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)]
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