Hafnium Complexes Research Articles

Zirconium and Hafnium Complexes Bearing Tridentate ONN-Ligands: Extremely High Activity toward Ethylene (Co)Polymerization.

The pursuit of high-performance catalysts in the realm of polyolefins is a constant goal. In this study, a range of zirconium (1-ZrCl3, 2-ZrCl3, 3-ZrCl4, 12-Zr) and hafnium (1-HfCl3, 12-Hf) complexes featuring phenoxy-imine-amine ONN-ligands (2,6-R2-C6H3-NH-C6H4-N═CH-C6H2-3,5-tBu2-OH; 1-L: R = H; 2-L: R = F; 3-L: R = iPr) were synthesized and characterized using NMR spectroscopy, as well as single-crystal X-ray diffraction for 2-ZrCl3, 3-ZrCl4, and 12-Zr. These Zr and Hf complexes exhibited remarkable efficiency for ethylene homopolymerization and copolymerization with 1-octene when paired with MAO as the cocatalyst. Notably, the Zr complexes outperformed the Hf complexes with the same ligand, underscoring the substantial impact of the metal center on catalytic performance. The substituents and coordination modes of the ligands also exerted significant influence on the catalytic behavior, affecting both the activity and properties of the resulting polymers. Particularly noteworthy was the exceptional activity of 1-ZrCl3, achieving activity as high as 6.30 × 108 g(PE)·mol-1(Zr)·h-1 for ethylene homopolymerization and generating bi- or multimodal distribution polyethylene. The activation of 1-ZrCl3 by 5 or 20 equiv of d-MAO afforded a dinuclear Zr complex bridged by two chlorides (μ-Cl2-(1-ZrCl2)2), which was analyzed and confirmed by in situ 1H NMR spectroscopy and single-crystal X-ray diffraction.

Half-Sandwich Zirconium and Hafnium Amidoborane Complexes: Precursors of Hydride Derivatives.

Half-sandwich zirconium(IV) and hafnium(IV) complexes with amidoborane and hydride ligands have been isolated in the stoichiometric reactions of mono(pentamethylcyclopentadienyl)metal alkyl and amido derivatives with the amine-boranes NHR2BH3 (R2 = H2, Me2, HtBu). Treatment of the tris(trimethylsilylmethyl) complexes [M(η5-C5Me5)(CH2SiMe3)3] with NH3BH3 (3 equiv) gives the seven-coordinate species [M(η5-C5Me5)(NH2BH3)3] (M = Zr (1), Hf (2)) with three κ2N,H-NH2BH3 ligands. The tris(neophyl) [M(η5-C5Me5)(CH2CMe2Ph)3] or tris(dimethylamido) [M(η5-C5Me5)(NMe2)3] derivatives react with NHMe2BH3 (≥3 equiv) to afford bis(dimethylamidoborane) hydride complexes [M(η5-C5Me5)H(NMe2BH3)2] (M = Zr (3), Hf (4)) via thermally unstable [M(η5-C5Me5)(NMe2BH3)3] species. The reaction of [M(η5-C5Me5)(NMe2)3] and NH2tBuBH3 (≥4 equiv) affords analogous mixed amidoborane hydride derivatives [M(η5-C5Me5)H(NHtBuBH3)(NMe2BH3)] (M = Zr (5), Hf (6)) with κ2N,H-NHtBuBH3 and κ3N,H,H-NMe2BH3 ligands. The addition of NHR2BH3 (≥1 equiv) on the mono(dimethylamido) complexes [M(η5-C5Me5)Cl2(NMe2)] in hexane leads to the precipitation of the ionic compounds [(NHR2)2BH2][{M(η5-C5Me5)Cl2}2(μ-H)3] (R2 = Me2, M = Zr (7), Hf (8); R2 = HtBu, M = Zr (9), Hf (10)). Molecular hydride species [Cl2(η5-C5Me5)M(μ-Cl)(μ-H)2M(η5-C5Me5)Cl(NH2tBu)] (M = Zr (11), Hf (12)) could be isolated from mixtures of complexes [M(η5-C5Me5)Cl2(NMe2)] and lower ratios of NH2tBuBH3. The zirconium complex 11 decomposes in solution to give the mononuclear tert-butylamido derivative [Zr(η5-C5Me5)Cl2(NHtBu)] (13) along with other byproducts.

