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A square-planar Co4 amide cluster, Co4{N(SiMe3)2}4 (2), and an octahedral Co6 hydride cluster, Co6H8(PiPr3)6 (4), were obtained from metathesis-type amide to hydride exchange reactions of a CoII amide complex with pinacolborane (HBpin) in the absence/presence of PiPr3. The crystal structure of 4 revealed face-capping hydrides on each triangular [Co3] face, while the formal CoII2CoI4 oxidation state of 4 indicated a reduction of the cobalt centers during the assembly process. Cluster 4 catalyzes the hydrosilylation of 2-cyclohexen-1-one favoring the conjugate reduction. Generation of the catalytically reactive Co cluster species was indicated by a trapping experiment with a chiral chelating agent.

A direct asymmetric alkynylation of ketones with new chiral CCN Rh catalysts containing N-heterocyclic carbene and oxazoline hybrid ligands is described. The catalytic reaction of fluoroalkyl-substituted ketones, ArCOCF2X (X=F, Cl, H), with aromatic and aliphatic alkynes yielded the corresponding chiral propargyl alcohols with high enantioselectivity. Control and kinetic experiments suggested a bis(alkynyl) Rh intermediate as the active species for the C−C bond-forming step.

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-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)