Zr Complexes Research Articles

Titanium and zirconium amido complexes supported by imidazole-containing ligands: syntheses, characterization and catalytic activities

A series of new titanium and zirconium amido complexes, incorporating 4,5-diphenyl-2-(2-pyridinyl)-1H-imidazole (HL1), 4,5-bis(4-chlorophenyl)-2-(2-pyridinyl)-1H-imidazole (HL2), 4,5-bis(4-methoxyphenyl)-2-(2-pyridinyl)-1H-imidazole (HL3) and 4,5-bis(2-methoxyphenyl)-2-(2-pyridinyl)-1H-imidazole) (HL4) as the ancillary ligands, have been prepared and are shown to be pre-catalysts for the hydroamination of alkynes. Treatment of Ti(NMe2)4 with 1 equivalent of HL1, HL2, HL3 and HL4, respectively, results in transamination with one dimethylamide group providing Ti(L1)(NMe2)3 (1), Ti(L2)(NMe2)3 (2), Ti(L3)(NMe2)3 (3), and Ti(L4)(NMe2)3·THF (4·THF). Reaction of Ti(NMe2)4 with 2 equivalents of HL1, HL2, HL3 and HL4, respectively, leads to production of titanium bisamido complexes Ti(L1)2(NMe2)2·THF (5·THF), Ti(L2)2(NMe2)2·THF (6·THF), Ti(L3)2(NMe2)2·THF (7·THF), and Ti(L4)2(NMe2)2 (8). Similarly, complexes Zr(L1)(NMe2)3 (9), Zr(L1)2(NMe2)2·1.5THF (10·1.5THF), Zr(L2)2(NMe2)2·0.5THF (11·0.5THF), and Zr(L3)2(NMe2)2·0.5THF (12·0.5THF) are generated by addition of 1 or 2 equivalents of the corresponding ligands to Zr(NMe2)4. All compounds have been characterized by elemental and spectroscopic analyses. The solid-state structures of compounds 2 and 6·THF have been further established by single X-ray diffraction analyses. The catalytic activities of 2 and 6·THF towards the hydroamination of alkynes were explored. Complexes 2 and 6·THF were found to be active pre-catalysts for the hydroamination reactions. Complex 2 showed higher catalytic activity and gave highly Markovnikov selective hydroamination of terminal alkynes.

Zirconium complexes incorporated with asymmetrical tridentate pincer type mono- and di-anionic pyrrolyl ligands: mechanism and reactivity as catalytic precursors

The reactions of Zr(NR(2))(4) (1, R = Me; 2, R = Et) with an asymmetrical tridentate pincer type pyrrole ligand precursor [C(4)H(2)NH(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))] and treatment of the derivatives with either PhNCS or PhNCO have been carried out and characterized. Reacting Zr(NR(2))(4) (1, R = Me; 2, R = Et) with [C(4)H(2)NH(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))] generates Zr[C(4)H(2)N(2-CH(2)N(t)Bu)(5-CH(2)NMe(2))](NR(2))(2) (3, R = Me; 4, R = Et) in high yield along with the elimination of 2 equiv of dimethylamine or diethylamine, respectively. Interestingly, while changing the solvent from Et(2)O to CH(2)Cl(2), the complex Zr[C(4)H(2)N(2-CH(2)N(t)Bu)(5-CH(2)NMe(2))][C(4)H(2)N(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))]Cl (5) is produced by undergoing C-Cl bond cleavage. Furthermore, reaction of either 3 or 4 with 1 or 2 equiv of PhNCS or PhNCO yields Zr[C(4)H(2)N(2-CH(2)N(t)Bu)(5-CH(2)NMe(2))](NMe(2))[PhNC(NMe(2))S] (6), Zr[C(4)H(2)N(2-CH(2)N(t)Bu)(5-CH(2)NMe(2))](NEt(2))[PhNC(NEt(2))O] (7) and Zr[C(4)H(2)N(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))][PhNC(NEt(2))O](3) (8), respectively. All the aforementioned complexes were characterized by (1)H and (13)C NMR spectrometry and the molecular structures of 5, 6, and 8 have been determined by single-crystal X-ray diffractometry. Complexes 4, 5, and 7 initiated the ethylene polymerization in the presence of MAO as the co-catalyst.

