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

The synthesis of a stable hydride triphenylstibine derivative, Nb­(η5-C5H4SiMe3)2(H)­(SbPh3) (1), 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 (2) followed by the coordination of a triphenylstibine ligand. Low-temperature protonation of 1 with a slight excess of CF3COOD led to the η2-dihydrogen complex 3 as the monodeuterated H–D isotopomers of [Nb­(η5-C5H4SiMe3)2(η2-HD)­(SbPh3)]+CF3CO2– (3-d1). When the temperature was increased to room temperature, complex 3 was converted into the transoid dihydride [Nb­(η5-C5H4SiMe3)2(H)2(SbPh3)]­CF3CO2 (4). 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)­(trans-η2-C,C-PhCHCHPh)] (5), can be synthesized by elimination of the stibine ligand from 1 followed by the addition of cis or trans stilbene. Complex 5 can also be obtained by reaction of 2 in the presence of cis or trans stilbene by the thermolytic loss of H2. All of these compounds were characterized by IR and multinuclear NMR spectroscopy, and the molecular structure of 5 was determined by single-crystal X-ray diffraction.