Zirconium Complexes Research Articles

Dissymmetric ansa zirconocene complexes with di- and trisubstituted indenyl ligands as catalysts for homogeneous ethylene homo- and ethylene/1-hexene copolymerization reactions

Different routes for the synthesis of 1,2- and 1,2,3-substituted indene derivatives are described. Representative substituents are: Me, Ph, PhCH2, PhCH2CH2, PhCH2CH2CH2, CH2CH=CH2. Subsequent deprotonation of these substituted indenes and reaction with indenyl zirconium trichloride gave the corresponding dissymmetric bis(indenyl) zirconium complexes. After activation with methylaluminoxane (MAO) these complexes show high activities both in ethylene homopolymerisation and ethylene/1-hexene copolymerisation. The rate of comonomer incorporation can reach 33.3% (15/MAO). The copolymers exhibit lower melting points than the homopolymers and their crystallinities α are lower compared with the homopolymers.

Immortal ring-opening polymerization of lactides with super high monomer to catalyst ratios initiated by zirconium and titanium complexes containing multidentate amino-bis(phenolate) ligands

Zirconium and titanium complexes containing amino-bis(phenolate) ligands were prepared. These complexes are highly active initiators for the ring-opening polymerization of lactide. And two zirconium complexes are highly active and excellent catalysts for immortal ring-opening polymerization of lactide.

Zirconium complexes based on an ethylene linked amidinate–amido ligand: synthesis, characterization and ethylene polymerization

Monomer/dimer zirconium complexes 4–6 were synthesized by changing the molar ratio of ZrCl4 : ligand. The catalytic behaviors of these zirconium complexes were investigated in the presence of MAO as a cocatalys.

Zirconium and hafnium complexes bearing pyrrolidine derived salalen-type {ONNO} ligands and their application for ring-opening polymerization of lactides.

The reactions of pyrrolidine derived salalen-type {ONNO} ligands (S)-L1-3-H2 with 1 equiv. M(OiPr)4(HOiPr) (M = Zr or Hf) in diethyl ether yielded complexes [L1-3M(OiPr)2] (L = L1, M = Zr (1); L = L2, M = Zr (2), Hf (3); L = L3, M = Zr (4), Hf (5)). All of these complexes were well characterized by NMR spectroscopy, elemental analyses and single-crystal X-ray analysis in the case of complexes 1 and 3-5. X-ray structural determination revealed that these complexes were analogous mononuclear species and had a similar structure in which the metal centers were six-coordinated to two oxygen atoms and two nitrogen atoms of one ligand and two oxygen atoms of two isopropoxy groups. All of these complexes efficiently initialized the ring-opening polymerization of lactides to afford polymers with controlled molecular weight and narrow polydispersity. Furthermore, the ring-opening polymerization of rac-lactide catalyzed by complexes 1-5 afforded isotactic-enriched polymers in solution (Pm = 0.74-0.80) and under melt conditions (Pm = 0.63-0.72).

Preparation of zirconium and hafnium complexes containing chiral N atoms from asymmetric tertiary amine ligands, and their catalytic properties for polymerization of rac-lactide

Preparation of Zr and Hf complexes containing chiral N atoms, and their use in polymerization of rac-lactide.

Benzylene-linked [PNP] scaffolds and their cyclometalated zirconium and hafnium complexes.

