Structural Chemistry of Methyl- and Allylpalladium(II) Complexes Containing Chiral Thioether Auxiliaries

The molecular structures of three Pd^II compounds are reported: a) the two [PdCl(Me)] complexes 7a and 8a each containing a different chiral N,S-chelate based on {[(dihydrooxazolyl)phenyl]methyl}-thioglucose backbones, e.g., chloro({2-[(4S)-4,5-dihydro-4-isopropyloxazol-2-yl-κN]phenyl}methyl 2,3,4,6-tetra-O-acetyl-1-(thio-κS)-β-D -glucopyranoside)methylpalladium(II) ( 7a ) and b) one [Pd(η³-C₃H₅)(P-S)]⁺ cation in which the P,S-chelate stems from a phosphinoferrocene and thioephedrine-derived thioether donor, i.e., [(S)-1-(diphenylphosphino-κP)-2-((1R)-1-{[(1R,2S)-1-phenyl-2-(piperidin-1-yl)propyl]thio-κS}ethyl)ferrocene] (η³-prop-2-enyl)palladium trifluoromethanesulfonate ( 11 ). In the methylpalladium compounds 7a and 8a the thioglucose-κS moiety is pseudo-axial (Figs. 2 and 3), whereas in the allyl complex, the thioephedrine-κS moiety is markedly pseudo-equatorial (Fig. 5). It is suggested, based on these results, that the shape (chiral pocket) of such coordinated chiral thioethers may not be readily predictable.     

Chiral Hybrid Germanium(II) Halide with Strong Nonlinear Chiroptical Properties

Due to the pronounced anisotropic response to circularly polarized light, chiral hybrid organic–inorganic metal halides have been regarded as promising candidates for the application in nonlinear chiroptics, especially for the second-harmonic generation circular dichroism (SHG-CD) effect. However, designing novel lead-free chiral hybrid metal halides with large anisotropy factors and high laser-induced damage thresholds (LDT) of SHG-CD remains challenging. Herein, we develop the first chiral hybrid germanium halide, (R/S-NEA)₃Ge₂I₇⋅H₂O (R/S-NGI), and systematically investigated its linear and nonlinear chiroptical properties. S-NGI and R-NGI exhibit large anisotropy factors (g_SHG-CD) of 0.45 and 0.48, respectively, along with a high LDT of 38.46 GW/cm²; these anisotropy factors were the highest values among the reported lead-free chiral hybrid metal halides. Moreover, the effective second-order nonlinear optical coefficient of S-NGI could reach up to 0.86 pm/V, which was 2.9 times higher than that of commercial Y-cut quartz. Our findings facilitate a new avenue toward lead-free chiral hybrid metal halides, and their implementation in nonlinear chiroptical applications.     

Applications of Intramolecular Cyclopropanations of Chiral Secondary Allylic Diazoacetates

The diastereomeric secondary allylic diazoacetates 6a,b and 8a,b , which were readily prepared from the common intermediate 4 , were cyclized in the presence of the achiral catalyst Cu(TBS)₂ to furnish mixtures of the adducts 9a,b/10a,b and 12a,b/13a,b , respectively; in these cyclizations, the diastereoselectivity of the reaction was substrate controlled. When 6a,b and 8a,b were cyclized in the presence of the chiral catalysts Rh₂[(5S)‐MEPY]₄ or Rh₂[(5R)‐MEPY]₄, the substrate‐based selectivity could be reversed if the chirality of the substrate and catalyst were matched. The advantages associated with the use of chiral catalysts to effect the diastereoselective cyclization of chiral allylic diazoacetates were demonstrated by the synthesis of 25 , which comprises the cyclopropane subunit found in the diterpene ingol B ( 14 ).     

