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2.6.2.3 Method 3: By Stoichiometric Alkyne Metathesis

DOI: 10.1055/sos-SD-002-00315

Poli, R.; Smith, K. M.Science of Synthesis, (20032299.

A variety of alk­oxocarbyne complexes may be obtained from a preexisting carbyne complex and an al­kyne by a metathesis process (Scheme 16). This exchange takes place via a metalla­cy­clo­butadiene intermediate 44, which has been observed or isolated for the corresponding aryl­oxo and fluorinated alk­oxo systems. Such intermediates have greater stability for the tungsten systems.[‌67‌] This procedure is synthetically useful for symmetrical, unsymmetrical, and terminal al­kynes. Like the reactions ex­amined in Section 2.6.2.2, these are also sensitive to steric factors.[‌67‌,‌74‌] Electronic factors are also important, however, fluo­ro­alk­ox­o complexes reacting more readily than the corresponding alk­oxo complexes without fluorine substituents. Terminal acet­y­lenes also react with bulkier carbyne complexes, but the reaction is often complicated and other products (e.g., deprotonated metalla­cy­clo­butadiene derivatives) may be obtained, limiting the synthetic utility.[‌67‌]

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