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Published on: November 9, 2019
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Enhanced Stibine Oxide Lewis Basicity Overcomes Steric Frustration.
Addis Getahun1, John S Wenger1, Timothy C Johnstone1
1Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, California 95064, United States.
Organometallics
|September 26, 2025
Summary
Heavier stibine oxides show enhanced Lewis basicity compared to phosphine and arsine oxides. This increased basicity allows stibine oxides to bind Lewis acids even with bulky substituents, overcoming steric hindrance.
Area of Science:
- Organometallic Chemistry
- Main-group Chemistry
- Lewis Acid-Base Interactions
Background:
- Phosphine oxides possess a stable P-O bond due to electronic effects, including O-to-P back-bonding.
- The oxygen atom in phosphoryl units exhibits Lewis basicity, influenced by the electronic properties of the central pnictogen.
- Back-bonding strength decreases with increasing atomic number of the pnictogen, potentially enhancing Lewis basicity in heavier congeners.
Purpose of the Study:
- To compare the Lewis acid binding abilities of R3PnO species (Pn = P, As, Sb).
- To investigate the influence of steric bulk on Lewis acid-base adduct formation.
- To evaluate the role of enhanced pnictogen basicity in overcoming steric hindrance.
Main Methods:
- Synthesis and characterization of various R3PnO compounds.
- Investigation of Lewis acid-base adduct formation with main-group Lewis acids, including B-(C6F5)3.
- Comparison of binding affinities across the series of pnictogen oxides with varying steric demands.
Main Results:
- Steric bulk significantly hinders Lewis acid binding in phosphine oxides (R3PO) and arsine oxides (R3AsO).
- Highly hindered Dipp3PO and Dipp3AsO (Dipp = 2,6-diisopropylphenyl) failed to bind the strong Lewis acid B-(C6F5)3.
- Stibine oxides (R3SbO) demonstrated enhanced Lewis basicity, enabling adduct formation even with bulky substituents like Dipp3SbO.
Conclusions:
- The Lewis basicity of R3PnO compounds increases significantly from P to Sb, overcoming steric limitations.
- Heavier pnictogen oxides are superior Lewis bases capable of forming stable adducts with strong Lewis acids, irrespective of steric hindrance.
- This study highlights the tunable electronic properties of pnictogen oxides for designing Lewis acid-base adducts.
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