(N-heterocyclic carbene)2-Pd(0) catalyzed silaboration of internal and terminal alkynes: scope and mechanistic studies

Pd(ITMe)2(PhC≡CPh) acts as a highly reactive precatalyst in the silaboration of terminal and internal alkynes to yield a number of known and novel 1-silyl-2-boryl alkenes. Unprecedented mild reaction temperatures for terminal alkynes, short reaction times, and low catalytic loadings are reported. During mechanistic studies, cis-Pd(ITMe)2(SiMe2Ph)(Bpin) was directly synthesized by oxidative addition of PhMe2SiBpin to Pd(ITMe)2(PhC≡CPh). This represents a very rare example of a (silyl)(boryl)palladium complex. A plausible catalyst decomposition route was also examined

Visible-Light-Mediated Deaminative Three-Component Dicarbofunctionalization of Styrenes with Benzylic Radicals

The visible-light-mediated three-component dicarbofunctionalization of styrenes using simple benzylic radicals is described. Notably, this work describes a rare example of undirected dicarbofunctionalization using unsubstituted benzyl radicals. Key to the success of this strategy was the rational design and use of benzylic pyridinium salts as radical precursors. Using this approach, abundant styrenes, electron-rich heterocycles, and benzylic amines were combined to rapidly afford a number of densely functionalized 1,1-diarylalkanes. A dipeptide-derived pyridinium salt was applied in this transformation, which resembles a visible-light-mediated deaminative generation of radicals from peptides

Experimental cross sections of Ho 165 (α,n) Tm 168 and Er 166 (α,n) Yb 169 for optical potential studies relevant for the astrophysical γ process

Background: Optical potentials are crucial ingredients for the prediction of nuclear reaction rates needed in simulations of the astrophysical γ process. Associated uncertainties are particularly large for reactions involving α particles. This includes (γ,α) reactions which are of special importance in the γ process. Purpose: The measurement of (α,n) reactions allows for an optimization of currently used α-nucleus potentials. The reactions Ho165(α,n) and Er166(α,n) probe the optical model in a mass region where γ process calculations exhibit an underproduction of p nuclei which is not yet understood. Method: To investigate the energy-dependent cross sections of the reactions Ho165(α,n) and Er166(α,n) close to the reaction threshold, self-supporting metallic foils were irradiated with α particles using the FN tandem Van de Graaff accelerator at the University of Notre Dame. The induced activity was determined afterwards by monitoring the specific β-decay channels. Results: Hauser-Feshbach predictions with a widely used global α potential describe the data well at energies where the cross sections are almost exclusively sensitive to the α widths. Increasing discrepancies appear towards the reaction threshold at lower energy. Conclusions: The tested global α potential is suitable at energies above 14 MeV, while a modification seems necessary close to the reaction threshold. Since the γ and neutron widths show non-negligible impact on the predictions, complementary data are required to judge whether or not the discrepancies found can be solely assigned to the α width. © 2014 American Physical Society.Peer reviewedFinal Accepted Versio

Visible-Light-Mediated Deaminative Three-Component Dicarbofunctionalization of Styrenes with Benzylic Radicals

The visible-light-mediated three-component dicarbofunctionalization of styrenes using simple benzylic radicals is described. Notably, this work describes a rare example of undirected dicarbofunctionalization using unsubstituted benzyl radicals. Key to the success of this strategy was the rational design and use of benzylic pyridinium salts as radical precursors. Using this approach, abundant styrenes, electron-rich heterocycles, and benzylic amines were combined to rapidly afford a number of densely functionalized 1,1-diarylalkanes. A dipeptide-derived pyridinium salt was applied in this transformation, which resembles a visible-light-mediated deaminative generation of radicals from peptides

Visible-Light-Mediated Charge Transfer Enables C−C Bond Formation with Traceless Acceptor Groups

The development and application of traceless acceptor groups in photochemical C−C bond formation is described. This strategy was enabled by the photoexcitation of electron donor–acceptor (EDA) complexes with visible light. The traceless acceptors, which were readily prepared from amino acid and peptide feedstocks, could be used to alkylate a wide range of heteroarene and enamine donors under metal- and peroxide-free conditions. The crucial role of the EDA complexes in the mechanism of these reactions was explored through combined experimental and computational studies

Covalent Adsorption of N-Heterocyclic Carbenes on a Copper Oxide Surface

Tuning the properties of oxide surfaces through the adsorption of designed ligands is highly desirable for several applications, such as catalysis. N-Heterocyclic carbenes (NHCs) have been successfully employed as ligands for the modification of metallic surfaces. On the other hand, their potential as modifiers of ubiquitous oxide surfaces still needs to be developed. Here we show that a model NHC binds covalently to a copper oxide surface under UHV conditions. In particular, we report the first example of a covalent bond between NHCs and oxygen atoms from the oxide layer. This study demonstrates that NHC can also act as a strong anchor on oxide surfaces

Promoted Thermal Reduction of Copper Oxide Surfaces by N-Heterocyclic Carbenes

The influence of metallic and oxide phases coexisting on surfaces is of fundamental importance in heterogeneous catalysis. Many reactions lead to the reduction of the oxidized areas, but the elucidation of the mechanisms driving these processes is often challenging. In addition, intermediate species or designed organic ligands increase the complexity of the surface. In the present study, we address the thermal reduction of a copper oxide overlayer grown on Cu(111) in the presence of N-heterocyclic carbene (NHC) ligands by means of scanning tunneling microscopy (STM) and density functional theory (DFT). We show that the NHC ligands actively participate in the copper oxide reduction, promoting its removal at temperatures as low as 470 K. The reduction of the oxide was tracked by employing scanning tunneling spectroscopy (STS), providing a chemical identification of metallic and oxide areas at the nanometric scale

Growth of N-Heterocyclic Carbene Assemblies on Cu(100) and Cu(111): from Single Molecules to Magic-Number Islands

N-Heterocyclic carbenes (NHCs) have superior properties as building blocks of self-assembled monolayers (SAMs). Understanding the influence of the substrate in the molecular arrangement is a fundamental step before employing these ligands in technological applications. Herein, we study the molecular arrangement of a model NHC on Cu(100) and Cu(111). While mostly disordered phases appear on Cu(100), on Cu(111) well-defined structures are formed, evolving from magic-number islands to molecular ribbons with coverage. This work presents the first example of magic-number islands formed by NHC assemblies on flat surfaces. Intermolecular interactions, diffusion and commensurability are key factors explaining the observed arrangements. These results shed light on the molecule-substrate interaction and open the possibility of tuning nanopatterned structures based on NHC assemblies