New reagents to introduce weakly coordinating anions of type Al(ORF)4-: synthesis, structure and characterization of Cs and trityl salts

The facile synthesis of five reagents (Cs+ and Ph3C+ salts) to introduce weakly coordinating anions (WCAs) Al(ORF)4- (ORF: OC(H)(CF3)2; OC(CF3)3) or lithium bridged {(RFO)2Al(m-ORF)2(m-Li)(m-ORF)2Al(ORF)2}- (Ph3C+ salt, ORF: OC(H)(CF3)2) is presented. All of the species were characterized spectroscopically; three {Cs[Al(OC(H)(CF3)2)4] (1); Cs[Al(OC(CF3)3)4] (2); [Ph3C]{Li[Al(OC(H)(CF3)2)4]2} (4)} also by a x-ray single crystal structure detn. In contrast to the known Ag+ salts, the solid Cs+ salts 1-2 crystallize unsolvated which makes them suitable starting materials to introduce them as counterions for highly electrophilic and oxidizing cations (i.e. by metathesis with MF6- salts (M: As, Sb); CsMF6 is insol. in SO2, CH2Cl2, etc.). The anions of 1-2 have thermochem. vols. of 599 A3 (1) and 758 A3 (2) with estd. low lattice potential energies of only 379(1) and 358(2) kJ/mol (cf. 759 kJ/mol for CsF). The trityl salts [Ph3C][Al(ORF)4] (RF: OC(H)(CF3)2 (3); OC(CF3)3 (5)) and [Ph3C]{Li[Al(OC(H)(CF3)2)4]2 (4)} are extremely robust and sealed NMR samples of 3-5 show no sign of decompn. even after storage at +70 Deg for 3 mo. The basicity of the anions decreases according to Al(OC(H)(CF3)2)4- > Li[Al(OC(H)(CF3)2)4]2- > Al(OC(CF3)3)4-. [on SciFinder (R)]