Chiral recognition and conglomerate crystallization induced by self-organization of cobalt(III) complexes of a tripodal ligand containing three imidazole groups

The effect of a counteranion on chiral recognition inducing conglomerate crystallization of a cobalt(III) complex is reported. An achiral tripodal ligand involving three imidazole groups, tris{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H3L), was prepared by condensation of tris(2-aminoethyl)amine and 4-formylimidazole in a 1:3 mole ratio. The reaction of H3L and trans-[CoIIICl2(py)4]+ afforded the chiral (Delta or Lambda) [CoIII(H3L)]3+ complex. The formally hemideprotonated complexes [CoIII(H(1.5)L)]X(1.5).nH2O (where X = Cl, Br, I, BF4, ClO4, or PF6) were synthesized by controlled deprotonation of the uncoordinated imidazole NH groups of [Co(H3L)]3+. In crystals of the hemideprotonated complex, two components, [Co(H3L)]3+ and [Co(L)], with the same absolute configuration are linked by imidazole-imidazolate hydrogen bonds to form an extended homochiral 2D sheet structure, which is composed of a hexanuclear unit with a trigonal void. There are two ways of stacking the sheets: One is via homochiral stacking, and the other is via heterochiral stacking. When the size of the counterion is small (i.e., X = Cl, Br, I, or BF4), adjacent homochiral sheets with the same chirality are stacked to form a homochiral crystal (conglomerate). With large anions (i.e., ClO4- and PF6-), a homochiral sheet consisting of Delta enantiomers and a sheet consisting of Lambda enantiomers are stacked alternately to give a heterochiral crystal (a racemic crystal). Optically active Lambda-[Co(H(1.5)L)](ClO4)(1.5).H2O was synthesized from Lambda-[Co(H3L)]3+, and the crystal structure was compared to that of the racemic complex. There are two conflicting factors governing the crystal structure: the skeletal density; the size of the channels. The 2D sheets are more closely packed in the homochiral crystal than in the heterochiral crystal. However, the channels, where the counterions are accommodated, are smaller in the homochiral crystal, and the steric congestion between the anions increases with increasing anion size. The heterochiral crystal has a flexible, zigzag channel structure, and the size of the channels can increase to accommodate larger anions. Thus, complexes with large anions (i.e., ClO4- and PF6-) preferentially form heterochiral crystals rather than homochiral crystals.     

A chiral porous 3D metal-organic framework with an unprecedented 4-connected network topology

A novel homochiral 3D metal-organic framework [CdL2(H2O)2][ClO4]2.2DMF.3EtOH.5/3H2O, 1, (L =(R)-6,6-dichloro-2,2-diethoxy-1,1-binaphthyl-4,4-bipyridine) exhibits an unprecedented 4-connected network topology owing to the cis- configuration of the Cd coordination and possesses permanent porosity as demonstrated by TGA, XRPD, and CO2 adsorption isotherm studies.     

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。     

A new family of spin crossover complexes with a tripod ligand containing three imidazoles: synthesis, characterization, and magnetic properties of [FeIIH3LMe](NO3)2.1.5H2O, [FeIIILMe].3.5H2O, [FeIIH3LMe][FeIILMe]NO3, and [FeIIH3LMe][FeIIILMe](NO3)2 (H3LMe) = Tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine)

