Synthesis, Reactivities, and Structural Studies on High-Valent Ruthenium Oxo Complexes. Ruthenium(IV), Ruthenium(V), and Ruthenium(VI) Oxo Complexes of Tertiary Amine Ligands

The synthesis and characterization of trans-[RuVI(L)02]2+, trans-[Ruv(L)02]+, and trans-[RuIV(L)0(X)]'I+complexes are described [L = 14-TMC (1,4,8,1 l-tetramethyl-1,4,8,11-tetraazacyclotetradecane), 15-TMC (l,4,8,12-tetramethyl-l,4,8,12-tet-raazapentadecane), 16-TMC (l,5,9,13-tetramethyl-l,5,9,13-tetraazacyclohexadecane), (TMEA)2(bis (N, N, N′N′-tetramethyl-1,2-diaminoethane)); n - 1, X = Cl, N3, NCO; n ~ 2, X = CH3CN], All trans-Ru(VI)-dioxd complexes are diamagnetic whereas the molar magnetic susceptibilities for trans-[Ruv(L)02]+and trans-[RuIV(L)0(X)]rt+systems are 1.94 and 2.10-2.95 p,B, respectively. In CH3CN, trans-[RuVI(L)02]2+and 7/yws-[ruv(l)02]+exhibit vibronic-structured dxy— dT* (d*.* = dxz, dy2) transition bands centered at — 380 and 430 nm, respectively. The X-ray structure of trans-[Rurv(14-TMC)0(NC0)]C104has been determined: C15H32N502RuC104, MT514.97, orthorhombic, space group Pnma, a = 12.507 (2) υ, b = 10.646 (1) υ, c = 15.681 (2) υ, V — 2088.1 υ34 5 6 7 8 910, Z = 4, dCiicd= 1.638 g cm-3, p(Mo2Ka) = 9.14 cm”1, m = 1943. The Ru=0 bond distances of trans-[RuIV(14-TMC)0(X)]B+are all 1.765 A, which are longer than those for rr-[RuVI(L)02]2+(1.70-1.71 A). The El/2value for the trows-[Ruv(L)0(X)]2+/?/,an5-[RuIV(L)0(X)]+couple lies between 0.70 and 1.10 V vs. the Cp2Fe+/f° couple and decreases in the order X = Cl > NCO > N3. All trans-[RuIV(L)0(X)]n+complexes are active electrocatalysts for the oxidation of benzyl alcohol to benzaldehyde. The £1/2values for the trans-[RuVI(L)02]2+trans-[RuIV(L)0(0H2)]2+and trans-[RuVI-(L)02]2+trans-[Ruv(L)02]+couples are insensitive to the macrocyclic hole size of L. Replacement of the σ-saturated tertiary amine by the π-aromatic pyridine or 2,2'-bipyridine weakens the Ru=0 bond and increases the oxidation potential of the Ru=0 complexes. Studies on the reactions of trans-[RuVI(L)02]2+and trans-[RuVI(TMP)02] (H2TMP = 5,10,15,20-tetramesitylporphyrin) with organic substrates indicated that the former system prefers attack on an activated C-H bond.