Chiral Amine Ligands Research Articles

Chiral cadmium-amine complexes for stimulating non-linear optical activity and photoluminescence in solids based on aurophilic stacks.

The design of high-performance optical materials can be realized using coordination polymers (CPs) often supported by non-covalent interactions, such as metallophilicity. The challenge is to control two or more optical effects, e.g., non-linear optics (NLO) and photoluminescence (PL). We present a new strategy for the combination of the NLO effect of second-harmonic generation (SHG) and the visible PL achieved by linking dicyanidoaurate(i) ions, which form luminescent metallophilic stacks, with cadmium(ii) complexes bearing chiral amine ligands, used to break the crystal's symmetry. We report a family of NLO- and PL-active materials based on heterometallic Cd(ii)-Au(i) coordination systems incorporating enantiopure propane-1,2-diamine (pda) ligands (1-S, 1-R), their racemate (2), and enantiopure trans-cyclopentane-1,2-diamine (cpda) ligands (3-S, 3-R). Due to acentric space groups, they exhibit the SHG signal, tunable within the range of 11-24% of the KDP reference, which was correlated with the dipole moments of Cd(ii) units. They show efficient blue PL whose energy and quantum yield, the latter ranging from 0.40 to 0.83, are controlled by Cd(ii) complexes affecting the Au-Au distances and vibrational modes. We prove that chiral Cd(ii)-amine complexes play the role of molecular agents for the stimulation of both the NLO and PL of the materials based on aurophilic stacks.

Control of chirality inversion kinetics of triple-helical metallocryptands

Abstract Dynamic helical molecules, which can undergo a reversible chirality inversion between the P and M forms, are useful as a platform for switchable chiral functional molecules. The chirality inversion of these molecules has been extensively studied. However, it has mostly been discussed from the viewpoint of the equilibrated P/M ratios before and after the inversion; control of the response speeds or kinetic profiles has rarely been explored. In order to construct helical structures with controllable kinetic profiles, triple-helical metallocryptands, LM3, have been designed and synthesized. These molecules can undergo a relatively slow dynamic P/M chirality inversion (helicity inversion) to produce an equilibrated mixture. The P/M equilibration was accelerated or decelerated based on the following two strategies. One is based on the guest binding in the cryptand cavity. The P/M racemization kinetics of LNi3 was significantly decelerated by recognition of guanidinium ion in the cavity. The other strategy is based on the ligand exchange reactions at the octahedral cobalt(III) centers in LCo3(amine)6. The P/M chirality inversion speeds were controlled by changing the initial and entering amine ligands. In addition, a unique transient chirality inversion behavior was observed when chiral amine ligands were removed from the metallocryptand by the ligand exchange reaction with piperidine.

Chiral amine ligands at rhenium(V) pentahydride complexes allow for characterization of an energetically accessible and reversible steric inversion of diastereotopic phosphorus atoms

Three new rhenium(V) pentahydride complexes stabilized by a pair of triphenylphosphine ligands and a chiral amine ligand were prepared. Dynamic 31P-{1H} NMR spectroscopy of the chiral complexes demonstrates an unusual steric inversion for the diastereotopic pair of phosphorus atoms in each chiral complex. One chiral ReH5(PPh3)2(amine) complex is supported by an aromatic amine ligand and demonstrates unambiguously that such ligands participate in a steric inversion dynamic process rather than a simple rotation about the Re-N bond. The activation parameters and rate constants for the steric inversion can be determined directly or indirectly for non-hydride atom dynamic processes in two of the three chiral complexes from simulations of dynamic NMR spectra. Characterization of the steric inversion step by atoms other than hydride ligands allows for a means to test whether any hydride ligand exchange processes are manifestations of the steric inversion process. Under the experimental conditions in this report, a pairwise exchange of hydride ligands that reside in pseudododecahedral A sites appears to be a separate manifestation of the steric inversion dynamic process. A change in the nominal coordination number seems likely to cause the steric inversion that is reported.

Asymmetric C(sp3)\u2013H functionalization of unactivated alkylarenes such as toluene enabled by chiral Br\xf8nsted base catalysts

Benzylic functionalisation of unactivated alkylarenes remains as a significant challenge in asymmetric catalysis due to their less reactive nature. Here, we show development of catalytic asymmetric C(sp3)–H functionalization of unactivated alkylarenes such as toluene with imines. The reactions proceeded smoothly under proton-transfer conditions using a chiral, strong Brønsted base catalyst system. A chiral Brønsted base prepared from an alkylpotassium and a chiral amine ligand was found to effectively form a promising asymmetric environment around a benzyl anion. Optimization of the reaction conditions revealed that the use of the alkaline metal amide, potassium hexamethyldisilazide (KHMDS), as an additive was most effective, and enantioselective and atom economical carbon–carbon bond-forming reactions at the benzylic positions of unactivated alkylarenes was achieved without using any transition-metal catalyst.

