With Cp3tAl, a monomeric Al(i) species was isolated, which reacted faster, more selectively, and under milder conditions than well-known tetrameric (Cp*Al)4.

The reduction of a cyclic alkyl(amino)carbene (CAAC)‐stabilized organoberyllium chloride yields the first neutral beryllium radical, which was characterized by EPR, IR, and UV/Vis spectroscopy, X‐ray crystallography, and DFT calculations.

Reactions between B III species and the novel nucleophilic cyclopentadienyl-stabilized Al I reagent (1)r esult in ad iversity of complexes bearing different Al/B oxidation states and coordination geometries.W ith the triarylborane B(C 6 F 5 ) 3 ,asimple Al I !B III adduct is formed. In contrast, ab ulky aryldihaloborane undergoes oxidative addition with the formation of ac ovalent bora-alane species.W itha nNheterocyclic carbene-stabilized amino(bromo)borenium ion, aredox reaction was observed, where the product is aborylenealane B I !Al III complex. Additionally,r eaction of 1 with BI 3 results in complete scrambling of all of the Al/B-bound substituents,a nd the formation of ac yclopentadienylboron-(I)!AlI 3 complex. These latter reactions are the first examples of the reduction of ab oron(III) compound to ab orylene by ap -blockr eagent, and illustrate how subtle changes in the nature of the borane can result in highly divergent reaction outcomes.

The concepts of aromaticity and antiaromaticity have a long history, and countless demonstrations of these phenomena have been made with molecules based on elements from the p, d, and f blocks of the periodic table. In contrast, the limited oxidation‐state flexibility of the s‐block metals has long stood in the way of their participation in sophisticated π‐bonding arrangements, and truly antiaromatic systems containing s‐block metals are altogether absent or remain poorly defined. Using spectroscopic, structural, and computational techniques, we present herein the synthesis and authentication of a heterocyclic compound containing the alkaline earth metal beryllium that exhibits significant antiaromaticity, and detail its chemical reduction and Lewis‐base‐coordination chemistry.