High Diastereoselection of a Dissymmetric Capsule by Chiral Guest Complexation

Encapsulation of chiral guests in the dissymmetric capsule 1?4 BF₄ formed diastereomeric supramolecular complexes G ? 1?4 BF₄ ( G : guest). When chiral guests 2 a – q were encapsulated within the dissymmetric space of the self‐assembled capsule 1?4 BF₄, circular dichroism (CD) was observed at the absorption bands that are characteristic of the π–π* transition of the bipyridine moiety of the capsule, which suggests that the P and M helicities of the capsule are biased by the chiral guest complexation. The P helicity of diastereomeric complex (S)‐ 2 l ? 1?4 BF₄ was determined to be predominant, based on CD exciton coupling theory and DFT calculations. The diastereoselectivity was highly influenced by the ester substituents, such that benzyl ester moieties were good for improving the diastereoselectivity. A diastereomeric excess of 98 % was achieved upon the complexation of 2 j . The relative enthalpic and entropic components for the distereoselectivity were obtained from a van’t Hoff plot. The enthalpic components were linearly correlated with the substituent Hammett parameters (σ_p⁺). The electron‐rich benzyl ester moieties generated donor–acceptor π–π stacking interactions with the bipyridine moiety, which resulted in a significant difference in energy between the predominant and subordinate diastereomeric complexes.     

Asymmetric Synthesis of Perfluoroalkylated α-Amino Acids through Generated Radicals Using a Chiral Ni(II) Complex

Perfluoroalkylated α-amino acids (PFAAs) are a unique class of compounds for biochemistry and pharmaceutical science. In this context, we report the successful intermolecular coupling of the Belokon’s chiral dehydroalanine Ni(II) complex with a variety of perfluoroalkyl iodides. A 4-cyanopyridine/B₂Pin₂ catalytic system generates perfluoroalkyl radicals, which after trapping by the ligand sphere of a chiral Ni(II) complex provide the diastereomeric complexes with up to >20 : 1 dr (seven examples). The obtained major (S,S)-diastereomers were easily isolated by simple silica column chromatography in 33–54 % yields. The perfluoroalkylated α-AA was subsequently released from the obtained Ni(II) complex through aqueous HCl treatment. The chiral auxiliary ligand ((S)-BPB=(S)-2-(N-benzylprolyl)aminobenzophenone) can be easily recycled after the acidic complex decomposition and reused for the synthesis of the starting dehydroalanine Ni(II) complex.     

Pentanuclear Gold(I) Cluster with an Axially Chiral Biaryl Center: Synthesis and Chiral Transformation

We synthesized and structurally characterized a novel pentanuclear gold(I) cluster by a Ag(I)‐mediated organometallic transformation. The racemic mixture of this pentanuclear gold cluster has been successfully transformed into an enantio‐rich hexanuclear cluster compound by adding adscititious chiral species [Au₂(S‐BINAP)₂]²⁺ (S‐BINAP = (S)‐2,2’‐bis(diphenylphosphino)‐1,1’‐binaphthyl). In this process, a [AuPPh₃]⁺ species in the pentanuclear cluster is replaced by [Au₂(S‐BINAP)₂]²⁺. This strategy represents a new method for the designed construction of chiral metal clusters.     

Planar Chiral Rhodium Complexes of 1,4-Benzoquinones

Diene rhodium complexes are important catalysts in modern organic synthesis. Herein, we report a new approach to such complexes with the uncommon planar chirality. The synthesis is achieved by face-selective coordination of the prochiral 2,5-disubstituted-1,4-benzoquinones (R₂-Q) with rhodium precursors containing the chiral auxiliary ligand S-salicyl-oxazoline (S-Salox). Such coordination leads to the formation of (R,R-R₂-Q)Rh(S-Salox) complexes in high yields and with exceptional diastereoselectivity (d. r.>20 : 1). Subsequent replacement of the auxiliary ligand provides various benzoquinone rhodium complexes with retention of the planar chirality. Combined theoretical and experimental studies show that due to their electron-withdrawing nature benzoquinones bind metals stronger than the related 1,4-cyclohexadiene, but weaker than other common diene ligands, such as cyclooctadiene.     

