Chiral Triphenylacetic Acid Esters: Residual Stereoisomerism and Solid-State Variability of Molecular Architectures.

We have proven the usability and versatility of chiral triphenylacetic acid esters, compounds of high structural diversity, as chirality-sensing stereodynamic probes and as molecular tectons in crystal engineering. The low energy barrier to stereoisomer interconversion has been exploited to sense the chirality of an alkyl substituent in the esters. The structural information are cascaded from the permanently chiral alcohol (inducer) to the stereodynamic chromophoric probe through cooperative interactions. The ECD spectra of triphenylacetic acid esters are highly sensitive to very small structural differences in the inducer core. The tendencies to maximize the C-H···O hydrogen bonds, van der Waals interactions, and London dispersion forces determine the way of packing molecules in the crystal lattice. The phenyl embraces of trityl groups allowed, to some extent, the control of molecular organization in the crystal. However, the spectrum of possible molecular arrangements is very broad and depends on the type of substituent, the optical purity of the sample, and the presence of a second trityl group in the proximity. Racemates crystallize as the solid solution of enantiomers, where the trityl group acts as a protecting group for the stereogenic center. Therefore, the absolute configuration of the inducer is irrelevant to the packing mode of molecules in the crystal.

Dynamic Induction of Optical Activity in Triarylmethanols and Their Carbocations.

A series of artificial triarylmethanols has been synthesized and studied toward the possibility of exhibiting an induced optical activity. The observed chiroptical response of these compounds resulted from the chiral conformation of a triarylmethyl core. The chirality induction from a permanent chirality element to the liable triarylmethyl core proceeds as a cooperative and cascade process. The OH···O(R) and/or (H)O···HorthoC hydrogen bond formation along with the C-H···π interactions seem to be the most important factors that control efficiency of the chirality induction. The position of chiral and methoxy electron-donating groups within a trityl skeleton affects the amplitude of observed Cotton effects and stability of the trityl carbocations. In the neutral environment, the most intense Cotton effects are observed for ortho-substituted derivatives, which undergo a rapid decomposition associated with the complete decay of ECD signals upon acidification. From all of the in situ generated stable carbocations, only two exhibit intense Cotton effects in the low energy region at around 450 nm. The formation of carbocations is reversible; after alkalization, the ions return to the original neutral forms. Unlike most triarylmethyl derivatives known so far, in the crystal, the triarylmethanol, para-substituted with the chiral moiety, shows a propensity for a solid-state sorting phenomenon.

Point-to-Axial Chirality Transmission: A Highly Sensitive Triaryl Chirality Probe for Stereochemical Assignments of Amines.

A readily available stereodynamic and the electronic circular dichroism (ECD)-silent 2,5-di(1-naphthyl)-terephthalaldehyde-based probe has been applied for chirality sensing of primary amines. The chiral amine (the inductor) forces a change in the structure of the chromophore system through the point-to-axial chirality transmission mechanism. As a result, efficient induction of optical activity in the chromophoric system is observed. The butterflylike structure of the probe, with the terminal aryl groups acting as changeable "wings", allowed for the generation of exciton Cotton effects in the region of 1Bb electronic transition in the naphthalene chromophores. The sign of the exciton couplets observed for inductor-reporter systems might be correlated with an absolute configuration of the inductor, whereas the linear relationship between amplitudes of the specific Cotton effect and enantiomeric excess of the parent amine gives potentiality for quantitative chirality sensing. Despite the structural simplicity, the probe turned out to be unprecedentedly highly sensitive to even subtle differences in the inductor structure (i.e., O vs CH2).

Trityl-Containing Alcohols-An Efficient Chirality Transmission Process from Inductor to the Stereodynamic Propeller and their Solid-State Structural Diversity.

The cascade process of a dynamic chirality transmission from the permanent chirality center to the stereodynamic triphenylmethyl group has been studied for series of optically active trityl derivatives. The structural analysis, carried out with the use of complementary methods, enabled us to determine the mechanism of chirality transfer. The process of chirality transmission involves a set of weak but complementary electrostatic interactions. The induction of helicity in a trityl propeller is revealed by rising non-zero cotton effects in the area of trityl UV-absorption. The presence of an additional stereogenic center in close proximity to the trityl-containing stereogenic center significantly affects the sign and, to a lesser extent, magnitude of the respective cotton effects. Despite the bulkiness of the trityl, in the crystalline phase, the molecules under study strictly fill the space. In the crystal, molecules form aggregates stabilized by OH•••O hydrogen bonds. However, the presence of two trityl groups precludes formation of OH•••O hydrogen bonding. Additionally, the trityl group seems to be responsible for the formation of the solid solutions by e.g., racemates of trans- and cis-2-tritylcyclohexanol. Therefore, the trityl group acts as a supramolecular protective group, which in turn can be used in the crystal engineering.

