Reaction of cobalt tetracarbonyl hydride with phenylacetylene

In C6H6 or hexane at room temperature, under an atmosphere of CO, excess HC o(CO)(4) reacts with phenylacetylene to give ethylbenzene and 2-phenylpropa nal, the same products that result from the similar reaction of styrene. Th is and other evidence show that styrene is an intermediate. However, when p henylacetylene is in large excess, neither ethylbenzene, 2-phenylpropanal, nor styrene is formed in more than trace quantity. Instead, a compound is f ormed whose spectral properties suggest that it is an alkyl- or acylcobalt carbonyl containing a 1-phenylethenyl group. This compound reacts with HCo( CO)(4) to give styrene. CIDNP suggests that the reaction of phenylacetylene with HCo(CO)(4) proceeds through radical pairs [1-phenylethenyl Co(CO)(4)] . (C) 1999 Elsevier Science S.A. All rights reserved.