Siloxanes have evolved into a multi‐million dollar business due to their manifold of commercial and industrial applications. As siloxanes have high hydrophobicity, low basicity, high flexibility and also high chemical inertness in common, their chemistry differs significantly from that of organic ethers. The discovery of organic crown ethers, for instance, is commonly accepted as the birth of synthetic host‐guest chemistry. Regarding the chemical properties of siloxanes, cyclic siloxanes which formally resemble silicon analogues of crown ethers, have received considerably less interest in terms of their host‐guest chemistry. Hence, only little is known about siloxane coordination chemistry in the chemical community and the number of published works in this field has been very low till lately. In the last few years, the field has significantly advanced and elegant methods were established to enable the Si−O−Si unit for coordination. This review therefore summarizes the recent developments in the field, recapitulates the historical aspects of siloxane coordination chemistry and describes the specific Si−O bond character with regard to different siloxane linkages. Implications on Si−O bond activation are included and the limits of siloxane coordination are redefined.

Heavier group 13/15 multiple bonds have been under investigation since the late 80s and to date, several examples have been published, which shows the obsoleteness of the so-called double bond rule. Especially in the last few years, more and more group 13/15 multiple bonds became synthetically feasible and their application in terms of small molecule activation has been demonstrated. Our group has recently shown that the combination of the pnictinidene precursor ^DipTer–Pn(PMe₃) (Pn = P, As) in combination with Al(I) synthons afforded the first examples of phospha- and arsaalumenes as isolable and thermally robust compounds. This feature article is intended to show the recent developments in the field, to outline early synthetic approaches and to discuss strategies to unlock the synthetic potential of these elusive chemical bonds.

N‐containing molecules are mostly derived from ammonia (NH₃). Ammonia activation has been demonstrated for single transition metal centers as well as for low‐valent main group species. Phosphinidenes, mono‐valent phosphorus species, can be stabilized by phosphines, giving so‐called phosphanylidenephosphoranes of the type RP(PR′₃). We demonstrate the facile, metal‐free NH₃ activation using ArP(PMe₃), affording for the first time isolable secondary aminophosphines ArP(H)NH₂. DFT studies reveal that two molecules of NH₃ act in concert to facilitate an NH₃ for PMe₃ exchange. Furthermore, H₂NR and HNR₂ activation is demonstrated.

Heterocycles containing group 13 and 15 elements such as borazines are an integral part of organic, biomedical and materials chemistry. Surprisingly, heterocycles containing P and Al are rare. We have now utilized phosphaalumenes in reactions with alkynes, alkenes and conjugated double bond systems. With sterically demanding alkynes 1,2‐phosphaalumetes were afforded, whereas the reaction with HCCH or HCCSiMe₃gave 1,4‐phosphaaluminabarrelenes. Using styrene saturated 1,2‐phosphaalumates were formed, which reacted further with additional styrene to give different regio‐isomers of 1,4‐aluminaphosphorinanes. Using ethylene, a 1,4‐aluminaphosphorinane is obtained, while with 1,3‐butadiene a bicyclic system containing an aluminacyclopentane and a phosphirane unit was synthesized. The experimental work is supported by theoretical studies to shed light on the mechanism governing the formation of these heterocycles.

The reaction of partially silicon based crown ethers with BeCl₂ yields eight-membered Be–O-heterocycles, which are annulated by two six-membered Be–O-cycles.

Compounds consisting of [M(1,2-disila-[3n]crown-n)]²⁺ (M = Mg, Ca, Sr, Ba; n = 5, 6) and [Ba(1,2-disila-benzo[18]crown-6)]²⁺ cations and different anions were obtained by equimolar reaction of the hybrid disila-crown ethers 1,2-disila[15]crown-5 (1), 1,2-disila[18]crown-6 (2) and 1,2-disila-benzo[18]crown-6 (7) with alkaline earth metal salts. Even with strongly coordinating anions such as Br⁻ or I⁻ stable complexes could be obtained, showing the good coordination ability of these ligands. The structures of all coordination compounds were determined via single crystal X-ray diffraction (XRD). By means of DFT calculations, the complexation ability of 1,2-disila[15]crown-5 (1) towards magnesium bromide was determined to be considerably higher compared to [15]crown-5. The opposite case was observed in solution as the exchange of calcium cations between [18]crown-6 and 1,2-disila[18]crown-6 (2) was studied via dynamic proton nuclear magnetic resonance (NMR) spectroscopy.