Scheme 3. Electrophilic Functionalization Pathway (Mechanism ii): One-Electron Oxidation of Palladacycle A Scheme 4. Electrophilic Functionalization Pathway (Mechanism iii): Two-Electron Oxidation of Palladacycle A Scheme 5. Pd(OAc) 2 -Catalyzed sp 2 C-H Acetoxylation with PhI(OAc) 2 8-10 Scheme 6. Pd(OAc) 2 -Catalyzed sp 3 C-H Acetoxylation with PhI(OAc) 2 8,10,14

This report details the effects of ligand variation on the mechanism and activity of ruthenium-based olefin metathesis catalysts. A series of ruthenium complexes of the general formula L(PR(3))(X)(2)Ru=CHR(1) have been prepared, and the influence of the substituents L, X, R, and R(1) on the rates of phosphine dissociation and initiation as well as overall activity for olefin metathesis reactions was examined. In all cases, initiation proceeds by dissociative substitution of a phosphine ligand (PR(3)) with an olefinic substrate. All of the ligands L, X, R, and R(1) have a significant impact on initiation rates and on catalyst activity. The origins of the observed substituent effects as well as the implications of these studies for the design and implementation of new olefin metathesis catalysts and substrates are discussed in detail.

This communication describes a new and highly practical Pd(II)-catalyzed method for the regio- and chemoselective oxidative functionalization of arenes and alkanes. Carbon-hydrogen bonds of substrates that contain a variety of directing groups (e.g., pyridine, azobenzene, pyrazole, and imine derivatives) are selectively transformed into esters, ethers, and aryl-halides under mild conditions. The scope of this reaction in terms of substrate, directing group, and oxidant is described, and a preliminary catalytic cycle is proposed.

The ruthenium complex (IMesH2)(Cl)2(C5H5N)2RuCHPh [IMesH2 = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene] (3) was prepared by the reaction of (IMesH2)(PCy3)(Cl)2RuCHPh (2) with an excess of pyridine. Complex 3 contains substitutionally labile pyridine and chloride ligands and serves as a versatile starting material for the synthesis of new ruthenium benzylidenes.

This communication demonstrates the homogeneous hydrogenation of CO(2) to CH(3)OH via cascade catalysis. Three different homogeneous catalysts, (PMe(3))(4)Ru(Cl)(OAc), Sc(OTf)(3), and (PNN)Ru(CO)(H), operate in sequence to promote this transformation.