Zirconium Complexes Research Articles

Mechanistic Insights on the Controlled Switch from Oligomerization to Polymerization of 1-Hexene Catalyzed by an NHC-Zirconium Complex

The benzimidazolylidene zirconium complex 1 switches from an oligomerization (without additive) to a polymerization catalyst by addition of an L-type ligand such as trimethylphosphine, while larger phosphines or amines completely inhibit catalysis. On the basis of the regioselectivity of the oligomers/polymers obtained, the time profiles of reactions as a function of added ligand, and the molecular structures of several cationic zirconium complexes, we propose a mechanistic framework for interpreting this complex catalytic behavior.

Reversible 1,2-Alkyl Migration to Carbene and Ammonia Activation in an N-Heterocyclic Carbene–Zirconium Complex

Addition of trimethylphosphine to a bis(phenolate)benzylimidazolylidene(dibenzyl)zirconium complex induces migration of a benzyl ligand from the metal center to the C(carbine) atom. This process may be reversed, resulting in Csp(3)-Csp(3) activation, by abstraction of the phosphine, an example of regulated, reversible alkyl migration. Addition of ammonia to the dibenzyl complex results in migration of one benzyl group and protonolysis of the other to generate a bis(NH2)-bridged dimer via an NMR-observable intermediate NH3 adduct.

ChemInform Abstract: Zirconium Catalyzed Intermolecular Hydroamination Reactions of Secondary Amines with Alkynes.

AbstractAn in situ generated cationic zirconium complex stabilized by an n‐butylamine‐bridged bis(phenolato) ligand is developed to catalyze hydroamination reactions of secondary amines.

Mono-boratabenzene and -phospholyl zirconocene(IV) derivatives: Towards mixed heterocycles zirconocene complexes

In hopes of extending the existing knowledge on the chemistry of phospholyl and boratabenzene complexes of zirconium, which have shown potential notably as polymerization catalysts, this study aims at exploring the synthesis of mono boratabenzene and mono phospholyl zirconium complexes and at studying their reactivity towards the formation of mixed (boratabenzene)(phospholyl)zirconium complexes. Several derivatives of (η5-phospholyl)Zr(NMe2)xCl3−x and (η6-boratabenzene-NMe2)Zr(NMe2)xCl3−x were synthesized and used as precursors for the formation of mixed (boratabenzene)(phospholyl)zirconium complexes.

Mononuclear complexes with heterocyclic ligands as ethylene polymerization catalysts for single-reactor bimodal polyethylene technology

27 complexes of titanium, zirconium and vanadium with 1,2-bis(benzimidazolyl)benzene, 1,2-bis(benzimidazolyl)ethane and 1,1-bis(benzimidazolyl)methane ligands have been synthesized and characterized. After activation with methylalumoxane (MAO) these complexes proved as good catalysts for ethylene polymerization inspite of the hetero atoms in the ligands and the oxophilicity of the metals. Nearly all produced polyethylenes showed bimodal or multimodal molecular weight distributions indicating more than one active site of the catalysts in the various polymerization steps. Obviously, after activation with MAO, a mononuclear catalyst molecule can interact differently with the cocatalyst. This is an easy and elegant approach to single-reactor bimodal/multimodal polyethylene technology. The polymerization activity of the catalyst system 1,2-bis(benzimidazolyl) benzene zirconium tetrachloride (29/MAO) was investigated at different polymerization temperatures and structure–property-relationships were studied. The effect of the polymerization temperature on both molecular weights and polydispersities of the polymers produced with catalyst 29/MAO was investigated at 20, 40, and 60°C. The molecular weights Mw were 1.3⋅106, 1.2⋅106 and 9.7⋅105g/mol and the polydispersity indices PDI 693, 248 and 223 respectively.