Chiral Alkoxy Side Chains from (-)-Amino Acids in Mediating Asymmetric Synthesis of Tricarbonyl(cyclohexadienyl)iron Complexes

The asymmetric induction in the complexation reaction of (S)-1-methyl-2-(5-methyl-cyclohexa-1,4-dienylmethyloxy)-pyrrolidine 5 and (S)-2-(2-N,N-dimethylamino-1-propanoxy)-5-methylcyclohexa-1,4-diene 6 having heteroatom adjacent the stereogenic center has been investigated. The diastereoselectivity was determined directly from the diastereotopic peaks in the ¹H NMR or by chemical correlation with 9 . The conversion of η-1,4-complexes 7a and 8a to 9 proceeded with high retention of configuration while that of the η-2,5-Fe(CO)₃ complexes 7b and 8b undergoes considerable racemization.     

Cations Controlling the Chiral Assembly of Luminescent Atomically Precise Copper(I) Clusters

Chiral assembly and asymmetric synthesis are critically important for the generation of chiral metal clusters with chiroptical activities. Here, a racemic mixture of [K(CH₃OH)₂(18‐crown‐6)]⁺[Cu₅(S^tBu)₆]^? ( 1?CH₃OH ) in the chiral space group was prepared, in which the chiral red‐emissive anionic [Cu₅(S^tBu)₆]^? cluster was arranged along a twofold screw axis. Interestingly, the release of the coordinated CH₃OH of the cationic units turned the chiral 1?CH₃OH crystal into a mesomeric crystal [K(18‐crown‐6)]⁺[Cu₅(S^tBu)₆]^? ( 1 ), which has a centrosymmetric space group, by adding symmetry elements of glide and mirror planes through both disordered [Cu₅(S^tBu)₆]^? units. The switchable chiral/achiral rearrangement of [Cu₅(S^tBu)₆]^? clusters along with the capture/release of CH₃OH were concomitant with an intense increase/decrease in luminescence. We also used cationic chiral amino alcohols to induce the chiral assembly of a pair of enantiomers, [d /l ‐valinol(18‐crown‐6)]⁺[Cu₅(S^tBu)₆]^? ( d /l ‐Cu_5V ), which display impressive circularly polarized luminescence (CPL) in contrast to the CPL‐silent racemic mixture of 1?CH₃OH and mesomeric 1 .     

Enantiomorphs of a carbene–ruthenium(II)–porphyrin complex with four `chiral pillars'

The chiral metalloporphyrin (dibenzoylmethylene‐κC)(ethanol‐κO){5,10,15,20‐tetrakis[(1S,4R,5R,8S)‐1,2,3,4,5,6,7,8‐octahydro‐1,4:5,8‐dimethanoanthracen‐9‐yl]porphyrinato‐κ⁴N}ruthenium(II)–ethanol–dichloromethane (1/2/2), [Ru(C₈₄H₇₆N₄)(C₁₅H₁₀O₂)(C₂H₆O)]·2C₂H₆O·2CH₂Cl₂, and its enantiomorph were prepared from enantiomerically pure porphyrins. The enantiomers are potential versatile catalysts for asymmetric cyclopropanation, aziridination or epoxidation. In each compound, the rather large dibenzoylcarbene group is squeezed between four columnar 1,2,3,4,5,6,7,8‐octahydro‐1,4:5,8‐dimethanoanthracen‐9‐yl groups at the meso positions resulting in a doming deformation of the porphyrin core. The dibenzoylcarbene group has an anti conformation. The benzoyl O atoms make short van der Waals contacts (< 2.6 Å) with the methine groups of the chiral columnar substituents at the 10 and 20 positions of the porphyrin rings. A hydrogen‐bonded supramolecular chain is formed parallel to the b axis by interactions between the benzoyl O atom and the hydroxy groups of the coordinated and uncoordinated ethanol molecules.     

