Revisiting the Bench Stability of B ₂ pin ₂

Bis(pinacolato)diboron (B 2 pin 2 ) is a widely used diboron reagent for the installation of modular boryl groups and is generally regarded as bench stable. Here we show that trace impurities can initiate an autocatalytic process that promotes oxidative decomposition of B 2 pin 2 in the solid state. Once initiated, this process renders B 2 pin 2 susceptible to reaction with molecular oxygen and HO–Bpin, leading to degradation of bulk material. Notably, decomposition propagates under closed container conditions but is suppressed in loosely capped containers, consistent with the involvement of volatile components in the degradation process. These findings reveal an unexpected vulnerability in a widely used boron reagent and establish practical guidelines for its storage and handling.