Abstract1,2‐Diaza‐3‐silacyclopent‐5‐ene – Synthesis and ReactionsThe dilithium salt of bis(tert‐butyl‐trimethylsilylmethylen)ketazine (1) forms an imine‐enamine salt. 1 reacts with halosilanes in a molar ratio of 1:1 to give 1,2‐diaza‐3‐silacyclopent‐5‐enes. Me3SiCH=CCMe3 [N(SiR,R′)‐N=C‐C]HSiMe3 (2‐7). (2: R,R′ = Cl; 3: R = CH3, R′ = Ph; 4: R = F, R′ = CMe3; 5: R = F, R′ = Ph; 6: R = F, R′ = N(SiMe3)2; 7: R = F, R′ = N(CMe3)SiMe3). In the reaction of 1 with tetrafluorosilane the spirocyclus 8 is isolated. The five‐membered ring compounds 2‐7 and compound 9 substituted on the silicon‐fluoro‐ and (tert‐butyltrimethylsilyl) are acid at the C(4)‐atom and therefore can be lithiated. Experiments to prepare lithium salts of 4 with MeLi, n‐BuLi and PhLi gave LiF and the substitution‐products 10‐12. 9 forms a lithium salt which reacts with ClSiMe3 to give LiCl and the SiMe3 ring system (13) substituted at the C(4)‐atom. The ring compounds 3‐7 and 10‐12 form isomers, the formation is discussed. Results of the crystal structure and analyses of 8, 10, 12, and 13 are presented.

The results of quantum chemical calculations on lithium ketazides suggest mainly four isomeric structures with different modes of lithium coordination (A-D). A monolithium ketazide thf-adduct (1) was isolated supporting the results of the quantum chemical calculations. In reactions of the lithiated di(tert-butyl-methyl)ketazine with BCl3 and Cl2BPh, 1,2-aza-azonia-3-borata-cyclopent-5-enes (2, 3) were isolated. Substitution of a chlorine atom of 2 and 3 with t-BuLi leads to the formation of derivatives 4 and 5. HCl elimination from 2 with Et3N gives - via a diazaboracyclopentene (6) - a bicyclus 7. In the reaction of the dilithiated ketazine with F2BN(SiMe3)2, the diaza-boracyclopentene 8 is obtained while with Cl4Si, F3SiN(SiMe3)2, and Cl2SiMe2 the diazasilacyclopentenes 9 - 11 are generated. SiF4 reacts with the dilithium ketazide to give a spirocyclus (12). The monolithium ketazide and Cl2SiMe2 react at 30 °C to give a four-membered ring isomer of the substitution product which is formed via a 1,3-chlorine shift from silicon to carbon (13). A tetrameric silanolate was isolated as a by-product in this reaction. It gives evidence for the structure of lithium ketazide A. Crystal structures of 5, 7, 10, and 14 are reported.

C-lithiated bis(tert-butyl-methyl)ketazine reacts with halosilanes to give the monosilylketazines, t-Bu(Me)C=N-N=C(t-Bu)-CH2R, (1 - 7). (1: R = SiMe3; 2: R = SiClMe2; 3: R = SiClMePh; 4: R = Cl2SiPh; 5: R = SiCl3; 6: R = SiMe2Ph; 7: R = F2SiN(t-Bu)SiMe3). The bis(ketazinyl)silanes [t-Bu(RCH2) C = N-N = CCH2-t-Bu]2 SiMe2 8, 9 are formed in the reaction of the same lithiated ketazine or 1 with Cl2SiMe2 in a molar ratio of 2 : 1, (8: R = H; 9: R = SiMe3). Di(silyl)ketazines (10, 11) are obtained from lithiated 1 and ClSiMe2Ph in a molar ratio of 1:1 and from dilithiated ketazine with F2Si(i-Pr)2 in a molar ratio of 1 : 2 [t-Bu(RH2C)C=N-N=C(CH2R’)t-Bu, 10: R = SiMe3, R’ = SiMe2Ph; 11: R,R’ = FSi(i-Pr)2]. The tris(ketazinyl)fluorosilane 12 is isolated from the reaction of SiF4 with the lithiated ketazine. 2-Alkenyl-1,2-diaza-3-sila-5-cyclopentenes, t-Bu(CH2)C- [N-SiR,R’-CH2-C(t-Bu)=N], (14 - 17) are obtained from the dilithiated ketazine and Hal2SiRR’. (14: Hal = Cl, R = Me, R’ = Ph; 15: Hal = F,R = t-Bu, R’ = Ph; 16: Hal = F,R = t-Bu, R’ = F; 17: Hal = F, R = N(t-Bu)SiMe3, R’ = F). X-ray structure analyses are presented for 7, 11, and 17.

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