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

Doubly oxido-bridged transition metal moieties, {M-2(mu-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 {Ru-2(III,IV)(mu-O)(2)}(3+) with a carbonato bridged between the two ruthenium centers, M[{Ru-III,Ru-IV(ebpma)}(2)(mu-O)(2)(mu-O2CO)](2)(PF6)(3) (M[1(CO3)](2)(PF6)(3); Carbonato complex, ebpma; ethylbis(2-pyridymethyl)amine), and explores the interactions of this complex with cations (H+ and M+). M[1(CO3)](2)(PF6)(3) was formed via reactions of a singly oxido-bridged complex, [{(RuCl2)-Cl-III,IV(ebpma)}(2)(mu-O)]PF6.(CH3)(2)CO, 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[1(CO3)](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, {Ru-2(III,IV)(mu-O)(2)}(3+) or {Ru-2(III,IV)(mu-O)(mu-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 ([1(CO3)H](2+) and [1(CO3)2H](3+)) were successfully characterized.

Automated summary

This study presents a diruthenium(III,IV) complex with a doubly oxido-bridged core and a carbonato bridged between the two ruthenium centers, exploring interactions with cations. In acidic aqueous solutions, the carbonato ligand remained bound to the doubly bridged core, undergoing reversible protonation/deprotonation reactions. The structures of the protonated complexes were successfully characterized.