Metal (Mg, Fe, Co, Zr and Ti) complexes derived from aminosilyl substituted aminopyridinato ligand: synthesis, structures and ethylene polymerization behaviors of the group 4 complexes

Lithium N-[(N,N-dimethylamino)dimethylsilyl]-2-pyridylamidate (2) was prepared from the reaction of new compound N-[(N,N-dimethylamino)dimethylsilyl]-2-pyridylamine (1) and LiBu(n). Treatment of the lithium salt (2) with an equal equivalent of MgBr(2)(THF)(2), FeCl(2) and CoCl(2) afforded the corresponding dinuclear complexes , , and , in which metal atoms possess similar trigonal bipyramidal geometries and each ligand functions as a bimetallic bridging binding aminopyridinato moiety with N-donation from the dimethylamino group. While the stoichiometric reaction of with ZrCl(4) gave the mononuclear zirconium complex (6); the seven coordinated zirconium atom adopts a distorted pentagonal bipyramid geometry and the ligand acts as monoanionic η(2)-aminopyridinato moiety with the pendant arm coordinated via N(CH(3))(2). The reaction of with one equivalent of TiCl(4)(THF)(2) produced the interesting dinuclear titanium complex (7) owing to the elimination of a (N,N-dimethylamino)dimethylsilyl group from the original ligand, and the two titanium centers present different coordination geometries. The molecular structures of the crystalline metal complexes have been confirmed by X-ray single crystal diffraction analysis. Upon activation with methylaluminoxane (MAO), both complexes and exhibited moderate catalytic activities toward ethylene polymerization and produced high molecular weight polyethylenes with broad molecular weight distributions.

Synthesis and structural study of an unsymmetrical aliphatic benzamidinato ligand and its use in the formation of selected Cu(i), Mg(ii) and Zr(iv) complexes

The reaction of a Et2O solution of LiN(Cy)SiMe3 (Cy = cyclohexyl) with PhCN in the presence of the Lewis-base donor tetrahydrofuran (THF) or Me2N(CH2)2NMe2 (TMEDA) gave the THF- or TMEDA-solvated unsymmetrical aliphatic lithium benzamidinato compound [{PhC(NCy)(NSiMe3)}Li(THF)]2 (1) or [{PhC(NCy)(NSiMe3)}Li(TMEDA)] (2). Treatment of LiN(Cy)SiMe3 with PhCN in diethyl ether, and further with CuCl, MgBr2(THF)2 or ZrCl4 at a ratio of 1 : 1, 2 : 1 and 3 : 1 allowed the formation of novel metal complexes [{PhC(NCy)(NSiMe3)}Cu]2 (3), [{PhC(NCy)(NSiMe3)}2Mg(OEt2)] (4) and [{PhC(NCy)(NSiMe3)}3ZrCl] (5), respectively. The X-ray structures of complexes 1–4 are presented. Complex 5/MAO system allows the moderate polymerization of ethylene.

How big is a Cp? Cycloheptatrienyl zirconium complexes with bulky cyclopentadienyl and indenyl ligands

A combination of phase-transfer and traditional alkylation strategies has been employed to synthesise sterically encumbered 1,3-di(cyclohexyl) and 1,3-di(tert-butyl) substituted indenes in multi-gram quantities. These indenyl ligands and sterically demanding alkyl cyclopentadienyl ligands have been used to prepare a series of [(η(7)-C(7)H(7))Zr(η(5)-L)] (L = Cp and Ind) complexes by straightforward salt metathesis between [(η(7)-C(7)H(7))ZrCl(tmeda)] and the corresponding sodium indenide or cyclopentadienide. All of these Zr complexes have been characterized by elemental analysis, NMR spectroscopy and single crystal X-ray diffraction. The structural information derived from these studies was employed to evaluate the steric demand of these ligands in a realistic manner.

