Using signal amplification by reversible exchange (SABRE) to hyperpolarise 119 Sn and 29 Si NMR nuclei

The hyperpolarisation of the Sn and Si nuclei in 5-(tributylstannyl)pyrimidine (A ) and 5-(trimethylsilyl)pyrimidine (B ) is achieved through their reaction with [IrCl(COD)(IMes)] (1a) or [IrCl(COD)(SIMes)] (1b) and parahydrogen via the SABRE process. 1a exhibits superior activity in both cases. The two inequivalent pyrimidine proton environments of A readily yielded signal enhancements totalling ∼2300-fold in its H NMR spectrum at a field strength of 9.4 T, with the corresponding Sn signal being 700 times stronger than normal. In contrast, B produced analogous H signal gains of ∼2400-fold and a Si signal that could be detected with a signal to noise ratio of 200 in a single scan. These sensitivity improvements allow NMR detection within seconds using micromole amounts of substrate and illustrate the analytical potential of this approach for high-sensitivity screening. Furthermore, after extended reaction times, a series of novel iridium trimers of general form [Ir(H) Cl(NHC)(μ-pyrimidine-κN:κN')] precipitate from these solutions whose identity was confirmed crystallographically for B .