Chiral heterocyclic ligands. XIV. Control of directionality in silver coordination polymers through ligand design

Four C(2)-symmetric homochiral ligands derived from (+)-camphor are shown to produce linear chain and ladder silver coordination polymers wherein the directionality and polarisation can be controlled by subtle differences in ligand design.     

Twisted perylene stereodimers reveal chiral molecular assembly codes

Unique perylene diastereomeric linear and cyclic dimers were synthesized from twisted perylene monomers, revealing that pi-stacking stereoisomerism imparted specific intermolecular self-assembly and intramolecular folding. Only the homochiral twisted tetrachloroperylene monomers cyclized via a cooperative reaction, forming the homochiral diastereomers. The heterochiral tetrachloroperylene monomers proceeded through a stepwise reaction and yielded a linear heterochiral dimer, which equilibrated with the linear homochiral dimers. The linear homochiral dimers cyclized to produce the same cyclic homochiral diastereomers. These results demonstrated that homochiral and heterochiral self-assemblies were two distinct molecular codes, directing two specific chemical pathways. The homochiral cyclic dimers remain isomerically pure at -20 degrees C but can be interconverted to the heterochiral cyclic dimer meso compound at room temperature. The diastereomers were readily separated by HPLC. While driven by solvophobic forces, foldable linear dimers synthesized from the same twisted monomers using phosphoramidite chemistry folded into homodimer and heterodimer, confirming the inherent molecular codes, which were dictated by the perylene chirality, ultimately gauged the weak pi-stack forces, and directed self-assembly and folding.     

Homo- and heterochiral alkylzinc fencholates: linear or nonlinear effects in dialkylzinc additions to benzaldehyde

Scalemic mixtures of chiral anisyl fenchols with different ortho-substituents (X) in the anisyl moieties [X = H (1), Me (2), SiMe3 (3) and tBu (4)] are employed as pre-catalysts in enantioselective additions of diethylzinc to benzaldehyde. While a remarkable asymmetric depletion is apparent for X = H and Me, a linear relationship between the enantiomeric purity of the chiral source and the product 1-phenylpropanol is observed for X = SiMe3 and tBu. X-ray single crystal analyses show that racemic methylzinc fencholates obtained from 1 (X = H) and 2 (X = Me) yield homochiral dimeric complexes, while for 3 (X = SiMe3) and 4 (X = tBu) the heterochiral dimeric alkylzinc structures are formed. The enantiopure fenchols 1-4 all yield homochiral dimeric methylzinc complexes. Computed relative energies of homo- and heterochiral fencholate dimers with X = H and Me reveal an intrinsic preference for the formation of the homochiral dimers, consistent with the observed negative NLE. In contrast, similar stabilities are computed for homo- and heterochiral complexes of ligands 3 (X = SiMe3) and 4 (X = tBu), in agreement with the absence of a nonlinear effect for bulky ortho-subsituents.     

Interlocked chiral nanotubes assembled from quintuple helices

Homochiral helical chains were rationally synthesized from C2-symmetric 1,1-binaphthyl-6,6'-bipyridine ligands and linear metal-connecting points, Ni(acac)2. Five such homochiral helices associate in parallel to form nanotubes of 2 x 2 nm in dimensions which further intertwine to form periodically ordered, interlocked nanotubular architectures that possess nanometer-scale open channels and have high affinity for aromatic molecules. Chiral crown ethers have also been successfully incorporated into the walls of these nanotubes, which promises to lead to novel chiral zeolitic materials applicable in enantioselective processes.     

Ligand-assisted, copper-catalyzed enantioselective benzylic amination

Several classes of ligands, including α-amino acids, diamines, diphosphines, bis-oxazolines, and diimines, support efficient copper-catalyzed amination of benzylic hydrocarbons by anhydrous chloramine-T. Catalysts derived from homochiral ligands, particularly chiral diimines, effect aminosulfonation with low to moderate enantioselectivity.     

New homochiral amino-phosphine ligands: application in asymmetric palladium catalyzed allylic alkylation

A new series of homochiral amino-phosphine ligands was prepared. The use of these ligands in the palladium catalyzed allylic alkylation of 1,3-diphenyl-1-acetoxy-2-propene with sodium malonate gave substitution products with up to 76% e.e. The enantioselectivity was largely dependent on the nitrogen substituent.     

