Metal nanoclusters (NCs) have unique
properties because of their
small size, which makes them useful as catalysts in reactions like
cross-coupling. Pd-catalyzed oxidative amination, which involves dehydrogenative
C–N bond formation, uses Pd complexes as the active species.
It is known that the catalytic conditions involve the formation of
Pd(0) species from Pd NCs, but the precise role of Pd NCs in the transformations
has not been established. In this study, we investigated the characteristic
properties of Pd NCs in oxidative amination of 1,3-dienes. The reaction
achieved direct amination of commercially accessible 1,3-dienes with
secondary aromatic amines, providing a variety of nitrogen containing
1,3-dienes. The compound was applicable to radical polymerization
to provide the nitrogen-fabricated 1,3-diene–based polymer,
which exhibited a different thermal stability compared to aliphatic
nitrogen-fabricated diene polymers. In addition to the synthetic utility,
by combining X-ray absorption fine structure and small-angle X-ray
scattering analysis, we revealed amines and 1,3-dienes affected metal
leaching from the Pd nanoparticles and stabilization of Pd NCs in
the catalytic reaction. Additionally, DFT calculation suggested that
the catalytic intermediate contained multiple adjacent Pd atoms and
was responsible for formation of an σ-allylic intermediate that
is difficult to form with the use of Pd complexes. These results could
be used to understand the underlying phenomenon in the oxidative coupling
reaction and develop Pd NCs-based dehydrogenation.