tBu3P·HBF4 (TTBP) | CAS 131274-22-1 | ≥98%

Technical Specifications

Product Description & Scientific Applications

Tri-tert-butylphosphonium tetrafluoroborate ([(t-Bu)₃PH]BF₄) is the bench-stable phosphonium-salt form of P(t-Bu)₃, a bulky, electron-rich phosphine that is among the workhorses of palladium-catalysed cross-coupling. Free P(t-Bu)₃ is pyrophoric and oxidises in air within minutes, which makes the free phosphine inconvenient and safety-sensitive to handle. The tetrafluoroborate salt is a free-flowing crystalline solid, weighable in air under normal laboratory precautions. Its conjugate acid has a pKa of about 11.4, among the highest for a tertiary phosphine, so the base present in a coupling reaction deprotonates the salt and liberates the free phosphine in situ. The user obtains the reactivity of P(t-Bu)₃ without isolating or storing the pyrophoric phosphine.

P(t-Bu)₃ is the most strongly electron-donating phosphine in Tolman's classic survey, and with a cone angle of about 182° it is among the bulkiest in common use. Strong σ-donation enriches the metal centre; the steric bulk favours a monoligated, coordinatively unsaturated 12-electron Pd(0) species with high oxidative-addition activity. That fragment inserts into the strong aryl C–Cl bond — a step largely beyond classical triarylphosphine catalysts under mild conditions. This brings inexpensive, widely available aryl chlorides into routine cross-coupling.

This C–Cl activation carries across the carbon–carbon couplings. In Suzuki–Miyaura reactions, Pd₂(dba)₃/P(t-Bu)₃ couples aryl and vinyl chlorides with arylboronic acids at room temperature and low loading. It also inverts the conventional reactivity order: on a substrate bearing both, an aryl chloride is engaged in preference to an aryl triflate, giving orthogonal control over which site reacts first. Negishi couplings with aryl- and alkylzinc reagents tolerate nitro groups, assemble sterically hindered biaryls, and can reach turnover numbers above 3000. Stille couplings extend to organostannanes including SnBu₄, build tetra-ortho-substituted biaryls, and couple aryl chlorides in the presence of triflates; for aryl bromides, the same system furnished the first general room-temperature Stille protocol.

The monoligated palladium also addresses long-standing side reactions in alkyne and alkene coupling. A copper-free Sonogashira coupling of aryl bromides with terminal alkynes removes the copper co-catalyst associated with Glaser-type oxidative homocoupling, while staying productive on electron-rich substrates such as 4-bromoanisole and tolerating ketones. In Mizoroki–Heck olefinations with Cy₂NMe as base, aryl bromides and activated aryl chlorides couple at room temperature; electron-neutral and electron-rich aryl chlorides react on warming.

Beyond C–C bonds, Buchwald–Hartwig amination couples aryl bromides and chlorides with amines at or near room temperature, N-arylates indoles and carbamates, and converts diarylamines into triarylamines. P(t-Bu)₃ also catalyses palladium α-arylation of carbonyl compounds, including monoarylation of tert-butyl acetate and arylation of α,α-disubstituted esters, ketones, malonates and 1,3-dicarbonyls.

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