Mechanistic Analysis and Characterization of Intermediates in the Phosphane‐Catalyzed Oligomerization of Isocyanates

Abstract

Abstract The mechanism of the oligomerization of aliphatic isocyanates catalyzed by trialkylphosphanes has been studied through low temperature 31 P and 15 N NMR spectroscopy combined with computational chemistry. A revised mechanism is proposed that contains several (spiro)cyclic pentacoordinate phosphorous intermediates. Previously reported spectroscopic data of a transient intermediate has been reevaluated and assigned to a cyclic intermediate containing a P−N bond by experiments with 15 N‐labeled isocyanate. 13 C, 15 N, and 31 P NMR shifts that support this assignment have been calculated using quantum chemical methods.