Bipyridine and related compounds are starting materials or precursors for a variety of valuable substances such as biologically active molecules, ligands for catalysts, photosensitizers, viologens, ...and supramolecular architectures. Thus, it is important to classify their synthesis methods and understand their characteristics. Representative examples include methods using homo and heterocoupling of pyridine derivatives in the presence of a catalyst. Because bipyridine compounds strongly coordinate with metal centers, a decrease in catalytic activity and yield is often observed in the reaction system. To address this issue, this review provides insights into advances over the last ~30 years in bipyridine synthesis using metal complexes under both homogeneous and heterogeneous conditions. Moreover, strategies for bipyridine synthesis involving sulfur and phosphorous compounds are examined. These alternative pathways offer promising avenues for overcoming the challenges associated with traditional catalysis methods, providing a more comprehensive understanding of the synthesis landscape.
The chemical functionalization of hydrogen-terminated silicon(111) surfaces with photochromic diarylethene using an ethylene anchoring group was achieved. Conductive atomic force microscopy ...measurements showed the current changes on modified silicon electrodes caused by light-induced isomerization of the diarylethene between an open form and a closed form.
We herein describe the development of an efficient enantioselective catalytic system that promotes the arylation of secondary silanes. Our method involves treatment of secondary silanes and aryl ...iodides with a Pd(2)(dba)(3)-asymmetric phosphoramidite ligand system to afford optically active tertiary silanes with good enantioselectivities.
ConspectusThis Account summarizes recent developments in metal-mediated coupling reactions between hydrosilanes and aryl iodides in the presence of Pd(P(
-Bu)
)
and base. Alkylated organosilanes are ...obtained when Pt(P(
-Bu)
)
and a base are employed in reactions between hydrosilanes and aliphatic iodides. These transformations show unusual reactivity compared to the typical behavior of hydrosilanes toward organoiodides in the presence of PdCl
or PtCl
, and they proceed in high yields under mild conditions. In addition, the reaction demonstrates (1) high functional group tolerances, (2) stepwise introduction of substituents onto silicon atoms from secondary silanes, and (3) transformation without cleavage of weak Si-Si σ bonds in the molecules.This transformation can serve as a powerful tool for the synthesis of functional organosilicon compounds. The advantage is the flexibility in the molecular structure due to the large size compared to carbon. These compounds have relatively sparse packing in the crystalline state, unlike π-conjugated molecules, which induce dense π-π interactions. Consequently, they have significantly different physical properties in solution and in the solid state. Among them, aromatic disilanes and oligosilanes are important substance groups, because the conjugated chain within these molecules expands due to σ-π interaction between Si-Si σ bond and π orbital of aromatic ring. σ-π Conjugation is most efficient when the dihedral angle between the aromatic ring and the Si-Si bond is 90°, resulting in the overlap of σ orbital and π orbital. The conformational structure, packing, and physical properties of these compounds can change in tandem in response to external stimuli through a crystal phase transition. The interlocking changes in structure and physical properties are reversible, easily returning to their original state with different external stimulus. This account covers several important aspects, including solid-state emission with high fluorescence intensity, aggregation-induced emission (AIE) in water-THF system, mechanochromic fluorescence, organic light emitting diode (OLED), second harmonic generation (SHG) and thermosalient phenomena.This reaction can synthesize optically active tertiary and quaternary silanes by the enantioselective arylation of secondary silanes with aryl iodides using a palladium catalyst modified with a TADDOL-derived amide phosphoric acid ester as a chiral ligand. These optically active compounds can be used as useful circularly polarized luminescence (CPL) materials due to their strong luminescence intensity (Φ) and luminescence dissymmetry factor (
) attributed to the chiral silicon atom. The efficient synthesis of sila-pharmaceuticals using this method as a key step is also described.The technique enables the design and synthesis of various silicon-containing bioactive substances and medical chemicals. Through the synthesis of organosilane compounds using this method, it is anticipated that the development of functional organic silanes will accelerate their practical applications in a wide range of fields.
A σ–π extended aryldisilane, comprising a thienopyrazine group as an acceptor fragment and phenothiazine groups as the donor moiety, has been prepared through the introduction of two Si−Si bridges ...(compound 1). X‐ray diffraction analysis determined the crystal structure of 1, and experimental and theoretical approaches investigated its optical properties. Solvatochromic studies revealed the dual emission of 1 in all solvents tested. Compound 1 also exhibited fluorescence in the solid state upon excitation with a hand‐held UV lamp, as well as mechanochromic luminescent properties. The packing mode in the crystal structure, variation of phenothiazine conformation, morphological changes between crystalline and amorphous phases are the major factors showing reversible fluorescence under external stimuli. A theoretical conformer study found that 1 exists in distinct conformational groups differing in Gibbs free energy by less than 3 kcal mol−1. The conformer in the crystalline state of 1 can promote the complete separation of the HOMO and LUMO between the phenothiazine donor and the thienopyrazine acceptor, linked by the disilane linker. HOMO–LUMO energy transition in the crystalline state is forbidden due to the lack of frontier orbital overlap. Crystalline state emission showed LUMO → HOMO−1 transition (locally excited (LE) state). In the amorphous state, the partial presence of quasi‐axial conformers allows intramolecular charge‐transfer type emission via energy transfer from dominant quasi‐equatorial conformers. The strategy proposed in this work provides important guidance for developing stimuli‐responsive materials with controlled excited states.
