Toward a 1,4-Diphosphinine-Based Molecular CPS-Ternary Compound

Area of Science:

• Organophosphorus Chemistry
• Heterocyclic Chemistry
• Synthetic Organic Chemistry

Background:

• 1,3-dithiole-2-thione derivatives are valuable precursors in heterocyclic synthesis.
• Tricyclic phosphorus-containing heterocycles are of interest due to their unique electronic and structural properties.
• Exploring novel synthetic routes to complex heterocyclic systems is crucial for advancing chemical science.

Purpose of the Study:

• To synthesize a novel tricyclic 1,4-dihydro-1,4-diphosphinine.
• To investigate the reactivity and properties of the synthesized diphosphinine and its derivatives.
• To provide indirect evidence for the aromaticity of the tricyclic diphosphinine system.

Main Methods:

• Base-induced ring formation protocol for synthesizing the tricyclic 1,4-dihydro-1,4-diphosphinine.
• P-oxidation reactions using chalcogens to form bis(P-oxide), bis(P-sulfide), and bis(P-selenide) derivatives.
• P-substitution reactions of the 1,4-dichloro-1,4-dihydro-1,4-diphosphinine with nucleophiles (potassium bis(trimethylsilyl)amide and alcohols).
• Reduction of the dichloro derivative to 1,4-diphosphinine and subsequent thermal [4 + 2] cycloaddition reaction.
• Density functional theory (DFT) studies for mechanistic insights and spectral data analysis (NMR, IR, UV/vis).

Main Results:

• Successful synthesis of the tricyclic 1,4-dihydro-1,4-diphosphinine via a base-induced ring formation.
• Formation of bis(P-oxide), bis(P-sulfide), and bis(P-selenide) derivatives, obtained as cis/trans mixtures.
• Conversion to 1,4-dichloro-1,4-dihydro-1,4-diphosphinine, which exhibited selective substitution reactions with nucleophiles, yielding bis(amino) and bis(alkoxy) derivatives.
• Reduction to 1,4-diphosphinine, which, despite insolubility, underwent thermal [4 + 2] cycloaddition with diethylacetylene dicarboxylate to form a diphosphabarrelene.
• DFT calculations provided insights into reaction pathways and supported experimental spectral data.

Conclusions:

• The study successfully established a synthetic route to a novel tricyclic 1,4-dihydro-1,4-diphosphinine.
• The reactivity of the dichloro derivative highlights its utility as a versatile intermediate for further functionalization.
• The [4 + 2] cycloaddition reaction, despite product insolubility, offers compelling indirect evidence for the aromatic nature of the tricyclic diphosphinine system.
• DFT studies complement experimental findings, enhancing the understanding of the compound's formation and properties.