Nickel-Catalyzed Hydroarylation of Alkynes under Reductive Conditions with Aryl Bromides and Water.

An operationally simple nickel-catalyzed hydroarylation reaction for alkynes is described. This three-component coupling reaction utilizes commercially available alkynes and aryl bromides, along with water and Zn. An air-stable and easily synthesized Ni(II) precatalyst is the only entity used in the reaction that is not commercially available. This reductive cross-coupling reaction displays a fairly unusual anti selectivity when aryl bromides with ortho substituents are used. In addition to optimization data and a preliminary substrate scope, complementary experiments including deuterium labeling studies are used to provide a tentative catalytic mechanism. We believe this report should inspire and inform other Ni-catalyzed carbofunctionalization reactions.

The direct anti-Markovnikov addition of mineral acids to styrenes.

The direct anti-Markovnikov addition of strong Brønsted acids to alkenes remains an unsolved problem in synthetic chemistry. Here, we report an efficient organic photoredox catalyst system for the addition of HCl, HF and also phosphoric and sulfonic acids to alkenes, with complete regioselectivity. These transformations were developed using a photoredox catalyst in conjunction with a redox-active hydrogen atom donor. The nucleophile counterion plays a critical role by ensuring high reactivity, with 2,6-lutidinium salts typically furnishing the best results. The nature of the redox-active hydrogen atom donor is also consequential, with 4-methoxythiophenol providing the best reactivity when 2,6-lutidinium salts are used. A novel acridinium sensitizer provides enhanced reactivity within several of the more challenging reaction manifolds. This Article demonstrates how nucleophilic addition reactions mediated by photoredox catalysis can change the way electrophilic and homofugal precursors are constructed.

Electron transfer dynamics of peptide-derivatized Ru(II) -polypyridyl complexes on nanocrystalline metal oxide films.

The performance of dye-sensitized solar and photoelectrochemical cells is strongly dependent on the electron transfer events at the electrode-sensitizer interface. Surface-bound peptides derivatized with chromophores have not been used in dye-sensitized solar and photoelectrochemical cells, but they have properties for these applications that could be advantageous by exploiting secondary structure and the attachment of multiple chromophores. In this manuscript, we have investigated structure-property relationships for three metallopeptide-based assemblies to solution and chemically bound to nanocrystalline MO(2) (M = Ti, Zr) films. A particular interest was exploring the influence of increasing separation distance between a common chromophore, [Ru(bpy)(2) (4-Me-4'-(NHCO)bpy)](2+) , and the underlying oxide substrate on excited and ground state electron transfer. Rates of Ru(II) oxidation to Ru(III) at the interface were measured by cyclic voltammetry on fluorine-doped tin oxide and cross-surface electron transfer on TiO(2) . Excited state injection by [Ru(III) (bpy)(2) (bpy(-) )](2+) was monitored by transient absorption and time-resolved emission. There are discernible trends in the electron transfer rate data with approximated, fully extended distances between the [Ru(bpy)(2) (4-Me-4'-(NHCO)bpy)](2+) sites and the interface. However, the distance dependences that are observed are smaller than anticipated, a result consistent with a lack of ordered secondary structure in the surface-bound peptide chains and a distribution of local orientations. For the surface-bound excited states, only a small fraction undergo quenching by electron transfer to TiO(2) , presumably from those oriented near the surface.

Tunable energy transfer rates via control of primary, secondary, and tertiary structure of a coiled coil peptide scaffold.

Herein we report energy transfer studies in a series of Ru(II) and Os(II) linked coiled-coil peptides in which the supramolecular scaffold controls the functional properties of the assembly. A general and convergent method for the site-specific incorporation of bipyridyl Ru(II) and Os(II) complexes using solid-phase peptide synthesis and the copper-catalyzed azide-alkyne cycloaddition is reported. Supramolecular assembly positions the chromophores for energy transfer. Using time-resolved emission spectroscopy we measured position-dependent energy transfer that can be varied through changes in the sequence of the peptide scaffold. High level molecular dynamics simulations were used in conjunction with the spectroscopic techniques to gain molecular-level insight into the observed trends in energy transfer. The most efficient pair of Ru(II) and Os(II) linked peptides as predicted by molecular modeling also exhibited the fastest rate of energy transfer (with k(EnT) = 2.3 × 10(7) s(-1) (42 ns)). Additionally, the emission quenching for the Ru(II) and Os(II) peptides can be fit to binding models that agree with the dissociation constants determined for the peptides via chemical denaturation.