Reversible Gas–Solid Ammonia N–H Bond Activation Mediated by an Organopalladium Complex

N–H
bond activation of gaseous ammonia is achieved at room temperature
in a reversible solvent-free reaction using a solid dicyclopalladated
azobenzene complex. Monitoring of the gas–solid reaction in
real-time by in situ solid-state Raman spectroscopy
enabled a detailed insight into the stepwise activation pathway proceeding
to the final amido complex via a stable diammine intermediate. Gas–solid
synthesis allowed for isolation and subsequent structural characterization
of the intermediate and the final amido product, which presents the
first dipalladated complex with the PdII−(μ-NH2)−PdII bridge. Gas–solid reaction
is readily followed via color changes associated with conformational
switching of the palladated azobenzene backbone. The reaction proceeds
analogously in solution and was characterized by UV–vis and
NMR spectroscopies showing the same stepwise route to the amido complex.
Combining the experimental data with density functional theory calculations
we propose a stepwise mechanism of this heterolytic N–H bond
activation assisted by exogenous ammonia.