Exploring the mechanism of the hydroboration of alkenes by amine-boranes catalysed by [Rh(xantphos)]+Electronic supplementary information (ESI) available: X-ray crystallographic data collection and refinement details. Crystallographic data have been deposited with the Cambridge Crystallographic Data Center (CCDC), CCDC 1001382 (3) and 1001383 (8). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4cy00597j

The [Rh(xantphos)] + fragment acts as an effective catalyst for the hydroboration of the alkene TBE ( tert -butyl ethene) using the amine-borane H 3 B·NMe 3 at low (0.5 mol%) catalyst loadings to give the linear product. Investigations into the mechanism using the initial rate method and labelling studies show that reductive elimination of the linear hydroboration product is likely the rate-limiting step at the early stages of catalysis, and that alkene and borane activation (insertion into a Rh-H bond and B-H oxidative addition) are reversible. The resting state of the system has also been probed using electrospray ionization mass spectrometry (ESI-MS) using the pressurised sample infusion (PSI) technique. This system is not as effective for hydroboration of other alkenes such as 1-hexene, or using phosphine borane H 3 B·PCy 3 , with decomposition or P-B bond cleavage occurring respectively. The [Rh(xantphos)] + fragment acts as an effective catalyst for the hydroboration of the alkene TBE ( tert -butyl ethene) using the amine-borane H 3 B·NMe 3 at low (0.5 mol%) catalyst loadings to give the linear product.