Potassium (4-Fluorophenyl)trifluoroborate | CAS 192863-35-7 | ≥97%

Suzuki–Miyaura cross-coupling for fluorinated biaryls: Potassium (4-fluorophenyl)trifluoroborate is a preferred coupling partner for the palladium-catalysed construction of fluorinated biaryl scaffolds via Suzuki–Miyaura reactions. The para-fluorine substituent is retained intact throughout the coupling, providing direct access to 4-fluorobiphenyl motifs that are prevalent structural features in medicinal chemistry programmes. The trifluoroborate salt undergoes controlled hydrolysis under aqueous basic conditions, slowly releasing the active boronate species and suppressing protodeboronation and homocoupling side reactions that can limit yields with the corresponding free boronic acid. Standard palladium catalysts including Pd(PPh₃)₄, Pd(dppf)Cl₂, and Pd(OAc)₂ with phosphine ligands are effective, and coupling proceeds efficiently with aryl bromides, chlorides, and triflates. Molander and Biolatto (J. Org. Chem. 2003, 68, 4302) demonstrated the broad substrate scope and functional group tolerance of potassium aryltrifluoroborates in Suzuki–Miyaura coupling, establishing their utility as bench-stable boronic acid replacements.

Fluorine introduction for metabolic stability in drug design: The introduction of fluorine at the para position of an aryl ring is one of the most widely used medicinal chemistry strategies for blocking oxidative metabolism at metabolically vulnerable sites, improving oral bioavailability, and fine-tuning lipophilicity. Potassium (4-fluorophenyl)trifluoroborate provides a convenient and stoichiometrically precise means of installing this motif via late-stage cross-coupling. The crystalline salt eliminates the variable boroxine content and uncertain hydration state that complicate the use of 4-fluorophenylboronic acid, making it particularly suited for parallel and combinatorial library synthesis where accurate reagent dosing is critical.

Rhodium-catalysed conjugate addition: In rhodium-catalysed 1,4-conjugate addition reactions, potassium (4-fluorophenyl)trifluoroborate transfers the 4-fluorophenyl group to α,β-unsaturated carbonyl acceptors with high efficiency. Using [Rh(cod)OH]₂ or Rh(acac)(CO)₂ with chiral bisphosphine ligands, enantioselective conjugate additions to cyclic and acyclic enones deliver fluorinated aryl ketone products that serve as valuable intermediates for further synthetic elaboration. The controlled nucleophilicity of the trifluoroborate salt relative to the free boronic acid often results in cleaner reaction profiles and reduced formation of protodeboronation by-products. Batey and Quach (Org. Lett. 2003, 5, 4397) demonstrated rhodium-catalysed additions of potassium organotrifluoroborates to aldehydes and enones as a general methodology for carbon–carbon bond construction.

Chan–Lam coupling for C–heteroatom bond formation: Potassium (4-fluorophenyl)trifluoroborate participates in copper-mediated Chan–Lam coupling reactions for the formation of C–N and C–O bonds under mild, open-air conditions. The 4-fluorophenyl group can be transferred to amines, amides, phenols, and heterocyclic nitrogen nucleophiles without the need for palladium catalysts or stringent exclusion of air and moisture. This reactivity provides a practical route to N-(4-fluorophenyl) heterocycles and diaryl ethers bearing the fluoroaryl motif, which are common pharmacophoric elements in bioactive molecules.

Practical advantages over boronic acids and esters: For both discovery and process-scale applications, potassium aryltrifluoroborates offer significant practical advantages over boronic acids and pinacol boronate esters. The crystalline, free-flowing solids have precisely defined molecular weights, enabling accurate batch-to-batch dosing without analytical correction for boroxine or hydrate content. They are indefinitely stable under ambient storage and transport conditions at room temperature, eliminating cold-chain requirements and simplifying inventory management. Their compatibility with aqueous and biphasic reaction media and straightforward workup procedures further enhance their attractiveness for large-scale manufacturing of fluorinated pharmaceutical intermediates. Darses and Genet (Chem. Rev. 2008, 108, 288) provide a comprehensive review of organotrifluoroborate preparation, reactivity, and synthetic applications across the full range of transition metal-catalysed transformations.