A new family of spin crossover complexes, [Fe(II)H(3)L(Me)](NO(3))(2).1.5H(2)O (1), [Fe(III)L(Me)].3.5H(2)O (2), [Fe(II)H(3)L(Me)][Fe(II)L(Me)]NO(3) (3), and [Fe(II)H(3)L(Me)][Fe(III)L(Me)](NO(3))(2) (4), has been synthesized and characterized, where H(3)L(Me) denotes a hexadentate N(6) tripod ligand containing three imidazole groups, tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine. It was found that the spin and oxidation states of the iron complexes with this tripod ligand are tuned by the degree of deprotonation of the imidazole groups and by the 2-methyl imidazole substituent. Magnetic susceptibility and M?ssbauer studies revealed that 1 is an HS-Fe(II) complex, 2 exhibits a spin equilibrium between HS and LS-Fe(III), 3 exhibits a two-step spin transition, where the component [Fe(II)L(Me)](-) with the deprotonated ligand participates in the spin transition process in the higher temperature range and the component [Fe(II)H(3)L(Me)](2+) with the neutral ligand participates in the spin transition process in the lower temperature range, and 4 exhibits spin transition of both the Fe(II) and Fe(III) sites. The crystal structure of 3 consists of homochiral extended 2D puckered sheets, in which the capped tripodlike components [Fe(II)H(3)L(Me)](2+) and [Fe(II)L(Me)](-) are alternately arrayed in an up-and-down mode and are linked by the imidazole-imidazolate hydrogen bonds. Furthermore, the adjacent 2D homochiral sheets are stacked in the crystal lattice yielding a conglomerate as confirmed by the enantiomeric circular dichorism spectra. Compounds 3 and 4 showed the LIESST (light induced excited spin state trapping) and reverse-LIESST effects upon irradiation with green and red light, respectively.     

Synthesis and resolution of benzylisopropylphenylphosphine,a monodentate P-chiral ligand

The synthesis of benzylisopropylphenylphosphine by reaction between the benzylphenylphosphide anion and isopropyl chloride and its subsequent resolution by means of an optically active palladium metallacycle is reported. The synthesis of the organometallic complex [Pd(η³-2-MeC₃H₄)Cl(PBnⁱPrPh)] is also described, as well as the assignment of the absolute configuration of the coordinated phosphine by mono- and bidimensional proton NMR spectra, using the homochiral palladacycle as a reference point. In order to estimate the height of the energy barrier corresponding to the rotation of the phosphine ligand around the PdP bond, several calculations were performed at the semiempirical PM3(tm) level.     

Assemblies of a new flexible multicarboxylate ligand and d10 metal centers toward the construction of homochiral helical coordination polymers: structures, luminescence, and NLO-active properties

Hydro(solvo)thermal reactions between a new flexible multicarboxylate ligand of 2,2',3,3'-oxydiphthalic acid (2,2',3,3'-H(4)ODPA) and M(NO(3))(2).xH(2)O (M = Zn, x = 6; M = Cd, x = 4) in the presence of 4,4'-bipyridine (bpy) afford two novel homochiral helical coordination polymers [[Zn(2)(2,2',3,3'-ODPA)(bpy)(H(2)O)(3)].(H(2)O)(2) for 1 and [Cd(2)(2,2',3,3'-ODPA)(bpy)(H(2)O)(3)].(H(2)O)(2) for 2]. Though having almost the same chemical formula, they have different space groups (P2(1)2(1)2(1) for 1 and P2(1) for 2) and different bridging modes of the 2,2',3,3'-ODPA ligand. Two kinds of homochiral helices (right-handed) are found in both 1 and 2, each of which discriminates only one kind of crystallographical nonequivalent metal atom. 1 has a 2D metal-organic framework and can be seen as the unity of two parallel homochiral Zn1 and Zn2 helices, in which the nodes are etheric oxygen atoms. In contrast, 2 has a 3D metal-organic framework and consists of two partially overlapped homochiral Cd1 and Cd2 helices in the two dimensions. Moreover, metal-ODPA helices give a 2D chiral herringbone structural motif in both 1 and 2 in the two dimensions, which are further strengthened by the second ligand of bpy. Bulk materials for 1 and 2 all have good second-harmonic generation activity, approximately 1 and 0.8 times that of urea.     

