EXAFS study of zirconium alkoxides as precursors in the sol-gel process: II. The influence of the chemical modification

EXAFS studies of primary zirconium alkoxides Zr(OR)₄ with OR = n-propoxide and n-butoxide, dissolved in their corresponding alcohols and chemically modified with acetylacetone (Hacac) and acetic acid (HOAc) in different molal ratios, are presented. The EXAFS-spectroscopic results, supported by FT-IR-studies, indicate a different chemical behavior of the complexing agents. In contrast to acetylacetone, the addition of acetic acid does not change the oligomeric structure of the zirconium alkoxides. Amazingly, the modification with acetic acid leads, in comparison to the pure compounds, to a shortened metal centre distance, whereas in the reaction with acetylacetone the Zr-Zr distance is not changed. With the determined distances and a rough quantitative inclusion of the coordination numbers it was possible to deduce detailed structure models.     

Homo- and heteroleptic lanthanide-iron alkoxides as precursors in materials synthesis

Bimetallic iron-lanthanide alkoxides were synthesized by reacting [Ln{N(SiMe₃)₂}₃] (Ln ?= ?Pr, Nd, Er) with [Fe₂(O^tBu)₆] in excess tert-butyl alcohol that triggered in-situ ligand exchange and Lewis acid-base interactions to form heterometallic compounds. Single crystal X-ray diffraction analyses of new compounds demonstrated that both Nd and Er containing compounds resulted in the formation of a hetero-bimetallic framework based on 1:1 Ln:Fe ratio, whereas higher Fe ratio (1:2) was observed when Pr was used as the rare earth metal, possibly due to its larger ionic radius (Pr(III): 0.99 ?Å). When the reaction was performed in the presence of chelating ligands (L: H-tfb-mea ?= ?N-(4,4,4-trifluorobut-1-en-3-on)-methoxyethyleneamine; H₂-tfb-en ?= ?N–N′-bis-(4,4,4-trifluorobut-1-en-3-on)-ethylenediamine), heteroleptic Ln-Fe derivatives were formed that were used in a representative case ([NdFe(L)(O^tBu)_m(HO^tBu)]) as efficient precursor to synthesize nanocrystalline NdFeO₃ ceramic.     

Macromolecule-metal complex interactions as precursors for the catalytic chemical modification of polymers

Chemical modification of polymers via catalysis has recently emerged as an area of increasing importance in macromolecular chemistry. It provides an efficient synthetic route for the production of novel polymers with desirable physical properties and functional groups which are often inaccessible by conventional polymerization techniques. Diene-based polymers and copolymers are ideal for chemical modification because of the technological importance associated with the parent materials and the reactivities of the double bonds in the polymer chain. In employing organometallic catalysts for such modifications, it has been found that the ligand environment of the catalyst as well as the functionality of the polymer has a profound effect on the nature of the macromolecule-metal complex interaction and the resulting polymer modification. The importance of the macromolecule metal complex interactions and the design of appropriate catalyst systems is illustrated for the hydrogenation, hydroformylation/hydroxymethylation and hydrosilylation of a number of polymers.     

Straightforward acid-catalyzed synthesis of pyrrolyldipyrromethenes

Three for one: Pyrrolyldipyrromethenes having different functional groups were efficiently synthesized from POCl(3)-promoted condensations between 5-chloro-2-formylpyrrole or isoindole derivatives and suitable pyrrole or indole fragments through a novel nucleophilic aromatic substitution of the initially formed protonated azafulvene rings.     

Straightforward synthesis of thiodisaccharides by ring-opening of sugar epoxides

3,4-Anhydro hexopyranosides have been prepared by diastereoselective epoxidation of derivatives of 2-propyl 3,4-dideoxy-alpha-D-erythro-hex-3-enopyranoside (5), selectively protected at HO-2 and HO-6. The allylic group at C-2, in 5 and derivatives, plays a critical role in the facial selectivity of the epoxidation reaction. Thus, the free HO-2 in 3 (the 6-O-acetyl derivative of 5) directs the attack of m-chloroperbenzoic acid from the more hindered alpha face of the molecule to give 2-propyl 6-O-acetyl-3,4-anhydro-alpha-D-allopyranoside (7) accompanied by the beta epoxide 6 as a very minor product. Reverse diastereoselectivity has been obtained when the HO-2 in 3 was substituted by a bulky tert-butyldimethylsilyl (TBS) group. In this case, the major isomer was the 2-O-TBS derivative of 6 (alpha-D-galacto configuration). The ring-opening of sugar epoxides by nucleophilic per-O-acetyl-1-thio-beta-D-glucopyranose (11) was employed as a convenient approach to the synthesis of (1-->3)- and (1-->4)-thiodisaccharides. For example, ring-opening of the oxirane 7 by 11 led to the expected regioisomeric per-O-acetyl thiodisaccharides beta-D-Glc-S-(1-->3)-4-thio-alpha-D-Glc-O-iPr (12) and beta-D-Glc-S-(1-->4)-4-thio-alpha-D-Gul-O-iPr (13). Regioselectivity in the construction of the (1-->4)-thioglycosidic linkage could be achieved by hindering C-3 of the 3,4-anhydro sugar with a bulky silyloxy group at the vicinal C-2. For instance, coupling of the 2-O-TBS derivative of 7 with 11 led regioselectively to the protected thiodisaccharide beta-D-Glc-S-(1-->4)-4-thio-alpha-D-Glc-O-iPr (27). The utility of the approach was demonstrated through the synthesis of sulfur-linked analogues of naturally occurring (laminarabiose and cellobiose) and non-natural disaccharides (i.e., beta-D-Glc-(1-->4)-alpha-D-Gul).     

