The reaction of an iridium PNP complex with parahydrogen facilitates polarisation transfer without chemical change

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 parahydrogen 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).