Synthesis of designed hetero-polytopic cryptands through Schiff base condensation
TL;DR: In this article, low-temperature synthesis of a number of hetero-polytopic cryptands has been achieved in good yields without employing any templating metal ion, and the cryptands are designed to hold more than one metal ion in its cavity.
Abstract: Low-temperature synthesis of a number of hetero-polytopic cryptands have been achieved in good yields without employing any templating metal ion. The cryptands are designed to hold more than one metal ion in its cavity.
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TL;DR: In this paper, the role of compartmental ligands, i.e. their ability to bind two or more metal ions in close proximity into two identical or different compartments, and their relevance in modulating the type and the extent of mutual interaction between the metal ions inside the adjacent chambers are reviewed.
Abstract: The design and synthesis of [1 + 1], [2 + 2], [3 + 3] or [3 + 2] macrocyclic or macrobicyclic Schiff bases, the multiple self-condensation procedure between appropriate polyformyl- and polyamine-precursors or the templating capability of different metal ions in directing the synthetic pathway toward specific compounds are reported together with the use of transmetalation reactions of particular complexes with a different metal salt in order to obtain not otherwise accessible complexes. The reduction of the cyclic Schiff base or the reductive demetalation of the related complexes to the polyamine homologues is also considered. These systems can form mononuclear, homo- and heterodinuclear (or polynuclear) complexes, when reacted with appropriate metal salts. Attention is especially devoted to the physico-chemical and structural aspects of the resulting systems, especially the magneto-structural relationships arising from the interaction of paramagnetic ions, coordinated inside a unique moiety. The role of compartmental ligands, i.e. their ability to bind two or more metal ions in close proximity into two identical or different compartments, the presence of bridging groups inside these coordination moieties and their relevance in modulating the type and the extent of mutual interaction between the metal ions inside the adjacent chambers is also reviewed. The insertion of asymmetry into these ligands provides important diversification of the coordinating sites and allows for different and well defined recognition processes involving specific cations and/or anions at the adjacent sites.
341 citations
TL;DR: A modular approach for the synthesis of cage structures is described, and an amine exchange process with ethylenediamine allows the clean conversion of a dodecanuclear cages into a hexanuclear cage without disruption of the metallamacrocyclic structures.
Abstract: A modular approach for the synthesis of cage structures is described. Reactions of [(arene)RuCl2]2 [arene = p-cymene, 1,3,5-C6H3Me3, 1,3,5-C6H3(i-Pr)3] with formyl-substituted 3-hydroxy-2-pyridone ligands provide trinuclear metallamacrocycles with pendant aldehyde groups. Subsequent condensation reactions with di- and triamines give molecular cages with 3, 6, or 12 Ru centers in a diastereoselective and chemoselective (self-sorting) fashion. Some of the cages can also be prepared in one-pot reactions by mixing [(arene)RuCl2]2 with the pyridone ligand and the amine in the presence of base. The cages were comprehensively analyzed by X-ray crystallography. The diameter of the largest dodecanuclear complex is ∼3 nm; the cavity sizes range from 290 to 740 A3. An amine exchange process with ethylenediamine allows the clean conversion of a dodecanuclear cage into a hexanuclear cage without disruption of the metallamacrocyclic structures.
145 citations
TL;DR: A review of reductive aminations using borohydride and borane reducing agents can be found in this article, where the authors focus on those conditions in which the carbonyl component, amine, and reducing reagent react in the same vessel.
Abstract: Reductive amination is an important tool for synthetic organic chemists in the construction of carbon-nitrogen bonds. This reaction, also termed reductive alkylation, involves condensation of an aldehyde or ketone with an amine in the presence of a reducing agent. A wide variety of substrates can be used including aliphatic and aromatic aldehydes and ketones, and even benzophenones. A range of amines from ammonia to aromatic amines, including those with electron-withdrawing substituents, can be employed. For particularly sluggish reactions, such as those involving weakly electrophilic carbonyl groups, poorly nucleophilic amines, or sterically congested reactive centers, additives such as molecular sieves or Lewis acids are often useful.
This chapter focuses on those conditions in which the carbonyl component, amine, and reducing reagent react in the same vessel. This review is restricted to reductive aminations using borohydride and borane reducing agents. This chapter concentrates on reductive amination chemistry mediated by borohydride and other boron-containing reducing agents from 1971, the year when sodium cyanoborohydride was introduced, through the middle of 1999. In addition to reductive aminations of aldehyde and ketone substrates, reactions of related structures including acetals, aminals, ketals, carboxylic acids, nitriles, and dicarbonyls that form a nitrogen-containing ring are reviewed. Intramolecular processes in which the substrate contains both the carbonyl and amine moieties are described. The intramolecular variant is a useful method for preparing cyclic amines. All of the various boron-containing hydride sources in reductive aminations, including labeled metal hydrides, are reviewed. Instances of reductive aminations that failed are described. Applications of this method to a solid support in parallel synthesis in combinatorial chemistry as well as reductive aminations that proceed in tandem with a second reaction such as reductive lactamizations are discussed.
