The borylation of ligated dinitrogen by 1,3-B–H bond addition over a M–N≡N unit using various hydroboranes has been examined. In a previous study, we have shown that Piers’ borane (1) reacted with the tungsten dinitrogen complex 2 to afford a boryldiazenido-hydrido-tungsten species. The ease and mildness of this reaction has pushed us to extend its scope, with the working hypothesis that 1 could potentially catalyse the 1,3-B–H bond addition of other hydroboranes. Under productive reaction conditions, dicyclohexylborane (HBCy2) and diisopinocampheylborane (HBIpc2) underwent retro-hydroboration to give cyclohexylborane (H2BCy) or isopinocampheylborane (H2BIpc), respectively, these monoalkylboranes acting as N2-borylating agents in the presence of a catalytic amount of 1. Under similar conditions, 9-borabicyclononane (9-BBN) slowly adds over the W–N≡N unit without rearrangement to a monoalkylborane. Catecholborane (HBcat) performs the 1,3-B–H bond addition without the need of a catalyst. We were not able to build more than one covalent B–N bond between the terminal N of the N2 ligand and the boron reagent with this methodology.