Structure and dynamics in metal phosphine complexes using advanced NMR studies with para-hydrogen induced polarisation

The iridium and rhodium phosphine complexes IrCl(CO)(PPh3)(2) 1 (Vaska's co mplex), Rh(PMe3)(4)Cl 2, and Rh(PMe3)(3)Cl 3, add H-2 to form the correspon ding dihydrides. Exchange with para-hydrogen (p-H-2) provides a means of ob serving H-1 NMR signals due to the metal bound hydrides at significantly en hanced levels of sensitivity. We show that monitoring these metal hydride c omplexes can be achieved by a range of 2D NMR methods, based on standard ex periments, which have been modified to achieve optimum signal. The assignme nt of heteronuclei, including low sensitivity nuclei such as Rh-103, determ ination of heteronuclear coupling constants and measurement of their relati ve signs, is described for these systems using p-H-2 derived starting magne tisation. In the case of Vaska's complex the dihydride addition product con tains a trans labilised carbonyl ligand, and substitution with appropriate phosphines brings about the formation of metal phosphine complexes with new ligand spheres. Appropriately modified NOESY experiments are demonstrated to rapidly probe structural arrangements, and monitor dihydride exchange. F or Ir(H)(2)Cl(PPh3)(3) dihydride exchange is shown to proceed mainly via Ir (H)(2)Cl(PPh3)(2), which is shown to contain inequivalent hydrides. The rea ctivity of the arsine complex IrCl(AsPh3)(3) 9 towards H-2 is examined, and the NOESY approach used to make structural assignments in the reaction pro duct.