Abstract
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.