Synthesis of Amido-quinoline Hafnium and Zirconium Complexes with Improved Performances toward Ethylene/1-Octene Copolymerization

Synthesis of Amido-quinoline Hafnium and Zirconium Complexes with Improved Performances toward Ethylene/1-Octene Copolymerization

Synthesis and characterization of pyrrole-based group 4 PNP pincer complexes

The synthesis, characterization, and reactivity of several group 4 metal complexes featuring a central anionic pyrrole moiety connected via CH2 linkers to two phosphine donors is described. Treatment of [P(NH)P-iPr] with [MCl4(THF)2] (M = Zr, Hf) in the presence of base yields the dimeric complexes [M(PNPiPr)(μ-Cl)(Cl)2]2 featuring two bridging chloride ligands. These complexes react with sodium cyclopentadienyl and SiMe3I to give the mononuclear complexes [M(PNPiPr)(η5-Cp)(Cl)2] and [M(PNPiPr)(I)3], respectively. The latter react with MeMgBr to form the trialkyl complexes [M(PNPiPr)(Me)3]. Upon treatment of [Ti(NMe2)4] with [P(NH)P-iPr] a complex with the general formula [Ti(PNPiPr)(NMe2)3] is obtained. DFT calculations revealed that the most stable species is [Ti(κ1N- PNPiPr)(NMe2)3] featuring a κ1N-bound PNP ligand. When [P(NH)P-iPr] is reacted with [Ti(NMe2)4] in CH2Cl2 complex [Ti(PNPiPr)(Cl)2(NMe2)] is formed. Treatment of a solution of [P(NH)P-iPr] and [Zr(NMe2)4] with SiMe3Br affords the anionic seven-coordinate tetrabromo complex [Zr(PNPiPr)(Br)4][H2NMe2]. The corresponding hafnium complex [Hf(PNPiPr)(Br)4][H2NEt2] is obtained in similar fashion by utilizing [Hf(NEt2)4] as metal precursor. All complexes are characterized by means of NMR spectroscopy. Representative complexes were also characterized by X-ray crystallography.Graphical abstract

Hafnium Complexes as Contrast Media and Dose Enhancing Agents for Radiology and Contrast-Enhanced Radiotherapy

Hafnium Complexes as Contrast Media and Dose Enhancing Agents for Radiology and Contrast-Enhanced Radiotherapy

Synthesis of dinuclear pyridyl-amido hafnium and zirconium complexes toward olefin polymerization with unexpected stereospecificity and ultra-high molecular weight capability

Dinuclear syn-Hf2 exerts an unexpected stereospecificity toward propylene polymerization and affords ultra-high molecular weight atactic polypropylene as a thermoplastic elastomer.

Amidoxime-Containing Zr and Hf Atomic Layer Deposition Precursors for Metal Oxide Thin Films.

In this article, we discuss the synthesis of eight novel zirconium and hafnium complexes containing amidoxime ligands as potential precursors for atomic layer deposition (ALD). Two amidoximes, viz., (E)-N'-hydroxy-N,N-dimethylacetimidamide (mdaoH) and (Z)-N'-hydroxy-N,N-dimethylpivalimidamide (tdaoH), along with their Zr and Hf homoleptic complexes, Zr(mdao)4 (1), Hf(mdao)4 (2), Zr(tdao)4 (3), and Hf(tdao)4 (4) were prepared. We further synthesized heteroleptic compounds with different physical properties by introducing cyclopentadienyl (Cp) ligand, namely, CpZr(mdao)3 (5), CpHf(mdao)3 (6), CpZr(tdao)3 (7), and CpHf(tdao)3 (8). Thermogravimetric analysis was used for the assessment of the evaporation characteristics of complexes 1, 2, 5, and 6, and it revealed multistep weight losses with high residues. On the other hand, the thermogravimetric analysis curves of complexes 3, 4, 7, and 8 comprising tdao ligands revealed single-step weight losses with moderate residues. Single-crystal X-ray diffraction studies of complexes 1, 3, and 7 showed that all of the complexes have monomeric molecular structures. Complex 7 exhibited a low melting point (75 °C), good volatility, and high thermal stability compared with other complexes. Therefore, an atomic layer deposition process for the growth of ZrO2 was developed by using ZrCp(tdao)3 (7) as a novel precursor.

