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

The aryl­(silyl)­aminotrichlorosilane 2,6-iPr2C6H3N­(SiMe2Ph)­SiCl3 (1) and aryl­(phosphanyl)­aminotrichlorosilane ArN­(PPh2)­SiCl3 (Ar = 2,6-iPr2C6H3 (2), 4-MeC6H4 (3), 2,4,6-Me3C6H2 (4)) were prepared and utilized for investigation in reactions with freshly prepared lithium alkynyls. Reaction of 1 with PhCCLi resulted in the compounds PhMe2SiCCPh and 2,6-iPr2C6H3N­[Li­(THF)3]­Si­(CCPh)3 (5), while 2 reacted with R′CCLi to produce the compounds Ph2PCCR′ and [2,6-iPr2C6H3NSi­(CCR′)2]2 (R′ = Ph (6), tBu (7), CH2CH2Ph (8)). Reaction of 3 with PhCCLi led to the formation of Ph2PCCPh and [4-MeC6H4NSi­(CCPh)2]3 (9a) as a major product and {4-MeC6H4NSi­(CCPh)­[N­(4-MeC6H4)­Si­(CCPh)3]}2 (9b) as a minor product. When 4 was reacted with PhCCLi, [2,4,6-Me3C6H2NSi­(CCPh)2]2 (10a) was isolated as the major product while [(2,4,6-Me3C6H2)3N3Si2(CCPh)4Li­(THF)]−[Li­(THF)4]+ (10b) 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 2, 5–8, 9a, and 10b were further distinguished by single-crystal X-ray crystallography. These results exhibit a route to the Si2N2- or Si3N3-based cyclosilazanes 6–8, 9a, 9b, and 10a via the N–P bond cleavage of the aryl­(phosphanyl)­aminotrichlorosilanes during multiple metathesis reactions.