Reactions of alkenes and alkynes with formaldehyde catalyzed by rhodium systems containing phosphine ligands

Abstract

The reaction of alkenes (allyl alcohol, styrene and C6 alkenes) with formaldehyde was efficiently performed by using Rh precatalysts formed in situ by the addition of triphenylphosphine (PPh3), 1,2-bis(diphenylphosphino)ethane (dppe) or 1,1,1-tris(diphenylphosphinomethyl) ethane (triphos) to the complex Rh(acac)(CO)2 at 130ºC in 1,4-dioxane, yielding their corresponding aldehydes; the best catalytic system was Rh(acac)(CO)2/2dppe, which generates the cationic complex [Rh(k2-P,P-dppe)2]+. However, the reaction of phenylacetylene with formaldehyde under the same reaction conditions generated styrene, which was found to be the product of transfer hydrogenation from formaldehyde.