Hafnium and Zirconium Complexes Bearing ONN-Tridentate Ligands and Their Catalytic Properties toward Olefin Polymerization

Hafnium and Zirconium Complexes Bearing ONN-Tridentate Ligands and Their Catalytic Properties toward Olefin Polymerization

Novel bimetallic oxido-bridged phenolato hafniumIV complex with enhanced anti-tumor activity and aqueous stability

A novel dimeric phenolato Hafnium complex [{HfIV(Salan2,4-Me)(OnBu)}2O] was synthesized by reacting [HfIV(Salan2,4-Me)2] in the presence of 100 equiv. of H2O. The structure was characterized by 1H, 13C NMR spectroscopy, HRMS and X-Ray diffraction. In comparison with [HfIV(Salan2,4-Me)2] and another precursor [{HfIV(Salan2,4-Me)(OnBu)}2O], this dimeric HfIV complex demonstrated enhanced aqueous stability and anti-tumor activity (IC50: 71.2 ± 25.3 μM against Hela S3 cells; 62.2 ± 27.7 μM against Hep G2 cells). Furthermore, this dimeric HfIV complex can only be synthesized from [HfIV(Salan2,4-Me)2] in low equivalent of H2O, upon addition of 2,6-dipicolinic acid, it can be transformed to a Salan/Dipic HfIVbis-chelated complex.

Jellyfish-type Dinuclear Hafnium Azido Complexes: Synthesis and Reactivity.

Di- and multinuclear hafnium complexes bridged by ligands have been rarely reported. In this article, a novel 3,5-disubstituted pyrazolate-bridged ligand LH5 with two [N2 N]2- -type chelating side arms was designed and synthesized, which supported a series of dinuclear hafnium complexes. Dinuclear hafnium azides [LHf2 (μ-1,1-N3 )2 (N3 )2 ][Na(THF)4 ] 3 and [LHf2 (μ-1,1-N3 )2 (N3 )2 ][Na(2,2,2-Kryptofix)] 4 were further synthesized and structurally characterized, featuring two sets of terminal and bridging azido ligands like jellyfishes. The reactivity of 3 under reduction conditions was conducted, leading to a formation of a tetranuclear hafnium imido complex [L1 Hf2 (μ1 -NH)(N3 ){μ2 -K}]2 5. DFT calculations revealed that the mixed imido azide 5 was generated via an intramolecular C-H insertion from a putative dinuclear HfIV -nitridyl intermediate.

Peculiarities of fluoride activation of porphyrin and phthalocyanine catalysts by the example of zirconium and hafnium in the production of cyclic carbonates

In this work, we have shown that fluoride additives can increase the catalytic activity of even 5- and 6-period metal complexes. Using tetraphenylporphyrin and phthalocyanine hafnium complexes as an example we were able to lower catalyst loading to 500 ppm. It was found out that after reaction tetraphenylporphyrin complex decomposed with the formation of meso‑tetraphenylporphyrin. Such process did not occur with the phthalocyanine complex. Moreover, in the presence of the fluoride additive hafnium tetrachloride showed high catalytic activity similar to both tetraphenylporphyrin and phthalocyanine comlpexes.

