New aspects of parahydrogen-induced polarization for C 2 —C 3 hydrocarbons using metal complexes

The parahydrogen-induced polarization technique allows one to significantly enhance the NMR signal. Novel results on the parahydrogen-induced polarization of C 2 —C 3 hydrocarbons using metal complexes are presented. Gaseous propane with the nuclear spin polarization level of at least 0.8% can be produced by bubbling parahydrogen through a solution of propylene and a homogeneous hydrogenation catalyst. Hydrogenation of acetylene with parahydrogen over Wilkinson’s catalyst can result in the formation of hyperpolarized ethylene. The shape of the NMR lines indicates that this reaction proceeds as a syn-addition of molecular hydrogen. The reactions of several ethylene complexes of rhodium and platinum with parahydrogen were studied. The [Rh(η 2 -C 2 H 4 ) 2 Cl] 2 complex reacts with parahydrogen to form hyperpolarized ethane, whereas [Pt(η 2 -C 2 H 4 )(PPh 3 ) 2 ] converts to the hyperpolarized dihydride complex cis -[Pt(H) 2 (PPh 3 ) 2 ].