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) of type Al(ORF)(4)(-) (ORF: OC(H)(CF3)(2); OC(CF3)(3)) or lithium bridged {(RFO)(2)Al(mu -ORF)(2)(mu -Li)(mu -ORF)(2)Al(ORF)(2)}(-) (Ph3C+ salt, ORF: OC(H)(CF3)(2)) is presented. All of the species were characterized spectroscopically, three of the species {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 determination. 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 insoluble in SO2, CH2O2, etc.). The anions of 1-2 have thermochemical volumes of 599 Angstrom (3) (1) and 758 Angstrom (3) (2) with estimated 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)] (R-F: OC(H)(CF3)(2) (3); OC(CF3)(3) (5)) and [Ph3C] {Li[Al(OC(H)(CF3)(2))(4)](2) (4)} are extremely robust and scaled NMR samples of 3-5 show no sign of decomposition even after storage at +70 degreesC for 3 months. 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)(-) (C) 2001 Elsevier Science B.V. All rights reserved.