Catalytic dehydrocoupling of methylamine borane using Yamashita's [Ir(PBP)] boryl complex – characterisation of a novel highly fluxional Ir tetrahydride

Abstract

We report the synthesis and characterisation of two iridium pincer monocarbonyl complexes possessing Yamashita's PBP boryl ligand. Both complexes can be prepared by reaction of the parent hydride chloride complex (1) with base in the presence of CO. Complex 1 as well as the 18-electron complex [(PBP)Ir(CO)(H)₂] (2) were tested as precatalysts for the catalytic dehydrocoupling of amine boranes, showing that only 1 selectively produces polyaminoboranes. A tetrahydride complex 4 was identified as the resting state of catalysis and characterised in solution and the solid state. Combination of NMR spectroscopy, X-ray analysis and DFT computation suggest the presence of a highly fluxional hydride environment with only one of the hydride ligands bridging the Ir centre and the boryl unit.