A Very Strong Methylation Agent: [Me₂Cl][Al(OTeF₅)₄]

Abstract

A new chloronium‐containing salt, [Me2Cl][Al(OTeF5)4], was synthesized on multigram scale by means of a simple one‐pot procedure. The isolated product can be handled at room temperature and used as a strong electrophilic methylation agent. This is demonstrated by the methylation of the very weak bases P(CF3)3, PF3, MeI, and MeBr.

Friedel–Crafts Type Methylation with Dimethylhalonium Salts

“…[16] The salts [ 4 ]w here synthesized as already described. [7] The salt [NEt 4 ][AlCl 4 ]w as synthesized according to the literature with MeCl as as olvent instead of thionyl chloride. [22] IR spectra were recorded on aB ruker ALPHA FTIR spectrometer inside ag lovebox equipped with ad iamond ATRa ttachment (resolution 4cm À1 ).…”

“…Also the dimethylchloronium salt 1 decomposes in SO 2 solution within days at room temperature under formation of MeOTeF 5 . [7] In contrast to this, the addition of dichloromethane at room temperature to solid 1 resultsinanimmediate decom-positiont oad ark brown suspension.A tÀ40 8Ct he [Me 2 Cl] + salt 1 has ap oor solubility in dichloromethanea nd decomposes upon slow warming with aq uantitative consumption of the weaklyc oordinating anion [Al(OTeF 5 ) 4 ] À to ay ellow solution. Using solvents uppression pulse sequences CH 2 Cl(OTeF 5 )a nd CH 2 (OTeF 5 ) 2 (ratio 10:1, 1000-fold excess of CH 2 Cl 2 )can be identified NMR spectroscopically as the only pentafluoro-ortho-tellurate-containings pecies [see Eqs.…”

“…Experimental and calculated proton affinities (PAs) and methyl cation affinities (MCAs). [a] Compound PA [kJ mol À1 ]M CA [b] [kJ mol À1 ] MeCl 647.3 [11] 260, [12] 279.2 [7] MeBr 647.3 [11] 260, [12] 279.2 [7] 1,2,3,4-tetrafluorobenzene7 00.4, [11] 714.9 310.0 MeI 691.7 [11] 323.7 [7] methyl-1,2,3,4-tetrafluorobenzene 746,1 338.3 1,2,3-trifluorobenzene724.3, [11] 738.0 361.4 1,2-difluorobenzene 731.2, [11] 742.9 369.0 4-methyl-1,2, 3 Colorless crystals of 2I were grown by slowly cooling ad ichloromethanes olution to À80 8C. It crystallizes in the triclinic space group P1(see Figure 2).…”

“…4 Table 3. Experimental and calculated PAsa nd MCAs [a] in kJ mol À1 as well as 15 628 AE 8, [18] 643.1 265.4 --CH 2 Cl (OTeF 5 ) 683.0 267.3 --MeCl 647.3 [11] 279.2 [7] --…”

“…[6] We recently synthesized the easilya ccessible and room temperature-stable dimethylchloronium salt [Me 2 Cl][Al(OTeF 5 ) 4 ]( 1,s ee Scheme1 bottom). [7] In this work we report on the role of the dimethylchloronium cation in Friedel-Crafts type methylation reactions, especially in the system MeCl-AlCl 3 ;and the reaction of 1 with electron-deficienta romatic systems.…”