Cationic Aluminum Alkyl Complexes Incorporating Aminotroponiminate Ligands (1998)

The synthesis, structures, and reactivity of cationic aluminum complexes containing the <i>N,N</i><i>‘</i>-diisopropylaminotroponiminate ligand (<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI<sup>-</sup>) are described. The reaction of (<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)AlR<sub>2</sub> (<b>1a</b>−<b>e</b>,<b>g</b>,<b>h</b>;\nR = H (<b>a</b>), Me (<b>b</b>), Et (<b>c</b>), Pr (<b>d</b>), <i><sup>i</sup></i><sup></sup>Bu (<b>e</b>), Cy (<b>g</b>), CH<sub>2</sub>Ph (<b>h</b>)) with [Ph<sub>3</sub>C][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] yields (<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)AlR<sup>+</sup>\nspecies whose fate depends on the properties of the R ligand. <b>1a</b> and <b>1b</b> react with 0.5 equiv of [Ph<sub>3</sub>C][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] to produce dinuclear monocationic complexes [{(<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)AlR}<sub>2</sub>(μ-R)][(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] (<b>2a</b>,<b>b</b>). The cation\nof <b>2b</b> contains two (<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)AlMe<sup>+</sup> units linked by an almost linear Al−Me−Al bridge; <b>2a</b> is presumed to\nhave an analogous structure. <b>2b</b> does not react further with [Ph<sub>3</sub>C][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>]. However, <b>1a</b> reacts with 1 equiv\nof [Ph<sub>3</sub>C][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] to afford (<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)Al(C<sub>6</sub>F<sub>5</sub>)(μ-H)<sub>2</sub>B(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> (<b>3</b>) and other products, presumably via C<sub>6</sub>F<sub>5</sub><sup>-</sup>\ntransfer and ligand redistribution of a [(<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)AlH][(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] intermediate. <b>1c</b>−<b>e</b> react with 1 equiv of [Ph<sub>3</sub>C][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] to yield stable base-free [(<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)AlR][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] complexes (<b>4c</b>−<b>e</b>). <b>4c</b> crystallizes from\nchlorobenzene as <b>4c</b>(ClPh)·0.5PhCl, which has been characterized by X-ray crystallography. In the solid state\nthe PhCl ligand of <b>4c</b>(ClPh) is coordinated by a dative PhCl−Al bond and an ATI/Ph π-stacking interaction.\n<b>1g</b>,<b>h</b> react with [Ph<sub>3</sub>C][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] to yield (<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)Al(R)(C<sub>6</sub>F<sub>5</sub>) (<b>5g</b>,<b>h</b>) via C<sub>6</sub>F<sub>5</sub><sup>-</sup> transfer of [(<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)AlR][(BC<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] intermediates. <b>1c</b>,<b>h</b> react with B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> to yield (<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)Al(R)(C<sub>6</sub>F<sub>5</sub>) (<b>5c</b>,<b>h</b>) via C<sub>6</sub>F<sub>5</sub><sup>-</sup> transfer of\n[(<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)AlR][RB(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>] intermediates. The reaction of <b>4c</b>−<b>e</b> with MeCN or acetone yields [(<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)Al(R)(L)][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] adducts (L = MeCN (<b>8c</b>−<b>e</b>), acetone (<b>9c</b>−<b>e</b>)), which undergo associative intermolecular\nL exchange. <b>9c</b>−<b>e </b>undergo slow β-H transfer to afford the dinuclear dicationic alkoxide complex [{(<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)Al(μ-O<i><sup>i</sup></i><sup></sup>Pr)}<sub>2</sub>][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>]<sub>2</sub> (<b>10</b>) and the corresponding olefin. <b>4c</b>−<b>e</b> catalyze the head-to-tail dimerization\nof <i>tert</i>-butyl acetylene by an insertion/σ-bond metathesis mechanism involving [(<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)Al(C⋮C<i><sup>t</sup></i><sup></sup>Bu)][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] (<b>13</b>) and [(<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)Al(CHC(<i><sup>t</sup></i><sup></sup>Bu)C⋮C<i><sup>t</sup></i><sup></sup>Bu)][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] (<b>14</b>) intermediates. <b>13</b> crystallizes as the\ndinuclear dicationic complex [{(<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)Al(μ-C⋮C<i><sup>t</sup></i><sup></sup>Bu)}<sub>2</sub>][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>]<sub>2</sub>·5PhCl from chlorobenzene. <b>4e</b> catalyzes\nthe polymerization of propylene oxide and <b>2a</b> catalyzes the polymerization of methyl methacrylate. <b>4c</b>,<b>e</b> react\nwith ethylene-<i>d</i><sub>4</sub> by β-H transfer to yield [(<i><sup>i</sup></i><sup></sup>Pr<sub>2</sub>-ATI)AlCD<sub>2</sub>CD<sub>2</sub>H][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] initially. Polyethylene is also\nproduced in these reactions by an unidentified active species.