Dynamic optical activity induction in the N-alkyl-N'-trityl ureas and thioureas.

Considered to be rigid, the urea and thiourea functionalities, often used in material chemistry and in asymmetric organocatalysis, are able to transmit information regarding 3D structure from a permanently chiral inducer part to a dynamically chiral (reporter) part of the molecule. Despite a considerable distance between the inducer and the reporter parts of the molecule, the chirality transfer phenomenon has been demonstrated for a series of secondary N-alkyl-N'-trityl ureas and thioureas. The induction of helicity in a stereodynamic trityl propeller is revealed by rising non-zero Cotton effects in the area of trityl absorption. The information regarding the 3D structure of the inducer is transferred to the reporter part of the system through a set of weak but complementary electrostatic interactions. The presence of two supramolecular motifs in the same molecule, characterized by opposite properties, significantly affected the molecular solid state structure of the thioureas and their abilities to assemble. In the crystalline phase, the model, a chiral N-tert-butyl-thiourea derivative that retains the extended Z,Z conformation of the linker, is prone to form a supramolecular network typical of secondary ureas and thioureas. In contrast, the presence of the hydrophobic trityl group suppresses the thioamide NHS[double bond, length as m-dash]C hydrogen bonds. Therefore, trityl acts as a supramolecular protecting group for thioamide functionality, hampering the formation of hydrogen bonded networks in the solid state.

Chiral Cocrystal Solid Solutions, Molecular Complexes, and Salts of N-Triphenylacetyl-l-Tyrosine and Diamines.

The molecular recognition process and the ability to form multicomponent supramolecular systems have been investigated for the amide of triphenylacetic acid and l-tyrosine (N-triphenylacetyl-l-tyrosine, TrCOTyr). The presence of several supramolecular synthons within the same amide molecule allows the formation of various multicomponent crystals, where TrCOTyr serves as a chiral host. Isostructural crystals of solvates with methanol and ethanol and a series of binary crystalline molecular complexes with selected organic diamines (1,5-naphthyridine, quinoxaline, 4,4'-bipyridyl, and DABCO) were obtained. The structures of the crystals were planned based on non-covalent interactions (O-H···N or N-H+···O- hydrogen bonds) present in a basic structural motif, which is a heterotrimeric building block consisting of two molecules of the host and one molecule of the guest. The complex of TrCOTyr with DABCO is an exception. The anionic dimers built off the TrCOTyr molecules form a supramolecular gutter, with trityl groups located on the edge and filled by DABCO cationic dimers. Whereas most of the racemic mixtures crystallize as racemic crystals or as conglomerates, the additional tests carried out for racemic N-triphenylacetyl-tyrosine (rac-TrCOTyr) showed that the compound crystallizes as a solid solution of enantiomers.

Correction: Simple synthetic access to [Au(IBiox)Cl] complexes.

Correction for 'Simple synthetic access to [Au(IBiox)Cl] complexes' by Ekaterina A. Martynova et al., Dalton Trans., 2023, 52, 7558-7563, https://doi.org/10.1039/D3DT01357J.

Synthesis of unsymmetrically and symmetrically functionalized disiloxanes via subsequent hydrosilylation of C≡C bonds.

A selective synthesis of unsymmetrically functionalized disiloxanes via the subsequent hydrosilylation of internal alkynes in the first step, and alkynes (terminal or internal) or 1,3-diynes in the second, with 1,1,3,3-tetramethyldisiloxane (1) is presented for the first time. Using developed approaches performed in a stepwise or one-pot manner a new family of disubstituted disiloxanes was obtained which had previously been inaccessible by other synthetic methods. Moreover, symmetrically functionalized disiloxanes were obtained by direct hydrosilylation of 2 equivalents of terminal or internal alkynes with 1, showing the unique versatility of the hydrosilylation process. Three examples of symmetric disiloxanes were characterized by single crystal X-ray diffraction for the first time. As a result, a wide group of new compounds which can find potential applications as building blocks or coupling agents was obtained and characterized.

