Chiral (–)‐DIOP Ruthenium Complexes for Asymmetric Radical Addition and Living Radical Polymerization Reactions

Abstract

AbstractA 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‐l,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 1 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 1 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)