Regioisomerism in coordination chemistry: oxidative addition of a bifunctional ligand to palladium, stabilized with 1,2-bis(diphenylphosphino)ethane.

A unique phenomenon of regioisomerism in coordination chemistry was discovered: the reaction of a sterically hindered o-quinone annelated with a dithiete ring with Pddba in the presence of 1,2-bis(diphenylphosphino)ethane (dppe) gave a mixture of two regioisomers: catecholate 3Cat and dithiolate 3Dit. Both isomers were isolated in crystalline form and characterized by NMR, IR and X-ray diffractometry studies. DFT calculations reveal that the 3Dit species is more thermodynamically stable than the isomer 3Cat. Isomerization of 3Cat to 3Dit in solution was observed.