295357-81-2Relevant academic research and scientific papers
Efficient metathesis of terminal alkynes
Haberlag, Birte,Freytag, Matthias,Daniliuc, Constantin G.,Jones, Peter G.,Tamm, Matthias
, p. 13019 - 13022 (2012)
Despite remarkable recent advances in the development of well-defined homogeneous catalysts for alkyne metathesis with regard to their activity, functional-group tolerance, and required reaction temperature,[1] this method is largely limited to the use of internal alkynes, RC≡CR' (R=alkyl, aryl; R'≠6 H). Commonly, methyl-capped alkynes (R'=Me) are employed,[2] resulting in the formation of RC≡CR and volatile 2-butyne, which can be removed by evaporation (b.p.=278C) or adsorption on molecular sieves (MS 5 A)[3,4] to drive these equilibrium reactions to completion.[5] In contrast, terminal alkyne metathesis (TAM) has rarely been achieved,[2c, 6] since many high-oxidation-state, Schrock-type alkylidyne complexes are known to degrade in the presence of terminal alkyne substrates. For most cases, it was suggested that deactivation occurs through deprotonation of intermediate metallacyclobutadiene species with formation of " deprotiometallacycles" (DMCs),[7, 8] which can be stabilized and made isolable by addition of donor (Don) molecules (Scheme 1).[9] These DMCs can be regarded as containing a chelating alkynylalkylidene ligand, and it was proposed that such carbene complexes are responsible for the observed high activity towards the polymerization of terminal alkynes.[8b, 10] In addition, dimerization of methylidyne complexes [HC-MX3] and formation of dimetallatetrahedrane species [X3M- (m-C2H2)MX3] should be considered as an alternative deactivation path.
