9-Mesityl-10-methylacridinium tetrafluoroborate
[CAS# 1442433-71-7]

Identification

• Classification: Catalysts and additives
• Name: 9-Mesityl-10-methylacridinium tetrafluoroborate
• Synonyms: 10-methyl-9-(2,4,6-trimethylphenyl)acridin-10-ium;tetrafluoroborate
• Molecular Formula: C₂₃H₂₂BF₄N
• Molecular Weight: 399.23
• CAS Registry Number: 1442433-71-7
• EC Number: 808-953-1
• SMILES: [B-](F)(F)(F)F.CC1=CC(=C(C(=C1)C)C2=C3C=CC=CC3=[N+](C4=CC=CC=C42)C)C

Safety Data

• Hazard Symbols: GHS07 Warning
• Hazard Statements: H315-H319-H335
• Precautionary Statements: P261-P264-P264+P265-P271-P280-P302+P352-P304+P340-P305+P351+P338-P319-P321-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	3	H335
Eye irritation	Eye Irrit.	2	H319

Discovory and Applicatios

The chemical substance 9-mesityl-10-methylacridinium tetrafluoroborate is a cationic acridinium salt with mesityl and methyl substituents, widely recognized in organic chemistry as a photocatalyst, particularly in photoredox catalysis, and as a synthetic intermediate in materials and pharmaceutical 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 linked to the study of acridinium salts, explored since the early 20th century for their fluorescence and redox properties. Initially used as dyes and chemiluminescent agents, acridinium derivatives gained prominence in the 2000s with the rise of visible-light-mediated photoredox catalysis, driven by the need for sustainable synthetic methods. The specific 9-mesityl-10-methyl substitution, paired with a tetrafluoroborate counterion, emerged to optimize photocatalytic efficiency, solubility, and stability. The mesityl (2,4,6-trimethylphenyl) group enhances excited-state stability and steric protection, while the N-methyl group tunes electronic properties. Advances in acridinium synthesis and photoredox chemistry during the 1980s and 1990s enabled the development of such tailored catalysts.

Synthetically, 9-mesityl-10-methylacridinium tetrafluoroborate is prepared through a multi-step process. A typical route starts with acridine, which is N-methylated using methyl iodide or dimethyl sulfate under basic conditions to form 10-methylacridine. The 9-position is functionalized with a mesityl group via a Grignard reaction with mesitylmagnesium bromide or through palladium-catalyzed cross-coupling with mesityl halide, followed by oxidation to form the acridinium cation. The tetrafluoroborate counterion is introduced via ion exchange with tetrafluoroboric acid or sodium tetrafluoroborate. These steps rely on well-established protocols in heterocyclic synthesis, alkylation, 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), enabling reactions such as C–H functionalization, cross-couplings, radical cyclizations, and atom-transfer radical additions. The mesityl group enhances solubility in organic solvents and stabilizes the excited state, while the tetrafluoroborate counterion ensures compatibility with various reaction conditions. This compound is widely used in the synthesis of pharmaceutical intermediates, natural product analogs, and complex organic molecules, offering mild, selective transformations under visible-light irradiation.

In materials chemistry, the compound is employed in organic light-emitting diodes (OLEDs), fluorescent sensors, and photoelectrochemical devices, 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 photocatalyst design and arylation techniques.

The significance of 9-mesityl-10-methylacridinium tetrafluoroborate lies in its role as an 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

2013. Anti-Markovnikov Hydroamination of Alkenes Catalyzed by an Organic Photoredox System. Journal of the American Chemical Society, 135(24).
DOI: 10.1021/ja4031616

2014. The direct anti-Markovnikov addition of mineral acids to styrenes. Nature Chemistry, 6(8).
DOI: 10.1038/nchem.2000

2023. Anti-Markovnikov hydrochlorination and hydronitrooxylation of a-olefins via visible-light photocatalysis. Nature Catalysis, 6(2).
DOI: 10.1038/s41929-023-00914-7