Directed Formation of Allene Complexes upon Reaction of Non-heteroatom-Substituted Manganese Alkynyl Carbene Complexes with Nucleophiles

The non-heteroatom-substituted alkynyl carbene Cp′(CO)<sub>2</sub>MnC(Tol)CCPh (<b>1</b>, Cp′ ≡ (η<sup>5</sup>-MeC<sub>5</sub>H<sub>4</sub>)) is first shown to react at low temperature with lithium diorganophosphide LiPR<sub>2</sub> (R = Ph, Cy) to form an anionic species. Subsequent treatment with CF<sub>3</sub>SO<sub>3</sub>H affords the η<sup>4</sup>-vinylketene complex Cp′(CO)<sub>2</sub>Mn[η<sup>4</sup>-{R<sub>2</sub>P(Ph)CCHC(Tol)CO}] (<b>2</b>; <b>2a</b>: R = Ph (70% yield), <b>2b</b>: R = Cy (55% yield)) as the major compound, along with trace amounts of the η<sup>2</sup>-allene complex <i>syn</i>-Cp′(CO)<sub>2</sub>Mn[η<sup>2</sup>-{Ph<sub>2</sub>P(Tol)CCC(Ph)H}] (<i>syn</i>-<b>3a</b>) for R = Ph, or along with the η<sup>2</sup>-allene complex Cp′(CO)<sub>2</sub>Mn[η<sup>2</sup>-{H(Tol)CCC(Ph)PCy<sub>2</sub>}] (<b>4b</b>, 26% yield, 1:2 mixture of <i>syn</i>/<i>anti</i> isomers) for R = Cy. On the other hand, subsequent treatment with NH<sub>4</sub>Cl<sub>aq</sub> affords only η<sup>2</sup>-allene complexes, obtained either as a ca. 1:9 mixture of <i>syn</i>-<b>3a</b> and Cp′(CO)<sub>2</sub>Mn[η<sup>2</sup>-{H(Tol)CCC(Ph)PPh<sub>2</sub>}] (<b>4a</b>) (75% yield) for R = Ph or as a 1:2 mixture of <i>syn</i>- and <i>anti</i>-<b>4b</b> for R = Cy (74% yield). Combined NMR and single-crystal X-ray diffraction studies (for <b>2a</b>, <i>anti</i>-<b>4b</b>, and <i>syn</i>-<b>4b</b>) revealed that both type <b>2</b> and type <b>4</b> species result from a nucleophilic attack of the diorganophosphide onto the remote alkynyl carbon atom in <b>1</b> (C<sub>γ</sub>), whereas type <b>3</b> species results from a nucleophilic attack of the carbene carbon atom (C<sub>α</sub>). Complexes <b>3a</b> and <b>4a</b>,<b>b</b> are prone to undergo a thermal rearrangement to give the η<sup>1</sup>-phosphinoallene complexes Cp′(CO)<sub>2</sub>Mn[η<sup>1</sup>-{Ph<sub>2</sub>P(Tol)CCC(Ph)H}] (<b>5a</b>) and Cp′(CO)<sub>2</sub>Mn[η<sup>1</sup>-{R<sub>2</sub>P(Ph)CCC(Tol)H}] (<b>6</b>; <b>6a</b>: R = Ph, <b>6b</b>: R = Cy), respectively. Reaction of <b>1</b> with <i>p</i>-toluenethiol in the presence of NEt<sub>3</sub> (20%) affords a 1.8:1 mixture of Cp′(CO)<sub>2</sub>Mn[η<sup>2</sup>-{TolS(Tol)CCC(Ph)H}] (<i>syn</i>-<b>11</b>), resulting from a nucleophilic attack at C<sub>α</sub> in <b>1</b>, and Cp′(CO)<sub>2</sub>Mn[η<sup>2</sup>-{H(Tol)CCC(Ph)STol}] (<b>12</b>), resulting from a nucleophilic attack at C<sub>γ</sub>, whereas treatment of <b>1</b> with lithium <i>p</i>-toluenethiolate at –80 °C followed by protonation with NH<sub>4</sub>Cl<sub>aq</sub> gave the same <i>syn</i>-<b>11</b> and <b>12</b> complexes now in a 1:2.3 ratio. Finally, <b>1</b> was found to react with cyclohexanone lithium enolate to afford, upon protonation, the η<sup>2</sup>-allene complex Cp′(CO)<sub>2</sub>Mn[η<sup>2</sup>-{H(Tol)CCC(Ph)CH(CH<sub>2</sub>)<sub>4</sub>C(O)}] (<i>syn</i>-<b>13</b>), resulting from a nucleophilic attack at C<sub>γ</sub> in <b>1</b>. The solid-state structures of <i>syn</i>-<b>11</b> and <i>syn</i>-<b>13</b> are also reported.