts [Zr(ABA n )(CH 2Ph)][(η 6-PhCH 2)B(C 6F 5) 3] 1 ( n=1) and 2 ( n=2), as shown by low temperature NMR experiments that, moreover, enabled an insight into the molecular structure of these compounds in solution. Two intermediates of the decomposition of 1 and 2, that leads to complexes Zr(ABA n )(C 6F 5) 2, were identified.

A Homoleptic Zirconium Complex with Four Bulky η2-Pyrazolato Ligands

Two new tetrakisη2-pyrazolato) zirconium complexes are prepared from the reaction of Zr(CH2Ph)4 with bulky pyrazolate ligands bearing indenylmethyl (HL1) or fluorenylmethyl (HL2) substituents, respectively. Zr(L2)4 has been analyzed by X-ray crystallography, which represents the first structural characterisation of a homoleptic η2-pyrazolato zirconium compound.

Syntheses, Characterization, and Structural Studies of Half-Open Zirconocenes

The reaction of Zr(C 5 H 5 )Cl 2 Br with 3 equiv of K(2,4-C 7 H 1 1 ) and 1 equiv of dmpe was found to lead to the 18-electron half-open zirconocene Zr(C 5 H 5 )(2,4-C 7 H 1 1 )(dmpe) (C 7 H 1 1 = dimethylpentadienyl; dmpe = Me 2 PC 2 H 4 PMe 2 ), which has been fully characterized. A structural study has revealed that the Zr-C bond distances for the open dienyl ligand are significantly shorter than those for the C 5 H 5 ligand. Alternatively, through a similar reaction involving the use of only 2 equiv of a more selective (pentadienyl)magnesium reagent, the two dienyl anions serve as one-electron reducing agents, and the Zr(II) complex ZriC 5 H 5 )-(Br)(dmpe) 2 is obtained, which has also been fully characterized. In the absence of dmpe, the reaction between Zr(C 5 H 5 )BrCl 2 and 3 equiv of the magnesium reagent leads to an unusual ZrlC 5 H 5 )(C 1 4 H 2 1 ) complex. The C 1 4 H 2 1 ligand was formed from the coupling of two 2,4-C 7 H 1 1 ligands, followed by the loss of one hydrogen atom, presumably abstracted by the third 2,4-C 7 H 1 1 ligand. The C 1 4 H 2 1 ligand bonds to the zirconium center through both η 5 -dienyl and η 4 -diene coordination, leading to an 18-electron complex. The structural parameters indicate that the diene coordination can be more appropriately described as enediyl coordination, leading to a formal Zr(IV) instead of Zr(II) complex. The presence of a high formal metal oxidation state would seem to explain the fact that in this complex, as opposed to Zr(C 5 H 5 )(2,4-C 7 H 1 1 )(dmpe) and many other related complexes, the M-C bond distances for the C 5 H 5 ligand are much shorter than those for the open dienyl ligand.