Chiral (-)-DIOP ruthenium complexes for asymmetric radical addition and living radical polymerization reactions

A series of ruthenium complexes with chiral phosphane ligands (Ru2Cl4[(-)-DIOP](3) (1), Ru(Ind)Cl[(-)-DIOP] (2), and Ru(Cp-.)Cl[(-)-DIOP] (3), DIOP = 2,3-(isopropylidenedioxy)2,3-dihydroxy-1,4-bis(diphenylphosphanyl)butane) were synthesized, characterized by X-ray crystallography, and employed in asymmetric halogen transfer radical addition and metal-catalyzed living radical polymerization reactions of olefins, such as styrene, methyl acrylate (MA), and methyl methacrylate (MMA). X-ray crystallographic analysis revealed the binuclear structure of I and the mononuclear structures of 2 and 3, which suggests that the chiral environments are established around the ruthenium center. Complexes 1 and 2 induced asymmetry in chiral addition reactions with high chemical yield and relatively high optical yield (10-30% ee) for styrene, MA, and MMA, whereas almost no significant chiral induction was observed with the use of 3. Specifically, the highest ee was obtained for I with the use of styrene (32% ee) whereas the highest ee for 2 was observed with the use of MA (21% ee) and MMA (13% ee). All of the metal complexes induced radical polymerizations of these vinyl monomers in conjunction with a series of haloesters as an initiator. Some systems can control the molecular weights and the terminal groups by the ruthenium-catalyzed reversible activation of the carbon-halogen bond. However, no tacticity control was achieved with all of these DIOP-based ruthenium complexes. (c) Wiley-VCH Verlag GmbH & Co. KGaA.