Synthetic and spectroscopic characterization of [Co(triphos)(chiral amino alcoholato)](BPh4) complexes

2,2,2-Tris(diphenylphosphinomethyl)ethane (triphos) coordinates to Co(BF₄)₂ · 6H₂O giving red-violet intermediate [Co(triphos)(S)₂](BF₄)₂ (S = solvent) in THF/EtOH. The addition of an equimolar amount of chiral amino alcohol (L-alaninol, S-2-phenylglycinol, R-1-amino-2-propanol and (±)-2-amino-1-phenyl-ethanol) and Na(OH) into this solution affords the green [Co(triphos)(chiral amino alcoholato)](BF₄) complexes. The addition of equimolar Na(BPh₄) precipitates the deep green [Co(triphos)(L-alaninolato)](BPh₄) (1), [Co(triphos)(S-2-phenylglycinolato)](BPh₄) (2), [Co(triphos)(R-1-amino-2-propanolato)](BPh₄) (3), and [Co(triphos)((±)-2-amino-1-phenyl-ethanolato)](BPh₄) (4) complexes, respectively. The complexes are isolated in good yields and characterized by elemental analysis, IR-, UV-Vis-, ¹H-/³¹P-NMR- and mass-spectroscopy. ¹H-/³¹P-NMR results show the paramagnetic nature of the complexes and magnetic moment values are μ_exptl(µB) = 3.65 (1), 3.78 (2), 3.82 (3), and 3.71µB (4) in methanol at 25 °C.     

Construction of Chiral 2,3-Allenols through a Copper(I)-Catalyzed Asymmetric Direct Alkynylogous Aldol Reaction

Chiral 2,3-allenols were constructed through copper(I)-catalyzed asymmetric direct alkynylogous aldol reaction. With aromatic and heteroaromatic aldehydes, the alkynylogous aldol reaction with (R)-DTBM-SEGPHOS as the ligand proceeded smoothly to furnish the products in excellent regioselectivity with good to high diastereoselectivity and excellent enantioselectivity. In the cases of aliphatic aldehydes, esters of but-2-yn-1-ol as the substrates and (R,R)-Ph-BPE as the ligand were found to be crucial to get good to high regio- and diastereoselectivity. The produced chiral 2,3-allenols are easily transformed into synthetically useful 2-furanones through cyclization. Finally, the developed method was successfully applied in the rapid synthesis of two chiral intermediates toward the synthesis of two pharmaceutically active compounds that have been proposed for the treatment of neurological disorders.     

New Chiral Reagent for Installation of Pharmacophoric (S)‐ or (R)‐2‐(Alkoxyphosphono)‐1‐amino‐2,2‐difluoroethyl Groups

A new chiral reagent has been developed for generalized installation of pharmacophoric (S)‐ or (R)‐2‐(alkoxyphosphono)‐1‐amino‐2,2‐difluoroethyl group into organic compounds. The original synthetic application of this new reagent is exemplified by Friedel–Crafts reactions with indoles, which proceed efficiently with excellent diastereoselectivity to give enantiomerically pure products.     

Chiral (Diphosphonite)platinum Complexes in Asymmetric Hydroformylation

The chiral diphosphonite ligand (11bR,11′bR)‐4,4′‐(9,9‐dimethyl‐9H‐xanthene‐4,5‐diyl)bis[dinaphtho[2,1‐d:1′,2′‐f][1,3,2]dioxaphosphepin] ((R,R)‐XantBino; (R)‐ 1 ), based on a rigid xanthene backbone, was applied in the Pt/Sn‐catalyzed hydroformylation of styrene ( 4a ), 4‐methylstyrene ( 4b ), vinyl acetate ( 4c ), and allyl acetate ( 4d ), by using a Pt/Sn ratio of 1 : 1. High ee of up to 80% were observed, along with good regioselectivities towards the desired branched aldehydes. For styrene, an interesting inversion in the stereoselection process was observed at elevated temperatures, and a mechanism is proposed considering the temperature dependence of the regioselectivity. The complex [PtCl₂{(S,S)‐XantBino}] ((S)‐ 2 ) was characterized by X‐ray crystal‐structure analysis, revealing an unusual out‐of‐plane ligand coordination of the metal fragment. The complex [PtCl(SnCl₃){(R,R)‐XantBino}] ((R)‐ 3 ) was characterized by means of ³¹P‐NMR spectroscopy.     

