Probing the Hydrogenation of Vinyl Sulfoxides Using para-Hydrogen

[Image: see text] Vinyl sulfoxides are an important functional group used in a wide range of organic transformations. Here, we use [IrCl(COD)(IMes)] where IMes = 1,3-bis(2,4,6-trimethyl-phenyl)imidazole-2-ylidene and COD = cis,cis-1,5-cyclooctadiene to rapidly hydrogenate phenylvinylsulfoxide. We use para-hydrogen-induced hyperpolarization (PHIP) to follow this reaction with [IrCl(H)(2)(IMes)(S(O)(Ph)(Et))(2)] dominating in the later stages. Decomposition to form the reduced C–S bond cleavage product [Ir(2)(H)(3)(κ(2)-H)(κ(2)-SPh)(2)(IMes)(2)(S(Et)(Ph)O)] limits turnover. The related product [Ir(2)(H)(4)(κ(2)-S)(IMes)(2)(S(O)(CH(2)Ph)(2))(2)] is formed from dibenzylsulfoxide, demonstrating the wider utility of this transformation.