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DMF-stabilized Au nanoparticles (NPs) with three different particle sizes were prepared by controlling the reaction temperatures and times. In the absence of any additional ligands, these Au NPs showed high catalytic activity in the Ullmann homocoupling of aryl iodides in DMF. The effects of Au particle size on the coupling reaction were investigated by the use of three Au catalysts with mean particle sizes of ca. 1.0 nm, 2.5 nm, and 5.5 nm, respectively. The catalytic activity of the Au NPs was found to be in the order of Au (2.5 nm) > Au (<1.0 nm) > Au (5.5 nm), indicating that surface Au atoms do not have the same catalytic activity toward such a homocoupling reaction. [ABSTRACT FROM AUTHOR]

The reaction of FeCl3 with a pincer ligand, 2,6-di(1H-pyrazol-3-yl)pyridine (bppyH2), produced a mononuclear Fe(III) complex [Fe(bppyH2)Cl3] (1), which could be reduced to the corresponding Fe(II) dichloride complex [Fe(bppyH2)Cl2] (2) by suitable reducing agents such as Cp2Co or Fe powder. 1 and 2 exhibited a reversible transformation from each other with appropriate redox reagents. 1 could be utilized as a precatalyst to initiate the ring-opening polymerization of ε-caprolactone in the presence of alcohol but 2 did not work. The 1/alcohol system displayed characteristics of a well-controlled polymerization with the resulting poly(ε-caprolactone) having low molecular weight distributions, a linear tendency of molecular weight evolution with conversion, and polymer growth observed for the sequential additions of e-caprolactone monomer to the polymerization reaction. The polymerization was completely turned off by the in situ reduction of the catalytic Fe center via Cp2Co and then turned back upon the addition of [Cp2Fe]-PF6. The rate of polymerization was modified by switching in situ between the Fe(III) and Fe(II) species. [ABSTRACT FROM AUTHOR]