Synthesis of N,N-bis[2-(2-pyridyl)ethyl]amino steroids and related compounds intended as chiral ligands for copper ions

Compounds with the N,N-bis[2-(2-pyridyl)ethyl]amino structure (RPY2) are useful tridentate ligands for copper(I) ions, which can bind and activate oxygen from the atmosphere. For diastereoselective and enantioselective oxidation reactions, hitherto unknown chiral ligands possessing tripodal structures have been synthesized starting from homochiral steroids. The double Michael addition of primary steroidal amines and aminoalcohols to 2-vinyl pyridine was not very succesful. However, homochiral bidentate ligands with N-[2-(2-pyridyl)ethyl]amino steroid structure could be obtained by this procedure in most cases. New routes (acylation of the bidentate ligands with 2-pyridylacetic acid followed by BH₃·THF reduction, or reductive amination of steroidal ketones, acylation and borane reduction) to the desired tridentate RPY2, also at sterically hindered positions, are described. In the last reaction sequence, ‘mixed’ tridentate ligands can also be obtained. Copper complexation and oxygen activation with these ligands are briefly discussed.     

Two-dimensional homochiral manganese(II)-azido frameworks incorporating an achiral ligand: partial spontaneous resolution and weak ferromagnetism

By incorporating an achiral diazine ligand, 2-pyridylmethylketazine, which can be locked in a chiral conformation upon coordination, into the manganese(II)-azido system, we induced a homochiral 2D network, in which neighboring Mn(II) ions are bridged via a diazine and two end-on azido ligands into chiral dimeric units, and neighboring units are interlinked via single end-to-end azido bridges. The interdimer chirality preservation is achieved via the homochiral 1D helical linkage formed by Mn(II) and end-to-end azido ions. The 2D layers are stacked in hetero- and homochiral fashion to yield simultaneously racemic and chiral crystals, indicating a partial spontaneous resolution. Both compounds behave as spin-canted weak ferromagnets, but the critical temperatures are different.     

A 2D homochiral inorganic-organic framework exhibiting a spin-flop transition

A 2D homochiral inorganic-organic framework {[Mn(NPTA)(4,4'-bpy)(H(2)O)]·(H(2)O)(2)}(n) was prepared by assembling achiral polar 4-nitrophthalic acid, manganese ions, and ancillary 4,4'-bipyridine ligands (NPTA = 4-nitrophthalate) (4,4'-bpy = 4,4'-bipyridine). The isomorphous Zn(ii) compound was also prepared as a diamagnetic analogue. Adjacent manganese spin centres are linked by the syn-anti carboxylate to form a helical chain, and chains of the same chirality are connected by 4,4'-bpy ligands to generate a homochiral layered framework. Edge-to-face aromatic interactions between neighboring layers lead to a 3D homochiral supramolecular structure. Magnetization and heat capacity measurements indicate that the framework is a weak antiferromagnet at low applied field. The magnetic interactions between adjacent manganese ions in the helical chain can be fitted using the 1D Fisher model, with 2J/k = -0.68 K and g = 2.00. Moreover, the compound displays a unique field-dependent spin-flop transition in high magnetic fields, with a critical field of 23.6 kOe at 1.9 K.     

异薄荷醇黄原酸镍的配合物(英)

The coordination geometry around Ni atom in the homochiral bis(2-isopropyl-5-methylcyclohexyl xanthalato) nickel(Ⅱ) (1) displays an approximately square plane defined by four S atoms from two xanthalato ligands. CCDC: 252343.     

1D and 2D homochiral metal-organic frameworks built from a new chiral elongated binaphthalene-derived bipyridine

Six homochiral coordination polymers 1-6 based on a new enantiopure elongated (S)-2,2'-diethoxy-1,1'-binaphthyl-6,6'-bis(4-vinylpyridine) ligand (L) and divalent metal (Zn, Cd, and Ni) connecting points were synthesized and characterized by single-crystal X-ray diffraction studies. These new homochiral coordination polymers adopt two distinct framework structures: a one-dimensional infinite chain structure with bridging L ligands occupying the axial positions of the metal centers and a two-dimensional rhombic grid structure formed by linking octahedrally coordinated metal centers with four pyridyl groups of bridging L ligands in the equatorial positions. The structures of these coordination polymers are sensitive to the nature of the anions as well as the solvents from which the coordination polymer crystals were grown. Powder X-ray diffraction studies showed that the two-dimensional chiral rhombic grids exhibited porosity, which could potentially find applications in enantioselective separations and catalysis.     

Asymmetric nickel-catalyzed hydrocyanation of vinylarenes by applying homochiral xantphos ligands

New homochiral xantphos-type diphosphonite ligands with binaphthoxy substituents have been prepared and characterized by NMR spectroscopy. These ligands have been applied in the nickel-catalyzed hydrocyanation of styrene and other vinylarenes. Enantioselectivities up to 63% ee have been obtained by using 4-isobutylstyrene as a substrate. Addition of an excess of ligand strongly inhibits the hydrocyanation reaction since the bis-chelate nickel complexes formed are highly stable and catalytically inactive.     

