Borane-catalysed dinitrogen borylation by 1,3-B-H bond addition

The borylation of ligated dinitrogen by 1,3-B-H bond addition over a W-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 have encouraged 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 (HBIpc(2)) underwent retro-hydroboration to give cyclohexylborane (H2BCy) or isopinocampheylborane (H(2)BIpc), respectively; these monoalkylboranes act as N-2-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 monoalkyl-borane. Catecholborane (HBcat) undergoes the 1,3-B-H bond addition without the need for a catalyst. We were not able to build more than one covalent B-N bond between the terminal N of the N-2 ligand and the boron reagent with this methodology.

Automated summary

The study examined the borylation of ligated dinitrogen by 1,3-B-H bond addition using various hydroboranes on a W-N N unit. Different hydroboranes were found to successfully react under different reaction conditions, with some cases showing the 1,3-B-H bond addition without the need for a catalyst.