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Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks (MOFs)
Published on: January 17, 2020
Stereodynamism in Pentacoordinate Al(Salen) Catalysts
Emanuel Studer1, Walter R Linke2,3, Mia A Müller1,3
1Institute for Organic Chemistry, University of Münster, 48149Münster, Germany.
Journal of the American Chemical Society
|July 17, 2026
Summary
Aluminum(Salen) complexes exhibit dynamic behavior in solution, involving rapid equilibria between different species. This stereodynamism, driven by changes in metal coordination geometry, is crucial for understanding and designing new asymmetric catalysis reactions.
Area of Science:
- * Inorganic Chemistry
- * Catalysis
- * Structural Chemistry
Background:
- * Metal(Salen) complexes are foundational in asymmetric catalysis, offering broad applicability and high selectivity.
- * Developing structural models for M(Salen) complex function is vital for continued innovation in catalysis.
- * The Jacobsen catalyst (M=Al) has significantly impacted modern synthesis, highlighting the importance of aluminum-Salen systems.
Purpose of the Study:
- * To conduct a comprehensive three-dimensional structural investigation of aluminum(Salen) complexes in solution.
- * To complement experimental findings with solid-state 27Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) and computational studies.
- * To revise existing models describing the behavior of pentacoordinate M(Salen) complexes.
Main Methods:
- * Solution-phase structural investigation of Al(Salen) complexes.
- * Solid-state 27Al MAS NMR spectroscopy.
- * Computational modeling and analysis using the Addison geometry parameter τ.
Main Results:
- * Al(Salen)Cl complexes exist in rapid equilibrium between R,R-(M) and R,R-(P) species in solution, facilitated by halide-catalyzed rearrangements.
- * The backbone conformation remains trans-diequatorial, with axial configurations (M/P) determined by shifts between square based pyramidal (sbp) and distorted trigonal bipyramidal (dtbp) coordination geometries.
- * Orthogonal helical diastereomers with conserved point chirality were identified, leading to a revised model for pentacoordinate M(Salen) complexes.
Conclusions:
- * Dynamic metal coordination geometry and stereodynamism are key factors in the behavior of pentacoordinate Al(Salen) complexes.
- * Established models for M(Salen) complexes require revision to account for observed dynamic equilibria and conformational changes.
- * Understanding this stereodynamism is essential for future reaction design and induction models in asymmetric catalysis.
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