Diazene dehydrogenation follows H2 addition to coordinated dinitrogen in an ansa-zirconocene complex

An activated side-on-bound ansa-zirconocene dinitrogen complex, [Me2Si(eta5-C5Me4)(eta5-C5H3-3-tBu)Zr]2(mu2,eta2,eta2-N2), has been prepared by sodium amalgam reduction of the corresponding dichloride precursor under an atmosphere of N2. Both solution spectroscopic and X-ray diffraction data establish diastereoselective formation of the syn homochiral dizirconium dimer. Addition of 1 atm of H2 resulted in rapid hydrogenation of the N2 ligand to yield one diastereomer of the hydrido zirconocene diazenido complex. Kinetic measurements have yielded the barrier for H2 addition and in combination with isotopic labeling studies are consistent with a 1,2-addition pathway. In the absence of H2, the hydrido zirconocene diazenido product undergoes swift diazene dehydrogenation to yield an unusual hydrido zirconocene dinitrogen complex. The N=N bond length of 1.253(5) A determined by X-ray crystallography indicates that the side-on-bound N2 ligand is best described as a two-electron reduced [N2]2- fragment. Comparing the barrier for deuterium exchange with [Me2Si(eta5-C5Me4)(eta5-C5H3-3-tBu)ZrH]2(mu2,eta2,eta2-N2H2) to diazene dehydrogenation is consistent with rapid 1,2-elimination of dihydrogen followed by rate-determining hydride migration to the zirconium. This mechanistic proposal is also corroborated by H2 inhibition and the observation of a normal, primary kinetic isotope effect for dehydrogenation.     

Planar chiral dianthranilide and dithiodianthranilide molecules: optical resolution, chiroptical spectra, and molecular self-assembly

Planar chiral dianthranilide (1) was resolved to enantiomers with use of (-)-(1S,4R)-camphanoyl chloride as a chiral derivatizing agent. The (+)-1 enantiomer was assigned the S absolute configuration from the X-ray crystal structure of its N,N'-dicamphanoyl derivative. Optical resolution of dithionodianthranilide (2) was accomplished by inclusion crystallization with (R,R)-1,2-diaminocyclohexane, and the X-ray structure of the corresponding adduct revealed the (-)-2stereoisomer has the R configuration. A slow boat-to-boat ring inversion (DeltaG(++) = 24.1 +/- 0.1 kcal mol(-1)) causes racemization of (+)-1 in solution as manifested by a gradual decrease of the CD spectrum whereas, (-)-2 is configurationally stable at these conditions. The analysis of the CD spectra of the title compounds showed that the n-pi* Cotton effect signs are determined by the helicity of the skewed benzamide and thiobenzamide chromophores. The solid-state structures of the racemic and homochiral forms of 1 and 2 show different self-assembly patterns: the racemate (+/-)-1 prefers the cyclic R(2)(2)(8) hydrogen bond motif, whereas the crystalline DMSO solvates of (+/-)-1 and (+)-1 consist of 1D homochiral hydrogen-bonded assemblies generated by the C(6) motif. In the case of dithionolactams (+/-)-2 and (-)-2 two types of 1D networks were observed: in the racemate they are generated by the centrosymmetric R(2)(2)(8) and R(2)(2)(12) hydrogen bond motifs, whereas the molecules in the homochiral crystals are connected solely with use of the strongly nonplanar R(2)(2)(8) motif.     

Syntheses of homochiral multinuclear ru complexes based on oligomeric bibenzimidazoles

The homochiral multinuclear Ru complexes of the oligomeric bibenzimidazoles were synthesized using Lambda-[Ru(bpy)2(py)2][(-)-O,O'-dibenzoyl-l-tartrate].12H2O as an enantiomerically pure building block. The complexations proceed with the retention of configuration to provide well-defined mononuclear, dinuclear, tetranuclear, and octanuclear Ru complexes successfully. The optical purity and the absolute configurations of the complexes were determined by NMR and circular dichroism spectrometry. The rare X-ray structure of a tetranuclear complex Lambda4-[(Ru(bpy)2)4(bis(BiBzIm))](PF6)4 was resolved. The crystallographic analysis reveals that all the four Ru centers have Lambda octahedral configurations, with a Ru-Ru separation of 5.509 A across the bridging bibenzimidazole ligand, which maintains near coplanarity. The UV-vis spectroscopic and electrochemical properties of the homochiral multinuclear assemblies were studied, indicating weak electronic communications between the metal centers.     

