Isocyanate-free Polyurea Synthesis via Ru-Catalyzed Car-bene Insertion into the N‒H Bonds of Urea

Polyureas have widespread applications due to their unique material properties. Due to the toxicity of isocyanates, sus-tainable isocyanate-free routes to prepare polyureas is a field of active research. Current routes to isocyanate-free poly-ureas 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, re-vealing the rate determining step to be nucleophilic attack of a Ru-carbene moiety by urea. This study paves the way to use transition-metal catalyzed reactions in alternative routes to polyureas.