Inverse Isotope Effects in Single-Crystal to Single-Crystal Reactivity and the Isolation of a Rhodium Cyclooctane Σ-Alkane Complex

The sequential solid/gas single-crystal to single-crystal reaction of [Rh(Cy2P(CH2)3PCy2)(COD)][BArF4] (COD = cyclooctadiene) with H2 or D2 was followed in situ by solid-state 31P{1H} NMR spectroscopy (SSNMR) and ex situ by solution quenching and GC-MS. This was quantified using a two-step Johnson-Mehl- Avrami-Kologoromov (JMAK) model that revealed an inverse isotope effect for the second addition of H2, that forms a cr-alkane complex [Rh(Cy2P(CH2)3PCy2)(COA)][BArF4]. Using D2, a temporal window is determined in which a structural solution for this cr-alkane complex is possible, which reveals an 12,12-binding mode to the Rh(I) center, as supported by periodic density functional theory (DFT) calculations. Extensive H/D exchange occurs during the addition of D2, as promoted by the solid-state microenvironment.

Automated summary

The sequential solid/gas single-crystal to single-crystal reaction of [Rh(Cy2P(CH2)3PCy2)(COD)][BArF4] with H2 or D2 was studied using solid-state NMR spectroscopy and solution quenching techniques. The quantification of the reaction was done using a two-step JMAK model, revealing an inverse isotope effect for the second addition of H2 and the possibility of obtaining the structural solution of the alkane complex using D2. The results were supported by periodic DFT calculations.