Simple synthetic access to [Au(IBiox)Cl] complexes.

Green and sustainable access to chiral and achiral gold-IBiox complexes is reported. The gold complexes were synthesized using a simple, air-tolerant, weak base protocol carried out in a green solvent. Their catalytic activity was examined in the hydroamination of alkynes. The steric protection afforded the gold center by these ligands was quantified using the %Vbur model and compared with the most commonly encountered NHCs.

Directed cis-hydrosilylation of borylalkynes to borylsilylalkenes.

Hydrosilylation of borylalkynes to borylsilylalkenes (with a different arrangement of substituents) has been successfully developed. The cis-addition of SiH group to the CC bonds was directed by using a specific catalyst. The obtained products are crucial synthons for the introduction of the CC bonds in organic synthesis.

5:1 and 2:1 cocrystals of 2,3,4,5,6-pentafluorophenol with phenazine.

2,3,4,5,6-Pentafluorophenol (pFp), unlike phenol, forms cocrystals with the weak heteroaromatic base phenazine (phz). Two types of cocrystals were prepared, (I) with a high content of pFp, 2,3,4,5,6-pentafluorophenol-phenazine (5/1), 5C(6)HF(5)O·C(12)H(8)N(2), and (II) with a 2:1 pFp-phz molar ratio, 2,3,4,5,6-pentafluorophenol-phenazine (2/1), 2C(6)HF(5)O·C(12)H(8)N(2). In both forms, homostacks are formed by the heterocyclic base and phenol molecules and no aryl-perfluoroaryl stacking interactions occur. The arrangement of the molecules in the crystal of (I) is determined by strong O-H···N and O-H···O hydrogen bonds, weak O-H···F, C-H···F and C-H···O interactions, π-π stacking interactions between the phz molecules and C-F···π(F) interactions within the pFp stacks. Among the specific interactions in (II) are a strong O-H···N hydrogen bond, weak C-H···F interactions and π-π stacking interactions between the phz molecules. In (I) and (II), the heterocyclic molecules are located around inversion centres and one of the symmetry-independent pFp molecules in (I) is disordered about an inversion centre. Remarkably, similar structural fragments consisting of six pFp stacks can be identified in cocrystal (I) and in the known orthorhombic polymorph of pFp with Z' = 3 [Gdaniec (2007). CrystEngComm, 9, 286-288].

(Carbonato-κO,O')bis-(di-2-pyridyl-amine-κN,N')cobalt(III) bromide.

In the title compound, [Co(CO(3))(C(10)H(9)N(3))(2)]Br, a distorted octa-hedral coordination of the Co(III) atom is completed by four N atoms of the two chelating di-2-pyridyl-amine ligands and two O atoms of the chelating carbonate anion. The di-2-pyridyl-amine ligands are nonplanar and the dihedral angles between the 2-pyridyl groups are 29.11 (9) and 37.15 (12)°. The coordination cation, which has approximate C(2) symmetry, is connected to the bromide ion via an N-H⋯Br(-) hydrogen bond. The ionic pair thus formed is further assembled into a dimer via N-H⋯O inter-actions about an inversion centre. A set of weaker C-H⋯O and C-H⋯Br(-) inter-actions connect the dimers into a three-dimensional network.

Diversity of N-triphenylacetyl-L-tyrosine solvates with halogenated solvents.

The structure of N-triphenylacetyl-L-tyrosine (C29H25NO4, L-TrCOTyr) is characterized by the presence of both donors and acceptors of classical hydrogen bonds. At the same time, the molecule contains a sterically demanding and hydrophobic trityl group capable of participating in π-electron interactions. Due to its large volume, the trityl group may favour the formation of structural voids in the crystals, which can be filled with guest molecules. In this article, we present the crystal structures of a series of N-triphenylacetyl-L-tyrosine solvates with chloroform, namely, L-TrCOTyr·CHCl3 (I) and L-TrCOTyr·1.5CHCl3 (III), and dichloromethane, namely, L-TrCOTyr·CH2Cl2 (II) and L-TrCOTyr·0.1CH2Cl2 (IV). To complement the topic, we also decided to use the racemic amide N-triphenylacetyl-DL-tyrosine (rac-TrCOTyr) and recrystallized it from a mixture of chloroform and dichloromethane. As a result, rac-TrCOTyr·1.5CHCl3 (V) was obtained. In the crystal structures, the amide molecules interact with each other via O-H...O hydrogen bonds. Noticeably, the amide N-H group does not participate in the formation of intermolecular hydrogen bonds. Channels are formed between the TrCOTyr molecules and these are filled with solvent molecules. Additionally, in the crystals of III and V, there are structural voids that are occupied by chloroform molecules. Structure analysis has shown that solvates I and II are isostructural. Upon loss of solvent, the solvates transform into the solvent-free form of TrCOTyr, as confirmed by thermogravimetric analysis, differential scanning calorimetry and powder X-ray diffraction.