手性金属-有机骨架[Cu_3(HL)_2(L)_2(bpy)_3]·4H_2O用于高效液相色谱拆分手性化合物

手性金属-有机骨架材料(MOFs)作为一种新型多孔材料,由于具有比表面积大、结构多样、孔尺寸可调和化学稳定性良好等特点,而备受色谱分离领域的关注。该文以(1R,2R)-1,2-环己烷二甲酸(H2L)和4,4'-联吡啶(bpy)为配体与铜离子反应,通过溶剂热法合成了一种具有二维手性网状结构的手性MOF[Cu_3(HL)_2(L)_2(bpy)_3]·4H_2O。将该手性MOF作为手性固定相制备了高效液相色谱柱。为了考察MOF[Cu_3(HL)_2(L)_2(bpy)_3]·4H_2O的手性识别能力,在正相色谱(流动相:正己烷-异丙醇)条件下,对一系列外消旋化合物在手性MOF柱上进行了拆分。该手性MOF柱对醇类、酮类、酸类、环氧化合物和醚类等10种手性化合物表现出较好的拆分效果。对该手性MOF柱的重现性、稳定性作了评价,考察了进样量对分离效果的影响,结果表明该手性MOF柱具有较好的重现性和稳定性。     

Chiral recognition of N-thiophosphorylated thioureas via nickel(ii) coordination assisted by 4-dimethylaminopyridine

Nickel(ii) complexes were synthesized using chiral N-thiophosphorylated thioureas as the starting compounds and 4-dimethylaminopyridine as a co-ligand. The reaction with racemic thiourea afforded homochiral complexes due to the distortion of the nickel coordination. The unsaturated coordination sphere of nickel ions results in the formation of supramolecular homochiral 1D chains in the crystal through steric key—lock interactions between adjacent molecules. Conformational flexibility of the ligands is responsible for disorder of molecules in the crystals and the occurrence of polymorphs.

     

Diastereomeric phosphite–pyridine ligands for enantioselective 1,4-conjugate additions

Diastereomeric phosphite–pyridine ligands derived from racemic biphenyl units and homochiral BINOL, achieved high enantioselectivities (up to 96.1% ee) in the Cu(I)-catalysed conjugate additions of Et₂Zn to a variety of acyclic enones.     

Ligand Self-Recognition in the Self-Assembly of a [{Cu(L)}2]2+ Complex: The Role of Chirality

The chirality alone of a conformationally restricted, bifunctional ligand (L) is the basis for the self-recognition process schematically represented below. A racemic mixture of these ligands reacts with Cu⁺ ions quantitatively to generate a racemic mixture of a [(CuL)₂]²⁺ homochiral complex (represented by cubes), where each complex contains ligands with identical configurations.     

From hetero- to homochiral bis(metallahelicene)s based on a Pt(III)-Pt(III) bonded scaffold: isomerization, structure, and chiroptical properties

Hetero- and homochiral diastereomeric bis(metallahelicene)s have been synthesized. They possess a rare Pt(III)-Pt(III) scaffold bridged by benzoato ligands. It is shown that heterochiral (P,M)-bis(Pt(III)-[6]helicene) can isomerize into the homochiral (P,P)- and (M,M)-bis(Pt(III)-[6]helicene). A theoretical study shows a unique σ-π conjugation between the two π-helices and the σ-Pt(III)-Pt(III) scaffold that impacts the strong chiroptical properties.     

手性催化剂负载的一种新方法: 自负载策略

较系统地介绍了手性催化剂负载的一种新方法(即“自负载”策略)及其在非均相不对称催化反应中应用的最新进展. 与传统的负载模式不同, “自负载”策略中利用含双或多官能团的配体与金属通过自组装形成的有机-无机聚合物做为催化剂, 因此不需使用任何载体. “自负载”手性催化剂在若干非均相不对称催化反应中显示了优秀的催化活性和对映选择性并且能够简单回收再利用, 为手性催化剂的负载化提供了一个新的策略.     

Modular chiral polyether podands and their lanthanide complexes

A novel series of modular chiral polyether podands derived from enantiomerically pure hydrobenzoin and binaphthol has been prepared using a NaH/15-crown-5 mediated Williamson ether synthesis. These new homochiral ligands form catalytically active complexes with lanthanide triflates, two of which have been characterised by X-ray diffraction.     

新型手性金属-有机配位聚合物的合成、结构与性质

在水热条件下, 分别用过渡金属离子Zn(Ⅱ)和Co(Ⅱ)与混合手性羧酸和含氮配体反应, 合成了2个手性金属-有机配位聚合物[M(D-cam)(H₂mbdpz)]_n[M=Zn(1), Co(2); D-H₂cam=D-(+)-樟脑酸; H₂mbdpz=4,4'-亚甲基二(3,5-二甲基吡唑)]. 通过单晶X射线衍射、粉末X射线衍射、元素分析、热重分析及荧光分析对其结构、组成和性质进行了表征. 单晶结构分析表明, 配合物1和2是异质同晶的手性三维开放骨架结构, 具有单节点三连接的ThSi₂型网络拓扑结构.