Reversible Hyperpolarization of Ketoisocaproate Using Sulfoxide-containing Polarization Transfer Catalysts.

The substrate scope of sulfoxide-containing magnetisation transfer catalysts is extended to hyperpolarize α-ketoisocaproate and α-ketoisocaproate-1-[ C]. This is achieved by forming [Ir(H) (κ -ketoisocaproate)(N-heterocyclic carbene)(sulfoxide)] which transfers latent magnetism from p-H via the signal amplification by reversible exchange (SABRE) process. The effect of polarization transfer field on the formation of enhanced C magnetization is evaluated. Consequently, performing SABRE in a 0.5 μT field enabled most efficient magnetisation transfer. C NMR signals for α-ketoisocaproate-1-[ C] in methanol-d are up to 985-fold more intense than their traditional Boltzmann derived signal intensity (0.8 % C polarisation). Single crystal X-ray diffraction reveals the formation of the novel catalyst decomposition products [Ir(μ-H)(H) (IMes)(SO(Ph)(Me) )] and [(Ir(H) (IMes)(SO(Me) )) (μ-S)] when the sulfoxides methylphenylsulfoxide and dimethylsulfoxide are used respectively.