(Salen)Ti(IV) complex catalyzed asymmetric ring-opening of epoxides using dithiophosphorus acid as the nucleophile

A series of chiral bis-Schiff bases were synthesized starting from (1R,2R)-(+)-diaminocyclohexane, (+)-cis-1,2,2-trimethyl-1,3-diaminocyclopentane, (R)-2,2^′-diamino-1,1^′-binaphthalene, and (1S,2S)-diphenyl-1,2-ethanediamine. The enantioselective ring-opening of meso epoxides with dithiophosphorus acids catalyzed by a (salen)Ti(IV) complex formed in situ upon the treatment of Ti(OPr-i)₄ and the aforementioned chiral Schiff base was realized. The resulting products were obtained with low to good enantioselectivities (up to 73% ee). The (salen)Ti(IV) complex containing the backbone of 1,2-diaminocyclohexane exhibited the best enantioselectivity. The substituents in dithiophosphorus acids and those on the salen aromatic ring have a significant influence on the reaction. Moderate enantioselectivity were obtained for the (salen)Ti(IV) complex catalyzed ring-opening of racemic monosubstituted epoxides. High regioselectivity was observed for the alkyl substituted epoxides, whereas poor regioselectivity was obtained for the aryl substituted ones.     

NHPI/Co(Salen)催化氧化取代甲苯

以分子氧为氧化剂,N-羟基邻苯二甲酰亚胺(NHPI)为引发剂,Co(Salen)配合物[NHPI/Co(Salen)]为催化剂,偶氮二异丁腈(AIBN)为助引发剂,AcOH为溶剂,催化氧化取代甲苯制备取代苯甲酸。最佳反应条件为:甲苯6mmol,q(NHPI)=10%,q[Co(Salen)]=0.5%,q(AIBN)=1%,O2(0.1MPa),AcOH10mL,于80℃反应20h,甲苯转化率92.7%,苯甲酸选择性88.9%。     

手性Salen及Ga(Salen)催化苯基锂对环氧环己烷对映选择性开环反应

合成了14个含1,2-环己二胺、1,2-二苯基乙二胺或邻苯二胺的手性Salen化合物, 研究了手性Salen直接催化苯基锂对环氧环己烷的不对称开环反应, 结果表明二胺的结构和苯环上3,3'-位取代基对反应的对映选择性有很大的影响. 用Salen与 Me₃Ga原位生成的Ga(Salen)催化苯基锂对环氧环己烷的不对称开环反应, 与用Salen直接催化相比, 得到了更好的化学产率和对映选择性. 当用Ga(Slane) 15为催化剂时, 最佳ee值为73%.     

Pamoic acid in forming metallo-organic framework: Synthesis, characterization and first crystal structure of a dimeric Ti(IV) complex

Two novel dinuclear Ti(IV) complexes of the ligand, 4,4′-methylene-bis (3-hydroxy-2-naphthalene carboxylic acid) (H₄L) or pamoic acid having compositions, [(HL)₂Ti₂(μ-O)(DMF)₂]·(DMF)₆ (1) and [(L)₂Ti₂(μ-O)(DMF)₂]·(DMF)₄(4,4′-Bipy-2H)(H₂O), (2) have been synthesized and characterized by analytical and spectral methods and the structure has been established by single crystal XRD. Unlike the reported polymeric structures observed in case of H₄L or pamoic acid, the anti-conformation of H₄L changes to syn - orientation to avoid poly-metallic complex formation, as noticed in 1 and 2. The dimeric Ti(IV) units stack in the lattice to form helical columns and the space between the adjacent columns is being filled by the solvent molecules in 1 and solvent plus the protonated 4,4′-bipy in the lattice of 2 and thus the neighbor columns are connected through weak interactions.     

大位阻手性吡咯烷(salen)Mn(III)配合物在烯烃不对称环氧化反应中的应用

设计合成了具有大位阻的手性吡咯烷(salen)Mn(III)配合物Mn3,并研究了其在NaClO水/有机两相氧化体系中催化烯烃的不对称环氧化反应性能。 具有叔胺基团的配合物Mn3具有比Jacobsen催化剂更高的反应活性、以及近似的产率和略高的对映选择性。 尤其是过量CH₃I的加入可以极大地缩短环氧化反应的时间,而高产率和高对映选择性依然保持。     

Ring-opening Polymerization of e-Caprolactone Using Lanthanide Tris(4-tert-butylphenolate)s as a Single-component Initiator

The ring-opening polymerization of e-caprolactone (CL) initiated by novel single lanthanide tris(4-tert-butylphenolate)s [Ln(OTBP)3] is reported. Single-component La(OTBP)3 can effectively prepare polycaprolactone (PCL) with over 90% yield and viscosity average molecular weight about 60 x 10 under quite mild conditions: molar ratio of CL to initiator is 1000, 60 C, 2 h in toluene. Mechanism study indicates that the monomer inserts into the growing chain via the break of acyl-oxygen bond of CL.     