Preparation and Characterization of Organically Modified MCM-48 as Heterogonous Catalyst for Oxidation of Sulfides and Thiols

MCM-48 mesoporous synthesized and grafted with aminopropyl triethoxysilane (APTES) and subsequently reacted by isatin to obtain the imine of MCM-48. Addition of ZrOCl2·8H2O, leading to form the complex of Zr(IV)/isatin-MCM-48 as new Schiff base complex of zirconium(IV)-modified-MCM-48. The synthesized catalyst was characterized by XRD, TGA, FT-IR and BET. The resulting catalyst was efficient for selective oxidation of sulfides to sulfoxides and oxidation of thiols to disulfides with hydrogen peroxide. In this method isolation and reusability of catalyst have been investigated

Synthesis of zirconium carbide nanoparticles by polymerised complex route

A polymerised complex route, based on polyesterification between tartaric acid–zirconium complex and ethylene glycol (EG), has been demonstrated to synthesise ZrC powders at a relatively low temperature (1300°C). The Fourier transform infrared results confirmed the coordination of tartaric acid to the zirconium ion. Furthermore, this complex reacted with EG through polyesterification to immobilise the metal ion in the rigid polymer. The intimate mixing of the reaction components has thus been achieved in ZrO2/carbon ‘coke” due to the suppression of segregation of the reaction components during pyrolysis. Finally, well crystallised ZrC nanoparticles (50–150 nm) were obtained through the carbothermal reduction of ZrO2/carbon ‘coke’, concerning the formation of the intermediate oxycarbide phase.

Synthesis, characterization and catalytic properties for olefin polymerization of two new dimeric zirconium(IV) complexes having diamine-bis(phenolate) and chloride ligands

Reaction of the zirconium tetrachloride with one equivalent of the sodium salt of the diamine bis (phenolate) ligand, L1H2 (Me2NCH2CH2N-(CH2-2-OH-3,5-tBu-C6H2)2) or L2H2 (Me2NCH2CH2N-(CH2-2-OH-3,5-tBu-C6H2)(CH2-2-OH-C6H4)) in the presence of air led to formation of [Lig1ZrCl]2(μ-O) and [Lig2ZrCl]2(μ-O), respectively. These novel oxo-bridged dinuclear zirconium complexes were characterized by elemental analysis, 1H NMR spectroscopy and by single-crystal X-ray diffraction. Their reactivities in polymerization of ethylene and 1-octene, upon activation with Al(iBu)3/Ph3CB(C6F5)4 and MAO, were examined. It was found that lack of t-Bu substituents on one phenolate ring cause a significant decrease in catalytic activity but leads to polymers with improving properties, i.e., to poly(1-olefin)s with significantly higher stereoregularity and polyethylenes with higher molecular weight. In addition, the interaction of the [Lig1ZrCl]2(μ-O) precursors with MAO and with the Me3Al activator was investigated by 1H NMR spectroscopy giving an insight into the catalyst transformations in the course of the polymerization reaction.

Controlled homo- and copolymerization of propene and 1-undecene catalyzed by post-metallocenes

Homo- and copolymers of propene and 1-undecene were synthesized by controlled olefin polymerization (quasi-living polymerization) using two bis(phenoxyamine) zirconium complexes as catalysts. The controlled character is demonstrated by an asymptotic growth of molar mass as a function of polymerization time. For the first time, it was possible to synthesize block-like copolymers incorporating long 1-olefins like 1-undecene and propene blocks using the strategy of sequential monomer addition. The obtained copolymers have been characterized in terms of molecular and thermal properties. The copolymer composition was determined by 1H NMR spectroscopy whereas the quantification of diads by 13C NMR spectroscopy proves the blocky character of the polymers. SEC results confirm indirectly the formation of block-like copolymers showing monomodal molar mass distribution excluding the formation of two homopolymers. The DSC measurements revealed that the blocky samples show two melting and two crystallization peaks, in contrast to statistical copolymers. These results of DSC and NMR measurements give distinct indication of the blocky type of the copolymer structure.