The benzylene-linked [PNP] scaffolds HN(CH2-o-C6H4PPh2)2 ([A]H) and HN(C6H4-o-CH2PPh2)2 ([B]H) have been used for the synthesis of zirconium and hafnium complexes. For both ligands, the dimethylamides [A]M(NMe2)3 ([A]1-M) and [B]M(NMe2)3 ([B]1-M) were prepared and converted to the iodides [A]MI3 ([A]2-M) and [B]MI3 ([B]2-M) (M = Zr, Hf). Starting from these iodides, the corresponding benzyl derivatives [A]MBn3 ([A]3-M) and [B]MBn3 ([B]3-M) (M = Zr, Hf) were obtained via reaction with Bn2Mg(OEt2)2. For zirconium, the benzylic ligand positions in [A]3-Zr and [B]3-Zr were found to cyclometalate readily, which led to the corresponding κ4-[PCNP]ZrBn2 complexes [A]4-Zr and [B]4-Zr. As these complexes failed to hydrogenate cleanly, cyclometalated derivatives with only one alkyl substituent were targeted and the mixed benzyl chlorides κ4-[PCNP]MBnCl ([B]5-M, M = Zr, Hf) were obtained in the case of ligand [B]. Upon hydrogenation of [B]5-Zr, the η6-tolyl complex [B]Zr(η6-C7H8)Cl ([B]6-Zr) was generated cleanly, but the corresponding hafnium complex [B]5-Hf was found to decompose unselectively in the presence of H2. Using a closely related carbazole-based [PNP] ligand, Gade and co-workers have shown recently that zirconium η6-arene complexes similar to [B]6-Zr may serve as zirconium(ii) synthons, namely when reacted with 2,6-Dipp-NC (L) or pyridine (py). Both these substrates were shown to react cleanly with [B]6-Zr, which led to the formation of the bis-isocyanide complex [B]ZrCl(L)2 ([B]7-Zr) and the 2,2'-bipyridine derivative [B]ZrCl(bipy) ([B]8-Zr), respectively. Upon reaction of [B]Zr(η6-C7H8)Cl ([B]6-Zr) with NaBEt3H, the cyclometalated derivative κ4-[PCNP]Zr(η6-C7H8) ([B]9-Zr) was isolated. In an attempt to synthesise terminal hydrides, complexes [A]MI3 ([A]2-M) were treated with KBEt3H, which led to the isolation of the cyclometalated hydrido complexes κ4-[PCNP]M(H)(κ3-Et3BH) ([A]10-M; M = Zr, Hf) featuring a κ3-bound triethyl borohydride moiety.

Coordination behavior of bis-phenolate saturated and unsaturated N-heterocyclic carbene ligands to zirconium: reactivity and activity in the copolymerization of cyclohexene oxide with CO2.

Tetravalent zirconium complexes supported by tridentate bis-phenolate imidazolidin-2-ylidene (L1), imidazol-2-ylidene (L2) and benzimidazol-2-ylidene (L3) NHC ligands were synthesized and evaluated as precursors for the copolymerization of cyclohexene oxide (CHO) with CO2. While the reactivity of the imidazolidinium [H3L1] chloride salt with Zr(OiPr)4(HOiPr), and subsequent ligand exchanges with either (CH3)3SiCl or LiOiPr lead to a series of heteroleptic compounds (κ3-O,C,O-L1)Zr(X)2(THF) (X = Cl, OiPr), both imidazolium [H3L2] and benzimidazolium [H3L3] chloride salts give a mixture of homoleptic (κ3-O,C,O-NHC)2Zr and zwitterionic (κ2-O,O-HL)ZrCl2(OiPr) compounds along with traces or the absence of the heteroleptic intermediate (κ3-O,C,O-NHC)Zr(Cl)(OiPr)(THF). Such dissimilar reactivity between the unsaturated and saturated NHC ligands is predominantly ascribed to the increased acidity of azolium salts along with the π-donor strength of the Ccarbene in L2 and L3-Zr moieties. The reactivity with the more acidic azolium salts (H3L2/3) and the destabilized Zr-Xtrans to NHCcarbene bond results in a significant increase in the amount of homoleptic compounds generating HCl. The released HCl reacts preferentially with the heteroleptic intermediates having non-planar NHC ligands (i.e. L2/3) promoting the formation of zwitterionic complexes. The in situ deprotonation of the isolated zwitterionic (κ2-O,O-HL3)ZrCl2(OiPr) compound by using Ag2O gives the homoleptic complex as the major component along with a bimetallic hydroxo-bridged [(κ3-O,C,O-L3)Zr(μ-OH)(OiPr)]2 compound. Of particular interest is that only the heteroleptic NHC-Zr(iv) complexes were identified to be active and highly selective towards the copolymerization of CHO with CO2 independently of the co-catalysts used (both anionic and neutral) under mild conditions (PCO2 < 1 bar, T = 60 °C), and gave atactic and completely alternating copolymers in a controlled manner (Mw/Mn ≈ 1.3-1.8). In contrast, the isolated homoleptic, zwitterionic and bimetallic zirconium species were found to be inactive under similar reaction conditions. Although the activity found for NHC-Zr(iv) complexes is nearly of the same order of magnitude as that of the NHC-Ti(iv) analogues, these results are the first examples of tetravalent zirconium complexes achieving high selectivity (99% in PCHC) in the catalyzed copolymerization of CHO with CO2.

