New complexes of zirconium(IV) and hafnium(IV) with heteroscorpionate ligands and the hydrolysis of such complexes to give a zirconium cluster

A series of zirconium and hafnium heteroscorpionate complexes have been prepared by the reaction of MCl4 (M = Zr, Hf) with the compounds [[Li(bdmpza)(H2O)](4)] [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate], [[Li(bdmpzdta)(H2O)](4)] [bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate], and (Hbdmpze) [bdmpze = 2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide] (the latter with the prior addition of Bu(n)Li). Under the appropriate experimental conditions, mononuclear complexes, namely, [MCl3(kappa3-bdmpzx)] [x = a, M = Zr (1), Hf (2); x = dta, M = Zr (3), Hf (4); x = e, M = Zr (5), Hf (6)], and dinuclear complexes, namely, [[MCl2(mu-OH)(kappa3-bdmpzx)]2] [x = a, M = Zr (7), Hf (8); x = dta, M = Zr (9); x = e, M = Zr (10)], were isolated. A family of alkoxide-containing complexes of the general formula [ZrCl2(kappa3-bdmpzx)(OR)] [x = a, R = Me (11), Et (12), iPr (13), tBu (14); x = dta, R = Me (15), Et (16), iPr (17), tBu (18); x = e, R = Me (19), Et (20), (i)Pr (21), (t)Bu (22)] was also prepared. Complexes 11-14 underwent an interesting hydrolysis process to give the cluster complex [Zr6(mu3-OH)8(OH)8(kappa2-bdmpza)8] (23). The structures of these complexes have been determined by spectroscopic methods, and the X-ray crystal structures of 7, 8, and 23 were also established.     

Adsorption of anions to zirconium(IV) and titanium(IV) chemically immobilized on gel-phase

Adsorption behaviors of 25 anions to zirconium(IV) and titanium(IV) chemically immobilized on a gel-phase were studied by ion chromatography and by batch adsorption experiments. The affinities of Zr(IV) to iminodiacetate as an anchoring group and to anions as a sample are much stronger than those of Ti(IV). On a Zr(IV) column, fourteen anions showed no retention, four anions showed pH-dependent retention in a low pH region, and seven anions were irreversibly adsorbed at pH <7. In the last group, fluoride was adsorbed both by the ligand exchange mechanism and the addition mechanism, while phosphate, arsenate and selenite were only by the ligand exchange mechanism. The structures of the adsorbed species are discussed.     

On the nature of oxoiron (IV) intermediate in dioxygen activation by non-heme enzymes

We discuss electronic properties of the molecular systems with the short distance Fe–O unit, which are presumably formed as reaction intermediates during oxygen activation by non-heme enzymes. By performing an analysis of electronic densities in terms of multiconfigurational expansions of wavefunctions with localized orbitals the electronic properties of the Fe–O moiety in two model complexes are compared. The first one refers to the enzymatic intermediate, and the second biomimetic complex models a synthetic compound [Fe(O)(TMC)(NCCH₃)](OTf)₂ with a terminal Fe–O unit, which is experimentally characterized as the Fe(IV)=O species. We show that the orbital pictures of the FeO unit in both model complexes share common features. According to these simulations, the non-heme enzymatic intermediates may be assigned to the systems with the oxidation state of Fe between III and IV, as recently proposed for the TauD enzyme in experimental spectroscopic studies.     

Efficient intramolecular hydroamination of aminoalkynes catalyzed by a zirconium(IV) complex

The neutral zirconium(IV) bis(thiophosphinic amidate) complex was demonstrated to be an effective precatalyst for 5-exo-, 6-exo-, and 7-exo-dig intramolecular hydroamination of aminoalkynes, producing the cyclic imines in excellent yields (92-98%).     

Formation of supramolecular complex between imidazole and dichloro(5,10,15,20-tetraphenylporphinato)zirconium(IV)

By the reaction of 5,10,15,20-tetraphenyl-21H,23H-porphin (H₂TPP) with zirconium tetrachloride in boiling benzonitrile a complex was obtained, dichloro(5,10,15,20-tetraphenylporphinato)zirconium(IV), (Cl)₂ZrTPP. The equilibrium and reaction rate of stepwise reactions of (Cl)₂ZrTPP with imidazole (Im) in toluene were investigated by spectrophotometry. It was established that the three steps of the complex formation include reversible processes of coordination of Im molecule and substitution of 2Cl⁻ by the second and third Im molecules. The products of the first and second stages of the reaction, (Cl)₂(Im)ZrTPP and [(Cl)(Im)₂ZrTPP]⁺Cl⁻, respectively, are unstable and dissociate slowly at one Zr-Cl bond. By the analysis of the numerical values of the reactions parameters with accounting for the existence of definite spectral response to the presence of an organic base was shown a better prospect of application of (Cl)₂ZrTPP in sensor systems than those of metallophtalocyianines and doubly charged cation complexes with porphyrins.     

