The metal–metal bond in the dibenzotetramethyltetraaza[14]annulene–ruthenium dinuclear complex: a structural, magnetic, and theoretical analysis

The thermal decomposition of [{Ru(tmtaa)}2(1,5-cyclooctadiene)] (1) in boiling toluene has led to the formation of the metal–metal bonded dinuclear complex [{Ru(tmtaa)}2] (2), (RuRu, 2.3829(4) Å). Upon oxidation using Cp2FeBPh4, the corresponding monocation [{Ru(tmtaa)}2]BPh4 (3) is synthesized with an RuRu bond distance of 2.2782(4) Å. The magnetic measurements of 2 and 3 are in agreement with a ground state s=1 and s=, respectively. Calculations indicate an RuRu σ2π4δ2δ*2π*2 electron configuration and suggest an RuRu double bond character for 2, while the significant shortening by 0.105 Å of the RuRu distance in 3 is in agreement with a σ2π4δ2δ*2π*1 electron configuration and an RuRu bond order of 2.5. Complex 2 serves as a source of the [Ru(tmtaa)] fragment in a variety of reactions, one of which is the reaction with ethylene in THF leading to the quite rare ethylene diamagnetic complex [Ru(tmtaa)(THF)(η2-C2H4)] (4), (Ru⋯(η2-C2H4), 2.009(2); CC, 1.384(5) Å).