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)(mu-eta(1):eta(2)-N-2)(mu-H)(2), 1 (where [NPN] = (PhNSiMe2CH2)(2)PPh), is described. The two end products are diastereomeric rotational isomers in which N-N bond cleavage has occurred with an Al(Bu-i)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)(mu-eta(1):eta(2)-NNA1(i)Bu(2))(mu-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 H-2, 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)(mu-eta(1):eta(2)-(NNAlBu)-Bu-i(mu-H))(mu-H)(2)(Ta[NPN), 3.