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Related Concept Videos

Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation02:47

Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation

Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
Benzene to 1,4-Cyclohexadiene: Birch Reduction Mechanism01:18

Benzene to 1,4-Cyclohexadiene: Birch Reduction Mechanism

Birch reduction uses solvated electrons as reducing agents. The reaction converts benzene to 1,4-cyclohexadiene. The reaction proceeds by the transfer of a single electron to the ring to form a benzene radical anion. This anion is highly basic—it abstracts a proton from the alcohol to form a cyclohexadienyl radical. Another single electron transfer gives the cyclohexadienyl anion. A proton transfer from the alcohol forms 1,4-cyclohexadiene. Since this reduction occurs via radical anion...
Vicinal Diols via Reductive Coupling of Aldehydes or Ketones: Pinacol Coupling Overview01:27

Vicinal Diols via Reductive Coupling of Aldehydes or Ketones: Pinacol Coupling Overview

Wilhelm Rudolph Fittig discovered the pinacol coupling reaction in 1859. It is a radical dimerization reaction and involves the reductive coupling of aldehydes or ketones in the presence of hydrocarbon solvent to yield vicinal diols.
Hydroboration-Oxidation of Alkenes03:08

Hydroboration-Oxidation of Alkenes

In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
Regioselectivity and Stereochemistry of Hydroboration02:36

Regioselectivity and Stereochemistry of Hydroboration

A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Nucleophilic Aromatic Substitution: Elimination–Addition01:11

Nucleophilic Aromatic Substitution: Elimination–Addition

Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is confirmed through isotopic...

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Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy
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Reductive borylene-CO coupling with a bulky arylborylene complex.

Holger Braunschweig1, Rian D Dewhurst, Christian Hörl

  • 1Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg (Germany) http://www-anorganik.chemie.uni-wuerzburg.de/Braunschweig/. h.braunschweig@uni-wuerzburg.de.

Angewandte Chemie (International Ed. in English)
|July 30, 2013
PubMed
Summary
This summary is machine-generated.

Reduction of bulky arylborylene complexes causes metal-boron bond cleavage and borylene coupling with CO ligands. In contrast, aminoborylene complexes undergo complete ligand loss, highlighting distinct reactivity pathways.

Keywords:
borylenechromiummetal carbonyl complexesreductionterphenyl

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Published on: September 18, 2016

Area of Science:

  • Organometallic Chemistry
  • Boron Chemistry

Background:

  • Borylene complexes are reactive intermediates with unique electronic properties.
  • Understanding their reactivity is crucial for developing new catalytic processes.

Purpose of the Study:

  • To investigate the reduction of bulky arylborylene complexes.
  • To compare the reactivity of arylborylene and aminoborylene complexes upon reduction.
  • To elucidate the factors governing borylene ligand behavior under reductive conditions.

Main Methods:

  • Synthesis and characterization of a novel bulky arylborylene complex.
  • Reductive experiments on arylborylene and aminoborylene complexes.
  • Structural and spectroscopic analysis (e.g., X-ray diffraction, NMR spectroscopy).
  • Density Functional Theory (DFT) calculations.

Main Results:

  • Partial metal-boron bond cleavage and coupling of the borylene ligand with two CO ligands upon reduction of the bulky arylborylene complex.
  • Structural and spectroscopic characterization of the borylene precursor and the dianionic product.
  • Complete loss of the borylene ligand and classical Hieber reduction upon reduction of the aminoborylene complex.
  • DFT calculations provided a rationale for the observed differences in reactivity.

Conclusions:

  • The steric bulk of the aryl group significantly influences the reduction pathway of borylene complexes.
  • Arylborylene complexes can undergo CO-coupling reactions, offering new synthetic possibilities.
  • Aminoborylene complexes follow a different reduction pathway, leading to ligand fragmentation.
  • Electronic and steric factors dictate the outcome of borylene complex reduction.