Preparation and Characterization of a Monocyclopentadienyl Osmium−Allenylcarbene Complex

The dihydride−dihydrogen complex [OsH2(η5-C5H5)(η2-H2)(PiPr3)]BF4 (1) reacts with phenylacetylene to give the allenylcarbene derivative [Os(η5-C5H5){CPh(η2-CHCCHPh)}(PiPr3)]BF4 (2) via the π-phenylacetylene intermediate [Os(η5-C5H5)(η2-PhC⋮CH)(PiPr3)]BF4 (3). The reactions of 2 with NaOMe and LiC⋮CPh afford 3:1 mixtures of two hydride−osmaindene isomers of formula (4 and 5) instead of the expected osmabenzyne complex.