The synthesis and structural characterisation of two polynuclear hafnium(IV) complexes

Attempts to form extended supramolecular structures incorporating hafnium(IV) complexes of p-sulfonatocalix[6]arene resulted in the serendipitous formation of two polynuclear-hafnium clusters. Subsequent reaction between hafnium triflate and 1 M sulfuric or p-toluenesulfonic acid solutions also led to the formation of the same clusters, identified as cations based on Hf₁₇ and Hf₄, respectively.     

Synthesis, structure, spectroscopic properties, and electrochemical behavior of mixed ligand bis(β-ketoesterato)zirconium (IV) and -hafnium (IV) phthalocyaninates

The synthesis of new zirconium and hafnium mixed ligand phthalocyanine complexes PcM(β-ketoester)₂, where M-Zr (IV), Hf (IV); Pc - the dianion of phthalocyanine, and β-ketoester - the out planed ligand, is reported. The obtained complexes are characterized by ¹H NMR, IR, UV-Vis spectroscopy and cyclic voltammetry. ¹H NMR and elemental analysis confirm the substitution of two Cl atoms for two β-ketoester fragments to the central atom of the macrocycle. The data of ¹H NMR, UV-Vis spectroscopy have allowed us to conclude that two β-ketoester ligands are in the cis geometry to the phthalocyanine plane. X-ray crystallography for bis(isopropyl 3-oxobutanoato)hafnium(IV)phthalocyanine confirms this conclusion. The central macrocycle of the phthalocyanine ligand is not exactly planar (deviations from the least-square plane exceed 0.15 Å) and has the conformation of an essentially flattened crown. The Hf(1) atom is 1.349(3) above this least-square plane. Cyclic voltammetry investigation shows that the introduction of two β-ketoester ligands to the central atom of phthalocyanine complex leads to both chemical and electrochemical stabilization of the whole Pc system.     

An expeditious synthesis of tamoxifen, a representative SERM (selective estrogen receptor modulator), via the three-component coupling reaction among aromatic aldehyde, cinnamyltrimethylsilane, and beta-chlorophenetole

Two new synthetic pathways to the anti-cancer agent tamoxifen and its derivatives were developed. The first route involved the aldol reaction of benzyl phenyl ketone with acetaldehyde followed by Friedel–Crafts substitution with anisole in the presence of Cl₂Si(OTf)₂ to produce 1,1,2-triaryl-3-acetoxybutane, a precursor of the tamoxifen derivatives. The second one utilized the novel three-component coupling reaction among aromatic aldehydes, cinnamyltrimethylsilane, and aromatic nucleophiles using HfCl₄ as a Lewis acid catalyst to produce 3,4,4-triarylbutene, that is also a valuable intermediate of the tamoxifen derivatives. The former strategy requires a total of 10 steps from the aldol formation to the final conversion to tamoxifen, whereas the latter needs only three or four steps to produce tamoxifen and droloxifene including the installation of the side-chain moiety and the base-induced double-bond migration to form the tetra-substituted olefin structure. This synthetic strategy seems to serve as a new and practical pathway to prepare not only the tamoxifen derivatives but also the other SERMs (selective estrogen receptor modulators) including estrogen-dependent breast cancer and osteoporosis agents.     

Chemical implantation of Group 4 cations on silica via cyclopentadienyl- and N,N-dialkylcarbamato derivatives

Chemical implantation of Group 4 cations [Ti(III), Ti(IV), Zr(IV), Hf(IV)] has been carried out under mild conditions by the reaction of polycyclopentadienyl- (MCp_n; M = Ti, n = 3, 4; M = Zr, Hf, n = 4), mixed cyclopentadienyl/N,N-dialkylcarbamato (ML_x(O₂CNEt₂)_y; M = Ti, L = Cp, C₅Me₅ (Cp*), x = 2, y = 1; M = Hf, L = Cp, x = 1, y = 3), and N,N-dialkylcarbamato (M(O₂CNR₂)_n, M = Ti, n = 3, R = ⁱPr; M = Ti, Hf, n = 4, R = Et; M = Zr, n = 4, R = ⁱPr) derivatives, with the silanol groups of amorphous silica. Cyclopentadiene/pentamethylcyclopentadiene and/or carbon dioxide and the secondary amine are released in the process. The amount of implanted cations depends on the metal and on the ligands, the pentamethylcyclopentadienyl complex being less reactive than the unsubstituted congener. The starting complexes and the final products have been characterized by EPR or by ¹³C CP-MAS NMR spectroscopy.     

