[58659-24-8] · C44H86CuP3 · Phenylethynylcopper(I)-Tris(tributylphosphine) · (MW 771.76)
Alternate Name: copper(I) phenylacetylide-tributylphosphine.
Physical Data: prepared in situ.
Solubility: sol THF, pyridine, DMF.
Preparative Method: metalation of phenylacetylene with Copper(I) t-Butoxide followed by addition of Tri-n-butylphosphine in THF.2
Handling, Storage, and Precautions: all copper(I) acetylides are potentially explosive when dry. Use in a fume hood.
When Phenylethynylcopper(I) is treated with tributylphosphine in THF and heated to 80 °C, addition to CO2 can be effected giving, on esterification, methyl phenylpropiolate in moderate yield (eq 1).2 In the absence of tributylphosphine, the addition does not take place, suggesting that the tributylphosphine may help solubilize and increase the effective nucleophilicity of the copper salt, presumably by dissociating its polymeric form.4,5 A similar effect is observed with the corresponding t-Butyl Isocyanide complex, where the yield of carboxylated product increases to 71%.2
When copper phenylpropiolate is heated to 35 °C in DMF, irreversible decarboxylation ensues, giving copper phenylacetylide. However, when tributylphosphine is added, the decarboxylation is not quantitative, and instead becomes reversible (eq 2).3 The equilibrium that exists at room temperature can be demonstrated by addition of Iodomethane as both methyl phenylpropiolate and methylphenylacetylene are isolated. The rate of carboxylation of copper phenylacetylide can be increased by elevating the number of equivalents of tributylphosphine from 1 to 3, but not beyond this, suggesting the species to be coordinatively saturated with three phosphine ligands attached.
Graham B. Jones & Brant J. Chapman
Clemson University, SC, USA