Heterolytic activation of H−X (X = H, Si, B, and C) bonds: an experimental and theoretical investigation

Nagaraja, C. M. ; Parameswaran, Pattiyil ; Jemmis, Eluvathingal D. ; Jagirdar, Balaji R. (2007) Heterolytic activation of H−X (X = H, Si, B, and C) bonds: an experimental and theoretical investigation Journal of the American Chemical Society, 129 (17). pp. 5587-5596. ISSN 0002-7863

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Official URL: http://pubs.acs.org/doi/abs/10.1021/ja069044j

Related URL: http://dx.doi.org/10.1021/ja069044j

Abstract

The highly electrophilic, coordinatively unsaturated, 16-electron [Ru(P(OH)3)(dppe)2][OTf]2 (dppe = Ph2PCH2CH2PPh2) complex 1 activates the H−H, the Si−H, and the B−H bonds, in H2(g), EtMe2SiH and Et3SiH, and H3B·L (L = PMe3, PPh3), respectively, in a heterolytic fashion. The heterolysis of H2 involves an η2-H2 complex (observable at low temperatures), whereas the computations indicate that those of the Si−H and the B−H bonds proceed through unobserved η1-species. The common ruthenium-containing product in these reactions is trans-[Ru(H)(P(OH)3)(dppe)2][OTf], 2. The [Ru(P(OH)3)(dppe) 2][OTf]2 complex is unique with regard to activating the H−H, the Si−H, and the B−H bonds in a heterolytic manner. These reactions and the heterolytic activation of the C−H bond in methane by the model complex [Ru(POH)3)(H2PCH2CH2PH2)2][Cl][OTf], 4, have been investigated using computational methods as well, at the B3LYP/LANL2DZ level. While the model complex activates the H−H, the Si−H, and the B−H bonds in H2, SiH4, and H3B·L (L = PMe3, PPh3), respectively, with a low barrier, activation of the C−H bond in CH4 involves a transition state of 57.5 kcal/mol high in energy. The inability of the ruthenium complex to activate CH4 is due to the undue stretching of the C−H bond needed at the transition state, in comparison to the other substrates.

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