Since the discovery of the first stable N-heterocyclic carbene (NHC) in the beginning of the 1990s, these divalent carbon species have become a common and available class of compounds, which have found numerous applications in academic and industrial research. Their important role as two-electron donor ligands, especially in transition metal chemistry and catalysis, is difficult to overestimate. In the past decade, there has been tremendous research attention given to the chemistry of low-coordinate main group element compounds. Significant progress has been achieved in stabilization and isolation of such species as Lewis acid/base adducts with highly tunable NHC ligands. This has allowed investigation of numerous novel types of compounds with unique electronic structures and opened new opportunities in the rational design of novel organic catalysts and materials. This Review gives a general overview of this research, basic synthetic approaches, key features of NHC-main group element adducts, and might be useful for the broad research community.

Silylenes have recently shown fascinating reactivity patterns, which are normally observed almost exclusively for transition-metal complexes. In particular, very reactive representatives are considered to be promising candidates, which may become powerful and economical alternatives for catalytic applications in the future. Here, we present the isolation of an equilibrium mixture consisting of a tetrasilyldisilene and its isomeric bis­(silyl)­silylene, the first isolable silylene of this type. Preliminary investigations demonstrate the extreme inherent reactivity via facile small-molecule activation even under very mild conditions. Thus, the oxidative addition of challenging targets such as H2 and NH3 was achieved. In addition, by synthesizing donor-stabilized bis­(silyl)­silylenes we gained further insights into the disilene–silylene rearrangement by 1,2-silyl migrations. Thorough theoretical calculations support the observed experimental results.

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The straightforward synthesis of a series of poly(thioether)s by photoinduced thiol-ene click polyaddition of α,ω-alkylene thiols is reported. It is found that linear and telechelic poly(thioether)s can be directly obtained from α,ω-alkylene thiols with, for example, alkyl chain length of m = 1,2,3, and 9. The reaction proceeds without additives such as (radical) initiators or metal compounds and can simply be carried out by UV-irradiation of the bulk monomer or monomer solution. Ex situ kinetic studies reveal that the reaction proceeds by a typical a step-growth polyaddition mechanism. As the homologue series of poly(thioether)s are now synthetically accessible, new direct pathways to tailored poly(alkyl sulphoxide)s and poly(alkyl sulfone)s are now possible.

DMAP-stabilized silylenes 1a–c, which are convenient, room temperature stable synthetic equivalents for the corresponding highly reactive free bis(silyl)silylenes are reported.