The reaction of an iridium PNP complex with parahydrogen facilitates polarisation transfer without chemical change† †Electronic supplementary information (ESI) available: Sample preparation, signal enhancements and raw data. CCDC 1026865. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt03088e Click here for additional data file. Click here for additional data file

The pincer complex [(C 5 H 3 N(CH 2 P( t Bu) 2 ) 2 )Ir(H) 2 (py)]BF 4 is shown to be active for signal amplification by reversible exchange. The short lived pincer complex [(C 5 H 3 N(CH 2 P( t Bu) 2 ) 2 )Ir(H) 2 (py)]BF 4 is shown to be active for signal amplification by reversible exchange. This catalyst formulation enables the efficient transfer of polarization from para hydrogen to be placed into just a single molecule of the hyperpolarisation target, pyridine. When the catalysts 1 H nuclei are replaced by 2 H, increased levels of substrate hyperpolarization result and when the reverse situation is examined the catalyst itself is clearly visible through hyperpolarised signals. The ligand exchange pathways of [(C 5 H 3 N(CH 2 P( t Bu) 2 ) 2 )Ir(H) 2 (py)]BF 4 that are associated with this process are shown to involve the formation of 16-electron [(C 5 H 3 N(CH 2 P( t Bu) 2 ) 2 )Ir(H) 2 ]BF 4 and the 18-electron H 2 addition product [(C 5 H 3 N(CH 2 P( t Bu) 2 ) 2 )Ir(H) 2 (H 2 )]BF 4 .