Aluminum(I)/Boron(III) Redox Reactions

All good things come in threes: Reactions of an Al^I nucleophile with B^III species leads to three distinct modes of reactivity: adduct formation (Al^I‐B^III), oxidative addition (Al^II‐B^II), and reduction (Al^III‐B^I). IMes=1,3‐dimesitylimidazol‐2‐ylidene, TerPh^iPr=bis‐2,6‐(2,4,6‐triisopropylphenyl)phenyl.

Abstract

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(C₆F₅)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 BI₃ results in complete scrambling of all of the Al/B‐bound substituents, and the formation of a cyclopentadienylboron(I)→AlI₃ 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.

from A via a.sfakia on Inoreader http://bit.ly/2RJAzWs