Ionic ruthenium(IV) trihydrides as intermediates in the heterolytic fission of dihydrogen by five-co-ordinate hydridoruthenium(II) cations. Direct evidence for an oxidative addition–reductive elimination pathway
The cations [RuH(L2)2(MeOH)]+[L2=(PMe2-Ph)2, (PMePh2)2, or bis(diphenylphosphino)ethane (dpe)] and the salts [RuH(L2)2]PF6[L2= bis(diphenylphosphino)-propane (dpp) and -butane (dpb)], formed from stoicheio-metric ligand additions to [(cod)RuH(NH2NMe2)3]PF6(cod = cyclo-octa-1,5-diene) in methanol under argon, react in situ with dihydrogen to give the trihydrides [RuH3(L2)2]PF6 for L2=(PMe2Ph)2, dpe, or dpp, and the dihydrides [RuH2(L2)2] for L2=(PMePh2)2 or dpb; the equilibrium [RuH3(L2)2]+⇌[RuH2(L2)2]+ H+ is demonstrated and used to prepare [RuH3(L2)2]PF6 for L2=(PMePh2)2 or dpb, and [RuH2(L2)2] for L2= dpp.