A σ–π extended aryldisilane comprising a thienopyrazine group as acceptor fragment and a phenothiazine group as donor moiety was prepared. The compound exhibits fluorescence in the solid state upon UV excitation and mechanochromic luminescent properties.
We describe here the preparation of soft crystals using disilanyl macrocycle C4 possessing four p-phenylenes circularly connected by four flexible disilane bonds. Single crystals of C4 exhibited a ...reversible thermal single-crystal-to-single-crystal (SCSC) phase transition behavior between two crystal phases accompanied by remarkable mechanical motion (thermosalient effect), as revealed by thermal analyses and X-ray diffraction measurements. Detailed structural analyses implied that flexibility of the parallelogram disilanyl architecture and molecular packing mode via weak intermolecular interactions facilitated a concerted structural transformation (parallel crank motion) of macrocycles in the crystal, thus resulting in the SCSC phase transition accompanied by anisotropic shrinking/elongation of the cells to induce the thermosalient effect. This work explores a new area of organosilicon chemistry and presents the potential utility of disilanyl macrocycles as soft crystals.
The synthesis, structural, and photophysical investigations of CuI complexes with a disilanylene-bridged bispyridine ligand 1 are herein presented. Dinuclear (2) and ladder-like (3) octanuclear ...copper(I) complexes were straightforwardly prepared by exactly controlling the ratio of CuI/ligand 1. Single-crystal X-ray analysis confirmed that dinuclear complex 2 had no apparent π…π stacking whereas octanuclear complex 3 had π…π stacking in the crystal packing. In the solid state, the complexes display yellow-green (λem = 519 nm, Φ = 0.60, τ = 11 µs, 2) and blue (λem = 478 nm, Φ = 0.04, τ = 2.6 µs, 3) phosphorescence, respectively. The density functional theory calculations validate the differences in their optical properties. The difference in the luminescence efficiency between 2 and 3 is attributed to the presence of π…π stacking and the different luminescence processes.
The development of disilane‐bridged donor–acceptor–donor (D‐Si‐Si‐A‐Si‐Si‐D) and acceptor–donor–acceptor (A‐Si‐Si‐D‐Si‐Si‐A) compounds is described. Both types of compound showed strong emission ...(λem=ca. 500 and ca. 400 nm, respectively) in the solid state with high quantum yields (Φ: up to 0.85). Compound 4 exhibited aggregation‐induced emission enhancement in solution. X‐ray diffraction revealed that the crystal structures of 2, 4, and 12 had no intermolecular π–π interactions to suppress the nonradiative transition in the solid state.
Disilane‐bridged donor–acceptor–donor (D‐Si‐Si‐A‐Si‐Si‐D) molecules and acceptor–donor–acceptor (A‐Si‐Si‐D‐Si‐Si‐A) compounds display strong solid‐state emission (see picture) and aggregation‐induced emission (AIE). X‐ray diffraction reveals there is no π–π stacking in crystals to suppress intermolecular interaction.
Six novel donor–acceptor–donor organic dyes containing a Si–Si moiety based on triarylamine functionalities as donor units were prepared by Pd-catalyzed arylation of hydrosilanes. Their ...photophysical, electrochemical, and structural properties were studied in detail. Most of the compounds showed attractive photoluminescence (PL) and electrochemical properties both in solution and in the solid state because of intramolecular charge transfer (ICT), suggesting these compounds could be useful for electroluminescence (EL) applications. The aggregation-induced emission enhancement (AIEE) characteristics of 1 and 3 were examined in mixed water/THF solutions. The fluorescence intensity in THF/water was stronger in the solution with the highest ratio of water because of the suppression of molecular vibration and rotation in the aggregated state. Single-crystal X-ray diffraction of 4 showed that the reduction of intermolecular π–π interaction led to intense emission in the solid state and restricted intramolecular rotation of the donor and acceptor moieties, thereby indicating that the intense emission in the solid state is due to AIEE. An electroluminescence device employing 1 as an emitter exhibited an external quantum efficiency of up to 0.65% with green light emission. The emission comes solely from 1 because the EL spectrum is identical to that of the PL of 1. The observed luminescence was sufficiently bright for application in practical devices. Theoretical calculations and electrochemical measurements were carried out to aid in understanding the optical and electrochemical properties of these molecules.
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