Isolation of Cyclic Aluminium Polysulfides by Stepwise Sulfurization

Aluminadichalcogeniranes and Aluminatrichalcogenetanes: Heavier Analogs of Dioxiranes and Trioxetanes

Dioxiranes and their heavier chalcogen analogs have long been recognized as pivotal reagents and intermediates in synthetic chemistry, while trioxetanes have largely remained theoretical constructs. In this work, we present the synthesis of neutral, isoelectronic aluminum/chalcogen analogs of dioxiranes and trioxetanes, specifically aluminadiselenirane, aluminaditellurirane, aluminatriselenetane, aluminatritelluretane, and a mixed Se/Te analog of aluminatrichalcogenetane. These compounds, featuring strained AlCh2 and AlCh3 ring (Ch=Se, Te), exhibit significant polarization between the aluminum and chalcogen components. Reactivity studies have revealed that both aluminadiselenirane and aluminaditellurirane show pronounced ambiphilic behavior when interacting with proximal substrates, undergoing facile ring-opening (cyclo)additions. Additionally, the coordination chemistry of aluminatriselenetane with a Lewis acid has been documented. These investigations not only broaden the repertoire of unique main group species but also provide access to heterocyclic structures that present synthetic challenges through conventional methods.

NHC aluminum chemistry on the rise

This perspective highlights recent developments of the use of N-heterocyclic carbenes (NHCs) and cyclic (alkyl)(amino)carbenes (cAACs) in alane and aluminum organyl chemistry. Especially in the last few years this flourishing research field led to some remarkable discoveries including various substitution patterns at the central aluminum atom, different oxidation states, neutral and charged compounds with varying coordination numbers and unique reactivities. Thereby NHCs play a vital role in the stabilization of these otherwise highly reactive compounds, which would not be realizable without the use of this intriguing class of ligands. Nevertheless, main group hydrides and especially NHC ligated alanes also tend to undergo NHC decomposition reactions, which are part of ongoing research and provide important information for NHC research in general.

NHC-ligated indenyl- and fluorenyl-substituted Alanes and Gallanes: synthons towards indenyl- and fluorenyl-bridged (AlC)n-heterocycles (n = 2,3)

Indenyl-(Ind) and fluorenyl-(Fl) substituted NHC-stabilized alanes and gallanes (NHC)·EH2R 1-12 (NHC = IiPrMe, IiPr, IMeMe; E = Al, Ga; R = Ind, Fl) were prepared via reaction of the corresponding NHC-iodoalanes and -gallanes with LiInd and LiFl, respectively. Analogously, the alane adducts with two Ind/Fl substituents (NHC)·AlHR213-18 (NHC = IiPrMe, IiPr, IMeMe; R = Ind, Fl) were obtained by using two equivalents of LiInd/LiFl. Elimination of indene and fluorene was induced thermally affording unusual dimeric and trimeric NHC-alane adducts {(NHC)·AlH2}2-μ-Fl 19-20 and {(NHC)·AlH-μ-R}n21-23 (R = Ind, Fl; n = 2, 3) with bridging indenyl and fluorenyl ligands.

An Aluminum Telluride with a Terminal Al=Te Bond and its Conversion to an Aluminum Tellurocarbonate by CO2 Reduction

Facile access to dimeric heavier aluminum chalcogenides [(NHC)Al(Tipp)-μ-Ch]₂ (NHC=IiPr (1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, IMe₄ (1,3,4,5-tetramethylimidazol-2-ylidene); Tipp=2,4,6-iPr₃ C₆ H₂ ; Ch=Se, Te) by treatment of NHC-stabilized aluminum dihydrides with elemental Se and Te is reported. The higher affinity of IMe₄ in comparison with IiPr toward the Al center in [(NHC)Al(Tipp)-μ-Ch]₂ can be used for ligand exchange. Additionally, the presence of excess IMe₄ allows for cleavage of the dimers to form a rare example of a neutral multiply bonded heavier aluminum chalcogenide in the form of a tetracoordinate aluminum complex, (IMe₄ )₂ (Tipp)Al=Te. This species reacts with three equivalents of CO₂ across two Al-C^NHC and the Al=Te bond affording a pentacoordinate aluminum complex containing a dianionic tellurocarbonate ligand [CO₂ Te]^2- , which is the first example of tellurium analogue of a carbonate [CO₃ ]^2- .