L-Proline/CeCl3·7H2O-NaI mediated stereoselective synthesis of α-2-deoxy glycosides from glucal

Glucal with different alcohols can be converted into the corresponding 2-deoxy glycosides without Ferrier rearrangement in high yield by treatment with eco friendly transition metal based catalysts [CuCl3·2H2O-NaI (A) or CeCl3·7H2O-NaI (B)] and chiral amine ligand L-proline at various reaction conditions which were optimized for stereoselectivity. The catalyst CeCl3·7H2O-NaI (B) and ligand L-proline in toluene, was found to be much more efficient and high atom economic for the stereoselective glycosidation of propargyl alcohol with glucal, afforded exclusively α-2-deoxy propargyl glycoside in 98% optimized yield. The ligand L-proline was used for the first time in stereoselective glycosidation of α-2-deoxy glycosides involving glucal and alcohols.

ChemInform Abstract: Asymmetric Transfer Hydrogenation of Ketones with Modified Grubbs′ Metathesis Catalysts: On the Way to a Tandem Process.

AbstractUpon addition of a chiral amine ligand, an alcohol and a base, the 1st generation Hoveyda—Grubbs catalyst is in situ transformed into an asymmetric transfer hydrogenation catalyst, promoting the enantioselective reduction of acetophenone to 1‐phenylethanol.

Asymmetric Transfer Hydrogenation of Ketones with Modified Grubbs Metathesis Catalysts: On the Way to a Tandem Process

AbstractHerein, we report the successful transformation of a 1st generation Grubbs metathesis catalyst into an asymmetric transfer hydrogenation (ATH) catalyst. Upon addition of a chiral amine ligand, an alcohol and a base, the 1st generation Hoveyda–Grubbs catalyst (HG‐I) was found to promote the enantioselective reduction of acetophenone to 1‐phenylethanol. After optimizing the order of addition and the reaction conditions, the substrate scope was assessed leading to enantiomeric excesses up to 97% ee. NMR experiments were run in order to get information about the in situ‐generated ATH catalyst. Furthermore, the possibility to perform olefin metathesis and ketone transfer hydrogenation sequentially in one pot was demonstrated, and the first tandem olefin metathesis–ketone asymmetric transfer hydrogenation was carried out.magnified image

Preparation and use of a chiral amine ruthenium hydrogenation catalyst supported on mesoporous silica

Abstract We report the synthesis and use of dichloro-( S )-6,6′-dimethyl-2,2′-diaminobiphenyl-ruthenium complex (( S )-MAB-Ru), an air-stable, highly active catalyst for the hydrogenation of α,β-unsaturated carboxylic acids at 25 °C and 4.85 atm hydrogen. The homogeneous hydrogenations of itaconic acid and α-acetamidocinnamic acid had yields above 97% in each case, and the enantiomeric excesses (e.e.) were 80 and 69.8% to the ( R )-products, respectively. When we used ( S )-MAB-Ru chemically bound to MCM-41, a mesoporous SiO 2 , the conversion of both acids was complete and both e.e. were practically 97%. The solid-bound catalyst was successfully reutilized in the hydrogenation of itaconic acid and the drop in asymmetric induction was only 3% after three runs. The fact that complexes containing chiral amine ligands provide such high yields and e.e. opens a potentially important area of research in the design of industrially relevant catalysts.

Chiral discrimination in platinum anticancer drugs.

In this article we review the biological activity of analogs of the antitumor drug cisplatin that contain chiral amine ligands. Interaction with DNA and formation of cross-links with adjacent purine bases are considered to be the crucial steps in the antitumor activity of this class of complexes. Because double-helical DNA has a chiral structure, interaction with enantiomeric complexes of platinum should lead to diastereomeric adducts. It has been demonstrated that DNA cross-links of platinum complexes with enantiomeric amine ligands not only can exhibit different conformational features but also can be processed differently by the cellular machinery as a consequence of these conformational differences. These results expand the general knowledge of how the stereochemistry of the platinum-DNA adduct can influence the cell response and contribute to understanding the processes that are crucial for antitumor activity. The steric requirements of the chiral ligands, in terms of configuration and flexibility, are also elucidated.

Enantiomer-Selective Radical Cyclopolymerization of rac-2,4-Pentanediyl Dimethacrylate Using ATRP Initiating System with Chiral Amine Ligand

Enantiomer-Selective Radical Cyclopolymerization of <i>r</i><i>ac</i>-2,4-Pentanediyl Dimethacrylate Using ATRP Initiating System with Chiral Amine Ligand

Deprotonation of Organic Compounds Bearing Acid Protons Promoted by Metal Amido Complexes with Chiral Diamine Ligands Leading to New Organometallic Compounds

Well-defined 16-electron metal amido complexes bearing chiral Ts-diamine ligands readily react with nitromethane, acetone, or phenylacetylene to give new organometallic compounds in almost quantitative yields. For example, an Ir amido complex, Cp*Ir[(R,R)-Tscydn], reacts with nitromethane at room temperature to give quantitatively a nitromethyl Ir complex, Cp*Ir(CH2NO2)[(R,R)-Tscydn], as a single diastereomer. The isolable organometallic compounds with chiral amine ligands are relevant to active catalysts for asymmetric C−C bond formation.

