Trifluoromethylboranes and ‐Borates: New Synthetic Strategies and Applications

Abstract

The synthesis of salts with the [B(CF(3))(4)](-) anion has been the starting point for new developments in the field of trifluoromethylboron chemistry. In contrast to the previous syntheses of (CF(3))(n)B derivatives (n=1-3), achieved exclusively by CF(3) transfer, the synthesis of the [B(CF(3))(4)](-) anion was accomplished by fluorination of the [B(CN)(4)](-) anion with ClF or ClF(3) in anhydrous HF. Owing to its thermal and chemical stability, [B(CF(3))(4)](-) is an attractive weakly coordinating anion. However, in concentrated sulfuric acid one of the four CF(3) groups is solvolyzed to a CO ligand to yield the neutral borane carbonyl (CF(3))(3)BC[triple bond]O. It has been shown that the borane carbonyl compound is a versatile synthetic building block, and numerous reactions have been investigated. The addition of nucleophiles to the C atom of the CO ligand is favored, and examples for new derivatives are the anions [(CF(3))(3)BC[triple bond]Pnic](-) (Pnic=N, P, As). Under certain conditions, ligand-exchange reactions are also observed, for example, the formation of (CF(3))(3)BN[triple bond]CH. Finally, the borane carbonyl compound is a component of the conjugated Brønsted-Lewis superacid HF/(CF(3))(3)BCO.

Bis(perchlorocatecholato)silane—A Neutral Silicon Lewis Super Acid

“…Pentacoordination at silicon was supported by ad oublet ( 1 J SiF = 196 Hz) at À105 ppm in the 29 Si-NMR spectrum and by X-ray diffraction. 1 Ha nd 13 CNMR spectra unequivocally showed the partial (23 %) formation of atrityl carbenium ion and at the same time, 29 Si and 13 3 ]a nd as trong signal of [1-F À ]i nE SI-MS(À)). [8] Addition of 2equivalents of tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF) led to the immediate formation of the bisfluorido(biscatecholato)silicate dianion [1-F 2 ][S(NMe 2 ) 3 ] 2 (see Figure 3b), showing at riplet ( 1 J SiF = 152 Hz) at À155 ppm in the 29 Si-NMR spectrum.…”

“…[1] Especially the search for ever more powerful, yet bottleable and easy-to-handle,s ocalled Lewis super acids is an active field. [2] Unfortunately,most known Lewis super acids are not accessible in bulk quantities,h ydrolyze under liberation of HF or are highly oxidizing.S everal of these drawbacks have been overcome by the installation of fluorinated aryl, alkyl, or pentafluoroorthotellurate substituents on boron, [3] aluminum, [2a,4] arsenic [5] or phosphonium [6] species.A lso for silicon(IV) as the central atom, strong neutral Lewis acids have been described (Figure 1). [2] Unfortunately,most known Lewis super acids are not accessible in bulk quantities,h ydrolyze under liberation of HF or are highly oxidizing.S everal of these drawbacks have been overcome by the installation of fluorinated aryl, alkyl, or pentafluoroorthotellurate substituents on boron, [3] aluminum, [2a,4] arsenic [5] or phosphonium [6] species.A lso for silicon(IV) as the central atom, strong neutral Lewis acids have been described (Figure 1).…”

Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions

“…[2,40] Thec losely related [BF(CF 3 ) 3 ] À anion is also accessible,f ormed by the reaction of (OC)B(CF 3 ) 3 with KF in anhydrous HF,and has also been applied as aWCA. [37,41,42] Interestingly,W CAso ft he type [B(F) n (CN) 4Àn ] À (where n = 0, 1, 2, or 3) have also found application in ionic liquids and show varying, but rather low,v iscosities depending on the number of fluoride ligands included. [43,44] Partially/perhalogenated tetraaryl borates are prevalent in the literature,a st he halogenation of the aryl residues attenuates the underlying coordinative strength of the aryl ring, thereby reducing the formation of undesirable arene complexes:A lthough an umber of h 6 -arene-coordinated [B(Ph) 4 ] À complexes are present in the literature, [33] the partially halogenated anions of [B(Ar CF3 ) 4 ] À and [B(Ar Cl ) 4 ] À both show reduced coordinative strengths.…”

“…[37,207,208] It has been employed for the formation of [Co(CO) 5 ] + [Eq. Theboron-based Lewis acid (CF 3 ) 3 Bstabilized as its CO adduct (CF 3 ) 3 B !…”

Bis(perchlorocatecholato)silan – eine neutrale Silicium‐Lewis‐Supersäure

“…[11] Verglichen mit SiF 4 (310 kJ mol À1 )e rhçht sich die FIA erheblich mit der Anwesenheit von Perfluoraryl-(SiF(C 6 F 5 ) 3 ,3 61 kJ mol À1 )o der Perfluoralkylgruppen (SiF(C 2 F 5 ) 3 ,4 43 kJ mol À1 ). [8,16] Reaktionen von HSiCl 3 mit Perchlorcatechol in Anwesenheit von Et 2 Oo der die Verdrängung von Acetonitril aus 1-(CH 3 [17] und zeigen eher ¾hnlichkeit zu Ether-Addukten von Silyliumkationen. Bisher untersuchtes tarke, neutrale Silicium-Lewis-Säuren und die in dieser Arbeit präsentierte Lewis-Supersäure 1.…”