Terpene dispersion energy donor ligands in borane complexes

Area of Science:

• Organometallic Chemistry
• Computational Chemistry
• Supramolecular Chemistry

Background:

• Non-covalent interactions, particularly London dispersion forces, play a crucial role in the stability and properties of molecular complexes.
• Terpenes, with their diverse stereochemistries, offer unique ligand frameworks for exploring these interactions.
• Understanding these forces is key to designing novel materials and catalysts.

Purpose of the Study:

• To investigate the role of London dispersion energies in organoboron complexes featuring terpene ligands.
• To characterize the structural and energetic contributions of β-pinane, camphane, and sabinane frameworks.
• To explore the coordination chemistry and dynamic behavior of these complexes.

Main Methods:

• X-ray crystallography for structural characterization of [B(β-pinane)3].
• Computational studies, including homolytic fragmentation and isodesmic exchange reactions, to determine dispersion energies.
• Nuclear magnetic resonance (NMR) spectroscopy to study the dynamic coordination equilibrium of [Me3P-B(β-pinane)3].

Main Results:

• Structural analysis of [B(β-pinane)3] identified H⋯H contacts indicative of London dispersion forces.
• Computational analysis revealed that the β-pinane framework provides the greatest dispersion free energy (ΔG = -7.9 kcal mol⁻¹).
• The coordination of PMe3 to [B(β-pinane)3] resulted in a dynamic equilibrium, with a slightly endergonic association process (ΔG = +0.29 kcal mol⁻¹ at 302 K).

Conclusions:

• London dispersion interactions are significantly influenced by the stereochemistry of terpene ligands in organoboron complexes.
• The β-pinane ligand framework offers a substantial contribution to the overall dispersion energy.
• The dynamic coordination behavior highlights the delicate balance of interactions in these systems.