Institute for Single Crystals

Abstract The encapsulation of squaraine dyes within a tetralactam macrocycle effectively mitigates their intrinsic limitations while maintaining favorable optical properties and improving both chemical and photochemical stability. However, the synthesis of such rotaxanes remains challenging due to the intricate balance of steric and electronic factors governing the macrocyclization. In this study, a series of rotaxanes derived from hemisquaraine dyes bearing primary and secondary amino groups was successfully synthesized using an oxocyclobutenolate template-assisted macrocyclization approach. Dyes with bulky tertiary amino groups, however, failed to undergo encapsulation. Upon encapsulation, the rotaxane systems in chloroform exhibited red-shifted absorption and emission bands, along with a substantial increase in fluorescence quantum yield. This enhancement is attributed to the restricted vibrational and rotational motions of the encapsulated dye. DFT calculations confirmed that all studied rotaxanes are thermodynamically viable, suggesting that the synthetic difficulties observed for tertiary amine derivatives arise from kinetic constraints. This hypothesis was supported by DFT calculations that simulated the macrocyclization process from the corresponding open-chain precursors. These calculations showed favorable energetics for hemisquaraine dyes that contain primary and secondary amino groups. In contrast, the significant steric effects of tertiary amino groups render the oxocyclobutenolate template-assisted macrocyclization energetically unfavorable.

Many ligands are structurally rigid and well-defined, e.g. N-heterocyclic carbenes display a fan-like structure with a defined buried volume. Here, we break this dogma by introducing more flexibility around the catalytically active center by using acyclic (diamino)carbene (ADC) ligands. The ADC ligand was constructed in a straightforward protocol on the ruthenium center via methyl isocyanide coordination and subsequent reaction with amines such as pyrrolidine. Ligand flexibility in the formed (pyrrolidine)(methylamine)carbene ruthenium complex Ru-2 was demonstrated both in solution (variable temperature NMR) and in the solid state through crystallographic identification with the protic NH site oriented either distal or proximal to the ruthenium center. In contrast to their cyclic analogues, the Ru-ADC complexes are highly active in base-free transfer hydrogenation, with turnover numbers >1000. The base-free conditions allowed for the transformation of substrates with base-sensitive groups such as esters, amides, acids, and amines, substrates that typically fail to undergo transfer hydrogenation under classical conditions. The absence of base also enabled late-stage hydrogenation of more complex substrates, and it avoids complications such as corrosion attributed to KOH and related strong bases.

This paper presents a novel 6D dynamic system derived from modified second-type 3D Lorenz equations using state feed- back control. While these original 3D equations are structurally simpler than the classical Lorenz equations, they generate more topologically complex attractors with a distinctive two-winged butterfly structure. The proposed system is the most compact of its kind in the literature, containing only 11 terms: two cross-product nonlinearities, two piecewise linear functions, one cosine function, five linear terms, and one constant. The newly developed 6D hyper- chaotic system exhibits rich dynamic properties, including hidden attractors and dissipative behavior. A detailed dynamic analysis has identified two unstable hyperbolic equilibrium points, indicating the potential for self-exciting attractors. Additionally, bifurcation diagrams were constructed, Lyapunov exponents were computed, and the maximum Kaplan-Yorke dimension DKY = 3.23 was obtained at parameter value a = 0.5, revealing the high complexity of the hyperchaotic dynamics. Furthermore, multistability and offset boosting control were examined to gain deeper insights into the system’s behavior. Finally, synchronization between two identical 6D hyperchaotic systems was successfully achieved using an adaptive control method.

Readily available 4‐bromo‐5‐(N,N,N′‐trimethyl‐N‐(trimethylsilyl)diamino‐methyl)pyrazoles are employed as starting materials for the synthesis of pyrazolyl phosphines. Subsequent hydrolysis yields the expected 4‐diphenylphosphino‐5‐formylpyrazoles, accompanied by the formation of cyclic phosphonium salts. The product distribution is found to depend on the concentration of hydrochloric acid: higher acid concentrations favored the formation of cyclic phosphonium salts. A similar behavior is observed for the methylimines derived from 4‐diphenylphosphino‐5‐formylpyrazoles. These imines acted as bidentate ligands, readily forming palladium(II) complexes. In contrast, the cyclic phosphonium salts reacted with dichlorobis(triphenylphosphine)palladium(II) to afford a palladium(IV) complex, the structure of which is confirmed by X‐ray crystallography.

We report a convenient and scalable strategy for the synthesis of 7-azaindolines and 7-azaindoles using O-vinylhydroxylamines as ring-annulation reagents. These fused nitrogen-containing heterocycles are prominent in numerous biologically active molecules, including FDA-approved pharmaceuticals. Traditional synthetic approaches to these motifs often rely on costly transition metal catalysts and/or high-temperature conditions, such as those employed in the Larock and Fischer indole syntheses. In our approach, O-vinylhydroxylamines undergo N-arylation with aza-arene N-oxides, triggering a rapid [3,3]-sigmatropic rearrangement. This is followed by rearomatization and cyclization to deliver 7-azaindolines, which can be readily dehydrated to afford the corresponding 7-azaindoles. The method offers a broad substrate scope, enabling access to a diverse array of highly functionalized derivatives. Moreover, the mild reaction conditions facilitate late-stage functionalization of complex molecules, demonstrating their value in both synthetic and medicinal chemistry.