I. Krossing et al., New reagents to introduce weakly coordinating anions of type Al(ORF)(4)(-): synthesis, structure and characterization of Cs and trityl salts, J FLUORINE, 112(1), 2001, pp. 83-90
The facile synthesis of five reagents (Cs+ and Ph3C+ salts) to introduce we
akly 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)A
l(ORF)(2)}(-) (Ph3C+ salt, ORF: OC(H)(CF3)(2)) is presented. All of the spe
cies 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 con
trast to the known Ag+ salts, the solid Cs+ salts 1-2 crystallize unsolvate
d which makes them suitable starting materials to introduce them as counter
ions for highly electrophilic and oxidizing cations (i.e, by metathesis wit
h MF6- salts (M: As, Sb); CsMF6 is insoluble in SO2, CH2O2, etc.). The anio
ns of 1-2 have thermochemical volumes of 599 Angstrom (3) (1) and 758 Angst
rom (3) (2) with estimated low lattice potential energies of only 379 (1) a
nd 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 Scienc
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