B-B vs. B-H Bond Activation in a (μ-Hydrido)diborane(4) Anion upon Cycloaddition with CO₂ , Isocyanates, or Carbodiimides.

ABSTRACT: The intriguing (μ-hydrido)diboranes(4) with their prominent pristine representative [B₂ H₅ ]^- have mainly been studied theoretically. We now describe the behavior of the planarized tetraaryl (μ-hydrido)diborane(4) anion [1H]^- in cycloaddition reactions with the homologous series of heterocumulenes CO₂ , iPrNCO, and iPrNCNiPr. We show that a C=O bond of CO₂ selectively activates the B-B bond of [1H]^- , while the μ-H ligand is left untouched ([2H]^- ). The carbodiimide iPrNCNiPr, in contrast, neglects the B-B bond and rather adds the B-bonded H^- ion to its central C atom to generate a formamidinate bridge across the B₂ pair ([3]^- ). As a hybrid, the isocyanate iPrNCO combines the reactivity patterns of both its congeners and gives two products: one of them ([4H]^- ) is related to [2H]^- , the other ([5]^- ) is an analog of [3]^- . We finally propose a mechanistic scenario that rationalizes the individual reaction outcomes and combines them to a coherent picture of B-B vs. B-H bond activation.

SUBMITTER: Trageser T 

PROVIDER: S-EPMC8252796 | biostudies-literature | 2021 Jun

REPOSITORIES: biostudies-literature