Synthesis, spectral characterization and crystal structure of a new precursor [(CH3COCHCOCH3)2Zr{C6H4(N=CHC6H4O)2}] for nano-zirconia: an investigation on the wettability of polyvinylidene fluoride–nano-zirconia composite material

A new octa-coordinated metallo-organic complex of zirconium (IV) [(CH3COCHCOCH3)2Zr{C6H4(N=CHC6H4O)2}] was synthesized quantitatively by treating Zr(OPri)4·PriOH with CH3COCH2COCH3 and tetradentate Schiff’s base ligand (L) [where L = {C6H4(N=CHC6H4OH)2}] in 1:2:1 stoichiometry in anhydrous refluxing toluene. The yellow solid complex was characterized by elemental analysis, FTIR, UV–visible, fluorescence and NMR (1H and 13C) spectra as well as by single-crystal XRD. The complex was processed to obtain nano-structured zirconia (ZrO2) by sol–gel technique, and oxide ceramic was subjected to powder XRD, TEM and EDX analyses. Further, the same zirconia was employed in preparing superhydrophobic PVDF–nano-ZrO2 composite coatings by spray coating method, and the effect of nano-oxide ceramic on the wettability of PVDF–nano-ZrO2 composite coatings was studied systematically. The composite material was also characterized by FTIR and powder XRD.

Behavior of Titania Nanoparticles in Cross-linking Hydroxypropyl Guar Used in Hydraulic Fracturing Fluids For Oil Recovery

Fluids pumped in hydraulic fracturing operations constitute highly viscous gels achieved via cross-linking of the polysaccharide derivative hydroxypropyl guar (HPG), e.g., with titanium or zirconium complexes. In this study, the mechanism underlying the cross-linking effect was clarified experimentally for the titanium system. It was found that the cross-linking effect is not based on a ligand exchange reaction with the cis-hydroxy functionalities present in HPG but instead relies on TiO2 nanoparticles resulting from hydrolysis of the Ti complexes. For example, 6 nm titania nanospheres (anatase polymorph) synthesized via acid hydrolysis of tetraisopropyl orthotitanate can increase the viscosity of a HPG solution by a factor of 25. However, this effect was observed only at pH = 2–4 where the nanoparticles are stable. At higher pH values, electrostatic repulsion between the nanoparticles decreases, resulting in agglomeration as was observed via zeta potential and pH-dependent particle size measurement. Such...

Bis(benzothiazolyl) titanium, zirconium and vanadium complexes as catalysts for ethylene polymerization

13 titanium, zirconium and vanadium complexes with 1,1-bis(benzothiazolyl)methane, 1,2-bis(benzothiazolyl)-ethane, 1,2-bis(benzothiazolyl)benzene and 2,6-bis(benzothiazolyl) pyridine ligands were synthesized and characterized. After activation with methylalumoxane (MAO), these complexes proved as good catalysts for ethylene polymerization in spite of the hetero atoms in the catalyst molecules and the oxophilicity of the metals. Structure–property-relationship studies indicated that the bridging unit connecting the two heterocyclic moieties has a strong influence on the performance of the catalysts. Different interactions of the catalyst cation and the bulky MAO anion, due to the various hetero atoms, could be responsible for this behavior. The produced polyethylenes show bimodal or multimodal molecular weight distributions indicating more than one active site in the polymerization process. Therefore such mononuclear catalysts are good candidates for single-reactor bimodal or multimodal polyethylene technology. The polymerization activity of the catalyst system [1,2-bis(benzothiazolyl)benzene zirconium tetrachloride] 13/MAO was investigated under different polymerization conditions.

A luminescent mesoporous zirconium complex and it as a precursor of environmentally benign catalysts

Much attention should be paid to developing new materials for energy saving and environmentally benign catalysis. Herein we report the broad-band direct white-light emission originating from a single-phased and single-doped phosphor,i.e., a luminescent mesoporous zirconium oxy-hydroxy acetate–persulfate complex and the complex doped by Eu3+. The amorphous complexes exhibit the photoluminescence and color properties comparable to or better than those of the crystalline MOFs. The attracting feature of this route to white-light emission comes from the single-phased and single-doped phosphors that can be prepared through a low-cost chemical synthesis approach. In addition to photoluminescence, the complexes show useful textural properties. The pristine complex has been used as a precursor of environmentally benign catalysts in the esterification of lauric acid with methanol and in n-hexane isomerization.