Synthesis and physicochemical properties of tin(IV), zirconium(IV), and hafnium(IV) 2(3),9(10),16(17),23(24)-tetrakis-(4-tritylphenoxy)phthhalocyaninates

The reaction of 4-tritylphenoxyphthalonitrile with SnCl2, ZrCl4 and HfCl4 in the presence of urea under ammonium molybdate catalysis was used to synthesize tetrakis-(4-tritylphenoxy)phthalocyaninates of tin(IV), zirconium(IV), and hafnium(IV). The complexes were characterized by spectral methods of analysis, including mass spectrometry, 1Н NMR, vibrational and electron spectroscopy. All of them form J -type dimer associates in chloroform at concentrations up to ~1.5×10-6 mol/L and lower, are not associated in a mixture of toluene and pyridine up to concentrations of ~3×10-5 mol/L and higher, have catalytic activity in electroreduction reactions of molecular oxygen. The complexes of zirconium and hafnium showed the highest activity. Tin and zirconium complexes are thermally stable in an inert atmosphere up to a temperature of 200°C.

Anti-tumoral Titanium(IV) Complexes Stabilized with Phenolato Ligands and Structure-Activity Relationship.

Titanocene dichloride and budotitane have opened a new chapter in medicinal chemistry of titanium(IV) complexes being novel non-platinum antitumor metallic agents. Numerous efforts have led to the discovery of the diamino bis-phenolato titanium(IV) complexes. Among which, the [ONNO] and [ONON] type ligands namely Salan, Salen and Salalen coordinated titanium(IV) alkoxyl complexes have demonstrated significantly enhanced aqueous stability, their in vitro and in vivo antitumor efficacy, mechanism of action, structure-activity relationships and combined tumor therapy have been intensively investigated. Replacement of the labile alkoxyls with a second chelator resulted in structural rigid titanium(IV) complexes, which showed exceedingly good aqueous stability and potent antitumor activity both in vitro and in vivo. The unique ligand system successfully allowed the access of isotopic [45Ti]Titanium(IV) complexes, post-synthetic modification, facile synthetic protocols and antitumor congeneric zirconium(IV) and hafnium(IV) complexes. This review presents recent research progress in the field of antitumor group 4 metal complexes stabilized with phenolato ligands; especially their structure-activity relationships are summarized.

Molecular Layer Deposition of Organic–Inorganic Hafnium Oxynitride Hybrid Films for Electrochemical Applications

The molecular layer deposition (MLD) method can be used to deposit hybrid organic–inorganic films with precisely defined composition, flexible properties, and conformality on different substrates. In this study, hafnium-based organic–inorganic hybrid polymer films were studied as potential coatings for silicon nanoparticles (SiNPs) used in composite lithium-ion battery (LIB) anodes, an application which requires the film to be both flexible and stable under electrochemical conditions. Hf-hybrid films were successfully deposited by MLD using sequential exposure of the homoleptic tetrakis(dimethylamido) hafnium complex and ethanolamine as the reactants. The self-limiting surface reactions lead to a constant growth per cycle (GPC) of ∼2.0 Å/cycle at 120 °C. Temperature-dependent growth was observed, with the GPC decreasing from ∼2.5 to ∼1.1 Å/per cycle as the temperature was increased from 65 to 145 °C. Scanning transmission electron microscopy and electron energy loss spectroscopy mapping confirm that a thin, dense, and conformal Hf-based MLD layer is deposited on the SiNPs. The presence of expected C–N, C–O, and −CH2 moieties in the MLD films was confirmed by Fourier transform infrared spectroscopy. Hafnium nitride and hafnium oxide bonds within the hybrid thin films were identified by X-ray photoelectron spectroscopy. Characterization results indicated that the deposited hafnium-based organic–inorganic hybrid films contain both metal oxynitride bonds and organic bonds, including C–C, C–O, and C–N. This Hf-based MLD thin film was tested on LIB SiNP composite anodes as an artificial solid–electrolyte interphase, with results showing that the capacity retention increased by about 35% after 110 cycles in a LIB application.

