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) Angstrom). Upon oxidation using Cp2FeBPh4, the corresponding monocation [{Ru(tmtaa)}(2)]BPh4 (3) is synthesized with an Ru-Ru bond distance of 2.2782(4) Angstrom. The magnetic measurements of 2 and 3 are in agreement with a ground state s=1 and s=1/2, respectively. Calculations indicate an Ru-Ru sigma(2)pi(4)delta(2)delta(*2)pi(*2) electron configuration and suggest an Ru-Ru double bond character for 2, while the significant shortening by 0.105 Angstrom of the Ru-Ru distance in 3 is in agreement with a sigma(2)pi(4)delta(2)delta(*2)pi(*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)(eta(2)-C2H4)] (4), (Ru ...(eta(2)-C2H4), 2.009(2); C-C, 1.384(5) Angstrom). (C) 2000 Elsevier Science S.A. All rights reserved.
