Palladium-Catalyzed Intermolecular Coupling of 2-Silylaryl Bromides with Alkynes: Synthesis of Benzosiloles and Heteroarene-Fused Siloles by Catalytic Cleavage of the C(sp3)Si Bond

Synthetic strategies to access silacycles

In comparison with all-carbon parent compounds, the incorporation of Si-element into carboskeletons generally endows the corresponding sila-analogues with unique biological activity and physical-chemical properties. Silacycles have recently shown promising application potential in biological chemistry, pharmaceuticals industry, and material chemistry. Therefore, the development of efficient methodology to assemble versatile silacycles has aroused increasing concerns in the past decades. In this review, recent advances in the synthesis of silacycle-system are briefly summarized, including transition metal-catalytic and photocatalytic strategies by employing arylsilanes, alkylsilane, vinylsilane, hydrosilanes, and alkynylsilanes, etc. as starting materials. Moreover, a clear presentation and understanding of the mechanistic aspects and features of these developed reaction methodologies have been high-lighted.

Nickel-Catalyzed Reductive [4 + 1] Sila-Cycloaddition of 1,3-Dienes with Dichlorosilanes

Transition-metal-catalyzed sila-cycloaddition has been a promising tool for accessing silacarbocycle derivatives, but the approach has been limited to a selection of well-defined sila-synthons. Herein, we demonstrate the potential of chlorosilanes, which are industrial feedstock chemicals, for this type of reaction under reductive nickel catalysis. This work extends the scope of reductive coupling from carbocycle to silacarbocycle synthesis and from single C-Si bond formation to sila-cycloaddition reactions. The reaction proceeds under mild conditions and shows good substrate scope and functionality tolerance, and it offers new access to silacyclopent-3-enes and spiro silacarbocycles. The optical properties of several spiro dithienosiloles as well as structural variations of the products are demonstrated.

Nickel(0)-Catalyzed Asymmetric Ring Expansion Toward Enantioenriched Silicon-Stereogenic Benzosiloles

The development of a straightforward strategy to obtain enantioenriched silicon-stereogenic benzosiloles remains a challenging yet appealing synthesis venture due to their potential future application in chiral electronic and optoelectronic devices. In this context, all of the existing methods rely on Rh-catalyzed systems and are somewhat limited in scope. Herein, we disclose the first Ni⁰ -catalyzed ring expansion process that enables the preparation of benzosiloles possessing tetraorganosilicon stereocenters in excellent yields and enantioselectivities. The presented catalysis strategy is further applied to the asymmetric synthesis of silicon-stereogenic bis-silicon-bridged π-extended systems. Preliminary studies reveal that such compounds exhibit fluorescence emission, Cotton effects and circularly polarized luminescence (CPL) activity.

Rhodium-Catalyzed Intramolecular C-H Silylation by Silacyclobutanes

Silacyclobutane was discovered to be an efficient C-H bond silylation reagent. Under the catalysis of Rh(I) /TMS-segphos, silacyclobutane undergoes sequential C-Si/C-H bond activations, affording a series of π-conjugated siloles in high yields and regioselectivities. The catalytic cycle was proposed to involve a rarely documented endocyclic β-hydride elimination of five-membered metallacycles, which after reductive elimination gave rise to a Si-Rh(I) species that is capable of C-H activation.

Recent advances in carbon dioxide capture, fixation, and activation by using N-heterocyclic carbenes

In the last two decades, CO2 emission has caused a lot of environmental problems. To mitigate the concentration of CO2 in the atmosphere, various strategies have been implemented, one of which is the use of N-heterocyclic carbenes (NHCs) and related complexes to accomplish the capture, fixation, and activation of CO2 effectively. In this review, we summarize CO2 capture, fixation, and activation by utilizing NHCs and related complexes; homogeneous reactions and their reaction mechanisms are discussed. Free NHCs and NHC salts can capture CO2 in both direct and indirect ways to form imidazolium carboxylates, and they can also catalyze the reaction of aromatic aldehydes with CO2 to form carboxylic acids and derivatives. Moreover, associated with transition metals (TMs), NHCs can form NHC-TM complexes to transform CO2 into industrial acid or esters. Non-metal-NHC complexes can also catalyze the reactions of silicon and boron complexes with CO2 . In addition, catalytic cycloaddition of epoxides with CO2 is another effective function of NHC complexes, and NHC ionic liquids perform excellently in this aspect.