Reactivity
with Electrophiles of Imido Groups Supported on Trinuclear Titanium
Systems
- Publication date
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Abstract
Several
trinuclear titanium complexes bearing amido μ-NHR, imido μ-NR,
and nitrido μ<sub><i>n</i></sub>-N ligands have been
prepared by reaction of [{Ti(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(μ-NH)}<sub>3</sub>(μ<sub>3</sub>-N)] (<b>1</b>) with 1 equiv of electrophilic reagents ROTf (R = H, Me,
SiMe<sub>3</sub>; OTf = OSO<sub>2</sub>CF<sub>3</sub>). Treatment
of <b>1</b> with triflic acid or methyl triflate in toluene
at room temperature affords the precipitation of compounds [Ti<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>3</sub>(μ<sub>3</sub>-N)(μ-NH)<sub>2</sub>(μ-NH<sub>2</sub>)(OTf)] (<b>2</b>) or [Ti<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>3</sub>(μ<sub>3</sub>-N)(μ-NH)(μ-NH<sub>2</sub>)(μ-NMe)(OTf)] (<b>3</b>). Complexes <b>2</b> and <b>3</b> exhibit a fluxional behavior in solution consisting
of proton exchange between μ-NH<sub>2</sub> and μ-NH groups,
assisted by the triflato ligand, as could be inferred from a dynamic
NMR spectroscopy study. Monitoring by NMR spectroscopy the reaction
course of <b>1</b> with MeOTf allows the characterization of
the methylamido intermediate [Ti<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>3</sub>(μ<sub>3</sub>-N)(μ-NH)<sub>2</sub>(μ-NHMe)(OTf)] (<b>4</b>), which readily rearranges
to give <b>3</b> by a proton migration from the NHMe amido group
to the NH imido ligands. The treatment of <b>1</b> with 1 equiv
of Me<sub>3</sub>SiOTf produces the stable ionic complex [Ti<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>3</sub>(μ<sub>3</sub>-N)(μ-NH)<sub>2</sub>(μ-NHSiMe<sub>3</sub>)][OTf] (<b>5</b>) with a disposition of the nitrogen ligands
similar to that of <b>4</b>. Complex <b>5</b> reacts with
1 equiv of [K{N(SiMe<sub>3</sub>)<sub>2</sub>}] at room temperature
to give [Ti<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>3</sub>(μ<sub>3</sub>-N)(μ-N)(μ-NH)(μ-NHSiMe<sub>3</sub>)] (<b>6</b>), which at 85 °C rearranges to the
trimethylsilylimido derivative [Ti<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>3</sub>(μ<sub>3</sub>-N)(μ-NH)<sub>2</sub>(μ-NSiMe<sub>3</sub>)] (<b>7</b>). Treatment of <b>7</b> with [K{N(SiMe<sub>3</sub>)<sub>2</sub>}] affords the potassium
derivative [K{(μ<sub>3</sub>-N)(μ<sub>3</sub>-NH)(μ<sub>3</sub>-NSiMe<sub>3</sub>)Ti<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>3</sub>(μ<sub>3</sub>-N)}] (<b>8</b>), which upon addition of 18-crown-6 leads to the ion pair
[K(18-crown-6)][Ti<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>3</sub>(μ<sub>3</sub>-N)(μ-N)(μ-NH)(μ-NSiMe<sub>3</sub>)] (<b>9</b>). The X-ray crystal structures of <b>2</b>, <b>5</b>, <b>6</b>, and <b>8</b> have
been determined
