Reactivity of the bis(dihydrogen) complex [RuH2(η2-H2)2(PCy3)2] toward N-heteroaromatic compounds. Regioselective hydrogenation of acridine to 1,2,3,4,5,6,7,8-octahydroacridine

The reaction of pyridine (Py), pyrrole (Pyr), or acridine with the bis(dihydrogen) complex [RuH2(η2-H2)2(PCy3)2] (1) produces compounds containing heteroaromatic ([RuH2(η2-H2)(η1(N)-C5H5N)(PCy3)2] (2), [RuH(η5-C4H4N)(PCy3)2]·Pyr (3)) or aromatic rings ([RuH2(η4-C13H9N)(PCy3)2] (5)) coordinated in η1(N) (2), η5(N,C) (3), or η4(C,C) (5) modes for Py, Pyr, and acridine, respectively. Complex 3 has been characterized by X-ray crystallography. Its protonation by HBF4 affords the cationic dihydride complex [RuH2(η5-C4H4N)(PCy3)2][BF4] (4). The coordinated Py ligand in 2 and acridine in 5 can readily be displaced by dihydrogen, with regeneration of 1. Regioselective hydrogenation of representative polynuclear heteroaromatic nitrogen compounds is achieved in the presence of 1 under mild reaction conditions (80 °C, 3 bar of H2). Quinoline (Q) and isoquinoline (iQ) are hydrogenated to 5,6,7,8-tetrahydro derivatives, while acridine is quickly reduced to 1,2,3,4-tetrahydroacridine followed by much slower saturation t...