Bis(amido)ruthenium(IV) complexes with 2,3-diamino-2,3-dimethylbutane. Crystal structure and reversible Ru(IV)-amide/Ru(III)-amine and Ru(IV)-amide/Ru(II) amine redox couples in aqueous solution

Two bis(amido)ruthenium(IV) complexes, [Ru-IV(bpy)(L-H)(2)](2+) and [Ru-IV(L)(L-H)(2)](2+) (bpy=2,2'-bipyridine, L=2,3-diamino-2,3-dimethyl butane, L-H=(H(2)NCMe(2)CMe(2)NH)(-)), were prepared by chemical oxidation of [Ru-II(bpy)(L)(2)](2+) and the reaction of [(n-Bu)(4)N][(RuNCl4)-N-VI] with L, respectively. The structures of [Ru(bpy)(L-H)(2)][ZnBr4] center dot CH3CN and [Ru(L)(L-H)(2)]Cl-2 center dot 2H(2)O were determined by X-ray crystal analysis. [Ru(bpy)(L-H)(2)][ZnBr4] center dot CH3CN crystallizes in the monoclinic space group P2(1)/n with a=12.597(2) Angstrom, b=15.909(2) Angstrom, c=16.785(2) Angstrom, Beta=91.74(1) degrees, and Z=4. [Ru(L)(L-H)(2)]Cl-2 center dot 2H(2)O crystallizes in the tetragonal space group I4(1)/a with a=31.892(6) Angstrom, c=10.819(3) Angstrom, and Z=16. In both complexes the two Ru-N(amide) bonds are cis to each other with bond distances ranging from 1.835(7) to 1.856(7) Angstrom. The N(amide)-Ru-N(amide) angles are about 110 degrees. The two Ru(IV) complexes are diamagnetic, and the chemical shifts of the amide protons occur at around 13 ppm. Both complexes display reversible metal-amide/metal-amine redox couples in aqueous solution with a pyrolytic graphite electrode. Depending on the pH of the media, reversible/quasireversible 1e(-)-2H(+) Ru(IV)-amide/Ru(III)-amine and 2e(-)-2H(+) Ru(IV)-amide/Ru(II)-amine redox couples have been observed. At pH-1.0, the E degrees is 0.46V for [Ru-IV(bpy)(L-H)(2)](2+)/[Ru-III(bpy)(L)(2)](3+) and 0.29 V vs SCE for [Ru-IV(L)(L-H)(2)](2+)/[Ru-III(L)(3)](3+). The difference in the E degrees values for the two Ru(IV)-amide complexes has been attributed to the fact that the chelating saturated diamine ligand is a better sigma-donor than 2,2'-bipyridine.