Synthesis and Characterization of Osmium(IV) Polyhydride Complexes of Stoichiometry (C5Me5)OsH3(L). Crystal Structures of (C5Me5)OsH3(AsPh3) and (C5Me5)OsH3(PPh3)

Abstract

Addition of Lewis bases to solutions of (C5Me5)2Os2Br4 in ethanol affords mononuclear osmium(III) complexes with the general formula (C5Me5)OsBr2(L), where L is AsPh3, PPh3, P(c-Hx)3, PEt3, pyridine, or tetrahydrothiophene. These paramagnetic complexes react with sodium borohydride in ethanol to afford the osmium(IV) trihydrides (C5Me5)OsH3(L), where L is AsPh3, PPh3, P(c-Hx)3, or PEt3. X-ray diffraction and NMR studies of the trihydride complexes show that they adopt classical structures (i.e., lacking molecular dihydrogen ligands). Unlike their ruthenium analogues, these osmium(IV) trihydrides show no evidence of quantum tunneling phenomena, probably because the H−Os−H bending motion is characterized by a steep potential energy well.