Highly substituted zirconium and hafnium cyclopentadienyl bifunctional β-diketiminate complexes – Synthesis, structure, and catalytic activity towards ethylene polymerization

A series of tetramethyl-(Cp′) and pentamethylcyclopentadienyl (Cp*) metal complexes (η5-C5Me4R)ZrCl2LCO (R = H(1), Me(2)) and (η5-C5Me4R)HfCl2LCO (R = H(3), Me(4)) where LCO is a bifunctional β-diketiminate ligand [2-(MeO)–C6H4)]NC(Me)CHC(Me)N[2-(MeO)–C6H4)] (LCO) were prepared from corresponding tetramethyl- and (pentamethylcyclopentadienyl)metal trichlorides and the lithium precursor LiLCO. All complexes were characterized by their melting point, elemental analysis, 1H and 13C NMR spectroscopy, IR spectroscopy. In addition their solid-state structures were determined by X-ray diffraction techniques. In all cases, a pseudo-tetragonal pyramidal coordination environment of the metal centre with cyclopentadienyl ligand on the top and nearly isobidentately bonded nitrogen atoms of the chelating LCO ligand in an open η5-fashion was observed. The oxygen atoms positioned at the diketiminate periphery remained uncoordinated to transition metal in the solid phase as well as in solution.Besides the desired compounds, two hafnium complexes bearing either 2-methoxyaniline or 2-methoxyanilide ligands were isolated and structurally characterized as minor decomposition and dismutation products of 3 and 4, respectively.Complexes containing the β-diketiminate ligand as well as its precursors were tested for catalytic activity in the polymerization of ethylene using different activators (MAO, MMAO and AliBu3/(Ph3C)+ [B(C6F5)4]−). Among the new complexes, the best activity as high as 340 kgPE (molMhbar)−1 was achieved with 1/AliBu3/(Ph3C)+ [B(C6F5)4]− system.In attempts to clarify the activation process of group 4 metal-based precatalysts, the synthesis and NMR studies of the aluminium β-diketiminate complex Al(iBu)2LCO were also carried out.

Facile Carbothermal Reduction Synthesis of ZrB2 Nanoparticles: The Effect of Starting Precursors

Zirconium diboride (ZrB2) ceramic nanoparticles were synthesized by using zirconium (IV) complexes as new precursors. The citrate sol–gel process, which included the mixing of ions at the atomic scale, affected hydrolysis reactions and finally led to the formation of the pure phase of the sample. Results showed that the different sizes of ZrB2 nanocrystals were produced by adjusting four potential chelating agents of bi- and tetra-dentate (N2O2 donor set) ligands by the sol-gel process during carbothermal reduction. The samples were characterized by thermal gravimetric analysis (TGA), X-ray diffraction, fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The results obtained from microscopic observations indicated that pure and homogeneous ZrB2 nanostructures have been formed by using 2-hydroxyacetophenone (hap).

Effect of the Bridging Unit in Bis-( Benzoxazolyl ) Titanium , Zirconium and Vanadium Complexes on Catalytic Ethylene Polymerization Reactions

A series of 32 complexes of 1,1-bis-(benzoxazolyl)methane, 1,2-bis-(benzoxazolyl) ethane, 1,2-bis-(benzoxazolyl)benzene and 2,6-bis-benzoxazolyl)pyridine compounds with Ti(IV) chloride, Zr(IV) chloride and V(III) chloride was synthesized and characterized. After activation with methylaluminoxane (MAO), these complexes proved as good ethylene polymerization catalysts. Surprisingly the activities of the corresponding catalysts depend considerably on the nature of the bridging unit of the ligand. Structure property relationship studies revealed that titanium complex 16 with a methylene bridge gave the best performance.

