Van Seggen, DM; Hurlburt, PK; Noirot, MD; Anderson, OP; Strauss, SH
The suitability of B(OTeF5)4- as a counterion for the generation of "coordinatively unsaturated" or weakly solvated metal and metalloid cations has been studied by IR and NMR spectroscopy and by single-crystal X-ray diffraction. Addition of B(OTeF5)3 to MOTeF5 (M = Ag, Tl) in the weakly coordinating solvents mesitylene, dichloromethane, 1,2-dichloroethane, and 1,1,2-trichlorotrifluoroethane produces solutions of [M(solv)x]+[B(OTeF5)4]-. In the case of Ag+ and 1,1,2-trichlorotrifluoroethane, the unsolvated compound AgB(OTeF5)4 was isolated as crystals belonging to the monoclinic system (P2(1)/n, a = 11.419 (7) angstrom, b = 10.329 (4) angstrom, c = 15.31 (1) angstrom, beta = 91.53 (5)-degrees, Z = 4, T = -127-degrees-C). The Ag+ ion is bonded weakly to three B(OTeF5)4-ions, with three Ag-O contacts (2.500 (5)-2.756 (5) angstrom) and six Ag-F interactions (2.644 (5)-3.017 (5) angstrom. In the case of Ti1 and either dichloromethane or 1,1,2-trichlorotrifluoroethane, the unsolvated salt TlB(OTeF5)4 is formed. Both AgB(OTeF5)4 and TlB(OTeF5)4 are thermally unstable, slowly forming MOTeF5 and volatile B(OTeF5)3. This decomposition is slower for Tl+ (days) than for Ag+ (hours). Oxygen-17 NMR experiments demonstrate that the OTeF5-sunstituents in B(OTeF5)4- do not exchange rapidly with free OTeF5- but are rapidly exchanged in the presence of Lewis acids such as H+, Ag+, and B(OTeF5)3. Reactions of AgB(OTeF5)4 or TlB(OTeF5)4 with Fe(Por)Cl (Por = tetraphenylporphyrinate dianion or octaethylporphyrinate dianion) or Ph3SiCl in dichloromethane or mesitylene produce B(OTeF5)3 and Fe(Por)OTeF5 or Ph3SiOTeF5, respectively-the putative unsaturated cations Fe(Por)+ or Ph3Si+ were not observed. In the case of Ph3SiCl, the unsaturated cation Ph3Si+ or some similar species may be an intermediate, since Ph3SiCl does not react directly with N(n-Bu)4B(OTeF5)4. The reaction of Ph3CB(OTeF5)4 with Ph3SiH in dichloromethane also produces Ph3SiOTeF5.