No abstract

A combined experimental and computational approach has been utilized to elucidate the mechanism of alkene hydrogenation by pincer-type [P 2 Si]Rh catalysts. Although [P 2 Si]Rh interacts with H 2 to afford a dihydrogen σ-complex rather than a dihydride (seemingly an indication of facile reductive elimination from Rh(III)), alkane release occurs by competitive σ-bond metathesis (bimolecular) and reductive elimination (unimolecular) pathways. This unusual behavior is attributed to the strong trans influence of the silyl donor.

Pincer-type [P 2 Si]Rh complexes featuring a rhodium−silicon bond are shown to facilitate well-defined stoichiometric reductions of CO 2 with Si−O bond formation by two different pathways: (a) hydride transfer to CO 2 followed by formate migration to silicon, or (b) complete scission of the CO bond at the Rh−Si unit to afford a product with siloxide and carbonyl ligands. A combined experimental and computational study shows that the latter process occurs by anomalous insertion of CO 2 into the polarized Rh δ− −Si δ+ bond, a finding that is confirmed by extending the reactivity to an unchelated system. The siloxide carbonyl product can be further elaborated by reaction with water or pinacolborane to give structurally distinct CO 2 reduction products. Taken together, these results demonstrate how metal/main-group bonds can be tuned to direct migratory insertion reactivity.

Activation of C–C bonds has the potential to revolutionize how molecules are made by altering the carbon skeleton and enabling new synthetic routes. Stereodefined cyclopropyl ketones have become readily available and would be an ideal source of linear 3-carbon fragments, but this reactivity is unknown. In this study we show how a new type of C–C activation catalyst, that relies upon a different, metalloradical mechanism, can enable new subsequent reactivity: the cross- coupling of cyclopropyl ketones with organozinc reagents and chlorotrimethylsilane to form 1,3- difunctionalized, ring-opened products. A mixture of experiment and theory sheds light on how cooperation between the redox-active ligand and the nickel catalyst enables the C–C bond activation step, suggesting how this approach could be applied in other systems.

Metal-metal bonded complexes are promising candidates for catalyzing redox transformations. Of particular interest is the oxidation of ammonia to dinitrogen, an important half reaction for the potential utilization of ammonia...