ChemInform Abstract: Catalytic Asymmetric α‐Iminol Rearrangement: New Chiral Platforms.

AbstractAmong a series of 19 different asymmetric catalysts screened for the rearrangement of α‐hydroxy imines to α‐amino ketones, the zirconium complex of VANOL (ZRV) shows the best catalytic activity although aluminum and titan complexes of VANOL, VAPOL, and 7,7′‐tBu2VANOL are also quite effective.

Aluminabenzene–Zirconium Complexes: Intramolecular Coordination of Chloride to Aluminum

The reaction of the previously reported anionic aluminabenzene with zirconium chlorides (CpZrCl3, Cp*ZrCl3, and ZrCl4) gave novel zirconium complexes bearing aluminabenzene ligand(s). The X-ray crystallographic analysis of the resulting complexes revealed that the aluminabenzene ligand(s) coordinated to the zirconium center in an η5-fashion as a six-electron donor. Chloride ligand(s) on the zirconium center intramolecularly coordinated to the Lewis acidic aluminum atom in the aluminabenzene ring. The variable-temperature 1H NMR experiment showed a dynamic process for dissociation and recoordination of chloride to the aluminum center.

Group 4 Lanthanide and Actinide Organometallic Inclusion Complexes

Reaction of the f-element complexes ThCl4(THF)3, Cp*2Sm(μ-Cl)2MgCl(THF)2, NdCl3, Cp*2UMe2, and Cp*2ZrMe2 with an excess of catecholborane (HBCat) yields macrocyclic complexes where the metal is encapsulated inside a 15-membered, hexaoxo, trianionic macrocycle built from alternating catechol and catecholborate fragments. With ThCl4(THF)3 as the starting material, the reaction produced a macrocyclic complex with one chloride ligand and three solvent molecules in the apical positions; however, for the zirconium and uranium complexes the apical positions are occupied by one C5Me5 ligand and a THF solvent molecule. In the samarium and neodymium complexes, only solvent molecules occupy the apical positions. Transmetalation of the ligand among different complexes in refluxing THF were performed. When the zirconium macrocycle was treated with a slight excess of ThCl4 or NdCl3, the corresponding (η2-catechol-μ-catecholborate)3ThCl(C4H8O)3·C4H8O (2) and (η2-catechol-μ-catecholborate)3Nd(C4H8O)3·C4H8O (4) macrocycles were obtained in 87% and 79% yields, respectively. In addition, the reaction of the samarium macrocycle complex (η2-catechol-μ-catecholborate)3Sm(C4H8O)3·C4H8O (3) with a slight excess of ThCl4 allowed the formation of complex 2 in 76% yield. While some of the pentamethylcyclopentadienyl (Cp*)-containing inclusion complexes were found to be catalytically inactive in the polymerization of ε-caprolactone, the lanthanides and thorium complexes were found to be active, yielding only short chains of polycaprolactone. The X-ray molecular structures for all of the complexes are presented and discussed. Experiments performed with Cp*2ThMe2 and catecholborane allowed us to trap the intermediate Cp*(H)BH2BH2 complex, which was trapped in situ and characterized by 11B NMR, allowing us to propose a possible mechanism for the formation of the macrocycle.

ChemInform Abstract: Intermolecular Zirconium‐Catalyzed Hydrophosphination of Alkenes and Dienes with Primary Phosphines.

Catalytic hydrophosphination of terminal alkenes and dienes with primary phosphines (RPH2; R = Cy, Ph) under mild conditions has been demonstrated using a zirconium complex, [κ5-N,N,N,N,C-(Me3SiNCH2CH2)2NCH2CH2NSiMe2CH]Zr (1). Exclusively anti-Markovnikov functionalized products were observed, and the catalysis is selective for either the secondary or tertiary phosphine (i.e., double hydrophosphination) products, depending on reaction conditions. The utility of the secondary phosphine products as substrates for further elaboration was demonstrated with a platinum-catalyzed asymmetric alkylation reaction.