Transformation of CO2 and isocyanates mediated by N-borane-substituted cyclic phosphine imides (BCPIs) via λ5-oxazaphosphetanes

Abstract

We herein report reliable evidence that λ⁵-oxazaphosphetane species are a key intermediate in the transformation of CO₂ and isocyanates through their reaction with N-borane-substituted cyclic phosphine imides (BCPIs). We have isolated and fully characterized several λ⁵-oxazaphosphetane species prepared via formal [2 + 2] cycloaddition reactions between BCPIs and CO₂ or isocyanates. The transformation of these λ⁵-oxazaphosphetanes via retro-ring opening reaction afforded an isocyanate and a carbodiimide from the CO₂- and isocyanate-derived λ⁵-oxazaphosphetanes.