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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, with rapid equilibria between species driven by halide catalysis. This stereodynamism, arising from changing coordination geometry, is crucial for understanding asymmetric catalysis and designing future 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 unifying structural models for M(Salen) complexes is vital for continued innovation in catalysis.
- * The Jacobsen catalyst (M = Al) has significantly impacted modern synthesis, necessitating detailed studies of its behavior.
Purpose of the Study:
- * To investigate the solution-phase behavior of aluminum(Salen) complexes using a three-dimensional structural approach.
- * To complement experimental findings with solid-state 27Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) and computational studies.
- * To revise existing models for pentacoordinate M(Salen) complexes based on structural and dynamic insights.
Main Methods:
- * Three-dimensional structural investigation of Al(Salen) complexes in solution.
- * 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 intermolecular 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 observed, leading to a revised model for pentacoordinate M(Salen) complexes.
Conclusions:
- * Dynamic metal coordination geometry, termed stereodynamism, is a critical factor in the behavior of pentacoordinate Al(Salen) complexes.
- * Established models for M(Salen) complexes require revision to incorporate the observed dynamic equilibria and conformational changes.
- * Understanding this stereodynamism is essential for future reaction design and asymmetric induction models, with potential applications beyond catalysis.
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