Synthesis and Reactivity of New Niobocene Hydride-Stibine and Hydride-Stilbene Complexes. X‑ray Crystal Structure of [Nb(η⁵‑C₅H₄SiMe₃)₂(H)(<i>trans</i>-η²‑C,C-PhCHCHPh)]

The synthesis of a stable hydride triphenylstibine derivative, Nb­(η⁵-C₅H₄SiMe₃)₂(H)­(SbPh₃) (<b>1</b>), has been achieved through the formation of the transient coordinatively unsaturated 16-electron species [Nb­(η⁵-C₅H₄SiMe₃)₂(H)] by thermolytic loss of H₂ from Nb­(η⁵-C₅H₄SiMe₃)₂(H)₃ (<b>2</b>) followed by the coordination of a triphenylstibine ligand. Low-temperature protonation of <b>1</b> with a slight excess of CF₃COOD led to the η²-dihydrogen complex <b>3</b> as the monodeuterated H–D isotopomers of [Nb­(η⁵-C₅H₄SiMe₃)₂(η²-HD)­(SbPh₃)]⁺CF₃CO₂^– (<b>3-</b><i><b>d</b></i>_<b>1</b>). When the temperature was increased to room temperature, complex <b>3</b> was converted into the <i>transoid</i> dihydride [Nb­(η⁵-C₅H₄SiMe₃)₂(H)₂(SbPh₃)]­CF₃CO₂ (<b>4</b>). Surprisingly, when CF₃COOH in deuterated solvents was used in the protonation process, the final η²-dihydrogen product always contained a substantial amount of deuterated isotopomers. Furthermore, a new hydrido olefin niobocene complex, [Nb­(η⁵-(C₅H₄SiMe₃)₂(H)­(<i>trans</i>-η²-C,C-PhCHCHPh)] (<b>5</b>), can be synthesized by elimination of the stibine ligand from <b>1</b> followed by the addition of <i>cis</i> or <i>trans</i> stilbene. Complex <b>5</b> can also be obtained by reaction of <b>2</b> in the presence of <i>cis</i> or <i>trans</i> stilbene by the thermolytic loss of H₂. All of these compounds were characterized by IR and multinuclear NMR spectroscopy, and the molecular structure of <b>5</b> was determined by single-crystal X-ray diffraction