A novel TGS-like inorganic-organic hybrid and a preliminary investigation of its possible ferroelectric behavior

The homochiral inorganic-organic hybrid compound (H(3)NHPA)(SnCl(3))(2)(H(2)O)(3) [1, (S)-4-(4'-aminophenyl)-2-aminobutanoic acid diammonium trichloride stannite triaqua] has a TGS (triglycine sulfate)-like structure. Preliminary investigation suggests a possible ferroelectric behavior with a saturation spontaneous polarization (P(s)) of ca. 3.5 microC.cm(-)(2), which is slightly greater than that of TGS (P(s) = 3.0 microC.cm(-)(2)).     

Dinuclear complexes of chiral tetradentate pyridylimine ligands: diastereoselectivity, positive cooperativity, anion selectivity, ligand self-sorting based on chirality, and magnetism

The synthesis and coordination chemistry of two chiral tetradentate pyridylimine Schiff base ligands are reported. The ligands were prepared by the nucleophilic displacement of both bromides of 1,3-bis(bromomethyl)benzene (2) or 3,5-bis(bromomethyl)toluene (3) by the anion of (S)-valinol, followed by capping of both amine groups with pyridine-2-carboxaldehyde. Both ligands react with CoCl(2) and NiCl(2) to give [M(2)L(2)Cl(2)](2+) complexes. Remarkably, neither fluoride nor bromide ions can act as bridging ligands. The formation of [Co(2)((S)-3)(2)Cl(2)](2+) is highly diastereoselective, and X-ray crystallography shows that both metal centers in the [Co(2)((S)-3)(2)Cl(2)](CoCl(4)) complex adopt the lambda configuration (crystal data: [Co(2)(C(31)H(40)N(4)O(2))(2)Cl(2)](CoCl(4)).(CH(3)CN)(3), monoclinic, P2(1), a = 11.595(2) A, b = 22.246(4) A, c = 15.350(2) A, V = 3705(1) A(3), beta = 110.643(3) degrees, Z = 2). Structurally, the dinuclear complex can be viewed as a helicate with the helical axis running perpendicular to the [Co(2)Cl(2)] plane. The reaction of racemic 2 with CoCl(2) was shown by (1)H NMR spectroscopy to yield a racemic mixture of Lambda,Lambda-[Co(2)((S)-2)(2)Cl(2)](2+) and delta,delta-[Co(2)((R)-2)(2)Cl(2)](2+) complexes; that is, a homochiral recognition process takes place. Spectrophotometric titrations were performed by titrating (S)-3 with Co(ClO(4))(2) followed by Bu(4)NCl, and the global stability constants of [Co((S)-3)](2+) (log beta(110) = 5.7), [Co((S)-3)(2)](2+) (log beta(120) = 11.6), and [Co(2)((S)-3)(2)Cl(2)](2+) (log beta(110) = 23.8) were calculated. The results revealed a strong positive cooperativity in the formation of [Co(2)((S)-3)(2)Cl(2)](2+). Variable-temperature magnetic susceptibility curves for [Co(2)((S)-2)(2)Cl(2)](BPh(4))(2) and [Co(2)((S)-3)(2)Cl(2)](BPh(4))(2) are very similar and indicate that there are no significant magnetic interactions between the cobalt(II) centers.     

Enzymatic Kinetic Resolution of 5-Hydroxy-4-oxa-endo-tricyclo[5.2.1.0(2,6)]dec-8-en-3-ones: A Useful Approach to D-Ring Synthons for Strigol Analogues with Remarkable Stereoselectivity

Racemic 5-hydroxy-4-oxa-endo-tricyclo[5.2.1.0(2,6)]dec-8-en-3-one and its 2-methyl analogue were resolved employing a lipase-catalyzed acetylation reaction. The latter compound thus gave access to a homochiral D-ring synthon for strigolactones. The enzymatic acetylation reaction occurred with a remarkable inversion of configuration at C-5, through which it is possible to achieve a highly efficient asymmetric synthesis of 5-acetoxy-2(5H)-furanone.     

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.     

