The Reaction of Ethylenediamine with 1,4-Bis(trimethylsilyl)butadiyne and the Role of Water: A Qualitative Method for the Determination of Water Impurities in Ethylenediamine

Alkenylation of [Ge-9](4-) and formation of the vinylated species [Ge-9(CH=CH2)(n)]((4-n)-) proceed only in ethylenediamine (en) as a solvent. Variation of the alkyne leads to coupling products between the alkyne and en. Herein, we investigated the coupling reactions between 1,4-bis(trimethylsilyl)butadiyne and en and showed that a water impurity in en plays a decisive role in the outcome of the reaction. NMR spectroscopic investigations revealed that 1-trimethylsilyl-7-amino-5-aza-hepta-3-en-1-yne is formed by addition of en at 1,4-bis(trimethylsilyl)butadiyne. Addition of another amino-functionality of en giving both the cyclization product and 1,9-di-amino-4-methyl-3,7-di-aza-nonadiene is only possible in presence of water. 1,9-Di-amino-4-methyl-3,7-di-aza-nonadiene is also formed by the reaction of deprotonated en with 1-trimethylsilyl-7-amino-5-aza-hepta-3-en-1-yne. Based on these results, we developed a simple method to detect water in en, supported by H-1 NMR spectroscopy. The finding that 1,9-di-amino-4-methyl-3,7-di-aza-nonadiene is also formed by reaction of 1-trimethylsilyl-7-amino-5-aza-hepta-3-en-1-yne with deprotonated en was exploited to indirectly proof the deprotonation of en upon the nucleophilic reaction of [Ge-9](4-) with alkynes in the solvent en.