The synthesis, molecular structure and supramolecular architecture of complexes between the ammonia adduct of tris(pentafluorophenyl)boron and a series of mono and polydentate hydrogen-bond acceptors.
The ammonia adduct of tris(pentafluorophenyl)boron, (C6F5)3B.NH3, is a potentially tri-functional hydrogen-bond donor. Co-crystallisation with the bases acetonitrile, pyridine, tetrahydrofuran, tetramethylethylenediamine, 15-crown-5, 1,4-diazabicyclo[2.2.2]octane (DABCO), pyrazine and 4,4'-bipyridine results, not in donor exchange, but in the formation of supermolecules assembled through hydrogen bonding to second coordination sphere acceptors. The complexes have been characterised by elemental analysis, multinuclear NMR and single-crystal diffraction methods. The solid-state architectures range in complexity, from the hydrogen bonded pairing of (C6F5)3B.NH3, with a single monodentate acceptor molecule (e.g. MeCN to form (C6F5)3B.NH3.NCMe), through complexation with all three N-H groups to the macrocycle 15-crown-5, to the formation of infinite one-dimensional chains with pyrazine and DABCO, and to two-dimensional networks with the divergent acceptor 4,4'-bipyridine.
Perfluorophenyl derivatives of the elements : I. Tris(pentafluorophenyl)boron
Abstract The relatively stable white solid tris(pentafluorophenyl)boron has been prepared in high yield from boron trichloride and pentafluorophenyllithium using pentane as a solvent. It shows strong acceptor properties towards the Lewis bases: ammonia, trimethylamine, triphenylphosphine, and pyridine. With excess of pentafluorophenyllithium the salt lithium tetrakis(pentafluorophenyl)borate is formed; the water-soluble borate precipitates the tetraethylammonium and potassium derivatives from concentrated aqueous solutions.
ARYLBORON COMPOUNDS AS ACID CATALYSTS IN ORGANIC SYNTHETIC TRANSFORMATIONS
Arylboron compounds, ArnB(OH)3–n (n = 1–3), bearing electron-withdrawing aromatic groups such as triarylboranes, diarylborinic acids, and arylboronic acids represent a new class of air-stable and water-tolerant Lewis acid or Bronsted acid catalysts in organic synthesis. In particular, while tris(pentafluorophenyl)borane has primarily been used as a co-catalyst in metallocene-mediated olefin polymerization, its potential as a Lewis acid catalyst for organic transformation is now much more extensive. Diarylborinic acids and arylboronic acids have shown themselves to be powerful tools in the design of chiral boron catalysts. This article provides a comprehensive summary of the organic transformations catalyzed by arylboron compounds as acids.