A three‐dimensional homochiral metal–organic framework constructed from manganese(II) with S‐carboxymethyl‐N‐(p‐tosyl)‐l‐cysteine and 4,4′‐bipyridine

In the chiral polymeric title compound, poly[aqua(4,4′‐bipyridine)[μ₃‐S‐carboxylatomethyl‐N‐(p‐tosyl)‐l ‐cysteinato]manganese(II)], [Mn(C₁₂H₁₃NO₆S₂)(C₁₀H₈N₂)(H₂O)]_n, the Mn^II ion is coordinated in a distorted octahedral geometry by one water molecule, three carboxylate O atoms from three S‐carboxyatomethyl‐N‐(p‐tosyl)‐l ‐cysteinate (Ts‐cmc) ligands and two N atoms from two 4,4′‐bipyridine molecules. Each Ts‐cmc ligand behaves as a chiral μ₃‐linker connecting three Mn^II ions. The two‐dimensional frameworks thus formed are further connected by 4,4′‐bipyridine ligands into a three‐dimensional homochiral metal–organic framework. This is a rare case of a homochiral metal–organic framework with a flexible chiral ligand as linker, and this result demonstrates the important role of noncovalent interactions in stabilizing such assemblies.     

Intramolecular Asymmetric Amidations of Sulfonamides and Sulfamates Catalyzed by Chiral Dirhodium(II) Complexes

Enantioselective intramolecular amidation of aliphatic sulfonamides was achieved for the first time by means of chiral carboxylatodirhodium(II) catalysts in conjunction with PhI(OAc)₂ and MgO in high yields and with enantioselectivities of up to 66% (Scheme 3, Table 1). The best results were obtained with [Rh₂{(S)‐nttl)₄] and [Rh₂{(R)‐ntv)₄] as catalysts ((S)‐nttl=(αS)‐α‐(tert‐butyl)‐1,3‐dioxo‐2H‐benz[de]isoquinoline‐2‐acetato, (R)‐nto=(αR)‐α‐isopropyl‐1,3‐dioxo‐2H‐benz[de] isoquinoline‐2‐acetato). In addition, these carboxylatodirhodium(II) catalysts were also efficient in intramolecular amidations of aliphatic sulfamates esters, although the enantioselectivity of these latter reactions was significantly lower (Scheme 4, Table 3).     

Synthesis of New Chiral Bidentate (Phosphinophenyl)benzoxazine P,N-Ligands

Two new chiral bidentate (phosphinophenyl)benzoxazine P,N-ligands 2a and 2b were synthesized from highly enantiomer-enriched 2-(1-aminoalkyl)phenols 4 . Ligand rac- 2a was obtained on refluxing the t-Bu-substituted (aminomethyl)phenol 4a with 2-(diphenylphosphino)benzonitrile in chlorobenzene in the presence of anhydrous ZnCl₂ followed by decomplexation (Scheme 2). This reaction, when carried out with (+)-(S)- 4a , was accompanied by racemization at the stereogenic center of the alkyl side chain. The enantiomerically pure ligands (+)-(R)- 2a and (−)-(S)- 2a were obtained using a stepwise procedure via the amides (−)-(R)- and (+)-(S)- 5b , respectively, followed by cyclization to benzoxazines (+)-(R)- and (−)-(S)- 7b , respectively, with triflic anhydride and by F-atom substitution by diphenylphosphide (Schemes 3 and 5). In the case of the i-Pr analogue 2b , this last step resulted in racemization (Scheme 6). This was overcome by preparing the bromo derivative and introducing the diphenylphosphine group via Br/Li exchange and reaction with chlorodiphenylphosphine (Scheme 7). The first application of (+)-(R)- 2a in an asymmetric Heck reaction showed high enantioselectivity (91%) (Scheme 8).     

