Oxidative Carbonylation of Unsaturated Substrates Promoted by Aryl [Alfa]-Diimine Pd(II) Complexes

The aryl -diimine compounds are well-known ligands used in organometallic chemistry. They might be employed together with transition metals to attain a variety of complexes able to catalyze a wide range of reactions. Although DAB ligands are stable, accessible, and efficient as ligands to palladium, they have not been used so far in the oxidative carbonylation. Due to the know-how of the group, in which I worked as a PhD student, in the CO/styrene copolymerization reaction promoted by aryl -diimine-Pd(II) complexes, I began a deep investigation on the use of these proficient ligands in the palladium-catalyzed oxidative carbonylation. Bis-alkoxycarbonylation reactions of aliphatic and aromatic olefins were successfully studied. By using the new aryl -diimine ligand with extended aromatic rings, Pd(TFA)2 and benzoquinone as the oxidant, esters of succinic acids were obtained with excellent yields and complete selectivity. The optimized reaction conditions could be successfully applied on alkenes in the presence of different alcohols as nucleophiles, including the sterically hindered i-PrOH. Moreover, the oxidative carbonylation allowed a complete conversion of cis and trans--methylstyrene into two biscarbonylated products with total diastereoselectivity. On the other hand, the mono-alkoxycarbonylation reaction of variously substituted phenylacetylenes was selectively achieved by means of a sterically hindered Pd(II) complex bearing an aryl -diimine as the ligand, formed in situ from (PhCN)2PdCl2 and AgOTf. For the first time, the same catalytic system was able to covert 1,2-substituted aliphatic and aromatic alkynes into a mixture of maleic acid esters and maleic acid cyclic derivatives.