Unprecedented Formation of Five-, Six-, and Seven-Membered Metallacycles by Single and Double Insertion of Mono- and Disubstituted Alkynes into an Rh-O Bond We thank Prof. Shigetoshi Takahashi and Dr. Fumie Takei at The Institute of Scientific and Industrial Research, Osaka University for the measurement of FAB mass spectra

Recent advances in well-defined, late transition metal complexes that make and/or break C-N, C-O and C-S bonds

Chemical transformations that result in either the formation or cleavage of carbon-heteroatom bonds are among the most important processes in the chemical sciences. Herein, we present a review on the reactivity of well-defined, late-transition metal complexes that result in the making and breaking of C-N, C-O and C-S bonds via fundamental organometallic reactions, i.e. oxidative addition, reductive elimination, insertion and elimination reactions. When appropriate, emphasis is placed on structural and spectroscopic characterization techniques, as well as mechanistic data.

Chemoselective acyl C–O bond activation in esters for Suzuki–Miyaura coupling

The use of palladium–NHC (bulky) catalyst enables selective acylative coupling in esters via blocking the potential C(aryl)–O oxidative addition and decarbonylation processes. Mechanistic studies elucidate the role of bulky carbene catalysts in promoting C(acyl)–O activation, and as a result, the acyl metal intermediates undergo coupling without the loss of carbonyl group.

A combined stopped-flow, electrospray ionization mass spectrometry and31P NMR study on the acetic acid-mediated fragmentation of the hydroxo-chalcogenide cluster [W3Se4(OH)3(dmpe)3]+(dmpe = 1,2-bis(dimethylphosphanyl)ethane) to yield the dinuclear [W2Se2(µ-Se)2(µ-CH3CO2)(dmpe)2]+complex

The reaction of the incomplete-cuboidal [W(3)Se(4)(OH)(3)(dmpe)(3)](+) ([1](+)) cluster with acetic acid in acetonitrile solution leads to cluster fragmentation with formation of the dinuclear [W(2)Se(2)(mu-Se)(2)(mu-CH(3)CO(2))(dmpe)(2)](+) ([2](+)) complex. The X-ray structure of [2]PF(6) presents two equivalent metal centres bridged by one acetate ligand. Each W atom is additionally coordinated by one terminal selenium atom, two bridging selenido and two diphosphane phosphorus atoms in an essentially octahedral environment. Stopped-flow and conventional UV-vis studies indicate that fragmentation of [1](+) into [2](+) occurs through a complex mechanism. Three steps can be distinguished in the stopped-flow time scale, all of them showing a first order dependence with respect to the acetic acid concentration, followed by very slow spectral changes that lead to the formation of [2](+). Phosphorus NMR, electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS) have been used to identify the nature of the reaction intermediates formed in the different steps. These studies indicate that the first two steps correspond to the formal substitutions of the hydroxo ligands at two metal centres by terminal acetate ligands. The third step involves bridging of one of the terminal acetate ligands, which actually prepares the trinuclear cluster to afford the acetate-bridged [W(2)Se(2)(mu-Se)(2)(mu-CH(3)CO(2))(dmpe)(2)](+) ([2](+)) complex. Although the precise details of the final conversion to [2](+) have not been established, the results obtained by combination of the different experimental techniques provide a complete picture of the speciation of the cluster [1](+) in acetonitrile solutions containing acetic acid.

Catalytic Cross-Coupling Reaction of Esters with Organoboron Compounds and Decarbonylative Reduction of Esters with HCOONH4: A New Route to Acyl Transition Metal Complexes through the Cleavage of Acyl−Oxygen Bonds in Esters

The Ru3(CO)12-catalyed cross-coupling reaction of esters with organoboron compounds leading to ketones is described. A wide variety of functional groups can be tolerated under the reaction conditions. Aromatic boronates function as a coupling partner to give aryl ketones. Acyl-alkyl coupling to dialkyl ketones is also achieved by the use of 9-alkyl-9-BBN in place of boronates. The Ru3(CO)12-catalyzed decarbonylative reduction of esters with ammonium formate (HCOONH4) leading to hydrocarbons is also described. No expected aldehydes are produced, and controlled experiments indicate that aldehydes are not intermediate for the transformation. A hydrosilane can also be used as a reducing reagent in place of HCOONH4. A wide variety of functional groups are compatible for both reactions. The key step for both catalytic reactions is the directing group-promoted cleavage of an acyl carbon-oxygen bond in esters, leading to the generation of acyl transition metal alkoxo complexes.