Application of the π-accepting ability parameter of N-heterocyclic carbene ligands in iridium complexes for signal amplification by reversible exchange (SABRE)

The new pi-accepting ability parameter (PAAP) appears to be the best tool to analyse the electronic properties of NHC ligands in [Ir(H)(2)(NHC)(Py)(3)](+) complexes for SABRE. Together with the buried volume, the efficiency of hyperpolarisation transfer in SABRE, depending on the exchange rate of pyridine, can be described.