ZIRCONIUM AND HAFNIUM DIHYDROXY­PHTHALO­CYANINATES: METHODS OF SYNTHESIS AND REACTIVITY

Usually in order to obtain out-of-plane sub­stituted phthalocyanine complexes of zirconium and hafnium (PcML2), the reaction of substitution of chlorine atoms in dichloridophthalocyaninates PcMCl2 is used. How­ever, this method has some limitations because during this reaction, hydrogen chloride is released, which can initiate the hydrolysis of starting compounds sensitive to an acidic environment, in particular, β-ketoesters, which, in turn, can lead to the formation of by-pro­ducts and, accordingly, to a decrease purity and yield of target complexes. At the same time, in similar reactions in which the initial phthalocyanine compounds are dihydroxyphthalocyaninates of zirconium and hafnium (PcM(OH)2), as a result of interaction with dicarbonyl compounds or carboxylic acids, water is formed, which does not have a negative effect on the starting substances or on the course of the reaction as a whole. Methods of obtaining zirconium and hafnium dihydroxyphthalocyaninates based on metal alkoxides and by hydrolysis of the corresponding PcMCl2 were investigated in the work. It was established that the synthesis of PcM(OH)2 based on the corresponding alkoxides occurs with low yields (25–40%), increasing the reaction temperature from 140 to 220oC does not lead to their significant increase. It was found that the hydrolysis of PcMCl2 should be carried out under more stringent conditions than previously described, which makes it possible to obtain PcM(OH)2 with high yields.
 The reactivity of PcM(OH)2 was investigated when interacting with β-diketones and aliphatic carboxylic acids and compared with the reactivity of PcMCl2. It was established that the reactivity of PcM(OH)2 is similar to PcMCl2. However, it should be noted that in the case of the synthesis of β-ketoesterphthalocyanine complexes, the use of the corresponding PcM(OH)2 leads to a significant increase in the yield of the final products of the reaction compared to PcMCl2. This effect can be explained by the fact that hydrogen chloride is not released during the reaction with PcM(OH)2 and, accordingly, hydrolysis of the ester group does not occur.

Organometallic Intermediates in the Synthesis of Photoluminescent Zirconium and Hafnium Complexes with Pyridine Dipyrrolide Ligands.

The two commercially available zirconium complexes tetrakis(dimethylamido)zirconium, Zr(NMe2)4, and tetrabenzylzirconium, ZrBn4, were investigated for their utility as starting materials in the synthesis of bis(pyridine dipyrrolide)zirconium photosensitizers, Zr(PDP)2. Reaction with one equivalent of the ligand precursor 2,6-bis(5-methyl-3-phenyl-1H-pyrrol-2-yl)pyridine, H2MePDPPh, resulted in the isolation and structural characterization of the complexes (MePDPPh)Zr(NMe2)2thf and (MePDPPh)ZrBn2, which could be converted to the desired photosensitizer Zr(MePDPPh)2 upon addition of a second equivalent of H2MePDPPh. Using the more sterically encumbered ligand precursor 2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine, H2MesPDPPh, only ZrBn4 yielded the desired bis-ligand complex Zr(MesPDPPh)2. Careful monitoring of the reaction at different temperatures revealed the importance of the organometallic intermediate (cyclo-MesPDPPh)ZrBn, which was characterized by X-ray diffraction analysis and 1H NMR spectroscopy and shown to contain a cyclometalated MesPDPPh unit. Taking inspiration from the results for zirconium, syntheses for two hafnium photosensitizers, Hf(MePDPPh)2 and Hf(MesPDPPh)2, were established and shown to proceed through similar intermediates starting from tetrabenzylhafnium, HfBn4. Initial studies of the photophysical properties of the photoluminescent hafnium complexes indicate similar optical properties compared to their zirconium analogues.

