Aluminum(I)/Boron(III) Redox Reactions

Reactions between BIII species and the novel nucleophilic cyclopentadienyl‐stabilized AlI reagent (1) result in a diversity of complexes bearing different Al/B oxidation states and coordination geometries. With the triarylborane B(C6F5)3, a simple AlI→BIII adduct is formed. In contrast, a bulky aryldihaloborane leads to oxidative addition and 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 BI→AlIII complex. Additionally, reaction of 1 with BI3 results in complete scrambling of all of the Al/B bound substituents, and the formation of a cyclopentadienyboron(I)→AlI3 complex. These latter reactions are the first examples of the reduction of a boron(III) compound to a borylene by p‐block reagent, and illustrate how subtle changes in the nature of the borane can result in highly divergent reaction outcomes.

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