Structural Characterization of Bismuth(III) and Antimony(III) Chlorotriflates: Key Intermediates in Catalytic Friedel−Crafts Transformations

Abstract

Chlorotriflates of antimony and bismuth ClnM(OSO2CF3)3−n (n = 1 or 2) are believed to be metallic intermediates of major importance in Friedel−Crafts reactions that use Bi(OSO2CF3)3, Sb(OSO2CF3)3, the systems BiCl3/CF3SO2OH or SbCl3/CF3SO2OH as catalysts. Unknown until now, the compounds ClBi(OSO2CF3)2 (1) and Cl2Sb(OSO2CF3) (2) have been synthesized by reaction of MCl3 (M = Bi, Sb) with triflic acid. After crystallization from THF, 1 and 2 were investigated in the solid state by X‐ray crystallography. Their use as catalysts in benzoylation of toluene, acylation of m‐xylene, and sulfonylation of toluene led to conclusive results, thus giving weight to their key role as intermediates in Friedel−Crafts reactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Total Synergistic Effect between Triflic Acid and Bismuth(III) or Antimony(III) Chlorides in Catalysis of the Methanesulfonylation of Arenes

“…Bismuth() chloride (2) [5f] is not an efficient catalyst for the arylsulfonylation of arenes and, just as 1 [3] and 3, proved to be inactive for the methanesulfonylation of toluene (4) (Table 1, Entry 1) and a variety of other arenes such as mesitylene (5), o-xylene (6), m-xylene (7), p-xylene (8), fluorobenzene (9), benzene (10), chlorobenzene (11), o-dichlorobenzene (12), 1,3-difluorobenzene (13), o-fluorotoluene (14), m-fluorotoluene (15) and p-fluorotoluene (16) (for purposes of clarity these results are not shown in the table). When system A or system B was used, however, an exothermic reaction occurred and a mixture of methyltolylsulfones (17) was obtained in almost quantitative yields, accompanied by the release of hydrogen chloride (Table 1, Entries 2, 3).…”

“…[ [12] Interestingly, with system B almost no reaction takes place in the case of 5 (Entry 5), while this system proved to be efficient with fluorobenzene (9) (Entry 13). Mesitylene (5) is a strong π donor arene capable of generating Menschutkin complexes, which are most probably involved in deactivation of the catalyst.…”

“…A similar mechanism is involved in the case of system Cat. Temp.°C, [b] Product [c] (time, days) (yield, %) (10), chlorobenzene (11), o-dichlorobenzene (12), m-difluorobenzene (13), o-fluorotoluene (14), m-fluorotoluene (15), and p-fluorotoluene (16). [b] Temperature of the oil bath.…”

“…Mesitylene (5) is a strong π donor arene capable of generating Menschutkin complexes, which are most probably involved in deactivation of the catalyst. [15] When 10% mol of pure SbCl 2 OTf [12] was used in the methanesulfonylation of 5, a 9% yield of methyl 2Ј,4Ј,6Ј-trimethylphenyl sulfone (18) was isolated (same conditions than for Entry 5), indicating that the deactivation of the system B arises from the inhibition of the reaction between 1 and 3 through its complexation with 5 (step a). In the case of 9, the difference between the two systems stems from the solubility of 3 in aromatics (a consequence of the respective ionic and covalent natures of 2 and 3).…”

Greener Friedel‐Crafts Acylation Using Microwave‐Enhanced Reactivity of Bismuth Triflate in the Friedel‐Crafts Benzoylation of Aromatic Compounds with Benzoic Anhydride

“…Under conventional heating, bismuth triflate catalyzes Friedel‐Crafts acylation of aromatic compounds. However, many of these methods involve acid chlorides, additive reagents, volatile organic solvents, low yields and long reaction times …”