5 research outputs found
From lithium ketazides to isomeric silylketazine-rings - imine-enamine tautomerism
No full textDi(tert-butylmethyl)ketazine (I) reacts with n-BuLi in a 1: 1 molar ratio to give a monolithium salt (II). The reaction of 11 with 'Bu2SiF2 in n-hexane leads, even in a 1:1 molar ratio, to the formation of the isomeric five- and four-membered ring compounds I and 2. Compound 1 has an endocyclic imine and an exocyclic enamine unit. The opposite is found for 2. The acyclic mono substitution product, 'Bu2SiFCH2-C'Bu=N-N=C'BuCH3 (III) could not be isolated. It reacts with the lithium ketazide to give 1 or 2. 1 is reformed. The reaction in THF yields only the four-membered ring 2. In a comparable reaction of the lithium ketazide and (H3C)(2)SiF2, the substitution product 3 could be isolated. A possible formation mechanism for 2 includes an intermediate silene IV. Both compounds 1 and 2 react with H3C-OH under cleavage of the endocyclic Si-N-bond to give the addition product 5. The reaction mechanism includes a hydrogen shift from a nitrogen atom to a carbon atom via an imine-enamine tautomerism. In a 2:1 molar ratio, n-BuLi and the di(tert-butylmethyl)-ketazine (I) form the dilithium salt, 6. Compound 6 crystallizes from THF as trimer with four imine and two enamine units. A seven-membered ring (7) isomeric to 1 and 2 is the result of the reaction of 6 with 'Bu2SiF2. Compound 7 contains one imine and one enamine unit in the ring skeleton. The comparable reaction of the (CH3)(3)Si-substituted dilithium-di(tert-butylmethyl)ketazide and 'Bu2SiF2 yields the five-membered ring compound 8 with one endocyclic imine and one exocyclic enamine unit. Quantum chemical calculations of 1, 2, 7 and the intermediate silene IV have been carried out and show a low energy difference between the cyclic silyl-ketazine isomers. (C) 2007 Elsevier B.V. All rights reserved
Synthesis and Cyclisation of Boryl- and Silylhydrazones
No full textReactions of the lithium salts of the tert-butylmethylhydrazones Me(3)C(Me)C=N-NLiR, (R = H, Me, CMe(3)) with fluorosilanes and -boranes in a molar ratio 1: 1 gave the silyl- (1-3, 5, 6) and borylhydrazones (4, 8) Me(3)C(Me)C=N-N(R)R'; 1: R = H. R' = SiFMe(2); 2: R = H, R' = SiMe(2)CMe(3); 3: R = H, R' = SiF(CMe(3))(2); 4: R = H, R' = BFN(SiMe(3))(2); 5: R = Me(3)C, R' = SiF(2)CMe(3); 6: R = Me(3)C, R' = F(2)SiC(SiMe(3))(3); 8: R = Me(3)C, R' = BFN(SiMe(3))(2). The lithiated hydrazone Me(2)C=N-NH(Me) reacted with F(3)SiC(SiMe(3))(3) to give the silylhydrazone Me(2)C=N- NHSiF(2)C(SiMe(3))(3), 7. Because of the fluoro functionality of 1 and 4, the bis-hydrazonylsilane 9 and the bis- and tris-hydrazonylboranes 10 and 11 could be synthesised, (Me(3)C(Me)C=N-NH)(2)R; 9: R = SiMe(2), 10: R = BN(SiMe(3))(2); 11: (Me(3)C(Me)C=N-NH)(3)B. Starting from 2 and its lithium salt, secondary substitutions are possible. Bis(silyl)- and silyl(boryl)hydrazones are formed (12-15): Me(3)C(Me)C=N(R) (SiMe(2)CMe(3)) 12: R = SiFMe(2); 13: R = SiF(CMe(3))(2); 14: R = SiF1CMe3: 15: R = BFN(SiMe3)2. Ring closure occurs in the reaction of dilithiated Me2C=N NHCMe(3) with F(2)Si(CHMe(2))(2). The 