Synthesis and Reactions of a Cyclopentadienyl-Amidinate Titanium <i>tert-</i>Butoxyimido Compound

We report the first detailed reactivity study of a group 4 alkoxyimido complex, namely Cp*Ti­{PhC­(NⁱPr)₂}­(NO^tBu) (<b>19</b>), with heterocumulenes, aldehydes, ketones, organic nitriles, Ar^F₅CCH, and B­(Ar^F₅)₃ (Ar^F₅ = C₆F₅). Compound <b>19</b> was synthesized via imide/alkoxyamine exchange from Cp*Ti­{PhC­(NⁱPr)₂}­(N^tBu) and ^tBuONH₂. Reaction of <b>19</b> with CS₂ and Ar′NCO (Ar′ = 2,6-C₆H₃ⁱPr₂) gave the [2 + 2] cycloaddition products Cp*Ti­{PhC­(NⁱPr)₂}­{SC­(S)­N­(O^tBu)} and Cp*Ti­{PhC­(NⁱPr)₂}­{N­(O^tBu)­C­(NAr′)­O}, respectively, whereas reaction with 2 equiv of TolNCO afforded Cp*Ti­{PhC­(NⁱPr)₂}­{OC­(NTol)­N­(Tol)­C­(NO^tBu)­O} following a sequence of cycloaddition–extrusion and cycloaddition–insertion steps. Net NO^tBu group transfer was observed with both ^tBuNCO and PhC­(O)­R, yielding the oxo-bridged dimer [Cp*Ti­{PhC­(NⁱPr)₂}­(μ-O)]₂ and either the alkoxycarbodiimide ^tBuNCNO^tBu or the oxime ethers PhC­(NO^tBu)­R (R = H (<b>25a</b>), Me (<b>25b</b>), Ph (<b>25c</b>)). DFT studies showed that in the reaction with PhC­(O)­R (R = H, Me) the product distribution between the <i>syn</i> and <i>anti</i> isomers of PhC­(NO^tBu)­R was under kinetic control. Reaction of <b>19</b> with ArCN gave the TiN_α insertion products Cp*Ti­{PhC­(NⁱPr)₂}­{NC­(Ar)­NO^tBu} (Ar = Ph (<b>28</b>), 2,6-C₆H₃F₂ (<b>27</b>), Ar^F₅ (<b>26</b>)) containing <i>tert</i>-butoxybenzimidamide ligands. Reaction of <b>19</b> or <b>26</b> with an excess of Ar^F₅CN gave Cp*Ti­{PhC­(NⁱPr)₂}­{NC­(Ar^F₅)­NC­(Ar^F₅)­N­(C­{Ar^F₅}­NO^tBu)} (<b>29</b>) following net head-to-tail coupling of 2 equiv of Ar^F₅CN across the TiN_α bond of <b>26</b>. Reductive N_α–O_β bond cleavage was observed with Ar^F₅CCH, forming Cp*Ti­(O^tBu)­{NC­(Ar^F₅)­C­(H)­N­(ⁱPr)­C­(Ph)­N­(ⁱPr)} (<b>30</b>). Addition of 2 equiv of [Et₃NH]­[BPh₄] to <b>19</b> in THF-<i>d</i>₈ resulted in protonolysis of the amidinate ligand, forming [PhC­(NHⁱPr)₂]­[BPh₄] and the cationic alkoxyimido complex [Cp*Ti­(NO^tBu)­(THF-<i>d</i>₈)₂]⁺. In contrast, reaction with B­(Ar^F₅)₃ resulted in elimination of isobutene and formation of Cp*Ti­{PhC­(NⁱPr)₂}­{η²-ON­(H)­B­(Ar^F₅)₃}