Heterochiral Self-Discrimination-Driven Supramolecular Self-Assembly of Decanuclear Gold(I)-Sulfido Complexes into 2D Nanostructures with Chiral Anions-Tuned Morphologies

Chiral self-recognition and self-discrimination are of vital importance to biological processes. In this work, 2D regular rhombic nanocrystals ( RS -NC ) were fabricated through heterochiral self-discrimination between chiral polynuclear gold(I)-sulfido complex enantiomers, [(R-BINAP)₄Au₁₀S₄]Cl₂ ( R -Au₁₀ ) and [(S-BINAP)₄Au₁₀S₄]Cl₂ ( S -Au₁₀ ), in MeOH without the need for any surfactants or templates. The monitoring of nanocrystals (NCs) formation by TEM and DLS has uncovered the self-assembly process and shape evolution of the NCs and revealed a screw-dislocation dictated spiral growth of the rhombic NCs. Upon addition of chiral anions, the morphology of the gold NCs was found to change from rhombic to strip and quasi-hexagonal nanosheets, arising from reverse and rotational layer-by-layer stacking to give the bilayer NCs. By applying a high temperature, rhombic gold nanoisland films were obtained from the rhombic NCs. The current study has provided a simple strategy towards the construction of regular geometric 2D NCs as well as their chiral anion-tuned and reverse and rotational stacking-determined morphology change by heterochiral self-discrimination.     

Monohydride-Dichloro Rhodium(III) Complexes with Chiral Diphosphine Ligands as Catalysts for Asymmetric Hydrogenation of Olefinic Substrates

We report full details of the synthesis and characterization of monohydride-dichloro rhodium(III) complexes bearing chiral diphosphine ligands, such as (S)-BINAP, (S)-DM-SEGPHOS, and (S)-DTBM-SEGPHOS, producing cationic triply chloride bridged dinuclear rhodium(III) complexes ( 1 a : (S)-BINAP; 1 b : (S)-DM-SEGPHOS) and a neutral mononuclear monohydride-dichloro rhodium(III) complex ( 1 c : (S)-DTBM-SEGPHOS) in high yield and high purity. Their solid state structure and solution behavior were determined by crystallographic studies as well as full spectral data, including DOSY NMR spectroscopy. Among these three complexes, 1 c has a rigid pocket surrounded by two chloride atoms bound to the rhodium atom together with one tBu group of (S)-DTBM-SEGPHOS for fitting to simple olefins without any coordinating functional groups. Complex 1 c exhibited superior catalytic activity and enantioselectivity for asymmetric hydrogenation of exo-olefins and olefinic substrates. The catalytic activity of 1 c was compared with that of well-demonstrated dihydride species derived in situ from rhodium(I) precursors such as [Rh(cod)Cl]₂ and [Rh(cod)₂]⁺[BF₄]⁻ upon mixing with (S)-DTBM-SEGPHOS under dihydrogen.     

Assemblies of 1D and 2D Copper(II) Chiral Coordination Polymers by Salicylaldehyde Schiff Bases: Synthesis,Crystal Structures,and Magnetic Properties

Reaction of CuCl₂ · 2H₂O with chiral Schiff bases and sodium dicyanamide led to the formation of two chiral copper(II) coordination polymers, namely [Cu₄(L¹)₂(dca)₄]_n ( 1 ) and [Cu₂(L²)(μ‐Cl)(dca)(H₂O)]_n · nH₂O ( 2 ) {H₂L¹ = (1R, 3S)‐N′,N′′‐bis[salicylidene]‐1,3‐diamino‐ 1,2,2‐trimethylcyclopentane, H₂L² = (1R, 3S)‐N′,N′′‐bis[3‐ethoxysalicylidene]‐1,3‐diamino‐ 1,2,2‐trimethylcyclopentane, dca = dicyanamide}. Both complexes were structurally characterized by elemental analyses, IR spectroscopy and single‐crystal X‐ray diffraction. Complex 1 exhibits a two‐dimensional polymeric structure formed by single dca bridging tetranuclear Cu₄ units. Complex 2 displays a left‐handed helical chain structure constructed from Cu₂ dimers with single dca bridges. The chirality of 1 and 2 was confirmed by circular dichroism (CD) measurements in solution. Both complexes exhibit strong antiferromagnetic couplings with J = –308(4) cm^–1 for 1 and J = –123(1) cm^–1 for 2 in 2–300 K.