Synthesis of Carbonato- and Doubly Oxido-Bridged Diruthenium(III,IV) Complex and Reactions with Cations.

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Doubly oxido-bridged transition metal moieties, {M2(μ-O)2}, play important roles as oxidation reaction centers in nature. This work features a diruthenium(III,IV) complex with a doubly oxido-bridged core {Ru2III,IV(μ-O)2}3+ with a carbonato bridged between the two ruthenium centers, M[{RuIII,IV(ebpma)}2(μ-O)2(μ-O2CO)]2(PF6)3 (M[1CO3]2(PF6)3; Carbonato complex, ebpma; ethylbis(2-pyridymethyl)amine), and explores the interactions of this complex with cations (H+ and M+). M[1CO3]2(PF6)3 was formed via reactions of a singly oxido-bridged complex, [{RuIII,IVCl2(ebpma)}2(μ-O)]PF6·(CH3)2CO, with M2CO3 (M = K, Na) or with CO2(g), adjusted to around pH 12 with NaOH(aq.), in a water-acetone mixed solvent. The Carbonato complex was isolated as a powder in the form of M[1CO3]2(PF6)3 (M = K, Na), because of the interactions between the carbonato moiety and K+ or Na+ in the solid structure. In acidic aqueous solutions, unexpectedly, the carbonato ligand remained bound to the doubly bridged core, {Ru2III,IV(μ-O)2}3+ or {Ru2III,IV(μ-O)(μ-OH)}4+, without decarboxylation even under pH 1.0. Two-step one-protonation/deprotonation occurred reversibly between pH 1.0 and 13.2 to the bridging oxido and carbonato ligands. The structures of the corresponding one- and two-protonated complexes ([1CO3H]2+ and [1CO32H]3+) were successfully characterized.