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 [H5Os10(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 (mu)2-H and two (mu)3-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 (mu)2- and (mu)3-hydrides have a very different mobility. While (mu)2-hydrides exchange easily by an edge-shift process, their exchange with (mu)3-hydrides is much more difficult, as the exchange between (mu)3-hydrides themselves.