Reaction of Tungsten η1-Acetylide Complexes [(η5-C5H5)(NO)(CO)W−C⋮C−R]Li with Iminium Ions

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The reaction of alkynyltungsten complexes [(CO)(NO)(Cp)W−C⋮C−R]Li (R = H, C6H5, C(CH3)3) with differently substituted iminium ions is investigated. Due to the relative high acidity of the hydrogen atoms on the β-carbon atom of the η1-vinylidene complex [(CO)(NO)(Cp)WCCH2)] (1), the parent η1-acetylide complex [(CO)(NO)(Cp)W−C⋮C−H)]- is generated in situ simultaneously with the iminium ion by the reaction of η1-vinylidene complex 1 with an enamine. The reaction of 1 with enamines 2a−e leads to vinylcarbene complexes 3a−e in good yield. The first step of this transformation is a Mannich reaction on the β-carbon atom of alkynyltungsten complexes, generating the expected β-amino-alkylated η1-vinylidene complexes 6. This intermediate reacts further to 3a−e by migration of the hydrogen atom adjacent to the nitrogen atom to the α-carbon atom of the η1-vinylidene moiety. The appearance of a η1-vinylidene complex as an intermediate is supported by NMR experiments, and the postulated retro-imino-ene reaction is con...