formation through dehydropolymerization of ammonia-borane by Brookhart's iridium pincer catalyst has been under intense scrutiny but a sound molecular level understanding has remained elusive. Herein, using DFT the mechanism outlined by us for IrH2POCOP catalyzed formation underscores the importance of generation of nucleophiles, in particular that of the metal bound NH2BH2 moiety armed with a nitrogen lone pair for chain initiation and chain propagation steps.