Facile Catalytic Hydrosilylation of Pyridines

Isolable Silicon-Based Polycations with Lewis Superacidity

Molecular silicon polycations of the types R2 Si2+ and RSi3+ (R=H, organic groups) are elusive Lewis superacids and currently unknown in the condensed phase. Here, we report the synthesis of a series of isolable terpyridine-stabilized R2 Si2+ and RSi3+ complexes, [R2 Si(terpy)]2+ (R=Ph 12+ ; R2 =C12 H8 22+ , (CH2 )3 32+ ) and [RSi(terpy)]3+ (R=Ph 43+ , cyclohexyl 53+ , m-xylyl 63+ ), in form of their triflate salts. The stabilization of the latter is achieved through higher coordination and to the expense of reduced fluoride-ion affinities, but a significant level of Lewis superacidity is nonetheless retained as verified by theory and experiment. The complexes activate C(sp3 )-F bonds, as showcased by stoichiometric fluoride abstraction from 1-fluoroadamantane (AdF) and the catalytic hydrodefluorination of AdF. The formation of the crystalline adducts [2(F)]+ and [5(H)]2+ documents in particular the high reactivity towards fluoride and hydride donors.

Regioselective 1,2-hydroboration of N-heteroarenes using a potassium-based catalyst

1,2-Regioselective hydroboration of quinolines achieved using a potassium-based catalyst.

Trivalent Zirconium and Hafnium Metal-Organic Frameworks for Catalytic 1,4-Dearomative Additions of Pyridines and Quinolines

We report the quantitative conversion of [M^IV₆(μ₃-O)₄(μ₃-OH)₄Cl₁₂]^6- nodes in the MCl₂-BTC metal-organic framework into the [M^III₆(μ₃-O)₄(μ₃-ONa)₄H₆]^6- nodes in M^IIIH-BTC (M = Zr, Hf; BTC is 1,3,5-benzenetricarboxylate) via bimetallic reductive elimination of H₂ from putative [M^IV₆(μ₃-O)₄(μ₃-OH)₄H₁₂]^6- nodes. The coordinatively unsaturated M^IIIH centers in M^IIIH-BTC are highly active and selective for 1,4-dearomative hydroboration and hydrosilylation of pyridines and quinolines. This work demonstrated the potential of secondary building unit transformation in generating electronically unique and homogeneously inaccessible single-site solid catalysts for organic synthesis.

Catalytic Electrophilic C-H Silylation of Pyridines Enabled by Temporary Dearomatization

A CH silylation of pyridines that seemingly proceeds through electrophilic aromatic substitution (SE Ar) is reported. Reactions of 2- and 3-substituted pyridines with hydrosilanes in the presence of a catalyst that splits the SiH bond into a hydride and a silicon electrophile yield the corresponding 5-silylated pyridines. This formal silylation of an aromatic CH bond is the result of a three-step sequence, consisting of a pyridine hydrosilylation, a dehydrogenative CH silylation of the intermediate enamine, and a 1,4-dihydropyridine retro-hydrosilylation. The key intermediates were detected by (1) H NMR spectroscopy and prepared through the individual steps. This complex interplay of electrophilic silylation, hydride transfer, and proton abstraction is promoted by a single catalyst.