Predicting the NMR chemical shifts of hydrides in SABRE-active Ir complexes by relativistic DFT

Abstract

Signal amplification by reversible exchange (SABRE) uses metal-mediated reversible binding of parahydrogen to transfer polarization via spin–spin couplings in transient complexes, particularly iridium complexes with N-heterocyclic carbenes (NHC). The magnetic parameters of such complexes, notably chemical shifts and coupling constant networks, are useful for elucidating their structure and assessing their effectiveness as spin catalysts. Moreover, Ir-bound hydrides have distinctive chemical shifts (−10 to −30 ppm) that provide valuable information about the complex geometry and, upon detailed analysis, about its substituents. However, interpreting the corresponding experimental NMR spectra becomes significantly more challenging than in simple organic molecules due to the presence of the heavy metal center which affects the hydrides resonance by the spin–orbit HALA (heavy atom on light atom) effect. In this work we show that density functional theory (DFT) can address these challenges by incorporating proper relativistic corrections, thus aiding the structural analysis of these systems.