Hydroalumination of a Dinuclear Tantalum Dinitrogen Complex: N−N Bond Cleavage and Ancillary Ligand Rearrangement

The addition of diisobutylaluminum hydride (DIBAL) to the side-on end-on dinitrogen
complex ([NPN]Ta)2(μ-η1:η2-N2)(μ-H)2, 1 (where [NPN] = (PhNSiMe2CH2)2PPh), is described.
The two end products are diastereomeric rotational isomers in which N−N bond cleavage
has occurred with an Al(iBu)H group attached to one of the nitride atoms. The reaction
proceeds through addition of DIBAL to 1 to generate a thermally sensitive intermediate
that has been characterized in solution as the result of Al−H addition across the TaN2 moiety,
namely, ([NPN]TaH)(μ-η1:η2-NNAliBu2)(μ-H)2(Ta[NPN), 2. This material subsequently rearranges via a second thermally labile intermediate to ultimately generate two diastereomeric
end products that show N−N bond cleavage, loss of H2, loss of an aluminum isobutyl group,
and NPN ligand migration from tantalum to aluminum. Both of these complexes have been
isolated in crystalline form and analyzed by single-crystal X-ray diffraction. The second
thermally sensitive intermediate has been characterized on the basis of multinuclear NMR
spectroscopy as ([NPN]TaH)(μ-η1:η2-NNAliBu(μ-H))(μ-H)2(Ta[NPN), 3.