Bimetallic complexes based on carboxylate and xanthate ligands: Synthesis and electrochemical investigations

The homobimetallic ruthenium(II) and osmium(II) complexes [{RuR(CO)(PPh₃)₂}₂(S₂COCH₂C₆H₄CH₂OCS₂)] (R = CHCHBu^t, CHCHC₆H₄Me-4, C(CCPh)CHPh, CHCHCPh₂OH) and [{Os(CHCHC₆H₄Me-4)(CO)(PPh₃)₂}₂(S₂COCH₂C₆H₄CH₂OCS₂)] form readily from the reactions of [MRCl(CO)(BTD)(PPh₃)₂] (M = Ru or Os; BTD = 2,1,3-benzothiadiazole) with the dixanthate KS₂COCH₂C₆H₄CH₂OCS₂K. Addition of KS₂COCH₂C₆H₄CH₂OCS₂K to two equivalents of cis-[RuCl₂(dppm)₂] leads to the formation of [{(dppm)₂Ru}₂(S₂COCH₂C₆H₄CH₂OCS₂)]²⁺. The benzoate complexes [RuR{O₂CC₆H₄(CH₂OH)-4}(CO)(PPh₃)₂] (R = CHCHBu^t, CHCHC₆H₄Me-4, C(CCPh)CHPh) are obtained by treatment of [RuRCl(CO)(BTD)(PPh₃)₂] with 4-(hydroxymethyl)benzoic acid in the presence of base. Reaction of [RuHCl(CO)(PPh₃)₃] or [RuRCl(CO)(BTD)(PPh₃)₂] with 4-(hydroxymethyl)benzoic acid in the absence of base leads to formation of the chloride analogue [RuCl{O₂CC₆H₄(CH₂OH)-4}(CO)(PPh₃)₂]. The unsymmetrical complex [{Ru(CHCHC₆H₄Me-4)(CO)(PPh₃)₂}₂(O₂CC₆H₄CH₂OCS₂)] forms from the sequential treatment of [Ru(CHCHC₆H₄Me-4){O₂CC₆H₄(CH₂OH)-4}(CO)(PPh₃)₂] with base, CS₂ and [Ru(CHCHC₆H₄Me-4)Cl(CO)(BTD)(PPh₃)₂]. The new mixed-donor xanthate-carboxylate ligand, KO₂CC₆H₄CH₂OCS₂K is formed by treatment of 4-(hydroxymethyl)benzoic acid with excess KOH and two equivalents of carbon disulfide. This ligand reacts with two equivalents of [Ru(CHCHC₆H₄Me-4)Cl(BTD)(CO)(PPh₃)₂] or cis-[RuCl₂(dppm)₂] to yield [{(dppm)₂Ru}₂(O₂CC₆H₄CH₂OCS₂)]²⁺ or [{Ru(CHCHC₆H₄Me-4)(CO)(PPh₃)₂}₂(O₂CC₆H₄CH₂OCS₂)], respectively. Electrochemical experiments are also reported in which communication between the metal centres is investigated.