Cyanide-bridged linkage isomers with catecholateruthenium(ii) centres bound to Mn(i) or M(alkyne) units

Abstract

Two series of stable cyanide-bridged linkage isomers, namely [(o-O₂C₆Cl₄)(Ph₃P)(OC)₂Ru(µ-XY)MnL(NO)(η-C₅Me₅)] (XY = CN or NC, L = CNBu^t or CNXyl) and [(o-O₂C₆Cl₄)L(OC)₂Ru(µ-XY)M(CO)(PhCCPh)Tp′] {M = Mo or W, L = PPh₃ or P(OPh)₃, Tp′ = hydrotris(3,5-dimethylpyrazolyl)borate} have been synthesised; pairs of isomers are distinguishable by IR spectroscopy and cyclic voltammetry. The molecular structure of [(o-O₂C₆Cl₄)(Ph₃P)(OC)₂Ru(µ-NC)Mo(CO)(PhCCPh)Tp′] has the catecholate-bound ruthenium atom cyanide-bridged to a Mo(CO)(PhCCPh)Tp′ unit in which the alkyne acts as a four-electron donor; the alignment of the alkyne relative to the Mo–CO vector suggests the fragment (CN)Ru(CO)₂(PPh₃)(o-O₂C₆Cl₄) acts as a π-acceptor ligand. The complexes [(o-O₂C₆Cl₄)(Ph₃P)(OC)₂Ru(µ-XY)Mn(NO)L(η-C₅Me₅)] undergo three sequential one-electron oxidation processes with the first and third assigned to oxidation of the ruthenium-bound o-O₂C₆Cl₄ ligand; the second corresponds to oxidation of Mn(I) to Mn(II). The complexes [(o-O₂C₆Cl₄)L(OC)₂Ru(µ-XY)M(CO)(PhCCPh)Tp′] are also first oxidised at the catecholate ligand; the second oxidation, and one-electron reduction, are based on the M(CO)(PhCCPh)Tp′ fragment. Chemical oxidation of [(o-O₂C₆Cl₄)(Ph₃P)(OC)₂Ru(µ-XY)MnL(NO)(η-C₅Me₅)] with [Fe(η-C₅H₄COMe)(η-C₅H₅)][BF₄], or of [(o-O₂C₆Cl₄)L(OC)₂Ru(µ-XY)M(CO)(PhCCPh)Tp′] with AgBF₄, gave the paramagnetic monocations [(o-O₂C₆Cl₄)(Ph₃P)(OC)₂Ru(µ-XY)MnL(NO)(η-C₅Me₅)]⁺ and [(o-O₂C₆Cl₄)L(OC)₂Ru(µ-XY)M(CO)(PhCCPh)Tp′]⁺, the ESR spectra of which are consistent with ruthenium-bound semiquinone ligands. Linkage isomers are distinguishable by the magnitude of the ³¹P hyperfine coupling constant; complexes with N-bound Ru(o-O₂C₆Cl₄) units also show small hyperfine coupling to the nitrogen atom of the cyanide bridge.