Application of High Performance Liquid Chromatography to Separation of Novel Chiral Tetrahedral Heterometal Clusters

A series of novel chiral tetrahedral heterometal clusters have firstly been separated on cellulose tris-(3,5-dimethylphenylcarbamate) stationary phase by high performance liquid chrom-atography, using hexane as the mobile phase with various alcohols as modifiers.     

Heterometal ammineaqua diphosphates

Heterometal (copper-nickel, copper-zinc, copper-cadmium, and nickel-zinc) ammineaqua diphosphates are synthesized. Their composition and structure are determined by chemical analysis, paper chromatography, electronic, IR, and ESR spectroscopy, and X-ray phase analysis.     

Chalcogen-Containing Manganese Carbonyl Clusters: Synthesis and Structural Transformations

Recently, we have developed several synthetic routes to the new classes of chalcogen-containing manganese carbonyl clusters, and the interesting structural transformations and reactivity of the resultant clusters have been investigated as well. In this short review, the syntheses and bonding modes of the sulfur, selenium, and tellurium-containing manganese carbonyl complexes reported by our laboratory will be presented, and the cluster growth and transformation will be systematically compared and discussed.     

Heterometal expansion of oxozirconium carboxylate clusters

Although representing a 'thermodynamic sink', the octahedral oxozirconium {Zr(6)O(4)(OH)(4)} cluster structure can be magnetically functionalized by up to six 3d metal cations with a combination of flexible aminoalkoxide and carboxylate ligands.     

A New Synthetic Methodology in the Preparation of Bimetallic Chalcogenide Clusters via Cluster-to-Cluster Transformations

A decanuclear silver chalcogenide cluster, [Ag₁₀(Se){Se₂P(OⁱPr)₂}₈] (2) was isolated from a hydride-encapsulated silver diisopropyl diselenophosphates, [Ag₇(H){Se₂P(OⁱPr)₂}₆], under thermal condition. The time-dependent NMR spectroscopy showed that 2 was generated at the first three hours and the hydrido silver cluster was completely consumed after thirty-six hours. This method illustrated as cluster-to-cluster transformations can be applied to prepare selenide-centered decanuclear bimetallic clusters, [Cu_xAg_10-x(Se){Se₂P(OⁱPr)₂}₈] (x = 0–7, 3), via heating [Cu_xAg_7−x(H){Se₂P(OⁱPr)₂}₆] (x = 1–6) at 60 °C. Compositions of 3 were accurately confirmed by the ESI mass spectrometry. While the crystal 2 revealed two un-identical [Ag₁₀(Se){Se₂P(OⁱPr)₂}₈] structures in the asymmetric unit, a co-crystal of [Cu₃Ag₇(Se){Se₂P(OⁱPr)₂}₈]_0.6[Cu₄Ag₆(Se){Se₂P(OⁱPr)₂}₈]_0.4 ([3a]_0.6[3b]_0.4) was eventually characterized by single-crystal X-ray diffraction. Even though compositions of 2, [3a]_0.6[3b]_0.4 and the previous published [Ag₁₀(Se){Se₂P(OEt)₂}₈] (1) are quite similar (10 metals, 1 Se²⁻, 8 ligands), their metal core arrangements are completely different. These results show that different synthetic methods by using different starting reagents can affect the structure of the resulting products, leading to polymorphism.     

Diastereoselective spiroannelation

The diastereoselection in the reaction of 1,4-di-(bromomagnesio) pentane with various structures of lactones and cyclic anhydrides is described.     

多核烷氧基簇合物Ln2Na8(OCH2CH2NMe2)12(OH)2作为均相催化剂催化Tishchenko反应

多核烷氧基稀土碱金属簇合物Ln2Na8(OCH2CH2NMe2)12(OH)2对Tishchenko反应显示良好的催化活性,高效催化一系列醛的二聚反应生成相应的酯。本文考察了多种因素对该催化反应活性的影响,并提出了可能的反应机理。     

Diastereoselective Darzens condensations

N,N-Diphenyl-α-haloacetamides undergo Darzens condensations with aldehydes under heterogeneous reaction conditions in the presence of a metal hydroxide base. By appropriate choice of solvent, base and halide, very high diastereoselectivities favouring formation of the cis- or trans-epoxide can be obtained.     

Studies on the Diastereoselective Preparation of Bis-cyclopropanes

The identification of two natural products, FR-900848 and U-106305, has stimulated interest concerning the relationship between configurational isomerism, conformational isomerism, and biological activity of polycyclopropanes. Efforts to investigate the relationship between configurational and conformational isomerism through molecular modeling suggest that significantly different three-dimensional structures will result from unique primary structures. Any effort to address these issues demands that stereoselective methods for the preparation of polycyclopropanes be developed. We have investigated the application of zinc-carbenoid cyclopropanation in the presence of chiral dioxaboralanes to the preparation of eight stereochemically unique bicyclopropanes. The trans-vinylcyclopropane starting materials demonstrated very little substrate-induced stereoselectivity, while the cis-vinylcyclopropane demonstrates modest to excellent stereocontrol. A model for the substrate-based stereocontrol is proposed. We also used the spectroscopic data gathered in this investigation to probe the substrate-mediated stereocontrol in the rhodium(II)-catalyzed cyclopropanation of vinylcyclopropanes with ethyl diazoacetate.     

Diastereoselective reductive nitro-Mannich reactions

A range of nitroalkenes 1 and imines 3 derived from alkyl, aryl, and heteroaryl aldehydes underwent a tandem 1,4-hydride addition nitro-Mannich reaction to afford anti-rich β-nitroamines 4. The crude anti-β-nitroamines 4 could be converted to the corresponding anti-β-nitroacetamides 5 (33 examples) to allow purification in good yield from the parent nitroalkenes (60-87%), and with a high diastereomeric ratio (90:10 to mostly >95:5). A representative selection of anti-β-nitroacetamides 5 (five examples) were reduced to vicinal diamines 7 with zinc hydrochloride; concomitant acyl migration provided differentially protected vicinal diamines 7 in good yield (80-91%).     

Diastereoselective synthesis of cyclosaligenyl-nucleosyl-phosphotriesters

A diastereoselective synthesis of cycloSal-phosphotriesters (cycloSal=cycloSaligenyl) based on chiral auxiliaries has been developed that allows the synthesis of single diastereomers of the cycloSal-pronucleotides. In previously described synthesis routes, the cycloSal-compounds were always obtained as 1:1 diastereomeric mixtures that could be separated in only rare cases. However, it was shown that the diastereomers have different antiviral activity, toxicity, and hydrolysis stabilities. Here, first a chiral thiazoline derivative was used to prepare nonsubstituted and 5-methyl-cycloSal-phosphotriesters in 48 and ≥95% de (de=diastereomeric excess). However, this approach failed to give the important group of 3-substituted cycloSal-nucleotides. Therefore, two other chiral groups were discovered that allowed the synthesis of (R(P))- and (S(P))-3-methyl-cycloSal-phosphotriesters as well. The antiviral activity was found to be five- to 20-fold different between the two individual diastereomers, which proved the importance of this approach.