Selective Reduction of Esters to Aldehydes under the Catalysis of Well-Defined NHC-Iron Complexes

Metal-Free Catalytic Hydrogenolysis of Silyl Triflates and Halides into Hydrosilanes

The metal-free catalytic hydrogenolysis of silyl triflates and halides (I, Br) to hydrosilanes is unlocked by using arylborane Lewis acids as catalysts. In the presence of a nitrogen base, the catalyst acts as a Frustrated Lewis Pair (FLP) able to split H₂ and generate a boron hydride intermediate capable of reducing (pseudo)halosilanes. This metal-free organocatalytic system is competitive with metal-based catalysts and enables the formation of a variety of hydrosilanes at room temperature in high yields (>85 %) under a low pressure of H₂ (≤10 bar).

Synthesis and Reactivity of N-Heterocyclic Silylene Stabilized Disilicon(0) Complexes

Synthesis and reactivity of disilicon(0) complexes are of fundamental and application importance. Herein, we report the development of an N-heterocyclic imino-substituted silylene (1), which has strong σ-donating ability and is significantly sterically hindered. The one-pot reaction of this silylene with [IPr→SiCl₂ ] (IPr=1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene) and KC₈ (2 equiv) in THF at -30 °C leads to a silylene-ligated disilicon(0) complex (2), isolated as red crystals in 60 % yield. Characterization data and DFT calculations show that the trans-bent Si₄ skeleton in 2 features a Si⁰ =Si⁰ double bond with significant π-π bonding and one lone pair of electrons on each of these two Si⁰ atoms. Complex 2 reacts readily with phenylacetylene, producing a structurally intriguing silatricyclic complex 6,8-diaza-1,2,5-trisilatricyclo-[3.2.1.0^2,7 ]-oct-3-ene (3), and revealing new aspects of low-valent silicon chemistry.

Iron-Catalysed Reductive Amination of Carbonyl Derivatives with ω-Amino Fatty Acids to Access Cyclic Amines

An efficient method for the reductive amination of carbonyl derivatives with ω-amino fatty acids catalysed by an iron complex Fe(CO)₄ (IMes) [IMes=1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] by means of hydrosilylation was developed. A variety of pyrrolidines, piperidines and azepanes were selectively synthesised in moderate-to-excellent yields (36 examples, 47-97 % isolated yield) with a good functional group tolerance.

Size-Exclusion Borane-Catalyzed Domino 1,3-Allylic/Reductive Ireland-Claisen Rearrangements: Impact of the Electronic and Structural Parameters on the 1,3-Allylic Shift Aptitude

The reductive Ireland-Claisen rearrangement through borane-mediated hydrosilylation is reported. The method employs a borane catalyst with a special structural design and affords access to synthetically relevant products with high diastereoselectivity. Depending on electronic and structural parameters, the reaction can be coupled with a 1,3-allylic shift, thus the valence isomer of the Ireland-Claisen product is formed.

Cation-Triggered Stannate(II)/Stannylenoid/Stannylene Conversion

The reaction of dipotassio-tetrasilan-1,4-diide (4) with anhydrous SnCl₂ at low temperature results in the formation of a five-membered cyclic potassio chlorostannate(II) ([(18-C-6)K](1)). By careful cation exchange reactions, it was transformed into the sodium chlorostannylenoid 2 (by using Na₂ [B₁₂ Cl₁₂ ]) or into the non-stabilized cyclic bissilylstannylene 3 (through applying Li[Al(OC(CF₃ )₃ )₄ ]). The increasing Lewis basicity of the bissilylstannylene 3 was analyzed by combined methods of DFT calculations and NMR spectroscopy and substantiated by the synthesis of the corresponding iron carbonyl complexes 7 and 8 from the chlorostannate 1 and the stannylene 3, respectively.

Selective Reductive Removal of Ester and Amide Groups from Arenes and Heteroarenes through Nickel-Catalyzed C-O and C-N Bond Activation

An inexpensive nickel(II) catalyst and a hydrosilane were used for the efficient reductive defunctionalization of aryl and heteroaryl esters through a decarbonylative pathway. This versatile method could be used for the removal of ester and amide functional groups from various organic molecules. Moreover, a scale-up experiment and a synthetic application based on the use of a removable carboxylic acid directing group highlight the usefulness of this reaction.

Lewis acid promoted ruthenium(II)-catalyzed etherifications by selective hydrogenation of carboxylic acids/esters

Ethers are of fundamental importance in organic chemistry and they are an integral part of valuable flavors, fragrances, and numerous bioactive compounds. In general, the reduction of esters constitutes the most straightforward preparation of ethers. Unfortunately, this transformation requires large amounts of metal hydrides. Presented herein is a bifunctional catalyst system, consisting of Ru/phosphine complex and aluminum triflate, which allows selective synthesis of ethers by hydrogenation of esters or carboxylic acids. Different lactones were reduced in good yields to the desired products. Even challenging aromatic and aliphatic esters were reduced to the desired products. Notably, the in situ formed catalyst can be reused several times without any significant loss of activity.