Polymer-supported lewis acid catalysts. VII. Polystyrene-bonded Ti(IV) chloride catalysts

A polystyrene-bonded Ti(IV) chloride catalyst was synthesized by the reaction of a polystyryl lithium (catalyst I , PS—TiCl₂) or a polystyryl magnesium (catalyst II , PS-TiCl₃) combined with titanium tetrachloride. The catalyst produced is a polymeric organometallic compound containing 0.479 mmol Ti/g catalyst, 0.986 mmol Cl/g catalyst (catalyst I ) and 0.281 mmol Ti/g catalyst, 0.766 mmol Cl/g catalyst (catalyst II ), depending on the method of synthesis. Both catalysts showed very good stability and good catalytic activity in such organic reactions as esterification, acetalation, and ketal formation. They can be reused many times without losing its catalytic activity. © 1993 John Wiley & Sons, Inc.     

Ring-opening Polymerization of ε-Caprolactone Using Lanthanide Tris（4-tert-butylphenolate）s as a Single-component Initiator

The ring-opening polymerization of ε-caprolactone (CL) initiated by novel singlelanthanide tris(4-tert-butylphenolate)s [Ln(OTBP)3] is reported. Single-component La(OTBP)3can effectively prepare polycaprolactone (PCL) with over 90% yield and viscosity averagemolecular weight about 60 × 103 under quite mild conditions: molar ratio of CL to initiator is 1000,60 ℃, 2 h in toluene. Mechanism study indicates that the monomer inserts into the growing chainvia the break of acyl-oxygen bond of CL.     

Chromatographic behaviour of metal ions on tin(IV) and titanium(IV) antimonate papers

Summary The chromatographic behaviour of 49 metal ions has been studied on papers impregnated with Sn(IV) and Ti(IV) antimonates in aqueous HNO₃ and mixed solvent systems containing dimethyl sulphoxide. Numerous separations have been achieved and the Alberti equation, for Sn(IV) and Ti(IV) antimonate papers, in the modified form: –nloga K⁺=R_M + constant (a K⁺=activity of K⁺), has been verified. The effect of the concentration of impregnating reagents on these papers has been determined and compared with other papers. The effect of pH on R_f, R_i, log R_f and R_M values of metal ions has also been examined in aqueous systems.     

Kinetic studies on the reduction of a nickel (III) oxime-imine complex by sulphur(IV) and selenium(IV)

The kinetics of the reduction of [Ni^III(L¹)]²⁺ (where HL¹ = 15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en-2-one oxime) by sulphur(IV) and selenium (IV) over the regions pH 2.50–8.02 and 2.01–4.00 respectively have been investigated at 30°C. Attempts were made to evaluate the reactivity of all the reacting species, of sulphur(IV) and selenium(IV) by considering suitable pH ranges. The oxidation of SC₂·H₂O and HSO ₃ ⁻ is proposed to proceed through the formation of a hydrogen-bonded adduct. The reaction with SO ₃ ²⁻ seems to follow a direct outer-sphere route which is well supported by Marcus crossrelation calculation. The oxidation of HSeO _l3 ⁻ is ≈ 10³ times slower than that of H₂SeO₃. The kinetic data indicate that the oxidation of sulphur(IV) by [Ni^IIIL¹)]²⁺ is much more favourable as compared to the corresponding oxidation of selenium(IV).     

Isomerization of Maleic Acid to Fumaric Acid Catalyzed by Cerium(IV) and N-Bromo Compounds

Maleic acid (MA) in aqueous sulfuric acid undergoes catalytic isomerization in the presence of small amounts of Cerium(IV) ion and N-bromosuccinimide (NBS) or N-bromoacetamide (NBA). The rate of isomerization is very fast even at room temperature and the yield is quite acceptable. The rate of isomerization depends on the relative amounts of MA, Ce(IV), NBS, NBA, and H₂SO₄. However, maleic acid has greater effect on the final yield. Sulfuric acid exhibits more chemical effect than physical effects. The competitive redox reactions of Ce(IV), NBS, and NBA with MA limit the yield of isomerization to about 85%. In the vicinity of room temperature, a raise of five degrees in temperature nearly doubles the rate of isomerization. Acrylamide shows inhibitive effect on the isomerization. The rate of hydrolysis of NBS or NBA in aqueous acidic solution depends on the concentrations of hydrogen ion, and NBS or NBA itself. The rate of hydrolysis of NBA is much faster than that of NBS. Mechanism involving bromine atom as catalyst is proposed to explain experimental results.     