Homochiral column structure of rac- and lambda-tris(ethylenediamine)cobalt(III) cyclotriphosphate dihydrate in crystal structures and cation-anion association in aqueous solution

rac- and Lambda-tris(ethylenediamine)cobalt(III) cyclotriphosphate dihydrate with the chemical formulas rac-[Co(en)(3)]P(3)O(9).2H(2)O (1) and Lambda-[Co(en)(3)]P(3)O(9).2H(2)O (2) were synthesized, and their crystal structures were determined by single-crystal X-ray analyses. In 1, the cationic complex molecule [Co(en)(3)](3+) with the Delta or Lambda enantiomer and cyclotriphosphate anion are alternately arrayed and connected by multiple hydrogen bonds to form a homochiral column structure. Adjacent homochiral columns with different chirality for 1 are connected by intercolumn hydrogen bonds through P(3)O(9)(3)(-) anions, as the bridging groups, to form a tetrameric cyclic cylindrical structure, while the adjacent columns with the same chirality are connected for 2 to form the cyclic cylindrical structure. All 6 amino groups per [Co(en)(3)](3+) participate in the formation of 12 hydrogen bonds, in which 8 hydrogen bonds contribute to the construction of a homochiral column and the remaining 4 hydrogen bonds contribute to the intercolumn interactions. The circular dichroism spectrum of the aqueous solution of Lambda-[Co(en)(3)](3+) changes drastically when excess P(3)O(9)(3)(-) is added, and this change is explained by ion-pair formation. The thermodynamic association constant of [Co(en)(3)](3+) with P(3)O(9)(3)(-), calculated from the conductivity data, was log K = 4.26 at 25 degrees C.     

An efficient multigram synthesis of the potent histamine H3 antagonist GT-2331 and the reassessment of the absolute configuration

GT-2331 is a potent histamine H(3) antagonist which has entered clinical trials. Efficient multigram syntheses of this compound and its enantiomer are described. The literature reports that GT-2331 is the dextrorotatory (+), more potent, enantiomer of 4-[2-(5,5-dimethylhex-1-ynyl)cyclopropyl]-1H-imidazole with the absolute configuration of (1R,2R)-1. However, we found that the dextrorotatory, more potent, enantiomer of 4-[2-(5,5-dimethylhex-1-ynyl)cyclopropyl]-1H-imidazole has the (1S,2S) absolute configuration. We suggest a reconsideration of the absolute configuration of GT-2331.     

From achiral ligands to chiral coordination polymers: spontaneous resolution, weak ferromagnetism, and topological ferrimagnetism

Using the achiral diazine ligands bearing two bidentate pyridylimino groups as sources of conformational chirality, five azido-bridged coordination polymers are prepared and characterized crystallographically and magnetically. The chirality of the molecular units is induced by the coordination of the diazine ligands in a twisted chiral conformation. The use of L(1) (1,4-bis(2-pyridyl)-1-amino-2,3-diaza-1,3-butadiene) and L(2) (1,4-bis(2-pyridyl)-1,4-diamino-2,3-diaza-1,3-butadiene) induces spontaneous resolution, yielding conglomerates of chiral compounds [Mn(3)(L(1))(2)(N(3))(6)](n) (1) and [Mn(2)(L(2))(2)(N(3))(3)](n)(ClO(4))(n).nH(2)O (2), respectively, where triangular (1) or double helical (2) chiral units are connected into homochiral one-dimensional (1D) chains via single end-to-end (EE) azido bridges. The chains are stacked via hydrogen bonds in a homochiral fashion to yield chiral crystals. When L(3) (2,5-bis(2-pyridyl)-3,4-diaza-2,4-hexadiene) is employed, a partial spontaneous resolution occurs, where binuclear chiral units are interlinked into fish-scale-like homochiral two-dimensional (2D) layers via single EE azido bridges. The layers are stacked in a heterochiral or homochiral fashion to yield simultaneously a racemic compound, [Mn(2)(L(3))(N(3))(4)](n) (3a), and a conglomerate, [Mn(2)(L(3))(N(3))(4)](n).nMeOH (3b). On the other hand, the ligand without amino and methyl substituents (L(4), 1,4-bis(2-pyridyl)-2,3-diaza-1,3-butadiene) does not induce spontaneous resolution. The resulting compound, [Mn(2)(L(4))(N(3))(4)](n) (4), consists of centrosymmetric 2D layers with alternating single diazine, single EE azido, and double end-on (EO) azido bridges, where the chirality is destroyed by the centrosymmetric double EO bridges. These compounds exhibit very different magnetic behaviors. In particular, 1 behaves as a metamagnet built of homometallic ferrimagnetic chains with a unique "fused-triangles" topology, 2 behaves as a 1D antiferromagnet with alternating antiferromagnetic interactions, 3a and 3b behave as spin-canted weak ferromagnets with different critical temperatures, and 4 also behaves as a spin-canted weak ferromagnet but exhibits two-step magnetic transitions.     

