Synthesis and Reactivity of Titanium Hydrazido Complexes
Supported by Diamido-Ether Ligands
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Abstract
The synthesis and reactivity of titanium
diphenyl hydrazido(2−) complexes supported by the diamido-ether
ligands O(2-C<sub>6</sub>H<sub>4</sub>NSiMe<sub>3</sub>)<sub>2</sub> (N<sub>2</sub><sup>Ar</sup>O) and O(CH<sub>2</sub>CH<sub>2</sub>NSiMe<sub>3</sub>)<sub>2</sub> (N<sub>2</sub>O) are described. Reaction
of Li<sub>2</sub>N<sub>2</sub><sup>Ar</sup>O or Li<sub>2</sub>N<sub>2</sub>O with Ti(NNPh<sub>2</sub>)Cl<sub>2</sub>(py)<sub>3</sub> afforded
Ti(N<sub>2</sub><sup>Ar</sup>O)(NNPh<sub>2</sub>)(py)<sub>2</sub> (<b>14</b>) or Ti(N<sub>2</sub>O)(NNPh<sub>2</sub>)(py)<sub>2</sub> (<b>15</b>) with κ<sup>3</sup>-<i>mer</i>-bound
diamido-ether ligands. Reaction with <sup>t</sup>Bu-bipy (4,4′-di-<i>tert</i>-butyl-2,2′-bipyridyl) or bipy (2,2′-bipyridyl)
gave a switch to κ<sup>3</sup>-<i>fac</i>-coordination.
Reaction of <b>15</b> with Ar′NCO (Ar′ = 2,6-C<sub>6</sub>H<sub>3</sub><sup>i</sup>Pr<sub>2</sub>) gave Ti{O(CH<sub>2</sub>CH<sub>2</sub>NSiMe<sub>3</sub>)(CH<sub>2</sub>CH<sub>2</sub>NC(O)N(SiMe<sub>3</sub>)Ar′)}-{N(NPh<sub>2</sub>)C(O)N(Ar′)},
in which the substrate has inserted into a Ti–N<sub>amide</sub> bond of N<sub>2</sub>O as well as adding to the TiN<sub>α</sub> multiple bond. With Ar′NCS the [2+2] cycloaddition
product Ti(N<sub>2</sub>O){N(NPh<sub>2</sub>)C(NAr′)S}(py)
was obtained, and with Ar′NCSe a mixture was formed including
Ti<sub>2</sub>(N<sub>2</sub>O)<sub>2</sub>(μ-Se)<sub>2</sub>. Both <b>14</b> and <b>15</b> reacted with Ar<sup>Fx</sup>CN (Ar<sup>Fx</sup> = C<sub>6</sub>H<sub>3</sub>F<sub>2</sub> or
C<sub>6</sub>F<sub>5</sub>) to give TiN<sub>α</sub> bond
insertion products of the type Ti(L){NC(Ar<sup>Fx</sup>)NNPh<sub>2</sub>}(py)<sub>2</sub> (L = N<sub>2</sub><sup>Ar</sup>O or N<sub>2</sub>O) containing hydrazonamide ligands. Reaction of <b>14</b> with
XylNC (Xyl = 2,6-C<sub>6</sub>H<sub>3</sub>Me<sub>2</sub>) gave only
the isonitrile σ-adduct Ti(N<sub>2</sub><sup>Ar</sup>O)(NNPh<sub>2</sub>)(py)(CNXyl), whereas <b>15</b> underwent N<sub>α</sub>–N<sub>β</sub> bond reductive cleavage with <sup>t</sup>BuNC or XylNC forming Ti(N<sub>2</sub>O)(NPh<sub>2</sub>)(NCN<sup>t</sup>Bu) or Ti{O(CH<sub>2</sub>CH<sub>2</sub>NSiMe<sub>3</sub>)(CH<sub>2</sub>CH<sub>2</sub>NCN(SiMe<sub>3</sub>)Xyl)}(NPh<sub>2</sub>)(NCNXyl) (<b>27</b>). Both contain metalated carbodiimide
ligands, but in <b>27</b> an additional reaction of XylNC with
the Ti–N<sub>amide</sub> bond of N<sub>2</sub>O has taken place.
Compound <b>15</b> also reacted with a number of internal alkynes
RCCR′ (R = R′ = Me or Ph; R = Me, R′ = aryl)
to give N<sub>α</sub>–N<sub>β</sub> bond reductive
cleavage products of the type Ti{O(CH<sub>2</sub>CH<sub>2</sub>NSiMe<sub>3</sub>)(CH<sub>2</sub>CH<sub>2</sub>NC(R)C(R′)NSiMe<sub>3</sub>}(NPh<sub>2</sub>), again involving a reaction of a Ti–N<sub>amide</sub> bond