Electron transfer. 147. Reductions with gallium(I)

Solutions 0.03-0.05 M in gallium(I) can be generated by treatment of the "m ixed" halide (GaGaCl4)-Ga-I-Cl-III with cold water under argon and then rem oving the precipitated metallic gallium and Ga(OH)(3) by centrifugation. Ga (I) is lost from such preparations with a half-life of about 3 h at 0 degre esC. These solutions, which may be handled by conventional techniques, read ily reduce I-3(-), IrCl62-, Fe(bipy)(3)(3+), Fe(NCS)(2+), aquacob(III)alami n, and a group of ring-substituted derivatives of Ru(NH3)(5)(py)(3+) but ar e inert to (NH3)(5)CoCl2+ and (NH3)(5)CoBr2+. All reactions give Ga(III). R eduction of HCrO4- in 2-ethyl-2-hydroxybutanoate buffers (pH 3.6) yields a Cr(IV) chelate of the buffering anion but forms Cr(III) when carried out in 0.01 M H+. Reactions of le(-) oxidants proceed via successive single chang es with the conversion Ga(II) --> Ga(III) much more rapid than Ga(I) --> Ga (II). Only for the reactions of I-3(-) and Fe(NCS)(2+) is there evidence fo r redox bridging.