Functionalization and cleavage of coordinated dinitrogen via hydroboration using primary and secondary boranes

The reaction of the side-on, end-on ditantalum dinitrogen complex ([NPN]Ta)(2)(mu-eta(1):eta(2)-N-2)(mu-H)(2) (where NPN = PhP(CH2SiMe2NPh)(2)) with a variety of secondary and primary boranes is reported. With 9-BBN, hydroboration of the Ta2N2 unit occurs via B-H addition, which in turn triggers a cascade of reactions that result in N-N bond cleavage, ancillary ligand rearrangement involving silicon group migration, and finally elimination of benzene from the N-Ph group and a B-H moiety to generate the imide-nitride derivative. In the presence of excess 9-BBN, the Lewis acid - base adduct of the imide-nitride ([NP mu-N]Ta(=NBC8H14)(mu-NB(H)C8H14)Ta[NPN]) is formed. A similar set of reactions is observed for dicyclohexylborane (Cy2BH), which hydroborates the dinitrogen complex to generate [NPN]Ta(H)(mu-eta(1):eta(2)-NNBCy2)(mu-H)(2)Ta[NPN], followed by loss of H-2 and silicon group migration to yield the imide-nitride [NP mu-N]Ta(=NBCy2)(mu-N)(Ta[NPN]. With thexyl borane (H2BCMe2CHMe2), a similar sequence of reactions is suggested starting with hydroboration to generate [NPN]Ta(H)(mu-eta(1):eta(2)-NNB(H)C6H13)(mu-H)(2)Ta[NPN], followed by loss of H-2 and ancillary ligand rearrangement. When bis(pentafluorophenyl)borane (HB(C6F5)(2)) is used, no hydroboration of coordinated N-2 is observed, rather simple adduct formation to give ([NPN]Ta)(2)(mu-eta(1):eta(2)-NN-B(H)(C6F5)(2))(mu-H)(2) occurs.