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‐[ 13 C]. This is achieved by forming [Ir(H) 2 ( κ 2 ‐ketoisocaproate)( N ‐heterocyclic carbene)(sulfoxide)] which transfers latent magnetism from p ‐H 2 via the signal amplification by reversible exchange (SABRE) process. The effect of polarization transfer field on the formation of enhanced 13 C magnetization is evaluated. Consequently, performing SABRE in a 0.5 μT field enabled most efficient magnetisation transfer. 13 C NMR signals for α ‐ketoisocaproate‐1‐[ 13 C] in methanol‐ d 4 are up to 985‐fold more intense than their traditional Boltzmann derived signal intensity (0.8 % 13 C polarisation). Single crystal X‐ray diffraction reveals the formation of the novel catalyst decomposition products [Ir( μ ‐H)(H) 2 (IMes)(SO(Ph)(Me) 2 )] 2 and [(Ir(H) 2 (IMes)(SO(Me) 2 )) 2 ( μ ‐S)] when the sulfoxides methylphenylsulfoxide and dimethylsulfoxide are used respectively.