Since the groundbreaking discovery in 2018 that the synthesis of a bottleable nucleophilic aluminyl anion is feasible, a handful of derivatives have been developed to date, which are, however, limited to diamino- and dialkyl-substituted species. Herein, we report the synthesis of a cyclic (alkyl)­(amino)­aluminyl anion based on a five-membered framework. The dicoordinate aluminum center features both a lone pair of electrons and an unoccupied 3p orbital, thus genuinely making it isoelectronic with carbenes. We show the bond formation and bond activation at the Al sphere: thus, not only does it undergo electron redistribution with borane to furnish a heteroatomic group 13 ring exhibiting a σ-aromatic nature concomitant with a three-center two-electron AlB2 bond but also the ambiphilic nature allows for oxidative addition of Si–H, N–H, and even C–C bonds at the aluminum center.

9-Phosphaanthracene (dibenzo[b,e]phosphorin, acridophosphine) has attracted interest as one of the heavier acenes. Herein, we demonstrate an efficient synthetic process that provides air-tolerant 1,8-bis(trifluoromethyl)-9-phosphaanthracenes. The sterically encumbered and electron-withdrawing trifluoromethyl (CF ) groups are quite advantageous not only to stabilize the intrinsically unstable heavier unsaturated phosphorus atom but also to facilitate construction of the phosphinine skeleton based on a putative increase in aromaticity. The isolated 9-phosphaanthracenes allowed characterization of their fluorescence functionality and planar heteroanthracene frameworks. The crystal structures of 9-phosphaanthracenes are remarkably dependent on the aryl substituents at the 10 position; anthryl-substituted 9-phosphaanthracene showed unique polymorphs that induced different-colored crystals.

Since aluminum is the most electropositive element among the p-block elements, the construction of molecules bearing a dianionic Al–Al σ-bond is inherently highly challenging. Herein, we report the first synthesis of a dianionic dialane(6) 2 based on the Al2O three-membered ring scaffold, namely, an aluminum analog of oxirane. The structure of 2 has been unambiguously ascertained by spectroscopic analysis as well as X-ray crystallography, and computational studies revealed that 2 bears a highly strained Al–Al σ-bond. 2 readily reacts with the unsaturated substrates such as isocyanide, ethylene, and ketone, concomitant with the cleavage of the Al–Al σ-bond under mild conditions, leading to the four- and five-membered heterocycles 3–5. Furthermore, the reaction of 2 with two molecules of benzonitrile (PhCN) furnishes a seven-membered heterocycle 6, resulting from the C–C coupling reaction of PhCN. We further delineate that 2 selectively activates an arene ring C–C bond of biphenylene, rendering a di-Al-substituted benzo[8]­annulene derivative 7. Preliminary computational studies propose that the stepwise reaction mechanism involves the Al–Al σ-bond cleavage, dearomative Al–C bond formation, subsequent sigmatropic [1,3]­shifts, and a pericyclic reaction.

A 1,3-diphosphacyclobutane-2,4-diyl contains a unique unsaturated cyclic unit, and the presence of radical-type centers have been expected as a source of functionality. This study demonstrates that the P-heterocyclic singlet biradical captures muonium (Mu=[μ e ]), the light isotope of a hydrogen radical, to generate an observable P-heterocyclic paramagnetic species. Investigation of a powder sample of 2,4-bis(2,4,6-tri-t-butylphenyl)-1-t-butyl-3-benzyl-1,3-diphosphacyclobutane-2,4-diyl using muon (avoided) level-crossing resonance (μLCR) spectroscopy revealed that muonium adds to the cyclic P C unit. The muon hyperfine coupling constant (A ) indicated that the phosphorus atom bearing the t-butyl group trapped muonium to provide a metastable P-heterocyclic radical involving the ylidic MuP(<)=C moiety. The observed regioselective muonium addition correlates the canonical formula of 1,3-diphosphacyclobutane-2,4-diyl.

The stable cyclic (alkyl)(amino)alumanyl anion (CAAAl) 3 reacts with white phosphorus (P 4 ) under ambient conditions, in which P 4 is fragmented into a P 1 unit to afford the bis(alumanyl)phosphide 2, demonstrating the direct formation of a P anion from an Al anion. Structural and electronic features of the latter were fully characterized by standard spectroscopic means, X-ray diffraction analysis, and computational studies, which revealed that 2 bears highly polarized Al (δ+) and P (δ−) and relatively short Al−P bonds, indicative of the σ-donating and π-accepting nature of CAAAl groups.