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In the absence of transition metal catalysts, the unsymmetrical diborane(4), pinB-BMes2, reacted with alkynes to afford diborylalkenes. The isomer ratio of the products could be controlled via temperature, solvent, and additive(s). A reaction mechanism was proposed on the basis of two isolated intermediates, and this reaction could furthermore be applied to synthesize a luminescent molecule.

The first catalytic asymmetric desymmetrization of azetidines is disclosed. Despite the low propensity of azetidine ring opening and challenging stereocontrol, smooth intermolecular reactions were realized with excellent efficiency and enantioselectivity. These were enabled by the suitable combination of catalyst, nucleophile, protective group, and reaction conditions. The highly enantioenriched densely functionalized products are versatile precursors to other useful chiral molecules. Mechanistic studies, including DFT calculations, revealed that only one catalyst molecule is involved in the key transition state, though both reactants can be activated. Also, the Curtin–Hammett principle dictates the reaction proceeds via amide nitrogen activation.

Cycloheptatrienyl aryl, hetaryl, and alkyl methanones are successfully converted according to the title reaction with aryl, hetaryl, alkyl, and alkenyl imino esters.

A new organocatalytic transfer hydrogenation strategy for the efficient asymmetric synthesis of 1,1-diarylethanes is given.

The regioselective Pd-catalyzed cyclization of a number of heterocyclic substrates without added phosphine ligands is reported.

The NMR spectra for three “natural” products: cephalosporolide C (Ces-C), cephalosporolide J (Ces-J), and bassianolone were found to be identical, and we proposed that Ces-C was the correct structure for the reported spectra. The first total synthesis of the proposed structure for Ces-J was achieved to support our structural revision for Ces-J. Chemical transformations of bassianolone and computational prediction of 13C NMR spectra allowed us to conclude that Ces-C was the correct structure for bassianolone. Our synthetic and computational studies suggested that these “different” natural products Ces-C, Ces-J, and bassianolone have the same structure: Ces-C.

The process is of special interest due to the high importance of chiral fluorine compounds in various fields of organic chemistry.

The reaction of benzeneseleninic anhydride and hexamethyldisilazane gives a reactive intermediate namely oligomeric (RSeN) 4 which oxidizes a phenol to the selenoiminoquinone 1. Both spectroscopic and crystallographic studies showed that the oxygen atom of the carbonyl group in the (phenylselenoimino)quinone 2 is involved in an attractive interaction with the selenium atom. The carbon atom of the phenyl ring is also found to be in the same plane as the O-C-C-N-Se plane. Theoretical studies of these systems clearly show a strong dependence of the Se-O interactions on the substituent on the selenium atom

Ab initio calculations with effective core potentials were completed on M 8 C 12 (M=Y, Zr, Nb, and Mo) clusters. Three different isomers (T h , D 3d , and T d ) have been investigated. The T h and D 3d isomers are derived from a dodecahedral geometry. In the former, the faces of a cube of the metal atoms are capped by ethylene-like C 2 units, while in the latter the 12 carbons form a cylindrical, closed chain capped by two M 4 units. In the T d isomer, six acetylene-like C 2 units link the vertices of a tetracapped tetrahedral metal framework in a butterfly fashion

Detailed structural and electronic analyses based on orbital interaction models for a large number of tetrahydroborato transition-metal complexes were provided to account for the relationship between their structure and bonding. Three points were made as the result of discussion: (a) most of the tetrahydroborato transition-metal complexes conform to the 18 electron rule, especially for complexes with only one BH 4 − ligand; (b) usually, complexes with more than 18 valence electrons are considered as ionic complexes. Our detailed analyses reveal that both ionic and electronic effects play important roles in the stereochemistry in these tetrahydroborato complexes. The ionic effect tends to maximize the coordination number while the electronic effect influences the orientation of ligands; (c) complexes with more than 18 valence electrons (which usually have two or more BH 4 − ligands) adopt structures allowing the extra electrons to be exclusively delocalized in the BH 4 − ligands. Although some complexes are formally 18-electron species, the number of electrons involved in the metal-ligand bonding is not necessarily 18.