Synthesis and conformational analysis of new cyclobutane-fused nucleosides

[structure: see text]. A stereselective synthesis of 3-oxabicyclo[3.2.0]heptane nucleoside analogues, which were designed as conformational mimics of the anti-HIV agents 2',3'-didehydro-2',3'-dideoxythimidine (stavudine, d4T) and 2',3'-didehydro-2',3'-dideoxyadenosine (d4A), is described. The target compounds were prepared by condensation of a common intermediate bicyclic acetate, derived from a homochiral 2(5H)-furanone, with pyrimidine and purine bases under modified Vorbrüggen conditions. The conformational behavior of the synthesized nucleoside analogues was studied by NMR spectroscopy and X-ray crystallography.     

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.     

The versatile, efficient, and stereoselective self-assembly of transition-metal helicates by using hydrogen-bonds

A diverse range of dinuclear double-stranded helicates in which the ligand strand is built up by using hydrogen-bonding has been synthesized. The helicates, formulated as [Co(2)(L)(2)(L-H)(2)X(2)], readily self-assemble from a mixture of a suitable pyridine-alcohol compound (L; for example, 6-methylpyridine-2-methanol, 1), and a CoX(2) salt in the presence of base. Nine such helicates have been characterized by X-ray crystallography. For helicates derived from the same pyridine-alcohol precursor, a remarkable regularity was found for both the molecular structure and the crystal packing arrangements, regardless of the nature of the ancillary ligand (X). A notable exception was observed in the solid-state structure of [Co(2)(1)(2)(1-H)(2)(NCS)(2)] for which intermolecular nonbonded contacts between the sulfur atoms (SS=3.21 A) lead to the formation of 1D chains. Helicates derived from (R)-6-methylpyridine-2-methanol (2) are soluble in solvents such as CH(3)CN and CH(2)Cl(2), and their self-assembly could be monitored in solution by (1)H NMR, UV/Vis, and CD titrations. No intermediate complexes were observed to form in a significant concentration at any point throughout these titrations. The global thermodynamic stability constant of [Co(2)(2)(2)(2-H)(2)(NO(3))(2)] was calculated from spectrophotometric data to be logbeta=8.9(8). The stereoisomerism of these helicates was studied in some detail and the self-assembly process was found to be highly stereoselective. The chirality of the ligand precursors can control the absolute configuration of the metal centers and thus the overall helicity of the dinuclear assemblies. Furthermore, the enantiomers of rac-6-methylpyridine-2-methanol (3) undergo a self-recognition process to form exclusively homochiral helicates in which the four pyridine-alcohol units possess the same chirality.     

(3+3)-Cyclocondensation of the enantiopure and racemic forms of trans-1,2-diaminocyclohexane with terephthaldehyde. Formation of diastereomeric molecular triangles and their stereoselective solid-state stacking into microporous chiral columns

The non-templated reaction of both the homochiral as well as the racemic form of trans-1,2-diaminocyclohexane with terephthaldehyde affords (3+3)-cyclocondensed molecular triangles in practically quantitative yields. The configuration of the diastereomeric products resulting in the individual reactions has been determined by ¹H and ¹³C NMR spectroscopy. Unambiguous proof has been obtained by X-ray crystal structure analysis of both alternative diastereomers, revealing also a stereoselective stacking of the triangles into microporous chiral columns.