Aluminum(I)/Boron(III) Redox Reactions

Reactions between B III species and the novel nucleophilic cyclopentadienyl‐stabilized Al I reagent ( 1 ) result in a diversity of complexes bearing different Al/B oxidation states and coordination geometries. With the triarylborane B(C 6 F 5 ) 3 , a simple Al I →B III adduct is formed. In contrast, a bulky aryldihaloborane undergoes oxidative addition with the formation of a covalent bora‐alane species. With an N‐heterocyclic carbene‐stabilized amino(bromo)borenium ion, a redox reaction was observed, where the product is a borylene‐alane B I →Al III complex. Additionally, reaction of 1 with BI 3 results in complete scrambling of all of the Al/B‐bound substituents, and the formation of a cyclopentadienylboron(I)→AlI 3 complex. These latter reactions are the first examples of the reduction of a boron(III) compound to a borylene by a p‐block reagent, and illustrate how subtle changes in the nature of the borane can result in highly divergent reaction outcomes.