A variety of structural types of transition metal clusters containing mainly π-donor ligands are reviewed. Their structure and bonding are analyzed using a simple and unified molecular orbital approach based on the consideration of metal-metal bonding as arising from the interaction of the frontier orbitals of individual metal fragments derived from their local MLn coordination. This kind of “local metal frontier orbital” approach allows us to construct metal-metal orbital interaction diagrams in a convenient way. Using these molecular orbital diagrams, relevant optimal electron counts for major structural types are discussed. It is emphasized that the “t2g” set fragment orbitals, which are non-bonding in carbonyl clusters, play the crucial role in metal-metal bonding for clusters with π-donor ligands. Bonding characteristics for Mo(W)-Fe-S, Ni-S(Se) and related clusters are also discussed.

Nitride cations of selenium clusters [SenN]+ (n = 1-11) were readily produced by laser ablation of a selenium disk that was surrounded by a trace amount of nitrogen seeded in helium and followed by supersonic expansion into a high vacuum. Even at high nitrogen partial pressures, the cluster mononitride cations were found to be essentially the only nitride products in the whole size range we studied. The exception was [Se3N2]+, which is known to be a stable five-membered ring with seven pi electrons. We propose that, in the laser-ablation plasma, the selenium clusters with n > 2 take on a chain conformation, and that the N species links the two ends of the selenium chains, thus forming stable mononitride cations of the cyclic selenium clusters. Their stability is supported by the results of ab initio calculations (at both B3LYP/ 6-31 + G* and MP2/6-31 + G* levels) and of mass-selected cluster-ion photodissociation experiments.

Transition metal–silane complexes containing metal–η2-H–Si coordination display different structural and bonding characteristics in comparison to other σ-complexes, such as dihydrogen and alkane (agostic) complexes. The different characteristics can be related to the strong σ*-accepting properties of the η2-silane ligand(s) because of the weaker H–Si σ bond. Various examples of metal–silane complexes have been reviewed and their structural stabilities have been systematically discussed. Silyl–hydride complexes having substantial silyl–hydrido interactions have also been emphasized.

The catalytic activity of a series of ruthenium complexes for C−H amination reactions of organic azides was investigated. The most active catalyst was found to be RuCl3, which promotes C−H amination reactions of ortho-aryl phenylazides, 1-azido-2-arylvinylazides, and 1-azido-1,3-butadienes to give carbazoles, indoles, and pyrroles, respectively. Both computational and experimental results support that a two-step process involving formal electrocyclization is involved in the catalytic reaction.

Transition metals such as Fe in porphyrin complexes are known to bind or react with O2, and such reactions are critical to many biological functions and catalytic oxidation using O2. The transition metals in these reactions often contain valence d electrons, and oxidation of metals is an important step. In recent years, reactions of O2 with d0 transition metal complexes such as Hf(NR2)4 (R = alkyl) have been used to make metal oxide thin films as insulating gate materials in new microelectronic devices. This feature article discusses our recent studies of such reactions and the formation of TiO2 thin films. In contrast to the reactions of many d n complexes where metals are often oxidized, reactions of d0 complexes such as Hf(NMe2)4 and Ta(NMe2)4(SiR3) with O2 usually lead to the oxidation of ligands, forming, e.g., -ONMe2 and -OSiR3 from -NMe2 and -SiR3 ligands, respectively. Mechanistic and theoretical studies of these reactions have revealed pathways in the formation of the metal oxide thin films as microelectronic materials.

A simple but effective copper-catalyzed borylation of aryl halides, including electron-rich and sterically hindered aryl bromides, with alkoxy diboron reagents occurs under mild conditions (see scheme). Preliminary DFT studies of the mechanism suggest that sigma-bond metathesis between a copper-boryl intermediate and the aryl halide generates the aryl boronate product.

Dihydrogen(olefin) complexes have been proposed as active species in catalytic hydrogenation reactions. We have studied the hydrogen-transfer reactions of dihydrogen(olefin) complexes, especially those containing the norbornadiene (NBD) ligand, in order to address the following questions: (i) how the alignment of a H2 ligand relative to an olefin ligand may affect their reactivity; (ii) in general, what is the detailed pathway for intramolecular hydrogen transfer from an H2 ligand to an olefin ligand; and (iii) how will the hydrogen transfer reactions proceed in the presence of both an H2 and a hydride ligand. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)