Synthesis and structure of the lithium, zirconium and hafnium N-silyl-N′-benzyl-benzamidinates

The interaction of LiN(SiMe₃)CH₂Ph with one equivalent of benzenitrile gave the N-silyl-N′-benzyl-benzamidinato-lithium compound [{Me₃SiNC(Ph)N(CH₂Ph)}Li(Et₂O)]₂ (1). The derivative zirconium and hafnium compounds were produced by the treatment of 1 with ZrCl₄ or HfCl₄ in tetrahydrofuran or diethyl ether at ambient temperature, respectively, with the general formula [Me₃SiNC(Ph)N(CH₂Ph)]₃MCl (M = Zr (2), Hf (3)). Compounds 1, 2 and 3 were also characterized by X-ray single crystal diffraction and NMR analysis.     

Synthesis and structure of a hafnium silylamide complex and the chemical vapor deposition of HfxSi1−xO2 films

The complex Hf[N(SiMe₂H)₂]₄ was synthesized, structurally characterized, and used as a precursor with oxygen to prepare hafnium silicate thin films at substrate temperatures ?500 °C in a low-pressure CVD process. The as-deposited films were amorphous, and they remained amorphous upon annealing up to 1100 °C.     

A method for rapid freeze fixation of plant cells

Summary We describe here an apparatus that permits rapid freeze fixation of whole cells, which are then prepared by freeze substitution and resin embedment for examination in the EM. The freezing device utilizes a rotary solenoid that rapidly plunges the specimen holder, a formvar-film-covered thin wire loop, into a well of stirred liquid propane at –180C. The rotary solenoid allows for an adjustable, repeatable immersion rate. Substitution takes place at –80 C in acetone with 2% OsO₄ and is followed by en bloc staining in either hafnium tetrachloride or uranyl acetate. We have utilized these techniques on plant cells, for which there has been relatively little published work when compared to other organisms. The results show that, with the versatile specimen holder and rapid, repeatable immersion rates, different cell types, including pollen, stamen hairs, and germinating moss spores, can be rapidly frozen with repeatable success. The improved preservation achieved with rapid freeze fixation over conventional chemical fixation reveals itself particularly in the structure of the plasmamembrane, the cytoskeleton, chromatin, and certain endomembrane systems.     

Hafnium chloride and hafnium methyl complexes bearing substituted pyrrolyl ligands: synthesis, characterization, and ethylene polymerization

Reactions of HfCl₄ with 2 and 3 equiv. of Li[C₄H₃N(CH₂NMe₂)-2] in toluene afford HfCl₂[C₄H₃N(CH₂NMe₂)-2]₂ (1) and HfCl[C₄H₃N(CH₂NMe₂)-2]₃ (2), respectively. Transmetallation reaction of 1 with 2 equiv. of MeLi results in a hafnium dimethyl compound HfMe₂[C₄H₃N(CH₂NMe₂)-2]₂ (3). A variable-temperature ¹H NMR spectroscopic study shows that the activation energy for the dissociation/association of the NMe₂ units of compound 2 in solution is ca. 13.6 kcal/mol. Compounds 1-3 are characterized by NMR spectroscopy and single crystal X-ray diffraction. A polymerization study shows that compounds 1 and 3 exhibit moderate activity toward ethylene in the presence of TIBA and MAO.     

Synthesis and structure of bulky phosphiniminato complexes of zirconium and hafnium: Aryl groups as “non-innocent” substituents in electrophilic systems

Sterically highly hindered phosphiniminato complexes MCl₃(NCP) were prepared from MCl₄ and Li[NPC] in toluene [M = Zr or Hf; NPC = 4-Bu^tC₆H₄C(SiMe₃)P(Ph)₂NC₆H₂Me₃-2,4,6]. Reaction with methyl lithium readily affords the corresponding zirconium and hafnium trimethyl complexes. The structures of representative zirconium and hafnium complexes MX₃(NPC) (X = Cl, M = Zr, Hf; X = Me, M = Hf) were determined by X-ray diffraction. In all cases the NPC ligand acts as C-N chelate, with an additional bonding contribution from the ipso-carbon atom of the C-bound aryl substituent, which results in a η¹:η²-coordination mode. The reaction of the hafnium trimethyl complex with salts of perfluoroarylborate anions results either in the diastereoselective formation of the binuclear cation [{(NPC)HfMe₂}₂(μ-Me)]⁺ or in the formation of the mononuclear cation [(NPC)HfMe₂]⁺, depending on the molar ratio of reagents.     

An efficient synthesis of 2,3-dideoxy-alpha,beta-unsaturated carbohydrate enals by mixed Lewis acid (HfCl4 and ZnI2) catalyzed hydration of glycals

A new, efficient method has been developed for converting acyl-, arylalkyl- and alkyl-protected glycals into corresponding 2,3-dideoxy-alpha,beta-unsaturated carbohydrate enals utilizing the in situ generated push-pull effect resulting from the synergistic combination of HfCl4 and ZnI2 in catalytic amounts. This new procedure eliminates the use of highly toxic Hg2+ ions and acidic conditions (0.01-0.02 N H2SO4), besides radically shortening the reaction time.