New chiral amine ligands for enantioselective synthesis of certain (S)- and (R)-monobactams

Two new tridentate chiral amine ligands I and II mediated the condensation reaction of lithium ester enolate III with benzaldehyde p-​anisidineimine IV providing selectively the required (S)​- or (R)​-​monobactam V. It is also noticed that the coexistence of III and chiral lithium amides that formed -​in situ- from I,​II is an important factor for the enhancement of the reactivity and enantioselectivity of III.

The first structurally characterized, quadruple-bonded complexes containing chiral amine ligands; syntheses, structures and optical activities of [Mo2Cl4(S-chea)4] and [Mo2Cl4(R-chea)4] (chea = 1-cyclohexylethylamine) †

The complexes [Mo2Cl4(S-chea)4] 1 (chea = 1-cyclohexylethylamine) and [Mo2Cl4(R-chea)4] 2 were prepared by reactions of [Mo2Cl4(PPh3)2(MeOH)2] with S- and R-chea, respectively, in acetone. Their NMR, UV/VIS and circular dichroism spectra have been recorded and the structures of both 1 and 2 have been determined. The molybdenum atoms in both crystal structures were found to be disordered, so that while only one set of ligand atoms can be resolved, there are two incompletely occupied sets of metal atoms. The ratios of the primary to the secondary form are 97∶3 and 94∶6 for 1 and 2, respectively. The lowest-energy bands of the absorption spectra at 531 nm for both 1 and 2 can be assigned to δxy → δxy* transitions. The solid-state CD spectra of these two complexes show two prominent bands at 520 and 455 nm and form mirror images of each other. The variable-temperature CD spectra of the complexes in toluene intersect in isosbestic points, indicating temperature-dependent equilibria between pairs of conformers for each complex. The Wood–Fickett–Kirkwood method has been used to calculate the free-energy changes of the Δ and Λ conformers and their populations in solution.

ChemInform Abstract: Construction of Contiguous Chiral Tertiary Carbon Centers by Enantioselective Michael Reaction of Ketone Lithium Enolates Using a Chiral Amine Ligand.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Construction of contiguous chiral tertiary carbon centers by enantioselective Michael reaction of ketone lithium enolates using a chiral amine ligand

The diastereo- and enantioselective Michael reaction of ketone lithium enolates using a chiral amine ligand ( 1) was examined. Michael adducts ( 4) were obtained in excellent chemical yields (95∼99%) with high stereoselectivities ( syn- 4 anti- 4 : 16 84 ∼ 1 99 ; ee of anti- 4: 81∼99 %) by the reaction between alkyl phenyl ketones ( 2) and Michael acceptors ( 3) having an alkylidene group.

Enantioselective Michael reaction of ketone lithium enolates using a chiral amine ligand

The enantioselective Michael reaction of ketone lithium enolates using a chiral amine ligand ( 1) was studied. Michael adducts ( 4) of up to 94% ee were obtained by the reaction between methyl ketones ( 2) and Michael acceptors ( 3) having a benzylidene group.

ChemInform Abstract: Enantioselective Palladium Catalyzed Allylic Alkylation with Phosphorus‐Containing C2‐Symmetric Chiral Amine Ligands.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Enantioselective palladium catalyzed allylic alkylation with phosphorus-containing C 2-symmetric chiral amine ligands

In the presence of the palladium complex with the phosphorus-containing C 2-symmetric chiral amine ligand 2, 3, the asymmetric allylic substitution of racemic 1,3-diphenyl-2-propenyl acetate 8 with dimethyl malonate proceeded in high yield with remarkable enantiomeric excess.

Addition of Tetrachloromethane to Styrene Catalyzed by Copper-Chiral Amine Complexes

Copper(I)-chiral amine complexes were found to be very efficient catalysts for addition reaction of tetrachloro- and bromotrichloromethane with styrene (yields over 90%). However, both monodentate and bidentate chiral amine ligands (I-VIII) gave a low asymmetric induction (up to 2.3% ee).

Asymmetric conjugate addition reactions with Chiral Amidocuprates: The effect of Cu(I) salts and coordinating heteroatoms

Chiral amidocuprates with methyl or n -butyl transferable ligands containing additional heteroatoms afforded higher asymmetric induction with CuBr than with CuI, although reactivity and chemical yields are generally higher with CuI. The enantiomeric excess generally increases with the number of heteroatoms in the chiral amine ligand available for coordination and was low and extremely variable for the bidentate system 1a.