Application of F−‐Selective Ionophores in Carboxylated or Aminated Poly(Vinyl Chloride)‐Based Membranes of Ion‐Selective Electrodes

AbstractIn this work, complexes of Zr(IV) and Al(III) cations with tert‐butyl substituted tetraphenylporphyrin or tetraazaporphine were tested as F−‐selective ionophores in plasticized aminated or carboxylated PVC membranes of ion‐selective electrodes. It was found that functional groups present in the backbone of applied polymers influence the complexing properties of tested ligands, causing changes of F−‐selectivity of electrodes prepared with their use in comparison with the electrodes with unmodified PVC membranes. This work shows, that application of functionalized PVC can eliminate the need of relatively expensive ionic sites addition to ion‐selective membranes doped with metallocomplexes.

Oscillating Non‐Metallocenes – from Stereoblock‐Isotactic Polypropylene to Isotactic Polypropylene via Zirconium and Hafnium Dithiodiphenolate Catalysts

AbstractOctahedral group 4 complexes of a new bulky tetradentate dithiodiphenolate {OSSO}‐type ligand that oscillate between two enantiomeric C2‐symmetric conformations are described. The dibenzyl Zr and Hf complexes led to active catalysts in propylene polymerization. Polypropylene having predominantly stereoblock‐isotactic microstructure or predominantly isotactic microstructure could be obtained by varying the polymerization conditions. Long isotactic blocks of 50 to more than 100 repeat units were formed at –10 °C in liquid propylene.

DFT modeling, UV-Vis and IR spectroscopic study of acetylacetone-modified zirconia sol-gel materials

Theoretical and spectroscopic studies of a series of monomeric and dimeric complexes formed through the modification of a zirconium butoxide precursor with acetylacetone and subsequent hydrolysis and/or condensation have been performed by applying DFT/B3LYP/6-31++G(d) and highly accurate RI-ADC(2) methods as well as IR and UV-Vis transmittance and diffuse reflectance spectroscopies. Based on DFT model calculations and simulated and experimental UV-Vis and IR spectra of all the studied structures, the most probable building units of the Zr(IV)-AcAc gel were predicted: the dimeric double hydroxo-bridged complex Zr(2)(AcAc)(2)(OH)(4)(OH)(2br) 9 and the monooxo-bridged complex Zr(2)(AcAc)(2)(OH)(4)O(br)·2H(2)O 12. In both structures, the two AcAc ligands are coordinated to one Zr atom. It was shown that building units 9 and 12 determine the photophysical and vibrational properties of the gel material. The observed UV-Vis and IR spectra of Zr(IV)-AcAc gel were interpreted and a relation between the spectroscopic and structural data was derived. The observed UV-Vis bands at 315 nm and 298/288 nm were assigned to partial ligand-metal transitions and to intra-/inter-AcAc ligand transitions, respectively.

Synthesis and olefin polymerization activity of (quinolin-8-ylamino)phenolate and (quinolin-8-ylamido)phenolate Group 4 metal complexes

New Zr and Hf complexes bearing either a tridentate monoanionic 2- tert-butyl-6-[(quinolin-8-ylamino)methyl]phenolate [N,N,O −] or a dianionic 2- tert-butyl-6-[(quinolin-8 ylamido)methyl]phenolate [N,N −,O −] ligand have been synthesized and characterized. The geometries of the zirconium complexes have been studied using DFT methods. The complexes were tested as catalysts in the polymerization of ethylene and α-olefins after activation with methylalumoxane, resulting in the production, with moderate activities, of high molecular weight linear polyethylene and prevailingly isotactic polypropylene, poly(1-butene), poly(1-pentene) and poly(1-hexene). The content of isotactic pentads of these poly(α-olefins) increases while the size of the monomer increases, ranging between 50% for polypropylene and 99% for poly(1-hexene).

