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Stereoisomerism02:52

Stereoisomerism

Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
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Cooperative allosteric transitions can occur in multimeric proteins, where each subunit of the protein has its own ligand-binding site. When a ligand binds to any of these subunits, it triggers a conformational change that affects the binding sites in the other subunits; this can change the affinity of the other sites for their respective ligands. The ability of the protein to change the shape of its binding site is attributed to the presence of a mix of flexible and stable segments in the...

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Ethylene tri- and tetramerization: a steric parameter selectivity switch from X-ray crystallography and computational

Nicoline Cloete1, Hendrik G Visser, Ilana Engelbrecht

  • 1R&D Division, SASOL Technology (Pty) Ltd., 1 Klasie Havenga Road, Sasolburg, South Africa.

Inorganic Chemistry
|February 12, 2013
PubMed
Summary

A new steric parameter, θN-sub, quantifies nitrogen bulk in PNP ligands for ethylene oligomerization. Increased steric bulk correlates with higher 1-hexene selectivity and a slight rise in 1-octene selectivity.

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Area of Science:

  • Organometallic Chemistry
  • Catalysis
  • Polymer Science

Background:

  • Ethylene oligomerization is crucial for producing alpha-olefins.
  • PNP ligands are effective in metal-catalyzed ethylene oligomerization.
  • Controlling selectivity in oligomerization remains a challenge.

Purpose of the Study:

  • To introduce and validate a new steric parameter (θN-sub) for PNP ligands.
  • To correlate ligand steric properties with catalytic performance in ethylene oligomerization.
  • To understand the influence of nitrogen substituents on product selectivity.

Main Methods:

  • Synthesis and characterization of various PNP ligands.
  • Preparation of metal complexes with these PNP ligands.
  • Evaluation of catalytic activity and selectivity in ethylene trimerization and tetramerization.
  • Calculation of the steric parameter (θN-sub) for ligands and complexes.

Main Results:

  • A quantitative steric parameter (θN-sub) was successfully developed for PNP ligands.
  • A clear correlation was observed between θN-sub values and 1-hexene selectivity.
  • Increased steric bulk at the nitrogen atom led to a slight increase in 1-octene selectivity.

Conclusions:

  • The θN-sub parameter effectively describes the steric environment around the nitrogen atom in PNP ligands.
  • Ligand sterics play a significant role in directing selectivity in ethylene oligomerization.
  • This parameter can aid in the rational design of catalysts for targeted alpha-olefin production.