Iridium trihydride and tetrahydride complexes and their role in catalytic polarisation transfer from parahydrogen to pyruvate

This work details how the unusual iridium tetrahydride [Ir(H)4(IMes)(sulfoxide)]Na can be formed in a solvent dependent reaction of [IrCl(COD)(IMes)] with sulfoxide (dimethyl or methylphenyl), base, and H2. In the case of dimethyl sulfoxide, the four hydride ligands are equivalent, and the IMes and sulfoxide ligands mutually trans. However, for phenyl methyl sulfoxide, this isomer forms alongside its cis counterpart where the remarkable symmetry breaking effect of the sulfoxide leads to it presenting four chemically distinct hydride ligands. Subsequent reaction leads to their replacement with the corresponding trihydrides [Ir(H)3(IMes)(sulfoxide)2], where ligand chirality again plays a role in product selection. These products and their ligand arrangements are characterised and the reaction pathways leading to their formation probed using NMR spectroscopy and parahydrogen-hyperpolarised methods. Subsequently, they form as previously unidentified low concentration by-products in the important SABRE-catalysed hyperpolarisation of pyruvate, and their concentration should be minimised for efficient polarisation transfer.