Elongated dihydrogen versus compressed dihydride in osmium complexes

Small modifications on the co-ligands of complexes containing two coordinated hydrogen atoms can determine the elongated dihydrogen versus compressed dihydride nature of these species and therefore their chemical behavior. 2,6-diphenylpyridine favors the formation of the osmium(IV) cation [OsH2(C6H4pyPh)(PiPr3)2]+, whereas 2-phenoxy-6-phenylpyridine, which contains an oxygen atom between the heterocycle and one of the phenyl groups, stabilizes the osmium(II) elongated dihydrogen species [Os(C6H4pyOPh)(η2-H2)(PiPr3)2]+. In contrast to the latter, the former shows a marked tendency to undergo reductive elimination of the heterocycle.Financial support from the MINECO of Spain (Project CTQ2014-52799-P), the Diputación General de Aragón (E-35), FEDER, and the European Social Fund is acknowledged.Peer reviewe