Incorporating the silicon element into bioactive organic molecules has received increasing attention in medicinal chemistry. Moreover, organosilanes are valuable synthetic intermediates for fine chemicals and materials. Transition metal-catalyzed C-H silylation has become an important strategy for C-Si bond formations. However, despite the great advances in aromatic C(sp)-H bond silylations, catalytic methods for aliphatic C(sp)-H bond silylations are relatively rare. Here we report a pincer ruthenium catalyst for intramolecular silylations of various primary C(sp)-H bonds adjacent to heteroatoms (O, N, Si, Ge), including the first intramolecular silylations of C-H bonds α to O, N, and Ge. This method provides a general, synthetically efficient approach to novel classes of Si-containing five-membered [1,3]-sila-heterocycles, including oxasilolanes, azasilolanes, disila-heterocycles, and germasilolane. The trend in the reactivity of five classes of C(sp)-H bonds toward the Ru-catalyzed silylation is elucidated. Mechanistic studies indicate that the rate-determining step is the C-H bond cleavage involving a ruthenium silyl complex as the key intermediate, while a η-silene ruthenium hydride species is determined to be an off-cycle intermediate.
A series
of new hydrido Ru(II) olefin complexes supported by isopropyl-substituted
pincer ligands have been synthesized and characterized. These complexes
are thermally robust and active for catalytic transfer and acceptorless
alkane dehydrogenation. Notably, the alkane dehydrogenation catalysts
are tolerant of a number of polar functional species.
Catalytic α-alkylation of esters with primary alcohols is a desirable process because it uses low-toxicity agents and generates water as the by-product. Reported herein is a NCP pincer/Ir catalyst which is highly efficient for α-alkylation of a broad scope of unactivated esters under mild reaction conditions. For the first time, alcohols alkylate unactivated α-substituted acyclic esters, lactones, and even methyl and ethyl acetates. This method can be applied to the synthesis of carboxylic acid derivatives with diverse structures and functional groups, some of which would be impossible to access by conventional enolate alkylations with alkyl halides.
Reported herein is the development of a simple but practical catalytic system for the selective reduction of amides with hydrosilane or hydrosiloxane. Low-cost and readily available triethylborane (1.0 M in THF), in combination with a catalytic amount of an alkali metal base, was found to catalyze the reduction of all three amide classes (tertiary, secondary, and primary amides) to form amines under mild conditions. In addition, the selective transformation of secondary amides to aldimines and primary amides to nitriles can also be achieved by using a proper combination of BEt 3 and base. The scope of these BEt 3 -base-catalyzed amide hydrosilylation reactions has been explored in depth. Preliminary results of mechanistic studies suggest a modified Piers' silane Si−H•••B activation mode wherein the hydride abstraction by BEt 3 is promoted by the coordination of an alkoxide or hydroxide anion to the Si center.
We report the first Co-catalyzed
borylation of aryl halides and
pseudohalides with bis(pinacolato)diboron (B2pin2). The synthesis of two new Co(II) complexes of oxazolinylferrocenylphosphine
ligands is described. Upon activation with LiMe, the Co complex catalyzes
the borylation reactions of aryl bromides, iodides, sulfonates, arenediazonium
salts, and even aryl chlorides under mild conditions, providing the
borylated products in excellent to moderate yields and with high functional
group tolerance.
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