Carboxylato complexes of zirconium(IV)

The preparation and thermal decomposition of several trifluoroacetatozirconium chlorides is described. A mechanism for the thermal decomposition is proposed and the formation of zirconium tetrafluoride discussed in terms of composition of the parent compound.

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Zusammenfassung Es wurde die thermische Zersetzung und die Darstellung einiger Trifluoroazetatozirkoniumchloride beschrieben. Für die Zersetzungsreaktion wurde ein Mechanismus vorgeschlagen und die Bildung von Zirkoniumtetrachlorid unter den Gesichtspunkten der Zersetzung der Mutterverbindung erläutert.

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One of us (CMS) wishes to thank the SERC, England, for a maintenance award.     

C-C bond-forming reductive elimination from a zirconium(IV) redox-active ligand complex

Carbon-carbon bond-forming reductive elimination of biphenyl is observed upon two-electron oxidation of the [ZrIVPh2(ap)2]2- dianion. Crossover experiments confirm that the C-C bond-forming step occurs at a single zirconium metal center. The reactivity is enabled by the participation of a redox-active amidophenolate ligand set.     

Schiff base derivatives of titanium(IV) and zirconium(IV)

The reactions of a few bifunctional and tridentate Schiff bases with titanium-(IV) and zirconium(IV) isopropoxides in equimolar and bimolar ratios are described. The resulting compounds have been obtained in almost quantitative yields and are of the general formulae M(SB)_x(OPrⁱ)_4?2X (where M = Ti or Zr; SB- = anion of the Schiff base SBH₂ and x = 1 or 2). Their molecular weights have been determined ebullioscopically and IR spectra recorded.     

Catalytic reactivity of a zirconium(IV) redox-active ligand complex with 1,2-diphenylhydrazine

Two-electron reactivity of [N2O2red]ZrL3 (1a, N2O2(red) = N,N'-bis(3,5-di-tert-butyl-2-phenoxy)-1,2-phenylenediamide, L = THF) was explored with halogens and 1,2-diphenylhydrazine. Despite a formal d0 zirconium(IV) metal center, halogen oxidative addition occurred to form [N2O2(ox)]ZrCl2(THF) (2) with two-electron oxidation of the ligand. This ligand redox activity allows catalytic reactivity with 1,2-diphenylhydrazine resulting in disproportionation to form aniline and azobenzene via a putative zirconium-imide intermediate.     

Tris(trimethylsilyl)silane: an unprecedented enhancement in the diastereoselectivity of radical cyclisations to give 2,4-disubstituted piperidines

Cyclisation of bromides 4a-f mediated by tributyltin hydride affords predominantly the trans piperidines 5a-f with modest diastereomeric ratios, while cyclisation with tris(trimethylsilyl)silane affords the same products with diastereomeric ratios of up to 99 : 1.     

Synergistic solvent extraction of zirconium(IV)

The extraction of Zr(IV) by 2-thenoyltrifluoroacetone (TTA) in carbon tetrachloride from aqueous hydrochloric acid solutions is a slow process. The addition of a neutral extractant, di-n-pentyl sulfoxide (DPSO) enhances considerably the rate as well as the percentage of extraction. The species extracted appears to be ZrCl₂(TTA)₂·2 DPSO. An increase in temperature results in a further increase in the rate and percentage of extraction. Studies have also been carried out on the extraction of the metal by mixtures of various neutral extractants. Thermodynamic parameters associated with the formation of the synergistic adducts have been evaluated.     

Titanium(IV) and zirconium(IV) derivatives of tetradentate schiff bases

Summary Titanium and zirconium isopropoxides react with the tetradentate Schiff bases, I)is-salicylaldehyde-o-phenylenediimine (SBH₂ ) and bis-salicylaldehyde-p-phenylencdiimine (SBH₂) in anhydrous benzene in 1: 1 and 1 :2 molar ratios to give almost quantitative yields of M(OPr-i)₂ (SB) and M(OPr-i)2(SB)(SBH), where M = Ti or Zr and [SB]² is the anion of the corresponding Schiff base, SBH₂. The i.r. spectra of the completes have been recorded and tentative assignments for C=N and C-O stretching frequencies made.     

Sitting-atop complex formation of free base meso-tetraarylporphyrins with zirconium(IV) chloride

We have succeeded in the preparation and spectroscopic characterization of sitting-atop (SAT) complexes of meso-tetraarylporphyrins (H₂t(X)pp) with zirconium(IV) chloride under mild conditions and at room temperature, where two pyrrolenine nitrogens in the SAT complexes, [(H₂t(X)pp)ZrCl₄], coordinate to a zirconium atom and two protons still remain on the pyrrole nitrogens. UV–Vis and NMR (¹H and ¹³C) spectral data show that the porphyrin core of the SAT complexes is distorted and two pyrrolenine nitrogen atoms of the porphyrin act as electron donors to the zirconium atom of ZrCl₄.