1,2-diaza-3-sila-5-cyclopentene 16 is isolated. The fluorofunctional silyl-hydrazones 7, 12, and 13 cyclise in reactions with t-BuLi to give 1,2-diaza-3-sila-5-cyclopentenes 17-20; RN(N=CR' CH(2))R"; 17: R = Me, R' = Me(3)C, R" = SiFC(SiMe(3))(2); 18: R = Me(3)C, R' = SiMe(2)CMe(3), R" = SiMe(2); 19: R = Me(3)C, R' = SiMe(2)CMe(3), R" = Si(CMe(3))(2). A 1,2-diaza-3-bora-5-cyclopentene 20 is the result of the reaction of 8 with t-BuLi: Me(3)CN(N=CCMe(3)-CH(2))BN(SiMe(3))(2). The H-acidic methylene group of the five-membered ring in 20 can be lithiated with n-BuLi and substituted with fluorosilanes. Starting from 16 and 20, the silyl-substituted rings Me(3)CN(N=CMe-CHR)Si(CHMe(2))(2) 21-23 and 25 are obtained; 21: R = SiMe(3); 22: R = SiF(2)C(SiMe(3))(3); 23: R = SiF(3); 25: Me(3)CN[N=CC(Me)(3)CHSiMe(3)]BN(SiMe(3))(2). Using SiF(4) as fluorosilane, the main product is the difluorosilane containing two rings; F(2)Si[CHC(Me)=N-NCMe(3)- Si(CHMe(2))(2)](2). The methine group in 4-position of the silyl-substituted rings is also acidic and reacts with n-BuLi to give lithium salts which react with aminodifluoroboranes giving the ring compounds Me(3)CN[N=C(CMe(3))C(SiMe(2)R)(FBNR'SiMe(3))]SiMe(2) 26-28; 26: R = Me, R' = CMe(3); 27: R = F, R' = CMe(3); 28: R = F, R' = SiMe(3). In contrast to the substitution reactions of fluorosilanes with lithiated rings, an unusual oxidation reaction occurs starting from lithiated Me(3)CN(N=C(CMe(3))CH(2))Si(CHMe(2))(2) and ClSiMe(2)CMe(3) to give 29, in which a C-C bond in 4-position links wo five-membered lines. The disilane (Me(3)CSiMe(2))(2) is formed as a by-product of this reaction. The combination of the N-SiF(2)CMe(3)-substituted hydrazones 5 and 14 with t-BuLi in a molar ratio 1 :2 leads to the colourless, crystalline tricyclic products 30 and 31 which are dimeric 1,2-diaza-3-sila-3,5-cyclopentadienes. The molecular structures of 3, 6, 11, 30, and 31 are reported
Synthesis and Cyclisation of Boryl- and Silylhydrazones
No full textReactions of the lithium salts of the tert-butylmethylhydrazones Me(3)C(Me)C=N-NLiR, (R = H, Me, CMe(3)) with fluorosilanes and -boranes in a molar ratio 1: 1 gave the silyl- (1-3, 5, 6) and borylhydrazones (4, 8) Me(3)C(Me)C=N-N(R)R'; 1: R = H. R' = SiFMe(2); 2: R = H, R' = SiMe(2)CMe(3); 3: R = H, R' = SiF(CMe(3))(2); 4: R = H, R' = BFN(SiMe(3))(2); 5: R = Me(3)C, R' = SiF(2)CMe(3); 6: R = Me(3)C, R' = F(2)SiC(SiMe(3))(3); 8: R = Me(3)C, R' = BFN(SiMe(3))(2). The lithiated hydrazone Me(2)C=N-NH(Me) reacted with F(3)SiC(SiMe(3))(3) to give the silylhydrazone Me(2)C=N- NHSiF(2)C(SiMe(3))(3), 7. Because of the fluoro functionality of 1 and 4, the bis-hydrazonylsilane 9 and the bis- and tris-hydrazonylboranes 10 and 11 could be synthesised, (Me(3)C(Me)C=N-NH)(2)R; 9: R = SiMe(2), 10: R = BN(SiMe(3))(2); 11: (Me(3)C(Me)C=N-NH)(3)B. Starting from 2 and its lithium salt, secondary substitutions are possible. Bis(silyl)- and silyl(boryl)hydrazones are formed (12-15): Me(3)C(Me)C=N(R) (SiMe(2)CMe(3)) 12: R = SiFMe(2); 13: R = SiF(CMe(3))(2); 14: R = SiF1CMe3: 15: R = BFN(SiMe3)2. Ring closure occurs in the reaction of