Rhenium pentahydride complexes: characterisation and protonation reactions. Crystal structure of ReH5L1L2 (L1=Ph2PO(CH2)2OPPh2; L2=P(OCH3)3, P(OCH2CH3)3)

Variable temperature NMR studies of the rhenium pentahydrides [ReH5L1L2] (L1=Ph2POCH2CH2OPPh2; L2=PPhn(OR)3−n, n=0–2; R=Me, Et) show a fluxional behaviour at all accessible temperatures. The coalescence events observed in the hydride region of the 1H-NMR spectra have coalescence temperatures increasing as the number of OR groups of L2 increases. Longitudinal T1(min) values (∼120 ms at 400 MHz) suggest a classical nature for these compounds. The crystal structure of compounds with L2=P(OR)3 has been determined by X-ray diffraction techniques at low temperature. Both compounds show a dodecahedral co-ordination geometry with the three phosphorus nuclei and one hydride in B sites and the remaining four hydrides in A sites. The protonation of pentahydrides with HBF4·Et2O yielded the non-classical cations [Re(η2-H2)H4L1L2]+ (T1(min)∼20 ms at 400 MHz) that slowly decompose between 253 and 273 K being more stable as the number of OR groups increases.