Летучие комплексы циркония со стерически затрудненными β-дикетонатами: структура и термические свойства

Летучие комплексы циркония со стерически затрудненными β-дикетонатами: структура и термические свойства

Regioselective addition of C(sp3)-H bonds of alkyl pyridines to olefins catalysed by cationic zirconium complexes.

In situ generated cationic zirconium complexes stabilized by amine-bridged bis(phenolato) ligands have been developed to catalyse C(sp3)-H addition of alkyl pyridines to olefins, which are the first examples of group 4 metal based catalysts in this transformation. Ligand-controlled regioselectivity was observed, which was verified by DFT study.

Oligomerization of ethylene in the presence of heterogenized complex catalytic systems based on ionic liquid‐type substituted zirconium phenolates

The oligomerization of ethylene was investigated in the presence of novel catalytic systems consisting of alkylaluminium chlorides and heterogenized zirconium phenolates containing amino and imino hydrochloride substituents. It was determined that the composition of a synthesized oligomer and the activity or selectivity of the catalyst systems depend on various parameters such as the molar ratio of Zr:Al, the composition of alkylaluminium, the temperature of the reaction, the pressure of ethylene and the structure of zirconium phenolates. The results showed that C4‐C10 linear α‐olefins were obtained with high selectivity when diethylaluminium chloride was used as a co‐catalyst. The process of the separation of a synthesized oligomer from the catalyst containing amino and imino hydrochloride ionic liquid substituents was carried out by simple decantation, and after this process zirconium complexes could be reused several times for successive ethylene oligomerizations.

Phosphanylphosphido and phosphanylphosphinidene complexes of zirconium(IV) supported by bidentate N,N ligands

Phosphanylphosphido complexes of zirconium, [NacNacZrCl2(η2-R2P–PSiMe3)] (R=t-Bu, i-Pr), were synthesized in the reaction of R2P–P(SiMe3)Li·nTHF (R=t-Bu, i-Pr) with a β-diketiminate complex, [NacNacZrCl3], in toluene. Elimination of Me3SiCl from [NacNacZrCl2(η2-R2P–PSiMe3)] provided the phosphanylphosphinidene complexes [NacNacZrCl(η2-R2P–P)] (R=t-Bu, i-Pr). Moreover, the reaction of [NacNacZrCl2(η2-R2P–PSiMe3)] with R2P–P(SiMe3)Li·nTHF yielded the phosphanylphosphinidenoid complexes [NacNacZrCl2(η2-R2P–PLi)] (R=t-Bu, i-Pr). The same reaction, but in the presence of 12-crown-4, gave rise to the phosphanylphosphinidene complexes [NacNacZrCl(η2-R2P–P)]. The X-ray structures of [NacNacZrCl2(η2-i-Pr2P–PSiMe3)] and [NacNacZrCl(η2-t-Bu2P–P)] revealed that the R2P-P ligands exhibit side-on coordination to the metal center. From the reaction of i-Pr2P–P(SiMe3)Li·3THF with [{PhN(CH2)3NPh)}ZrCl2], a triple-core, anionic, phosphanylphosphinidene complex, [{PhN(CH2)3NPh)}Zr3Cl2(μ2-Cl)(μ2-i-Pr2P–P)2(μ3-i-Pr2P–P)2]−[Li(DME)3]+, was obtained in which the i-Pr2P–P ligands exhibit bridging coordination.

