A novel application of para H-2: the reversible addition/elimination of H-2 at a Ru-3 cluster revealed by the enhanced NMR emission resonance from molecular hydrogen

Polarization transfer from the NMR silent p-H-2 to o-H-2 is possible throug h the intermediacy of a triruthenium his-hydride cluster. In fact, a strong emission signal for the molecular Wt resonance is observed when p-H-2 is a llowed to react with Ru-3(CO)(11)(NCCH3) in the NMR tube at RT. The break o f symmetry in p-H-2 is achieved at the intermediate. H(mu-H)Ru-3(mu-CO)(CO) (10) compound where the two hydrides form an AX spin system; the build-up o f the longitudinal magnetization leaves a "memory" of this intermediate in the signal of the H-2 molecule formed by reductive elimination from the bis -hydride species. The observed behavior is fully accounted for in terms of the established relaxation theory.