Spectroscopic studies, thermal analyses and biological evaluation of new V(IV), Zr(IV) and U(VI) moxifloxacin complexes

The synthesis and characterization of the new solid complexes [VO(MOX)2H2O]SO4·11H2O, [ZrO(MOX)2Cl]Cl·15H2O and [UO2(MOX)3](NO3)2·3H2O formed in the interaction of moxifloxacin (MOX) with VOSO4·H2O, ZrOCl2·8H2O and UO2(NO3)2·6H2O in methanol and acetone as a solvents at room temperature were reported. The isolated solid complexes have been characterized with melting points, elemental analysis, molar conductance, magnetic moments studies, spectral (UV–Visible, IR and 1HNMR) as well as thermal analyses (TGA and DTG). The results support the formation of the complexes and indicate that moxifloxacin reacts as a bidentate ligand chelate to the metal ion through the pyridone oxygen and one carboxylato oxygen. The kinetic parameters of thermogravimetric (TGA) and its differential (DTG), such as activation energies, E*, enthalpies, ΔH*, entropies, ΔS* and Gibbs free energies, ΔG*, have been evaluated by using Coats–Redfern (CR) and Horowitz–Metzeger (HM) methods. The proposed structure of the ligand and their complexes were detected by using the density functional theory (DFT) at the B3LYP/CEP-31G level of theory. The bond stretching force constant and length of the UO for the [UO2(MOX)3](NO3)2·3H2O complex were calculated. The antibacterial activity of the free moxifloxacin ligand and their metal complexes have been tested against some selected bacterial strains such as: Streptococcus aureus K1, Bacillus subtilis K22, Brevibacterium otitidis K76, Escherichia coli K32, Pseudomonas aeruginosa SW1 and Klebsiella oxytoca K42. The complexes showed good antibacterial effect to the selected bacterial strains as compared to the free ligand and Zr(IV) complex is very highly significant compared with the other two complexes.

Metal-complex compounds as components of initiating systems for the controlled radical polymerization of vinyl monomers

The effect of initiating systems based on substituted and unsubstituted metallocenes; polynuclear macrocyclic semi- and clathrochelates of Fe(II); and metal complexes of Ti(IV), Zr(IV), Fe(III), and Co(III) porphyrins on the free-radical polymerization of MMA and styrene is analyzed. Experimental data are systematized, general relationships are ascertained, and specific features of the process related to the structure of metal-complex compounds and the nature of initiators and monomers are revealed.

Synthetic, spectroscopic and thermal studies of some complexes of unsymmetrical Schiff base ligand

New unsymmetrical Schiff base ligand (H2L) is prepared via condensation of 2-hydroxy-5-methyl acetophenone, 2-hydroxy-5-chloro-3-nitro acetophenone and carbohydrazide in 1:1:1 ratio. Metal complexes of VO(IV), Cr(III), Mn(III), Fe(III), Zr(IV), MoO2(VI), WO2(VI) and UO2(VI) have been prepared. These complexes were characterized by elemental analysis, UV–Vis and IR spectroscopy and magnetic moment and thermogravimetric analysis. The purity of the ligand and the metal complexes is confirmed by microanalyses, while unsymmetrical nature of ligand was further corroborated by 1H NMR. All the complexes are air stable and insoluble in water and common organic solvents but fairly soluble in DMSO. The elemental analysis shows 1:1 metal to ligand stoichiometry for all the complexes. Thermal behaviour of the complexes was studied, the complexes were found to be quite stable and their thermal decomposition was generally via partially loss of the organic moiety and ended with respective metal oxide as a final product. Comparison of the IR spectrum of ligand and its metal complexes confirm that Schiff base behave as a dibasic tetradentate ligand towards the central metal ion with an ONNO donor sequence. The dc electrical conductivity is studied and data obtained obeyed the relation σ = σ 0 exp(−E a/kT) over the temperature range 40–130 °C. X-ray diffraction study of VO(IV) complex shows its crystalline nature with triclinic crystal system.

Enhanced catalytic activity of Zr(IV) complex with simple tetradentate Schiff base ligand in the clean synthesis of indole derivatives

Zirconium (IV) tetradentate Schiff base (salphen) complex has been successfully used for efficient synthesis of wide variety of indole derivatives in EtOH as a standard green solvent under mild conditions. The investigation of turnover number and reusability of the catalyst indicate well the high efficiency and relative stability of the Zr-complex in this reaction.

