Synthesis, Characterization, and Reactivity of Ruthenium Diene/Diamine Complexes Including Catalytic Hydrogenation of Ketones

Thermal reactions between [RuCl2(diene)]n (diene = 2,5-norbornadiene, nbd; 1,5-cyclooctadiene, cod) with an
excess of N,N,N‘,N‘-tetramethylethylene diamine (tmeda) afforded derivatives [RuCl2(diene)(tmeda)] (diene = nbd,
1; cod, 2) as a mixture of cis and trans isomers. When thermolysis was performed under H2 mixtures of hydride
species [RuCl(H)(diene)(tmeda)] (diene = nbd, 3; cod, 4) and the bis-tmeda adduct trans-[RuCl2(tmeda)2] (5) were
obtained in different ratios depending upon the reaction conditions and reaction times. Heating polymeric Ru(II)
precursors in toluene in the presence of a 5-fold excess of the bulkier N,N,N‘,N‘-tetraethylethylene diamine (teeda)
resulted in a rare diamine dealkylation process with formation of trans-[RuCl2(nbd)(Et2NCH2CH2NHEt)] (6) and
trans-[RuCl2(cod)(EtHNCH2CH2NHEt)] (7) in high yields. The presence of N−H functionalities in the coordinated
diamine ligands of 6 and 7 was unambiguously established by single-crystal X-ray diffraction studies. The dealkylation
process of the teeda ligand seems to proceed intramolecularly as shown by solution NMR studies performed with
the soluble Ru(II) precursors trans-[RuCl2(amine)2(diene)] (diene = nbd, amine = morpholine, 9; diene = cod,
amine = Et2NH, 10). The above complexes [RuCl2(diene)(diamine)] have been tested as precatalysts in the
hydrogenation of ketones both for transfer as well as direct hydrogenation, the latter route being the most effective.