Computational studies on modulation of structure and reactivity through metal ion coordination

Abstract

Computational Studies on Modulation of Structure and Reactivity through Metal Ion Coordination

Abstract and Synopsis Introduction This thesis addresses chemical problems using modern computational methods, focusing on the quantification of metal ion interactions with organic molecules and their subtle chemical consequences. Insights derived from model systems are extended to interpret more complex experimental systems.

Chapter 1 Provides an overview of computational methods employed. Discusses the importance of cation- interactions with examples and outlines the chemistry of zeolites, which serve as experimental reaction media.

Chapter 2 Quantifies cation-molecule interactions in alkali metal ion (Li to Cs ) assemblies with olefins (ethylene, propylene, isobutene, trimethylethylene).

Lighter cations (Li , Na ) show stronger binding.

Methyl substitution enhances binding, especially with lighter cations.

Smaller cations induce greater polarization of olefin -orbitals. These results provide a basis for interpreting reactivity patterns of metal-bound olefins.

Chapter 3 Examines cation- interactions in aromatic aggregation using benzene dimers.

Smaller cations enhance aggregation.

Metal ions interact more strongly with benzene dimers than single benzene molecules. Findings explain photophysical properties of aromatic molecules in metal ion-exchanged zeolites.

Chapter 4 Explores sandwich-type structures in cis-diaryl derivatives (diphenylcyclobutane, diphenylcyclopropane, stilbene).

Binding energies comparable to benzene sandwich complexes.

Cis-isomers bind effectively with alkali metal ions, avoiding entropic costs.

Binding energies show regular gradation from Li to Cs . Implications for cis-trans photoisomerization studies in zeolites are highlighted.

Chapter 5 Investigates state switching in carbonyls due to metal ion coordination.

Systems studied: enones, acetophenones, and lithium-coordinated analogues.

Li destabilizes n- * states relative to - * states, switching the lowest triplet state.

Substituents (e.g., -OMe) and Li coordination stabilize n- * states. Predictions rationalize product distribution dependence on cations.

Chapter 6 Analyzes metal ion interactions with organic radicals, intermediates in photo-Fries and photo-Claisen rearrangements.

Radicals from photolysis of phenylacetate and phenylallyl ether interact favorably with metal ions.

Binding may inhibit radical mobility.

Predicted trends align with experimental product distributions.

Chapter 7 Explores metal ion coordination effects on singlet oxygen ene reactions with unsymmetrical olefins (e.g., trimethylethylene).

Transition states for hydrogen abstraction are located.

Li coordination makes the ene reaction more concerted compared to the parent olefin.

Conclusions Metal ion coordination significantly modulates structure, reactivity, and excited-state behavior of organic molecules.

Lighter cations show stronger binding and greater orbital polarization.

Metal ions enhance aromatic aggregation and stabilize cis-diaryl complexes.

Coordination influences photochemical state switching and radical mobility.

Computational predictions provide elegant explanations for experimental observations in zeolite-mediated reactions.