title: Metal-mediated dihydrogen activation. What determines the transition-state geometry?
abstract: Density functional theory and absolutely localized molecular orbital energy decomposition analysis calculations were used to calculate and analyze dihydrogen activation transition states and reaction pathways. Analysis of a variety of transition-metal complexes with d(0), d(6), d(8), and d(10) orbital occupation with a diverse range of metal ligands reveals that for transition states, akin to dihydrogen σ complexes, there is a continuum of activated H-H bond lengths that can be classified as "dihydrogen" (0.8-1.0 Å), "stretched or elongated" (1.0-1.2 Å), and "compressed dihydride" (1.2-1.6 Å). These calculations also quantitatively for the first time reveal that the extent to which H(2) is activated in the transition-structure geometry depends on back-bonding orbital interactions and not forward-bonding orbital interactions. This is true regardless of the mechanism or whether the metal ligand complex acts as an electrophile, ambiphile, or nucleophile toward dihydrogen.
authors.affiliation: Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: Deepa
authors.initials: D
authors.lastname: Devarajan
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Ess