dilithiated Me2C=N NHCMe(3) with F(2)Si(CHMe(2))(2). The 1,2-diaza-3-sila-5-cyclopentene 16 is isolated. The fluorofunctional silyl-hydrazones 7, 12, and 13 cyclise in reactions with t-BuLi to give 1,2-diaza-3-sila-5-cyclopentenes 17-20; RN(N=CR' CH(2))R"; 17: R = Me, R' = Me(3)C, R" = SiFC(SiMe(3))(2); 18: R = Me(3)C, R' = SiMe(2)CMe(3), R" = SiMe(2); 19: R = Me(3)C, R' = SiMe(2)CMe(3), R" = Si(CMe(3))(2). A 1,2-diaza-3-bora-5-cyclopentene 20 is the result of the reaction of 8 with t-BuLi: Me(3)CN(N=CCMe(3)-CH(2))BN(SiMe(3))(2). The H-acidic methylene group of the five-membered ring in 20 can be lithiated with n-BuLi and substituted with fluorosilanes. Starting from 16 and 20, the silyl-substituted rings Me(3)CN(N=CMe-CHR)Si(CHMe(2))(2) 21-23 and 25 are obtained; 21: R = SiMe(3); 22: R = SiF(2)C(SiMe(3))(3); 23: R = SiF(3); 25: Me(3)CN[N=CC(Me)(3)CHSiMe(3)]BN(SiMe(3))(2). Using SiF(4) as fluorosilane, the main product is the difluorosilane containing two rings; F(2)Si[CHC(Me)=N-NCMe(3)- Si(CHMe(2))(2)](2). The methine group in 4-position of the silyl-substituted rings is also acidic and reacts with n-BuLi to give lithium salts which react with aminodifluoroboranes giving the ring compounds Me(3)CN[N=C(CMe(3))C(SiMe(2)R)(FBNR'SiMe(3))]SiMe(2) 26-28; 26: R = Me, R' = CMe(3); 27: R = F, R' = CMe(3); 28: R = F, R' = SiMe(3). In contrast to the substitution reactions of fluorosilanes with lithiated rings, an unusual oxidation reaction occurs starting from lithiated Me(3)CN(N=C(CMe(3))CH(2))Si(CHMe(2))(2) and ClSiMe(2)CMe(3) to give 29, in which a C-C bond in 4-position links wo five-membered lines. The disilane (Me(3)CSiMe(2))(2) is formed as a by-product of this reaction. The combination of the N-SiF(2)CMe(3)-substituted hydrazones 5 and 14 with t-BuLi in a molar ratio 1 :2 leads to the colourless, crystalline tricyclic products 30 and 31 which are dimeric 1,2-diaza-3-sila-3,5-cyclopentadienes. The molecular structures of 3, 6, 11, 30, and 31 are reported
Thermal Isomerisation of a Sileneketazine to a Diazasilacyclopentene: Experimental and Theoretical Studies
No full textLithium-tert-butylmethylhydrazonide II, Me(3)C(Me)C=N-NHLi, reacts with F(2)Si[N(CHMe(2))(2)](2) to give Me(3)C(Me)C=N NH-SiF[N(CHMe(2))(2)](2) 1. The lithium salt of 1, Me(3)C(Me)C=N-N(Li)SiF[N(CHMe(2))(2)](2), 1a, prepared in the reaction of 1 with n-C(4)H(9)Li, is substituted with F(2)BN(SiMe(3))(2) forming Me(3)C(Me)C=N-NBFN(SiMe(3))(2)SiF[N(CHMe(2))(2)](2), 2. Experiments to synthesise the silaketazine, Me(3)C(Me)C=N-N=Si[N(CHMe(2))(2)], III, via LiF-elimination from 1a lead to the intramolecular formation of an N-functional 1,2-diaza-3-silacyclopentene, H(2)C-C(CMe(3))=N-NHSi[N(CHMe(2))(2)](2), 3, which is a structural isomer of III. The NH unit of 3 can be lithiatal with n-C(4)H(9)Li. The lithium salt reacts with F(2)BN(SiMe(3))(2) forming the substituted ring compound 4. The rearrangement of the silaketazine III to the ring compound 3 is described by density functional calculations predicting a three-step reaction mechanism correlated with the experimental data. The structures of 3 and 4 are discussed in detail
