Isocyanate-Free Polyurea Synthesis via Ru-Catalyzed Carbene Insertion into the N–H Bonds of Urea

Polyureas have widespread applications due to their unique
material
properties. Because of the toxicity of isocyanates, sustainable isocyanate-free
routes to prepare polyureas are a field of active research. Current
routes to isocyanate-free polyureas focus on constructing the urea
moiety in the final polymerizing step. In this study we present a
new isocyanate-free method to produce polyureas by Ru-catalyzed carbene
insertion into the N–H bonds of urea itself in combination
with a series of bis-diazo compounds as carbene precursors. The mechanism
was investigated by kinetics and DFT studies, revealing the rate-determining
step to be nucleophilic attack on a Ru–carbene moiety by urea.
This study paves the way to use transition-metal-catalyzed reactions
in alternative routes to polyureas.