Keywords:
organic reaction(s);
organic synthesis;
reaction(s);
synthesis;
reductive amination;
condensation;
alkylation;
reductive alkylation;
reduction;
amination;
carbonyl;
amine;
reducing agent(s);
borohydride;
borane;
carbon-nitrogen bond(s);
CN bond(s)
136 citations
TL;DR: A simple, clean, and highly efficient green protocol has been developed for synthesis of bis(indolyl), di(bis-indolyL), and tris-indolel methanes by the reaction of indole with aldehydes and ketones in the presence of oxalic acid dihydrate.
Abstract: A simple, clean, and highly efficient green protocol has been developed for synthesis of bis(indolyl), di(bis-indolyl), and tris-indolyl methanes by the reaction of indole with aldehydes and ketones irn the presence of oxalic acid dihydrate [(CO2H)2·2H2O] and N-cetyl-N, N, N-trimethylammonium bromide (CTAB) in water. Also, tri(bis-indolyl) and tetra(bis-indolyl)methanes as new bis(indolyl)methanes were prepared under thermal conditions.
60 citations
TL;DR: Laterally non-symmetric cryptands are defined as cryptands where the two bridgehead atoms like N or C or benzene units are connected by three bridges such that the donor atoms about the bridgeheads are different as mentioned in this paper.
Abstract: Cryptands where the two bridgehead atoms like N or C or benzene units are connected by three bridges such that the donor atoms about the bridgeheads are different can be called laterally non-symmetric cryptands These cryptands constitute a class which can be useful in several contemporary areas of research The present article describes the synthesis of the cryptands and the use of metal cryptates in homogeneous catalysis, in the photochemical splitting of water to generate H 2 , in the cleavage of nucleic acids as chemical nucleases These cryptands can be derivatized to have new receptors which might be useful as well
35 citations
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TL;DR: The synthesis of a new macrobicyclic cryptand (L) with heteroditopic receptor sites has been achieved in good yields by the [1 + 1] Schiff base condensation of tris(2-aminoethyl)amine (tren) with the tripodal trialdehyde, tris{[2-(oxomethyl)phenyl)oxy]ethyl}amine at 5 degrees C temperature.
Abstract: The synthesis of a new macrobicyclic cryptand (L) with heteroditopic receptor sites has been achieved in good yields by the [1 + 1] Schiff base condensation of tris(2-aminoethyl)amine (tren) with the tripodal trialdehyde, tris{[2-(3-(oxomethyl)phenyl)oxy]ethyl}amine at 5 degrees C temperature. The crystal structure of L (P2(1)/c, a = 10.756 (5) A, b = 27.407(9) A, c = 12.000(2) A, beta = 116.22(3) degrees, Z = 4, R = 0.060, R(w) = 0.058) shows a pseudo-3-fold symmetry axis passing through the two bridgehead nitrogens. This symmetry is maintained in chloroform solution also, as indicated from its (1)H-NMR spectral data. The cryptand readily forms inclusion complexes with the Cu(II) ion at the tren end of the cavity. The tetracoordinated Cu(II) cryptate (1) thus formed with Cu(picrate)(2) exhibits a very small A(II) value (60 x 10(-)(4) cm(-)(1)) in its EPR spectrum and low-energy ligand field bands in its electronic spectrum in MeCN at room temperature. The bound Cu(II) ion readily accepts the anions CN(-), SCN(-), or N(3)(-), forming distorted trigonal bipyramidal complexes (2-4). The crystal structure of [Cu(L)(CN)](picrate) (2) (P2(1)/C, a = 13.099(1) A, b = 11.847(8) A, c = 25.844(7) A, beta = 91.22(1) degrees, Z = 4, R = 0.056, R(w) = 0.054) has been determined. The equatorial coordination is provided by the three secondary amino N atoms of the tren unit in L, while the two axial positions are occupied by the bridgehead N of the tren unit and the C atom of the cyanide group. One of the equatorial Cu-N bond distances is 2.339(6) A, which is longer than normal values. The crystal structure of [Cu(L)(NCS)](picrate) (3) (C2/c, a = 47.889(10) A, b = 10.467(5) A, c = 16.922(2) A, beta = 93.90(2) degrees, Z = 8, R = 0.054, R(w) = 0.055) shows the coordination geometry around the Cu(II) ion to be very similar to that in the case of 2. The electronic spectral and EPR spectral data obtained on 2-4 are characteristic of trigonal bipyramidal Cu(II) complexes. The three meta-substituted benzene rings present in L makes the donor atom somewhat rigid in nature which enforces a distorted geometry around the Cu(II) ion.
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