Novel ruthenium-oxo complexes of saturated macrocycles with nitrogen and oxygen donors and X-ray crystal structure of trans-[RuIV(L)O(H2O)][ClO4]2

Abstract

Reaction of K2[RuCl5(H2O)] with L (1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane) in refluxing ethanol yielded trans-[RuIII(L)Cl2]2+, isolated as chloride salt. Treatment of trans-[RuIII(L)Cl2]+ with Ag+ in water led to the formation of trans-[RuIII(L)(OH)(H2O)]2+, which could be oxidized to trans-[RuIV(L)O(H2O)]2+ and trans-[RuVI(L)(O)2]2+ by electrochemical and Ce(IV) oxidation, respectively. Magnetic susceptibility measurements on the perchlorate salts of trans-[RuIII(L)(OH)(H2O)]2+, trans-[RuIV(L)(O)(H2O)]2+, and trans-[RuVI(L)(O)2]2+ showed that their μeff values are 1.86, 2.87, and 0 μB, respectively, in accordance to their electronic formulation [Ru(III), (dxy)2(dxz + dyz)2(dxz - dyz)1; Ru(IV), (dxy)2(dxz)1(dyz) 1; Ru(VI), (dxy)2]. The Ru=O stretching frequencies for the Ru(IV) and Ru(VI) complexes are 845 and 865 cm-1. The X-ray crystal structure of trans-[RuIV(L)(O)(H2O)][ClO4] 2·2H2O has been determined: C21H34N2Cl2O14Ru; Mr 710.47; triclinic, space group P1; a = 11.157 (5), b = 11.697 (3), c = 12.598 (2) Å; α = 74.05 (1), β = 61.55 (2), γ = 71.33 (2)°; V 1354.7 Å3; Z = 2; 4calcd = 1.742, dmeasd = 1.72 g cm-3; μ(MO Kα) = 8.4 cm-1. The coordinated oxo and aquo groups are trans to each other. The measured Ru=O distance of 1.739 (2) Å is the shortest one ever reported for oxoruthenium(IV) complexes. The intermolecular separation of two Ru=O moieties is 2.8 Å, which features significant nonbonded [Ru=O⋯O=Ru] interaction. At pH = 1.1, the E1/2 values for the trans-[RuVI(L)(O)2]2+/trans-[Ru IV(L)(O)(H2O)]2+ and trans-[RuIV(L)O(H2O)]2+/trans-[Ru III(L)(OH)(H2O)]2+ couples are, respectively, 0.92 and 0.58 V vs SCE. Thus, trans-[RuVI(L)(O)2]2+ is a powerful oxidant and is 0.26 V more oxidizing than trans-[RuVI(TMC)(O)2]2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane). trans-[RuVI(L)(O)2]2+ is capable of oxidizing a wide variety of organic substrates, including alcohols, olefins, aromatic hydrocarbons, and adamantane under mild conditions. Electrocatalytic oxidation of benzyl alcohol and oxidation of organic substrates with PhIO are achieved with the [RuIII(L)(OH)(H2O)]2+ or [RuIV(L)(O)(H2O)]2+ complex as catalyst. © 1989 American Chemical Society.