Variable temperature 1H NMR and X-ray diffraction characterisation of [H5Os10(CO)24]- obtained in reproducible and high yields by hydrogenation of silica-supported [Os(CO)3(OH)2]n

The hydrides localisation in the hydrido carbonyl cluster [H 5Os10(CO)24]-, obtained in excellent and reproducible yields by hydrogenation (1 atm, 200°C) of silica-supported [Os(CO)3(OH)2]n, has been investigated by variable temperature 1H NMR and X-ray diffraction of the [(Ph3P)2N]+ salt. Using both stereochemical and potential energy considerations, three μ2-H and two μ3-H have been localised in sites strictly related to those of the parent [H4Os10(CO)24] 2- anion, where hydrides location had been obtained by neutron diffraction of the corresponding [(Ph3P)2N]+ salt. Such locations are in agreement with low temperature 1H NMR findings. Variable temperature 1H NMR investigation has also shown that μ2- and μ3-hydrides have a very different mobility. While μ2-hydrides exchange easily by an edge-shift process, their exchange with μ3-hydrides is much more difficult, as the exchange between μ3-hydrides themselves. © 2003 Elsevier B.V. All rights reserved.