Electrochemical synthesis of metal alkoxides. Prospects of commercial alkoxides production

A production method of Ti, Zr, Nb, Ta, Y, Sn, Cu, Ge, Mo, W and some other metals alkoxides at their anode polarization in alcohols (methanol, ethanol, i-propanol, butanol, methoxy-ethanol) in the presence of an electroconductive additive has been developed.As a result of theoretical and experimental studies and engineering development, a universal low-waste technological processes of the electrochemical production of the above high purity alkoxides have been established.Metal efficiency coefficient in the electrosynthesis process is 0.85–0.90, current efficiency is 75–80%, and specific power consumption is within 5–10 kW-h/kg range.The total of impurities provided by this technology does not exceed 10^–3% mass.The developed electrochemical technology has been realized at a pilot-commercial scale at AO NIPIM plant (Russia, Tula) in order to manufacture a high purity titanium tetrabutoxide at 1.5–2.0 t/year plant operation the actual advantages of the electrochemical technology comparing to a traditional chemical one have been revealed.A considerable simplification of the developed electrochemical technology has been achieved at the anode polarization of metals in the methxyethanol due to elimination from the diagram scope of units for the alkoxides separation from after electrolysis solutions and recovery of unreacted raw components.     

Straightforward stereoselective synthesis of spiro-epoxyoxindoles

[reaction: see text] The in situ preparation of a sulfonium ylide reagent achieved the highly diastereoselective epoxidation of isatins, so that a new and straightforward access to biologically significant spiro-epoxyoxindoles is provided. The first investigations of an asymmetric version are reported with enantiopure sulfides.     

Meerwein-Ponndorf-Verley alkynylation of aldehydes: essential modification of aluminium alkoxides for rate acceleration and asymmetric synthesis

A novel carbonyl alkynylation has been accomplished based on utilization of the Meerwein-Ponndorf-Verley (MPV) reaction system. The success of the MPV alkynylation crucially depends on the discovery of the remarkable ligand acceleration effect of 2,2'-biphenol. For example, the alkynylation of chloral (2c) with the aluminium alkoxide 6(R = Ph), prepared in situ from Me(3)Al, 2,2'-biphenol and 2-methyl-4-phenyl-3-butyn-2-ol (1a) as an alkynyl source, proceeded smoothly in CH(2)Cl(2) at room temperature to give the desired propargyl alcohol 3ca in almost quantitative yield after 5 h stirring. The characteristic feature of this new transformation involving no metal alkynides can be visualized by the fact that the alkynyl group bearing keto carbonyl was transferred successfully to aldehyde carbonyl without any side reactions on keto carbonyl. Although the use of (S)-1,1[prime or minute]-bi-2-naphthol and its simple analogues was found to be unsuitable for inducing asymmetry in this reaction, design of new chiral biphenols bearing a certain flexibility of the biphenyl axis led to satisfactory results in terms of enantioselectivity as well as reactivity.     

Straightforward enantioselective synthesis of (+)-ancistrofuran

This paper reports the straightforward enantioselective synthesis of (+)-ancistrofuran starting from a readily available enantiopure building block. A stereofacial directed diastereoselective addition of an organocerate for the installation of the required stereogenic center served as the key step. In addition, the efficient conversion of an intermediate hydroxy aldehyde to the one-carbon homologated cyanide was developed. The sequence was achieved by the mild formation of a cyanohydrin and the subsequent one-pot two-step Barton-McCombie double deoxygenation of the hydroxyl groups.     

