Photocatalyzed regioselective hydrosilylation for the divergent synthesis of geminal and vicinal borosilanes.

Geminal and vicinal borosilanes are useful building blocks in synthetic chemistry and material science. Hydrosilylation/hydroborylation of unsaturated systems offer expedient access to these motifs. In contrast to the well-established transition-metal-catalyzed methods, radical approaches are rarely explored. Herein we report the synthesis of geminal borosilanes from α-selective hydrosilylation of alkenyl boronates via photoinduced hydrogen atom transfer (HAT) catalysis. Mechanistic studies implicate that the α-selectivity originates from a kinetically favored radical addition and an energetically favored HAT process. We further demonstrate selective synthesis of vicinal borosilanes through hydrosilylation of allyl boronates via 1,2-boron radical migration. These strategies exhibit broad scopes across primary, secondary, and tertiary silanes and various boron compounds. The synthetic utility is evidenced by access to multi-borosilanes in a diverse fashion and scaling up by continuous-flow synthesis.

Ni(II)-Catalyzed Transfer Hydrogenation of Azoarenes with NH3BH3.

A nickel-catalyzed semihydrogenation of azoarenes to hydrazoarenes with NH3BH3 is developed. The catalytic system exhibits good functional group tolerance and a high turnover frequency at room temperature. Results of control and deuterium-labeling experiments indicate that the ethanol hydroxyl and BH3 groups each donated one hydrogen to this transfer hydrogenation, and the main byproducts were B(OEt)3 and H2. Moreover, density functional theory calculations indicated that the reaction proceeded via a ligand-to-ligand hydrogen transfer mechanism. This study presents a novel nickel catalytic system for the semihydrogenation of azoarenes.

Bidentate Ru(II)-NC Complex as a Catalyst for Semihydrogenation of Azoarenes to Hydrazoarenes with Ethanol.

The transfer hydrogenation of azoarenes to hydrazoarenes using ethanol as a hydrogen source by a bidentate Ru(II)-NC complex is developed. A weak base is crucial for this semihydrogenation that can efficiently avoid hydrazoarene dehydrogenation under strongly basic conditions. Control experiments and density functional theory calculations demonstrate the mechanism via a Meerwein-Ponndorf-Verley mechanism, and the only byproduct is ethyl acetate. This study offers a new and simple approach for the synthesis of hydrazoarenes.

Highly Regio- and Stereoselective Hydrosilylation of Alkynes Catalyzed by Tridentate Cobalt Complexes.

Several cobalt complexes bearing tridentate (NNN) ligands were synthesized and served as precatalysts for alkyne hydrosilylation with Ph2 SiH2 . For terminal alkynes, the catalyst L2 b-CoCl2 was selected, and resulted in the corresponding α-vinylsilanes with high (Markovnikov) regioselectivity and extensive functional-group tolerance. For internal diaryl alkynes, the catalyst L2 c-CoCl2 exhibited the best activity, and afforded E-selective vinylsilanes through syn-addition in excellent yield under mild conditions.