Kinetics and Mechanism of Iridium（Ⅲ）-Catalyzed Oxidation of Ethanol Amine by Cerium（ Ⅳ ） in Sulfuric Acid Media

In this study, the kinetics and mechanism of the iridium(Ⅲ)-catalyzed oxidation of ethanol amine(EAN) by cerium(Ⅳ) in a sulfuric acid medium was investigated using titrimetric technique of redox in a temperature range of 298—313 K. It was found that the reaction is of first order with respect to Ce(Ⅳ) and Ir(Ⅲ), and a positive fractional order with respect to EAN. It was also found that the pseudo-first-order([EAN][Ce(Ⅳ)]) rate constant kobs decreases with the increase of [H ] and [HSO-4]. Under the protection of nitrogen gas, the reaction system can initiate the polymerization of acrylonitrile, indicating the generation of free radicals. On the basis of the experimental results, a suitable mechanism was proposed. From the dependence of kobs on the concentration of hydrogen sulfate, Ce(SO4)2 was found to be the kinetically active species. The rate constants of the rate-determining step together with the activation parameters were evaluated.     

Comparative Study of Aerobic Alkene Epoxidations Catalyzed by Optically Active Manganese(iii) and Cobalt(ii) Salen Complexes

A comparative study of aerobic alkene epoxidations in the presence of pivalaldehyde catalyzed by the optically active Mn(III)Salen and Co(II)Salen complexes has been performed. The nature of the asymmetric induction is discussed.     

The Spectrophotometry Determination of Mn(III) in the Presence of Mn(IV)

Abstract

The spectra of complex of Mn(III) and Mn(IV) with pyrophosphoric acid are investigated. The molar absorption coefficient of the complex of Mn(III) with pyrophosphoric acid is 80.6/Mcm at 510nm which is close to that of Mn(IV), 110/Mcm, however, the molar absorption coefficient of the complex of Mn(HI) with pyrophosphoric acid is only 4.98/Mcm at 398nm which is much less than that of Mn(IV), 390/Mcm. Based on this absorbance difference between Mn(III) and Mn(IV) at wavelength 398nm and 510nm, a procedure of determination of Mn(III) in the presence of Mn(IV) has been developed.     

47, 49Ti NMR spectra of half-sandwich titanium(IV) complexes

The 47, 49Ti chemical shifts, resonance line half-widths (Deltanu1/2) and energies of the first electronic charge-transfer transitions (lambdamax1.CT) of Cp'TiX3, where Cp' = eta5-C5H5 (Cp), eta5-C5H4Me (MeCp), eta5-C5HMe4 (Me4Cp), eta5-C5Me5 (Me5Cp), eta5-C5H4SiMe3 (SiCp), eta5-C5H4SnMe3 (SnCp) and eta5-C5H4SiMe2Cl (Si'Cp) and X = Cl, Br, I and OBut, half-sandwich complexes are reported. For the compounds studied, a direct linear relationship between delta(49Ti) and lambdamax1.CT was found.     

Spectrophotometric studies on the platinum(IV)-prochlorperazine bismethanesulfonate complex

We have studied the formation of a platinum complex and developed a simple, rapid and sensitive spectrophotometric method for the determination of platinum in solution. The method is based on the complexation reaction of the chromogen, prochlorperazine bismethane-sulfonate (PCPMS), with platinum(IV) in phosphoric acid medium which forms a reddish brown 1 1 complex with an absorption maximum around 528 nm. The reaction is fast in the presence of copper(II) and goes to completion within 1 min. Beer's law is obeyed over the concentration range 0.3–7.2 g/ml of platinum(IV) with an optimal range of 1.2–6.6 g/ml. The molar absorptivity is 2.65 × 10⁴1 mol^–1 cm^–1 and the Sandell's sensitivity is 7.8 ng cm^–2. The stability constant, logK, of the complex is 4.96±0.1 at 25 ° C. The effects of time, temperature, concentrations of acids, PCPMS and copper(II), and the interference by various ions are investigated. The method has been successfully applied to the determination of platinum content in alloys and minerals.     

Synthesis of Macrocyclic Compounds Using Diorganotin(IV) Dicarboxylates as Covalent Templates

A series of new macrocyclic compounds have been prepared by treating di- n -butyltin(IV) dicarboxylates of diphenic acid (biphenyl-2,2′-dicarboxylic acid), thiodiacetic acid and maleic anhydride with succinyl, adipoyl and sebacoyl dichlorides. The compounds have been characterized with the help of elemental analyses and spectral data (mass, IR, ^IH and ¹³C NMR).     

Exploitation of Dimeric Cyclic Cysteine as Helix Inducer in Ultra-Short Peptides for Cu(II)-Catalyzed Asymmetric Michael Addition on Chalcones

A dimeric cyclic cysteine analogue, i.e. (1R,1′R,2R,2′R)-2,2′-disulfanediylbis (aminocyclohexane-1-carboxylic acid), was used as a constrained unnatural amino acid and as a folding inducer in ultra-short Leu-Val-containing peptide. Our results showed that both free dimer amino acid L1 and its peptide derivative L2 are able to chelate Cu(II). The obtained complexes resulted to be catalytically active in Michael addition reaction of nitromethane on different types of chalcones. L1-Cu(II) was shown more reactive in terms of conversion, while, in neat conditions, L2-Cu(II) allows to obtain an interesting 60 % e.e. on pyridine chalcone.