Highly stereoselective proton/hydride exchange: assistance of hydrogen bonding for the heterolytic splitting of H2.

The dihydrido amine complex [Ru(H)(2)PMe(3){HN(CH(2)CH(2)P(i)Pr(2))(2)}] and H(2)O exhibit highly unusual, stereoselective H(+)/H(-) exchange, as derived using (1)H 2D EXSY NMR spectroscopy. While H(RuA) rapidly exchanges with H(2)O [k = 337(20) L mol(-1) s(-1)], no direct H(RuB)/H(2)O proton exchange was detected. Methylation of the pincer amine nitrogen results in unselective slow exchange of both hydrides with H(2)O. These results emphasize the important role of hydrogen bonding of N with Brønsted acids (e.g., water) for heteroloytic H(2) activation with Ru-amide hydrogenation catalysts, which was confirmed computationally.