3,6-Di-tert-butyl-9-mesityl-10-phenylacridinium Tetrafluoroborate
[CAS# 1810004-87-5]

Identification

• Classification: Catalysts and additives
• Name: 3,6-Di-tert-butyl-9-mesityl-10-phenylacridinium Tetrafluoroborate
• Molecular Formula: C₃₆H₄₀BF₄N
• Molecular Weight: 573.51
• CAS Registry Number: 1810004-87-5
• EC Number: 969-539-5
• SMILES: [B-](F)(F)(F)F.CC1=CC(=C(C(=C1)C)C2=C3C=CC(=CC3=[N+](C4=C2C=CC(=C4)C(C)(C)C)C5=CC=CC=C5)C(C)(C)C)C

Properties

• Melting point: 277.2 ºC (Expl.)

Safety Data

• Hazard Symbols: GHS05;GHS07 Danger
• Hazard Statements: H302-H314-H315-H319-H335
• Precautionary Statements: P260-P261-P264-P264+P265-P270-P271-P280-P301+P317-P301+P330+P331-P302+P352-P302+P361+P354-P304+P340-P305+P351+P338-P305+P354+P338-P316-P319-P321-P330-P332+P317-P337+P317-P362+P364-P363-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin corrosion	Skin Corr.	1B	H314
Acute toxicity	Acute Tox.	4	H302

Discovory and Applicatios

The chemical substance 3,6-di-tert-butyl-9-mesityl-10-phenylacridinium tetrafluoroborate is a cationic acridinium salt with tert-butyl, mesityl, and phenyl substituents, widely recognized in organic chemistry as a photocatalyst and synthetic intermediate, particularly in photoredox catalysis and materials chemistry. Its discovery and applications are well-documented in the literature, rooted in the development of acridinium-based chromophores and organocatalysis.

The origins of this compound are tied to the study of acridinium salts, which have been explored since the early 20th century for their fluorescence and redox properties. Acridinium derivatives gained prominence in the mid-20th century as dyes and chemiluminescent agents, but their use in photoredox catalysis surged in the 2000s with the rise of visible-light-mediated organic transformations. The specific substitution pattern—3,6-di-tert-butyl, 9-mesityl, and 10-phenyl, paired with a tetrafluoroborate counterion—emerged to enhance solubility, stability, and photocatalytic efficiency. The tert-butyl groups provide steric bulk and solubility, the mesityl (2,4,6-trimethylphenyl) group stabilizes the excited state, and the phenyl group tunes electronic properties. Advances in aromatic functionalization and photoredox chemistry during the 1980s and 1990s enabled the synthesis of such tailored acridinium salts.

Synthetically, 3,6-di-tert-butyl-9-mesityl-10-phenylacridinium tetrafluoroborate is prepared through a multi-step process. A typical route starts with acridine, which is functionalized at the 3,6-positions with tert-butyl groups via Friedel-Crafts alkylation using tert-butyl chloride and a Lewis acid catalyst like aluminum chloride. The 9-position is arylated with mesityl via a Grignard reaction or cross-coupling with mesityl halide, followed by oxidation to form the acridinium core. The 10-position is N-arylated with phenyl using a phenyl halide under Buchwald-Hartwig or Ullmann coupling conditions. The resulting acridinium cation is paired with tetrafluoroborate by ion exchange with a tetrafluoroboric acid or sodium tetrafluoroborate. These steps rely on well-established protocols in heterocyclic synthesis, cross-coupling, and ion pairing, ensuring high purity and yield.

The primary application of this compound is as a photocatalyst in photoredox catalysis. Its acridinium core absorbs visible light, generating a long-lived excited state capable of single-electron transfer (SET) processes, making it ideal for reactions like C–H functionalization, cross-couplings, and radical cyclizations. The tert-butyl and mesityl groups enhance solubility in organic solvents and stabilize the excited state, while the tetrafluoroborate counterion ensures stability and compatibility with various reaction conditions. This compound is widely used in the synthesis of pharmaceutical intermediates, natural product analogs, and complex organic molecules, where photoredox catalysis enables mild, selective transformations.

In materials chemistry, the compound is employed in the development of organic light-emitting diodes (OLEDs) and fluorescent sensors, leveraging its strong fluorescence and redox properties. In academic research, it serves as a model for studying photoredox mechanisms, excited-state dynamics, and acridinium photophysics. Its synthesis has contributed to advancements in tailored photocatalyst design and arylation techniques.

The significance of 3,6-di-tert-butyl-9-mesityl-10-phenylacridinium tetrafluoroborate lies in its role as a highly efficient photocatalyst and versatile intermediate, combining the photophysical properties of acridinium with optimized steric and electronic features. Its development reflects progress in photoredox catalysis and heterocyclic functionalization. By enabling selective, light-mediated transformations, it has become a critical tool in advancing pharmaceutical, materials, and chemical research.

References

2021. Amination and Related Processes. Science of Synthesis, 1.
URL: https://science-of-synthesis.thieme.com/app/text/?id=SD-225-00001

2022. (2 + 1 + 2 + 1)-Strategy for Synthesizing Acridinium Salts. Science of Synthesis, 1.
URL: https://science-of-synthesis.thieme.com/app/text/?id=SD-225-00135

2024. Photocatalytic carbyne reactivity of phosphorus ylides for three-component formal cycloaddition reactions. Nature Synthesis, 3(8).
DOI: 10.1038/s44160-024-00612-7