N–P Bond Cleavage Induced Ring Formation of Cyclosilazanes from Reactions of Aryl(phosphanyl)aminotrichlorosilanes with Lithium Alkynyls

The aryl­(silyl)­aminotrichlorosilane 2,6-<i>i</i>Pr₂C₆H₃N­(SiMe₂Ph)­SiCl₃ (<b>1</b>) and aryl­(phosphanyl)­aminotrichlorosilane ArN­(PPh₂)­SiCl₃ (Ar = 2,6-<i>i</i>Pr₂C₆H₃ (<b>2</b>), 4-MeC₆H₄ (<b>3</b>), 2,4,6-Me₃C₆H₂ (<b>4</b>)) were prepared and utilized for investigation in reactions with freshly prepared lithium alkynyls. Reaction of <b>1</b> with PhCCLi resulted in the compounds PhMe₂SiCCPh and 2,6-<i>i</i>Pr₂C₆H₃N­[Li­(THF)₃]­Si­(CCPh)₃ (<b>5</b>), while <b>2</b> reacted with R′CCLi to produce the compounds Ph₂PCCR′ and [2,6-<i>i</i>Pr₂C₆H₃NSi­(CCR′)₂]₂ (R′ = Ph (<b>6</b>), <i>t</i>Bu (<b>7</b>), CH₂CH₂Ph (<b>8</b>)). Reaction of <b>3</b> with PhCCLi led to the formation of Ph₂PCCPh and [4-MeC₆H₄NSi­(CCPh)₂]₃ (<b>9a</b>) as a major product and {4-MeC₆H₄NSi­(CCPh)­[N­(4-MeC₆H₄)­Si­(CCPh)₃]}₂ (<b>9b</b>) as a minor product. When <b>4</b> was reacted with PhCCLi, [2,4,6-Me₃C₆H₂NSi­(CCPh)₂]₂ (<b>10a</b>) was isolated as the major product while [(2,4,6-Me₃C₆H₂)₃N₃Si₂(CCPh)₄Li­(THF)]⁻[Li­(THF)₄]⁺ (<b>10b</b>) was the minor product. The formation of Ph₂PCCPh was also detected. All reported compounds were characterized by multinuclear NMR (¹H, ¹³C, ²⁹Si, and/or ³¹P) and/or IR spectroscopy, and compounds <b>2</b>, <b>5</b>–<b>8</b>, <b>9a</b>, and <b>10b</b> were further distinguished by single-crystal X-ray crystallography. These results exhibit a route to the Si₂N₂- or Si₃N₃-based cyclosilazanes <b>6</b>–<b>8</b>, <b>9a</b>, <b>9b</b>, and <b>10a</b> via the N–P bond cleavage of the aryl­(phosphanyl)­aminotrichlorosilanes during multiple metathesis reactions