Substitution and Redox Chemistry of [Bu4N]2[Ta6Cl12(OSO2CF3)6]

Two sequential electrochemical reductions occur for the cluster anion [Ta6Cl12(OSO2CF3)6]2- at 0.89 and 0.29 V vs Ag/AgCl, with the generation [Ta6Cl12(OSO2CF3)6]3- and [Ta6Cl12(OSO2CF3)6]4-. Chemical reduction of [Ta6Cl12(OSO2CF3)6]2- by ferrocene produces [Ta6Cl12(OSO2CF3)6]3- with the concomitant shift of the ν(SO2) stretch from 1002 to 1018 cm-1. Reaction of [Bu4N]2[Ta6Cl12(OSO2CF3)6] (1) with [Bu4N]X (X = Cl, Br, I, NCS) occurs by reduction and substitution, yielding [Bu4N]3[Ta6Cl12X6], where the clusters with X = Br, I, and NCS are new. Spectroscopic (IR and UV−vis) evidence indicates that the reduced cluster core {Ta6Cl12}2+ is produced in reaction mixtures of 1 with the halide and pseudohalide ions. Concomitant substitution of the triflate ligands of 1 by X- occurs and the rates for the overall reduction and substitution increase in the order X- = Cl- < Br- < NCS- < I- < CN-. Reduction of 1 with ferrocene followed by addition of [Bu4N]O2CCH3 produces the new cluster [Ta6Cl12(O2CCH3)6]3- isolated as the tetrabutylammonium salt. Cyclic voltammetry and UV−vis spectroscopy on the new clusters [Bu4N]3[Ta6Cl12X6] (X = Br, I, NCS, and O2CCH3) are reported. Crystal data for [Bu4N]3[Ta6Cl12(NCS)6]·CH2Cl2: monoclinic, space group, P21/c (No. 14); a = 25.855(6) Å, b = 21.843(6) Å, c = 16.423(3) Å; β = 100.03(2)°; V = 9133(3) Å3; Z = 4.