Volatile zirconium compounds: Prospects for use in gas-phase isotope separation

Data on volatile zirconium(IV) complexes are considered from the viewpoint of search for compounds exhibiting the required thermal parameters for centrifugal separation of stable isotopes. The results of studies concerning thermodynamics of vaporization of volatile zirconium compounds with inorganic and organic ligands are summarized and analyzed. The influence of the electronic structure of the central atom and of the molecular and crystal structure on the volatility of zirconium compounds is discussed. Promising lines of searching for volatile zirconium compounds for the development of low-activation materials based on isotopically altered elements are outlined.

B-site substituted solid solutions on the base of sodium-bismuth titanate

The paper presents results of studies of the formation of phases during the solid-state synthesis in the [([Formula: see text] system of solid solutions with [Formula: see text]-site substitutions. The substitutions by zirconium, tin and ion complexes (In[Formula: see text]Nb[Formula: see text] and (Fe[Formula: see text]Nb[Formula: see text] have been studied. It has been found that the synthesis is a multi-step process associated with the formation of a number of intermediate phases (depending on the compositions and calcination temperatures). Single-phase solid solutions have been produced at the calcination temperatures in the interval 1000–1100[Formula: see text]C. An increase in the substituting ions concentration leads to a linear increase of the crystal cell size. At the same time, the tolerance factor gets reduced boosting the stability of the antiferroelectric phase as compared to that of the ferroelectric phase.

ChemInform Abstract: Zirconocene‐Mediated Carbonylative Coupling of Grignard Reagents.

AbstractThe transmetalation of Grignard reagents with zirconocene dichloride under a CO atmosphere generates acyl zirconium(IV) complexes that are inaccessible with the Schwartz reagent, including those derived from secondary and tertiary alkyl and aryl Grignard reagents.

Design of Efficient Molecular Catalysts for Synthesis of Cyclic Olefin Copolymers (COC) by Copolymerization of Ethylene and α-Olefins with Norbornene or Tetracyclododecene

Selected results for the synthesis of cyclic olefin copolymers (COCs)—especially copolymerizations of norbornene (NBE) or tetracyclododecene (TCD) with ethylene and α-olefins (1-hexene, 1-octene, 1-dodecene)—using group 4 transition metal (titanium and zirconium) complex catalysts have been reviewed. Half-titanocenes containing an anionic ancillary donor ligand, Cp’TiX2(Y) (Cp’ = cyclopentadienyl; X = halogen, alkyl; Y = anionic donor ligand such as aryloxo, ketimide, imidazolin-2-iminato, etc.), are effective catalysts for efficient synthesis of new COCs; ligand modifications play an important role for the desired copolymerization. These new COCs possess promising properties (high transparency, thermal resistance (high glass transition temperature), low water absorption, etc.), thus it is demonstrated that the design of an efficient catalyst plays an essential role for the synthesis of new fine polyolefins with specified properties.

A tripodal aminothioether ligand scaffold: Synthesis and coordination to zirconium and hafnium

The heptadentate ligand, tris-(2-(2-(methylthio)phenylamino)ethyl)amine (2), has been synthesized from the condensation of nitrilotriacetyl chloride with 2-(methylthio)aniline, to generate 2,2′,2″-nitrilotris(N-(2-(methylthio)phenyl)acetamide) (1), followed by a lithium aluminum hydride reduction. The zirconium (3) and hafnium (4) complexes of this ligand were generated via transamination reactions. Both complexes are isostructural, exhibiting a hexadentate N4S2 coordination from the ligand, with one diethylamido ligand also bound. The solid state structures of all compounds are reported.

