Ethene)bis(acetylacetonato) Complexes of Divalent and Trivalent Ruthenium

Zinc dust reduction of tris(acetylacetonato)ruthenium(III), [Ru(acac)3], in hot aqueous THF in the presence of ethene gives cis-[Ru(acac)2(η2-C2H4)2] (5), isolated as an orange solid in ca. 60% yield. A single-crystal X-ray crystallographic study shows the metal atom to be coordinated octahedrally by a pair of bidentate O-bonded acac groups and two mutually cis orthogonal ethene ligands. In the NMR spectra of 5, the ethene carbon atoms remain equivalent, while the protons are inequivalent in pairs, down to −95 °C; intermolecular exchange with ethene is slow on the NMR time scale at room temperature but becomes fast above ca. 80 °C. One of the ethene molecules of 5 is replaced by ligands at room temperature to give [Ru(acac)2(η2-C2H4)(L)] [L = SbPh3 (6), MeCN (7), NH3 (8), and C5H5N (9)]. Complexes 6 and 7 are isolated as cis-isomers, 9 as a cis−trans mixture, and 8 in the form of the trans-isomer which transforms into the cis-isomer when heated or chromatographed on alumina. The structures of cis-8 and tr...