C-H Insertion via Ruthenium Catalyzed -Hydrogenation of 1,3-Enynes.

-Hydrogenation of an internal alkyne with the aid of [Cp*RuCl] as the precatalyst is a highly unorthodox transformation, in which one C atom of the triple bond is transformed into a methylene group, whereas the second C atom gets converted into a ruthenium carbene. In the case of 1,3-enynes bearing a propargylic steering substituent as the substrates, the reaction occurs regioselectively, giving rise to vinyl carbene complexes that adopt interconverting η/η-binding modes in solution; a prototypical example of such a reactive intermediate was characterized in detail by spectroscopic means. Although both forms are similarly stable, only the η-vinyl carbene proved kinetically competent to insert into primary, secondary, or tertiary C-H bonds on the steering group itself or another suitably placed ether, acetal, orthoester, or (sulfon)amide substituent.

Hydrogenative Metathesis of Enynes via Piano-Stool Ruthenium Carbene Complexes Formed by Alkyne -Hydrogenation.

The only recently discovered -hydrogenation of internal alkynes is a fundamentally new transformation, in which both H atoms of dihydrogen are transferred to the same C atom of a triple bond while the other position transforms into a discrete metal carbene complex. [Cp*RuCl] is presently the catalyst of choice: the resulting piano-stool ruthenium carbenes can engage a tethered alkene into either cyclopropanation or metathesis, and a prototypical example of such a reactive intermediate with an olefin ligated to the ruthenium center has been isolated and characterized by X-ray diffraction. It is the substitution pattern of the olefin that determines whether metathesis or cyclopropanation takes place: a systematic survey using alkenes of largely different character in combination with a computational study of the mechanism at the local coupled cluster level of theory allowed the preparative results to be sorted and an intuitive model with predictive power to be proposed.

Optical Manipulation of F-Actin with Photoswitchable Small Molecules.

Cell-permeable photoswitchable small molecules, termed , are introduced to optically control the dynamics of the actin cytoskeleton and cellular functions that depend on it. These light-dependent effectors were designed from the F-actin-stabilizing marine depsipeptide jasplakinolide by functionalizing them with azobenzene photoswitches. As demonstrated, can be employed to control cell viability, cell motility, and cytoskeletal signaling with the high spatial and temporal resolution that light affords.

Mechanistic Divergence in the Hydrogenative Synthesis of Furans and Butenolides: Ruthenium Carbenes Formed by gem-Hydrogenation or through Carbophilic Activation of Alkynes.

Enynes with a tethered carbonyl substituent are converted into substituted furan derivatives upon hydrogenation using [Cp*RuCl] as the catalyst. Paradoxically, this transformation can occur along two distinct pathways, each of which proceeds via discrete pianostool ruthenium carbenes. In the first case, hydrogenation and carbene formation are synchronized ("gem-hydrogenation"), whereas the second pathway comprises carbene formation by carbophilic activation of the triple bond, followed by hydrogenative catalyst recycling.

Hydrogenative Cyclopropanation and Hydrogenative Metathesis.

The unusual geminal hydrogenation of a propargyl alcohol derivative with [Cp RuCl] as the catalyst entails formation of pianostool ruthenium carbenes in the first place; these reactive intermediates can be intercepted with tethered alkenes to give either cyclopropanes or cyclic olefins as the result of a formal metathesis event. The course of the reaction is critically dependent on the substitution pattern of the alkene trap.

Alkyne gem-Hydrogenation: Formation of Pianostool Ruthenium Carbene Complexes and Analysis of Their Chemical Character.

Parahydrogen (p-H ) induced polarization (PHIP) NMR spectroscopy showed that [Cp Ru] complexes with greatly different electronic properties invariably engage propargyl alcohol derivatives into gem-hydrogenation with formation of pianostool ruthenium carbenes; in so doing, less electron rich Cp rings lower the barriers, stabilize the resulting complexes and hence provide opportunities for harnessing genuine carbene reactivity. The chemical character of the resulting ruthenium complexes was studied by DFT-assisted analysis of the chemical shift tensors determined by solid-state C NMR spectroscopy. The combined experimental and computational data draw the portrait of a family of ruthenium carbenes that amalgamate purely electrophilic behavior with characteristics more befitting metathesis-active Grubbs-type catalysts.