Two cobalt(III) mono-dimethylglyoximates isolated from one reaction.

The reaction of cobalt(II) nitrate hexahydrate with dimethylglyoxime (DMGH(2)) and 1,10-phenanthroline (phen) in a 1:1:2 molar ratio results in two Co(III) mono-dimethylglyoximates having two chelating phen ligands in cis positions and the Co(III) atom coordinated by six N atoms in a distorted octahedral coordination geometry. The isolated products differ in the deprotonation state of the DMGH(2) ligand. In [mu-hydrogen bis(N,N'-dioxidobutane-2,3-diimine)]tetrakis(1,10-phenanthroline)cobalt(III) trinitrate ethanol disolvate 1.87-hydrate, [Co(2)(C(4)H(6)N(2)O(2))(C(4)H(7)N(2)O(2))(C(12)H(8)N(2))(4)](NO(3))(3).2C(2)H(6)O.1.87H(2)O, (I), the C(2)-symmetric cation is formed with the coordination [Co(DMG)(phen)(2)](+) cations aggregating via a very strong O(-)...H(+)...O(-) hydrogen bond with an O...O distance of 2.409 (4) A. Crystals of (I) exhibit extensive disorder of the solvent molecules, the nitrate anions and one of the phen ligands. Compound (I) is a kinetic product, not isolated previously from similar systems, that transforms slowly into (N-hydroxy-N'-oxidobutane-2,3-diimine)bis(1,10-phenanthroline)cobalt(III) dinitrate ethanol monosolvate 0.4-hydrate, [Co(C(4)H(7)N(2)O(2))(C(12)H(8)N(2))(2)](NO(3))(2).C(2)H(6)O.0.40H(2)O, (II), with the DMGH(-) ligand hydrogen bonded to one of the nitrate anions. In (II), the solvent molecules and one of the nitrate anions are disordered.

Cocrystals of 2,3,5,6-tetrafluorobenzene-1,4-diol with diaza aromatic compounds.

2,3,5,6-Tetrafluorobenzene-1,4-diol easily forms cocrystals with heteroaromatic bases containing the pyrazine unit. In the 1:1 complexes with pyrazine, C(6)H(2)F(4)O(2) x C(4)H(4)N(2), (I), and quinoxaline, C(6)H(2)F(4)O(2) x C(8)H(6)N(2), (II), the crystal components are linked via O-H...N hydrogen bonds into one-dimensional chains. With the largest base, phenazine, the 1:2 benzenediol-phenazine complex, C(6)H(2)F(4)O(2) x 2 C(12)H(8)N(2), (III), was obtained, with the molecules linked via O-H...N interactions into a discrete heterotrimer. In all three cocrystals, the two types of molecules are organized into layers via softer C-H...O and C-H...F interactions and pi-pi stacking interactions, with stronger hydrogen bonds linking molecules of adjacent layers. In (II) and (III), molecules are arranged into heterostacks, whereas in (I) separate stacks are formed by the heterocyclic base and the benzenediol molecule.

A new polymorph of benzene-1,2-diamine: isomorphism with 2-aminophenol and two-dimensional isostructurality of polymorphs.

