Cyclisierung von Di(tert-butyl-methyl)ketazin zu 1,2-Diaza-3-bora- und 1,2-Diaza-3-sila-cyclopent-5-enen / Cyclization of Di(tert-butyl-methyl)ketazine to 1,2-Diaza-3-bora- and 1,2-Diaza-3-sila-cyclopent-5-enes

Abstract

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.

From lithium ketazides to isomeric silylketazine-rings – imine-enamine tautomerism

“…Unfortunately, we did not succeed in preparing single crystals of 1 or 2 suitable for a crystal structure analysis, but the isomers 1 and 2 are definitely identified. The NMR data of 1 are comparable with those of known 1,2-diaza-3-silacyclopentenes [5].…”

“…In this case the five-membered ring [5] is formed in a second step, Complex 1 has an endocyclic imine and an exocyclic enamine unit, whereas the opposite is true for 2. The substitution product III, primarily formed, has two types of acidic H-atoms, the CH 2 Si-and the CH 3 C-group.…”

“…Bulky substituents are able to prevent this isomerization [4]. Due to quantum chemical calculations [5], four stable structures of the monolithium salt and one structure of the dilithium salt of I exist and give an indication of an imine-enamine tautomerism in ketazides.…”

“…Crystals, isolated from THF, of the lithiated di(tertbutylmethyl)ketazine (I) were characterized as the dimer II [5], which contains two imine-and two enamine units, …”

“…Recently represented reactions of lithiated ketazines with haloboranes [5,6], -silanes [7,8], and -phosphanes [6] yielded surprising results, e.g., the backbone of the ketimine structure is maintained in reactions with halotriorganylsilanes [7,8]. On the other hand, half an imine-enamine isomerization occurs in reactions with dihaloboranes, -silanes, and -phosphanes [4,8].…”