The metal-catalyzed hydrogenolysis of polymers is important
in
waste recycling; however, it is limited by the harsh reaction conditions
and the low activities of catalysts, especially for earth-abundant
metal-based catalysts. Herein, we perform a comprehensive study on
the hydrogenolysis of polyurethane model catalyzed by Fe-, Mn-, Ru-,
and Ir-iPrMACHO pincer complexes and propose a cascade
mechanism comprising two-level hydrogenolysis and the hydrogenation
of formaldehyde. In addition, the substrates and ligands are modulated
to improve the activities of chemical recycling to monomer. It is
found that the pincer ligands could dissociate from the metal centers
at high reaction temperatures and further result in the deactivation
of catalysts. The rigid Fe and Mn catalysts with tetradentate cyclic
ligands are designed following the guidance, and the computations
suggest that those designed catalysts could have high stabilities
and activities.
Understanding controlling factors is important for the development of the bifunctional outer-sphere C=C hydrogenations. A dominant view is that the polarization of C=C bonds is imperative for these reactions. However,...
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