Butynes Hydrogenation with Parahydrogen over Immobilized Iridium Catalyst

The Ir–P@SiO2 catalyst was prepared by immobilizing a dimeric Ir complex via interaction with –PPh2 groups of 2-diphenylphosphinoethyl-functionalized silica gel. The catalyst was tested in hydrogenations of butynes (1-butyne and 2-butyne) with parahydrogen. The experimentally observed 1H NMR spectra of hyperpolarized products are well-fitted with theoretical PASADENA spectra simulated with the use of spin density matrix formalism. The analysis of 1H NMR spectral lines of the products reveals that the catalyst is stereoselective in such reactions and the syn-addition of p-H2 takes place. Moreover, we demonstrate that the lineshape of hyperpolarized NMR signals of cis-2-butene is indicative of the mechanism of its formation. It was found that 2-butene produced during 1-butyne hydrogenation is formed from hyperpolarized 1-butene via isomerization. The maximum observed 1H polarization levels for 1-butene were 5.2 ± 0.5%.