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Thermodynamic and kinetic studies of H2 and N2 binding to bimetallic nickel-group 13 complexes and neutron structure of a Ni(η2-H2) adduct
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DOI：10.1039/c9sc02018g.png)
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Abstract
En 中文
Understanding H-2 binding and activation is important in the context of designing transition metal catalysts for many processes, including hydrogenation and the interconversion of H-2 with protons and electrons. This work reports the first thermodynamic and kinetic H-2 binding studies for an isostructural series of first-row metal complexes: NiML, where M = Al (1), Ga (2), and In (3), and L = [N(o-((NCH2PPr2)-Pr-i)C6H4)(3)](3-). Thermodynamic free energies (Delta G degrees) and free energies of activation (Delta G(double dagger)) for binding equilibria were obtained via variable-temperature P-31 NMR studies and lineshape analysis. The supporting metal exerts a large influence on the thermodynamic favorability of both H-2 and N-2 binding to Ni, with Delta G degrees values for H-2 binding found to span nearly the entire range of previous reports. The non-classical H-2 adduct, (eta(2)-H-2)NiInL (3-H-2), was structurally characterized by single-crystal neutron diffraction-the first such study for a Ni(eta(2)-H-2) complex or any d(10) M(eta(2)-H-2) complex. UV-Vis studies and TD-DFT calculations identified specific electronic structure perturbations of the supporting metal which poise NiML complexes for small-molecule binding. ETS-NOCV calculations indicate that H-2 binding primarily occurs via H-H sigma-donation to the Ni 4p(z)-based LUMO, which is proposed to become energetically accessible as the Ni(0)-> M(iii) dative interaction increases for the larger M(iii) ions. Linear free-energy relationships are discussed, with the activation barrier for H-2 binding (Delta G(double dagger)) found to decrease proportionally for more thermodynamically favorable equilibria. The Delta G degrees values for H-2 and N-2 binding to NiML complexes were also found to be more exergonic for the larger M(iii) ions.
Keywords:
DIHYDROGEN COMPLEXES
MOLECULAR-HYDROGEN
BASIS-SETS
NMR
METALS
LIGAND
BOND
REACTIVITY
EXCHANGE
COBALT
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