Rapid Entry to Functionalized Boratabenzene Complexes through Metal-Induced Hydroboration at the Anionic 1-H-Boratabenzene Ligand

The hydroboration of alkenes, alkynes, imines, and carbodiimides using the anionic 1-H-boratabenzene ligand bound to rare-earth (RE = Y, Lu), transition (Zr and Rh), and main-group (Li) metals is reported. This hydroboration is metal ion dependent; in the case of 1-H-boratabenzene transition metal complexes, the reactivity follows the trend RE > Zr > Rh. Hydroboration with 1-H-boratabenzene rare-earth metal complexes works well for a range of unsaturated substrates, including 1-hexene, allyl propyl ether, allyl ether, 3-hexyne, benzylidene-n-propylamine, and N,N′-diisopropylcarbodiimide, thus generating a series of new alkyl-, alkenyl-, amino-, or amidino-functionalized boratabenzene rare-earth metal complexes in high yields. The reactions are highly anti-Markovnikov selective, and the mechanism has been investigated by deuterium-labeling experiments. In comparison, a 1-H-boratabenzene Zr complex reacts with benzylidene-n-propylamine and N,N′-diisopropylcarbodiimide, and a 1-H-boratabenzene Rh complex reacts with N,N′-diisopropylcarbodiimide. In contrast, the 1-H-boratabenzene lithium salt reacts only with the activated substrate benzylidene-n-propylamine at elevated temperature to give the corresponding hydroboration product. Boratabenzene Y complexes undergo ligand redistribution with Rh chlorides to give boratabenzene Rh complexes. Studies of the novel monoanionic amidino-boratabenzene ligand by X-ray diffraction and DFT calculations have revealed interesting structural features.

Rotational Libration of a Porphyrin/Phthalocyanine Double-decker Complex with Ce(IV) as Revealed by 1H NMR and STM

Abstract We provide evidence that a heteroleptic double-decker complex of Ce with phthalocyanine and porphyrin ligands undergoes rotational libration in solution for the first time on the basis of variable-temperature 1H NMR. On the other hand, the Zr complex with the same set of ligands undergoes no rotational motion. These molecules deposited on graphite surfaces exhibited different shapes in STM images, revealing difference in the rotational motion at the molecular level.

Novel complexes of zirconium and uranium derived from bifunctional azodyes donor ligands containing hydrogen bonds

Novel complexes of zirconium(IV) and uranium(II) with selective azodyes containing nitrogen and oxygen donor ligands have been prepared and characterized by elemental analysis, 1H NMR and electronic spectral techniques. The important bands in the IR spectra and main 1H NMR signals are assigned and discussed in relation to the proposed molecular structure of the complexes. The IR data of the azodye ligands suggested a bidentate binding involving azodye nitrogen and C–O/OH oxygen atom of enolic group. They also showed the presence of Cl/OAc coordinating with the metal ion. The prepared complexes of Zr(IV) fall into four types. In the stoichiometric formulae of (1:1), the chelate rings are six-membered/five coordinate; whereas in the (1:2) they are six-membered/six coordinate and all of the complexes possess non-electrolytic properties. The UO2(II) complex, in the mean time, possesses a planar hexagonal structure with nitrogen and oxygen atoms in the axial position. The stretching vibrations and force constant interactions of the uranyl complexes have been determined and from which the U–O bond distances are calculated. These bond distances as well as the effect of Hamett’s constant are also, in turn, calculated and discussed.