Straightforward synthesis of nitroolefins by microwave- or ultrasound-assisted Henry reaction

β-Nitroalcohol or nitroethylene derivatives can be obtained from aryl aldehydes and nitromethane under Henry condensation conditions. We present a new modification using microwave irradiation or ultrasound as the energy source. Microwave irradiation allowed a novel one-pot synthesis of nitroolefins from aryl aldehydes using ammonium acetate as a catalyst without solvent. Different reaction conditions, such as base, solvent, and reaction time were studied. Only small amounts of β-hydroxyl nitro compounds were isolated, using microwave irradiation for less than 25 min. In contrast, the use of ultrasound increased the yield of the nitroalcohols.     

Straightforward synthesis of sulfur bridged oligopyrrolic macrocycles

Di- and trisulfide linked oligopyrrolic macrocycles are obtained when appropriate alpha,alpha'-free pyrrolic precursors are reacted with sulfur dichloride; these systems represent the first examples of what might be a general new class of porphyrin analogues.     

Metal alkoxides as versatile precursors for group 4 phosphonates: synthesis and X-ray structure of a novel organosoluble zirconium phosphonate

Reactions of Ph2P(O)(OH) and t-BuP(O)(OSiMe3)(OH) with Ti(O-i-Pr)4 in equimolar ratios gave titanium phosphonates of the type [(O-i-Pr)3Ti(mu-O)2PR1R2]2 (1, R1 = R2 = Ph; 2, R1 = t-Bu, R2 = OSiMe3) as colorless crystalline solids in moderate yields. Reactions of Ph2P(O)(OH) and the isopropoxides of zirconium and hafnium resulted in products of the composition [(O-i-Pr)3M(mu-O-i-Pr)2(mu-OPOPh2)M(O-i-Pr)2]Ph2P(O)(OH) (M = Zr (3), Hf (4)) in high yields. The compounds were characterized by 1H, 31P, and 29Si NMR, infrared (IR), and mass spectroscopic (MS) techniques. The molecular structures of 2 and 3 were confirmed by X-ray crystallography.     

Straightforward synthesis of indolizidine alkaloid 167B

The synthetic access to indolizidines, substituted in C-5 position, was reported with good diastereoselectivity. The strategy developed was based on a key step of Michael addition associated with a Clauson-Kaas condensation.     

Straightforward copper-catalyzed synthesis of pyrrolopyrazoles from halogenated pyrazolecarbaldehydes

Straightforward synthesis of a variety of pyrrolo-fused pyrazoles via a cascade reaction between halopyrazolecarbaldehydes and ethylisocyanoacetate in the presence of copper and a base is described.     

Non-formaldehyde,crease-resistant modification of cellulosic material by means of an organotrialkoxysilane and metal alkoxides

Cellulosic material is chemically modified to impart crease-resistant properties to textile products. Due to health considerations formaldehyde-free chemicals are preferred. For this purpose, (3-glycidyloxy)propyltrimethoxysilane (GPTMS) in combination with metal alkoxides aluminium isopropoxide (AIP), titanium tetraisopropoxide (TTP), zircon tetrabutoxide (ZTB) were applied to cotton raw material and cotton fabrics which were pre-treated with butane-1,2,3,4-tetracarboxylic acid (BTCA)/sodium hypophosphite. The as-prepared samples were tested for dry crease recovery angle, tensile strength, tear strength, air permeability, contact angle and whiteness index. The application of GPTMS/AIP resulted in excellent crease resistance values, whereas TTP and ZTB provided a moderate improvement of the wrinkle resistance. The application of the hydrophobic methyltriethoxysilane, octyltriethoxysilane and Dynasylan F8815 (fluoroalkylfunctional water-borne oligosiloxane) caused a significant increase in the contact angle. Fourier-transform-infrared spectroscopy proved the formation of an ester-linkage between BTCA and the cellulose.     

Straightforward three-component synthesis of diarylmethylpiperazines and 1,2-diarylethylpiperazines

Several functionalized diarylmethylpiperazines and 1,2-diarylethylpiperazines have been synthesized in moderate to high yield according to a one-step three-component coupling between an aromatic or a benzylic organozinc reagent, a piperazine derivative, and an aromatic aldehyde. The procedure can be extended to the synthesis of benzylpiperazine derivatives or β-arylethylpiperazines toward the use of paraformaldehyde or aliphatic aldehydes.     

Lithiation directed by amino alkoxides. Application to the synthesis of new disubstituted dihydrodipyridopyrazines

The synthesis of new 4,6-disubstituted dihydrodipyridopyrazines starting from corresponding carboxaldehydes via lithiation directed by alpha-amino alkoxides is described. The N,N,N'-trimethylethylenediamine was used as amine component for in situ formation of the alpha-amino alkoxides. After optimization, this reaction allowed easy access to new interesting starting materials for further applications by palladium-catalyzed reactions.