Aminopyridine stabilized group-IV metal complexes and their applications

During the last two decades, group-IV metals-based aminopyridinato complexes have attracted a tremendous research interest because of immense industrial needs for the catalyst which would be of higher activity and selectivity with lower toxicity and lower cost. Chemistry of titanium (Ti) and zirconium (Zr) complexes was more extensively explored as compared to hafnium (Hf) complexes. Direct synthesis, salt metathesis, amine elimination, alkane elimination, silyl chloride elimination, hydrogen chloride elimination and toluene elimination protocols have been used for the synthesis of group-IV metal complexes. Changes in ligand and complex design were made to optimize these catalysts for olefin polymerization. Most of these complexes have shown good catalytic activities when activated with dry methyl aluminoxane. Ligand transfer to aluminum was found in these complexes, particularly with less bulky ligands, and this ligand transfer problem was overcome by tridentate ligands but the activities of these complexes were not competitive to complexes with bidentate aminopyridinato ligands. Majority of these complexes produce high-molecular-weight polymers with broader molecular weight distributions, and Hf-complexes produce longer chain polymers than their comparative Ti and Zr aminopyridinato complexes. It could be deduced that group-IV metals inherit the potential for optimal polymerizing catalysts probably, because of their almost vacant d-orbitals, these act as hard acids which on combination with soft bases carry the opportunity to design and develop polymerization catalysts which could overcome the problems associated with existing systems.

A Luminescent Zirconium(IV) Complex as a Molecular Photosensitizer for Visible Light Photoredox Catalysis

Titanium and zirconium complexes carrying two 2,6-bis(pyrrolyl)pyridine ligands have been synthesized and characterized. The neutral complexes Ti(MePDP)2 and Zr(MePDP)2 (MePDP = 2,6-bis(5-methyl-3-phenyl-1H-pyrrol-2-yl)pyridine) show intense ligand-to-metal charge-transfer bands in the visible region and undergo multiple reversible redox events under highly reducing conditions. Zr(MePDP)2 exhibits photoluminescent behavior and its excited state can be quenched by mild reductants to generate a powerful electron transfer reagent with a ground state potential of -2.16 V vs Fc+/0. This reactivity was utilized to facilitate dehalogenation reactions, the reduction of electron-poor olefins, and the reductive coupling of benzyl bromide via photoredox catalysis. In these reactions, the earth-abundant metal complex Zr(MePDP)2 acts as a substitute for the precious metal photosensitizer [Ru(bpy)3]2+.

Enantio- and Stereoselective Cyclopolymerization of Hexa-1,5-diene Catalyzed by Zirconium Complexes Possessing Optically Active Bis(phenolato) Ligands.

Enantio- and stereoselective cyclopolymerization of hexa-1,5-diene was achieved by enantiomerically pure dichloro zirconium(IV) pre-catalysts 2 possessing chiral [OSSO]-type bis(phenolate) ligands (-)-1 and (+)-1 in combination with dried methylaluminoxane (dMAO) as an activator. The corresponding activities were recorded with quite high values up to 1,960 g mmol(2)-1 h-1 , which are extremely larger than those of the related complexes. The microstructure analysis for the PMCPs furnished by pre-catalysts (Λ,S,S)-2 and (Δ,R,R)-2 showed good isotacticity factors (α = 75-78%) and relatively high proportions of trans-cyclopentane rings (σ = 14-21%). These enantiomeric PMCPs exhibited large specific optical rotations ([α]D = +28 to +32° from (Λ,S,S)-2, -26 to -34° from (Δ,R,R)-2).

Arylimido zirconium and titanium complexes: characteristic structures and application in ethylene polymerization

Abstract Dimeric anilidolithium (ArHNLi·Et2O)2 (Ar=2,6- i Pr2C6H3) reacted with zirconium tetrachloride in THF to give the heterometallic zirconium–lithium complex [(Et2O)2Li(μ-Cl)2(ArHN)(ArN=)Zr(μ-Cl)]2 (C1) and with titanium tetrachloride in toluene to give the titanium complex [(ArN=)TiCl2·(Et2O)2] (C2) each in good isolated yields. Their molecular structures in the solid state were confirmed by X-ray diffraction analysis. Upon activation with methylaluminoxane, both arylimido zirconium and titanium complexes exhibited good catalytic activities toward ethylene polymerization.