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

The hyperpolarisation of the Sn-119 and Si-29 nuclei in 5-(tributylstannyl)-pyrimidine (A(Sn)) and 5-(trimethylsilyl)pyrimidine (B-Si) 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 ASn readily yielded signal enhancements totalling similar to 2300-fold in its H-1 NMR spectrum at a field strength of 9.4 T, with the corresponding Sn-119 signal being 700 times stronger than normal. In contrast, B-Si produced analogous H-1 signal gains of similar to 2400- fold and a Si-29 signal that could be detected with a signal tonoise 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)(2)Cl(NHC)(mu-pyrimidine-kappa N:kappa N ')](3) precipitate from these solutions whose identity was confirmed crystallographically for B-Si.