A NEW CYCLOPENTADIENE AND ITS USE AS A LIGAND FOR CATALYTICALLY ACTIVE RHODIUM COMPLEXES

Dimethyl 4-methoxycarbonylcyclopenta-1,3-diene-1,2-diacetate has been prepared from benzyl methyl malonate by reaction with 2-propynyl bromide, followed by palladium-catalyzed ring-forming oxidative carbonylation and by elimination of the benzyloxycarbonyl group and double bonds isomerization. The anion of the diacetate readily reacts with transition metal complexes, to give the corresponding cyclopentadienyl derivatives. We describe here some complexes, obtained from [{RhCl(L)(2)}(2)] [L = CO, C2H4, or 1,5-cyclooctadiene (COD)], which are efficient catalysts for the alkyne-nitrile co-cyclization to pyridines and for the hydroformylation of styrene and 1-hexene.