Ruthenium-Catalyzed Alkyne trans-Hydrometalation: Mechanistic Insights and Preparative Implications.

[Cp*RuCl] (1) has previously been shown to be the precatalyst of choice for stereochemically unorthodox trans-hydrometalations of internal alkynes. Experimental and computational data now prove that the alkyne primarily acts as a four-electron donor ligand to the catalytically active metal fragment [Cp*RuCl] but switches to adopt a two-electron donor character once the reagent RMH (M = Si, Ge, Sn) enters the ligand sphere. In the stereodetermining step the resulting loaded complex evolves via an inner-sphere mechanism into a ruthenacyclopropene which swiftly transforms into the product.

Formation of Ruthenium Carbenes by -Hydrogen Transfer to Internal Alkynes: Implications for Alkyne -Hydrogenation.

Insights into the mechanism of the unusual -hydrogenation of internal alkynes catalyzed by {Cp*Ru} complexes were gained by para-hydrogen (p-H) induced polarization (PHIP) transfer NMR spectroscopy. It was found that the productive -reduction competes with a pathway in which both H atoms of H are delivered to a single alkyne C atom of the substrate while the second alkyne C atom is converted into a metal carbene. This " hydrogenation" mode seems unprecedented; it was independently confirmed by the isolation and structural characterization of a ruthenium carbene complex stabilized by secondary inter-ligand interactions.

Dynamic behaviour of monohaptoallylpalladium species: internal coordination as a driving force in allylic alkylation chemistry.

Contemporary catalytic procedures involving alkylpalladium(ii) have enriched the arsenal of synthetic organic chemistry. Those transformations usually rely on internal coordination through "directing groups", carefully designed to maximize catalytic efficiency and regioselectivity. Herein, we report structural and reactivity studies of a series of internally coordinated monohaptoallylpalladium complexes.

Formation of ruthenium carbenes by gem-hydrogen transfer to internal alkynes: implications for alkyne trans-hydrogenation.

Insights into the mechanism of the unusual trans-hydrogenation of internal alkynes catalyzed by {Cp*Ru} complexes were gained by para-hydrogen (p-H2 ) induced polarization (PHIP) transfer NMR spectroscopy. It was found that the productive trans-reduction competes with a pathway in which both H atoms of H2 are delivered to a single alkyne C atom of the substrate while the second alkyne C atom is converted into a metal carbene. This "geminal hydrogenation" mode seems unprecedented; it was independently confirmed by the isolation and structural characterization of a ruthenium carbene complex stabilized by secondary inter-ligand interactions.

A Striking Case of Enantioinversion in Gold Catalysis and Its Probable Origins.

The cyclization of the hydroxy-allene 2 to the tetrahydrofuran 3 catalyzed by the gold-phosphoramidite complex 1, after ionization with an appropriate silver salt AgX, is one of the most striking cases of enantioinversion known to date. The major reason why the sense of induction can be switched from (S) to (R) solely by changing either the solvent or the temperature or the nature of the counterion X is likely found in the bias of the organogold intermediates to undergo assisted proto-deauration. Such assistance can be provided by a protic solvent, a reasonably coordinating counterion or even by a second substrate molecule itself; in this case, the reaction free energy profile gains a strong entropic component that can ultimately dictate the stereochemical course.

Origin of inversion versus retention in the oxidative addition of 3-chloro-cyclopentene to Pd(0)L(n).

The preference for syn versus anti oxidative addition of 3-chloro-cyclopentene to Pd(0)L(n) was investigated using density functional theory (L = PH3, PMe3, PF3, ethylene, maleic anhydride, pyridine, imidazol-2-ylidene). Both mono- and bis-ligation modes were studied (n = 1 and 2). The pathways were analyzed at the B2PLYP-D3/def2-TZVPP//TPSS-D3/def2-TZVP level, and an interaction/distortion analysis was performed at the ZORA-TPSS-D3/TZ2P level for elucidating the origin of the selectivity preferences.

A theoretical investigation on the mechanism and stereochemical course of the addition of (E)-2-butenyltrimethylsilane to acetaldehyde by electrophilic and nucleophilic activation.

The diastereoselectivity of the addition of (E)-2-butenyltrimethylsilane to acetaldehyde under electrophilic (BF3, H3O(+)) and nucleophilic (F(-)) activation is investigated using density functional theory (M06-2X). The interaction-distortion/activation-strain model of reactivity is used to rationalize the origin of the selectivity. Consistent with experimental model systems, the synclinal transition states are determined to be preferred over the antiperiplanar transition states in the electrophilic-activated manifolds and vice versa for the fluoride-activated manifold.

A systematic investigation of quaternary ammonium ions as asymmetric phase-transfer catalysts. Application of quantitative structure activity/selectivity relationships.

Although the synthetic utility of asymmetric phase-transfer catalysis continues to expand, the number of proven catalyst types and design criteria remains limited. At the origin of this scarcity is a lack in understanding of how catalyst structural features affect the rate and enantioselectivity of phase transfer catalyzed reactions. Described in this paper is the development of quantitative structure-activity relationships (QSAR) and -selectivity relationships (QSSR) for the alkylation of a protected glycine imine with libraries of quaternary ammonium ion catalysts.

A systematic investigation of quaternary ammonium ions as asymmetric phase-transfer catalysts. Synthesis of catalyst libraries and evaluation of catalyst activity.

Despite over three decades of research into asymmetric phase-transfer catalysis (APTC), a fundamental understanding of the factors that affect the rate and stereoselectivity of this important process are still obscure. This paper describes the initial stages of a long-term program aimed at elucidating the physical organic foundations of APTC employing a chemoinformatic analysis of the alkylation of a protected glycine imine with libraries of enantiomerically enriched quaternary ammonium ions. The synthesis of the quaternary ammonium ions follows a diversity-oriented approach wherein the tandem inter[4 + 2]/intra[3 + 2] cycloaddition of nitroalkenes serves as the key transformation.