Synthesis of Si‐O‐Si bridged diamido Group 4 complexes and the applications to polymerization of olefins

Titanium, zirconium, and hafnium complexes O[Me2Si(Dip)N]2MCl2 [Dip = 2,6‐iPr2C6H3; M = Ti (1), Zr (2), Hf (3)], O[Me2Si(tBu)N]2ZrCl2 (4), and O[iPr2Si(Dip)N]2ZrCl2 (5) supported by Si‐O‐Si bridged diamido ligands were synthesized. X‐ray diffraction analysis disclosed that complex 2 displays a distorted trigonal bipyramidal geometry. Complexes 1–5, upon the activation with sMAO, exhibited diverse catalytic performance for the polymerization of ethylene and copolymerization of ethylene with norbornene or 1‐octene. For ethylene homopolymerization, both complexes 1–2 are good catalysts giving polymer with high molecular weight and narrow polydispersities. Complex 2 catalyzed copolymerization of ethylene with 1‐octene exhibiting high catalytic activity but with norbornene showing moderate activity, affording corresponding high molecular weight copolymers with relatively high comonomer incorporations of 11% and 29%, respectively.

Synthesis of Ethylene-Bridged Bis(indenyl) Zirconium, Hafnium Complexes and Their Catalytic Behavior on Selective Propylene Oligomerization: the Effect of 3-Substituent on Indenyl Ring

Synthesis of Ethylene-Bridged Bis(indenyl) Zirconium, Hafnium Complexes and Their Catalytic Behavior on Selective Propylene Oligomerization: the Effect of 3-Substituent on Indenyl Ring

Synthesis and X-ray structure analysis of cytotoxic heptacoordinated Salan hafnium(IV) complexes stabilized with 2,6-dipicolinic acid

Four novel Salan Hf(IV) complexes stabilized by 2,6-dipicolinic acid (Dipic) were synthesized and characterized by 1H, 13C NMR and X-ray diffraction spectroscopy. These Hf(IV)bis-chelates could be obtained in good to excellent yields (88%–91%) and demonstrated rather good stability in aqueous media and on silica gel. [L2Hf(IV)Dipic4-H,Cl] containing steric bulk L2 were stable in about 10% H2O (H2O/THF (v/v)), however, [L1Hf(IV)Dipic4-H,Cl] with non-steric L1 could slowly dissociate and release nontoxic L1. [L1–2Hf(IV)Dipic4-Cl] showed excellent anti-tumoral activity in the range of cisplatin (Hela S3: IC50 = 3.5 ± 0.4 μM, Hep G2: IC50 = 11.2 ± 2.1 μM). In addition, the cellular uptake and apoptosis investigation of [L1Hf(IV)Dipic4-Cl] suggested a fast cellular uptake process against Hela S3 cells with an almost exclusive induced apoptosis cell death path.

On the Ratio of Cathodic and Anodic Processes during Electroreduction-Electrooxidation of Hafnium in Molten Salts

Investigation of hafnium cathodic and anodic processes in chloride melts containing HfCl4 revealed that two-hafnium electroreduction processes are corresponded two electrooxidation processes. The only difference between these processes was the presence of salt passivation under certain dissolution conditions. In chloride-fluoride melts containing K2HfF6 the number of cathodic and anodic processes can be different due to the amount of hafnium ions passing into the melt during anodic dissolution exceeding the amount of fluorine anions necessary to bind them into fluoride complexes. Based on the experimental data it was found that the conclusion about the mirror reflection of cathodic and anodic processes is invalid in the case of a heteroligand composition of melts. It was determined that the dissolution in the NaCl-KCl-K2HfF6 (10 wt%) melt at the anodic current density of >0.02 А∙cm−2 was accompanied by the formation of Hf(IV) fluoride complexes and Hf(II) chloride complexes. It was shown that the appearance of hafnium complexes with different valence during anodic process in the NaCl-KCl-K2HfF6 (10 wt%) melt is a highly undesirable phenomenon, which leads to the formation of metallic film on the surface of the melt decreasing the current efficiency for coating deposition.