Palladium-Catalyzed Solid-State Polyfluoroarylation of Aryl Halides Using Mechanochemistry

The Suzuki-Miyaura cross-coupling between poly-fluorinated arylboron nucleophiles and aryl halides enables the efficient construction of polyfluorinated structural motifs frequently found in organic materials and catalysts. A key challenge associated with this transformation involves the slow transmetalation with weakly nucleophilic polyfluorinated organoboron reagents, which often reduces the yield of the coupling products. Here, we show that solid-state high-temperature ball-milling conditions facilitate a palladium-catalyzed cross-coupling with polyfluorinated arylboronic acids and pinacol esters employing a simple catalytic system in the absence of any stoichiometric additives. This reaction exhibits a broad substrate scope and can be carried out in air, and the use of large amounts of dry and degassed organic solvents is not required. The successful cross-coupling of weakly nucleophilic polyfluorinated organoboron reagents was ascribed to the extremely high concentrations of the substrates and the catalyst under solid-state conditions

A Glove-Box- and Schlenk-Line-Free Protocol for Solid-State C-N Cross-Coupling Reactions Using Mechanochemistry

Carbon-nitrogen (C-N) bond-forming cross-coupling reactions catalyzed by palladium-based catalysts, the so-called Buchwald-Hartwig aminations, have been widely employed for the synthesis of pharmaceuticals and aryl-amine-based organic materials in academic and industrial settings. However, in solution, these reactions usually require glovebox and Schlenk line techniques, which greatly reduces their practical utility. Here, we report the development of operationally simple mechanochemical C-N cross-coupling reactions in the solid-state. Intensive investigations of various ball milling parameters revealed that the air-stable ligand tri(1-adamantyl)phosphine can be used to achieve solid-state coupling reactions between aryl halides and diarylamines with high efficiency. Notably, all experimental operations of the developed protocol can be carried out in air, thus providing a more convenient, industrially attractive, and sustainable alternative to conventional solution-based palladium-catalyzed C-N coupling reactions

General Synthesis of Trialkyl- and Dialkylarylsilylboranes: Versatile Silicon Nucleophiles in Organic Synthesis

Compared to carbon-based nucleophiles, the number of silicon-based nucleophiles that is currently available remains limited, which significantly hampers the structural diversity of synthetically accessible silicon-based molecules. Given the high synthetic utility and ease of handling of carbon-based boron nucleophiles, silicon-based boron nucleophiles, i.e., silylboranes, have attracted considerable interest in recent years as nucleophilic silylation reagents that are activated by transition-metal catalysts or bases. However, the range of practically accessible silylboranes remains limited. In particular, the preparation of sterically hindered and functionalized silylboranes remains a significant challenge. Here, we report the use of rhodium and platinum catalysts for the direct borylation of hydrosilanes with bis(pinacolato)diboron, which allows the synthesis of new trialkylsilylboranes that bear bulky alkyl groups and functional groups as well as new dialkylarylsilylboranes that are difficult to synthesize via conventional methods using alkali metals. We further demonstrate that these compounds can be used as silicon nucleophiles in organic transformations, which significantly expands the scope of synthetically accessible organosilicon compounds compared to previously reported methods. Thus, the present study can be expected to inspire the development of efficient methods for novel silicon-containing bioactive molecules and organic materials with desirable properties. We also report the first B-11{H-1} and Si-29(H-1) NMR spectroscopic evidence for the formation of i-Pr3SiLi generated by the reaction of i-Pr3Si-B(pin) with MeLi

General Synthesis of Trialkyl- and Dialkylarylsilylboranes: Versatile Silicon Nucleophiles in Organic Synthesis

Compared to carbon-based nucleophiles, the number of silicon-based nucleophiles that is currently available remains limited, which significantly hampers the structural diversity of synthetically accessible silicon-based molecules. Given the high synthetic utility and ease of handling of carbon-based boron nucleophiles, silicon-based boron nucleophiles, i.e., silylboranes, have attracted considerable interest in recent years as nucleophilic silylation reagents that are activated by transition-metal catalysts or bases. However, the range of practically accessible silylboranes remains limited. In particular, the preparation of sterically hindered and functionalized silylboranes remains a significant challenge. Here, we report the use of rhodium and platinum catalysts for the direct borylation of hydrosilanes with bis(pinacolato)diboron, which allows the synthesis of new trialkylsilylboranes that bear bulky alkyl groups and functional groups as well as new dialkylarylsilylboranes that are difficult to synthesize via conventional methods using alkali metals. We further demonstrate that these compounds can be used as silicon nucleophiles in organic transformations, which significantly expands the scope of synthetically accessible organosilicon compounds compared to previously reported methods. Thus, the present study can be expected to inspire the development of efficient methods for novel silicon-containing bioactive molecules and organic materials with desirable properties. We also report the first B-11{H-1} and Si-29(H-1) NMR spectroscopic evidence for the formation of i-Pr3SiLi generated by the reaction of i-Pr3Si-B(pin) with MeLi