Hydrogen-Bond and Solvent
Dynamics in Transition Metal
Complexes: A Combined Simulation and NMR-Investigation
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Abstract
Self-assembling ligands through complementary hydrogen-bonding
in the coordination sphere of a transition metal provides catalysts
with unique properties for carbon–carbon and carbon–heteroatom
formation. Their most distinguishing chemical bonding pattern is a
double-hydrogen-bonded motif, which determines much of the chemical
functionality. Here, we discuss the possibility of double proton transfer
(DPT) along this motif using computational and experimental methods.
The infrared and NMR spectral signatures for the double-hydrogen-bonded
motif are analyzed. Atomistic simulations and experiments suggest
that the dynamics of the catalyst is surprisingly complex and displays
at least three different dynamical regimes which can be distinguished
with NMR spectroscopy and analyzed from computation. The two hydrogen
bonds are kept intact and in rapid tautomeric exchange down to 125
K, which provides an estimate of 5 kcal/mol for the barrier for DPT.
This is confirmed by the simulations which predict 5.8 kcal/mol for
double proton transfer. A mechanistic interpretation is provided and
the distribution of the solvent shell surrounding the catalyst is
characterized from extensive simulations