Analysis of the Activation and Heterolytic Dissociation of H2 by Frustrated Lewis Pairs: NH3/BX3 (X = H, F, and Cl)

Journal Article · Thu Jul 05 04:00:00 EDT 2012 · Journal of Physical Chemistry A

DOI:https://doi.org/10.1021/jp3039829· OSTI ID:1047357

Camaioni, Donald M; Ginovska-Pangovska, Bojana; Schenter, Gregory K; Kathmann, Shawn M; Autrey, Thomas

We present results of our computational study aimed at understanding the mechanism of H2 activation and heterolytic dissociation by 'frustrated' Lewis pairs (FLPs). We studied the pairs of ammonia (NH3) with BH3, BF3, and most extensively, BCl3. While these pairs are capable of forming a strong dative bond, electronic structure theories make it possible to explore the potential surface in regions away from the dative complex relevant to H2 activation by frustrated Lewis pairs. We analyzed in great detail the changes that occur along the minimum energy path between the FLP and the product ion pair complex. For X = Cl, the mechanism involves a precursor complex, H3N-H2-BCl3, with a B-H-H angle of {approx}80{sup o} and nearly linear N-H-H angle. At the transition state (TS), the H2 bond is weakened but not broken, and the BCl3 moiety has undergone significant pyramidal distortion. As such, the FLP is prepared to accept the incipient proton and hydride ion on the product-side. The interaction energy of the H2 with the acid/base pair and the different contributions for the precursor and TS complex from an energy decomposition analysis expose the dominant factors affecting the reactivity. We find that structural reorganization of precursor complex plays a significant role in the 'activation' and that charge-transfer interactions are the dominant stabilizing force in the activated complex. The electric field clearly has a role in polarizing H2, but its contribution to the overall interaction energy seems to be smaller. Our detailed study of the nature of the bonding and the different types of interaction between the prototypical Lewis pair and H2 provides insight into the important components that should be taken into account when designing related systems to activate hydrogen.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1047357
• Report Number(s): PNNL-SA-85092; 39979
• Journal Information: Journal of Physical Chemistry A, Journal Name: Journal of Physical Chemistry A Journal Issue: 26 Vol. 116
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
AMMONIA
BONDING
DECOMPOSITION
DISSOCIATION
ELECTRIC FIELDS
ELECTRONIC STRUCTURE
ENERGY
Environmental Molecular Sciences Laboratory
Frustrated Lewis pairs
HYDRIDES
HYDROGEN
INTERACTIONS
ION PAIRS
IONS
POTENTIALS
PRECURSOR
PROTONS
REACTIVITY
SURFACES
amine borane
computational study
energy storage
hydrogen activation