Hydrosilylation of Allenes Over Palladium-Gold Alloy Catalysts: Enhancing Activity and Switching Selectivity by the Incorporation of Palladium into Gold Nanoparticles

Transition-Metal-Free Synthesis of Enantioenriched Tertiary and Quaternary α-Chiral Allylsilanes

Access to enantioenriched tertiary and quaternary α-chiral allysilanes without any transition-metal catalyst is reported. This was achieved by enantioselective allylic displacement of γ-silylated allylic bromides through Lewis base activation of Grignard reagents by a bidentate chiral NHC ligand. The process afforded both high γ-regio- and enantioselectivity and is compatible with a wide range of silyl groups on the substrates.

Enantioselective Nickel-Catalyzed Hydrosilylation of 1,1-Disubstituted Allenes

Here, we report the first example of Ni-catalyzed asymmetric hydrosilylation of 1,1-disubstituted allenes with high level of regioselectivities and enantioselectivities. The key to achieve this stereoselective hydrosilylation reaction was the development of the SPSiOL-derived bisphosphite ligands (SPSiPO). This protocol features broad substrate scope, excellent functional group, and heterocycle tolerance, thus provides a versatile method for the construction of enantioenriched tertiary allylsilanes in a straightforward and atom-economic manner. DFT calculations were performed to reveal the reaction mechanism and the origins of the enantioselectivity.

Bulky NHC–Cobalt Complex-Catalyzed Highly Markovnikov-Selective Hydrosilylation of Alkynes

The hydrosilylation of alkynes is one of the most attractive and, at the same time, most challenging catalytic transformations, usually demanding the use of noble transition metals. We describe a catalytic system, based on cobalt(0) complex and bulky N-heterocyclic carbene (NHC) ligands, permitting the highly effective hydrosilylation of a broad scope of alkynes and silanes. The application of bulky NHC ligands allowed a decrease in the amount of cobalt necessary for an effective reaction run to 2.5 mol% and provided excellent selectivity towards challenging α-vinylsilanes. The developed method tolerates a number of substituted aryl, alkyl, and silyl acetylenes. Moreover, it is suitable for both tertiary and secondary silanes. Our findings confirm that steric hindrance around the metal center can effectively increase the activity of a catalyst and ensure better selectivity than those of analogous complexes bearing smaller ligands.

Catalysis of Alloys: Classification, Principles, and Design for a Variety of Materials and Reactions

Alloying has long been used as a promising methodology to improve the catalytic performance of metallic materials. In recent years, the field of alloy catalysis has made remarkable progress with the emergence of a variety of novel alloy materials and their functions. Therefore, a comprehensive disciplinary framework for catalytic chemistry of alloys that provides a cross-sectional understanding of the broad research field is in high demand. In this review, we provide a comprehensive classification of various alloy materials based on metallurgy, thermodynamics, and inorganic chemistry and summarize the roles of alloying in catalysis and its principles with a brief introduction of the historical background of this research field. Furthermore, we explain how each type of alloy can be used as a catalyst material and how to design a functional catalyst for the target reaction by introducing representative case studies. This review includes two approaches, namely, from materials and reactions, to provide a better understanding of the catalytic chemistry of alloys. Our review offers a perspective on this research field and can be used encyclopedically according to the readers' individual interests.

Copper-catalyzed regio- and stereo-selective hydrosilylation of terminal allenes to access (E)-allylsilanes

Regioselectivity and stereoselectivity control in hydrosilylation of terminal allenes is challeging. Although the selective synthesis of vinylsilanes, branched allylsilanes or linear (Z)-allylsilanes have been achieved, transition-metal catalyzed hydrosilylation of terminal allenes to access (E)-allylsilane is difficult. Herein, we report a copper-catalyzed selective hydrosilylation reaction of terminal allenes to access (E)-allylsilanes under mild reaction conditions. The reaction shows broad substrate scope, representing an efficient method to prepare trisubstituted (E)-allylsilanes through hydrosilylation reaction of allenes and can also be applied in the synthesis of disubstituted (E)-allylsilanes. The mechanism study reveals that the E-selectivity is kinetically controlled by the catalyst but not by the thermodynamically isomerization of the (Z)-isomer.

Regio- and stereoselective transition-metal catalysed hydrosilylation of terminal allenes to access (E)-allylsilanes are challenging organic transformations. Herein, the authors synthesize (E)-allylsilanes via copper-catalyzed hydrosilylation of terminal allenes.

Silylium-Ion-Promoted Hydrosilylation of Aryl-Substituted Allenes: Interception by Cyclization of the Allyl-Cation Intermediate

A trityl-cation-initiated, silylium-ion-promoted hydrosilylation of aryl-substituted allenes is reported. Depending on the hydrosilane-to-initiator ratio, the hydrosilylation can be intercepted by an intramolecular electrophilic aromatic substitution or a Nazarov electrocyclization of an allyl-cation intermediate in the form of its endo isomer. By this, the selective formation of either the conventional 1,2-hydrosilylation product (vinylsilane) or a cyclized product (silylated indane) can be controlled.

Volcano-type correlation between particle size and catalytic activity on hydrodechlorination catalyzed by AuPd nanoalloy

Although changing the size of metal nanoparticles (NPs) is a reasonable way to tune and/or enhance their catalytic activity, size-selective preparation of NPs possessing random-alloy morphology has been challenging because of the differences in the ionization potential of each metal ion. This study demonstrates a time-controlled aggregation-stabilization method for the size-selective preparation of random alloy NPs composed of Au and Pd, which are stabilized by poly(N-vinyl-2-pyrrolidone) (PVP). By adjusting the mixing time in the presence of a small amount of PVP, aggregation was induced to produce AuPd:PVP with sizes ranging between 1.2 and 8.2 nm at approximately 1 nm intervals. Transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), and extended X-ray absorption fine structure (EXAFS) analyses indicated the formation of various sizes of AuPd nanoalloys, and size-dependent catalytic activity was observed when hydrodechlorination of 4-chloroanisole was performed using 2-propanol as a reducing agent. AuPd:PVP with a size of 3.1 nm exhibited the highest catalytic activity. A comparison of the absorption edges of X-ray absorption near edge structure (XANES) spectra suggested that the electronic state of the Au and Pd species correlated with their catalytic activity, presumably affecting the rate-determining step.