Reactions of Tris(amino)phosphines with Arylsulfonyl Azides:  Product Dependency on Tris(amino)phosphine Structure

The Staudinger reaction of N(CH<sub>2</sub>CH<sub>2</sub>NR)<sub>3</sub>P [R = Me (<b>1</b>), <i><sup>i</sup></i><sup></sup>Pr (<b>2</b>)] with 1 equiv of N<sub>3</sub>SO<sub>2</sub>C<sub>6</sub>H<sub>4</sub>Me-4 gave the ionic phosphazides [R = Me (<b>3</b>), R = <i><sup>i</sup></i><sup></sup>Pr (<b>5a</b>)], and the same reaction of <b>2</b> with N<sub>3</sub>SO<sub>2</sub>C<sub>6</sub>H<sub>2</sub>Me<sub>3</sub>-2,4,6 gave the corresponding aryl sulfinite <b>5b</b>. On the other hand, the reaction of <b>1</b> with 0.5 equiv of N<sub>3</sub>SO<sub>2</sub>Ar (Ar = C<sub>6</sub>H<sub>4</sub>Me-4) furnished the novel ionic phosphazide {[N(CH<sub>2</sub>CH<sub>2</sub>NMe)<sub>3</sub>P]<sub>2</sub>(μ-N<sub>3</sub>)}[SO<sub>2</sub>Ar] (<b>6</b>). Data that shed light on the mechanistic pathway leading to <b>3</b> were obtained by low temperature <sup>31</sup>P NMR spectroscopy. A crystal and molecular structure analysis of the phosphazide sulfonate (<b>4</b>), obtained by atmospheric oxidation of <b>3</b>, indicated an ionic structure, the cationic part of which is stabilized by a transannular P−N bond. A crystal and molecular structure analysis of <b>6</b> also indicated an ionic structure in which the cation features two untransannulated N(CH<sub>2</sub>CH<sub>2</sub>NMe)<sub>3</sub>P cages bridged by an azido group in an η<sup>1</sup>:μ:η<sup>1</sup> fashion. The reaction of P(NMe<sub>2</sub>)<sub>3</sub> with N<sub>3</sub>SO<sub>2</sub>Ar (Ar = C<sub>6</sub>H<sub>4</sub>Me-4) in a 1:0.5 molar ratio furnished {[(Me<sub>2</sub>N)<sub>3</sub>P]<sub>2</sub>(μ-N<sub>3</sub>)}[SO<sub>2</sub>Ar] (<b>11</b>) in quantitative yield. On the other hand, the same reaction involving a 1:1 molar ratio of P(NMe<sub>2</sub>)<sub>3</sub> and N<sub>3</sub>SO<sub>2</sub>Ar produced a mixture of <b>11</b>, [(Me<sub>2</sub>N)<sub>3</sub>PN<sub>3</sub>][SO<sub>2</sub>Ar] (<b>12</b>), and the iminophosphorane (Me<sub>2</sub>N)<sub>3</sub>PNSO<sub>2</sub>Ar (<b>10</b>). In contrast, the bicyclic tris(amino)phosphines MeC(CH<sub>2</sub>NMe)<sub>3</sub>P (<b>7</b>) and OP(CH<sub>2</sub>NMe)<sub>3</sub>P (<b>8</b>) reacted with N<sub>3</sub>SO<sub>2</sub>Ar (Ar = C<sub>6</sub>H<sub>4</sub>Me-4) to give the iminophosphorane MeC(CH<sub>2</sub>NMe)<sub>3</sub>PNSO<sub>2</sub>Ar (<b>14</b>) (structured by X-ray means) and OP(CH<sub>2</sub>NMe)<sub>3</sub>PNSO<sub>2</sub>Ar (<b>16</b>) via the intermediate phosphazides MeC(CH<sub>2</sub>NMe)<sub>3</sub>PN<sub>3</sub>SO<sub>2</sub>Ar (<b>13</b>) and OP(CH<sub>2</sub>NMe)<sub>3</sub>PN<sub>3</sub>SO<sub>2</sub>Ar (<b>15</b>), respectively. The variety of products obtained from the reactions of arylsulfonyl azides with proazaphosphatranes (<b>1</b> and <b>2</b>), acyclic P(NMe<sub>2</sub>)<sub>3</sub>, bicyclic tris(amino)phosphines <b>7</b> and <b>8</b> are rationalized in terms of steric and basicity variations among the phosphorus reagents.