A DFT Study of the Mechanism of the Spontaneous Activation of H2 by Ni, Pd, Pt, and Pd2

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 107; no. 27; pp. 5352 - 5355
• Main Authors: Alikhani, M. E, Minot, C
• Format: Journal Article
• Language: English
• Published: American Chemical Society 10-07-2003
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp027519x

The bending energy profiles of 1 A 1 and 3 B 2 electronic states have been calculated for the M:H2 (M = Ni, Pd, and Pt) compounds using three parameters functional (B3LYP). It has been shown that the σH - H-bond activation leading to the dihydride species in a singlet state is possible for the nickel and platinum atoms, while for Pd, the complex Pd−H2, weakly bound with respect to Pd(1 S 0) + H2, is formed spontaneously. In the first case, Ni and Pt, the interaction beginning from the triplet state of the metal center correlates with the hydride species (3 B 2 state) after passing a high barrier height (46.5 and 11.5 kcal/mol, for Ni and Pt, respectively). An inter-system crossing favors the activation of the σH - H-bond in the singlet state (1 A 1). For Pd, another mechanism occurs. The dihydride species may be formed starting from the molecular complex (1 A 1) by a slightly endothermic process through low activation energy (6 kcal/mol). For the Pd2 dimer, whose ground state is a triplet state, the dissociation of H2 is similar to that of the Ni and Pt atoms. The mechanism implies an inter-system crossing between the singlet and triplet states. After the crossing point, a nonplanar mechanism implying a folding of the Pd−Pd−H2 planes is proposed.