A new crystalline form of benzene-1,2-diamine, C(6)H(8)N(2), crystallizing in the space group Pbca, has been identified during screening for cocrystals. The crystals are constructed from molecular bilayers parallel to (001) that have the polar amino groups directed to the inside and the aromatic groups, showing a herringbone arrangement, directed to the outside. The known monoclinic form and the new orthorhombic polymorph exhibit two-dimensional isostructurality as the crystals consist of nearly identical bilayers. In the monoclinic form, neighbouring bilayers are generated by a unit translation along the a axis, whereas in the orthorhombic form they are generated by a c-glide. Moreover, the new form of benzene-1,2-diamine is essentially isomorphous with the only known form of 2-aminophenol.

p-Phenylenediamine and its dihydrate: two-dimensional isomorphism and mechanism of the dehydration process, and N-H...N and N-H...pi interactions.

p-Phenylenediamine can be obtained as the dihydrate, C(6)H(8)N(2) x 2 H(2)O, (I), and in its anhydrous form, C(6)H(8)N(2), (II). The asymmetric unit of (I) contains one half of the p-phenylenediamine molecule lying about an inversion centre and two halves of water molecules, one lying on a mirror plane and the other lying across a mirror plane. In (II), the asymmetric unit consists of one molecule in a general position and two half molecules located around inversion centres. In both structures, the p-phenylenediamine molecules are arranged in layers stabilized by N-H...pi interactions. The diamine layers in (I) are isostructural with half of the layers in (II). On dehydration, crystals of (I) transform to (II). Comparison of their crystal structures suggests the most plausible mechanism of the transformation process which requires, in addition to translational motion of the diamine molecules, in-plane rotation of every fourth p-phenylenediamine molecule by ca 60 degrees. A search of the Cambridge Structural Database shows that the formation of hydrates by aromatic amines should be considered exceptional.

Phenazine-naphthalene-1,5-diamine-water (1/1/2).

The asymmetric unit of the title compound, C(12)H(8)N(2)·C(10)H(10)N(2)·2H(2)O, contains one half-mol-ecule of phenazine, one half-mol-ecule of naphthalene-1,5-diamine and one water mol-ecule. The phenazine and naphthalene-1,5-diamine mol-ecules are located on inversion centers. The water mol-ecules serve as bridges between the naphthalene-1,5-diamine mol-ecules and also between the naphthalene-1,5-diamine and phenazine mol-ecules. The naphthalene-1,5-diamine and water mol-ecules are connected via N-H⋯O and O-H⋯N hydrogen bonds, forming a T4(2) motif. They are arranged into a two-dimensional polymeric structure parallel to (10) in which the water mol-ecule is a single donor and a double acceptor, whereas the amino group is a double donor and a single acceptor in the hydrogen bonding. These two-dimensional assemblies alternate with the layers of phenazine mol-ecules arranged into a herringbone motif. Each phenazine mol-ecule is hydrogen bonded to two water mol-ecules and thus a three-dimensional framework of hydrogen-bonded mol-ecules is generated.

5-Amino-1-naphthol.

In the title compound, C(10)H(9)NO, the amino and the hydr-oxy groups act both as a single donor and a single acceptor in hydrogen bonding. In the crystal, mol-ecules are connected via chains of inter-molecular ⋯N-H⋯O-H⋯ inter-actions, forming a two-dimensional polymeric structure resembling the hydrogen-bonded mol-ecular assembly found in the crystal structure of naphthalene-1,5-diol. Within this layer, mol-ecules related by a translation along the a axis are arranged into slipped stacks via π-π stacking inter-actions [inter-planar distance = 3.450 (4) Å]. The amino N atom shows sp(3) hybridization and the two attached H atoms are located on the same side of the aromatic ring.

Optical Activity and Helicity Enhancement of Highly Sensitive Dinaphthylmethane-Based Stereodynamic Probes for Secondary Alcohols.

Chirality transfer from circular dichroism (CD)-silent secondary alcohol (inductor) to the stereodynamic bichromophoric di(1-naphthyl)methane probe (reporter) led to the generation of intense, induced exciton-type Cotton effects (CEs) in the ultraviolet-visible absorption region. The di(1-naphthyl)methane probe exhibits extraordinarily high sensitivity to even small structural variations of the alcohol skeleton, that is, the probe is able to distinguish between an oxygen atom and a methylene group in a 3-hydroxytetrahydrofurane skeleton. Signs and amplitudes of the exciton couplets of 1Bb electronic transition might be correlated with the type of stereo-differentiating parts of the molecule flanking the stereogenic center, however, not with the absolute configuration. The origin of the induced CEs was established by means of experimental and theoretical methods. As a result, a mechanism of chirality transfer from the permanent stereogenic center to the bichromophore is proposed.