An Isolable Azide Adduct of Titanium(II) Follows Bifurcated Deazotation Pathways to an Imide

AdN(3) (Ad = 1-adamantyl) reacts with the tetrahedral Ti-II complex [(Tp(tBu,Me))TiCl] (Tp(tBu,Me) = hydrotris(3-tert-butyl-5-methylpyrazol-1-yl)borate) to generate a mixture of an imide complex, [(Tp(tBu,Me))TiCl(NAd)] (4), and an unusual and kinetically stable azide adduct of the group 4 metal, namely, [(Tp(tBu,Me))TiCl(gamma-N(3)Ad)] (3). In these conversions, the product distribution is determined by the relative concentration of reactants. In contrast, the azide adduct 3 forms selectively when a masked Ti-II complex (N-2 or AdNC adduct) reacts with AdN(3). Upon heating, 3 extrudes dinitrogen in a unimolecular process proceeding through a titanatriazete intermediate to form the imide complex 4, but the observed thermal stability of the azide adduct (t(1/2) = 61 days at 25 degrees C) is at odds with the large fraction of imide complex formed directly in reactions between AdN(3) and [(Tp(tBu,Me))TiCl] at room temperature (similar to 50% imide with a 1:1 stoichiometry). A combination of theoretical and experimental studies identified an additional deazotation pathway, proceeding through a bimetallic complex bridged by a single azide ligand. The electronic origin of this deazotation mechanism lies in the ability of azide adduct 3 to serve as a pi-backbonding metallaligand toward free [(Tp(tBu,Me))TiCl]. These findings unveil a new class of azide-to-imide conversions for transition metals, highlighting that the mechanisms underlying this common synthetic methodology may be more complex than conventionally assumed, given the concentration dependence in the conversion of an azide into an imide complex. Lastly, we show how significantly different AdN(3) reacts when treated with [(Tp(tBu,Me))VCl].