Electron-rich organosilicon compounds, such as 1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (2a), 2,5-dimethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (2b), 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (2c), and 1,1'-bis(trimethylsilyl)-1,1'-dihydro-4,4'-bipyridine (4), served as versatile reducing reagents of group 4-6 metal chloride complexes, such as Cp2TiCl2, Cp*2TiCl2 (Cp* = η(5)-C5Me5), Cp*TiCl3, Cp*TaCl4, and WCl4(PMe2Ph)2, to generate the corresponding low-valent metal species in a salt-free manner. Nitrogen-containing reductants, such as 2a-c and 4, had stronger reducing ability than the parent organosilicon reductants, 3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (1a) and 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (1b), as well as a pyridine-derived reductant, 1,4-bis(trimethylsilyl)-1-aza-2,5-cyclohexadiene (3). These greater effects of 2a-c and 4 are likely due to their negative one-electron redox potentials, as typically demonstrated in the reduction of Cp2TiCl2, for which compounds 2a and 4 gave the corresponding one-electron reduced products, pyrazine-bridged and 4,4'-bipyridyl-bridged dimeric Ti(III) complexes 5 and 6, and compounds 2b and 2c afforded the same double chloride-bridged dimeric Ti(III) complex, [Cp2Ti]2(μ-Cl)2 (7), though 1a and 1b could not reduce Cp2TiCl2. Application of the organosilicon compounds as reducing agents for catalytic reactions revealed that the combination of 2c and a catalytic amount of Cp2TiCl2 assisted a Reformatsky reaction of nonanal and ethyl 2-bromoisobutyrate and its derivatives to give ethyl 3-hydroxy-2,2-dimethylundecanoate and its derivatives. In this coupling reaction, 2c served as the best reductant among 2a-c and 4 due to the suppression of an undesired reaction between 2c and ethyl 2-bromoalkanoates.

Bright light rings: The direct coupling of phenylazoles with an internal alkyne proceeds efficiently in the presence of a rhodium catalyst and a copper oxidant to selectively give either the 1‐naphthyl‐ or 1‐anthrylazole derivatives through the cleavage of multiple CH bonds (see scheme; 1‐naphthylazole derivative not shown). Some of the products exhibit intense fluorescence in the solid state.

Alkene metathesis is a widely and increasingly used reaction in academia and industry because of its efficiency in terms of atom economy and its wide applicability. This reaction is notably responsible for the production of several million tons of propene annually. Such industrial processes rely on inexpensive silica-supported tungsten oxide catalysts, which operate at high temperatures (>350 °C), in contrast with the mild room temperature reaction conditions typically used with the corresponding molecular alkene metathesis homogeneous catalysts. This large difference in the temperature requirements is generally thought to arise from the difficulty in generating active sites (carbenes or metallacyclobutanes) in the classical metal oxide catalysts and prevents broader applicability, notably with functionalized substrates. We report here a low temperature activation process of well-defined metal oxo surface species using organosilicon reductants, which generate a large amount of active species at only 70 °C (0.6 active sites/W). This high activity at low temperature broadens the scope of these catalysts to functionalized substrates. This activation process can also be applied to classical industrial catalysts. We provide evidence for the formation of a metallacyclopentane intermediate and propose how the active species are formed.

The palladium-catalyzed oxidative vinylation of indole-3-carboxylic acids with alkenes effectively proceeds via directed C-H functionalization and decarboxylation to produce the corresponding 2-vinylated indoles. Similarly, pyrrole-, furan-, and thiophenecarboxylic acids also undergo decarboxylative vinylation.

We found that in situ generated cerium(IV) carboxylate generated by mixing the precursor Ce(O t Bu) 4 with the corresponding carboxylic acids served as efficient photocatalysts for the direct formation of carboxyl radicals from carboxylic acids under blue light-emitting diodes (blue LEDs) irradiation and air, resulting in catalytic decarboxylative oxygenation of aliphatic carboxylic acids to give C−O bond-forming products such as aldehydes and ketones. Control experiments revealed that hexanuclear Ce(IV) carboxylate clusters initially formed in the reaction mixture and the ligand-to-metal charge transfer nature of the Ce(IV) carboxylate clusters was responsible for the high catalytic performance to transform the carboxylate ligands to the carboxyl radical. In addition, the Ce(IV) carboxylate cluster catalyzed direct lactonization of 2-isopropylbenzoic acid to produce the corresponding peroxy lactone and γ-lactone via intramolecular 1,5-hydrogen atom transfer (1,5-HAT).