Acceleration and deceleration of chirality inversion speeds in a dynamic helical metallocryptand by alkali metal ion binding.

We report that the chirality inversion kinetics of a trinickel(II) cryptand can be controlled by guest recognition in the cryptand cavity. When the guest was absent, the nickel(II) cryptand underwent a dynamic interconversion between the and forms in solution, preferring the form, with a half-life of = 4.99 min.

Induction and rationalization of supramolecular chirality in a highly flexible Zn(II)porphyrin dimer: structural, spectroscopic and theoretical investigations.

A highly flexible pyrrole-bridged Zn(II)porphyrin dimer has been successfully utilized as an efficient host which enables an accurate determination of the absolute configuration directly for a large number of chiral amino alcohols and 1,2-diols. The addition of substrates resulted in the formation of 1 : 1 complexes which, after the addition of excess substrates, produced 1 : 2 host-guest complexes. In principle, the 1 : 2 host-guest complexes can be stabilized in three possible conformations, -, -, and - based on how a substrate binds to the metal.

A chiral spirobifluorene-based bis(salen) zinc(ii) receptor towards highly enantioselective binding of chiral carboxylates.

We have designed a new chiral receptor based on two salen zinc(ii) complex units connected with a spirobifluorene framework. The chiral receptor is proven to enantioselectively bind chiral carboxylate guests and the differences between the binding constants of enantiomeric guests were up to more than one order of magnitude.

Complexation of Chiral Zinc(II)Porphyrin with Chiral Guests: Control, Discrimination and Rationalization of Supramolecular Chirality.

A series of 1:1 complexes consisting of chiral zinc(II) bisporphyrin hosts and a series of chiral guests has been synthesized and has rationalized the underpinning mechanism of chirality transfer in the host-guest supramolecular assemblies. The number of stereogenic centers is also varied in both the host and guests, which provides insight into the overall helicity of the assembly. The interactions between the chiral host and chiral guests have been investigated by UV-visible, CD, and H NMR spectroscopic titrations along with extensive DFT studies.

Bioinspired Oxidation of Methane in the Confined Spaces of Molecular Cages.

Non-heme iron, vanadium, and copper complexes bearing hemicryptophane cavities were evaluated in the oxidation of methane in water by hydrogen peroxide. According to H nuclear magnetic resonance studies, a hydrophobic hemicryptophane cage accommodates a methane molecule in the proximity of the oxidizing site, leading to an improvement in the efficiency and selectivity for CHOH and CHOOH compared to those of the analogous complexes devoid of a hemicryptophane cage. While copper complexes showed low catalytic efficiency, their vanadium and iron counterparts exhibited higher turnover numbers, ≤13.

Complexation of Chiral Zinc-Porphyrin Tweezer with Achiral Diamines: Induction and Two-Step Inversion of Interporphyrin Helicity Monitored by ECD.

We report here the synthesis of a new chiral Zn(II) bisporphyrin tweezer in which two achiral Zn(II) porphyrin moieties are covalently linked by (1R,2R)-diphenylethylenediamine, which produces a strong chiral field around the porphyrin moieties. The chiral tweezer exhibits not only intensity modulation in UV-vis and CD exciton couplets but also a dramatic change, namely, the inversion in the sign of the interporphyrin helicity upon binding of achiral diamines of varying lengths. The stoichiometry-controlled formation of a 1:1 sandwich complex followed by a 1:2 open complex was realized with smaller achiral diamines (n: 2-5) at their low and high concentration regions, respectively, leading to two-step inversion of chirality.

Induction and Rationalization of Supramolecular Chirality in the Tweezer-Diamine Complexes: Insights from Experimental and DFT Studies.

A series of supramolecular chiral 1:1 sandwich complexes (1·L and 2·L) consisting of diphenylether/ethane bridged metallobisporphyrin host (1 and 2; M: Zn/Mg) and chiral diamine guest (L) have been presented. The host-guest complexes are compared just upon changing the metal ion (Mg vs Zn) or the bridge (highly flexible ethane vs rigid diphenylether) keeping other factors similar. The factors that would influence the chirality induction process along with their contributions toward the sign and intensity of the CD couplet of the overall complex have been analyzed.

A Nonempirical Approach for Direct Determination of the Absolute Configuration of 1,2-Diols and Amino Alcohols Using Mg(II)bisporphyrin.

We report here a simple, facile, and direct nonempirical protocol for determining the absolute stereochemistry of a variety of chiral 1,2-diols and amino alcohols at room temperature with no chemical derivatization using Mg(II)bisporphyrin as a host. Addition of excess substrates resulted in the formation of a 1:2 host-guest complex in which two substrates bind in an unusual endo-endo fashion because of interligand H-bonding within the bisporphyrin cavity leading to the formation of a unidirectional screw in the bisporphyrin moiety that allowed us an accurate absolute stereochemical determination of the chiral substrate via exciton-coupled circular dichroism (ECCD). The sign of the CD couplet has also been found to be inverted when the stereogenic center is moved by one C atom simply from the bound to an unbound functionality and thus able to discriminate between them successfully.