Synthesis of Titanium(IV) and Zirconium(IV) Complexes with an [OSSO]-Type Bis(phenolate) Ligand Bearing a trans-Cyclohexane-1,2-diyl Ring and 1-Hexene Polymerization

The Ti(IV) and Zr(IV) complexes 9 and 11 with a new [OSSO]-type bis(phenolate) ligand bearing a trans-cyclohexane-1,2-diyl ring (6) were synthesized. The reaction of 6 with Ti(OiPr)4 in toluene gave the two C2-symmetric, diastereomeric Ti complexes (Λ*,S*,S*)-9 and (Δ*,S*,S*)-9, the latter of which was characterized by X-ray crystallography. The reaction of 6 with Zr(CH2Ph)4 also provided a mixture of the two C2-symmetric diastereomers (Λ*,S*,S*)-11 and (Δ*,S*,S*)-11. Polymerization of 1-hexene employing 11 as the precatalyst yielded isotactic poly(1-hexene) with high activity. In relation to the activity, an NMR study was carried out for the cationic zirconium complex 12+[B(CH2Ph)(C6F5)3]− in comparison with the corresponding complex 13+[B(CH2Ph)(C6F5)3]−, bearing a trans-cyclooctane-1,2-diyl ring in the ligand.

Coordination Chemistry and Organic Synthesis Utilizing Cycloalkane-1,2-dithiol

An [OSSO]-type tetradentate ligand was prepared starting from trans-cyclooctane-1,2-dithiol. Hexacoordinated dibenzyl Zr complex was synthesized by the reaction of the ligand with Zr(CH2Ph)4 and its structure was fully characterized by nuclear magnetic resonance (NMR) spectroscopy and X-ray crystallography. The zirconium complex has the C2 symmetry in solution. The zirconium complex activated with B(C6F5)3 or (Ph3C)[B(C6F5)4] provided a highly active catalytic system for coordinate polymerization of 1-hexene to yield poly(1-hexene)s with high isospecificity.

Subtle Differences Between Zr and Hf in Early/Late Heterobimetallic Complexes with Cobalt

The phosphinoamide-linked Co/Hf complexes ICo(Ph(2)PN(i)Pr)(3)HfCl (4), ICo((i)Pr(2)PNMes)(3)HfCl (5), and ICo((i)Pr(2)PN(i)Pr)(3)HfCl (6) have been synthesized from the corresponding tris(phosphinoamide)HfCl complexes (1-3) for comparison with the recently reported tris(phosphinoamide) Co/Zr complexes. Very minor structural and electronic differences between the Zr and Hf complexes were found when the N-(i)Pr-substituted phosphinoamide ligands [Ph(2)PN(i)Pr](-) and [(i)Pr(2)PN(i)Pr](-) were utilized. The reduction products [(THF)(4)Na-{N(2)-Co(Ph(2)PN(i)Pr)(3)HfCl}(2)]Na(THF)(6) (7) and N(2)-Co((i)Pr(2)PN(i)Pr)(3)Hf (9) are also remarkably similar to the corresponding Zr/Co analogues. In the case of Hf/Co and Zr/Co complexes linked by the N-Mes ligand [(i)Pr(2)PNMes](-) (Mes = 2,4,6-trimethylphenyl), however, more pronounced differences in structure, bonding, and reactivity are observed. While differences associated with 5 are still modest, larger variations are observed when comparing the two-electron reduction product [N(2)-Co((i)Pr(2)PNMes)(3)Hf-X][Na(THF)(5)] (8) with its Zr congener. In addition to structural and spectroscopic differences, vastly different reactivity is observed, with 8 undergoing one-electron oxidation to form ClHf(MesNP(i)Pr(2))(3)CoN(2) (11) in the presence of MeI, while a two-electron oxidative addition process occurs in a similar reaction with the Zr derivative. The activity of 5 toward Kumada coupling was investigated, finding significantly diminished activity in comparison to Co/Zr complexes.

Bis-ligated Ti and Zr complexes of chelating N-heterocyclic carbenes

In this communication we report the synthesis of novel titanium and zirconium complexes ligated by bidentate “salicylaldimine-like” N-heterocyclic carbenes (NHC). Double addition of the NHC chelate to either TiCl 4(thf) 2 or ZrCl 4 forms bis-ligated organometallic fragments with a distorted octahedral geometry. These complexes are rare examples of group IV transition-metal NHC adducts. Preliminary catalytic tests demonstrate that in the presence of methylaluminoxane (MAO) these complexes are useful initiators for the polymerization of ethylene and the copolymerization of ethylene with norbornene and 1-octene.