Synthese und Cyclisierung von Boryl- und Silylhydrazonen / Synthesis and Cyclisation of Boryl- and Silylhydrazones

Abstract

Reactions of the lithium salts of the tert-butylmethylhydrazones Me3C(Me)C=N-NLiR, (R = H, Me, CMe3) with fluorosilanes and -boranes in a molar ratio 1 : 1 gave the silyl- (1 - 3, 5, 6) and borylhydrazones (4, 8) Me3 C(Me)C=N-N(R)Rʹ; 1: R = H, Rʹ = SiFMe2 ; 2: R = H, Rʹ = SiMe2CMe3; 3: R = H, Rʹ = SiF(CMe3 )2; 4: R = H, Rʹ = BFN(SiMe3)2; 5: R = Me3 C, Rʹ = SiF2CMe3; 6: R = Me3C, Rʹ = F2SiC(SiMe3)3; 8: R = Me3C, Rʹ = BFN(SiMe3)2. The lithiated hydrazone Me2C=N-NH(Me) reacted with F3SiC(SiMe3)3 to give the silylhydrazone Me2C=N- NHSiF2C(SiMe3)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, (Me3C(Me)C=N-NH)2R; 9: R = SiMe2 , 10: R = BN(SiMe3)2; 11: (Me3C(Me)C=N-NH)3B. Starting from 2 and its lithium salt, secondary substitutions are possible. Bis(silyl)- and silyl(boryl)hydrazones are formed (12 - 15); Me3C(Me)C=N(R) (SiMe2CMe3) 12: R = SiFMe2; 13: R = SiF(CMe3)2; 14: R = SiF2CMe3; 15: R = BFN(SiMe3 )2. Ring closure occurs in the reaction of dilithiated Me2C=N- NHCMe3 with F2Si(CHMe2)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=CRʹ-CH2)Rʺ; 17: R =Me,Rʹ = Me3C, Rʺ = SiFC(SiMe3)3; 18: R = Me3C, Rʹ = SiMe2CMe3, Rʺ = SiMe2; 19: R =Me3C, Rʹ = SiMe2CMe3, Rʺ = Si(CMe3)2. A 1,2- diaza-3-bora-5-cyclopentene 20 is the result of the reaction of 8 with t-BuLi: Me3CN(N=CCMe3- CH2)BN(SiMe3)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 Me3CN(N=CMe-CHR)Si(CHMe2)2 21 - 23 and 25 are obtained; 21: R = SiMe3; 22: R = SiF2C(SiMe3)3; 23: R = SiF3; 25: Me3CN[N=CC(Me)3CHSiMe3]BN(SiMe3)2. Using SiF4 as fluorosilane, the main product is the difluorosilane containing two rings; F2Si[CHC(Me)=N-NCMe3- Si(CHMe2)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 Me3CN[N=C(CMe3)C(SiMe2R)(FBNRʹ SiMe3)]SiMe2 26 - 28; 26: R = Me, Rʹ = CMe3; 27: R = F, Rʹ = CMe3 ; 28: R = F, Rʹ = SiMe3. In contrast to the substitution reactions of fluorosilanes with lithiated rings, an unusual oxidation reaction occurs starting from lithiated Me3CN(N=C(CMe3)CH2)Si(CHMe2)2 and ClSiMe2CMe3 to give 29, in which a C-C bond in 4- position links two five-membered rings. The disilane (Me3CSiMe2)2 is formed as a by-product of this reaction. The combination of the N-SiF2CMe3-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.