Metal-coordination-driven mixed ligand binding in supramolecular bisporphyrin tweezers.

Mg(II)bisporphyrin has been used as an efficient host for the selective binding of guest ligands. In the presence of heterogeneous guest pairs, 2-aminopyrimidine/pyrazine and 2-aminopyrimidine/1,4-dioxane, 2-aminopyrimidine is bound selectively inside the bisporphyrin cavity whereas pyrazine/1,4-dioxane is bound outside to produce 1D mixed ligand polymers. UV-vis, (1)H NMR spectra and X-ray structure confirm such a selective and orthogonal binding of the guest ligands.

Step-wise induction, amplification and inversion of molecular chirality through the coordination of chiral diamines with Zn(II) bisporphyrin.

For the first time, a clear and unambiguous rationalization of chirality induction, inversion and subsequent amplification process has been demonstrated for the 1 : 1 sandwich and 2 : 3 host-guest supramolecular complexes consisting of Zn(II) host and chiral diamines as guests that has so far remained the most outstanding issue for the chirogenic process.

Transfer and control of molecular chirality in the 1 : 2 host-guest supramolecular complex consisting of Mg(II)bisporphyrin and chiral diols: the effect of H-bonding on the rationalization of chirality.

A clear rationalization of the origin of chirality transfer from an optically active diol guest to an achiral Mg(ii)bisporphyrin host in a series of 1 : 2 host-guest supramolecular complexes has been reported here that has so far remained the most outstanding issue for the chirogenic process.

Highly enhanced bisignate circular dichroism of ferrocene-bridged Zn(II) bisporphyrin tweezer with extended chiral substrates due to well-matched host-guest system.

Four new chiral tweezer-diamine complexes, consisting of an achiral ferrocene-bridged Zn(II)bisporhyrin host (1) and two small diamines (1R,2R)-1,2-diphenylethylene diamine {(1R,2R)-DPEA} and (1S,2S)-1,2-cyclohexane diamine {(1S,2S)-CHDA} and two extended diamines (1R,2R)-N,N'-bis-(isonicotinoyl)-1,2-diphenylethylene diamine {(1R,2R)-DPEApy} and (1S,2S)-N,N'-bis-(isonicotinoyl)-1,2-cyclohexane diamine {(1S,2S)-CHDApy} chiral guests, are reported. Additions of (1R,2R)-DPEA and (1S,2S)-CHDA separately to 1 in dichloromethane result in the formation of 1:1 sandwich complexes 1·DPEA(R,R) and 1·CHDA(S,S), respectively, at low guest concentration and 1:2 anti complexes 1·(DPEA(R,R))2 and 1·(CHDA(S,S))2, respectively, at higher guest concentration. In contrast, separate additions of (1R,2R)-DPEApy and (1S,2S)-CHDApy to 1 produce only 1:1 sandwich complexes of 1·DPEApy(R,R) and 1·CHDApy(S,S), respectively.

Synthesis, structure, and properties of a series of chiral tweezer-diamine complexes consisting of an achiral zinc(II) bisporphyrin host and chiral diamine guest: induction and rationalization of supramolecular chirality.

We report here the synthesis, structure, and spectroscopic properties of a series of supramolecular chiral 1:1 tweezer-diamine complexes consisting of an achiral Zn(II) bisporphyrin (Zn2DPO) host and five different chiral diamine guests, namely, (R)-diaminopropane (DAP), (1S,2S)-diaminocyclohexane (CHDA), (S)-phenylpropane diamine (PPDA), (S)-phenyl ethylenediamine (PEDA), and (1R,2R)-diphenylethylene diamine (DPEA). The solid-state structures are preserved in solution, as reflected in their (1)H NMR spectra, which also revealed the remarkably large upfield shifts of the NH2 guest protons with the order Zn2DPO·DAP > Zn2DPO·CHDA > Zn2DPO·PPDA> Zn2DPO·PEDA ≫ Zn2DPO·DPEA, which happens to be the order of binding constants of the respective diamines with Zn2DPO. As the bulk of the substituent at the chiral center of the guest ligand increases, the Zn-Nax distance of the tweezer-diamine complex also increases, which eventually lowers the binding of the guest ligand toward the host.

Building-up remarkably stable magnesium porphyrin polymers self-assembled via bidentate axial ligands: synthesis, structure, surface morphology, and effect of bridging ligands.

A series of supramolecular architectures of magnesium tetranitrooctaethylporphyrins mediated by several bidentate axial ligands have been synthesized in excellent yields and structurally characterized. Six conjugated axial ligand with increasing chain lengths have been utilized in the present investigations in which the Mg···Mg nonbonding distance between successive ions also increases from 0.73 to 2.

Induction of supramolecular chirality in di-zinc(II) bisporphyrin via tweezer formation: synthesis, structure and rationalization of chirality.

Two new supramolecular complexes consisting of an achiral bisporphyrin host and a chiral diamine guest are reported. One shows a remarkably high amplitude bisignate CD signal while the other one shows a very low value. X-ray structure and other spectroscopic investigations of the tweezer complexes clearly rationalize the origin of the optical activity that has so far remained an unresolved issue.